Elucidating the Reactivity of TMSPi and TMSPa Additives in Carbonate Electrolytes - A Comparative OEMS Study

The electrolyte additives tris(trimethylsilyl)phosphite (TMPSi) and tris(trimethylsilyl)phosphate (TMSPa) have shown their potential to improve lifetime and decrease impedance build-up in lithium ion batteries (LIBs) in several studies. Online electrochemical mass spectrometry (OEMS) was applied to study the effect of TMSPi and TMSPa on gas releasing parasitic reaction during cycling of HE-NCM/graphite cells in different electrolytes to elucidate their working mechanisms, for which so far contradictive claims can be found in literature. The results underline the chemical instability of the two additives in solution and show that they have, amongst for one exception, little or no effect on the release of O2 and CO2 which would be expected in case of a passivating surface layer suppressing electrolyte decomposition. The decreased POF3 evolution and the formation of Me3SiF indicates that the main role of both additives is that of a chemical scavenger, e.g. for HF, which lead to decreased acidification of the...