Activating and stabilizing ORR in P2-type cathode by modulating orbital hybridization and local covalency towards high-rate and long-cycle sodium-ion batteries

Constructing the high sodium content manganese-based cathode materials (HSMC) with high-rate and long-cycle performances can effectively improve the practical application of sodium-ion batteries (SIBs). However, the irreversible oxygen redox reaction (ORR) and unstable crystal structure at high voltage make it impossible to meet the above requirements. Herein, an innovative mechanism is proposed to simultaneously formulate the orbital hybridization and local covalency for enhancing ORR reversibility and structural stability in HSMC (Na_0.8Li_0.12Ni_0.22Mn_0.66O_1.95F_0.05, NLNMOF). In this configuration, the doping of Li into transition metal (TM) site promotes the transition of O lone-pair electrons and triggers the positively shift in projected density of state (PDOS) of Mn, contributing to the high capacity and structural stability. Meanwhile, the substitution of F into oxygen site increases the covalency of Mn-O and pins adjacent oxygen layers, improving the ORR reversibility. As a result, the NLNMOF exhibits extremely competitive high-rate and long-cycle performance, retaining 85.6 % capacity after 500 cycles at 5 C and delivering 68 mAh g^–1 at 30 C. This unprecedented electrochemical performance provides a feasible scheme for the design of cathode materials for high-performance sodium-ion batteries.