Oxygen vacancy defect improves the long cycle performance of NaCuxMn1-xO2-z cathode material of sodium ion battery

Abstract The sodium-ion battery O3-type layered oxide cathode material NaMnO₂ has severe capacity attenuation due to the irreversible migration of Mn under high voltage. In this paper, a Cu-doped strategy for constructing oxygen vacancies is proposed to improve its structural stability. The O3-type NaCuxMn1-xO₂ material was prepared by the high-temperature solid-phase method. The influence mechanism of Cu doping on the formation of oxygen vacancies and electrochemical performance was studied by combining experiments and the DFT calculation system. The results show that Cu doping effectively induces the generation of oxygen vacancies and promotes the increase of Na⁺ diffusion rate. The best sample, NCMO-0.1, exhibited excellent electrochemical performance within the 2-4 V voltage window: The specific discharge capacity of the first cycle reached 150.08 mAh/g at a rate of 0.2 C, and the capacity retention rate was 61.2%(166.52 mAh/g) after 100 cycles. Theoretical calculations reveal that Cu doping significantly inhibits the Ginger-Taylor distortion activity of Mn³⁺ by reducing the electron density of the Mn3d orbitals, effectively alleviating the structural stress of the material and stabilizing the O3 phase structure of the material.