A dual-additive electrolyte enables highly reversible Zn electrochemistry

Abstract

Aqueous zinc-ion batteries (AZIBs) are regarded as strong competitors to lithium-ion batteries due to their inherent safety and low cost. However, parasitic side reactions and uncontrolled growth of Zn dendrites prevent their further development. Herein, we introduce a dual-additive of nicotinamide (NI) and potassium acetate (KOAc) into Zn(OTF)₂ electrolyte. The three zincophilic sites (amino, carbonyl and pyridine) of NI can combine with Zn²⁺ to alter the solvated structure of [Zn(H₂O)₆]²⁺, act as hydrogen bond donors/acceptors to form a new hydrogen bond network with H₂O, and adsorb onto the Zn anode surface to promote the redistribution of Zn²⁺ and regulate the charge distribution, thus reducing the activity of the H₂O molecule, inhibiting H₂O-related side reactions and guiding homogeneous deposition of Zn. Meanwhile, KOAc acts as a pH buffer to stabilize the pH of the electrolyte system during electrochemical processes, preventing the corrosion reaction. Moreover, K⁺ tends to adsorb onto the surface of protrusions and form an electrostatic shield, which can induce oriented deposition of Zn and suppress Zn dendrite formation. With the assistance of the synergistic effect of the dual-additive, the Zn//Zn cells demonstrate stable cycling for over 1600 h at 1 mA cm⁻² and 1 mA h cm⁻² and for 820 h at 5 mA cm⁻² and 5 mA h cm⁻², which are nearly 22 and 29 times that of the pure Zn(OTF)₂ electrolyte. Moreover, Zn//Cu asymmetric cells deliver highly reversible Zn plating/stripping with a high and stable coulombic efficiency of 99.4%, and Zn//I₂ full cells exhibit excellent cycle stability (95.4% capacity retention after 4000 cycles). Even at a low temperature of −10 °C, Zn//Zn cells still survive up to 750 h at 5 mA cm⁻² and 5 mA h cm⁻².