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

Aqueous rechargeable Zinc (Zn) batteries incorporating MnO₂ 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/MnO₂ battery with a Co²⁺ -stabilized, tunnel-structured α-MnO₂ cathode (Co_x MnO₂ ). It is shown that Co²⁺ can be pre-intercalated into α-MnO₂ and occupy the (2 × 2) tunnel structure, which improves the structural stability of MnO₂ , facilitates the proton diffusion and Zn²⁺ adsorption on the MnO₂ surface upon battery cycling. It is further revealed that for the MnO₂ cathode, the charge storage reaction proceeds mainly by proton intercalation with the formation of α-H_y Co_x MnO₂ , and that the anode design (with or without Zn metal) affects the surface adsorption of by-product Zn₄ SO₄ (OH)₆ ·nH₂ O on MnO₂ surface. This work advances the fundamental understanding of rechargeable Zn batteries and also sheds light on efficient electrode modifications toward performance enhancement.