Abstract:

Sodium-ion batteries (SIBs), benefiting from their environmental friendliness, abundant reserves, and low cost, have become the most important supplement, even an alternative, for lithium-ion batteries and hold broad application potential in the field of energy storage. However, manganese-based cathode materials for SIBs face challenges such as structural instability and poor cycling stability, which severely limit their practical application. In this study, O3-NaMnO₂ was used as the matrix to investigate the effects and underlying mechanisms of K/Cu dual-site doping on its electrochemical performance. Both theoretical calculations and experimental results demonstrate that the introduction of K⁺ into the sodium layer effectively enhances the diffusion rate of sodium ions, while Cu²⁺ doping in the transition metal layer effectively suppresses the Jahn-Teller distortion of Mn³⁺, thereby mitigating the complex phase transitions of the cathode material during charging and discharging, and improving its structural stability. K/Cu co-doping disrupts the vacancy structure formed by the ordered arrangement of sodium ions, activates anionic redox reactions, contributes additional specific capacity, and significantly enhances the electronic conductivity of the material. Na_0.94K_0.06Cu_0.05Mn_0.95O₂ achieves an initial discharge specific capacity of 201.16 mAh/g at 0.2C (1C = 226.28 mAh/g), and retains 85.67% of its specific capacity after 100 cycles. After high-current cycling at 1C and 2C, it still delivers 170.87 mAh/g at 0.5C, showing excellent cycling and rate performance. This co-doping strategy offers a new approach for the design of high-performance sodium-ion battery cathode materials.

Key words: sodium-ion battery, dual-site doping, cathode material, electrochemical performance