X-Ray Absorption and Diffraction Studies of LiNiO2-Derivatives with or without Electrolyte at Elevated Temperature

Simultaneous measurement of X-ray absorption and diffraction at elevated temperature was developed and carried out to examine thermal decomposition of LiNi(0.75)Co(0.15)Al(0.05)Mgo(0.05)O(2) (NCA-Mg) electrode charged at 4.2 V vs. Li+/Li with or without electrolyte. Our measurement clearly displays accelerated reduction of NCA-Mg by the electrolyte in terms of the change in crystal structure and the oxidation states of nickel and cobalt species. Reduction of nickel and cobalt species by XANES occurs at about 50 degrees C lower temperature than the structural collapse detected by XRD, which will be a key to understand the mechanisms for onset temperature of the exothermic reactions. (C) 2014 The Electrochemical Society. All rights reserved.