Engineering Electrolyte Network Structure for Improved Kinetics and Dendrite Suppression in Zn-S Batteries

Aqueous zinc-sulfur batteries (Zn-S) are promising alternatives to conventional lithium-ion technology due to their high energy density, low cost, and enhanced safety. However, challenges such as slow redox kinetics of sulfur cathode conversion and inadequate anode stability persist. This study demonstrates that by tuning the electrolyte structure with the introduction of propylene glycol methyl ether (PM) as a co-solvent and ZnI₂ as an electrolyte additive, and significant improvements at both electrodes could be achieved. Experimental and theoretical calculations reveal that the larger polar -OH and C-O-C electron-donating groups in the PM molecule can donate electrons for the redox reaction of I^-/I₃ ^-. Its role as a redox mediator improves the reversibility of the sulfur cathodic transformation. Additionally, the dipole moment induced by the hydroxyl groups in PM enhances electron transfer from the zinc anode to the electrolyte and promote the decomposition of anions (OTF^-), improving the interfacial stability of the zinc anode. The synergistic effect of PM and the I^-/I₃ ^- redox mediator pair enables the zinc-sulfur battery to deliver an impressive capacity of 1456 mAh g^-1 and a high energy density of 471.8 Wh kg^-1 at a current density of 0.2 A g^-1.