Solvation structure regulation of an organic small molecule additive for dendrite-free aqueous zinc-ion batteries

The aqueous zinc-ion battery is a potential energy storage device due to its environmental sustainability and cost-effectiveness. Nonetheless, the reduced reversibility of the Zn anode arising from continuous parasitic reactions (hydrogen evolution reaction (HER) and corrosion) and random dendrite growth has a significant impact on its life and performance. Herein, organic small-molecule formamide (FA) is proposed as an additive to the aqueous ZnSO₄ electrolyte and realizes a dendrite-free and highly reversible Zn anode by regulating the solvation structure. Through theoretical calculation, as well as physicochemical and electrochemical characterization, it is evidenced that FA additive shows the following characteristics: (1) it replaces some of the H₂O molecules in the solvation structure to participate in the solvation structure of Zn²⁺, and significantly inhibit the HER, (2) breaks the original hydrogen bonding network, resulting in the improvement of the low temperature performance of the battery, (3) preferentially adsorbs on the Zn surface to regulate the charge distribution at the Zn anode/electrolyte interface and inhibit Zn corrosion during the initial cycling process, and (3) contributes to the formation of an inorganic-organic double-layer solid electrolyte interface (SEI) for dendrite-free uniform zinc deposition. Benefiting from these advantages, Zn‖Cu asymmetric batteries assembled with this electrolyte show more than 1700 highly reversible zinc plating/stripping cycles, and the average coulombic efficiency reaches 99.24%. Zn‖Zn symmetric batteries survive more than 1600 h of stable cycling at 1 mA cm⁻² and 0.5 mA h cm⁻². As a proof of concept, the Zn‖MnO₂ full cells provide excellent cycle performance over 2000 cycles at the current density of 4 A g⁻¹, and maintain a high capacity retention of 85.1%.