Highly Reversible Positive-Valence Conversion of Sulfur Chemistry for High-Voltage Zinc–Sulfur Batteries

Abstract

Sulfur is a promising conversion-type cathode for zinc batteries (ZBs) due to its high discharge capacity and cost-effectiveness. However, the redox conversion of multivalent S in ZBs is still limited, only having achieved S⁰/S²⁻ redox conversion with low discharge voltage and poor reversibility. This study presents significant progress by demonstrating, for the first time, the reversible S²⁻/S⁴⁺ redox behavior in ZBs with up to six-electron transfer (with an achieved discharge capacity of ≈1284 mAh g⁻¹) using a highly concentrated ClO<inf>4</inf>⁻-containing electrolyte. The developed succinonitrile–Zn(ClO<inf>4</inf>)<inf>2</inf> eutectic electrolyte stabilizes the positive-valence S compound and contributes to an ultra-low polarization voltage. Notably, the achieved flat discharge plateaus demonstrate the highest operation voltage (1.54 V) achieved to date in Zn‖S batteries. Furthermore, the high-voltage Zn‖S battery exhibits remarkable conversion dynamics, excellent cycling performance (85.7% capacity retention after 500 cycles), high efficiency (98.4%), and energy density (527 Wh kg <inf>S</inf>⁻¹). This strategy of positive-valence conversion of sulfur represents a significant advancement in understanding sulfur chemistry in batteries and holds promise for future high-voltage sulfur-based batteries.