Synergistic cation-anion regulation of active water within inner Helmholtz plane enables ultra-stable aqueous Zn ion batteries

The issues related to corrosion, dendrite growth, and hydrogen evolution reaction (HER) of the Zn anode in aqueous environments have significantly obstructed the practical implementation of aqueous zinc ion batteries (AZIBs). Herein, the strategy of synergistically regulating the content of active water molecules located within the inner Helmholtz plane (IHP) by anions and cations is used to address the above-mentioned water-related issues of zinc metal anodes via using the 1-Ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (IL) as an highly effective electrolyte additive. Theoretical computations and empirical outcomes show that the IL indirectly regulates IHP by tailoring solvation structure of Zn2+ via anions and adsorbing cations on the surface of the zinc anode, directly and effectively reducing the content of chemically active H2O molecules in IHP and thus significantly inhibiting the adverse reactions related to active H2O molecules. As a proof of concept, the Zn||Zn cells operate stably for over 4550 h at 1 mA cm-2 and 1 mAh cm-2, while the Zn//VO2 cells exhibit a capacity retention rate of 86 % after 1000 cycles at 5 A g-1. This investigation provides a feasible strategy for reducing the content of active H2O molecules in IHP to develop highly reversible and stable zinc metal anodes for AZIBs