Cu 2 Sb 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 Cu 2 Sb by the following three-step reaction: (1) Li incorporation into Cu 2 Sb formed LiCuSb accompanying extrusion of Cu metals, (2) the solid solution process of Li 1+x CuSb (0 e x < ∼0.5) with a Heusler-type structure was followed, and then (3) by further lithiation Li 3 Sb was formed with Cu extrusion as a threephase coexistence reaction. The irreversible capacity at the first cycle was assigned to the structural phase transition from Cu 2 Sb 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.
This paper deals with the reaction dynamics of phase transition for the electrochemical lithium insertion into Cu 2 Sb intermetallic compound. Electrochemical lithium insertion/removal, alternating current ͑ac͒ impedance technique, and electrochemical calorimetric measurement have been applied in this study. The electrochemical charge-discharge test indicated a large irreversible capacity at the onset of first charging ͑Li insertion͒, where a flat voltage plateau appeared around 0.7 V. In other instances, following cycles showed good reversibility. In addition, the voltage profiles of Ͼ0.7 V region after the second cycle showed higher than the one at the first cycle charging and clear solid solution manner. Thus, the difference of the electrochemical Li insertion mechanism between the first and following cycles caused irreversibility accompanying large electrochemical polarization. To explain the above phenomena, we assumed that the nucleation was rate determined at the onset of phase transition from tetragonal Cu 2 Sb to cubic Li 1+x CuSb. After the phase transition was completed, following cycles did not need to expend the formation of different phase nuclear, showing a good reversibility reaction. The reaction mechanism suggested above was supported by ac impedance and electrochemical calorimetric measurements.
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