A Polydopamine Coating Enabling the Stable Cycling of MnO2 Cathode Materials in Aqueous Zinc Batteries

MnO2 is a desired cathode candidate for aqueous zinc batteries. However, their cycling stability is seriously limited by active material dissolution, and pre-addition of Mn2+ salts in electrolytes is widely required to shift the dissolution equilibrium. Herein, we synthesize a polydopamine (PDA) coated MnO2 composite material (MnO2/PDA) to realize stable cycling in zinc cells without relying on pre-added Mn2+. The functional groups on PDA exhibit strong coordination ability with the Mn active material. It not only confines dissolved species within the cathode during discharge, but also enhances their deposition back to the cathode during charge to retrieve the active material. Thanks to this effect, the cathode achieves 81.1% capacity retention after 2000 cycles at 1 A g(-1) in the 1 M ZnSO4 electrolyte, superior to 37.3% with the regular MnO2 cathode. This work presents an effective strategy to realize the stable cycling of manganese oxide cathode materials in aqueous zinc batteries.