The bulk crystal ingot of n-type In4Se2.85 was synthesized by conventional melting and annealing process with high purity In (>99.999%, CERAC) and Se granules (>99.999%, 5N Plus Materials Inc., USA). The raw materials in an evacuated quartz tube (under 10−4 Torr) were congruently melted by torch. Then, two-step annealing of the ingot was performed at 773 K for 48 h, and then at 733 K for 24 h in order to produce ha tag homogenous In4Se2.85 phase. The anion deficiency in the In4Se3 phase was introduced to enhance its electrical conductivity by n-type self-doping effect. Graphene nanopowder (AO-1, THK∼3 nm) was purchased from graphene supermarket inc. (USA). The In4Se2.85@carbon-black and In4Se2.85@graphene nanocomposites were prepared by HEMM (Spex-8000) for the mixture of In4Se2.85 and carbon-black/graphene; The pristine In4Se2.85 and carbon-black/graphene were put into a hardened steel vial having a capacity of 80 cm3 with stainless steel balls (diameter: 3/8′′ and 3/16′′, a ball-to-powder ratio of 20:1). The HEMM process was conducted under an Ar atmosphere for 6 h. The mass ratio of In4Se2.85 (ingot):C (graphene or Super P) was adjusted to an optimal value of 7:3. As a reference, the carbon-free ball-milled In4Se2.85 material was prepared by applying the same HEMM process for the pristine In4Se2.85 ingot without carbon species.