Cu2Se exhibits an ultralow lattice thermal conductivity owing to its high mobility of Cu+ ions. However, irreversible Cu precipitation at high current densities undermines its electrical stability. In this work, by incorporating the superionic conductor CuCrSe2 into the Cu2Se matrix, both the electrical stability and the mechanical properties are significantly enhanced. Variable-temperature X-ray diffraction (XRD) and first-principles calculations reveal that the solubility of Cu+ ions in CuCrSe2 varies with the temperature, enabling this composite phase to function as a dynamic Cu+ ion reservoir. The Cu+ ion concentration gradient and the built-in electric field at the Cu2Se/CuCrSe2 interface drive the reversible intercalation of Cu+ ions into CuCrSe2, increasing Cu vacancies in Cu2Se and lowering the Cu+ ion chemical potential, thus significantly improving the electrical stability. The resultant composite maintains a ZT value of 1.5 over multiple test cycles. Furthermore, the increased grain boundaries and composite interfaces inhibit dislocation movement, increasing the compressive strength to 312 MPa for the composite (a 142% improvement relative to Cu2Se). Our findings provide a strategy for the development of electrically stable superionic thermoelectric devices.
Xiao et al. (Thu,) studied this question.