The electrochemical properties of isotropic and anisotropic carbon fib
ers were studied using the two-electrode method in a 1 M LiPF6 electro
lyte solution dissolved in a 1:1 volume mixture of ethylene carbonate
(EC) and dimethyl carbonate (DMC). Isotropic carbon fiber had a larger
irreversible capacity than that of the other carbon fibers and might
have many sites for the electrolyte decompositon and residual lithium
ions. Active carbon fibers prepared from isotropic carbon fibers by st
eam gasiformation at 850 degrees C showed large specific surface areas
. After steam gasiformation, the active carbon fibers changed into a m
ore crystalline state and had electrochemical characteritics similar t
o the anisotropic carbon fibers. Impedance profiles of the carbon fibe
rs were fitted by equivalent analogs of a three-resistance-capacitance
(RC) circuit in series and the thickness of passivation layers in the
carbon fibers was calculated. (C) 1997 Published by Elsevier Science
S.A.