Successes and failures predicting the solubility of solid electrolyte interphase (SEI) species

The stability of the solid electrolyte interphase (SEI) is crucial for the cycle-life and safety of modern rechargeable batteries. The SEI is most often addressed by electrochemical and advanced surface characterization methods. A less trodden path is the solubility of the very species making up the SEI-a fundamental property that can be addressed both experimentally and computationally. Herein promises and problems of solubility assessments are highlighted, including successes and failures and how to possibly overcome them. Specifically, we experimentally contrast literature data vs. inductively coupled plasma mass spectrometry, and computationally we use a combination of density functional theory and statistical mechanics. Proof-of-concept is made for a few alkali and alkali earth metal, i.e. Li/Na/Mg/Ca, inorganic salts, but it can easily be expanded to e.g. organic species. Overall, experimentally determined solubilities are laden with large uncertainties and correlate only fairly with calculated solubilities. Deviations are especially pronounced for Mg and Ca-salts. Pushing this route further to create a general tool to assist in the very design of more stable SEIs, by finding and predicting non-soluble species for current and next generation battery technologies, is most probably viable, but both the experimental and the computational approaches need to be refined.