New Insight into Electrochemical Differences in Cycling Behaviors of a Lithium-ion Battery Cell Between the Ethylene Carbonate- and Propylene Carbonate-Based Electrolytes

Abstract

ABSTRACTDensity functional theory (DFT) calculations and classical molecular dynamics (MD) simulations have been performed to gain insight into the difference in cycling behaviors between the ethylene carbonate (EC)-based and the propylene carbonate (PC)-based electrolytes in lithium-ion battery cells. DFT calculations for the ternary graphite intercalation compounds (Li+(S)iCn: S=EC or PC), in which the solvated lithium ion Li+(S)i (i=1~3) was inserted into a graphite cell, suggested that Li+(EC)iCn was more stable than Li+(PC)iCn in general. Furthermore, Li+(PC)3Cn was found to be energetically unfavorable, while Li+(PC)2Cn was stable, relative to their corresponding Li+(PC)i in the bulk electrolyte. The calculations also revealed severe structural distortions of the PC molecule in Li+(PC)3Cn, suggesting a rapid kinetic effect on PC decomposition reactions, as compared to decompositions of EC. In addition, MD simulations were carried out to examine the solvation structures at a high salt concentration: 2.45 mo kg-1. The results showed that the solvation structure was significantly interrupted by the counter anions, having a smaller solvation number than that at a lower salt concentration (0.83 mol kg-1). We propose that at high salt concentrations, the lithium desolvation may be facilitated due to the increased contact ion pairs, so that a stable ternary GIC with less solvent molecules can be formed without the destruction of graphite particles, followed by solid-electrolyte-interface film formation reactions. The results from both DFT calculations and MD simulations are consistent with the recent experimental observations.