Tuning the Electrochemical Stability of Zinc Hexacyanoferrate through Manganese Substitution for Aqueous Zinc-Ion Batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) attract intensive attention as an alternative battery technology for large-scale electrochemical energy storage applications because of their low cost, intrinsic safety, and environmental friendliness. Prussian blue analogues (PBAs), as a promising candidate for cathode materials, possess severe capacity decay issues in ARZIBs. In this article, a small amount of Mn ions is successfully introduced into the N-bonded metal sites of zinc hexacyanoferrate to adjust its electrochemical stability. The N-bonded metal composition of PBAs directly affects the Zn-ion intercalation chemistry. The coexistence of Mn and Zn in the PBAs shows a synergistic effect on the electrochemical stability, resulting in superior cycle performance than that of the PBAs with a single N-bonded metal (Mn or Zn). Optimized capacity retention, 94% of the initial discharge capacity after 500 galvanostatic cycles, is achieved with the Mn content of 7%. The Mn substitution suppresses the cubic–rhombohedral phase transition and makes the solid–solution mechanism dominant during the Zn-ion insertion. It furthermore suppresses the solubility in the aqueous solution and thus reduces the active material loss of electrodes in the aqueous electrolyte. This research indicates the important role of the N-bonded metals of PBAs in improving their electrochemical stability in ARZIBs.