Revealing Hybrid Mn²⁺/H⁺ Storage in Copper Vanadate Cathodes for Aqueous Manganese Batteries

Aqueous manganese batteries are emerging as safe and low-cost energy-storage systems, yet the fundamental charge-storage chemistry related to Mn ion transport remains undeveloped enough and poorly understood. Here, we report monoclinic Cu_0.3V₂O₅ as a cathode that reveals hybrid Mn and proton storage in aqueous manganese batteries. In saturated MnCl₂ electrolyte, Cu_0.3V₂O₅ delivers a high reversible capacity of 330.5 mAh/g and retains 70.4% capacity after 1500 cycles. Combined spectroscopic analysis, Fourier electron-density mapping, ICP-OES, and SoftBV calculations demonstrated that Mn mainly forms Mn(OH)₂ surface by-products, while partial Mn intercalation is verified by Fourier electron-density mapping. In contrast, electrolyte-derived protons dominate reversible lattice insertion and act as the primary charge carriers. The substantially lower migration barrier of protons compared with Mn ions further confirms proton-dominated transport within the host structure. When paired with Mn metal anodes, full cells exhibited an average operating voltage higher by 0.43 V than aqueous Zn batteries comprising similar cathodes and Zn metal anodes. This work clarifies the hybrid Mn ions and protons chemistry of aqueous manganese batteries and provides mechanistic insight for the design of next-generation multivalent aqueous energy-storage systems.