Quantitative Analysis of Transition-Metal Migration Induced Electrochemically in Lithium-Rich Layered Oxide Cathode and Its Contribution to Properties at High and Low Temperatures

摘要

Lithium-rich layered oxides (LLOs) have attracted much attention as high-capacity electrodes in lithium-ion batteries. Especially, LLOs are known to show high performance at high temperature. The transition metal (TM) migrates from the TM layer to the Li layer in the LLO active material during the charge-discharge cycle, which complicates our understanding of its electrochemical properties. In this study, we applied X-ray diffraction spectroscopy (XDS) for acquiring quantitative data on TM migration depending on the crystallographic site in Li1.2-xNi0.13Co0.13Mn0.53O2, and we discuss their influence on the electrochemical properties at 40 and -10 degrees C. The XDS analysis shows that both Mn and Ni in the TM layer migrate to the Li layer during the charge process and return during the discharge process. This reversible migration, observed at 40 degrees C, corresponds to a high capacity. On the other hand, the operation at -10 degrees C decreases the degree of TM migration as well as the charge-discharge capacity. In particular, Mn and Ni hardly migrate to the TM layer and remain at the Li layer at the end of discharge. This clogged interlayer space, which would lower the Li+ diffusion, accounts for the capacity drop.