(665h) Electrolyte Engineering Enables High-Performance Span-Based Lithium-Sulfur Batteries Under Practical Conditions

Lithium-sulfur (Li-S) batteries are emerging as a highly promising candidate for next-generation energy storage systems, distinguished by their impressive energy output, cost-effectiveness in materials, and environmental benignancy characteristics. Lithium polysulfides, as the discharge intermediates, show great reaction activity towards Li anode which result in continuous sulfur loss and Li corrosion, contributing to capacity decreased and poor cycle stability. Applying chemical sequestration that covalently bond sulfur to a carbonaceous host presents as a promising alternative to eliminate polysulfides generation. Among them, sulfur-polyacrylonitrile (SPAN) stands out as one of the most promising materials. Li-SPAN batteries have been demonstrated with stable cycling up to hundreds of cycles which is benefiting from the negligible polysulfides dissolution that react with carbonate-based electrolytes to form a stable cathode electrolyte interface (CEI). However, challenges remain in maintaining high performance under high loading and lean electrolyte conditions because of the poor compatibility between carbonate-based electrolytes and Li anode.

In this work, we first distinguish ethylene carbonate (EC) as the optimized selection among carbonate solvents for constructing the robust CEI. In order to get insight into the behind mechanism, kinetic study and galvanostatic intermittent titration technique (GITT) combined with electrochemical impedance spectroscopy (EIS) technology using three-electrodes pouch cells are developed. Chemical analysis like solid NMR and surface analysis such as XPS are applied to study the components of CEI formed in different carbonate electrolytes. Furthermore, as addressing the compatibility issue between carbonates and Li anodes, ether and fluorinated ether solvents are introduced with improved columbic efficiency. Befitting from the robust CEI and SEI, a Li-SPAN pouch cell with high loading of 7 mg cm^-2, thin Li anode of 100 µm and lean electrolyte condition of 2.5 µl mg^-1 was demonstrated with stable stability of 150 cycles and deliver a high energy density of 170 Wh kg^-1 (based on whole system).