Self-initiated coating of polypyrrole on MnO2/Mn2O3 nanocomposite for high-performance aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries based on Mn-based cathode materials are of considerable interest for large-scale energy storage. However, the intrinsic low electronic conductivity and the dissolution issue of Mn-based cathode materials result in slow reaction kinetics and fast capacity fading. Herein, a facile and scalable strategy combining molten salt synthesis and self-initiated polymerization is developed to in-situ generate a thin layer of polypyrrole onto the surface of MnO2/Mn2O3 nanocomposite, aiming to resolve the problems mentioned above. The obtained product provides large specific capacity (289.8 mAh g(-1) at 0.2 A g(-1)), remarkable rate capability (199.8 mAh g(-1) at 3 A g(-1)), and excellent cycling stability (96.7% after 1000 cycles at 1 A g(-1), compared to the 2nd cycle). The cyclability remains good when Mn2+ ions are not pre-added into the electrolyte. Also, the obtained product exhibits slight electrochemical polarization, low charge transfer impedance after cycling, high capacitive contribution, and large electrolyte ion diffusion coefficient. All these performances and properties are significantly superior to that of MnO2/Mn2O3 nanocomposite without polypyrrole coating. This work opens a new path towards long-life and fast-discharging electrode materials.