Ni, Co, and Mn L3-edge X-ray absorption micro-spectroscopic study on LixNi0.88Co0.08Mn0.04O2 primary particles upon annealing from room temperature to 800 °C

Abstract

LixNi0.88Co0.08Mn0.04O2 primary particles for lithium ion battery (LIB) applications were annealed in situ from room temperature (RT) to 200, 400, 600, and 800 °C. At each of these temperatures, space-resolved Ni L3-, Co L3-, and Mn L3-edge X-ray absorption spectra of the particles were acquired with 30 nm focused X-rays by using synchrotron-based scanning transmission X-ray microscopy (STXM). This study aimed to investigate the changes induced by the annealing temperature in the local oxidation number, phase, and microscale shape within the particles. At RT, the average oxidation numbers of the Ni, Co, and Mn ions were +3, +3, and +4, respectively. At 200 °C, the average oxidation numbers of the Co and Mn ions were basically the same as those at RT, and those of the Ni ions were between +2 and +3. At 400 °C, the average oxidation numbers of the Ni and Co ions decreased to +2, whereas that of the Mn ions was +4. The average oxidation number of the Ni ions was noticeably lower for smaller particles and on the edges of the particles. At 600 °C, the Ni and Co ions were mostly in the metallic state, the Mn ions were reduced to an oxidation number of +2, and the distribution of Mn ions differed from that of the Ni and Co ions. At 800 °C, the Ni and Co ions were mostly in the metallic state, and the oxidation number of the Mn ions was predominantly +2. At this temperature, strong changes in density distributions of the Mn, Ni, and Co ions occurred.