Electrochemical Properties of Electrodeposited Sn Anodes for Na-Ion Batteries

The electrochemical properties and sodiation/desodiation mechanism of Sn electrodes prepared by electrodeposition were investigated for Na-ion batteries. The sodiation of the electrodeposited Sn electrodes proceeded via three conjugated reactions in the cutoff voltage range of 0.001–0.65 V, as follows: the β-Sn phase, which contains a small amount of Na, was sodiated into amorphous NaSn, and crystalline Na9Sn4 and Na15Sn4 were then formed sequentially. However, the cycle performance of the electrode was highly dependent on the morphologies and the crystallographic orientations of the electrodeposits. The Sn electrode composed of coarse particles had the poor cycle performance due to the electrical isolation of Sn caused by the large volume changes during cycling. In contrast, the thin-layered Sn electrode exhibited a stable cycle performance in which the charge capacity was maintained at 607.51 mAh g–1 after 40 cycles, which corresponds to 98.21% of its initial charge capacity. The improvement in the cyclability of the layered Sn electrode was attributed not only to reduced structural degradations by restricting the cutoff voltage but also to an improved bond between the Sn electrodeposit and the Cu substrate.