Tuning aprotic solvent properties with long alkyl chain ionic liquid for lithium-based electrolytes

Abstract

Lithium–metal batteries, such as Li–O₂, are some of the most promising candidates for high-performance energy storage applications, however, their performance is still limited by the electrolyte instability. To overcome this limitation it is necessary to develop improved electrolytes with good electrochemical stability and decent ionic transport. Here, we are the pioneers to investigate the influence of the imidazolium-based ionic liquid crystal (ILC) 1-hexadecyl-3-methylimidazole bromide [C₁₆mim][Br] as an additive for an aprotic electrolyte, dimethyl sulfoxide (DMSO) 0.100 M LiClO₄. Combining experimental and theoretical methods, we studied the influence of the [C₁₆mim][Br] addition on the electrolyte properties from a macroscopic up to an atomistic level. The unique structural features of the ILC were investigated and an enhancement in the electrolyte stability was shown due to its self-aggregation ability, which suggests fewer DMSO molecules available to react during the battery operation and consequent less electrolyte degradability. For the ionic transport perspective, the ILC addition leads to an ionic conductivity increase until 1.456 M concentration, after this point, a further ILC addition causes a small decrease in the conductivity due to the high viscosity and the decay in the ions self-diffusion coefficient. By combining Raman spectroscopy and molecular dynamics simulations, we confirmed that the [C₁₆mim][Br] interactions within the ions and molecules of this ternary system enabled the ILC to organize itself into large aggregates at high ILC concentrations. Besides DMSO, these ILC features can be reached in other aprotic and also aqueous electrolytes.