Ionic Liquid-Based Membranes as Electrolytes for Advanced Lithium Polymer Batteries

Gel‐type polymer electrolytes are formed by immobilizing a solution of lithium N,N‐bis(trifluoromethanesulfonyl)imide (LiTFSI) in N‐n‐butyl‐N‐ethylpyrrolidinium N,N‐bis(trifluoromethanesulfonyl)imide (Py24TFSI) ionic liquid (IL) with added mixtures of organic solvents, such as ethylene, propylene and dimethyl carbonates (EC, PC, and DMC, respectively), into a poly(vinylidenefluoride‐co‐hexafluoropropylene) (PVdF‐HFP) matrix, and their properties investigated. The addition of the organic solvent mixtures results in an improvement of the ionic conductivity and in the stabilization of the interface with the lithium electrode. Conductivity values in the range of 10−3–10−2 S cm−1 are obtained in a wide temperature range. These unique properties allow the effective use of these membranes as electrolytes for the development of advanced polymer batteries based on a lithium metal anode and an olivine‐type lithium iron phosphate cathode. Electrolyte orchestration: Polymer membranes based on a unique ionic liquid have been prepared and characterized as electrolytes for lithium batteries. The addition of a discrete amount of a selected organic solvent mixture was found to greatly improve the ionic conductivity and the interface properties of the composite membrane in contact with lithium electrodes, thus allowing the formation of a high‐performance Li‐metal–polymer battery.