Understanding the Electrochemical Properties of Li-Rich Cathode Materials from First-Principles Calculations

The lithium-rich layered oxide materials (LLOs) have attracted much attention as candidates for the next generation of LIBs because of their high voltage and high capacity, which are still poorly understood. In this study, the origin of high voltage and high capacity of LLOs has been comprehensively investigated through first-principles calculations. It is revealed that due to the asymmetric oxidation behavior of Li2MnO3/LiMO2 interface, the transition-metal-oxygen (TMO) layer of Li2MnO3 phase in Li-rich materials gains more electrons from Li layer than that in pure Li2MnO3, which results in the stronger hybrid between Mn-3d and O-2p states enhancing the activity of Mn in Li2MnO3. Moreover, the deintercalated Li-rich models possess smaller spacing than pure LiMO2, which reflects stronger electrostatic interaction between TMO and Li layers. The two factors are both beneficial to the high voltage of the Li-rich materials. However, the asymmetric interface also results in the increase of electronic states of transition metal atoms near the Femi level, which changes the oxidized sequence of Ni2+/Ni4+ and Co3+/Co, and reduces the participation of oxygen in the redox process. As a result, the voltage and reversible capacity of Li-rich materials are significantly enhanced compared with that of pure LiMO2.