Diglyme-Based Thermoelectrochemical Cells Operable at Both Subzero and Elevated Temperatures

Thermoelectrochemical cells (TECs) are promising devices for harvesting low-grade waste heat (<200 °C). Most TEC researches have thus far focused on aqueous redox couples, but aqueous solutions suffer from a limited operating temperature range (0–100 °C). Herein, TECs based on nonaqueous Li⁺/Li redox couples (Li-TECs) using diglyme (2G) electrolytes featuring a wide liquidus range (from −64 to 162 °C) are introduced. Notably, a Li-TEC with 1.8 m lithium bis(fluorosulfonyl)imide (LiFSI) 2G surpasses the current best nonaqueous TECs based on ionic liquid (IL) electrolytes at elevated temperatures: 30% higher output power for cold side temperature (T_cold) and hot side temperature (T_hot) of 60 and 130 °C, respectively. In addition, unlike the TECs using ILs, the Li-TEC displays stable operation even at T_cold of −25 °C, which, for T_hot of 150 °C, yields an unprecedented high output voltage of 270 mV from a single Li-TEC. Herein, the wide-temperature-range operation demonstrated takes the TECs one step closer to practical applications.