Ion-exchange synthesis of high-energy-density prussian blue analogues for sodium ion battery cathodes with fast kinetics and long durability

Prussian blue and its analogues are regarded as promising cathodes for sodium ion batteries. However, the structural stability and interfacial compatibility of Prussian blue cathode are major issues for achieving superior performance. Sodium copper hexacyanoferrate is synthesized by an ion-exchange method, with large specific surface area and hierarchical core-shell structure. When used as cathode for half-cell, the material delivers an initial capacity of ~90 mAh g⁻¹ and maintain more than 81% capacity retention after 1000 cycles. Even at a high rate of 20C, an impressive capacity of ~50 mAh g⁻¹ is retained. Especially, a full-cell assembled by sodium copper hexacyanoferrate cathode and NaTi₂(PO4)₃@C anode shows a high capacity of more than 80 mA h g⁻¹ for 400 cycles. A series of electrochemical techniques and in situ tests are carries out to confirm the advantages of stable structure and high conductivity after dopping copper ions. Furthermore, the low adsorption energy of Na⁺ on cathode surfaces is revealed by the first principle calculation.