Cu/F cross-lattice substitution enables synergistic regulation of electronic structure and charge transport to enhance structural stability in P2-type sodium-ion battery cathodes

P2-type layered transition-metal oxides are promising cathodes for sodium-ion batteries but suffer from unstable electronic structure, sluggish charge transport, and voltage-induced phase transitions. Herein, a Cu/F cross-lattice co-substitution strategy is proposed to develop a Cu/F co-doped layered oxide, Na_0.67Fe_0.3Mn_0.5Cu_0.2O_1.95F_0.05 (NFMCF), enabling synergistic regulation of electronic structure and charge transport to enhance structural stability. First-principles calculations reveal that Cu/F co-doping increases the density of states near the Fermi level and narrows the band gap, facilitating electron transport, while reinforcing the anionic framework to suppress oxygen instability and the P2-Z phase transition. In-situ EIS and DRT analysis confirm reduced interfacial polarization and improved kinetic uniformity at high states of charge. Benefiting from these synergistic effects, NFMCF delivers 164.9 mAh·g⁻¹at 0.1 C and retains 92.63% and 78.8% of its capacity at 1 C and 5 C, respectively. Moreover, the assembled full cells achieve energy densities of 287.7 and 122.7 Wh·kg⁻¹ at power densities of 82.2 and 2942.4 W·kg⁻¹, demonstrating an effective strategy for designing high-stability, high-rate, and high-energy-density sodium-ion battery cathodes.