Manganese–Zinc Synergy in Prussian Blue Analogues for Long-Cycle Aqueous Zinc-Ion Battery Cathodes

Aqueous zinc-ion batteries (AZIBs) are regarded as promising electrochemical energy storage devices owing to their low cost, intrinsic safety, abundant zinc reserves, and desirable specific capacity. Prussian blue analogues (PBAs) have been extensively investigated because of their inexpensive raw materials, ease of fabrication, open frameworks, and high theoretical specific capacity; however, the application of PBAs as cathode materials for aqueous zinc-ion batteries (AZIBs) is hindered by poor cycling performance and limited capacity. In this work, a small amount of manganese ions was successfully introduced into the N-coordinated metal sites of zinc hexacyanoferrate (ZnHCF) to tailor its electrochemical stability. The N-coordinated metal species in PBAs directly influence the intercalation chemistry of Zn ions. The coexistence of manganese and zinc in manganese-substituted zinc hexacyanoferrates (MZHCFs) generates a synergistic effect that suppresses Jahn–Teller distortion and cathode material dissolution, endowing MZHCFs with superior cycling performance compared with PBAs containing a single N-coordinated metal (Mn or Zn). At a Mn content of 10%, a specific discharge capacity of 100 mAh g−1 is achieved at a current density of 1 A g−1, and the capacity retention is optimized, showing no decay relative to the initial discharge capacity after 2000 galvanostatic cycles. This study demonstrates that substituting the N-coordinated metal in PBAs with other metal ions is an effective strategy to improve their electrochemical cycling stability and capacity.