Quantifying and Suppressing Proton Intercalation to Enable High‐Voltage Zn‐Ion Batteries

Abstract Rechargeable Zn‐ion batteries (ZIBs) are widely regarded as promising candidates for large‐scale energy storage applications. Like most multivalent battery systems (based on Zn, Mg, Ca, etc.), further progress in ZIB development relies on the discovery and design of novel cathode hosts capable of reversible Zn²⁺ (de)intercalation. Herein, this work employs VPO₄F as a ZIB cathode and explores ensuing intercalation mechanisms along with interfacial dynamics during cycling to quantify the water dynamics in concentrated electrolytes and/or hybrid aqueous‐non aqueous (HANEs) electrolyte(s). Like most oxide‐based cathode materials, proton (H⁺) intercalation dominates electrochemical activity during discharge of Zn_xH_yVPO₄F in aqueous media due to the hydroxylated nature of the interface. Such H⁺ electrochemistry diminishes low‐rate and/or long‐term electrochemical performance of ZIBs which inhibits implementation for practical applications. Thus, quantification of the water dynamics in various electrolytes is demonstrated for the first time. Detailed investigations of water mobility in various concentrated electrolytes and HANEs systems enable the design of an electrolyte that enhances aqueous anodic stability and suppresses water/proton activity during discharge. Tuning Zn²⁺/H⁺ intercalation kinetics simultaneously allows for a high voltage (1.9 V) and long‐lasting aqueous zinc‐ion battery: Zn|Zn(OTf)₂·nH₂O‐PC|Zn_xH_yVPO₄F.