Effects of Aging in Electrolyte on the Structural and Electrochemical Properties of the Li[Li0.18Ni0.15Co0.15Mn0.52]O2 Cathode Material

Li-excess Li[Li0.18Ni0.15Co0.15Mn0.52]O-2 layered cathode material is prepared by the sol-gel method. The material is aged in a LiPF6 based electrolyte and then is subjected to a series of structural and electrochemical analyses. X-ray diffraction shows that aging in electrolyte does not change the C2/m ordering of the material crystal lattice. But the surface of the material is etched by the electrolyte which is confirmed by transmission electron microscope and Raman scattering. This causes dissolution of some transition metal elements (especially Ni and Co) and formation of a spinel-like surface layer. Also, some by-products resulted from the electrolyte decomposition are detected on the surface of the material. Electrochemical impedance spectroscopy shows that aging in electrolyte severely hinders the electrochemical kinetics of the material. Cyclic voltammetry indicates that the aged sample has large electrode polarization which prevents the oxygen loss process and the activation of Mn4+ ions. As a result, the discharge capacity of the aged sample continuously increases from 134 mAh g(-1) to 215 mAh g(-1) in the initial several cycles. (C) 2013 Elsevier Ltd. All rights reserved.