Comparative calculation on Li^+ solvation in common organic electrolyte solvents for lithium ion batteries

It is important for the electrolytes to maintain and enhance the lithium ion battery electrochemical performance,and solvation of Li^+is a key parameter for the property of the electrolytes.The comparative study on Li^+ solvation structures,energy,enthalpy,Gibbs free energy,infrared and Raman spectra in common organic electrolyte solvents is completed by density functional theory(DFT)method.The solvation reaction energy results suggest that the Li^+solvation priority order is propylene carbonate(PC)>ethylene carbonate(EC)>ethyl methyl carbonate(EMC)>diethyl carbonate(DEC)>tetrahydrofuran(THF)>dimethyl carbonate(DMC)>1,3-dioxolane(DOL)>dimethoxyethane(DME)to form 5sol Li^+.It is also indicated that the most innermost solvation shell compounds formations by stepwise spontaneous solvation reaction are four cyclic solvent molecules and three linear solvent molecules combining one Li^+ forming 4sol-Li^+ and 3sol-Li^+,respectively,at room temperature.Besides,the vibration peaks for C=O and C-O bonds in carbonate ester solvents-Li^+ compounds shift to lower frequency and higher frequency,respectively,when the Li^+ concentration increases in the solvation compounds.All Li-O stretching vibration peaks shift to higher frequency until forming 2solvent-Li^+ complexes,and C-H stretching also shifts to higher frequency except for nDME-Li^+ solvation compounds.The Raman spectrum is more agile to characterize C-H vibrations and IR is agile to C=O,C-O,and Li-O vibrations for Li^+solvation compounds.