Lithium-ion batteries (LIBs) are widely popular due to their excellent electrochemical performance and availability in different sizes and shapes. The electrolyte used in LIBs makes an essential component of these batteries, providing a medium for transporting lithium ions between electrodes. Conventional electrolytes often used in LIBs show good electrochemical properties but suffer from high flammability, increasing the risk of fire or explosion. Ionic liquids (ILs) have been proposed as alternative electrolytes to remedy the current safety issues of LIBs due to their promising characteristics, such as negligible vapor pressure. Most recently protic ionic liquids (PILs) have been the subject of experiments for LIBs applications, showing promising properties, and in some cases better performance over aprotic ionic liquids (AILs). Motivated by recent experimental findings, and with the aim of a direct comparison between the performance of PIL and AIL electrolytes in LIBs, we conducted molecular dynamics simulations of lithium-doped electrolytes of PILs and AILs. Our PIL and AIL electrolytes consisted of triethylammonium bis(trifluoromethanesulfonyl)imide and triethylmethylammonium bis(trifluoromethanesulfonyl)imide, respectively, each doped with lithium bis(trifluoromethanesulfonyl)imide. We observed that the density and viscosity of these electrolytes increase with increasing lithium salt concentration, while self-diffusivity of ions and ionic conductivity decrease. The lithium ionic conductivity showed nonmonotonous profile, reaching a maximum at the intermediate salt concentration range. This anomalous behavior implies a balance between the competing effects of the number of charge carriers and viscosity. The dynamics of these electrolytes were rationalized based on the structure of underlying electrolytes.

Structure and transport properties of lithium-doped aprotic and protic ionic liquid electrolytes

2019 Fall National Meeting

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