September 2018

Owing to the high theoretical gravimetric energy density based on the conversion reaction between S and Li2S, Li-S batteries have attracted attention as a promising candidate for the next-generation energy storage system. Although the notorious shuttle effect, deteriorating the battery capacity due to the formation of polysulfides soluble to the conventional electrolytes, can be physically hindered by employing solid electrolytes (SEs), the mechanically rigid property of inorganic materials causes another crucial issue: the chemo-mechanical failure. The liquid electrolyte maintains good contacts to active materials by infiltrating the gaps and cracks formed during the lithiation/delithiation. However, while Li2S shrinks significantly when it is converted to S by charging, the contacts between components can be lost as seen in the SEM cross-section image of the charged cell, which leads to the capacity loss. Cathode composites shown here contain active material S, conductive carbon additives, and the SE containing P. A deeper understanding of the failure mechanisms is key to the further development of solid-state Li-S batteries. (Picture submitted by Saneyuki Ohno.)