Anode behavior of electroplated rough surface Sn thin films for lithium-ion batteries

Electroplated Sn thin films with a rough surface were prepared on a Cu foil by using an electroplating bath consisting of SnSO4, sulfuric acid, thiourea, and non-ionic surface-active agent (polyoxyethelen(8)octylphenylether) at room temperature. The apparent density of the thin film increased as increasing amounts of the non-ionic surface-active agent were added and it exhibited its maximum value at about 1 mM. This suggests that the apparent density of the thin film was controlled by the amount of added non-ionic surface-active agent. In addition, the rough surface Sn thin films worked as negative electrode materials for lithium-ion batteries. The discharge capacities of the thin film electrodes exhibited high values of over 700 mAh g−1 but their cycle performance was poor. In contrast, Sn-based alloy thin film electrodes, containing intermetallic compounds of Cu6Sn5 and Cu3Sn, obtained by the heat treatment of the electroplated rough surface Sn thin films on the Cu foil, improved the cycle life of the Sn thin film electrodes compared with that prior to heat treatment. Intermetallic compounds of Cu6Sn5 and/or Cu3Sn formed into thin films should limit any great volume change caused by lithium insertion and extraction.