PNNL

Abstract

The lithium-sulfur (Li-S) battery is a promising next-generation energy storage technology for vehicle electrification and grid energy storage because of its high theoretical energy and low cost. Extensive research efforts are being pursued on new materials and advanced characterization techniques for mechanistic studies. However, it is uncertain how discoveries made on the material level apply to realistic batteries because of limited analysis and characterization of real high-energy cells such as pouch cells. Herein, we design, fabricate pouch cells over 300 Wh kg-1, compare the cell parameters required for high-energy pouch cells, and investigate the reaction processes and their correlation to cell cycling behavior and failure mechanisms. We used spatially resolved characterization techniques and transient simulation to reveal the impacts of the liquid electrolyte diffusion within the pouch cells. We found that catastrophic failure of high-energy Li-S pouch cell is caused by uneven sulfur/polysulfide reactions and electrolyte depletion for the first tens of cycles, rather than sulfur dissolution as commonly reported in the literature. The uneven reaction is attributed to the limited electrolyte diffusion through the nanosized porous channels into the central part of thick cathodes during cycling, which is amplified both across the sulfur electrodes and within the same electrode plane. A combination of strategies is suggested to increase sulfur utilization, improve nanoarchitectures for electrolyte diffusion, and reduce consumption of the electrolytes and additives.