Structure and electrochemical applications of boron-doped graphitized carbon nanofibers

Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d ₀₀₂) of the boron-doped graphitized CNFs reached 3.356, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d ₀₀₂ is less than 3.400, were selected for further heat treatment. The first heat treatment of PCNFs at 2800°C yielded a d ₀₀₂ between 3.357 and 3.365. Successive nitric acid treatment and a second heat treatment with boric acid reduced d ₀₀₂ to 3.356. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338mAhg ¹ between 0 and 0.5V versus Li/Li ⁺ and 368mAhg ¹ between 0 and 1.5V versus Li/Li ⁺. The first-cycle Coulombic efficiency was also enhanced to 71-80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C.