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.