Regulation of P2/O3 layered-oxide cathode by cation potential and dual-site doping provides excellent electrochemical performance

Abstract

Enhancing the cycle stability of sodium-ion battery cathode materials at high current rates remains a critical challenge. Although layered oxides exhibit high capacity, their long-term stability requires improvement. In this study, we present a low-Ni, Co-free P2/O3-Na_0.8K_0.05Ca_0.05Ni_0.2Fe_0.2Mn_0.55Mg_0.05O₂ layered oxide, engineered through dual-site doping and cation potential to create a stable two-phase structure The synergistic effects of K-Ca-Mg co-doping and the P2/O3 hybrid structure effectively suppress detrimental phase transitions and Na⁺/vacancy ordering at high voltage, enhancing both rate capability and cycle stability. The material exhibits a high reversible discharge capacity of 143 mAh g⁻¹ at 0.1C, and maintains over 80 % capacity retention after 250 cycles at 1C and excellent rate performance (96 mA h g⁻¹ at 5C and 82 mA h g⁻¹ at 10C. Even after 600 cycles at 10C, the capacity retention remains 80 %). Galvanostatic intermittent titration technique (GITT) analysis also confirms superior Na⁺ diffusivity compared to conventional Ni-Fe-Mn layered oxides and density functional theory (DFT) calculations further validate the feasibility of the dual-position doping strategy, demonstrating its effectiveness in enhancing electrochemical performance through the synergistic effect of K-Ca-Mg. In conclusion, these findings highlight the potential of P/O-KCNFMM as a high-performance cathode material, leveraging the combined advantages of dual-site doping and the P2/O3 hybrid structure, thus providing new insights into the design of sodium-ion battery cathodes.