Unveiling the origin of high reversible capacity in Li-rich layered oxide in Li-ion batteries

Lithium-rich layered oxides are promising cathode candidates for Li-ion batteries due to their high specific capacity than the commercial cathode material, LiCoO2. However, the mechanism of the incredibly high capacity and inherent problems of lithium-rich layered oxides, such as low initial Columbic efficiency and poor capacity retention, has not been explored in detail. Herein, lithium-rich layered oxide, Li1.2 Mn0.54Ni0.13Co0.13O2, has been synthesized by sol-gel method, which could be charged to 5 V (versus Li/Li+) and delivered a specific capacity of 248 mAh g−1. Then, a combination of XRD Rietveld refinement and HRTEM analysis has been employed to investigate the microstructure and phase composition of as-prepared Li1.2 Mn0.54Ni0.13Co0.13O2. The results revealed that Li1.2 Mn0.54Ni0.13Co0.13O2 nanoparticles consist of different phases, including LiCoO2 with R-3m symmetry, LiNiO2 with R-3m symmetry, LiMnO2 with R-3m symmetry, Li2MnO3 with c2/m symmetry, and Li2MnO3 with cmc/21 symmetry. It has been demonstrated that O2-Li2MnO3 phase with cmc/21 symmetry is responsible for the high reversible capacity of Li1.2 Mn0.54Ni0.13Co0.13O2 compound. However, the complex phase composition caused abundant stacking faults in the nanoparticles, which led to poor rate performance. The present study provides useful insights into the charge storage mechanism of a promising Li-ion battery cathode, Li1.2 Mn0.54Ni0.13Co0.13O2, which can be used for the development of novel electrode materials for next-generation LIBs due to its lower consumption of element Co and good electrochemical performance.