Innovative three-layered FeHCF@MnHCF@FeHCF core-shell design for enhanced sodium-ion battery cathode performance

This study focuses on significantly enhancing sodium-ion battery cathode materials' cycling stability and rate performance. Addressing the structural instability and capacity fade issues of sodium manganese hexacyanoferrate (MnHCF) due to Jahn-Teller distortion during charge-discharge cycles, an innovatively refined coprecipitation strategy was employed to precisely construct a sodium iron hexacyanoferrate (FeHCF) shell with excellent low strain characteristics on the core and periphery of MnHCF. This approach successfully built a unique FeHCF@MnHCF@FeHCF three-layered core-shell structured Prussian blue analogues (PBAs). The FeHCF@MnHCF@FeHCF composite material demonstrated extraordinary performance in electrochemical tests: it achieved a high reversible capacity of 140.2 mAh g- 1 at a low current density of 10 mA g- 1; even at a high current density of 500 mA g- 1, it maintained a stable specific capacity of 99.8 mAh g- 1, showing excellent rate response capability. Particularly noteworthy is that after 500 cycles at a current density of 200 mA g- 1, its capacity retention rate was as high as 81.8 %, highlighting its outstanding cycling stability. In this design strategy, the inner and outer FeHCF shells work in synergy to effectively suppress the Jahn-Teller effect of the MnHCF core. In contrast, the outer FeHCF shell acts as a robust barrier, significantly reducing the leaching of manganese ions, and thereby strengthening the overall structural stability and durability. This study not only paves a new way to design high-performance sodium-ion battery cathode materials but also provides a solid theoretical foundation and practical guidance for the further development of energy storage technology.