Free-Standing Binder-Free Multi-Wall Carbon Nanotube/Silicon Anodes for Lithium-Ion Batteries

Abstract

Silicon is of interest owing to its high theoretical capacity (4200 mAh/g). However, its enormous volume expansion of silicon during cycling is one of the main reasons for the rapid capacity fading and pulverisation of the anode commonly observed. Here, freestanding multi-wall carbon nanotube (MWCNT)/silicon anodes were prepared using so-called MWCNT buckypapers (BPs) as current collectors instead of the traditional metallic foils. To prepare the anodes, silicon was deposited on these MWCNT BPs to form silicon nanoparticles (SiNPs) and subsequent annealing resulted in the formation of a connecting SiC interface preventing the SiNPs from detaching. An amorphous carbon coating was applied in order to enhance electrical conductivity and overall integrity of these hierarchical anode materials. The morphology and chemical composition of the Si-BP anodes were characterised by means of SEM, TEM, EDX, STEM, XRD, RAMAN, etc. Cycling tests of these binder and additive-free anodes revealed an areal capacity of 0.55 mAh/cm2 after 300 cycles with 99.7% of Columbic efficiency and showed that the presence of the SiC interface and a-C coating played a crucial role in improving their rate capability and stability.