Theoretical Screening for Electronic and Solvation Characteristics of Common Molecules as Electrolyte Additives and Co‐Solvents for Alkali Metal Batteries

Abstract This study employs semiempirical molecular orbital methods to evaluate the electronic and solvation characteristics of five common molecules as electrolyte additives and co‐solvents for alkali metal batteries. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) suggest that 1,2‐dimethoxyethane (DME), 1,2‐diethoxyethanes (DEE) and 1,3‐dioxolane (DOL) exhibit suitable redox activity for electrochemical process. However, after binding with one Li ion, DME distinguishes itself as a more promising solvent for alkali metal batteries. The solvation structure of DME with alkali metal ions is investigated. The geometric relaxation and electronic transfer imply that partial crystallization happens as the number of DME reaches the saturation point (maximum three DMEs). This crystallization improves the electrochemical stability and mediates the redox activity. In addition, fluorination of DME enhance DME's oxidation resistance and chemical stability, and partial fluorination with 4 F atoms (F4DME) displays the optimum properties. On the other hand, fluorination destabilizes the solvation structures with alkali metal ions, and reduces the saturated DMEs from three to two. The desolvation tendency and enhanced binding energy provide a viable way to tune the electrochemical performance of solvent, and thus enable a balance between chemical stability and electrochemical kinetics.