Amorphous silicon-metal core-shell

A more common strategy to achieve core-shell structures is to deposit a film of a-Si onto metallic NWs or nanofibers. C-Si and TiC/C-Si coreshell nanofiber structures were obtained by using CVD of SiH4 onto carbon nanofiber (CNF) and TiC/C nanofibers. In the case of the C-Si core-shell nanofiber structures (Fig. 1.32), the amorphous CNF cores displayed a reversible capacity of 280 mAh/g, much smaller than the capacity for lithiation of crystalline Si. 

Synthesis of CNF-Si core-shell nanostructures (a) CNFs are coated with a-Si using CVD of SiH4 to form (b) CNF-Si coreshell structures. SEM images of (c) CNFs and (d) a-Si coated CNFs. (e) Galvanostatic cycling performance of CNF-Si coreshell nanostructures. Reproduced with permission from Ref. 112. Copyright 2009, American Chemical Society. 

To overcome this voltage restriction, TiC/C-Si core-shell NWs utilize an inert TiC/C scaffold (Fig. 1.33a,b) so that charging can occur down to low potentials, for example, 10 mV vs. Li/Li, in order to fully lithiate the Si shell. TiC/C nanofibers were S5mthesized through thermochemical reaction of a titanium alloy (Ti 6A1-4V) foil in acetone vapor at 850°C. Detailed TEM analysis showed that the nanofibers consisted of a 30 nm crystalline TiC core coated with a 20-40 nm amorphous carbon shell (Fig. 1.33c). Cyclic voltammetry on 

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