Gas Evolution in Lithium-Ion Batteries: Solid versus Liquid Electrolyte.

Gas evolution in conventional lithium-ion batteries using Ni-rich layered oxide cathode materials presents a serious issue that is responsible for performance decay and safety concerns, among others. Recent findings revealed that gas evolution also occurred in bulk-type solid-state batteries. To further clarify the effect that the electrolyte has on gassing, we report in this work-to the best of our knowledge-the first study comparing gas evolution in lithium-ion batteries with NCM622 cathode material and different electrolyte types, specifically solid (β-LiPS and LiPSCl) versus liquid (LP57). Using isotopic labeling, acid titration, and in situ gas analysis, we show the presence of O and CO evolution in both systems, albeit with different cumulative amounts, and possible SO evolution for the lithium thiophosphate-based cells. Our results demonstrate the importance of considering gas evolution in solid-state batteries, especially the formation and release of highly corrosive SO, due to side reactions with the electrolyte.