Selective tuning cation coordination variations for developing high- performance N-type solid-state ionic thermoelectric materials

L Chen and ZJ Xu and K Meng and MS Du and XY Wu and C Chi, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 245, 127042 (2025).

DOI: 10.1016/j.ijheatmasstransfer.2025.127042

With rising global energy consumption and heightened environmental awareness, ionic thermoelectric (i-TE) materials, offering millivolt- level thermopower at low cost, hold significant promise for harnessing low-grade thermal energy to boost energy efficiency. However, i-TE materials await significant enhancements in performance and stability, especially the scarcity of n-type variants and the unclear thermopower control mechanism limiting their practical application. This study introduces a novel strategy for manipulating ionic thermoelectric properties by selectively incorporating cations (X = Li+, Na+, Mg2+, Zn2+) and harnessing their distinct coordination abilities with the ether oxygen atoms in polyethylene oxide (PEO). Through precise control of cationanion diffusion coefficients and Eastman entropy changes, the high-performance n-type solid-state i-TE materials are obtained. The MD simulations reveal that divalent cations (Mg2+ and Zn2+) outperform monovalent cations (Li+ and Na+) in enhancing thermopower, exhibiting larger entropy changes and diffusivity differences at an X/EO ratio of 0.15. Furthermore, experimental results show that the thermopower of divalent composite of PEO/MgTFSI2 (-6.18 mV K- 1) is significantly higher than that of monovalent PEO/LiTFSI (-1.6 mV K- 1). These findings align well with the simulation results, validating the effectiveness of cation coordination tuning in modulating thermoelectric properties, offering a promising route for designing PEO-based n-type solid-state i-TE materials.

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