Thermally Induced Reactions between Lithiated Nano-Silicon Electrode and Electrolyte for Lithium-Ion Batteries

The thermal stability of nano-silicon electrodes before and after lithiation was studied by means of differential scanning calorimetry (DSC). It was found that pristine Si electrodes heated in presence of EC/DEC 1M LiPF6 electrolyte show exothermic reactions between sodium carboxymethylcellulose (Na CMC binder) and LiPF6. The products of thermal decomposition of a lithiated nano-Si electrode with electrolyte at different temperatures were identified using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). SEI layer was found to be responsible for the thermal reactions in the range between 77 and 107°C. Exothermic events between 107 and 140°C were caused by partial decomposition of LiPF6 salt, which products initiated further transformations of SEI layer compounds and esterification of Na CMC. Interaction between nano-LixSi and EC/DEC 1M LiPF6 was the reason for the main exothermic peaks at temperatures between 150 and 300°C. Nano-LixSi heated with EC/DEC solvent mixture without LiPF6 resulted in electrolyte decomposition at much lower temperatures (>105°C). Therefore, the important role of LiPF6 in the thermal stabilization of nano-LixSi with electrolyte at temperatures <140°C was confirmed while LiTFSI salt added to EC/DEC was ineffective in the prevention of the main exothermic reaction starting at 105°C.