Effects of solvent-salt charge-transfer complexes on oxidative stability of Li-ion battery electrolytes*

Electrochemical stability windows of multi-component electrolytes, both solid polymer and organic liquid, largely determine the operating regime limits of Li-ion batteries. In order to increase energy densities and lifetimes of batteries, new electrolyte materials need to be discovered and optimized which requires better understanding of their degradation and oxidation.
Using computational tools, we present new insights into the oxidation mechanism that governs stability of multi-component polymer and liquid electrolytes. We find that explicitly including solvent molecules in the computation of the anion stability has a strong impact, and we show that this effect stems from electrostatic interactions between the molecules. Particularly, we find that across all chemistries studied, only one molecule in the system is oxidized. Building on this, we construct a model where two oxidation scenarios lead to different stability behaviors for the anion-solvent pairs, depending on their relative strength and geometry. This understanding of the microscopic details of oxidation allows one to formulate design rules and provides a good framework for screening electrolyte materials.