Chemical environment regulation of P2-Na0.6Mn0.62Ni0.22Fe0.16O2 for cycling stability

Sodium-ion batteries (SIBs) have emerged as the most promising secondary battery technology to replace lithium-ion batteries in large-scale energy storage applications. Layered oxides, as important cathode materials for SIBs, face primary challenges in improving cycling stability and enhancing energy density. P2-type Na0.6Mn0.62Ni0.22Fe0.16O2 cathode material boasts a high specific capacity but undergoes phase transitions at high voltage, resulting in poor cycling stability. X-ray diffraction refinement demonstrates that an appropriate addition of fluoride (F−) increases the interlayer spacing of sodium, thereby accelerating sodium-ion diffusion rates. Charge density distribution and electronic state density calculations indicate that F- doping enhances the interactions between Mn and O, as well as Ni and O, thereby inhibiting the dissolution of Mn3+ and Ni3+ and contributing to structural stability. The optimized Na0.6Mn0.62Ni0.22Fe0.16O1.95F0.05 can deliver a high capacity of 138.8 mAh g−1 at a 2 C rate and retain a capacity of 80 mAh g−1 after 100 cycles, demonstrating significantly improved cycling stability. This work achieves an increase in specific capacity cycling stability by regulating the activity and stability of transition metals through F− substitution, providing a new strategy for regulating the chemical environment of Na-Mn-Ni-Fe-O cathodes.