Regulation of local chemistry in O3-type layered oxide cathodes for practical sodium-ion batteries

Abstract

O3-type layered oxide cathodes have emerged as promising candidates for advanced sodium-ion batteries (SIBs) due to their high theoretical specific capacity. However, undesirable phase transitions, irreversible O₂ release, and transition metal (TM) ion dissolution severely deteriorate their long-cycle stability. Herein, a cation–anion dual-site high-entropy doping strategy is proposed to modulate the local chemistry of O3-type layered oxide cathodes, aiming to enhance the covalency of TM–O bonds. The robust covalent TM–O bonds can effectively suppress adverse phase transitions, inhibit irreversible oxygen redox reactions, and reduce TMⁿ⁺ dissolution. Consequently, NaNi_0.25Fe_0.14Mn_0.3Li_0.1Ti_0.15Cu_0.03Zn_0.03O_1.94F_0.06 (HEO) delivers a high specific capacity of 152.27 mA h g⁻¹ and a capacity retention of 73.69% after 500 cycles. More importantly, HEO exhibits impressive temperature tolerance, superior air stability and acceptable full-cell performance, demonstrating its huge potential for practical SIBs application. This work develops a versatile cation–anion dual-site high-entropy doping strategy to modulate the local chemistry of O3-type layered oxide cathodes, furnishing a robust foundation for advancing cathode materials for practical SIBs.