Electrical conductivity of solutions of lithium bis(fluorosulfonyl)imide in mixed organic solvents and multi-objective solvent optimization for lithium-ion batteries

Abstract

Lithium bis(fluorosulfonyl)imide (LiFSI) is an interesting novel electrolyte for lithium-ion batteries. In the present work, the electrical conductivity of solutions of LiFSI in binary and ternary mixtures of the solvents dimethyl carbonate (DMC), ethylene carbonate (EC) and propylene carbonate (PC) was studied experimentally for concentrations of LiFSI up to 0.2 mol mol−1 at ambient pressure and temperatures between 293 and 333 K. Information on the electrical conductivity of LiFSI in the pure solvents DMC, EC, and PC is available from previous work. An empirical correlation of the electrical conductivity σ of the studied solutions of LiFSI is presented that describes the dependence of σ on the LiFSI concentration, the solvent composition, and the temperature. Based on this correlation, a multi-objective optimization of the LiFSI concentration and the solvent composition was carried out with two conflicting objectives relevant to the performance and costs of batteries: maximizing electrical conductivity and minimizing the amount of the expensive electrolyte LiFSI. The solubility limits of the ternary solvent system DMC-EC-PC were included in the optimization as constraints. The multi-objective optimization applied here, is shown to be useful for obtaining a rational basis for decision-making in the design of electrolyte solutions for batteries.