Electrochemical behaviors of functionalized carbon nanotubes in LiPF ₆/EC+DMC electrolyte

The effect of oxidation on the surface functional groups of carbon nanotubes (CNT) through acidic agents (nitric acid and a mixture of sulfuric and nitric acid) was studied. The correlation between the amount of surface functional groups and the electrochemical properties of CNT in LiPF6/EC+DMC Electrolyte was then investigated. Transmission electron microscopy (TEM) and Fourier transform infrared spectrophotometer (FTIR) suggested that oxygen-containing surface groups were successfully introduced and the highly tangled long ropes of CNT were cut into short, open-ended pipes during the acid treatment. The amount of functional groups was evaluated by acid-base titration. Charged and discharged testing and cyclic voltammetry (CV) were used to characterize the electrochemical behaviors of the samples. It is found that the electrochemical properties of functionalized CNT are primarily dependent on the amount of carboxyl groups. The sample treated with mixed acid at 70°C, which has the highest amount of carboxyl groups, exhibits both high capacity and good rate capability. The additional capacity contributed by the reversible faradic reaction from the surface groups on CNT make it possible to be assembled as a promising material in combining the distinguished properties of batteries and capacitors.