A Polydopamine‐Coated Strategy of Mn‐Based Prussian Blue Cathode Enabled Mn Dissolution Suppression for Aqueous Zinc Ion Batteries

The manganese hexacyanoferrate (MnHCF) is a promising cathode material in aqueous zinc‐ion batteries (AZIBs). However, MnHCF suffers from low structural stability due to abundant [Fe(CN) 4 ] 2− vacancies and manganese dissolution. Herein, ethylenediaminetetraacetic acid (EDTA) is used as a chelating agent to regulate the precipitation process, and low‐defect polyhedral MnHCF particles are obtained. To suppress manganese dissolution, polydopamine (PDA) conductive polymer is coated on MnHCF (PDA@MnHCF) as a protection layer. The PDA layer successfully slows down manganese (Mn) dissolution and even gradually raises the capacity during the first 100 cycles. Through dQ/dV fitting, the rise in capacity can be understood as the increased contribution of ZnHCF and MnO 2 , which partially compensated for the decrease in MnHCF contribution. As a result, PDA@MnHCF exhibits superior electrochemical performance with a high specific capacity of 100.7 mAh g −1 at 0.2 A g −1 , while bare MnHCF fails at the 190th cycle with 63.6 mAh g −1 . PDA@MnHCF can also maintain more than twice the specific capacity (45.5 mAh g −1 ) than bare MnHCF (22.6 mAh g −1 ) at 2.0 A g −1 after 2000 cycles. The results not only found a feasible method to suppress the dissolution of Mn but also quantitatively revealed how electrochemical evolution of MnHCF occurs in AZIBs.