Strategically Modulating Proton Activity and Electric Double Layer Adsorption for Innovative All‐Vanadium Aqueous Mn2+/Proton Hybrid Batteries

Abstract Aqueous Mn‐ion batteries (MIBs) exhibit a promising development potential due to their cost‐effectiveness, high safety, and potential for high energy density. However, the development of MIBs is hindered by the lack of electrode materials capable of storing Mn 2+ ions due to acidic manganese salt electrolytes and large ion radius. Herein, the tunnel‐type structure of monoclinic VO 2 nanorods to effectively store Mn 2+ ions via a reversible (de)insertion chemistry for the first time is reported. Utilizing exhaustive in situ/ex situ multi‐scale characterization techniques and theoretical calculations, the co‐insertion process of Mn 2+ /proton is revealed, elucidating the capacity decay mechanism wherein high proton activity leads to irreversible dissolution loss of vanadium species. Further, the Grotthuss transfer mechanism of protons is broken via a hydrogen bond reconstruction strategy while achieving the modulation of the electric double‐layer structure, which effectively suppresses the electrode interface proton activity. Consequently, the VO 2 demonstrates excellent electrochemical performance at both ambient temperatures and −20 °C, especially maintaining a high capacity of 162 mAh g −1 at 5 A g −1 after a record‐breaking 20 000 cycles. Notably, the all‐vanadium symmetric pouch cells are successfully assembled for the first time based on the “rocking‐chair” Mn 2+ /proton hybrid mechanism, demonstrating the practical application potential.