Activation of MnO hexagonal nanoplates via in situ electrochemical charging toward high-capacity and durable Zn-ion batteries

Rechargeable aqueous Zn-MnO₂ batteries hold great promise in grid-scale energy storage owing to their merits of high specific energy, inexpensiveness, environmental benignity, and high safety. However, MnO₂ cathodes suffer from extremely poor cycling stability in pure ZnSO₄ electrolyte. In this work, MnO hexagonal nanoplates constructed by porous nanocrystals are reported to show superior zinc-ion storage performance in pure ZnSO₄ electrolyte. Mechanistic investigation reveals that the MnO cathode experiences an in situ gradual oxidation during electrochemical charging to form active MnO₂ ultrathin nanosheets, which subsequently allow for a reversible and consecutive insertion of H⁺ and Zn²⁺. Notably, a high specific capacity of 292 mAh g⁻¹ can be obtained in the activated cathode at a current density of 0.1 A g⁻¹. In particular, the cathode could sustain a long 1000-cycling operation without noticeable capacity degradation, which is comparable to the reported MnO₂ cathodes in an electrolyte containing MnSO₄ additive. The present study will shed light on the development of low-valence Mn-oxides by in situ electrochemical charging toward high-capacity and durable zinc-ion batteries.