Recent Advances in Liquid-Like Thermoelectric Materials

Thermoelectric technology has attracted great attention due to its ability to recover and convert waste heat into readily available electric energy. Among the various candidate materials, liquid-like compounds have received tremendous research interest on account of their intrinsically ultralow lattice thermal conductivity, tunable electrical properties, and high thermoelectric performance. Despite their complex phase transitions and diverse crystal structures, liquid-like materials have two independent sublattices in common: one rigid sublattice formed by immobile ions for the free transport of electrons and one liquid-like sublattice consisting of highly mobile ions to interrupt the thermal transports. This review first outlines the common structural features of liquid-like thermoelectrics, along with their unusual electron and phonon transport behaviors that well satisfy the concept of "phonon-liquid electron-crystal." Next, some commonly adopted strategies for further improving their thermoelectric performance are highlighted. The main progress achieved in the typical liquid-like TE materials is then summarized, with an emphasis on their diverse crystal structures, common characteristics, and unique transport properties. The recent understandings on the stability issue of liquid-like TE materials are also introduced. Finally, an outlook is given for the liquid-like materials with the aim to boost further development in this exciting scientific subfield.