Effects of Structural Phase Transition on Thermoelectric Performance in Lithium-Intercalated Molybdenum Disulfide (Li _x MoS ₂ )

Layered transition metal dichalcogenides (TMDCs) intercalated with alkali metals exhibit mixed metallic and semiconducting phases with variable fractions. Thermoelectric properties of such mixed-phase structure are of great interest because of the potential energy filtering effect, wherein interfacial energy barriers strongly scatter cold carriers rather than hot carriers, leading to enhanced Seebeck coefficient (S). Here, we study the thermoelectric properties of mixed-phase Li _x MoS ₂ as a function of its phase composition tuned by in situ thermally driven deintercalation. We find that the sign of Seebeck coefficient changes from positive to negative during initial reduction of the 1T/1T′ phase fraction, indicating crossover from p- to n-type carrier conduction. These anomalous changes in Seebeck coefficient, which cannot be simply explained by the effect of deintercalation-induced reduction in carrier density, can be attributed to the hybrid electronic property of the mixed-phase Li _x MoS ₂ . Our work shows that careful phase engineering is a promising route toward achieving thermoelectric performance in TMDCs.