Synergistic Modification of Fe-Based Prussian Blue Cathode Material Based on Structural Regulation and Surface Engineering

The Fe-based Prussian blue (Fe-PB) composite is considered as one of the most potential cathode materials for sodium-ion batteries because of its abundant iron resources and high theoretical capacity. However, the crystal water and vacancy in the Fe-PB structure will lead to poor capacity and cycle stability. In this work, a Cu-modified Fe-PB composite (FeCu-PB@CuO) is successfully prepared through regulating the Fe-PB structure by Cu doping and engineering the surface by CuO coating. The density functional theory calculation results confirm that Cu preferentially replaces Fe^HS in the Fe-PB lattice and Cu doping reduces the bandgap. Our experiment results reveal that CuO coating can provide more active sites, inhibit side reactions, and potentially enhance the activity of Fe^HS. Due to the synergistic effect of Cu doping and CuO coating, FeCu-PB@CuO has a considerable initial discharge capacity of 123.5 mAh g^-1 at 0.1 A g^-1. In particular, at 2 A g^-1, it delivers an impressive initial capacity of 84.3 mAh g^-1, and the capacity decreasing rate of each cycle is only 0.02% over 1500 cycles. Therefore, the synergistic modification strategy of metal ion doping and metal oxide coating has tremendous application potential and can be extended to other electrode materials.