Single-phase Cu–Sn intermetallics were used to investigate their phase transformations during lithiation/delithiation, together with their negative-electrode properties. The stoichiometric Cu–Sn samples were prepared as thermodynamically warranted phases using a reduction-diffusion method with controlled potentials. Potentiostatic lithiation tests suggested that Cu3Sn directly changes into Li x Sn, while Cu6Sn5 becomes Li2CuSn before Li x Sn forms. We also revealed that separation from Li2CuSn into Cu and Li x Sn occurs at +0.11 to +0.10V vs. Li. Additionally, charging/discharging tests with cutoff potentials of +1.5V to +0.11V showed better cycling performance than that with +1.5V to +0.00V, probably due to the suppression of Li x Sn formation. Such a tendency can be expected in other Cu6Sn5 electrode materials.