Boosting the kinetic properties and suppressing the irreversible oxygen redox of lithium-rich manganese-based cathode materials through combined strategies of fast ionic conductor and oxygen vacancy

Abstract

Oxygen-anion charge compensation facilitates lithium-rich manganese-based cathode materials (LRMCs) to possess higher specific capacity than other conventional layered oxide cathode materials. Nevertheless, irreversible oxygen redox makes LRMCs suffer from oxygen loss, structure degradation, and interfacial side reactions and thus resulting in low initial coulombic efficiency (ICE), poor cyclic stability and rate capacity. To inhibit the irreversible anionic redox and improve the kinetic properties of Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO), herein, an interfacial engineering with sodium hypophosphite (NaH2PO2) is used to modify the LMNCO. The results demonstrate that the Na2HPO4 and reducing gas PH3 that are produced by NaH2PO2 decomposition can react with the residual lithium and unstable surface oxygen to form a stable Li3PO4 protective layer and generate oxygen vacancies on the LMNCO surface. It has been found that the optimum content of NaH2PO2 is 5 wt%, and the electrochemical performance of LMNCO-NP 5% is significantly improved. The ICE of LMNCO-NP 5% is 82.79%, which is much higher than the LMNCO (73.76%). Meanwhile, the capacity retentions of LMNCO-NP 5% are 94.85% and 78.45% at 1 C and 5 C after 100 cycles, respectively. Therefore, the modification strategy based on the formation of Li3PO4 protective layer and generation of oxygen vacancies can play effectively promote the electrochemical performances of LMNCO.