Multi-functional electrolyte additive facilitating reversible and uniform zinc deposition for sustainable alkaline zinc-iron flow batteries

Abstract

Alkaline zinc‑iron flow batteries (AZIFBs) have undergone rapid development since their merits of high open-circuit voltage, exceptional battery efficiency, and robust system stability. However, AZIFBs always suffer from the issues of the side reaction and zinc dendrites lead to irreversible and uneven zinc deposition, ultimately shortening the battery lifespan. To address these challenges, a multi-functional additive of sulfoxide (SL) is added as a typical [Zn(OH)₄]²⁻ electrolyte. The comprehensive research reveals that the incorporation of SL as an additive effectively modifies the solvation structure of electrolytes. Consequently, the functional additive enhances the stability of the electrolyte, suppressing the hydrogen evolution reaction, corrosion, and side reaction, thereby enhancing the reversible deposition of zinc. Furthermore, the functional additive slows down the diffusion coefficient during the deposition process, inducing even nucleation. Therefore, the multi-functional electrolyte additive enables reversible and uniform zinc deposition. As a proof of concept, the AZIFBs with multi-functional additive demonstrated remarkable stability with over 320 cycles. Furthermore, the average coulomb efficiency reached about 99.53 %, while the energy efficiency hovered around 75.54 % at a current density of 80 mA cm⁻², which is much higher than that of a typical electrolyte. Even at a large current density of 160 mA cm⁻², the coulomb efficiency was still maintained exceeding 99 %. This work offers a strategy for designing the multi-functional electrolyte additive for sustainable zinc-based flow batteries.