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

Abstract 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 Zn 2+ 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//V 2 O 5 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.