Catholyte Formulations for High-Energy Li-S Batteries

The sulfur electrode in LiS batteries suffers from rapid capacity loss and low efficiency due to the solubility of long chain polysulfides formed during discharge. Herein, we demonstrate the beneficial effect of original catholyte formulations containing redox active organyl disulfides (PhS₂Ph) on the capacity utilization and retention as well as the efficiency in LiS batteries. Resulting from the chemical equilibria in the electrolyte between the sulfur/polysulfides (S₈/S_x^2-) and disulfide/thiolates (PhS₂Ph/PhS_x^-), the polysulfide redox shuttle phenomenon is minimized due to the suppression of formation of soluble polysulfides (S_x^2-, x > 4). Using the catholyte containing 0.4 M Ph₂S₂ as an additive in a standard base electrolyte (DOL/DME + LiTFSI/LiNO₃), a stable capacity of 1050 mAh·g^-1 is obtained under galvanostatic cycling at C/5 with a Coulombic efficiency of >99.5%. At 45 °C, it is shown that the formulated catholyte enables galvanostatic cycling at a high c-rate of 1C over 500 cycles with a capacity above 900 mAh·g^-1 and a high energy efficiency of 82%.