This document summarizes an experiment studying the origins of large voltage hysteresis in metal fluoride lithium-ion battery conversion electrodes. Specifically, it examines iron fluoride (FeF3) as a model system using in situ X-ray absorption spectroscopy, transmission electron microscopy, density functional theory calculations, and galvanostatic intermittent titration technique. The results reveal that the phase evolution during charging and discharging is actually symmetrical, with the same intermediate phases forming. However, the spatial distribution of the electrochemically active phases differs due to kinetic effects. This leads to differences in ohmic voltage drop, reaction overpotential, and compositional inhomogeneity, causing the large observed voltage hysteresis which is kinetic rather than thermodynamic in nature
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
This document summarizes manipulation strategies for two-dimensional amorphous nanomaterials (2D ANMs) to enhance their performance in electrochemical energy storage and conversion applications. It discusses two main categories of manipulation: 1) geometric configuration design, including spatial structure design (e.g. creating porous structures) and coordination environment design (e.g. defect creation); and 2) component interaction, including elemental doping/coupling and heterophase compositing. Recent examples manipulating 2D ANMs through these approaches for applications in batteries, supercapacitors and electrocatalysis are reviewed. The document concludes by discussing opportunities to further optimize manipulation of 2D ANMs.
This document summarizes a study that characterized graphite anodes from lithium-ion battery cells after fast charging. Multi-scale characterization techniques revealed increased disorder near the edges of graphite particles in anodes that experienced lithium plating during fast charging. Specifically, transmission electron microscopy showed wavy graphite fringes and higher d-spacings near particle edges, indicating greater lattice disorder extending 20 nm into the bulk. This disorder hinders lithium ion intercalation and favors lithium plating during repeated fast charging. Scanning electron microscopy also showed fast-charged anodes were thicker due to accumulated electrolyte reduction products in pores.
2021 a new in situ and operando measurement method to determine the electri...Ary Assuncao
This document summarizes a new method for measuring the electrical conductivity of the negative active material in lead-acid batteries during operation. The method uses a model electrode with four embedded probe wires to conduct in-situ four-point probe measurements of resistance during battery cycling. Numerical simulations support the analysis of measurement results. Using this method, the document studies the evolution of discharge capacity, electrical resistance, and electrical conductivity over 10 cycles and correlates the results to known structural changes in the active material that occur during cycling.
2021 influence of basic carbon additives on the electrochemical performance ...Ary Assuncao
This study investigates the effect of carbon surface basicity on the electrochemical performance and dynamic charge acceptance of lead-carbon batteries. Five activated carbons with different pH values ranging from 9.5 to 11.1 were prepared by ammonia and hydrogen gas treatments. Cyclic voltammetry showed that the hydrogen evolution reaction activity increased with higher carbon surface basicity. Testing of lead-carbon electrodes found a correlation between carbon pH and dynamic charge acceptance, with higher pH carbons showing improved charge currents and final dynamic charge acceptance. The carbon content also affected charge currents during simulated microcycles, demonstrating that surface chemistry and amount of carbon additive both influence the electrochemical properties and performance of lead-carbon batteries.
The document describes a study that uses design of experiments (DoE) to optimize slurry-cast cathodes for solid-state batteries. Various combinations of polymer binder type and content and conductive carbon additive type and content were tested as cathode composites. Electrochemical and mechanical performance data from the experiments were analyzed using statistical software to identify optimal combinations. The predictions identified polyisobutene as the best binder and vapor-grown carbon fibers as the best additive to maximize specific capacity. Hydrogenated nitrile butadiene rubber and vapor-grown carbon fibers provided the best combination to maximize capacity retention. Additional tests were conducted to understand changes during cycling.
Electrolyte Solutions for Rechargeable Li-Ion Batteries Based on Fluorinated ...AMAL THOMAS
High voltage lithium ion batteries have been a focus in the current energy storage research due to their
potential application as high energy density batteries for electric vehicles. With more energy stored in
a system with the same weight and volume, the impact of battery fabrication and its utilization on the
environment will be minimized .Electrolyte solutions based on fluorinated solvents were studied in
high-voltage Li-ion cells using lithium as the anode has a great enhancement over conventional
electrolyte and Li1.2Mn0.56Co0.08Ni0.16O2 as the cathode provides excellent voltage stability on the 5.0
V at both ambient and elevated temperatures. Performance can be reach peak by replacing convectional
alky carbonate solvents in electrolyte solution by fluorinated cosolvents. Fluorinated electrolyte
solution act as a buffering surface film which is highly reactive electrophilic alkyl carbonates, from
continuous detrimental reactions with solution species. Excellent cyclic performance was recorded in
solution containing fluorinated solvents. The extraordinary electrochemical stability of this electrolyte
solution makes it a suitable candidate for other high-voltage cathode materials.
1. The document describes a new nanohybrid material composed of polyoxomolybdate, polypyrrole, and graphene oxide for use as a high-power symmetric supercapacitor electrode.
2. The nanohybrid was synthesized via a one-pot reaction where polyoxomolybdate acted as an oxidizing agent to polymerize pyrrole monomers onto graphene oxide nanosheets.
3. Structural and morphological analysis showed the nanohybrid had an excellent architecture with good interfacial contact between components, enabling fast redox reactions for high capacitive performance.
Investigating Hybrid Organic-Inorganic Tin Perovskites for Li-ion Battery App...Jiankun Pu
We investigated tin perovskites (ASnX3) for lithium-ion batteries by analyzing their intercalation energy, formation energy, octahedral distortion factor, etc. We hope to utilize these data to establish a machine learning model to help us fast predict the intercalation energy of other tin-based perovskites.
This document summarizes manipulation strategies for two-dimensional amorphous nanomaterials (2D ANMs) to enhance their performance in electrochemical energy storage and conversion applications. It discusses two main categories of manipulation: 1) geometric configuration design, including spatial structure design (e.g. creating porous structures) and coordination environment design (e.g. defect creation); and 2) component interaction, including elemental doping/coupling and heterophase compositing. Recent examples manipulating 2D ANMs through these approaches for applications in batteries, supercapacitors and electrocatalysis are reviewed. The document concludes by discussing opportunities to further optimize manipulation of 2D ANMs.
This document summarizes a study that characterized graphite anodes from lithium-ion battery cells after fast charging. Multi-scale characterization techniques revealed increased disorder near the edges of graphite particles in anodes that experienced lithium plating during fast charging. Specifically, transmission electron microscopy showed wavy graphite fringes and higher d-spacings near particle edges, indicating greater lattice disorder extending 20 nm into the bulk. This disorder hinders lithium ion intercalation and favors lithium plating during repeated fast charging. Scanning electron microscopy also showed fast-charged anodes were thicker due to accumulated electrolyte reduction products in pores.
2021 a new in situ and operando measurement method to determine the electri...Ary Assuncao
This document summarizes a new method for measuring the electrical conductivity of the negative active material in lead-acid batteries during operation. The method uses a model electrode with four embedded probe wires to conduct in-situ four-point probe measurements of resistance during battery cycling. Numerical simulations support the analysis of measurement results. Using this method, the document studies the evolution of discharge capacity, electrical resistance, and electrical conductivity over 10 cycles and correlates the results to known structural changes in the active material that occur during cycling.
2021 influence of basic carbon additives on the electrochemical performance ...Ary Assuncao
This study investigates the effect of carbon surface basicity on the electrochemical performance and dynamic charge acceptance of lead-carbon batteries. Five activated carbons with different pH values ranging from 9.5 to 11.1 were prepared by ammonia and hydrogen gas treatments. Cyclic voltammetry showed that the hydrogen evolution reaction activity increased with higher carbon surface basicity. Testing of lead-carbon electrodes found a correlation between carbon pH and dynamic charge acceptance, with higher pH carbons showing improved charge currents and final dynamic charge acceptance. The carbon content also affected charge currents during simulated microcycles, demonstrating that surface chemistry and amount of carbon additive both influence the electrochemical properties and performance of lead-carbon batteries.
The document describes a study that uses design of experiments (DoE) to optimize slurry-cast cathodes for solid-state batteries. Various combinations of polymer binder type and content and conductive carbon additive type and content were tested as cathode composites. Electrochemical and mechanical performance data from the experiments were analyzed using statistical software to identify optimal combinations. The predictions identified polyisobutene as the best binder and vapor-grown carbon fibers as the best additive to maximize specific capacity. Hydrogenated nitrile butadiene rubber and vapor-grown carbon fibers provided the best combination to maximize capacity retention. Additional tests were conducted to understand changes during cycling.
Electrolyte Solutions for Rechargeable Li-Ion Batteries Based on Fluorinated ...AMAL THOMAS
High voltage lithium ion batteries have been a focus in the current energy storage research due to their
potential application as high energy density batteries for electric vehicles. With more energy stored in
a system with the same weight and volume, the impact of battery fabrication and its utilization on the
environment will be minimized .Electrolyte solutions based on fluorinated solvents were studied in
high-voltage Li-ion cells using lithium as the anode has a great enhancement over conventional
electrolyte and Li1.2Mn0.56Co0.08Ni0.16O2 as the cathode provides excellent voltage stability on the 5.0
V at both ambient and elevated temperatures. Performance can be reach peak by replacing convectional
alky carbonate solvents in electrolyte solution by fluorinated cosolvents. Fluorinated electrolyte
solution act as a buffering surface film which is highly reactive electrophilic alkyl carbonates, from
continuous detrimental reactions with solution species. Excellent cyclic performance was recorded in
solution containing fluorinated solvents. The extraordinary electrochemical stability of this electrolyte
solution makes it a suitable candidate for other high-voltage cathode materials.
1. The document describes a new nanohybrid material composed of polyoxomolybdate, polypyrrole, and graphene oxide for use as a high-power symmetric supercapacitor electrode.
2. The nanohybrid was synthesized via a one-pot reaction where polyoxomolybdate acted as an oxidizing agent to polymerize pyrrole monomers onto graphene oxide nanosheets.
3. Structural and morphological analysis showed the nanohybrid had an excellent architecture with good interfacial contact between components, enabling fast redox reactions for high capacitive performance.
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
This document summarizes research on using graphene nanosheets as electrode materials for supercapacitors. The researchers investigated the effect of ion size and properties on the pseudocapacitance and double layer capacitance of graphene electrodes in different electrolytes. They found that the electrode showed better double layer characteristics in NaOH electrolyte compared to LiBr electrolyte. This was attributed to the smaller size and higher mobility of ions in NaOH, allowing more ions to be stored on the graphene surface. Electrochemical tests showed the electrode exhibited both double layer capacitance and pseudocapacitance, with pseudocapacitance contributing more in LiBr electrolyte. The morphology of the graphene nanosheets formed a continuous porous network suitable for
Double layer energy storage in graphene a studytshankar20134
This document summarizes research on using graphene for energy storage in electrochemical double layer capacitors (EDLCs). Graphene has potential as an EDLC electrode material due to its high surface area and electrical conductivity. Studies have found specific capacitances of graphene electrodes ranging from tens of F/g to over 1000 F/g depending on preparation methods and electrolytes. However, graphene sheets tend to restack reducing surface area availability. Methods to prevent restacking like adding metal oxides or curving graphene sheets have improved capacitance. Research is optimizing graphene properties and composites to enhance energy and power densities for applications requiring high power such as filtering alternating current.
2021 understanding li-based battery materials via electrochemical impedance...Ary Assuncao
The document discusses the use of electrochemical impedance spectroscopy (EIS) to understand lithium-based battery materials. It states that while EIS is a powerful technique, its potential has not been fully exploited for batteries. It provides examples of advanced EIS measurement approaches and physics-based modeling that can provide new insights. These include using specialized electrode configurations, complementary techniques, and transmission line modeling to deconvolute overlapping impedance spectra features into fundamental electrochemical processes. The document advocates designing experiments with well-controlled conditions and advanced data analysis to further unlock insights from EIS into battery mechanisms.
This document provides an overview of interfacial electrochemistry. It discusses how interfaces form boundaries between different phases of matter and influence interactions with the environment due to changed atomic structures. Most electrochemical events occur at interfaces, making interfacial electrochemistry important. When two dissimilar materials contact, charge separation occurs across the interface, creating an interfacial potential difference. The document also describes models of the electrical double layer that forms at electrode-electrolyte interfaces, such as the Helmholtz-Perrin and Gouy-Chapman models.
This document discusses the electrical properties of solid inorganic materials. It begins by defining solid electrolytes as crystalline solids that conduct electricity via the movement of ions. Some key solid electrolyte materials discussed include silver iodide (AgI), sodium beta-alumina, and lithium cobalt oxide (LiCoO2). Applications of solid electrolytes mentioned include use in solid oxide fuel cells, lithium-ion batteries, oxygen gas sensors, and as separators in electrochemical cells.
1. The document discusses electrochemical processes in biology, which involve the transfer of electrons between sites of oxidation and reduction separated by membranes. Energy from electron transfer is stored as electrochemical proton gradients across membranes and used to synthesize ATP.
2. Key components of biological electron transfer systems include quinones, flavins, iron-sulfur proteins, and the electron transfer chains in mitochondria and chloroplasts. These systems facilitate the transduction of chemical energy into work through redox reactions.
3. The concept of redox potential can be applied to small, non-statistical biological systems by considering their equilibrium with larger macrosystems. This explains why electron transfer chains contain many components overlapping a wide range of potential levels
This document discusses principles of ionization and ion dissociation in mass spectrometry. It covers topics like ionization energy, processes that occur during electron ionization like formation of molecular ions and fragment ions, and ionization by energetic electrons. It also discusses concepts like vertical transitions, where electronic transitions occur much faster than nuclear motions. The document provides background information on fundamental gas phase ion chemistry concepts in mass spectrometry.
Electrochemistry 1 the basic of the basicToru Hara
This document discusses key concepts in electrochemistry including the interface between electrode and electrolyte, thermodynamics and kinetics of electrode reactions, and overpotential. The interface contains an electric double layer consisting of an inner monomolecular layer, an outer diffuse region, and an intermediate layer. Overpotential arises from factors like activation energy needed for electrode reactions, concentration gradients that develop at the electrode surface, and resistance of the electrolyte. Overpotential is composed of ohmic drop, activation overpotential, and diffusion overpotential.
Superconductivity in Al-substituted Ba8Si46 clathratesYang Li
There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed
that Ba8Si42Al4 is superconductive with transition temperature at TC=5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x=6 sample Ba8Si40Al6, the superconducting transition was observed down to TC=4.7K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC=8K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a
decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated
by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensiveunderstanding of the doping effect on superconductivity of clathrates.
This presentation discusses the application of electromotive force (E.M.F.) measurement. It describes eight applications: 1) determination of equilibrium constants, 2) determination of solubility of sparingly soluble salts, 3) determination of valence, 4) determination of thermodynamic functions, 5) determination of pH of a solution, 6) potentiometric titrations, 7) determination of activity coefficients, and 8) determination of transference numbers. Potentiometric titration techniques are discussed for acid-base, oxidation-reduction, and precipitation titrations. Determination of E.M.F. using cells allows calculation of various chemical properties and equilibrium constants.
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document summarizes research on the electrical conductivity of Ba-Sr-Co-Fe cathode materials for solid oxide fuel cells (SOFCs). Single phase cubic Ba0.5Sr0.5Co1-xFexO3-δ compositions were synthesized via gel combustion and cation complexation routes. Electrical conductivity measurements showed that conductivity initially increased with temperature up to a maximum then decreased, attributed to oxygen loss from the lattice. Fe substitution had little effect on conductivity. While BSCF shows potential as an SOFC cathode, further work is needed to increase conductivity to meet requirements of current IT-SOFCs.
Juornal of Physics Condensed Matter - Article IRossen Hristov
This document summarizes a study that investigated the mobility of counterions condensed on carboxymethyl cellulose (CMC) polymer chains adsorbed onto alumina colloid particles. Previous studies using electro-optical techniques reported that condensed counterions are mobile in alternating electric fields. However, the current study uses an amplitude approach, measuring particle polarizability at increasing CMC concentration rather than frequency dependence. Results indicate condensed counterions do not contribute to particle polarization at 1 kHz, suggesting they are immobile in sinusoidal fields up to 0.5 kV/cm and 1 kHz. Comparison of polarizability and electrophoretic mobility supports the conclusion that condensed counterions are immobilized on the CMC chains.
Introduction to electrochemistry 2 by t. haraToru Hara
This document provides an overview of electrochemistry concepts including:
1. Electrochemistry involves redox reactions where electrons are gained or lost at electrode interfaces.
2. Thermodynamics and kinetics control redox reactions based on potential differences and charge/mass transfer limitations.
3. The electric double layer forms at electrode interfaces and can be modeled by the Helmholtz and Stern models.
This document provides an overview of basic electrochemistry concepts. It discusses the charge and current involved in electrochemical processes. It introduces Faraday's laws relating the amount of material transformed to the quantity of electricity passed. It also covers conductivity, Nernst equation, different types of electrodes, potentiometry, and various electrochemical techniques including cyclic voltammetry. The key concepts covered include electron transfer processes, Butler-Volmer equation, mass transport by diffusion and convection, and reversible cyclic voltammograms.
CBSE Class 12 Chemistry Chapter 3 (Electrochemistry) | Homi InstituteHomi Institute
1. Electrochemistry is the study of chemical processes involving the movement of electrons, which can generate electricity through oxidation-reduction reactions.
2. A salt bridge is a device used in electrochemical cells to connect the half cells and maintain electrical neutrality, preventing the accumulation of charges that would stop the reaction.
3. Common reference electrodes include the standard hydrogen electrode and silver-silver chloride electrode, but the standard hydrogen electrode is difficult to assemble and maintain precisely.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
This document summarizes an investigation of the adsorption of carboxymethyl cellulose (NaCMC) onto gamma-aluminum oxide (γ-Al2O3) particles. Key findings include:
1) Electrophoretic and electro-optical measurements both show that NaCMC adsorption causes the particle charge to be overcompensated above a concentration of 1x10-3 g/L NaCMC.
2) Frequency plateaus in electro-optical effect measurements shift to lower frequencies with NaCMC adsorption, indicating a decrease in particle relaxation frequency.
3) Relaxation times increase with NaCMC concentration as the adsorbed polymer enlarges the particle size, though the effect is
Nelson Mandela arrived in Johannesburg to find work in the mines but was unsuccessful and fired from his jobs. He stayed with relatives and expressed his desire to become a lawyer. He was taken on as a clerk at a law firm, where he was warned against getting involved in politics. However, he became aware of racial oppression in South Africa and attended political meetings. He passed his BA exam but knew a degree alone would not lead to success. He enrolled in law school, where he was exposed to political debates, and became increasingly involved in politics despite warnings.
O prezentare realizata in PowerPoint care explica conceptul modern de Blended Learning.
Toate elementele grafice sunt realizate cu ajutorul unor programe prezente in orice computer.
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
This document summarizes research on using graphene nanosheets as electrode materials for supercapacitors. The researchers investigated the effect of ion size and properties on the pseudocapacitance and double layer capacitance of graphene electrodes in different electrolytes. They found that the electrode showed better double layer characteristics in NaOH electrolyte compared to LiBr electrolyte. This was attributed to the smaller size and higher mobility of ions in NaOH, allowing more ions to be stored on the graphene surface. Electrochemical tests showed the electrode exhibited both double layer capacitance and pseudocapacitance, with pseudocapacitance contributing more in LiBr electrolyte. The morphology of the graphene nanosheets formed a continuous porous network suitable for
Double layer energy storage in graphene a studytshankar20134
This document summarizes research on using graphene for energy storage in electrochemical double layer capacitors (EDLCs). Graphene has potential as an EDLC electrode material due to its high surface area and electrical conductivity. Studies have found specific capacitances of graphene electrodes ranging from tens of F/g to over 1000 F/g depending on preparation methods and electrolytes. However, graphene sheets tend to restack reducing surface area availability. Methods to prevent restacking like adding metal oxides or curving graphene sheets have improved capacitance. Research is optimizing graphene properties and composites to enhance energy and power densities for applications requiring high power such as filtering alternating current.
2021 understanding li-based battery materials via electrochemical impedance...Ary Assuncao
The document discusses the use of electrochemical impedance spectroscopy (EIS) to understand lithium-based battery materials. It states that while EIS is a powerful technique, its potential has not been fully exploited for batteries. It provides examples of advanced EIS measurement approaches and physics-based modeling that can provide new insights. These include using specialized electrode configurations, complementary techniques, and transmission line modeling to deconvolute overlapping impedance spectra features into fundamental electrochemical processes. The document advocates designing experiments with well-controlled conditions and advanced data analysis to further unlock insights from EIS into battery mechanisms.
This document provides an overview of interfacial electrochemistry. It discusses how interfaces form boundaries between different phases of matter and influence interactions with the environment due to changed atomic structures. Most electrochemical events occur at interfaces, making interfacial electrochemistry important. When two dissimilar materials contact, charge separation occurs across the interface, creating an interfacial potential difference. The document also describes models of the electrical double layer that forms at electrode-electrolyte interfaces, such as the Helmholtz-Perrin and Gouy-Chapman models.
This document discusses the electrical properties of solid inorganic materials. It begins by defining solid electrolytes as crystalline solids that conduct electricity via the movement of ions. Some key solid electrolyte materials discussed include silver iodide (AgI), sodium beta-alumina, and lithium cobalt oxide (LiCoO2). Applications of solid electrolytes mentioned include use in solid oxide fuel cells, lithium-ion batteries, oxygen gas sensors, and as separators in electrochemical cells.
1. The document discusses electrochemical processes in biology, which involve the transfer of electrons between sites of oxidation and reduction separated by membranes. Energy from electron transfer is stored as electrochemical proton gradients across membranes and used to synthesize ATP.
2. Key components of biological electron transfer systems include quinones, flavins, iron-sulfur proteins, and the electron transfer chains in mitochondria and chloroplasts. These systems facilitate the transduction of chemical energy into work through redox reactions.
3. The concept of redox potential can be applied to small, non-statistical biological systems by considering their equilibrium with larger macrosystems. This explains why electron transfer chains contain many components overlapping a wide range of potential levels
This document discusses principles of ionization and ion dissociation in mass spectrometry. It covers topics like ionization energy, processes that occur during electron ionization like formation of molecular ions and fragment ions, and ionization by energetic electrons. It also discusses concepts like vertical transitions, where electronic transitions occur much faster than nuclear motions. The document provides background information on fundamental gas phase ion chemistry concepts in mass spectrometry.
Electrochemistry 1 the basic of the basicToru Hara
This document discusses key concepts in electrochemistry including the interface between electrode and electrolyte, thermodynamics and kinetics of electrode reactions, and overpotential. The interface contains an electric double layer consisting of an inner monomolecular layer, an outer diffuse region, and an intermediate layer. Overpotential arises from factors like activation energy needed for electrode reactions, concentration gradients that develop at the electrode surface, and resistance of the electrolyte. Overpotential is composed of ohmic drop, activation overpotential, and diffusion overpotential.
Superconductivity in Al-substituted Ba8Si46 clathratesYang Li
There is a great deal of interest vested in the superconductivity of Si clathrate compounds with sp3 network, in which the structure is dominated by strong covalent bonds among silicon atoms, rather than the metallic bonding that is more typical of traditional superconductors. A joint experimental and theoretical investigation of superconductivity in Al-substituted type-I silicon clathrates is reported. Samples of the general formula Ba8Si46xAlx, with different values of x were prepared. With an increase in the Al composition, the superconducting transition temperature TC was observed to decrease systematically. The resistivity measurement revealed
that Ba8Si42Al4 is superconductive with transition temperature at TC=5.5 K. The magnetic measurements showed that the bulk superconducting Ba8Si42Al4 is a type II superconductor. For x=6 sample Ba8Si40Al6, the superconducting transition was observed down to TC=4.7K which pointed to a strong suppression of superconductivity with increasing Al content as compared with TC=8K for Ba8Si46. Suppression of superconductivity can be attributed primarily to a
decrease in the density of states at the Fermi level, caused by reduced integrity of the sp3 hybridized networks as well as the lowering of carrier concentration. These results corroborated
by first-principles calculations showed that Al substitution results in a large decrease of the electronic density of states at the Fermi level, which also explains the decreased superconducting critical temperature within the BCS framework. The work provided a comprehensiveunderstanding of the doping effect on superconductivity of clathrates.
This presentation discusses the application of electromotive force (E.M.F.) measurement. It describes eight applications: 1) determination of equilibrium constants, 2) determination of solubility of sparingly soluble salts, 3) determination of valence, 4) determination of thermodynamic functions, 5) determination of pH of a solution, 6) potentiometric titrations, 7) determination of activity coefficients, and 8) determination of transference numbers. Potentiometric titration techniques are discussed for acid-base, oxidation-reduction, and precipitation titrations. Determination of E.M.F. using cells allows calculation of various chemical properties and equilibrium constants.
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document summarizes research on the electrical conductivity of Ba-Sr-Co-Fe cathode materials for solid oxide fuel cells (SOFCs). Single phase cubic Ba0.5Sr0.5Co1-xFexO3-δ compositions were synthesized via gel combustion and cation complexation routes. Electrical conductivity measurements showed that conductivity initially increased with temperature up to a maximum then decreased, attributed to oxygen loss from the lattice. Fe substitution had little effect on conductivity. While BSCF shows potential as an SOFC cathode, further work is needed to increase conductivity to meet requirements of current IT-SOFCs.
Juornal of Physics Condensed Matter - Article IRossen Hristov
This document summarizes a study that investigated the mobility of counterions condensed on carboxymethyl cellulose (CMC) polymer chains adsorbed onto alumina colloid particles. Previous studies using electro-optical techniques reported that condensed counterions are mobile in alternating electric fields. However, the current study uses an amplitude approach, measuring particle polarizability at increasing CMC concentration rather than frequency dependence. Results indicate condensed counterions do not contribute to particle polarization at 1 kHz, suggesting they are immobile in sinusoidal fields up to 0.5 kV/cm and 1 kHz. Comparison of polarizability and electrophoretic mobility supports the conclusion that condensed counterions are immobilized on the CMC chains.
Introduction to electrochemistry 2 by t. haraToru Hara
This document provides an overview of electrochemistry concepts including:
1. Electrochemistry involves redox reactions where electrons are gained or lost at electrode interfaces.
2. Thermodynamics and kinetics control redox reactions based on potential differences and charge/mass transfer limitations.
3. The electric double layer forms at electrode interfaces and can be modeled by the Helmholtz and Stern models.
This document provides an overview of basic electrochemistry concepts. It discusses the charge and current involved in electrochemical processes. It introduces Faraday's laws relating the amount of material transformed to the quantity of electricity passed. It also covers conductivity, Nernst equation, different types of electrodes, potentiometry, and various electrochemical techniques including cyclic voltammetry. The key concepts covered include electron transfer processes, Butler-Volmer equation, mass transport by diffusion and convection, and reversible cyclic voltammograms.
CBSE Class 12 Chemistry Chapter 3 (Electrochemistry) | Homi InstituteHomi Institute
1. Electrochemistry is the study of chemical processes involving the movement of electrons, which can generate electricity through oxidation-reduction reactions.
2. A salt bridge is a device used in electrochemical cells to connect the half cells and maintain electrical neutrality, preventing the accumulation of charges that would stop the reaction.
3. Common reference electrodes include the standard hydrogen electrode and silver-silver chloride electrode, but the standard hydrogen electrode is difficult to assemble and maintain precisely.
Iron, cobalt and Nickel -ligand bonding in metallocene: Differentiation betwe...AI Publications
The electronic structure and geometry optimization of ferrocene, cobaltocene and nickelocene molecules using DFT/B3LYP with the basis set of 6-31G (d) calculations. The Eigen values, Eigen vector and population analysis of the molecules show that the first 13 molecular orbitals in ferrocene, 12 in cobaltocene and 14 in nickelocene have contribution from 2pzorbitals of carbon of (C5H5)− and4s,4pand 3dorbitals of iron, cobalt or nickel, respectively. We found that the extents of involvement of metal orbitals in the three cases are different. In ferrocene the maximum involvement out of 4s and 4porbitals in the order 4pz >4py >4s > 4pxand out of 3d orbitals the order of involvement is 3dyz >3dxz >3d2z>3dx2−y2>3dxy. The involvement of corresponding orbital in cobaltocene with respect to the 4sand 4porbitals is in the order of 4s >4pz >4py >4pxand in 3d orbitals the order is 3dx2−y2>3dxz >3d2z>3dx2−y2 and in the nickelocene molecule it is 4py >4p>4s >4pz and in 3d orbitals the order is 3dyz >3dx2−y2>3dxy >3dxz >3d2z. The total involvement of 3d, 4s and 4porbitals of metal and 2pz orbitals of the ten carbon atoms of both ligands of (C5H5) −in ferrocene, cobaltocene and nickelocene respectively are 42.2528, 40.2388 and 38.3776
This document summarizes an investigation of the adsorption of carboxymethyl cellulose (NaCMC) onto gamma-aluminum oxide (γ-Al2O3) particles. Key findings include:
1) Electrophoretic and electro-optical measurements both show that NaCMC adsorption causes the particle charge to be overcompensated above a concentration of 1x10-3 g/L NaCMC.
2) Frequency plateaus in electro-optical effect measurements shift to lower frequencies with NaCMC adsorption, indicating a decrease in particle relaxation frequency.
3) Relaxation times increase with NaCMC concentration as the adsorbed polymer enlarges the particle size, though the effect is
Nelson Mandela arrived in Johannesburg to find work in the mines but was unsuccessful and fired from his jobs. He stayed with relatives and expressed his desire to become a lawyer. He was taken on as a clerk at a law firm, where he was warned against getting involved in politics. However, he became aware of racial oppression in South Africa and attended political meetings. He passed his BA exam but knew a degree alone would not lead to success. He enrolled in law school, where he was exposed to political debates, and became increasingly involved in politics despite warnings.
O prezentare realizata in PowerPoint care explica conceptul modern de Blended Learning.
Toate elementele grafice sunt realizate cu ajutorul unor programe prezente in orice computer.
This document contains a resume for Amr Mohamed Abd eldeym. It lists his work experience from 2012-2015 as a site civil engineer for various construction companies in Egypt. It also outlines his education as a civil engineering graduate from Zagazig University in 2012, along with various certificates, computer skills, and language proficiency.
Enkele resultaten van demo's met steenmeel op dalgrond in de Veenkoloniën in de periode 2013 - 2015. Deze resultaten werden gepresenteerd op 2 januari 2015 op een bijeenkomst georganiseerd door Gebroeders Eckhardt b.v.
As an IT Staffing Firm, we love technology. But sometimes we end up with too much tech in our lives as we continue buying new products and newer models. What should you do with all your old and unused electronics? Recycle them! Bridge holds a biannual e-Waste Drive serving Rhode Islanders looking to do their part and protect the environment.
В отделении осуществляется обслуживание детей, выписанных из неонатальных отделений Центра и направленных из других учреждений. В отделении работают высококвалифицированные специалисты различного профиля: педиатры, неврологи, офтальмологи, врачи УЗИ, хирурги, детские эндокринологи, травматолог-ортопед и ЛОР врач.
This document contains instructions and submission forms for collecting data on surface activity in humpback whales and marine debris as part of other projects. Researchers are asked to record details of surface behaviors exhibited by whales like breaching and flipper slapping, as well as information about debris sightings like location and type. The data sheets should be submitted to Tegan Mortimer at teg.mortimer@gmail.com by the 1st of each month with the filename including the contributor's initials, month, and year.
Hussam Eldin Sidgi Mohamed Farah is a Sudanese national who received a Bachelor of Computer Application degree from Sikkim Manipal University in India. He has over 10 years of experience in roles such as Network Engineer, IT Team Leader, and Network Administrator. His skills include Microsoft Office, various Windows operating systems, CCNA, MCITP, CCTV installation and operation, and network and security systems administration.
Роды и ведение беременности в научном Центре акушерства, гинекологии и перина...damnedney
Роды, ведение беременности, неонатология. Контракты на ведение беременности и роды в научном Центре акушерства, гинекологии и перинатологии им. В.И.Кулакова
Maximilian Mayo-Dell reflects on improvements from a preliminary task to a full thriller film opening. Key areas of growth include skills with equipment, framing shots professionally, using lighting and white balance effectively, improved pre-production with storyboards and location selection, allowing enough time for proper production and multiple takes, incorporating useful props, coaching actors, and advanced editing with sound and titles. Overall, the thriller opening was much more polished and tense compared to the preliminary task due to these lessons learned.
The document instructs four groups to quickly draw flowcharts representing different scenarios using different flowchart elements. The groups are told the winning team will be exempt from a bonus homework question. The homework question asks for a flowchart representing a university student needing to complete 100 computing hours to pass a unit and graduate, or else having to re-enroll and start over if not completed.
This document reviews recent progress in using metal-organic frameworks (MOFs) as electrode materials for lithium-ion batteries, sodium-ion batteries, lithium-air batteries, lithium-sulfur batteries, and supercapacitors. MOFs show potential as electrode materials due to their unique morphology, high surface area, functional linkers, and metal sites. The document discusses MOFs and MOF-derived materials that have been studied for battery cathodes and anodes, highlighting examples that demonstrate high capacity and cycling stability. It also notes challenges for MOFs such as improving conductivity and chemical/structural stability in battery environments.
- FePS3, a 2D layered material, was investigated as a potential anode material for magnesium ion batteries using density functional theory calculations.
- The calculations found that magnesium is most stably adsorbed at iron sites on the FePS3 monolayer, with an adsorption energy of -4.45 eV.
- The maximum magnesium storage capacity of the FePS3 monolayer corresponds to the formula Mg2FePS3, providing a theoretical specific capacity of 585.6 mAh/g. This capacity is achieved through magnesium adsorption on both sides of the FePS3 layer at the iron sites.
Study the effect of Mn2+ ions on the ac electrical properties of some iron do...IJRES Journal
Oxide glasses doped with transition metal ions are of high interest because of their variant applications in both science and technology fields. However, the normal melt quench method have used to prepared some iron doped phosphate glasses according the following molecular formula: (65-x) mol% P2O5 - 20 mol% Na2O - 15 mol% Fe2O3 - x mol% MnO, Where x= 0, 5,10, 20, 25. The room temperature Mössbauer Effect ME Spectra used to characterized the glassy state homogeneity of these glasses. ME spectra show, for all glasses, no magnetic field participate which mean good glassy state formation. The ac electrical transport properties were also measured, as function of temperature up to 500k. It was found that the ac conductivity increased with the gradual increase of Mn2+ cations, while the electrical activation energy decreased.
This document describes how synchrotron-based X-ray spectroscopy techniques like XANES and STXM can provide insights into structure-performance relationships in battery materials to enable faster optimization. These techniques allow mapping of local chemistry, bonding structure, and phase distributions. Studies have shown how surface coatings and composite designs can influence properties like conductivity and stability. Chemical mapping of electrodes also revealed non-uniform reactions related to "hot spots" that correlate with performance. Faster screening of materials and correlation of structural properties with electrochemical data could significantly reduce battery development timelines.
Lithium Iron Phosphate: Olivine Material for High Power Li-Ion Batteries - Cr...CrimsonPublishersRDMS
Lithium Iron Phosphate: Olivine Material for High Power Li-Ion Batteries by Christian M Julien* in Crimson Publishers: Peer Reviewed Material Science Journals
This document summarizes a thesis submitted for a Master's degree in nano-optoelectronics. The thesis focuses on synthesizing and characterizing bismuth sodium titanate (BNT), a lead-free ferroelectric material. BNT is studied as an alternative to lead zirconate titanate (PZT), which is widely used but toxic. The thesis will synthesize BNT using solid-state and sol-gel methods, characterize its structure and properties, and compare the results. Characterization tools like XRD, SEM, and dielectric measurements will be used. If successful, BNT could replace PZT in applications like sensors and actuators while avoiding lead's toxicity issues.
The document describes a method for synthesizing NiFe2O4 nanoparticles fully anchored within a carbon network using a facile pyrolysis technique. Key points:
- NiFe2O4 nanoparticles were synthesized within a carbon network using a polyol-assisted pyrolysis method without an external carbon source.
- Characterization with SEM and TEM showed the NiFe2O4 nanoparticles were uniformly distributed and fully embedded within the carbon network.
- Electrochemical testing showed the NiFe2O4/C anode delivered a reversible capacity of 381.8 mAh/g after 100 cycles at 1C rates and 263.7 mAh/g at a high rate of 5C, demonstrating enhanced performance over bare
Electron Diffusion and Phonon Drag Thermopower in Silicon NanowiresAI Publications
The field of thermoelectric research has undergone a renaissance and boom in the fast two decades, largely fueled by the prospect of engineering electronic and phononic properties in nanostructures, among which semiconductor nanowires (NWs) have served both as an important platform to investigate fundamental thermoelectric transport phenomena and as a promising route for high thermoelectric performance for device applications. In this report we theoretical studied the carrier diffusion and phonon-drag contribution to thermoelectric performance of silicon nanowires and compared with the existing experimental data. We observed a good agreement between theoretical data and experimental observations in the overall temperature range from 50 – 350 K. Electron diffusion thermopower is found to be dominant mechanism in the low temperature range and shows linear dependence with temperature.
Study of Boron Based Superconductivity and Effect of High Temperature Cuprate...IOSR Journals
This paper illustrates the main normal and Boron superconducting state temperature properties of magnesium diboride, a substance known since early 1950's, but lately graded to be superconductive at a remarkably high critical temperature Tc=40K for a binary synthesis. What makes MgB2 so special? Its high Tc, simple crystal construction, large coherence lengths, high serious current densities and fields, lucidity of surface boundaries to current promises that MgB2 will be a good material for both large scale applications and electronic devices. Throughout the last seven month, MgB2 has been fabricated in various shape, bulk, single crystals, thin films, ribbons and wires. The largest critical current densities >10MA/cm2 and critical fields 40T are achieved for thin films. The anisotropy attribution inferred from upper critical field measurements is still to be resolved, a wide range of values being reported, γ = 1.2 ÷ 9. Also there is no consensus about the existence of a single anisotropic or double energy cavity. One central issue is whether or not MgB2 represents a new class of superconductors, being the tip of an iceberg that waits to be discovered. Until now MgB2 holds the record of the highest Tc among simple binary synthesis. However, the discovery of superconductivity in MgB2 revived the interest in non-oxides and initiated a search for superconductivity in related materials, several synthesis being already announced to become superconductive: TaB2, BeB2.75, C-S composites, and the elemental B under pressure.
This study investigated the relationship between ionic transport and lithium bis(trifluoromethane) sulfonamide (Li-TFSI) concentration in a copolymer matrix of vinylene carbonate and diethylene glycol methyl ether methacrylate. Analysis of conductivity data using Random Barrier and Macdonald-Trukhan models revealed that transport coefficients deviate from ideal mixing behavior and reach limiting values at a specific optimal charge density. Increasing ion concentration beyond this value may hinder highly conductive polymer electrolyte synthesis.
This document summarizes a research study on a novel zinc-ion hybrid supercapacitor (Zn-HSC) for long-life and low-cost energy storage. The key points are:
1) The Zn-HSC was fabricated using zinc foil as both the anode and current collector, and bio-carbon derived porous material as the cathode.
2) The Zn-HSC demonstrated superior electrochemical performance including a high discharge capacitance of 170 F g-1, good rate performance with 85% capacitance retention, a high energy density of 52.7 Wh kg-1, and excellent cycling stability with 91% capacitance retention after 20,000 cycles.
3) The bivalent
Electrical transport properties of nanocrystalline and bulk nickel.pdfProximaCentauri15
In this work, the comparative study on the electrical transport properties of nanocrystalline nickel
ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance
spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The
dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model
and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel
ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric
permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple
relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power
law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to
correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters
are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by
scaling curves of imaginary impedance (Z) andmodulus (M). The comparison between the Z and
M spectra indicates that both long-range and short-rangemovement of charge carriers contribute to
dielectric relaxation with short-range charge carriers predominating at low temperatures while longrange
charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist
plot indicates the presence of grain boundary contribution to the electrical conduction process for the
nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by
stretching exponential factor (β) which has been estimated by fitting the modifiedKWW
(Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is
found to be strongly temperature dependent and its value for the nanocrystalline sample is less than
that of the bulk system which is explained on the basis of dipole-dipole interaction.
The document describes a study where V2C MXene nanosheets were synergistically coupled with hypophosphite-intercalated FeNi layered double hydroxide (LDH) nanosheets to create an electrocatalyst for the oxygen evolution reaction (OER). The hybrid material, denoted H2PO-2/FeNi-LDH-V2C, was synthesized via a hydrothermal method. Electrochemical tests showed the material had excellent OER performance in 1.0 M KOH electrolyte, with an overpotential of 250 mV at 10 mA/cm2 and a small Tafel slope of 46.5 mV/dec. The strong interaction and electronic coupling between the
Few-layered MoSe2 nanosheets an an advanced...suresh kannan
This document summarizes the synthesis and characterization of few-layered molybdenum diselenide (MoSe2) nanosheets as an electrode material for supercapacitors. The MoSe2 nanosheets were synthesized using a facile hydrothermal method. Characterization with Raman spectroscopy, TEM, and XRD confirmed the formation of few-layered nanosheets. Electrochemical testing of the MoSe2 electrode in a symmetric cell configuration showed a maximum specific capacitance of 198.9 F g−1 and capacitance retention of approximately 75% after 10,000 cycles, indicating potential for supercapacitor applications.
Probing electrical energy storage chemistry and physics over broad time and ...Andrew Gelston
This document discusses emerging techniques for characterizing electrical energy storage devices with high spatial and temporal resolution. It describes how neutron scattering, X-ray scattering, electron microscopy, nuclear magnetic resonance, and nonlinear laser techniques can provide insights into chemical and physical phenomena over broad time and length scales. Developing combinations of in situ techniques with both high spatial resolution (down to the atomic scale) and high temporal resolution (down to the femtosecond range) could lead to improvements in battery and capacitor performance and a better understanding of failure mechanisms.
Modulus spectroscopy study on Ferroelectric Lithium and Titanium modified Lea...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
This document discusses in situ irradiated X-ray photoelectron spectroscopy (ISIXPS) and its ability to investigate electron transfer mechanisms in S-scheme photocatalysts. S-scheme photocatalysts have shown promise for solar fuel production. ISIXPS is an effective technique for studying electron transfer pathways in S-scheme heterojunctions, but the mechanism by which it identifies these pathways is not fully understood. This document aims to provide insight into how ISIXPS can be used to confirm interfacial electron transfer and better understand the electron transfer mechanism in S-scheme photocatalysts.
This document presents a thesis analyzing the stability margin of superconducting cables for the High Luminosity Large Hadron Collider (HiLumi-LHC) project at CERN. It uses both zero-dimensional and one-dimensional numerical models to simulate the electro-thermal behavior of Nb3Sn cables during a quench induced by beam losses. The results show the quench energy for the Nb3Sn inner triplet quadrupole magnet is significantly different than for the existing NbTi magnets. Comparisons with NbTi cables highlight differences in quench performance between impregnated Nb3Sn cables and non-impregnated NbTi cables in their typical operating conditions.
Lattice Energy LLC - Japanese confirm Lattice hypotheses re importance of ads...Lewis Larsen
Survival of 40% of world’s population heavily depends on higher food production enabled by Ammonia fertilizer produced in large plants via Haber-Bosch process as commercialized in 1909.
Progress is being made with new catalyst technology that could potentially reduce capital and operating costs of future Ammonia plants which would be cost-effective in much smaller sizes that enable distributed production.
Recent Japanese papers confirm Lattice’s hypotheses about importance of adsorbed protons and high
local electric fields for boosting reaction rates on some types of metallic catalyst surfaces.
Manabe et al. achieved high yield Haber-Bosch-like synthesis of Ammonia by applying DC electric fields
along with N2, H2, Cs/Ru catalyst and SrZrO3 support at just room temperature and ~1 atmosphere pressure versus ~450o C and ~200 atm in commercial NH3 plant.
Widom-Larsen theory of LENRs predicts deep causal connection between many-body collective physics of electroweak nuclear catalysis and chemical catalysis: very high local electric fields ≥ 1010 V/m and mobile surface patches of Q-M entangled protons. In LENRs these enable: electron + proton --> neutron + neutrino.
1. The document discusses electrochemistry and its application to proteins. It examines how electrochemical parameters like pH, potential difference, and electrode material can be varied to selectively modify amino acids in proteins.
2. It also discusses electron transfer reactions in proteins, noting that proteins contain redox-active groups that facilitate intramolecular charge transport and electron exchange. Special orientations of the protein on electrode surfaces and use of mediators are often required.
3. The kinetics of electron transfer in proteins is slow due to diffusion limitations and the need to overcome reorganization energy for electron transfer to occur. Marcus theory provides an explanation for electron transfer rates.
2. current belief is that a large portion of the voltage hysteresis
originates from the asymmetric reaction pathways during
discharge and charge and consequently the existence of
different intermediate phases results in the large split in
electrochemical potential.14,19,20
According to the DFT-GGA
calculations and associated models, FeF3 is first lithiated to
Lix[Fe1−x
3+
Fex
2+
]F3 before full reduction of Fe to LiF/Fe during
discharge, and a series of Fe3+
-containing compounds
(Li3−3xFe3+
xF3) form sequentially during charge before
formation of a defect trirutile FeF3.14
However, the under-
standing of the reaction pathways is not fully justified by ex situ
solid nuclear magnetic resonance (NMR),15
pair distribution
function analysis (PDF),15
transmission electron microscopy
(TEM),13
in situ X-ray absorption spectroscopy (XAS),25
and in
situ X-ray spectroimaging experiments,26
all of which suggest
the existence of Fe2+
-containing intermediate phases during
and/or after charge. Additionally, different interpretations of
the intermediate phases that form during discharge exist
between the ex situ15
and in situ experimental works25
(e.g.,
trirutile Li0.5FeF3 vs rhombohedral Li0.92FeF3, respectively).
These discrepancies in reaction pathways have constrained the
understanding of voltage hysteresis and therefore need to be
reconciled through systematic and definitive studies into both
thermodynamic and kinetic aspects of the reaction mechanism.
Here we use in situ synchrotron XAS to track changes in Fe
oxidation states and local bonding structure during cycling of
three iron fluoride model samples, FeF2 nanowires (NWs),
FeF3 NWs, and FeF3 microwires (MWs). Combining results
from in situ TEM experiments and hybrid functional DFT
calculations (HSE06), we show that the reaction pathway is
symmetrical and as follows: rhombohedral FeF3 → trirutile
Li0.25FeF3 → trirutile Li0.5FeF3 ⇄ rutile FeF2 + LiF ⇄ Fe +
3LiF. However, reaction homogeneity (completeness and
spatial evolution of each electrochemical reaction) is strongly
influenced by reaction kinetics in these sequential multiple-step
reaction processes. Based on the new mechanistic under-
standing and results from galvanostatic intermittent titration
technique (GITT) experiments, we show that the large voltage
hysteresis of the FeF3 electrode is due to iR (ohmic) drop,
reaction overpotential, and difference in apparent potentials
which are a result of different spatial distributions of
electrochemically active phases. These results have general
implications for understanding voltage hysteresis in other
conversion electrode materials and provide the basis of new
strategies to minimize its adverse effect.
■ RESULTS
Iron Fluoride Model Samples. We prepared FeF3 NWs18
and MWs26
according to previous work and synthesized the
FeF2 NWs for the first time via thermal reduction of FeF3 NWs
using a small amount of glucose at 450 °C under flowing argon
(see Experimental Section for synthetic details; see morphology
in Figure S1a−c). The phase identities of these samples are
confirmed using powder X-ray diffraction (PXRD, Figure S1d).
Further TEM characterization reveals that all of these wire
samples are polycrystalline and made of attached particle
domains (Figure S2). We chose these materials as the model
samples because of their higher electrochemical activity at room
temperature compared with other iron fluoride samples.11,15,16
They can all reach near theoretical capacity at a moderate
current rate (Figure S3), which is critical for finishing the in situ
experiments in a reasonable amount of beam time and
collecting useful mechanistic information.
In Situ XAS on an FeF2 Electrode. We first studied the
reaction mechanism of an FeF2 electrode using in situ XAS as a
comparison to the FeF3 electrode, because Li-FeF2 is a simpler
conversion system (ideally only Fe2+
and Fe0
are involved) than
Li-FeF3 (Fe3+
, Fe2+
, and Fe0
are involved). Figure 1a shows the
electrochemical profile of a Li/FeF2 battery discharged at a
current of C/12 (1 C = 571 mA g−1
for FeF2) to ∼1.2 V. The
discharge cutoff voltage was chosen based on previous
literature15
and to ensure that the FeF2 electrode achieved
near theoretical capacity (2 Li per FeF2). During charge, the
battery was charged at a rate of C/6 to 4.2 V (the current was
doubled due to limited time). After the constant-current
charging step, a constant-voltage charging step was applied at
4.2 V until the current dropped to ∼C/50. Fe K-edge XAS
spectra were collected every 18 min during the electrochemical
Figure 1. In situ XAS results on an FeF2 electrode. (a) Voltage profile of an FeF2 NW electrode discharged at a current rate of 1/12 C (1 C = 571
mA g−1
for FeF2) and recharged at a current rate 1/6 C. (b) XANES and (c) EXAFS spectra taken at every 18 min during active discharge (+0.05 xLi
per spectrum) and charge (−0.10 xLi per spectrum), respectively. The black arrows indicate the isosbestic points shared by the XANES spectra.
Journal of the American Chemical Society Article
DOI: 10.1021/jacs.6b00061
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
B
3. cycling so that the change in average states of lithiation (xLi)
was +0.05 per spectrum during discharge and −0.1 per
spectrum during charge (see xLi for each spectrum in Table
S1). The change in Fe oxidation state and local bonding
structure was monitored, respectively, by X-ray absorption
near-edge structure (XANES, Figure 1b) and extended X-ray
absorption fine-structure spectroscopy (EXAFS, Figure 1c).
During discharge (xLi = 0 → 1.99 Li per FeF2, region I in
Figure 1), we observed that the absorption edge of the XANES
spectra gradually shifted toward lower energies, the white line
intensity concurrently decreased, and an isosbestic point is
shared by all the spectra (indicated by the arrow), indicating a
two-phase conversion reaction FeF2 + 2Li+
+ 2e−
→ Fe + 2LiF.
Accordingly, in the EXAFS patterns, the intensity of FeF2-
related peaks gradually decreases (marked with “−”) as the
intensity of Fe-related peaks increases (marked with “+”).
Standard EXAFS patterns of FeF2 and Fe are shown in Figure
S4 for comparison. It appears that FeF2 became lithium
saturated and started to decompose into LiF and Fe quickly, as
we observed the metallic Fe-related EXAFS peaks as soon as
the cell voltage hit the plateau at ∼1.75 V (<0.05 Li insertion).
This result is consistent with the calculations done by local
environment-dependent GGA+U (DFT-LD-GGA+U)29
but
different from those by DFT-GGA,14,17
which show that
lithiation of rutile FeF2 first produces a mixture of metallic Fe
and substoichiometric Li0.5FeF3 prior to producing LiF.14,17
Interestingly, we also observed progressive shifts in the
EXAFS peaks during discharge. For example, the Fe-related
peak shifted toward smaller R values as the discharge reaction
proceeded, decreasing from ∼2.3 Å (∼0 Li insertion) to ∼2.1 Å
Figure 2. In situ XAS and TEM on FeF3 NW electrodes. (a) Voltage profile of an FeF3 NW electrode discharged and recharged at a current rate of
1/10 C (1 C = 712 mAh g−1
). (b) XANES and (c) EXAFS spectra taken every 18 min during active discharge (+0.09 xLi per spectrum) and charge
(−0.09 xLi per spectrum). The black arrows indicate the isosbestic points. (d) Voltage profile of an FeF3 MW electrode discharged and recharged at a
current rate of 1/10 C, shown as a comparison to the NW electrode. (e) Phase evolution during the cycling of the FeF3 NW electrodes, which is
estimated by linear combinational fitting analysis of the XANES spectra. (f) High-angle annular dark-field, bright-field STEM images and schematic
illustration showing the microstructure of a bundle of fully lithiated FeF3 NWs, which is made of interconnected Fe domains surrounded by LiF. The
STEM images were recorded in the in situ TEM experiment.
Journal of the American Chemical Society Article
DOI: 10.1021/jacs.6b00061
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
C
4. (∼1.99 Li insertion). Further EXAFS fittings revealed that the
Fe−Fe bond length gradually decreases (Figure S5), which
indicates that the Fe nanoparticles formed initially have a larger
lattice constant than those formed later during discharge
(conversion), consistent with results from the previous in situ
TEM experiments on FeF2 nanoparticles.17
During charge (xLi = 1.99 → 0.02 Li per FeF2, region II in
Figure 1), the changes in both XANES spectra and EXAFS
patterns closely mirror what occurred during discharge,
indicating that Fe and LiF are gradually reconverted into a
rutile phase highly similar to FeF2 in the local structure. This
rutile phase most likely nucleates first at the interface between
the electrolyte and the active particles (now made of LiF/Fe
nanocomposites), where Li-ions are extracted and transferred
into the electrolyte most easily. When the cell was charged to
>∼3.3 V, some Fe was overcharged to +3 oxidation state, as
evidenced by the absorption edge of the XANES spectra
shifting toward higher energy and the Fe−F related peaks in the
EXAFS patterns shifting toward smaller R value than that of the
pristine Fe2+
F2 electrode. We also performed a linear
combination fitting analysis (LCA; see fitting examples in
Figure S6a and fitting parameters in Table S1) to estimate the
relative mole fraction of different Fe oxidations states (Figure
S7). The results reveal that the electrode was charged back to a
multiple phase mixture containing Fe, Fe2+
, and Fe3+
, not the
pure rutile FeF2 phase.
In Situ XAS and TEM on FeF3 Electrodes. Next, we
studied the reaction mechanism of an FeF3 NW electrode. An
Li/FeF3 battery was discharged at a current of C/10 (1 C = 712
mA g−1
) to 1.0 V and then charged at a rate of C/10 to 4.5 V,
after which a constant-voltage charging step was applied at 4.5
V until the current dropped to ∼C/50 (Figure 2a). Fe K-edge
XAS spectra were collected every 18 min during the
electrochemical cycling so that the change in average states of
lithiation (xLi) was about +0.09 per spectrum during discharge
and −0.09 per spectrum during charge (see xLi for each
spectrum in Table S2). The electrochemical profile (Figure 2a)
is divided into four different regions based on features observed
in the XANES spectra (Figure 2b) and EXAFS patterns (Figure
2c).
In discharge region I in Figure 2a−c (xLi = 0 → 0.78 Li per
FeF3), the Fe3+
in FeF3 is gradually reduced to Fe2+
with Li
uptake, as evidenced by the shift in absorption edge of the
XANES spectra. Meanwhile, the change in EXAFS peak
position and intensity indicates that the local structure deviates
from that of the original rhombohedral FeF3 and becomes
increasingly rutile-like, which resembles rutile FeF2 after 0.78 Li
insertion (Figure S8). We further carried out EXAFS fitting and
found out that the first set of data collected after discharge
region I (xLi = 0.79) could be best modeled using the scattering
paths generated from rutile FeF2 (see fitting results in Figure S9
and Table S2). For the FeF3 electrode at a state of lithiation of
xLi = 0.79, the coordination numbers are slightly smaller, while
coordination distances are slightly larger than those of rutile
FeF2 standard, indicative of a slightly defective rutile structure.
In another Li-FeF3 NW battery discharged at a slower rate of 1/
20 C, we observed two different isosbestic points in the XANES
spectra (Figure S10) in region I, which may be indicative of two
different trirutile LixFeF3 phases. No additional isosbestic
points were observed afterward. In the subsequent discharge
region II in Figure 2a−c (xLi = 0.78 → 2.82 Li per FeF3), in the
changes of the absorption edge, white line intensity, and
EXAFS peak position and intensity, we observed changes that
are highly similar to those which occurred during the discharge
of the FeF2 NW electrode (Figure 1, region I), indicating
reduction of a rutile Fe2+
-containing phase to metallic Fe. We
also studied the phase and microstructural evolution of the
FeF3 NW electrode by in situ TEM electron diffraction (ED)
and scanning transmission electron microscopy (STEM), which
show results consistent with the in situ XAS experiments. The
in situ ED patterns (Figure S11 and Movie S1) show that the
FeF3 NWs were first lithiated to form rutile FeF2 phase before
full reduction to metallic Fe. The in situ STEM (Movie S2)
shows that the lithiation reaction initiated from the surface and
propagated toward the core of each electrochemically active
domain. Notably, after being fully lithiated, the microstructure
of the FeF3 NW electrode is similar to that of the fully lithiated
FeF2 nanoparticles.16,17
Nanocomposites consisting of bicon-
tinuous LiF/Fe networks were formed (Figure 2f). The average
size of the Fe domains is 2−3 nm. As the starting point for the
charge process, this microstructure also provides the key to
understanding the phase evolution during delithiation. The
charge reaction (delithiation) most likely first initiates from the
surface of the active particles (now made of LiF/Fe
nanocomposites), where Li-ions are extracted and transferred
into the electrolyte most easily.
We performed LCA (see fitting examples in Figure S6b and
fitting parameters in Table S3) to estimate the relative mole
fraction of different Fe oxidation states (Figure 2e) during the
discharge (and charge) of the FeF3 electrode. We found that a
noticeable amount of Fe (>5%) already existed at xLi = 0.61 and
Fe3+
, Fe2+
, and Fe coexisted in the electrode between xLi = 0.61
and 2.15 (<5% Fe3+
, Figure 2e, Table S3). This result indicates
that the reduction of Fe2+
to Fe had already started on the
outside (Fe2+
-containing region) surface before the first
reduction (Fe3+
to Fe2+
) fully finished in the whole electro-
chemically active particle. An interesting question is what Li
composition in the Li-FeF3 system is necessary for metallic Fe
to begin forming, since different values xLi = 0.75, 0.92, or 1.0
were previously reported in FeF3/carbon nanocomposite
samples.14,15,25
In order to understand this issue, we studied
the reaction mechanism of FeF3 MWs for comparison (Figure
S12), which consist of larger particle domains than the NWs
(Figure S2). The FeF3 MW/Li cell was cycled at the same rate
as the FeF3 NW/Li cell, but its voltage profile (Figure 2d)
shows different features. The first sloping plateau at higher
voltages (region I) is much shorter, but the second flat plateau
(region II) is much longer than those of the FeF3 NW/Li cell.
Accordingly, the XANES spectra and EXAFS patterns of the
FeF3 MW electrode (Figure S12a−c) are also different from
those of the NW electrode (Figure 2a−c). LCA fittings
performed on the XANES spectra (fitting examples in Figure
S6c and fitting parameters in Table S4) reveal that a noticeable
amount of metallic Fe started to exist at xLi = 0.31 (>5% mole
fraction) and Fe3+
, Fe2+
, and Fe coexisted in the electrode until
xLi = 2.41 (Fe3+
< 5%, Figure S13 and Table S4). We also note
that the energy density of the Li-FeF3 MW battery is lower than
the Li-FeF3 NW battery due to the loss of the high-voltage
plateau.
The comparison between the reaction behavior of FeF3 NWs
and MWs reveals how reaction homogeneity and voltage
profiles (energy density) are affected by the size of the active
domains, which correlates with the reaction kinetics. As shown
by the in situ STEM experiment (Movie S2), the lithiation
reaction of FeF3 proceeds from the surface to the core of each
electrochemically active domain. In FeF3 MWs that consist of
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D
5. larger active domains (and thus smaller surface area) than the
NWs, the applied current (1/10 C) is more likely to exceed
what the reaction kinetics (Li+
and/or electron transport) can
keep up with. Therefore, the Fe2+
-containing rutile phase
produced in the initial reduction (lithiation) on the outside is
further lithiated to produce LiF and Fe early at xLi = 0.31 before
the interior FeF3 domains can begin to react (see schematic
illustration in Figure S14). The occurrence of the reduction of
Fe2+
to Fe dictates the voltage profile despite the presence of
unreacted FeF3 at the interior so that the second flat plateau
becomes much longer (Figure 2d). By contrast, in the NWs,
faster reaction kinetics (shorter distance for Li+
and/or electron
transport) allow the first reduction step (Fe3+
→ Fe2+
) to
further complete before Fe formation (at xLi = 0.61).
Furthermore, in the FeF3/carbon nanocomposite samples
reported previously,14,15,25
even smaller particle size, better
electrical contact afforded by the carbon matrix, and small
current densities likely facilitate the first reduction to complete
even more, which explains the initial formation of Fe
approaching xLi at 1.0. Now we can see that xLi is better
considered a measure of the state of lithiation averaged within
the entire electrode, and it does not necessarily reflect the
stoichiometric information on the LixFeF3 phase that readily
extrudes Fe upon further lithiation, especially in the kinetically
limited situations (such as the MWs). It is possible that in all
cases Fe starts to form at y = 1, but the existence of unreacted
FeF3 phase at the core of the active particles leads to xLi < 1.
These results illustrate the critical role of reaction kinetics and
inhomogeneity in governing the conversion processes and
voltage curves for the FeF3 conversion electrode and have
implications for other electrode materials operating through
sequential multiple-step processes.
Additionally, we compared the electrochemical capacity with
the capacity estimated from the LCA fittings for the FeF2 and
FeF3 NW electrode and found reasonable matches (Figure
S15). These results suggest that electrolyte decomposition (or
any other nonmetal-center side reactions) does not contribute
significantly to the observed discharge capacity in the iron
fluoride conversion electrodes studied in this work (when low
cutoff voltage ≥1 V is used). This reaction behavior is different
from metal oxide conversion electrodes that are discharged to
lower voltages (<1 V),28,30−33
in which additional capacity was
often observed.
During charge of the FeF3 NW electrode (region III of
Figure 2a−c, xLi = 2.82 → 1.03 Li per FeF3), the changes in
XANES spectra and EXAFS patterns not only mirror what
occurred in discharge (region II of Figure 2a−c) but also were
highly similar to those observed during the charge of the FeF2
electrode (region II of Figure 1). EXAFS fitting was also
performed, and the data could be best modeled using scattering
paths generated from rutile FeF2 and Fe (Figure S16). These
results provide clear evidence that a rutile-FeF2-like phase is
formed during charge of the FeF3 electrode. These findings are
actually consistent with previous results from ex situ NMR and
PDF experiments15
but in disagreement with the DFT-GGA-
based reaction mechanism,14,17
which suggested formation of
Fe3+
-containing intermediate phases rather than the FeF2
intermediate during charge. In fact, we only observed oxidation
of Fe2+
into Fe3+
when the cell voltage exceeded ∼3.3 V in
charge region IV (Figure 2a−c, xLi = 1.03 → 0.53 Li per FeF3),
as evidenced by the absorption edge further shifting toward
higher energies. Further, the local structure at the final state
(0.53 Li per FeF3) still resembles rutile FeF2. According to
EXAFS patterns, the Fe-F peak position is slightly smaller than
that in rutile FeF2 but larger than that in rhombohedral FeF3
(Figure 2c) in R value. Therefore, we suggest that some trirutile
Li0.5FeF3 may exist at the end of the charge process.
DFT Calculations and Reaction Pathway of FeF3
Electrodes. To corroborate the experimental findings, we
performed a detailed multicomponent phase analysis using
DFT calculations of materials in the Li-Fe-F ternary system.
The DFT calculations were performed using GGA, GGA+U,
and hybrid HSE functionals,34
which have been shown to more
accurately reproduce experimental formation energies and Li
insertion voltages for transition-metal-containing compounds
than GGA.35,36
The Li-Fe-F phase diagrams calculated using
GGA and GGA+U are shown in Figures S17 and S18,
respectively. The results are consistent with those previously
reported (GGA,14,17
GGA+U29
). The HSE phase diagram
shown in Figure 3a is very similar to the GGA+U diagram
(Figure S18), with the exception that Li0.25FeF3 is not stable
from GGA+U. As HSE is a somewhat more general method
than GGA+U (due to GGA+U generally requiring a fitted U for
every transition metal), we chose to include and discuss our
HSE results in the main text and provide our GGA+U (and
GGA) results in the Supporting Information section for
comparative purposes. In all the phase diagrams presented in
this work (Figures 3a, S17, and S18), the red dots represent
stable phases, the black dots represent materials that were
predicted to be unstable, and the purple dots are important
composition points where no lithiated FeF2 or FeF3 materials
were calculated due to an insufficient number of interstitial sites
for Li insertion.
When examining the stable FeF2 lithiation path (green
dotted line in Figure 3a), FeF2 immediately begins to dissociate
upon lithiation to precipitate metallic Fe and LiF. This three-
phase region persists over the entire lithiation path until xLi = 2,
at which point the reduction from Fe2+
to metallic Fe is
complete and produces a two-phase mixture of metallic Fe and
LiF. This lithiation path is consistent with the in situ XAS
results on the FeF2 electrode (Figure 1, region I) and the
previous DFT-LD-GGA+U calculations,29
but clearly different
than the one predicted by DFT-GGA calculations.14,17
In
delithiation of the Fe/LiF (1:2 in mole ratio), FeF2 should be
formed as the stable phase, but Li0.5FeF3 may also be produced
from FeF2 if there is excess LiF, which is likely the case at the
surface of the active particles and indeed observed by the in situ
XAS experiment (Figure 1, region II).
The stable lithiation path for FeF3 (red dotted line in Figure
3a) shows direct Li intercalation when x ≤ 0.5. Upon lithiation
to xLi = 0.25 (Li0.25FeF3), the pristine rhombohedral FeF3 phase
is no longer stable, and a phase change to the defected trirutile
structure occurs. This defected trirutile phase is stable up to xLi
= 0.5 (Li0.5FeF3), after which dissociation to FeF2 and LiF
occurs because no more interstitial sites for lithium insertion
are available. When xLi = 1, all Fe3+
has been reduced to Fe2+
,
and the system is a two-phase mixture of FeF2 and LiF. Further
lithiation promotes the reduction of Fe2+
to metallic Fe, which
is exactly the same process as the lithiation of FeF2. In
delithiation of Fe/LiF (1:3 in mole ratio), FeF2 should be
formed as the stable phase first; Li0.5FeF3 can be produced later
from the FeF2 and the remaining LiF. These DFT-HSE
calculation results are in good agreement with the in situ XAS
results (Figure 2a−c) and the corresponding discussion on the
FeF3 electrode and the previous DFT-LD-GGA+U calcula-
tions.29
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E
6. Figure 3c shows the DFT lithiation voltages. Since they are
representative of equilibrium voltages, in which case no
polarization or overpotential is included, they are higher than
those experimentally observed when a current was applied
(Figures 1a and 2a). When the experimental battery is allowed
to relax to approach equilibrium conditions, its voltages should
become closer to the DFT calculated values. This trend is
indeed seen from the GITT measurements after relaxation,
which is discussed in more detail below.
Combining the results from the in situ XAS, TEM, and HSE-
DFT calculations, we can now propose complete and consistent
reaction pathways for FeF3 (and FeF2) electrodes (Figure 3c),
which is quite symmetrical just like what the XAS data displays
(Figures 1b,c and 2b,c; better seen in surface contour plots of
XANES and EXAFS in Figure S19). We note that kinetic
limitations can cause one reaction not proceed completely over
the entire particle domain before the subsequent one being
forced to initiate in the prereacted region under galvanostatic
condition, causing compositional inhomogeneity and less
symmetrical phase evolution profile (FeF3 MWs vs NWs,
Figures S13 vs 2e). This new proposed understanding is clearly
different from the one proposed previously based on DFT-
GGA calculations,14,17
which was the basis for understanding
the large voltage hysteresis in FeF3 and other conversion
electrode materials. The previous model assumes that the
electrochemical reaction is controlled by the slow diffusion of
Fe so that Fe is oxidized to the highest oxidation state (Fe3+
)
during charge in order to maximize lithium extraction. A series
of Fe3+
-containing phases, such as spinel Li15/8Fe3+
3/8F3,
ilmenite Li3/2Fe3+
1/2F3, and rutile Li3/4Fe3+
3/4F3 are predicted
to form sequentially during charge, which constituents a
fundamentally different reaction pathway from that taken
during discharge (reduction of rutile Fe2+
F2 like phase to
Fe).14,17
This model provided a seemingly reasonable
explanation for the voltage hysteresis because the presence of
different phases (and with Fe at different oxidation states)
during discharge and charge would indeed lead to different
potentials. However, our new mechanistic understanding
clearly suggests that other mechanisms are responsible for the
voltage hysteresis.
GITT Analysis. To better understand the possible causes of
the hysteresis, we performed GITT experiments on the FeF3
NW and MW electrodes (Figure 4a). The cells were allowed to
relax for 4 h after every 1 h discharging/charging at 50 mA g−1
.
The GITT profiles are also divided into four regions based on
the understanding of phase evolution in the FeF3 NW and MW
Figure 3. DFT-HSE calculation results and FeF3 reaction pathway. (a) DFT-calculated Fe-Li-F phase diagram using the HSE approach. The
lithiation pathways for FeF3 and FeF2 are indicated by the red and green dashed arrows, respectively. Red dots represent stable phases, black dots
represent unstable lithiated phases, and purple dots indicate potentially active compositions where no lithiated compound was calculated. The
fractions of lithiation x for LixFeF2 and LixFeF3 are labeled for both pathways. (b) Calculated DFT-voltage curves for FeF3 and FeF2 at different
states of lithiation. (c) Discharge and charge reaction pathways of the FeF3 electrode and their crystal structures, which are derived from both the
experimental and DFT calculation results. Li, Fe, and F atoms are represented by green, blue, and red spheres. Ref 14 was used as a guide for the
range of Li compositions to test in these structures.
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F
7. electrodes. Figure 4b provides a close-up view of the GITT
process. In the discharge half-cycle (red curve), as soon as the
current is removed, the voltage first suddenly increases a small
amount and then gradually increases as the electrode
approaches equilibrium condition.37
The opposite occurs in
the charge half-cycle (blue curve in Figure 4b). We found that
the voltage after the 4 h relaxation (Vrelax, black dashed lines in
Figure 4a) correlates with the composition of the electrodes
inferred from the in situ XAS results. For example, since the
Fe3+
F3 phase in the MW electrode is reacted more slowly than
that in the NW electrode during discharge, Vrelax observed in
the MW electrode is higher initially (black dashed lines in
Figure 4a). As the Fe3+
F3 phase is consumed, the two Vrelax
curves of the MW and NW electrodes become more
comparable. Figure 4c shows how much the voltage relaxes
after 4 h for the FeF3 NW and MW electrodes, respectively, at
different states of lithiation. During discharge, the voltage
relaxes a lot more in the MW electrode than the NW electrode
(Figure 4c), which is a direct consequence of inhomogeneity:
The intermediate phase Fe2+
F2 is already being further lithiated
to produce LiF and Fe on the outside despite the presence of
unreacted FeF3 at the interior of the active particle. After all
FeF3 is consumed, the magnitude of the voltage relaxation in
the MW and the NW electrode becomes comparable. Similar
analysis based on reaction homogeneity can be made for the
charging process. Figure 4d shows the remaining voltage
difference at the same state of lithiation between charge and
discharge steps after the 4 h relaxation (Vgap) for both the MW
and NW electrodes. Vgap can become slightly smaller based on
its changing trend if the relaxation time is further increased.
However, it did not become zero after 24 h relaxation in a
separate experiment. In addition, it was previously reported by
Liu et al. that a 280 mV voltage gap remained even after 72 h
relaxation (measured at states of lithiation of xLi = ∼2.0).19
■ DISCUSSION
Proposed Origins of Voltage Hysteresis in FeF3
Conversion Electrodes. By integrating all experimental and
theoretical simulation results, we can identify the following
components from the GITT that contribute to the voltage
hysteresis observed at nonzero current (see Figure 4b). The
first one is the iR voltage drop, which is the sudden voltage
jump after the current is removed and typically <100 mV in our
measurements. The second component is the reaction
Figure 4. GITT of FeF3 NW and MW electrodes. (a) GITT profiles of an FeF3 NW electrode and a MW electrode. The cells were allowed to relax
for 4 h after every 1 h discharging/charging at 50 mA g−1
. Inset is a schematic illustration of the microstructures of an active domain in the FeF3
electrode at states close to full lithiation (xLi = ∼3), which are drawn based on the STEM results. (b) Close-up view of the GITT curve for the NW
electrode. IR drop, reaction overpotential (η), and the remaining voltage difference after relaxation (Vgap) are marked to show the components that
contribute to the large voltage gap during cycling. (c) Voltage change after the 4 h relaxation at different states of discharge and charge of the NW
and MW electrodes, respectively. (d) Voltage difference (Vgap) between charge and discharge steps after the 4 h relaxation at the same state of
lithiation of the NW and MW electrodes, respectively.
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8. overpotential (η) that is required to nucleate and grow new
phases, drive mass transport, and overcome the interfacial
penalty for making nanophases. This overpotential is
manifested in the voltage plummet when the current is applied
and the spike when the current is removed. However, its
magnitude is not straightforward to quantify using the GITT
results, because the active particles undergo phase trans-
formations and cannot achieve a truly homogeneous
composition over the entire particle simply through Li+
diffusion during the relaxation. Reverse-step potentiostatic
intermittent titration technique may be a more suitable
approach to provide the quantitative evaluation, according to
which the overpotential is 300 mV for the conversion reaction
(reduction of intermediate product FeF2 to LiF/Fe, measured
at xLi = 1.2 per FeF3) and 70 mV for reconversion reaction
(LiF/Fe to FeF2, measured at xLi = 1.2 per FeF3).20
The third component that leads to the hysteresis, but has not
been considered in detail in previous literature, is the difference
in spatial distribution of electrochemically active phases during
discharge and charge as well as the way these phases are
connected in the electrochemical system (i.e., access to Li+
and
electron). For example, we can infer from the in situ TEM and
XAS results that at states of lithiation close to xLi = 3 per FeF3,
during discharge the intermediate phase FeF2 is located at the
interior of the active particles, while Fe/LiF is on the outside
and has contact with the electrolyte and current collector (see
schematic illustration in Figure 4a inset, left). In contrast,
during charge, the intermediate phase FeF2 should first formed
on the outside, while Fe is located inside and may be screened
or even isolated from the electrochemical system by the
electrically and ionically insulating FeF2 phase (Figure 4a inset,
right). The different distribution of active phases (Fe, LiF and
FeF2) during conversion and reconversion was also predicted
by phase-field simulation recently.38
The correlation between
phase distribution in an active particle and voltage hysteresis
can be better seen in the schematic illustration in Figure 5.
Even though the system is at the same state of lithiation, a
FeF2-rich (Li-poor) surface (during charge) and a Fe/LiF (Li-
rich) surface (during discharge) will set the system at different
potentials versus the Li+
/Li potential, which introduces a
voltage gap (similar to concentration overpotential). This
hysteresis caused by compositional inhomogeneity cannot be
fully eliminated by voltage relaxation (zero current) because it
is very difficult, if not impossible, to make the relevant phases
(or Li+
distribution), such as FeF2 (“Li-poor” phase) and Fe/
LiF (“Li-rich” phase) at the states of lithiation close to xLi = 3
per FeF3, become spatially homogeneous simply by Li+
diffusion. Such relaxation process also requires the migration
of F−
and Fe2+
ions, which typically move very slowly. The
situation is different from that of intercalation electrode
materials (such as LiCoO2 and graphite), in which during
relaxation the Li+
distribution can become homogeneous more
easily because there is no need for other ions or atoms to
migrate. Here we use Vgap to estimate the nonvanishing
hysteresis at different states of lithiation, which is typically 300−
500 mV for the NW electrode and 300−600 mV for the MW
electrode when only Fe2+
and Fe0
are present (Figure 4d).
When Fe3+
is formed during charge and thus more significant
inhomogeneity is introduced, the hysteresis gets significantly
larger for both the NW (>550 mV, xLi = 0.63) and the MW
electrode (>700 mV, at xLi = 1.26 and 1.05). Now it is easier to
understand why ∼1 V voltage gap was observed even when the
phases present are the same. For example, at states of lithiation
xLi = ∼1.8 (approximately the middle point in Figure 5), if we
add the hysteresis caused by compositional inhomogeneity
(∼400 mV according to Figure 4d) to the hysteresis caused by
reaction overpotential (300 mV during discharge + 70 mV
during recharge = 370 mV according to ref 20) and iR drop
(∼100 mV combined discharge and charge according to Figure
4a), we can expect a voltage gap ∼1 V, which is consistent with
what we observed during the galvanostatic discharge and charge
experiments (Figure 5).
This newly proposed compositional-inhomogeneity mecha-
nism for driving hysteresis likely plays a role in many kinetically
limited conversion materials where during Li insertion
(extraction), the most reduced (oxidized) phases are present
at the active surface and drive the potential down (up)
compared the theoretical open-circuit voltage. Interesting
comparisons may also be made with Li-S and Li-O2 batteries
during discharging/charging: After voltage relaxation, a voltage
gap remains in the Li-S system possibly due to presence of
different Li2Sn (n = 8, 6, 4, 2, and 1) phases,39
but approaches
zero in the Li-oxygen system because there is only Li2O2.
40
These new understandings suggest strategies to minimize the
voltage hysteresis, which is important for improving the battery
energy efficiency. One straightforward approach is constructing
a composite electrode consisting of nanostructured active
particles whose size must be comparable to the length scale of
the conversion reaction (<10 nm for FeF3) and directly
connected to electrically conductive scaffolds. A promising
example could be embedding active materials between
graphene layers to make a graphite intercalation compound.41
This is expected to minimize the voltage hysteresis caused by
compositional inhomogeneity as well as the iR drop. However,
sufficient amount of active materials needs to be embedded so
that the overall volumetric energy density is not severely
compromised. Another approach that deserves further explora-
tion is incorporating another cation or anion into the lattice
(similar to the function of a “catalyst”) to create a more
disordered microstructure and improve ionic and electrical
transport properties so that the reaction overpotential can be
Figure 5. Schematic illustration of the phase evolution in an active
FeF3 particle with compositional inhomogeneity and voltage
hysteresis. For the sake of clarity and simplicity, the volume change
during the lithiation/delithiation process is ignored, and compact
layers are shown in this schematic illustration. Note that ohmic voltage
drop and reaction overpotential also contribute to the voltage
hysteresis at nonzero current, in addition to that caused by
compositional inhomogeneity. The voltage profile is collected from
an FeF3 NW electrode cycled at 1/10 C rate. The FeF3 domain size is
∼10−20 nm according to the TEM characterization.
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H
9. reduced. It is proposed that this approach can achieve higher
energy density than the first one because no additional inactive
components are introduced. As an example, the ternary fluoride
CuyFe1−yF2 solid-solution exhibits a smaller hysteresis than a
pure FeF2 electrode.42
One major challenge is to preserve the
beneficial effect in repeated cycling, as Cu is rapidly lost
through Cu+
dissolution into the liquid electrolyte.42,43
■ CONCLUSION
In summary, we elucidate the electrochemical reaction
mechanism of the FeF3 (and FeF2) conversion electrode
through integrated (in situ) experimental and theoretical
studies. The phase evolution in the electrode is symmetrical
during discharge and charge, but the spatial distribution of the
electrochemically active phases at the single-particle level,
which is controlled by reaction kinetics, is very different. Such
compositional inhomogeneity changes the way the active
phases are connected to electrolyte (Li+
) and current collector
(electron) during discharge and charge, which consequently
introduces a voltage gap. This, along with reaction over-
potential and the iR voltage drop, leads to the large voltage
hysteresis. This understanding is contrary to the popular belief
that attributes the voltage hysteresis of the FeF3 electrode to
asymmetric reaction pathways during discharge and charge.
Further, since the issues that contribute to the hysteresis are
kinetic in nature, it is hopeful that the voltage hysteresis can be
reduced to a reasonable level (<300 mV) by designing and
optimizing material microstructure and electrode architecture.
These results can help understand and minimize the voltage
hysteresis in other conversion electrode materials, where
compositional inhomogeneity was observed but not scruti-
nized,43−46
despite their asymmetrical reaction pathways
controlled by reaction kinetics. This work brings new hope to
the development of high-energy-density LIBs based on
conversion chemistry and provides insight to the hysteresis
problems in other next-generation battery chemistries, such as
Li-S and Li-O2.
■ EXPERIMENTAL SECTION
Synthesis of FeF3 Samples. FeF3 NWs and MWs were
synthesized by thermal dehydration of α-FeF3·3H2O NWs and
MWs, respectively, at 350 °C for 2.5 h in argon atmosphere, based
on previous work.18,26
Briefly, the precursor α-FeF3·3H2O NWs and
MWs were first synthesized, respectively, by reacting different amounts
of Fe(NO3)3·9H2O and HF aqueous solution in ethanol at 60 °C for
18 h. The concentration ratio of c(Fe3+
):c(HF):c(H2O) is
13.3:5560:6760 mM for the NW synthesis and 53.2:500:11575 mM
for the MW synthesis. FeF2 NWs were prepared by heating FeF3 NWs
(90 wt %) with a small amount of glucose (10 wt %) at 450 °C for 2.5
h.
Characterization. SEM images were collected using a LEO 55 VP
scanning electron microscope at 5 kV. TEM images and ED patterns
were recorded using either a Philips FEI FM200 (200 kV) or a FEI
Titan TEM (200 kV). PXRD data were collected on a Bruker D8
diffractometer using Cu Kα radiation. Electrochemical measurements
were performed on electrodes made of 70 wt % active material, 20 wt
% carbon black, and 10 wt % binder. The electrodes were packed into
CR2032-type coin cells in an argon-filled glovebox, with Li metal as
the counter/quasi-reference electrode, 1 M LiPF6 in EC/DMC (1/1
by volume, BASF) as the electrolyte, and electrolyte-soaked poly-
ethylene-polypropylene films as the separator. Galvanostatic cycling
and GITT experiments were performed using either a Biologic SP-200
or a VMP-3 Potentiostat/Galvanostat controlled by EC-Lab software.
In situ XAS. In situ X-ray absorption spectra were collected at
beamline X18A, NSLS, BNL, using a perforated 2032-type coin cell
with holes on both sides sealed by Kapton tapes. The electrodes were
made of 70 wt % active material, 20 wt % carbon black, and 10 wt %
binder and coated on aluminum foil (25 μm thickness). The
measurements were performed in transmission mode using a Si
(111) double-crystal monochromator, which was detuned to ∼35% of
its original maximum intensity to eliminate the high order harmonics
in the beam. A reference X-ray absorption spectrum of metallic Fe (K-
edge 7112 eV) was simultaneously collected using a standard Fe foil.
Energy calibration was done using the first inflection point of the Fe K-
edge spectrum as the reference point. The X-ray absorption data were
processed and analyzed using IFEFFIT-Athena, Artemis, and Atoms.
Standard reference spectra from FeF3, FeF2, and Fe powders were
collected to carry out spectrum fitting and estimate the ratio between
different Fe oxidation states.
In situ TEM Experiments. In-situ STEM images, ED patterns were
recorded at 200 kV in a JEOL2100F microscope. The in situ
nanobattery consists of a copper half-grid (current collector), FeF3
NWs supported on the amorphous carbon film (cathode), and Li
metal (anode) was fabricated in an argon-filled glovebox and
transferred into the TEM chamber by using an argon-filled plastic
bag. A thin passivation layer of LiNxOy on the surface of the Li that
formed due to brief exposure to air before transferring to the TEM
chamber acted as the solid electrolyte. The biasing probe was
connected to the carbon membrane, and the reaction was initiated by
applying a negative bias typically at a value of 2 V.
Computational Methods. All calculations were performed using
DFT with the Vienna ab initio simulation package (VASP)47
and a
plane wave basis set. The hybrid functional of Heyd, Scuseria and
Ernzerhof (HSE06)34
with Perdew−Burke−Ernzerhof (PBE)-type
pseudopotentials48
utilizing the projector augmented wave (PAW)49
method was used for Fe, F, and Li atoms. The valence electron
configurations of Fe, F, and Li atoms were Fe: 3p6
3d7
4s1
, F: 2s2
2p5
, Li:
2s1
. All calculations were performed with spin polarization enabled and
with a plane wave cutoff energy set at least 30% larger than the
maximum plane wave energy for the chosen set of pseudopotentials,
equal to 520 eV. Reciprocal space integration in the Brillouin zone was
performed with the Monkhorst−Pack scheme with k-point densities
set for each material such that total energy convergence errors were <1
meV/cell.50
Bulk Li, Fe, LiF, FeF2, and FeF3 materials were simulated within the
Im3̅m (body-centered cubic structure, Li and Fe), Fm3̅m (rocksalt
structure), P42/mnm (rutile structure), and R3̅c (rhombohedral
structure) space groups, respectively. The lithiated FeF2 structures,
LixFeF2 (x = 0.25, 0.5, 1), and lithiated FeF3 structures, LixFeF3 (x =
0.25, 0.5, 1), were simulated as direct Li insertion into the interstitial
sites of the rutile structure (LixFeF2) and rhombohedral, monoclinic,
and defected trirutile structures (LixFeF3). The monoclinic structure
possesses the Cc space group, while the defected trirutile structure is
based on the P42/mnm space group and the ZnSb2O6 structure with
the 2a Wyckoff sites vacant. These vacant sites serve as interstitial
positions for direct Li insertion. The average voltage to insert Li
V̅x1 → x2
(in V/Li) from composition x1 to composition x2 in these
structures is expressed as
̅ = −
−
− − −→V
x x
E E x x E
1
( )
( ( ) )x x x x
2 1
FeF /FeF FeF /FeF
2 1 Li1 2 2
3 2
1
3 2
(1)
where Ex2
FeF3/FeF2
and Ex1
FeF3/FeF2
are the calculated DFT energies of a
lithiated FeF2 or FeF3 material with Li composition x2 and x1,
respectively, and ELi is the DFT energy of metallic Li.
The phase stability of the Li-Fe-F system was analyzed by plotting
the formation energies (relative to the pure elements Li, Fe, F) of each
calculated compound at their respective compositions. The phase
diagram is constructed by calculating the convex hull from these
formation energies. Specific material compositions that are thermody-
namically stable lie on the convex hull, while those that are unstable
are above the convex hull.
Journal of the American Chemical Society Article
DOI: 10.1021/jacs.6b00061
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
I
10. ■ ASSOCIATED CONTENT
*S Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.6b00061.
Supporting figures and tables (PDF)
In situ ED patterns (AVI)
In situ STEM (AVI)
■ AUTHOR INFORMATION
Corresponding Authors
*ddmorgan@wisc.edu
*jin@chem.wisc.edu
Present Addresses
∥
Department of Materials Science and Engineering, Massachu-
setts Institute of Technology, Cambridge, MA 02139, United
States.
⊥
School of Physics, Peking University, Beijing 100871, China.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This research is supported by NSF grant DMR-1106184 and
DMR-1508558 for the synthesis and structural characterization
of the materials, and a UW-Madison WEI Seed Grant and
Research Corporation SciaLog Award for the electrochemical
and theoretical studies. The in situ X-ray absorption spectros-
copy experiments were performed at beamline X18A, National
Synchrotron Light Source, Brookhaven National Laboratory,
which are supported by the U.S. Department of Energy, Office
of Basic Energy Sciences under contract no. DE-AC02-
98CH10886. R.J. and D.M. were supported by the NSF
Software Infrastructure for Sustained Innovation (SI2
) award
no. 1148011. P.G. and F.W. were supported by the Laboratory
Directed Research and Development (LDRD) program at
Brookhaven National Laboratory. L.L. also thanks Vilas
Research Travel Awards for partially supporting the travel
cost to the synchrotron facilities.
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