A Janus Membranewith Asymmetrical Proton Transportfor Cross-Communication Harmony for an Extreme Lean Electrolyte Zn–VBattery

The Zn metal anode demands a reduction in water activity and proton concentration to prevent undesirable side reactions, while the V-based cathode necessitates water as a “lubricant” and protons as intercalation guests, presenting a challenge in balancing these needs. Herein, we report a Janus membrane with asymmetrical proton transport for cross-communication harmony in Zn–V batteries, designed to harmonize these contrasting requirements. The MXene-rich phase blocks the proton/water transport through the F-termination site and effectively suppresses dendrite formation through epitaxial growth. Meanwhile, the proton selective cellulose-rich phase (H⁺/Zn²⁺ selectivity of over 21) stabilizes the cathode/electrolyte interface by capturing dissolved vanadium and enhancing proton intercalation into the cathode. This designed Janus membrane enables a practical Zn–V full battery at a high depth of discharge of 66.7% and extreme lean electrolyte (1 g/Ah) conditions, enabling the high energy zinc battery (214.8 Wh/kg_electrode). Our approach introduces a sustainable separator for long-lasting, high-performance zinc metal batteries.