Enhancement of Electrical Stability and Mechanical Properties of Cu ₂ Se through CuCrSe ₂ as a Copper Ion Reservoir

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.