Multifunctional pH‐Controlling Electrolyte Enables Ultrastable and Highly Reversible Zinc Anode

Abstract

Abstract The application of aqueous zinc‐ion batteries in large‐scale energy storage systems is significantly limited by the hydrogen evolution reaction (HER). Although conventional pH‐adjusting additives can reduce the overpotential of HER, it is imperative to simultaneously modulate the composition of the solid electrolyte interphase (SEI) and the electrical double layer (EDL) structure to enhance the utilization of zinc metal. This research develops a multifunctional pH‐controlling additive, the bis(2‐hydroxyethyl)amino‐tris(hydroxymethyl)methane (BT). First, the addition of BT increases the pH of the electrolyte to 5.9, which is within its effective buffer zone, and simultaneously reduces the HER potential to −1.107 V versus Ag/AgCl. Second, the inhibitory effect on HER can be further enhanced by the preferential adsorption of BT molecules containing multiple hydroxyl functional groups on the zinc anode, leading to a reduction in the number of active water molecules in the EDL. Third, BT molecules participate in the solvation structure to accomplish preferential reduction, which promotes the uniform deposition of Zn 2+ ions by forming nitrogen‐containing SEI. Ultimately, the symmetric battery accomplishes 2700 stable cycles in BT‐3 electrolyte. More crucially, the corresponding Zn//MnO 2 full battery (1 A g −1 ) is able to release a specific capacity of 117.2 mA h g −1 after 600 cycles.