Thermoelectrochemical cells based on Li/Li redox couples in LiFSI glyme electrolytes

Thermoelectrochemical cells (TECs) provide conspicuous advantages, including a high Seebeck coefficient ( S e ), design flexibility, and low cost compared with conventional thermoelectric devices. Here, we investigated TECs employing Li metal electrodes (Li-TECs) and a series of glyme (CH 3 O[CH 2 CH 2 O] n CH 3 , n = 1-4, n G) solvents with 0.5-3.0 M lithium-imide salts (lithium bis [fluorosulfonyl]imide, LiFSI, and lithium bis[trifluoromethane sulfonyl]imide, LiTFSI). The S e value and power performance of Li-TECs markedly depend on the nature of glyme solvents and Li salt concentration. The dependency of S e on the solvation structure of the Li-ions is examined via Raman measurements, and the internal resistance of Li-TECs is analyzed using electrochemical impedance spectroscopy. Notably, a Li-TEC with 1.0 M LiFSI 1G displays about two times higher power density and about eight times higher conversion efficiency than a conventional Cu-TEC utilizing aqueous electrolytes, which is ascribed to the high S e value and low thermal conductivity of the former. In addition, for a Li-TEC with 1.0 M LiFSI 1G, the low-temperature performance is examined to assess its practical feasibility. The interplay between the solvation structure of the electrolytes and the thermoelectrochemical performance was elucidated.