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

A Cu3Sn film electrode (thickness = ca. 3 mu m) is prepared by DC magnetron sputtering deposition of Sn on Cu substrate and subsequent annealing at 300 degrees C for 30 h. At 25 degrees 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 degrees 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 degrees C and Cu6Sn5 at 25 degrees 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 degrees C and subsequent de-lithiation at 25 degrees 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). (C) 2011 Elsevier B.V. All rights reserved.