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Abstract: Silicon which has a theoretical capacity around 3500mAhg−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. [Copyright &y& Elsevier]

Abstract: The effect of vinylene carbonate (VC) as electrolyte additive on the properties of the silicon electrode / liquid electrolyte interface was studied in this paper. Galvanostatic cycling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the SEI layer properties and the morphology at different stages of the cycling of thin film electrodes. The electrochemical performances were drastically improved by the introduction of a few per cent of VC additive. It was found that the SEI layer formed in VC-containing electrolyte has a different chemical composition and better resists to the stress caused by large volume variations associated with lithiation and delithiation reactions. The chemical and topographic modifications of the electrode surface at various stages of cycling are discussed in correlation with the evolution of the reversible capacity over cycling with and without VC. This study highlights the importance of the SEI which governs the electrochemical performances of Si thin film model electrodes. [Copyright &y& Elsevier]