Low ion concentration ionic liquid enable drastically improvement in liquid thermoelectric performance

Ionic liquids (ILs) are considered as the next generation of compact thermoelectric materials, but their thermoelectric performance still requires enhancement. To overcome the thermoelectric performance bottlenecks caused by the strong Coulombic interactions and high viscosity of ILs, based on the selective solvation effect by solvents, this study proposes the idea of low-concentration IL with highly polar organic solvent as diluent to enhance both the ion mobility and the mobility difference between cations and anions. The measured Seebeck coefficient, conductivity, and thermal conductivity, the figure of merit ZT and power factor PF of the thermoelectric materials of 13 ILs + solvent binary mixtures obtained verified that our idea is feasible. The optimal combination was determined to be 0.5M 1-ethyl-3-methylimidazolium dicyanamide + dimethyl sulfoxide (0.5M [EMIM][DCA]+DMSO), with ZT of 0.039 which is 6.7 times as [EMIM][DCA]. This performance is comparable to that of thermoelectric gels. The capacitor used the designed thermoelectric materials shows an energy density of 0.45μJ/(m 2 ·K) with 5kΩ load, which is 71.5% larger than [EMIM][DCA]. This work proposes a new strategy based on binary mixtures of low-concentration IL + dipolar aprotic solvent to significantly improve IL thermoelectric performance and make liquid thermoelectric materials reach a new milestone.