Electrochemical performance of arc-produced carbon nanotubes as anode material for lithium-ion batteries

The effects of etching process on the morphology, structure and electrochemical performance of arc-produced multiwalled carbon nanotubes (CNTs) as anode material for lithium-ion batteries were systematically investigated by TEM and a variety of electrochemical testing techniques. It was found that the etched CNTs exhibited four times higher reversible capacity than that of raw CNTs, and possessed excellent cyclability with almost 100% capacity retention after 30 cycles. The kinetic properties of three kinds of CNTs electrodes involving the pristine (CNTs-1), etched (CNTs-2) as well as etch-carbonized samples (CNTs-3) were characterized via ac impedance measurement. It was indicated that, after 30 cycles the exchange current density i₀ of etched CNTs ((7.6-7.8) × 10⁻³ A cm⁻²) was higher than that of the raw CNTs (5.9 × 10⁻³ A cm⁻²), suggesting the electrochemical activity of CNTs was enhanced by the etching treatment. The storage characteristics of the CNTs electrodes at room temperature and 50 °C were particularly compared. It was found that the film resistance on CNTs electrode generally tended to become large with the elongation of storage time, especially storage at high temperature. In comparison with CNTs-1 and CNTs-3, CNTs-2 exhibited more distinctly increase of film resistance, which is related with the surface properties.