(Invited) Surface Modification Effect on the First Charging Process over 4.5 V and the Enhancement of Energy of LiNi1/3Co1/3Mn1/3O2

Surface modification of the positive electrode materials by coating technique with metal oxides, phosphate, and so on is commonly used in these days for stabilizing the electrolyte/positive electrode material interface [1-3]. We can not only extend the battery life, but also have a chance to increase the battery energy by charging to higher voltage by the stabilization.

Authors have developed the sol-gel based coating procedure to make the thin and uniform layer of Al oxide on the commercially available LiNi_1/3Co_1/3Mn_1/3O₂ (NCM), by which the decrease of the initial capacity was suppressed [4]. Using this modified NCM, first charging process was precisely investigated electrochemically varying the charge cut-off voltage up to 4.8 V. Below 4.7 V, discharge capacity increased as the charge cut-off voltage was elevated with/without modification. Coulombic efficiency, average voltage, cycling properties were improved by surface modification.

Comparison of AC impedance spectra and dQ/dVof the galvanostatic charge-discharge curves, with the aid of TEM results of the surface region, for modified/bare NCM revealed that the surface of the bare NCM was damaged to be high-resistant in very early stage of first charge, as was observed by surface analysis using synchrotron facilities [5]. Al-oxide modification suppressed the increasing rate of interfacial resistance of Li⁺ intercalation/deinercalation at the surface.

References

[1] Z. H. Chen, et al., Electrochimica Acta, 49(7), 1079 (2004).

[2] B. C. Park, et. al., Journal of Power Sources, 178(2), 826 (2008).

[3] .A. T. Appapillai, et.al., Chemistry of Materials, 19(23),5748 (2007).

[4] A. Yano, H. Sakaebe, et. al., J. Electrochem. Soc., 162(2), A3137-A3144 (2015).

[5] D. Takamastu, et. al., Angewandte Chemie, 124(46), 11765–11769 (2012).