Effects of surface chemical treatment on silicon negative electrodes for lithium-ion batteries: an in situ infrared spectroscopic study

Abstract : Silicon represents an expressive gain in energy density for negative electrodes in Li-ion batteries. Reversible cycling and long term stability of silicon electrodes are both dependent of the passivation efficiency of the solid electrolyte interface (SEI) layer formed at the electrode surface. Surface and bulk phenomena of amorphous silicon were studied by in-situ FTIR spectroscopy during electrochemical cycling. Electrodes were prepared by thin-film deposition of hydrogenated amorphous silicon on ATR crystals, allowing for the measurements of electrode reactions in the original chemical environment. The results reveal a dynamic surface passivation layer which is intensively formed during the first lithiation, partially dissolved during delithiation and that grows continuously along the cycling life. Electrolyte components play a major role on the chemical composition of the SEI layer. Various electrode treatments were obtained by chemical and electrochemical grafting of different molecular layers on silicon surface. The results show that the silicon electrochemical performance is strongly affected by the chemical nature, chain size and covering ratio of the grafted species. Carboxyl-terminated monolayers represent an attractive functionalization for silicon electrodes due to their densely packed structure, strong covalent attachment to the active material and chemical similarity with typical SEI products. Such a surface treatment leads to a good anchoring support for the SEI, increasing its stability and improving silicon electrochemical performance. On the other hand, the use of plasma enhanced chemical vapor deposition technique for preparing the amorphous silicon electrodes allow us to add carbon (as -CH3) to the silicon layer, with verified improvements in cycling performance. This methylated silicon material show improved electrochemical performances at same time as it develops a thicker SEI layer.
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Submitted on : Monday, October 28, 2013 - 5:49:26 PM
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Daniel Alves Dalla Corte. Effects of surface chemical treatment on silicon negative electrodes for lithium-ion batteries: an in situ infrared spectroscopic study. Materials Science [cond-mat.mtrl-sci]. Ecole Polytechnique X, 2013. English. ⟨pastel-00877545⟩

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