context: After structural comparison, the activity of oxygen and manganese was further probed to reveal the charge compensation in electrochemistry. Operando DEMS was performed to monitor the released anionic species during the charging process. The operando DEMS data was collected with active material loading of around 8 mg (Fig. 3). In the initial charge process for typical LMO, carbon dioxide gas was evolved at the beginning, accompanied by a large amount of oxygen gas release with maximum carbon dioxide evolution. The total gas evolution was summed to be 59.3 mmol CO2 per mol of active material and 70.2 mmol O2 per mol of active material. The CO2 gas may result from the electrolyte decomposition, the reaction between the electrolyte and O2, and impurity Li2CO3 decomposition. In contrast, the T-LMO electrode delivered a minimal amount of carbon dioxide and oxygen gas release. The cumulative CO2 and O2 detected from T-LMO during the initial charge process was 10.5 mmol and 9.1 mmol per mol of active material, respectively. The reduced gas release in the treated sample indicates the improved electrochemical stability of the T-LMO material when operating at high voltage in the battery. The different outgassing behaviors of LMO and T-LMO under identical cycling conditions imply that the two materials have different oxygen activities.