Surface Adsorption and Proton Chemistry of Ultra‐Stabilized Aqueous Zinc–Manganese Dioxide Batteries

Abstract Aqueous rechargeable Zinc (Zn) batteries incorporating MnO 2 cathodes possess favorable sustainability properties and are being considered for low‐cost, high‐safety energy storage. However, unstable electrode structures and unclear charge storage mechanisms limit their development. Here, advanced transmission electron microscopy, electrochemical analysis, and theoretical calculations are utilized to study the working mechanisms of a Zn/MnO 2 battery with a Co 2+ ‐stabilized, tunnel‐structured α ‐MnO 2 cathode (Co x MnO 2 ). It is shown that Co 2+ can be pre‐intercalated into α ‐MnO 2 and occupy the (2 × 2) tunnel structure, which improves the structural stability of MnO 2 , facilitates the proton diffusion and Zn 2+ adsorption on the MnO 2 surface upon battery cycling. It is further revealed that for the MnO 2 cathode, the charge storage reaction proceeds mainly by proton intercalation with the formation of α ‐H y Co x MnO 2 , and that the anode design (with or without Zn metal) affects the surface adsorption of by‐product Zn 4 SO 4 (OH) 6 ·nH 2 O on MnO 2 surface. This work advances the fundamental understanding of rechargeable Zn batteries and also sheds light on efficient electrode modifications toward performance enhancement.