Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of LiNi0.8Co0.15Al0.05O2 positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where Ni3+ turned to Ni2+, deduced from relative intensity ratios and fine structures of the L-2,L-3 white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3076137] All rights reserved.