OPTIMIZATION OF THE DIMENSIONS OF VAPOR-GROWN CARBON-FIBER FOR USE ASNEGATIVE ELECTRODES IN LITHIUM-ION RECHARGEABLE CELLS

Electrochemical performance examinations of a new generation of carbon whisker were carried out in 1 M LiClO4 in a 50:50 mixture of ethylene carbonate and diethyl carbonate. The whisker has a high reversible ca pacity (363 mAh/g), and the coulombic efficiency was 100%. This capaci ty depends strongly on the diameter of the fiber and the preparation m ethod. When the length of graphite whisker is 23 mu m, it gives the hi ghest first cycle coulombic efficiency (96%). We investigated the char ge-discharge characteristics with different current densities. When me asuring the slow cyclic voltammogram of the graphite whiskers, five ca thodic peaks could be seen. The kinetics of electrochemical intercalat ion of lithium ions into the graphite whisker was studied by impedance spectroscopy The diffusion coefficient of lithium in the carbon is la rger when the fibers were graphitized and then chopped, than when they were chopped first, and it decreased linearly as x in LixC6 increased . This is related directly to the microstructure of fiber.