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Copper sulfide Cu2S is a p-type semiconducting compound that has attracted great attentions in the thermoelectric (TE) community most recently.Considering the intrinsic ultralow lattice thermal conductivity,the enhancement of TE performance in Cu2S should be achieved through improving its electrical transport properties.To achieve this goal,lithium element was doped into Cu2S in this study.A series of Cu2-xLixS samples with different Li contents (x =0,0.005,0.010,0.050,and 0.100) was synthesized by the melting-annealing method.When x ≤ 0.05,the Cu2-xLixS samples are stable and pure phases,having the same monoclinic structure with the pristine Cu2S at room temperature.The electrical conductivities in the Cu2-xLixS samples are greatly improved with the Li-doping content increasing due to the enhanced carrier concentrations.Meanwhile,doping Li into Cu2S increases the ionic activation energy and lessens the influence of mobile Cu ions on the heat-carrying phonons.Thus,the thermal conductivities of the Li-doped Cu2S samples increase.A maximal figure of merit (zT) of 0.84 at 900 K is obtained in Cu1.99Li0.01S,about 133％ improvement as compared with that in Cu2S matrix.