Carbon anodes for a lithium secondary battery based on polyacrylonitrile

Carbon anode materials for a lithium secondary battery based on polyacrylonitrile (PAN) are studied by using elemental analysis, X-ray powder diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The reversible lithium capacity and charging voltage curves of carbons from PAN are affected by the heat-treatment temperature the rate of temperature rise and the soak time. These factors lead to a change in nitrogen content, cyclization and cross-linking processes, the carbon structure, and the number of micropores. The reversible capacity reaches 426 mAh g−1 at 600°C; the lower the rate of temperature rise, the higher the reversible capacity. The addition of phosphoric acid can favour the cyclization process of PAN, and can increase the number of micropores in the resulting carbon. It can also act as setting agent for graphene molecules and can improve the regularity of the carbon structure. In addition, the doped phosphorus is bonded with C and O, and dispersed homogeneously in the bulk carbon structure. This results in an increase in d002. Such doping can enhance the reversible capacity above and below 0.9 V.