Can sulfide solid electrolytes for lithium-ion batteries be handled in dry rooms? – A multiprobe approach

• Commercial Li 3 PS 4 and Li 6 PS 5 Cl were investigated at dry room and ambient atmospheres • Detailed mechano-chemical degradation mechanism for the SEs is presented • H 2 S amounts evolved are in linear relationship with pellets’ surface area • Both materials lose ∼30% of ionic conductivity upon 2h exposure to D.P. -40°C • Compression helps to reduce the impact of hydrolysis on SEs at D.P. 12°C. Sulfide-based solid electrolytes (SSEs) are promising for solid-state batteries (SSBs) due to their high room-temperature ionic conductivity and scalability. However, their strong moisture sensitivity hinders safe handling, even in dry-room atmospheres. Although hydrolysis has been extensively studied on SSE powders, there is a lack of understanding of its mechanism at multiple length scales in SSE pellets. Herein, we investigate the transformations occurring within a commercial Li₃PS₄ SSE exposed to humidity at dew points (D.P.) of –40°C and 12°C using a multi-technique approach, including X-ray nano-tomography and X-ray diffraction computed tomography, to systematically track morphological and chemical changes. Results reveal that SSE hydrolysis is a complex, multi-step cyclic process in which chemical and morphological evolution are closely linked. The main stages identified include a fast reaction at the pellet surface, leading to the formation of new compounds and accumulation of structural strains in the SSE main phase. It is subsequently followed by crack propagation and porosity increase, promoting deeper humidity penetration into the bulk of the pellet and exposing fresh surface to further hydrolysis. Comparison with another commercial SSE, Li₆PS₅Cl, provides broader insight into humidity-driven degradation mechanisms. This research provides practical guidance for handling SSEs in dry room environments and highlights the potential consequences of accidents involving ruptured SSB packages. The multi-probe approach presented here can be applied to a wide range of SSB components to quantify safety risks and performance impacts. These insights can help optimize dry room conditions and reduce the overall cost of SSBs processing.