Asymmetric Ion Transport in Tunnel-Type Cobalt Vanadate for High-Performance Mn²⁺/H⁺ Hybrid Aqueous Batteries

Aqueous manganese batteries are attractive owing to the deeper Mn/Mn²⁺ redox potential (-1.19 V vs SHE) compared with Zn, yet their development has been hindered by sluggish Mn²⁺ diffusion and parasitic interfacial reactions. Here, the concept of asymmetric-ion transport is introduced, where Mn²⁺ and protons occupy distinct diffusion channels and act synergistically rather than competitively. Using Co(VO₃)₂·2H₂O as a model host, direct structural evidence is provided from Fourier electron density maps and ICP-OES that 0.50 mol of Mn²⁺ is reversibly accommodated alongside 0.14 mol of H⁺. Migration-barrier calculations further reveal orthogonal pathways with balanced activation energies (0.602 eV for Mn²⁺, 0.334 eV for H⁺), rationalizing the coexistence of Mn-dominant storage and proton-assisted kinetics. This dual-ion mechanism enables high reversibility, robust cycling stability, and quasi-zero-strain behavior. When paired with a Mn metal anode, the full cell delivers 1.3 V, substantially 0.4 V higher than Zn analogues, while highlighting the necessity of Mn anode interface stabilization. Beyond a new cathode material, this study establishes asymmetric-ion transport as a generalizable paradigm for reconciling multivalent-ion storage with fast kinetics in high-voltage aqueous batteries.