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???) of the boron-doped graphitized CNFs reached 3.356 ?, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d??? is less than 3.400 ?, were selected for further heat treatment. The first heat treatment of PCNFs at 2800?°C yielded a d??? between 3.357 and 3.365 ?. Successive nitric acid treatment and a second heat treatment with boric acid reduced d??? to 3.356 ?. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g?1 between 0 and 0.5 V versus Li/Li? and 368 mAh g?1 between 0 and 1.5 V 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.