Copper-Activated Dynamic Lattice Adaptation and Bond Reinforcement for Enhanced Sodium Storage of Prussian Blue...

Prussian blue analogs (PBAs) have garnered considerable attention as promising cathode materials for sodium-ion batteries (SIBs) in recent years, owing to their high theoretical capacity, three-dimensional ionic channels, and low cost. Nevertheless, the electrochemical properties of PBAs are severely compromised by the excessive Fe(CN)₆ vacancies and crystalline water within the structure. Herein, a copper ion (Cu²⁺) doping strategy is adopted to enhance the structural stability of PBAs, reduce the content of crystalline water, and thereby enhance its high-rate performance and cyclic durability. In situ XRD and density functional theory (DFT) calculations confirm that the material exhibits dynamic lattice adaptation and reduced Na⁺ migration energy barrier after Cu²⁺ doping. Local lattice distortion and electronic reconfiguration resulting from Cu²⁺ incorporation enhance the metal-cyano-metal (M─CN─M') bond strength, significantly improving the rate performance and cycling performance of PBA. Thus, the prepared CuFePB-2 exhibits a high capacity of 112.2 mAh g^-1 at 1C and a retention of 82.0% after 200 cycles. Additionally, even at 20C, it still delivers a capacity of 57.1 mAh g^-1. This work develops a novel strategy to synergistically enhance the rate capability and cycling stability of PBA materials, thereby enabling high-performance SIBs.