Doping of manganese hexacyanoferrate with cobalt for improving electrochemical performance in high-energy sodium-ion batteries

Manganese hexacyanoferrate’s (MnHCF) high theoretical specific capacity and high voltage platform make it a promising material for a wide range of applications. Nevertheless, the conversion of Mn²⁺ and Mn³⁺ during the charging and discharging process of MnHCF might result in a severe Jahn-Teller distortion, which would cause lattice deformation and structural collapse, compromising its cycle stability. The strategy of Co-doping can reduce lattice defects, increase the initial sodium content in the material, raise the material’s conductivity, and enhance the diffusion kinetics of sodium ions. Furthermore, Co-doping can effectively reduce the changes in unit cell volume and Mn-N bond length during charge and discharge processes, alleviate the Jahn-Teller effect of Mn, and enhance the cycling stability of the material, as verified by the Ex-situ XRD. The MnCoHCF-5 % sample exhibits excellent discharge capacity and cycling stability, with a specific capacity high up to 149.80 mAh g⁻¹ at 0.1C and 60.14 % capacity retention at 1C after 300 cycles. This study provides an effective method for developing PBAs cathode materials with high specific capacity and cycling stability.