Construction of the Ternary Phase Diagram for the Li−Cu−Sb System as the Anode Material for a Lithium Ion Battery

Cu2Sb is known as a promising anode material for a lithium ion battery due to its good cycle performance and large volumetric capacity. In the present study we aimed to construct the ternary phase diagram for the Li−Cu−Sb system to elucidate the reaction mechanism upon charge−discharge reaction. In this procedure, a new intermediate phase of LiCuSb with a half-Heusler-type structure was found by combining experimental results with theoretical study. The obtained ternary phase diagram accounted for the electrochemical lithiation of Cu2Sb by the following three-step reaction: (1) Li incorporation into Cu2Sb formed LiCuSb accompanying extrusion of Cu metals, (2) the solid solution process of Li1+xCuSb (0 ≤ x < ∼0.5) with a Heusler-type structure was followed, and then (3) by further lithiation Li3Sb was formed with Cu extrusion as a three-phase coexistence reaction. The irreversible capacity at the first cycle was assigned to the structural phase transition from Cu2Sb to LiCuSb and Cu. Thus, the present study suggested that the intermetallic compounds with a Heusler-type structure have a promising potential as the anode material for a lithium ion battery with a long life and a large capacity.