Internal Doping and Surface Coating: Mn/La-HCF @ Fe-HCF Composites as High-Performance Cathode Materials for Sodium-Ion Batteries

Manganese-based Prussian blue analogue (Mn-HCF) has outstanding advantages such as a high discharge platform, high discharge capacity and high energy density compared with other PB and PBAs, which is a very valuable cathode material for sodium-ion batteries. However, the rapid decrease in capacity in the cycle process by the Jahn–Teller effect caused by Mn[Formula: see text] is the main obstacle to the commercialization of Mn-HCF. In this work, Mn/La-HCF @ Fe-HCF was synthesized by doping La element into the Mn-HCF phase to suppress the Jahn–Teller effect of Mn ions and coating the Fe-HCF phase outside to protect the Mn-HCF phase from electrolyte corrosion. Benefiting from the inhibition of the Jahn–Teller effect of Mn[Formula: see text] by the abundant electronic energy level structure of La element and the protection of Fe-HCF phase relative to Mn-HCF phase, the initial discharge capacity of Mn/La-HCF @ Fe-HCF can reach 135.6 mAh g[Formula: see text] at current density of 0.1 C, and it still has a high discharge capacity of 112.2[Formula: see text]mAh g[Formula: see text] at current density of 5 C. After 300 cycles at a current density of 2 C, the reversible capacity of 117.6[Formula: see text]mAh g[Formula: see text] is maintained (capacity retention rate is 86.1%). The results show that this method of internal doping and outsourcing can greatly improve the electrochemical performance of Mn-HCF, and provide feasible ideas for the commercialization of Mn-HCF.