Ionic Liquids and Electrolytes with Flexible Aromatic Anions

Abstract

Five new n‐tetrabutylphosphonium (P4444)+ cation‐based ionic liquids (ILs) with oligoether substituted aromatic carboxylate anions have been synthesized. The nature and position of the oligoether chain affect thermal stability (up to 330 °C), phase behaviour (Tg<−55 °C) and ion transport. Furthermore, with the aim of application in lithium batteries, electrolytes were created for two of the ILs by 10 mol% doping using the corresponding Li‐salts. This affects the ion diffusion negatively, from being higher and equal for cations and anions to lower for all ions and unequal. This is due to the stronger ionic interactions and formation of aggregates, primarily between the Li+ ions and the carboxylate group of the anions. Electrochemically, the electrolytes have electrochemical stability windows up to 3.5 V, giving some promise for battery application.

Pyrrolidium‐ and Imidazolium‐Based Ionic Liquids and Electrolytes with Flexible Oligoether Anions

“…In addition, we here exploit the characteristics of glyme solvents with those of ILs based on small organic cations such as pyrrolidinium and imidazolium. Undoubtedly, electrolytes based on ILs offer a range of suitable advantages including low volatility and high thermal and electrochemical stabilities and can additionally be made fluorine‐free and task‐specific with synthetic diversity [17–19] . In general, their physicochemical and transport properties are determined by the sizes of ions and the interactions between the cations and anions, which can be functionalized due to the vast freedom in structural design to reduce these interactions and enhance the ion mobilities [20–23] …”