Carbon fibers, production process therefor and electrode for batteries
Fine carbon fibers having a fiber diameter of 1 μm or less, an interlayer distance d 002 between carbon layers as determined by an X-ray diffraction method of 0.335 to 0.342 nm or less and satisfying d 002 <0.3448-0.0028 (log φ) where φ stands for the diameter of the carbon fibers, and a thickness Lc of the crystal in the C axis direction of 40 nm or less. Fine carbon fibers containing boron in crystals of the fiber. The fine carbon fibers can be produced by using vapor-grown fine carbon fibers as a raw material, adding a boron or a boron compound to the material; pressing the mixture to regulate the bulk density to preferably 0.05 g/cm 3 or more; and heating at a temperature of 2000° C. or higher.
1. A process for producing fine carbon fibers comprising:
adding vapor-grown fine carbon fibers having a diameter of 1 μm or less to boron or a boron compound;
compacting the mixture of fine carbon fibers and boron or a boron compound to obtain a solidified shaped mixture;
relieving pressure after completion of shaping;
regulating the bulk density of the mixture of fine carbon fibers and boron or a boron compound during compacting such that the solidified mixture has a bulk density of 0.05 g/cm 3 or more after pressure relief; and
heat treating said fine carbon fibers to a temperature of 2000° C. or higher while said bulk density is maintained, to produce fine carbon fibers having an interlayer distance d002 between carbon layers as determined by an X-ray diffraction method of 0.335 to 0.342 nm, and satisfying d002<0.3448-0.0028 (blog φ) where φ represents the diameter the carbon fibers and the units of d002 are nm, and a thickness Lc of the crystal in the C axis direction of 40 nm or less.
2. A process for producing fine carbon fibers according to claim 1 , wherein the amount of the boron or boron compound is 0.1-10 mass % in terms of boron atoms with respect to the carbon fibers.
3. A process for producing fine carbon fibers according to claim 2 , wherein the fine carbon fibers to which the boron is mixed have a diameter of 0.01 to 1 m and an aspect ratio of 10 or more.
4. A process for producing fine carbon fibers according to claim 3 , wherein the fine carbon fibers prior to said heat treatment to which the boron or boron compound is to be added are a fired product of vapor-grown carbon fibers fired after growth.
5. A process for producing fine carbon fibers in according to claim 3 , wherein the fine carbon fibers prior to said heat treatment to which the boron or boron compound is to be added are unfired product of vapor-grown carbon fibers not fired after growth.