H.Q. Wu

Effects of carbon coatings on nanocomposite electrodes for lithium-ion batteries

Nanocomposites of LiFePO 4 and TiO 2 coated with carbon were prepared by different methods. They exist in the forms of olive and rutile, respectively. Results from cyclic voltammetry show that the carbon coating markedly enhances the reversibility and kinetics of lithium intercalation into and deintercalation from the active materials. Both kinds of carbon coated nanocomposites exhibited better electrochemical performance than their pure counterparts due to the favorable carbon coatings, which provide passages for lithium ions, promote charge transfer, and prevent phase changes.

Charge–discharge characteristics of raw acid-oxidized carbon nanotubes

Abstract Lithium intercalation with raw acid-oxidized carbon nanotubes was studied. The results show that the total capacity of 660 mA h g −1 was obtained after the first discharge. The reversible part is 200 mA h g −1 . The solid electrolyte interface (SEI) is formed by reaction of surface groups on the carbon nanotubes with lithium upon discharge. The nature of this interface to a large extent determines the reversible and irreversible capacities of the carbon nanotubes. During oxidation in the mixture of acid, the residual acids will play an important role in this work. The residual acids will react with Li ion and cause irreversible capacity. The H 2 SO 4 and HNO 3 can easily permeate through the graphene sheets, then they will make defects or pores in graphene sheets and cause the reversible capacity. The surface groups formed upon oxidation have been characterized using Fourier transform infrared spectroscopy.