Controlling the ratio of Ni and Fe co-doping in a Prussian-white cathode to improve the structural stability and redox performance of advanced sodium-ion batteries

Abstract

Prussian white, also known as manganese-based hexacyanoferrate (MHCF), has garnered significant attention as a promising cathode material for next-generation sodium-ion batteries due to its high energy density, low cost, and straightforward synthesis process. However, MHCF suffers from low structural stability caused by the Jahn–Teller effect, which leads to performance degradation and a short battery life. To address this issue, this study investigates the effects of Ni and Fe co-doping on the structural stability of MHCF when used as a cathode material for sodium-ion batteries. By regulating the ratio of co-doped Ni and Fe metal ions, the structural stability of MHCF was significantly improved, resulting in enhanced and steady electrochemical performance. Among the different co-doping ratios studied, the MNFHCF-631 sample composed of manganese (Mn), nickel (Ni), and iron (Fe) in a 6 : 3 : 1 ratio demonstrated the most promising results. It achieved an excellent capacity retention of 96.30% and stable particle morphology after 100 cycles at a current rate of 0.2C. This study also explores the specific roles of each doping ion, highlighting that nickel ions act as inert transition metals to improve structural integrity, while co-doping with iron contributes additional electrochemical activity. This dual effect enhances both the structural and electrochemical performance of the material, making it a strong candidate for high-performance sodium-ion battery cathodes.