Observation of chemo-mechanical failure and influence of cut-off potentials in all-solid-state Li-S batteries

Owing to 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 chemo-mechanical 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 Li₂S formation in the cathode composites. Reducing the particle size is key to minimizing the influence of volume changes and a capacity of over 1000 mAh g_sulfur^-1is achieved by ball-milling of the cathode composites. In addition, the long-term stability of the ball-milled cathode is investigated by varying upper and lower cut-off potentials for cycling, which results in unveiling the significantly detrimental role of the lower cut-off potential. Preventing a deep-discharge leads to a reversible capacity of 800 mAh g_sulfur^-1over 50 cycles in the optimized cell. This work highlights the importance of mitigating chemo-mechanical failure using microstructural engineering as well as the influence of the cut-off potentials in all-solid-state Li-S batteries.