Issues and Opportunities Facing Aqueous Mn²⁺ /MnO₂ -based Batteries

Aqueous Mn²⁺ /MnO₂ -based batteries have attracted enormous attentions in aqueous energy storage fields, owing to their high working voltage and theoretical capacity (616 mAh g^-1 ) brought by the two-electron reaction (Mn²⁺ /Mn⁴⁺ ). However, there are currently several tricky challenges facing Mn²⁺ /MnO₂ -based batteries: their complicated working mechanisms, existing issues, and optimization strategies. This Perspective aims to provide a mechanistic understanding and an overview of the insufficiency, optimization, and future development for Mn²⁺ /MnO₂ -based batteries. The existing issues and deficiency in Mn²⁺ /MnO₂ -based batteries have been systematically analyzed, and optimization strategies have also been rationally summarized and discussed with deep insights. Also, the often-overlooked optimized objects and aspects have been highlighted with unique perspectives. The proposals of testing methods and performance assessment are presented, containing different degradation mechanisms. Based on the above points, this Perspective will provide guidance and contribute to the further development of aqueous Mn²⁺ /MnO₂ -based batteries.