Anodic performances of anisotropic carbon derived from isotropic quinoline pitch Original Research Article

The anodic performances of anisotropic carbon derived from quinoline pitch (CQP) to be used in the lithium ion battery were studied to clarify the influence of nitrogen in the carbon hexagonal sheet. The quinoline pitch was synthesized by using HF/BF3 as a catalyst. Nitrogen in the carbon existed as pyridinic, pyrrolic and quaternary types to be converted in this sequence, depending upon HTT. Above 1000°C, nitrogen started to evolve, leaving vacancies in the sheet which were filled by graphitization at higher HTT. CQP prepared below 700°C showed much lower discharge capacity than that derived from naphthalene pitch (CNP) at the same temperature. Higher temperature treatment reduced the capacity as observed commonly in the anisotropic carbon, however, the extent of reduction was smaller. Hence, the capacity became the same at 800°C and larger at 1000 and 1200°C than those of CNP. The capacity of CQP after the heat-treatment at 1000°C, where the cycle stability was acceptable was 320 mAh g−1. The nitrogen in the ring disturbs the growth and stacking of hexagonal sheets by the carbonization below 700°C to reduce the capacity of CQP, whereas the vacancies due to nitrogen evolution by the heat-treatment at 1000°C appeared to provide new type sites for lithium charge. Such sites gave potentials of charge and discharge at 0.5–1.0 V reversibly and capacity of 468 mAh g−1. Higher temperature may remove such sites by graphitization.