Zn2+-mediated catalysis for fast-charging aqueous Zn-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs), renowned for their safety, high energy density and rapid charging, are prime choices for grid-scale energy storage. Historically, ion-shuttling models centring on ion-migration behaviour have dominated explanations for charge/discharge processes in aqueous batteries, like classical ion insertion/extraction and pseudocapacitance mechanisms. However, these models struggle to account for the exceptional performance of AZIBs compared to other aqueous metal-ion batteries. Here we present a catalysis model elucidating the Zn2+ anomaly in aqueous batteries, explaining it through the concept of adsorption in catalysis. Such behaviour can serve the charge/discharge role, predominantly dictated by solvated metal cations and cathode materials. First-principles calculations suggest optimal adsorption/desorption behaviour (water dissociation process) with the Zn2+–vanadium nitride (VN) combination. Experimentally, AZIBs implementing VN cathodes demonstrate fast-charging kinetics, showing a capacity of 577.1 mAh g−1 at a current density of 300,000 mA g−1. The grasp of catalysis steps within AZIBs can drive solutions beyond state-of-the-art fast-charging batteries. Aqueous Zn-ion batteries are promising devices but their energy storage mechanism remains elusive. Now it is shown that these involve a catalytic mechanism based on water dissociation.