Carbon Coated Helical Carbon Nanotubes used as Anode Materials of Li―ion Battery

The helical carbon nanotubes (HCNTs) was modified with carbon through thermal vapor deposition (TVD) of benzene at 900 , and characterized by X―ray powder diffraction, transmission electronic microscope, scanning electronic microscope and Brunau―Emmertt―Teller method. The specific surface area of the HCNTs decreased after carbon coating. The obtained carbon coated HCNTs used as anode materials of Li―ion battery were studied. The results revealed that appropriate amount of carbon coating could improve the first columbic efficiency, the cycling stability and rate charge/discharge performance of the HCNTs. After 45 min carbon coating, HCNTs gained a weight increase approximately 220wt%, with its first columbic efficiency increasing from 59.2% to 77.8%, and delivered a discharge capacity of 265.6, 245.7, 196.0, 163.2 mAh/g at the rates of 1.0C, 2.0C, 5.0C and 10.0C, respectively. After 95 cycles at 10.0C, its discharge capacity retention was 93.3%. Although excessive carbon coating could further improve the first coulumbic efficiency and cycling stability of HCNTs, it also degraded the rate capability.