Copper Hexacyanoferrate Solid-State Electrolyte Protection Layer on Zn Metal Anode for High-Performance Aqueous Zinc-Ion Batteries

Zinc (Zn) metal possesses broad prospects as an anode for aqueous zinc-ion batteries (AZIBs) due to its considerable theoretical capacity of 820 mAh g^-1. However, the Zn anode suffers from dendrite growth and side reactions during Zn stripping/plating. Herein, a Prussian blue analog of copper hexacyanoferrate (CuHCF) with a 3D open structure and rich polar groups (CN) is coated on Zn foil as a solid-state electrolyte (SSE) protection layer to protect the Zn anode. The CuHCF protection layer possesses low activation energy of 26.49 kJ mol^-1, the high ionic conductivity of 7.6 mS cm^-1, and a large Zn²⁺ transference number of 0.74. Hence, the Zn@CuHCF||Zn@CuHCF symmetric cell delivers high cycling stability over 1800 h at 5 mA cm^-2, an excellent depth of discharge of 51.3%, and the accumulative discharge capacity over 3000 mAh cm^-2. In addition, the Zn//Ti@CuHCF asymmetric cell achieves the coulombic efficiency (CE) of 99.87% after 2000 cycles. More importantly, the Zn@CuHCF//V₂O₅ full cell presents outstanding capacity retention of 87.6% at 10 A g^-1 after 3000 cycles. This work develops a type of material to form an artificial protection layer for high-performance AZIBs.