Structural and electrochemical properties of (SnxCo100-x)50C50 anodes for Li-ion batteries

Abstract Phase formation and electrochemical characteristics of (Sn x Co 100-x ) 50 C 50 (x = 34, 71, 85 wt %) composite anodes prepared by ball milling of melt spun alloys and graphite powder is studied for Li-ion battery applications. The maximum specific capacity of these anodes is 260 mAh g −1 for the Co rich alloy, 400 mAh g −1 for the equi-atomic alloy and a fading capacity of 335 mAh g −1 to 205 mAh g −1 in Sn rich alloy. Anodes made of Co rich and equi-atomic composition deliver stable capacity of 74% of the theoretical value due to the presence of nanocrystalline Sn–Co compounds. Sn rich composition exhibits a large fading in capacity below 55% of the theoretical value, due to the presence of soft Sn phase. The formation of nanocrystalline structure by ball milling is prevented in the Sn rich alloy due to the presence of this soft phase. A highly non uniform porous structure is formed during cycling of the Sn rich anodes, causing poor reversibility. Ball milling leads to the dissolution of Sn–Co compounds in the matrix phase, whereas the softer Sn and C elements do not dissolve. The structure of Sn–Co phase is further completely lost by charge-discharge cycling, forming non-crystalline Li–Sn phase in all the alloys. The equi-atomic Sn–Co composition is shown to be most suitable for making SnCoC anode compared to the Sn rich or Co rich compositions.