Carbon Nanotube–Carbon Nanocoil Hybrid Film Decorated by Amorphous Silicon as Anodes for Lithium-Ion Batteries

Silicon (Si) as the anode material for lithium-ion batteries (LIBs) has attracted much attention due to its high theoretical specific capacity (4200 mAh/g). However, the specific capacity and cycle stability of the LIBs are reduced due to the pulverization caused by the expansion of Si coated on Cu (copper) foil during cycles. In order to solve this problem, researchers have used an ultra-thin Si deposition layer as the electrode, which improves cyclic stability and obtains high initial coulomb efficiency of LIBs. However, suitable substrate selection is crucial to fabricate an ultrathin Si deposition layer electrode with excellent performance, and a substrate with a three-dimensional porous structure is desirable to ensure the deposition of an ultrathin Si layer on the whole surface of the substrate. In this paper, the Si thin layer has been deposited on a binder-free hybrid film of carbon nanotubes (CNTs) and carbon nanocoils (CNCs) by magnetron sputtering. Compared with densely packed CNT film and flat Cu foil, the loose and porous film provides a large surface area and space for Si deposition, and Si can be deposited not only on the surface but also in the interior part of the film. The film provides a large number of channels for the diffusion and transmission of Li+, resulting in the rapid diffusion rate of Li+, which improves the effective lithium storage utilization of Si. Furthermore, the CNC itself is super elastic, and film provides an elastic skeleton for the Si deposition layer, which eases its volume expansion during charge and discharge processes. Electrochemical tests have showed that the Si/CNT–CNC film electrode has excellent performance as anode for LIBs. After 200 cycles, the Si/CNT–CNC film electrode still had possessed a specific capacity of 2500 mAh/g, a capacity retention of 92.8% and a coulomb efficiency of 99%. This paper provides an effective way to fabricate high performance Si-nanocarbon composite electrodes for LIBs.