Silicon nanowires with hydride, methyl and siloxane surfaces terminations were evaluated as anodes in lithium-ion half cells using LiPF6in EC/DMC electrolytes. Voltammetry, FT-IR and XPS analyses show hydride-terminated nanowires react with the electrolyte and methyl termination tends to passivate silicon surfaces. Silicon anodes pretreated with trimethoxymethylsilane show decreased lithium capacities similar to methylated anodes; however, the addition of 5% trimethoxymethylsilane as an electrolyte additive resulted in the formation of significantly more OPFx compounds while improving capacity retention relative to hydride-terminated nanowires (2348 mAh g-1at 15 cycles at C/10 rates). FTIR analysis show trimethoxymethylsilane additives covalently bond silicon surfaces and other SEI components. AFM nano-indentation tests also suggest the alkoxy silane additives in the electrolyte function as a binder to improve silicon's ability to withstand the large reversible volume changes. The results indicate silicon surface terminations play a key role in chemical and mechanical behaviors that control reversibility. © 2011 Elsevier B.V. All rights reserved.
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