Chemical Origin of in Situ Carbon Dioxide Outgassing from a Cation-Disordered Rock Salt Cathode.

In situ carbon dioxide (CO) outgassing is a common phenomenon in lithium-ion batteries (LiBs), primarily due to parasitic side reactions at the cathode-electrolyte interface. However, little is known about the chemical origins of the in situ CO released from emerging Li-excess cation-disordered rock salt (DRX) cathodes. In this study, we selectively labeled various carbon sources with C in cathodes containing a representative DRX material, LiMnTiO (LMTO), and performed differential electrochemical mass spectrometry (DEMS) during galvanostatic cycling in a carbonate-based electrolyte. When charging LMTO cathodes, electrolyte solvent (EC) decomposition is the dominant source of the CO outgassing. The amount of EC-originated CO is strongly correlated with the total surface area of carbon black in the electrode, revealing the critical role of electron-conducting carbon additives in the electrolyte degradation mechanisms. In addition, unusual bimodal CO evolution during the first cycle is found to originate from carbon black oxidation. Overall, the underlying chemical origin of in situ CO release during battery cycling is highly voltage- and cycle-dependent. This work further provides insights into improving the stability of DRX cathodes in LiBs and is envisioned to help guide future relevant material design to mitigate parasitic reactions in DRX-based batteries.