Optimizing the Structural Evolution of Li-Rich Oxide Cathode Materials via Microwave-Assisted Pre-Activation

Preactivation can play a promising role in suppressing oxygen loss during the first charging process in Li-rich oxide cathode materials, relieving a series of problems such as large initial irreversible capacity loss, structure transformation due to ion rearrangement, and oxidation/decomposition of the electrolyte. However, the strategies previous adopted are mainly chemical delithiation, which has violent effect on the crystal structure and deteriorates the cycle performance. Here, we report a facile and effective microwave-assisted treatment method to preactivate Li-rich layered oxides without structural distortion. The microwave-treated sample shows a high discharge capacity of about 281 mAh g–1 with a Coulombic efficiency of 87% at 0.1 C and exhibits unnormal continuous increase of discharge capacity from 203 mAh g–1 to 218 mAh g–1 during 110 cycles at 1 C as well as presents distinctly improved cycling stability. EIS, GITT and XRD studies reveal that the kinetics of electrochemical reaction on electrode surface and Li ionic migration coefficient in crystal structure become progressively enhanced due to the gradual expansion of interplanar spacing upon cycling. Those results demonstrate that preactivation by microwave-assisted treatment contributes to optimize the structure evolution of Li-rich material for rate performance in cyclic process, which also provides new thinking in modifying Li-rich layered cathode materials.