Investigation on the part played by the solid electrolyte interphase on the electrochemical performances of the silicon electrode for lithium-ion batteries

Abstract : Silicon which has a theoretical capacity around 3500 mAh g−1 and low insertion/deinsertion potentials is one of the most promising candidates to replace graphite as a negative electrode in lithium-ion batteries. Electrochemical performances of Si electrodes are highly dependent on the quality of the SEI. Therefore, the effect of an electrolyte additive, the vinylene carbonate (VC) on electrochemical performances was investigated on sputtered silicon thin films which constitute a simple system (avoiding the use of binders or any conducting additive material). The addition of only 2% of VC significantly improves the capacity retention as well as the coulombic efficiency leading to a capacity retention of 84% after 500 cycles and a coulombic efficiency around 99.5%. To explain the behaviour differences, thorough electrochemical analyses (capacity, coulombic efficiency, polarization at half charge...) combined with scanning electron and atomic force microscopies were carried out. Some correlations have been established between the electrochemical performances and the morphology evolution of the electrode. Thus, VC limits the formation of cracks induced by repeated expansion/contraction cycles and the liquid electrolyte/electrode interactions. In addition, the mechanical pressure locally applied to the thin film allows to maintain a dense morphology and hence has a beneficial effect, too. These two key parameters limit the deterioration of the electrode over cycles.