Structural changes of bare and AIPO(4)-coated LixCoO2 (x = 0.24 and 0.1) upon thermal annealing >= 200 degrees C

Abstract

Structural changes of bare and AIPO(4)-coated LiCoO2 with a coating thickness of 20 and 200 nm are investigated at x = 0.24 and 0. 1 after thermal annealing at 200, 300, and 400 degrees C using XRD and Co K-edge XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure). Both the bare and coated cathodes exhibit faster phase transformation into spinel phases at lower annealing temperatures as x in LixCoO2 is decreased. Bare LixCoO2 cathodes exhibit phase transitions from LixCo2O4 to Co3O4 spinel as the annealing temperature is increased and the x is value decreased, which suggests a possible reaction according to (1/2)LixCo2O4 -> xLi(2)CO(3) + (1/3)Co3O4 + (2/3)O-2. However, the coated cathodes sustain a Li(x)Co(2)O(4)phase even at 400 degrees C and x=0.1. This indicates that the AIPO(4) coating layer suppresses the Li,C0204 phase decomposition into Co3O4.