Study on the anode behavior of Sn and Sn–Cu alloy thin-film electrodes

Anodes based on tin metal powder offer large specific capacity, but also exhibit large irreversible capacity and poor cycle performance. In order to use them as a negative electrode for lithium secondary batteries, we focused on the electrodepositing process and investigated an electrodeposited tin layer on copper foil. In the full charge–discharge condition, charging and discharging between 0 and 2.0 V versus Li/Li+, the first discharge capacity was 940 mAh g−1, which was 2.5 times as large as that of graphite, and the coulomb efficiency in the first cycle was 93%, but its cycle performance was not improved. In order to enhance the interface strength between the active material and the copper foil, we investigated an anode which was fabricated by annealing an as-deposited anode. In the full charge–discharge condition, the first charge–discharge characteristics were almost equivalent to the as-deposited anode, and the retention capacity ratio after 10 cycles was improved from 20 to 94%. It is considered that this improvement resulted from the formation of two different tin–copper intermetallic compound layers between the tin layer and the copper current collector due to the heat treatment. A small cell using this annealed anode as a negative electrode was also investigated. This cell offered good cycle performance for the first 20 cycles.