general battery introduction and Lithium-ion anode, cathode types

1. BATTERY AND ITS
COMPONENTS
BY
S. GOKULNATH
PA – II
ECPS DIVISION
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2. WHAT IS BATTERY?
• It is a device consists of one or more electrochemical
cells with external connections to provide power
electrical devices
• the word “battery” was used to describe a “series of
similar objects grouped together to perform a function,”
as in a battery of artillery
• In 1749, Benjamin Franklin first used the term to
describe a series of capacitors he had linked together
for his electricity experiments
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3. GALVANIC CELL
• In 1780 Luigi Galvani, was dissecting a frog attached to a brass hook,
As he touched the frog’s leg with an iron scalpel, the leg twitched.
Galvani theorized that the energy came from the leg itself
• Volta hypothesized that the frog’s leg impulses were actually caused
by different metals soaked in a liquid. He repeated the experiment
using cloth soaked in brine instead of a frog corpse, which resulted in
a similar voltage. Volta published his findings in 1791 and later
created the first battery, the voltaic pile, in 1800
• Galvanic cell is an electrochemical cell that derives electrical energy
from spontaneous redox reactions taking place within the cell
• E = - ∆G/nF
Voltaic pile
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4. COMPONENTS OF CELL
• Anode - oxidation
• Cathode - reduction
• Electrolyte - ion conduction
• Separator – eliminate electrical
conduct
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5. CLASSIFICATION OF CELL
• Primary cell - cannot be recharged after one
use
• Secondary cell - can be electrically recharged
after use to their original pre-discharge
condition
• Reserve cell - a key component of the cell is
separated from the remaining components,
until just prior to activation
• Fuel cell - all active materials are not an
integral part of the device (as in a battery),
they are fed into batteries from an outside
source
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6. ENERGY AND POWER DENSITY
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7. ANODES
• Initially Lithium (Li) metal was
used, but due to hazardous
effect caused by dendrite
formation
• It reduces the efficiency of the
cell
• It slowly grows and reaches
other electrode causing short-
circuit
• It leads to firing of the battery
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8. ANODES
• Intercalation materials : Positioning of the Li-ions in the
interstitial vacancies of the host material. Low gravimetric
capacity. Eg: Carbon, graphites, LTO
• Alloying/ Dealloying materials : Forms alloys with Li . Very
high gravimetric capacities, but large volume expansion
(>300%). Si, Al, Mg
• Conversion materials : Exchange reaction 𝑀𝑥𝑁 + 𝑦𝐿𝑖
+
+ 𝑦𝑒
−
⟷ 𝑥𝑀 + 𝐿𝑖𝑦𝑁 where M is transition elements (Fe, Co,
Mn, etc.,) and N is electronegative element (such as O, S, P),
but these materials also experience volume expansion.
Materials Today 17(3):110–121
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9. CATHODES
• It serves as host for the Li-ions comes from the anode
during discharge
• Most generally intercalation type materials are commercially
used such as layered oxides LiMO2, spinel LiM2O4, olivine
LiMPO4 , vanadium oxides, Polyoxyanion (orthosilicates
Li2MSiO4). Low theoretical capacity.
• Conversion type materials are under research which provide
high capacities.
• Transition metal compounds such as transition metal oxides,
sulfides, fluorides, phosphides, and nitrides can undergo
conversion reactions yielding materials with high theoretical
capacity (generally from 500 to 1500 mAh/g)
Materials Today 17(3):110–121
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10. COMMERCIAL ELECTRODE MATERIALS
Materials Today 17(3):110–121
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11. ELECTROLYTES
• It is next major component of a battery, provides ion movements between the electrodes
• Should have good ionic conductance, minimum internal resistance, low electronic conductance,
low viscosity, work in wide temperature range, wide electrochemical voltage window, cost
• Generally corresponding ion salts dissolved in solvents are used as electrolytes (liquid
electrolytes)
• Also solid polymer electrolytes, solid electrolytes, ionic liquid electrolytes are under research to
enhance the safety issues
• Majorly non-aqueous based electrolytes are chosen for the high voltage cells because of high
electrochemical voltage window.
• The electrochemical potential window is based on the redox potential of the solvents used in it.
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12. ADDITIVES TO ELECTROLYTES
• Added to enhance the ionic conductivity, battery life or safety
• SEI formation additives : To form and maintain the SEI layer at carbon anode surface. Eg: vinylene
carbonate
• Overcharge inhibitors : To solve safety issues caused by overcharging
• Redox shuttle type : Added redox species gets oxidized at cathode when cell exceeds cut-off voltage goes to
anode gets reduced and shuttles back. Eg: n-butylferrocene
• Cathode Layer Forming : More stable than redox shuttle. High insulating polymer is formed at cathode to
block current and ion diffusion. Eg: Biphenyl
• Ionic Conductivity Enhancers : Increase ionic conductivity. Eg: Crown ethers, anion receptors
(perfluoro borates), cation receptors (polyethylene glycol)
• Flame Retardants : To supress flammability of electrolytes. Eg: LiPF6 (in liquid electrolytes),
polyacrylonitrile (in polymer electrolytes), mostly phosphate additives like trimethylphosphate (TMP)
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13. SOLID ELECTROLYTE INTERPHASE (SEI)
• A passivation layer appears on the surface of the
anode due to the reduction of the electrolyte
below 0.8 V
• It is ionically conducting but electrically insulating
• Thickness of SEI ranges from 20 to hundreds Å
• Complex composition of inorganic and organic
decomposition products
• Cause small capacity loss in first cycle
• Prevents further decomposition of electrolyte
• Prevents co-intercalation of solvent molecules
• Prevents exfoliation of the carbon layer
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14. TERMINOLOGY
• Open Circuit Voltage (Voc) = (µa - µc)/(-nF) µa & µc are electrode potential of anode and cathode
• Operating Voltage (voltage measured in closed circuit) V = Voc – IR (R – internal resistance)
• Theoretical Specific Capacity C0 = 26.8*n/M (unit Ah/g)
• Specific Capacity (Qs) = 1/m0 t1
∫
t2
I(t) dt (unit mAh/g)
• Energy density = Qs * V (unit Wh/kg)
• Power density = Energy density / time (unit W/kg)
• C rate (charge / discharge rate) nC rate means 1/n hours to reach theoretical specific capacity
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15. THANK YOU
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