Ks. Ko et al., Preparation of Kevlar-derived carbon fibers and their anodic performances in Li secondary batteries, CARBON, 39(11), 2001, pp. 1619-1625
We report here the preparation of Kevlar-derived carbon fibers and the prel
iminary results on their anodic performances in Li secondary batteries. The
single- or two-step carbonization process is employed for the preparation.
In the single-step process, the Kevlar flocks are heat-treated under At at
mosphere from 25 to 800 degreesC with a heating rate of 5 degreesC min(-1),
but an additional intermediate heating at a fixed temperature between 330
and 510 degreesC for 2 h is applied in the two-step preparation. The two-st
ep carbonization allows a higher carbon yield than that achieved in the sin
gle-step one (ca. 36%). In particular, a maximum yield (ca. 50%) is observe
d with an intermediate heating at 400-410 degreesC. The infrared study indi
cates that the higher carbon yield achieved in the two-step process is inde
bted to the formation of condensed/cross-linked polyaromatic molecules duri
ng the intermediate heating period, which seemingly alleviates the volatile
loss in the subsequent higher temperature heating. The Kevlar-derived carb
on fibers exhibit the charge-dis charge behaviors that are commonly observe
d in non-graphitizable carbons. Here, the carbon made by the two-step proce
ss (intermediate heating at 410 degreesC) delivers a higher discharge capac
ity than the single-step ones. In particular, a notably high capacity near
zero volts is observed in the two-step carbon that is associated with the L
i+ removal from the micropores. The higher population of micropores in the
two-step carbons may be explained by the enriched formation of cross-linked
polyaromatics during the intermediate heating. (C) 2001 Elsevier Science L
td. All rights reserved.