Jz300480w singh presentation on li ion battery

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Synthesis of Surface-Functionalized WS2 Nanosheets and Performance as Li-Ion Battery Anodes
R. Bhandavat, L. David, and G. Singh
J. Phys. Chem. Lett., 2012, 3 (11), pp 1523–1530

Separation of bulk tungsten disulfide (or WS2) into few-layer two-dimensional (2-D) crystals is of interest because of their high surface area for certain chemical processes and size-dependent optical and electronic characteristics. Herein, we demonstrate a process that involves the physical separation of weakly bonded WS2 layers by use of a strong acid treatment (chlorosulfonic acid) at 2 mg/mL, followed by quenching in deionized (DI) water. X-ray photoelectron spectroscopy of the superacid-treated WS2 suggests the formation of W–O type bonds, signifying oxidation of tungsten and reduction of the sulfur phase. Thermogravimetric analysis showed a three-phase weight-loss pattern, suggesting acid functionalization of WS2 surfaces. We also studied the electrochemical behavior of an acid-treated WS2 anode in a lithium half-cell configuration that showed a three-step charge–discharge behavior, characteristic of a conversion reaction. The electrochemical capacity was 118 mAh/g after 50 cycles.

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  • 1.WS2 is a 2-D structured TMDC, with W sandwiched between sulfur atoms. Each WS2 sheets are weakly bonded by vanDerWal forces. 2. Large scale functionalization, with dimension as large as possible is desired for use in industrial applications like energy storage, electronic switches and coatings. 3. Encouraged by the methodology of Prof. Coleman for exfoliating graphene sheets by organic solvents, generating surface charge and resulting in electrostatic repulsion.
  • 4.Figure a- Comparison with organic solvents, showed most stable dispersion for WS2 in cholorosulfonic…it was stable even after few days. 5.Figure b- UV showing maximum absorption intensity for WS2 in superacid, confirms the visual observations 6.Figure c- Surface potential of the sheets, quantifies the charge on the surface results in repulsion force between the sheets which keeps them separated. 7. Figure d- TGA plot : Presence of functional groups on WS2 sheet surfaces are seen as weight loss when the exfoliated sheets are heated up to 200 C; then follows a typical weight WS 2 profile. 8. XPS characterizes the surface functionalization of sheets as W-O bonds are formed.
  • And (c) are SEM and TEM images of as obtained untreated WS2 sheets and (b) and (d) are superacid treated sheets. Sizes ranged from about 3-5 micro meter large.
  • Put the exfoliated WS 2 sheets into application and made LIB anodes. Figure a: First 2 EC cycles, when anode is cycled between 0 to 2.5 V at CC of 25mA/g. Left to right is Li-ion intercalation in the WS2 sheets and right to left is extraction. 3-phases representing diffusion rates and type of chemical reactions involved. Phase 2: conversion reaction ; Phase 3: decomposition of LixWOyS2 and electrolyte. Figure c: clearly depicts the 2 staged insertion cycle, whereas the dealloying is mostly a uniform diffusion rate process. Capacity fading for initial few cycles is probably due to electrolyte degradation (reported earlier as polysulfide formation).
  • Stable C-rate performance is observed. As with increasing current extraction and insertion rates, the capacity for the initial and final cycles remains mostly constant. Exfoliated WS2 cycled at low rate exhibited high capacity, low ICL and low hysteresis.
  • Jz300480w singh presentation on li ion battery

    1. 1. Synthesis of Surface- Functionalized WS2 Nanosheets and Performance as Li-Ion Battery Anodes R. Bhandavat (presenter), L. David, and G. Singh* (advisor)Department of Mechanical and Nuclear Engineering, Kansas State University *gurpreet@ksu.edu http://www-personal.ksu.edu/~gurpreet/ J. Phys. Chem. Lett. 2012, 3, 1523-1530 1
    2. 2. Acknowledgements• Financial support from Kansas State University• Prof. Ken Klabunde, Prof. Stefan Bossmann, Dr. John Desper, and Dr. Hongwang Wang (all Kansas State University)Proprietary and Confidential 2 American Chemical Society
    3. 3. Motivation(a) (c) Adv. Mater. 2010, 22, E170–E192 (b) Proprietary and Confidential 3 American Chemical Society
    4. 4. Exfoliated WS2 : CharacterizationProprietary and Confidential 4 American Chemical Society
    5. 5. Exfoliated WS2 : Morphology As-received As-receivedProprietary and Confidential 5 American Chemical Society
    6. 6. Exfoliated WS2 : Li-ion Battery Anode (1) (2)Proprietary and Confidential 6 American Chemical Society
    7. 7. Exfoliated WS2 : Varying Current DensityProprietary and Confidential 7 American Chemical Society
    8. 8. Summary• Exfoliation results of weakly bonded WS2 sheets prepared using superacid are most stable.• UV-vis spectroscopy - High absorbance - high sheet concentration.• ξ-potential measurements- surface charge- electrostatic repulsion.• W4f elemental XPS - W-O bonds- edge functionalization. The Team (L to R): Romil Bhandavat (PhD• Electrochemical performance-reversible student), Prof. Gurpreet Singh (Advisor), Uriel Barrera (UG), Alexander Wu (UG) and Lamuel capacity of 470 mAh/g (= 5.3Li+ / WS2) @ 25 David (PhD student) mA/g. http://www-personal.ksu.edu/~gurpreet/• Future approach-polymer intercalated TMDCs for enhanced performance.Proprietary and Confidential 8 American Chemical Society

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