Integrating surface modification to improve the electrochemical performance of Li-rich cathode materials†

Li-rich cathode materials (LLO) exhibit a high specific capacity, but their application is impeded by their poor cycling stability and rate performance which arises from the irreversible anionic redox reaction and their poor electrical conductivity. In this regard, a simple phytic acid surface treatment technique was employed to form an integrated surface structure comprising Li₃PO₄ and oxygen vacancies (Vos) on the surface of LLO materials. In particular, the effect of the Li₃PO₄ layer on the defect structure and their synergistic effect on the electrochemical performances of LLO were researched through experimental and theoretical calculations. The results prove that the existence of Li₃PO₄ can improve the Vo content obviously. The coating layer and the synchronously formed Vo can also facilitate Li⁺ diffusion, improve the electrical conductivity, and inhibit the irreversible O₂ release effectively, thus increasing the cycling stability and rate performance of LLO. Consequently, the initial coulombic efficiency (ICE) increases from 62.8% to 72%. After 200 cycles at 0.5C, the capacity retention has improved significantly from 78% to 92.3%, accompanied by a minimal voltage fading value of 108.8 mV. The discharge specific capacity still reaches 125 mA h g⁻¹ even at a current density of 5C. This work proves the effect of the Li₃PO₄ coating layer on the defect structure and electrochemical properties of the LLO material and provides an effective clue to improve its performance.