Single-Walled Carbon Nanotube Film as an Efficient Conductive Network for Si-Based Anodes

Silicon-based anodes are considered ideal candidate materials for next-generation lithium-ion batteries due to their high capacity. However, the low conductivity and large volume variations during cycling inevitably result in inferior cyclic stability. Herein, a dry method without binders is designed to fabricate Si-based electrodes with single-walled carbon nanotubes (SWCNTs) network and to explore the different mechanisms between SWCNT and multiwalled carbon nanotubes (MWCNTs) as a conductive network. As expected, higher initial discharge capacity (1785 mAh g(-1)), higher initial Coulombic efficiency (ICE, 81.52%) and outstanding cyclic stability are obtained from the SiOx@C|SWCNT anodes. Furthermore, its lithium-ion diffusion coefficient (DLi+) is 3-4 orders of magnitude higher than that of SiOx@C|MWCNT. The underlying mechanism is clarified by in situ Raman spectroscopy and theoretical analysis. It is found that the SWCNTs can maintain good contact with SiOx@C even under tensile stresses up to 6.2 GPa, while the MWCNTs lose electrical contact due to alternating compressive stress up to 8.9 GPa and tensile stress up to 2.5 GPa during long-term cycling. Under such very large stresses, the more flexible SWCNTs and their stronger van der Waals forces ensure that SiOx@C still has good contact with SWCNTs.