JPS63254667A - Activated carbon fiber electrode - Google Patents

Abstract

PURPOSE:To improve the filling density and make a cell small-sized by applying a polymer binder to the cloth width of activated carbon fibers with the aligned fiber axis direction then compressing and molding it. CONSTITUTION:A woven fabric made of a dehydrated and carbonized carbonaceous fiber is activated in the fuel gas to form a woven fabric-shaped activated carbon fiber sheet. This is immersed in the aqueous dispersion of Teflon as a binder then heated and dried. Then, two sheets are overlapped, heated, pressed, compressed, and molded. The fiber axis direction of the sheet thus obtained from the woven fabric is aligned, and its specific gravity is larger than that of the sheet obtained from a random nonwoven fabric-shaped activated carbon fiber in the same method. The filling density is improved accordingly, and a cell can be made small-sized.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a highly densified activated carbon fiber electrode. [Prior Art] In recent years, electrodes using activated carbon fibers having a large specific surface area have been actively developed. Applications of these electrodes include electrode plates for fuel cells (JP-A-59-46762, JP-A-58-
100364), polarizable electrode for electric double layer capacitor (JP-A No. 58-206116, JP-A No. 59-4114),
Electrodes for secondary batteries (JP-A-59-157974, JP-A-59-
163765, counter electrode for electrochemical display device (JP-A-5
9-143130) have been proposed. Activated carbon fibers having a large specific surface area such as 100 to 3000 yy1 are extremely useful as various electrode materials because of their large contact area with solutions. For example, in the case of electric double layer capacitors using activated carbon fibers as polarizable electrodes, a large amount of doping is possible due to the large specific surface area, which makes it possible to fabricate capacitors with high energy output. have [Problems to be Solved by the Invention] However, electrodes using such useful activated carbon fibers also have the drawback of low packing density. For this reason, there was a drawback that the volume of various batteries became large. There has been a strong desire among those in the industry to improve the packing density of electrodes made of activated carbon fibers. For example, as a method of increasing the packing density, an electrode in which a general activated carbon powder is solidified with a Teflon binder has already been reported (Japanese Patent Application Laid-Open No. 6O-17871). However, even when this method was used, the packing density of the electrodes was not sufficient. [Means for Solving the Problems] The present inventors conducted extensive studies in view of the above objectives, and found that in order to improve the packing density of activated carbon fibers, the fiber axis of the activated carbon fibers should be changed. The present invention was realized by recognizing that aligning the directions is most effective. That is, the present invention is a high-density activated carbon fiber electrode characterized in that a polymer binder is applied to a fabric made of activated carbon fibers whose fiber axes are aligned in at least one direction, and then compression molded. . It has been found that by using this electrode, highly packed electrodes can be achieved without losing any of the useful properties of conventional activated carbon electrodes. The fabric used in the present invention is composed of activated carbon fibers whose fiber axes are aligned in at least one direction. Such a fabric includes, for example, an activated carbon fiber sheet obtained from a nonwoven fabric in which the fiber axes are arranged in parallel, and yarns belonging to the second group in a direction approximately perpendicular to the 1fIl yarns arranged in approximately parallel directions. Examples include an activated carbon fiber sheet obtained from a fabric, such as a woven fabric, in which the yarns of the second group are sequentially combined in a predetermined manner so that the yarns of the second group also maintain a generally parallel relationship with each other. A compression molded product obtained from a sheet made of fibers that are sequentially combined in a direction perpendicular to at least two directions of the seraglio is characterized by an increased packing density and a high strength of the resulting molded product. It is particularly suitable for use. The activated carbon fiber used in the present invention is a carbon fiber that has particularly excellent absorption ability, and generally has a specific surface area of 100 ηg or more. The preferred specific surface area is s o
It is preferable to use od/g or more, especially 1400 d/g or more. The electrode according to the present invention can be used for various things such as electric double layer capacitors, but it is particularly suitable for use as a positive electrode for lithium secondary batteries. In this case, it is particularly preferable to use activated carbon fibers having an Ip/Io of 0.3 or less and mainly having a non-standard structure. Here, IP is the maximum intensity value above the tangent line drawn on both phases of the diffraction peak on the (o02) plane of the X-ray diffraction intensity curve, and 0 is the diffraction angle 2θ that indicates the IP. This is the X-ray intensity remaining after subtracting the air scattering intensity from the measured diffraction intensity at . It has already been reported by the same applicant as the applicant of the present invention that a lithium secondary battery using activated carbon, particularly activated carbon fiber, as a positive electrode, which has a mainly non-standard structure, has extremely excellent performance. 61-238951)
. However, although this activated carbon has extremely excellent performance per unit weight, its performance per unit volume is still insufficient, and there has been a strong demand for higher density activated carbon electrodes. The raw material for the activated carbon fiber used in the present invention is not particularly limited, and includes, for example, those made of synthetic organic polymers or pitch. The synthetic organic polymers include polyvinyl alcohol and phenol! Fat, polyac! J@nido! It includes semi-synthetic polymers such as cellulose derivatives as well as pure synthetic polymers such as J.I. The diameter of the activated carbon fiber used in the present invention is not particularly limited, but it is preferable to use one having a diameter of 1 μm or more and 30 μm or less, since a wl pole with good performance can be obtained. In order to increase the packing density of activated carbon fibers, it was necessary to align the fiber axes in at least one direction. If the fiber axes were not aligned, the space within the electrode would increase, and the apparent density of the electrode would not improve. In the present invention, a polymer resin binder is applied prior to compression molding. The polymer resin binder

〔Example〕

The present invention will be explained in more detail with reference to Examples below. Synthesis Example 1 [Synthesis of activated carbon fiber] P was spun by a wet spinning method from a PVA (polyvinyl alcohol) aqueous solution with an average degree of polymerization of 1700 as a starting material.
VA fiber (denier 1800d, number of filaments 100
A woven fabric obtained from a fabric with a strength of 10.5 Q/d and an elongation of 796 was used. Next, as a dehydration and carbonization agent (N) 114
)2804 and (NH4)2HPO4 each sog to 100
09 in water, heated this aqueous solution to 60°, immersed the woven fabric in it for 5 minutes, and then squeezed the liquid with a mangle.
It was dried for 3 minutes at 5°C. The adhesion rate of the dehydrating agent is 1 by gravimetric method.
It was 096. The woven fabric coated with this dehydrating agent was heated to 210°C.
The shrinkage rate of the fibers was controlled to 4096 by applying a low tension of 50 g per width of the woven fabric during heating for 30 minutes. When heating in two stages: rough carbonization at 330°C for 10 minutes and then 400°C for 20 minutes, a low tension of 3 og per 10 widths of the woven fabric was applied to determine the fiber shrinkage rate from the starting PVA fiber. It was set to 6096. The weight reduction rate at that time was 55LX). A woven fabric made of black carbonaceous fibers that has been dehydrated and carbonized as described above is placed in a combustion gas for 9 minutes.
An activated carbon fiber sheet was obtained by performing activation at 50° C. for 1 hour and 30 minutes. The specific surface area of the BET method using N7 gas is 2
It was 300 rIVg. The X-ray diffraction intensity curve of this activated carbon fiber was measured using a rotating anticathode type X-ray diffractometer manufactured by Rigaku Denki.
It was measured using ype RAD-rA. Measurement conditions are 4
0 kVl 00mA, OuKa a-line (λ=1.54
18A), slit 1/2.0.15+++m, scanning speed 1°'/min, full scale 800 cps, the peak based on the (002) plane that should exist around 25° a2θ measured by transmission method almost disappeared. and
It was found that activated carbon fibers mainly consisting of a non-standard structure were produced (IP/IO = 0.071°. The internal rough and fine structure was examined by solid-state high-resolution NMR. MA, The data points measured by the S GATE method are 8K, 140P was measured at a sampling point of 1.5, and the number of scans was 10,000 times.
Since a curve with a peak near PM was obtained, it was confirmed that the structure was centered around a phenyl group skeleton. No absorption of C-■ was observed in surface reflection infrared, and it was confirmed that carbonization was almost complete. The apparent specific gravity of this woven activated carbon fiber was 0.2.Also, random non-woven activated carbon fiber was obtained by the same method, but its apparent specific gravity was 0.07. Example 1 The woven activated carbon fiber obtained in Synthesis Example 1 was immersed in an aqueous Teflon dispersion (containing Teflon at a yield of 5 wt %) for 30 minutes. Thereafter, it was dried at 120°C for 1 hour. After that, the above woven fabric was layered in two layers and heated at 170℃ and 100℃.
Pressure compression molding was performed for 30 minutes under the condition of kg/Ai. After cooling to room temperature, it was taken out from the press and vacuum dried at 120° C. for 2 hours. Even though the apparent specific gravity of the sheet thus obtained was 0.8, it was greatly improved compared to the original value (0,2). Further, the amount of resin contained in the electrode was 10 wt96. Comparative Example 1 The random nonwoven activated carbon fiber obtained in Synthesis Example 1 was compression-molded under the same conditions as in Example 1 to obtain a sheet. The apparent specific gravity of this sheet was 0.2, which was significantly lower than that when woven activated carbon fibers were used. The apparent specific gravity of the sheet did not substantially increase even when the compression force was doubled or the pressing time was increased to 1 hour. Comparative Example 2 The activated carbon fiber obtained in Synthesis Example 1 was processed using a ball mill.
The mixture was pulverized for 4 hours to obtain powdered activated carbon fibers. The particle size distribution was 99.696 below 350 mesh.
A Teflon binder was added as a binder, and pressure compression molding was performed (170°C, 100 kgAi). The apparent specific gravity of the sheet thus obtained is 0.5
However, the density was not higher than that when woven activated carbon fibers were used. The apparent specific gravity of the sheet did not substantially increase even when the compression force was doubled or the pressing time was increased to 1 hour. Usage Example 1 The sheet of approximately one size obtained in Example 1 was punched out into a disk shape with a diameter of 10 circles. A secondary battery using this as a positive electrode and metallic lithium as a negative electrode was fabricated in an argon atmosphere. The positive and negative electrodes were placed through a glass fiber filter with a thickness of 0.5 ft. The electrolytic solution used was one in which lithium perchlorate was dissolved in propylene carbonate at a concentration of IM 7'l. Nickel expanded metal was used as the current collecting electrode on the positive electrode side. The voltage of this secondary battery immediately after assembly is 3. It was OV. Also 3, 2 from OV. The capacity until the open circuit voltage decreased to OV was 4.8 mAh (current capacity that allows a current of 4.8 mA to flow for 1 hour). Using the sheets obtained in Comparative Examples 1 and 2, a disc-shaped electrode having a diameter of about 1M and 10 circles was obtained. 3. Lithium secondary battery using this. The current capacities until the open circuit voltage decreased from OV to 2.0V were 1.2 mAh and 3 mAh, respectively. Use Example 2 The sheet with a thickness of about 1 m obtained in Example 1 was punched out into a disk shape with a diameter of 10 m. An electric double layer capacitor using this as both positive and negative electrodes was fabricated in an argon atmosphere. The positive electrode and the negative electrode were placed through a glass fiber filter with a thickness of 0.5 mm. The electrolyte was prepared by dissolving lithium perchlorate in propylene carbonate at a concentration of 1 part to 9 parts. As current collecting electrodes, nickel expanded metal was used on the positive electrode side, and aluminum expanded metal was used on the negative electrode side. The voltage of this electric double layer capacitor immediately after assembly is OV
Met. 2. After 1 hour of constant voltage charging at OV voltage, 1. It was discharged to OV. The current capacity at this time was 1.2 mAbr. The sheets obtained in Comparative Examples 1 and 2 were roughly 1 m thick.
A disc-shaped electrode with a diameter of 10 m was obtained. The current capacities (from 2.0V to 1.0V) of the capacitors using this were 0.3 mAh and 0.7 mAh, respectively. From the above results, it was found that the secondary battery capacity and the electric double layer capacitor capacity are approximately proportional to the specific gravity of the electrode, and the largest capacity is obtained in the case of Example 1, which has a large specific gravity. [Effects of the Invention] The electrode of the present invention has a high packing density and is extremely useful industrially as an electrode for electric double layer capacitors, lithium secondary batteries, etc.

Claims (1)

[Claims] A densified activated carbon fiber electrode obtained by applying a polymer resin binder to an activated carbon fiber fabric whose fiber axes are aligned in at least one direction and then compression molding the fabric.