Tailored core-shell PW@PB cathodes for enhanced sodium-ion battery stability and rate capability

Prussian blue and its analogues (PBA) are promising cathode materials for economical large-scale sodium-ion batteries (SIBs). Manganese-based PBA, abbreviated as "PW", offers advantages such as high voltage, high capacity, and good cost-effectiveness but faces challenges with manganese dissolution and structural distortion during cycling. In contrast, iron-based PBA, abbreviated as "PB", maintains more stable structural integrity but exhibits relatively lower capacity. In this study, we introduce an ion-exchange technique to create core-shell structural cathode materials with PW as the main active ingredient and PB as the protective shell (PW@PB). This approach achieves more than doubled capacity retention after 500 cycles compared to naked PW. Furthermore, PW@PB demonstrates notable rate capability enhancements, retaining 80 % of its capacity at 0.1C when subjected to a high rate of 10C, proving its potential for use in fast-charging SIBs. The improved performance is primarily attributed to the reduced lattice and bound water in the structure of PW@PB. Additionally, the stable outer layer of PB inhibits the leaching of Mn and Fe, minimizing lattice distortion during the charge- discharge process.