Approaching convergence in the electrochemical mechanism of aqueous Zn–MnO2 sustainable batteries

Abstract

Manganese oxide cathodes are quite appealing when considering moderate energy/power aqueous rechargeable zinc-ion batteries (ARZIBs) and long-term cycling. However, due to the variety of potential reaction pathways that are periodically proposed, the electrochemistry of manganese oxides with zinc is still unclear and fraught with dispute. Several mechanisms have been hypothesized/proposed over time for Zn–MnO₂ in most common electrolyte of ZnSO₄, including exclusive Zn²⁺ insertion, exclusive H⁺ conversion along with reversible layer hydroxide formation–dissolution, mixed insertion–conversion with and without layer formation–dissolution, exclusive MnO₂/Mn²⁺ electrodeposition–dissolution with layer formation–dissolution, and mixed electrodeposition–dissolution and Zn²⁺/H⁺ insertion with layer formation–dissolution. To tackle this problem, we propose three potential roadmap approaches: selection of operando analyses, fine-tuned electrolyte pH, and electrolyte isotope labelling.