Lithium Doping to Enhance Thermoelectric Performance of MgAgSb with Weak Electron-Phonon Coupling

Despite the unfavorable band structure with twofold degeneracy at the valence band maximum, MgAgSb is still an excellent p-type thermoelectric material for applications near room temperature. The intrinsically weak electron-phonon coupling, reflected by the low deformation potential E_def ≈ 6.3 eV, plays a crucial role in the relatively high power factor of MgAgSb. More importantly, Li is successfully doped into Mg site to tune the carrier concentration, leading to the resistivity reduction by a factor of 3 and a consequent increase in power factor by ≈30% at 300 K. Low lattice thermal conductivity can be simultaneously achieved by all-scale hierarchical phonon scattering architecture including high density of dislocations and nanoscale stacking faults, nanoinclusions, and multiscale grain boundaries. Collectively, much higher average power factor ≈25 μW cm^-1 K^-2 with a high average ZT ≈ 1.1 from 300 to 548 K is achieved for 0.01 Li doping, which would result in a high output power density ≈1.56 W cm^-2 and leg efficiency ≈9.2% by calculations assuming cold-side temperature T_c = 323 K, hot-side temperature T_h = 548 K, and leg length = 2 mm.