β-MnO2 with proton conversion mechanism in rechargeable zinc ion battery

Rechargeable aqueous zinc ion battery (RAZIB) is a promising energy storage system due to its high safety, and high capacity. Among them, manganese oxides with low cost and low toxicity have drawn much attention. However, the under-debate proton reaction mechanism and unsatisfactory electrochemical performance limit their applications. Nanorod β-MnO2 synthesized by hydrothermal method is used to investigate the reaction mechanism. As cathode materials for RAZIB, the Zn//β-MnO2 delivers 355 mAh g−1 (based on cathode mass) at 0.1 A g−1, and retain 110 mAh g−1 after 1000 cycles at 0.2 A g−1. Different from conventional zinc ion insertion/extraction mechanism, the proton conversion and Mn ion dissolution/deposition mechanism of β-MnO2 is proposed by analyzing the evolution of phase, structure, morphology, and element of β-MnO2 electrode, the pH change of electrolyte and the determination of intermediate phase MnOOH. Zinc ion, as a kind of Lewis acid, also provides protons through the formation of ZHS in the proton reaction process. This study of reaction mechanism provides a new perspective for the development of Zn//MnO2 battery chemistry.