Characteristics of Boron Doped Mesophase Pitch-Based Carbon Fibers as Anode Materials for Lithium Secondary Cells

Mesophase pitch-based Carbon Fibers(MCF) have been investigated as anode materials for lithium secondary cells by examining their physical and electrochemical properties. Discharge capacity and initial charge-discharge efficiency of the materials were studied in relation to the heat treatment temperatures of MCF. MCF heat treated at about 3,000 C gave high discharge capacity over 310mAh/g, good efficiency (93%) and superior current capability of 600mA/g (6mA/cm2). On the other hand, to improve the battery capacity, Boron was doped to the fiber about several {degree} by adding B{sub 4}C to the pre-carbonized milled fibers and then heat-treated up to 3,000 C in Ar. Then heat treated at 2,500 C under vacuum condition to remove remained B{sub 4}C. The structure of Boron-doped fibers was characterized and compared with that of non-doped standard fibers, and also Li ion battery performances are evaluated. The Boron-doped MCF indicated improvement in graphitization and increased discharge capacity as high as 360mAh/g. The voltammograms of both fibers are different from each other. The cell mechanism is discussed based on the unique structure of Boron-doping to the MCF is very effective for the battery performance.