Hydration‐Mediated Mn ²⁺ /H ⁺ Storage in Tunnel‐Type MnV ₂ O ₆ ·4H ₂ O as High‐Voltage and Durable Aqueous Mn Metal Batteries

ABSTRACT Manganese‐based aqueous batteries hold promise as low‐cost and sustainable energy‐storage systems, yet progress has been hindered by the absence of cathode frameworks that can reversibly host multivalent ions without severe structural degradation. Here, we introduce MnV 2 O 6 ·4H 2 O as the first hydration‐engineered open framework that enables cooperative Mn 2 + /H + storage with exceptional reversibility. Structural water and crystal water synergistically construct a hydration‐mediated shielding environment that mitigates lattice strain and activates fast proton‐coupled transport pathways. As a result, MnV 2 O 6 ·4H 2 O delivers high capacity, fast kinetics, and unprecedented cycling durability, retaining 91.6% capacity over 1750 cycles. Spectroscopic and computational analyses reveal a hybrid storage mechanism in which H + functions as the primary charge carrier, while Mn 2 + contributes predominantly through surface‐confined reactions with limited bulk involvement. Furthermore, pairing MnV 2 O 6 ·4H 2 O with a Mn metal anode unlocks high operating voltages (1.19 V), demonstrating a viable route to sustainable, high‐energy aqueous batteries beyond Zn‐based chemistries. This work establishes hydration‐mediated stabilization as a mechanistic foundation for multivalent storage and provides a blueprint for designing high‐voltage aqueous batteries based on earth‐abundant materials.