Electrochemical Properties of Si-Alloy/Graphite/Carbon Nanotubes Blending Electrode for Li-Ion Batteries

Si-based alloy[1] is one of the most promising anode materials for substituting graphite due to its excellent characteristics such as high gravimetric capacity exceeding 1000mAh/g, high safety, good electrochemical stability and low production cost, etc. Currently, graphite anode material is widely used with water-based SBR binder in commercial Li-Ion Batteries and its electrode capacity is about 350mAh/g. In order to increase the energy density of anode electrode there have been many attempts of blending small (less than 10%) quantity of Si-based anode materials with graphite without changing water-based SBR binder system.

In this study, we made Si-alloy/Graphite/Single-walled Carbon nanotubes(SWCNTs) blending electrode and evaluate the electrochemical properties. In case of 8% of Si-alloy / 89% of Graphite / 0% SWCNT / 2% of SBR /1% of CMC electrode, the initial discharge capacity is 387mAh/g, initial the coulombic efficiency is 86.2% and the capacity retention after 50^th cycle is 80.7%. In case of 8% of Si-alloy/89.7% of Graphite/ 0.3% SWCNT/ 2% of SBR /1% of CMC electrode, the initial discharge capacity is 393.5mAh/g, the initial coulombic efficiency is 88.4% and the discharge capacity retention after 50cycle is 99.2%.

This improvement in the electrochemical properties of the SWCNT added electrode was mainly attributed to the good electric contact between Si-alloy particles and graphite particles during cycles. In other words, the main cause of initial capacity lose in Si-alloy/Graphite blending electrode is to lose electric contact due to the volume change of Si-alloy. This result gives many hints to improve Si-based anode materials.

[1] M. Kim et al. Journal of Electroanalytical Chemistry 687 (2012) 84-88