Thermo-electrochemical activation of Cu3Sn negative electrode for lithium-ion batteries

A Cu3Sn film electrode (thickness = ca. 3 μm) is prepared by DC magnetron sputtering deposition of Sn on Cu substrate and subsequent annealing at 300 °C for 30 h. At 25 °C, this Cu–Sn binary intermetallic compound is inactive for lithiation, but becomes active at elevated temperatures due to facilitation of Cu–Sn bond cleavage for the conversion-type lithiation. The lithiated product at 120 °C is the most Li-rich Li–Sn alloy (Li17Sn4). Upon de-lithiation, the Cu–Sn intermetallics of different compositions are generated by the reaction between the metallic Sn that is restored from Li17Sn4 and the idling metallic Cu. The nature of the resulting intermetallics is dependent on the de-lithiation temperature: Cu10Sn3 at 120 °C and Cu6Sn5 at 25 °C. Only the latter is active for lithiation in the subsequent room-temperature cycling. That is, Cu3Sn is thermo-electrochemically activated to be Cu6Sn5 by lithiation at 120 °C and subsequent de-lithiation at 25 °C. The higher lithiation activity observed with the more Sn-rich phase (Cu6Sn5) compared to the initial one (Cu3Sn) has been accounted for by the higher equilibrium lithiation potential (thermodynamic consideration) and smaller number of Cu–Sn bonds to be broken (kinetic consideration).

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The Cu3Sn phase is inactive for lithiation at room temperature. ► The Cu3Sn phase is lithiated to Li17Sn4 phase at 120 °C. ► The more Sn-rich Cu6Sn5 phase is generated after de-lithiation at 25 °C. ► The thermo-electrochemically activated Cu6Sn5 phase is now active for lithiation at 25 °C. ► A higher lithiation activity is observed with the more Sn-rich phase.