LiTDI and solvent mixture based electrolytes for lithium-ion cells

Abstract

Electrolyte optimization for both best performance and low use of materials is described in this paper. Electrochemical performance and material utility are reported to achieve the goal of optimal combinations of salt concentration and solvent ratios for several solvent mixtures. A lithium 4,5-dicyano-2-trifluoromethanoimidazolide (LiTDI) salt was used for its thermal stability, ease of handling (stable in the presence of air and moisture) and high ionic conductivity at low concentration in solvents. Solvent mixtures were chosen based on industrial practice and performance at low temperature. The conductivity dependence of salt concentration is reported. In all systems, low concentration onset and a broad range of high conductivity was observed. Lithium cation transference numbers were measured for highly conductive samples and used as the secondary parameter in the optimization procedure. Both high ionic conductivity and transference number values were recorded, even for samples with low salt content: 0.3molkg−1 LiTDI in 1EC:2EMC (σ=4.18mScm−1, TLi+=0.544) and 0.4molkg−1 LiTDI in EC:DMC:EMC (σ=4.69mScm−1, TLi+=0.455). Cycling with anodic material was also carried out, showing good capacity for retention of the mixtures chosen containing average salt concentrations. Hence, material savings in comparison to other commercially available lithium salts is possible.