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

Aqueous rechargeable Zn batteries incorporating MnO 2 cathodes possess favourable 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, we utilize advanced transmission electron microscopy, electrochemical analysis, and theoretical calculations 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 ). We show 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 , facilitate the proton diffusion and Zn 2+ adsorption on the MnO 2 surface upon battery cycling. We further reveal 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. Our work advances the fundamental understanding of rechargeable Zn batteries and also sheds light on efficient electrode modifications toward performance enhancement. This article is protected by copyright. All rights reserved.