Carbon-Encapsulated Copper Sulfide Leading to Enhanced Thermoelectric Properties

Copper sulfide has been regarded as a promising thermoelectric material with relatively high thermoelectric performance and abundant resource. Large-scale synthesis and low-cost production of high-performance thermoelectric materials are keys to widespread application of thermoelectric technology. Here, Cu_{2- x}S particles encapsulated in a thin carbon shell are fabricated by a scalable wet chemical method (19.7 g/batch). The synthesized particles go through the crystal-phase transition from orthorhombic to tetragonal during high-temperature annealing and sintering. After the phase transition, electrical conductivity of this composite (Cu_{2- x}S@C) increases by approximately 50% compared to that of the pure Cu_{2- x}S sample, and can be attibuted to an increase in carrier concentration. Phonon scattering interface formation and superionic phase of Cu_{2- x}S@C results in very low lattice thermal conductivity of 0.22 W m^-1 K^-1, and maximum thermoelectric figure of merit ( ZT) of 1.04 at 773 K, which is excellent for thermoelectric performance in pure-phase copper sulfide produced via chemical synthesis. This discovery sets the stage for the use of facile wet chemical synthesis methods for large-scale transition-metal chalcogenide thermoelectric material production.