(A) study on the electrochemical properties of sn-based anodes fabricated by electrodeposition for li-ion batteries

Abstract

The preparation of Sn-based anodes for Li-ion batteries is a viable, advantageous process, for the following reasons; First, the electroplating process is simpler than currently-used powder process because there is no need for any binder or conductive agents. Second, owing to their low impurity, a comparatively high initial coulombic efficiency can be obtained. However, a Sn anode has the intrinsic problem of crumbling due to the large amount of volume expansion (up to 300 %) during Li insertion, resulting in the electrical isolation of the Sn anode from the Cu substrate with a significant decrease in the charge/discharge capacity of cell. In order to overcome the problem, the possibility of using a nodule-type Cu substrate was explored by comparison with a smooth and a pyramid-type Cu substrate, and its proper aging condition was proposed. Comparing the cycle performance of the Sn electrodes electro-plated on the three different Cu substrates, the Sn electrode electroplated on the nodule-type showed the highest reversible capacity $(700 mAh/g (1^{st} cycle)$, $450 mAh/g (2^{nd} cycle)$, and $377 mAh/g (20^{th} cycle)$, which demonstrates that the nodule-type Cu substrate enhanced the adhesion and electrical contact properties between the Sn and the Cu substrate. In addition, Sn an-ode electroplated and aged for 1 h at 200℃ exhibited a high reversible capacity and cycle performance, which is due to the enhanced adhesion strength by formation of the thin $Cu_3$ Sn phase. However, when aged for longer than 1 h at 200 ℃, the reversible capacity decreased due to the thickening of the inactive $Cu_3$ Sn phase. The best performance of the Sn anode was obtained when the Sn anode was electroplated on the nodule-type Cu substrate and aged for 1 h at 200 ℃, which exhibited high reversible capacity (~600 mAh/g) and good cycleability. Recently, a strange phenomenon named as ‘high-voltage irreversible capacity’ was reported. This occurs during lithiation process of a Sn...