High performance silicon free-standing anodes fabricated by low-pressure and plasma-enhanced chemical vapor deposition onto carbon nanotube electrodes

High capacity silicon and alternative current collectors are being evaluated as a viable approach to increase the energy density of lithium ion batteries. Presently, silicon is deposited onto lightweight single-walled carbon nanotube (SWCNT) current collectors by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) to form Si-SWCNT free-standing anodes. The electrode morphology is characterized by scanning electron microscopy (SEM) and Raman spectroscopy, and the electrochemical performance is studied for each CVD method at silicon weight loadings between 25% and 70%. Results demonstrate that PECVD fabricated Si-SWCNT anodes outperform LPCVD fabricated anodes, with electrode extraction capacities as high as 2500 mAh g−1. When only the Si mass is considered, PECVD-Si-SWCNT anodes have up to 2x higher extraction capacities than LPCVD-Si-SWCNT anodes at low Si loadings. The highest Si-only extraction capacity measured was 3780 mAh g−1. Full cells were demonstrated to have stable cycling for 100 cycles. Postmortem analysis (via SEM and Raman) reveals that PECVD-Si-SWCNT anodes undergo more significant morphological and crystallographic changes during cycling than LPCVD-Si-SWCNT anodes. This work demonstrates that the choice of CVD method for Si deposition onto SWCNT current collectors greatly impacts the resulting electrode morphology, which, in turn, affects the electrochemical performance.

► Silicon–carbon nanotube anodes fabricated by two chemical vapor deposition methods. ► Electrochemical performance studied as function of silicon loading for both methods. ► Anode capacities of 2500 mAh g−1 and Si-only capacities of 3780 mAh g−1 measured. ► Anode morphology and performance depends on chemical vapor deposition method. ► Postmortem analysis shows significant differences in anode morphology after cycling.