Insights into inhibiting Mn dissolution in Mn‐based Prussian blue cathode by polydopamine‐coated strategy for aqueous zinc ion batteries

The manganese hexacyanoferrate (MnHCF) is a promising cathode material in aqueous zinc‐ion batteries (AZIBs). However, MnHCF suffers from the low structure stability due to abundant [Fe(CN)4]2‐ vacancies and manganese dissolution. Herein, we used ethylenediaminetetraacetic acid (EDTA) as a chelating agent to regulate the precipitation process and obtained low defect polyhedral MnHCF particles. To suppress manganese dissolution, polydopamine (PDA) conductive polymer was coated on MnHCF (PDA@MnHCF) as a protection layer. The PDA layer successfully slowed manganese dissolution and even gradually rose the capacity in first 100 cycles. Through dQ/dV fitting, the rise in capacity could be understood as the increased contribution of ZnHCF and MnO2, which partially compensated for the decrease in MnHCF contribution. As a result, PDA@MnHCF exhibited superior electrochemical performance with a high specific capacity of 100.7 mAh g‐1 at 0.2 A g‐1, while bare MnHCF failed at 190th cycle with 63.6 mAh g‐1. PDA@MnHCF could also keep more than double specific capacity (45.5 mAh g‐1) than bare MnHCF (22.6 mAh g‐1) at 2.0 A g‐1 after 2000 cycles. Our results not only found a feasible method to suppress the dissolution of MnHCF, but also quantitatively revealed how electrochemical evolution of MnHCF in AZIBs.