Theoretical Studies on the Reductive Decompositions of Solvents and Additives for Lithium-Ion Batteries near Lithium Anodes

The reduction reactions of various solvents and additives for lithium-ion battery electrolytes have been investigated by ab initio calculations in the presence of the lithium anode at the Hartree-Fock level. The solvents and the additives studied included ethylene carbonate, propylene carbonate, vinylene carbonate, vinylethylene carbonate, ethylene sulfite, and tetrahydrofuran. Vinyl vinylene carbonate was also examined as a model compound. A cluster of 15 lithium atoms was used to model a lithium electrode to explicitly include the interactions of the solvent molecules with the lithium metal. The transition state in the reduction reaction was determined for each solvent or additive by searching for the saddle point of the potential energy surface. Internal reaction coordinate calculations were performed both to verify the transition state and also to locate the reactant and the product of the reduction reaction. From the calculations, the activation barrier and the reaction energy were determined. The reaction mechanism was also discussed in terms of the solid electrolyte interface film formation characteristics of each solvent and additive.