Intrinsic Chemical Reactivity of Silicon Electrode Materials: Gas Evolution

In this work, we explore how the chemical reactivity toward an aprotic battery electrolyte changes as a function of lithium salt and silicon surface termination chemistry. The reactions are highly correlated, where one decomposition reaction leads to a subsequent decomposition reaction. The data show that the presence of silicon hydrides (SiHx) promotes the formation of CO gas, while surface oxides SiOx drive the formation of CO2. The extent and rate of oxidation depend on the surface basicity of the SiO2 surface species. The most acidic surfaces seem to hinder CO2 generation but not the decomposition of the salt. Indeed, the presence of F-containing salts (LiPF6 and LiTFSI) promotes the reactions between carbonate electrolyte and silicon surfaces. Surfaces with high Li content seem to be the most passivating to gassing reactions, pointing to a pathway to stabilize the interfaces during cell formation and assembly.