Lithiation behavior of single-phase Cu–Sn intermetallics and effects on their negative-electrode properties

•Thermodynamically warranted single-phase Cu–Sn intermetallics were lithiated/delithiated.•Potentiostatic lithiation of Cu3Sn directly gave LixSn and Cu.•Potentiostatic lithiation of Cu6Sn5 gave Li2CuSn before LixSn forms.•Separation from Li2CuSn into LixSn occurs at +0.11 to+0.10 V vs. Li.•By suppressing LixSn formation, cycling performance improved.

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 LixSn, while Cu6Sn5 becomes Li2CuSn before LixSn forms. We also revealed that separation from Li2CuSn into Cu and LixSn occurs at +0.11 to +0.10 V vs. Li. Additionally, charging/discharging tests with cutoff potentials of +1.5 V to +0.11 V showed better cycling performance than that with +1.5 V to +0.00 V, probably due to the suppression of LixSn formation. Such a tendency can be expected in other Cu6Sn5 electrode materials.

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