Understanding the stepwise capacity increase of high energy low-Co Li-rich cathode materials for lithium ion batteries

Abstract

Li-rich layered materials as promising high-energy cathode candidates have attracted much attention in recent years for next generation lithium ion batteries. However, the fundamental mechanism of high specific capacity in these cathode materials has not been fully revealed so far. In this work, we report a new class of Li-rich cathode materials Li[Co_xLi_1/3−x/3Mn_2/3−2x/3]O₂ (x = 0.087, 0.1, and 0.118) with a very low level of Co doping, which exhibit impressive stepwise capacity increase over dozens of cycles from less than 50 mA h g⁻¹ to around 250 mA h g⁻¹. A systematic study on their composition, crystal structure and electrochemical performance revealed that the small change of Co content has negligible effect on the crystal structure and morphology, but plays an important role in enhancing the activation rate of the Li₂MnO₃ phase. In addition, the optimized cycling potential window and current rate were proven to be critically important for effective Li₂MnO₃ activation and better long-term cycling stability.