The role of polysulfide-saturation in electrolytes for high power applications of real world Li-S pouch cells

The lithium-sulfur(Li-S)technology is the most promising candidate for next-generation batteries due to its high theoretical specific energy and steady progress for applications requiring lightweight batteries such as aviation or heavy electric vehicles.For these applications,however,the rate capability of Li-S cells requires significant improvement.Advanced electrolyte formulations in Li-S batteries enable new pathways for cell development and adjustment of all components.However,their rate capability at pouch cell level is often neither evaluated nor compared to state of the art(SOTA)LiTFSI/dimethoxyethane/dioxolane(LITFSI:lithium-bis(trifluoromethylsulfonyl)imide)electrolyte.Herein,the combination of the sparingly polysulfide(PS)solvating hexylmethylether/1,2-dimethoxyethane(HME/DME)electrolyte and highly conductive carbon nanotube Buckypaper(CNT-BP)with low porosity was evaluated in both coin and pouch cells and compared to dimethoxyethane/dioxolane reference electrolyte.An advanced sulfur transfer melt infiltration was employed for cathode production with CNT-BP.The Li+ion coordination in the HME/DME electrolyte was investigated by nuclear magnetic resonance(NMR)and Raman spectroscopy.Additionally,ionic conductivity and viscosity was investigated for the pristine electrolyte and a polysulfide-statured solution.Both electrolytes,DME/DOL-1/1(DOL:1,3-dioxolane)and HME/DME-8/2,are then combined with CNT-BP and transferred to multi-layered pouch cells.This study reveals that the ionic conductivity of the electrolyte increases drastically over state of(dis)charge especially for DME/DOL electrolyte and lean electrolyte regime leading to a better rate capability for the sparingly polysulfide solvating electrolyte.The evaluation in prototype cells is an important step towards bespoke adaption of Li-S batteries for practical applications.