A hydro-stable and phase-transition-free P2-type cathode with superior cycling stability for high-voltage sodium-ion batteries

A dual-site substitution strategy was applied to enhance the electrochemical performance of sodium-ion batteries, leading to the development of the Na_0.80Mg_0.03Li_0.18Mn_0.67Cu_0.15O₂ cathode material. By introducing Mg and Cu ions at multiple sites, the local chemical environment was optimized, resulting in improved ion diffusion kinetics and charge transfer dynamics, which accelerate the overall electrochemical reactions. Mg ions substituted at Na sites act as “pillars” effectively mitigating detrimental O²⁻–O²⁻ electrostatic repulsion and enabling stable anion redox activity. This novel cathode demonstrates a high specific capacity of 162 mAh/g, excellent rate capability with 114 mAh/g at 1000 mA g⁻¹ (8C), and superior cycling stability with 80.3 % capacity retention after 300 cycles. Furthermore, the dual-site substitution minimizes volume variation to just 1.3 % during electrochemical processes and significantly enhances moisture resistance, offering promising potential for practical sodium-ion battery applications.