Solid-state electrolytes have been identified as promising candidates to overcome limitations of lithium-sulfur batteries in polysulfide shuttle and lithium dendrite growth. However, an essential mechanistic understanding of composite sulfur (S) cathodes is still lacking in all-solid-state lithium-sulfur (ASSLS) batteries. Herein, in situ atomic force microscopy and Raman spectroscopy were conducted to unravel S cathode processes during cycling. The S particles gradually expand and fuse upon discharge, which is ascribed to the electrochemical conversion to lithium sulfide. The volume variation exhibits poor reversibility upon charge, which is the origin of the capacity fading of the S cathode. Moreover, side reactions occur at the interface of S/Li10GeP2S12 (LGPS) in the cathode, manifested as simultaneous S dissolution and LGPS decomposition, which aggravate consumption of active materials and increase ion transport resistance. These straightforward evidence and in-depth studies uncover the S cathode process and enrich fundamental comprehensions of reaction mechanisms in ASSLS batteries.
Liu et al. (Tue,) studied this question.