Proton-dominant charge storage in layered H2V3O8 for Mn2+/H+ hybrid aqueous batteries

Abstract

Aqueous rechargeable batteries (ARBs) are compelling for grid‑scale storage owing to their cost effectiveness, promising safety features, and sustainability. Within this landscape, Mn‑based batteries offer a deeper redox potential (−1.19 V vs. SHE), high theoretical energy density, abundance, and low toxicity. However, the large hydrated radius and strong electrostatic interactions of Mn²⁺ in water severely hinder bulk intercalation and, thus, reversible capacity. Here we demonstrate a Mn²⁺/H⁺ hybrid chemistry using layered H₂V₃O₈ as the cathode host. These electrodes may deliver high specific capacity > 320 mAh g⁻¹ at 0.2 A g⁻¹ and may retain around 70 % of their initial capacity after 3500 cycles. Comprehensive spectroscopic and structural analyses revealed that Mn²⁺ mainly forms surface by‑products and functions as a secondary charge carrier, whereas protons dominate the charge compensation. This dual‑ion mechanism underpins the high capacity, fast kinetics, and durable cycling. Mn metal//H₂V₃O₈ full cells can operate at 1.23 V, benefiting from the large electrodes’ potential gap, and exhibits robust electrochemical performance. Our results clarify the interplay between Mn²⁺ and H⁺ in aqueous media and position H₂V₃O₈ as a promising cathode platform for next‑generation, safe, and sustainable energy storage devices.