Observation of Chemomechanical Failure and the Influence of Cutoff Potentials in All-Solid-State Li–S Batteries

Because of a remarkably high theoretical energy density, the lithium–sulfur (Li–S) battery has attracted significant attention as a candidate for next-generation batteries. While employing solid electrolytes can provide a new avenue for high-capacity Li–S cells, all-solid-state batteries have unique failure mechanisms such as chemomechanical failure due to the volume changes of active materials. In this study, we investigate all-solid-state Li–S model cells with differently processed cathode composites and elucidate a typical failure mechanism stemming from irreversible Li 2 S formation in the cathode composites. Reducing the particle size is key to minimizing the influence of volume changes, and a capacity of >1000 mAh g sulfur –1 is achieved by ball milling of the cathode composites. In addition, the long-term stability of the ball-milled cathode is investigated by varying the upper and lower cutoff potentials for cycling, which results in the unveiling of the significantly detrimental role of the lower cutoff potential. Preventing a deep discharge leads to a reversible capacity of 800 mAh g sulfur –1 over 50 cycles in the optimized cell. This work highlights the importance of mitigating chemomechanical failure using microstructural engineering as well as the influence of the cutoff potentials in all-solid-state Li–S batteries.