Chemical bonding in amorphous Si-coated carbon nanotubes as anodes for Li ion batteries: a XANES study

The nature of the chemical bonding in an amorphous Si-coated carbon nanotube (Si-CNT) anode, and its evolution upon electrochemical cycling, have been investigated using comprehensive X-ray absorption spectroscopy (XANES) at the Si L-and K-edges, along with the C and O K-edges. The Si nanolayer on the CNT is found to be anchored to the CNT via Si-O-C bonding. This bond weakens upon electrochemical cycling, accompanied by the generation of Li2CO3 on the surface of the Si-CNT. These findings are crucial in designing further improved Si-C composite anodes for lithium ion batteries.