Promoting the Rate Performances of Weakly Solvating Electrolyte-Based Lithium‒Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices due to their theoretical energy density of 2600 Wh kg^-1. Employing weakly solvating electrolyte (WSE) effectively alleviates the polysulfide shuttle effect and improves the cycling lifespan. However, the sulfur cathode kinetics in WSE is highly sluggish to render degraded rate performances. Herein, the sulfur cathode kinetics of WSE-based Li-S batteries is systematically investigated to help promote the rate performances in practical pouch cells. Concretely, the sluggish cathode kinetics of the previous charging process is identified as the main limitation for specific discharge capacity loss at high rates. Further polarization decoupling manifests activation polarization corresponding to polysulfide oxidation to elemental sulfur constitutes the dominant kinetic challenge. Accordingly, a redox mediation strategy is proposed to accelerate the charge-transfer kinetics of polysulfide oxidation in WSE. 3 Ah-level pouch cells cycle stably under a high rate of 0.2 C, and 5 Ah level pouch cells achieve an actual energy density of 470 Wh kg^-1. This work deepens the comprehension of the sulfur cathode kinetics in WSE and highlights the redox mediation strategy in achieving high-energy-density and high-rate Li-S batteries.