Achieving high capacity and long cycling life in aqueous zinc–sulfur batteries with improved kinetics through electrolyte solvation engineering

Abstract

Aqueous Zn/S batteries are emerging as promising next-generation high-energy density rechargeable storage devices. The cost-effective and abundant reserve of sulfur, when paired with a zinc anode, significantly enhances both specific capacity and energy density. However, their practical applications face challenges such as poor sulfur utilization in aqueous electrolytes, sluggish sulfur redox kinetics and parasitic reactions at the Zn anode. To address these challenges, electrolyte engineering strategies have been introduced using high donor number (DN) organic co-solvents. Extensive investigation into the impact of DN on sulfur conversion kinetics and the Zn anode reveals that DMSO, a high-DN solvent, facilitates efficient reversibility of sulfur and prevents the hydrogen evolution reaction (HER) and dendrite formation on the zinc anode by modulating the solvation sheath of Zn²⁺ ions. Notably, the high DN of DMSO enables a lower concentration of additives while improving the kinetics of both the sulfur cathode and the zinc anode, compared to higher concentrations of low-DN solvents like acetonitrile and DMF. As a result, the Zn/S battery with a DMSO-containing electrolyte achieved a high specific capacity of 1502 mA h g⁻¹ at 0.1 A g⁻¹ and long-term cycling stability with 92% capacity retention over 1000 cycles at 5 A g⁻¹.