CARBON ANODES FOR A LITHIUM SECONDARY BATTERY BASED ON POLYACRYLONITRILE

Carbon anode materials for a lithium secondary battery based on polyac rylonitrile (PAN) are studied by using elemental analysis, X-ray powde r diffraction, scanning electron microscopy and X-ray photoelectron sp ectroscopy. The reversible lithium capacity and charging voltage curve s of carbons from PAN are affected by the heat-treatment temperature t he 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 cap acity reaches 426 mAh g(-1) at 600 degrees C; the lower the rate of te mperature rise, the higher the reversible capacity. The addition of ph osphoric acid can favour the cyclization process of PAN, and can incre ase 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 d(002). Such doping can enhance the r eversible capacity above and below 0.9 V. (C) 1998 Elsevier Science S. A. All rights reserved.