Effect of Electrolyte Chemistry and Sulfur Content in Li||Sulfurized Polyacrylonitrile (SPAN) Batteries

Sulfurized polyacrylonitrile (SPAN) is considered as a high-value cathode material, which leverages the high energy of S redox while mitigating the negative externalities that limit elemental S cycling. As such, the sulfur content in Li-SPAN batteries plays a critical role. In this work, we demonstrate that high-S loading SPAN cathodes, where the PAN backbone approaches the saturation point without signs of elemental S, are highly dependent on the electrolyte chemistry for long-term reversibility. Specifically, we find that a localized-high-concentration electrolyte (LHCE) further enhances the reversible capacity and cycling stability of SPAN cathode with optimized S content relative to a carbonate control, largely due to the formation of a compatible interphase. With this LHCE as the electrolyte and 43% sulfur ratio of SPAN as the cathode, a full cell applying N/P ratio = 1.82, a cathode loading of 6 mAh cm^-2 (9.2 mg cm^-2), and an electrolyte loading of 7 μL mg^-1 SPAN can be cycled for 100 cycles with 433 mAh g^-1 retained capacity and retains much of this reversibility even at 60 °C. This work reveals the molecular origin of optimized sulfur ratio in SPAN cathodes while providing guidance in electrolyte design for Li||SPAN cells with high capacity and cyclability.