JPS63218159A - activated carbon electrode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrode using activated carbon obtained by pulverizing activated carbon fibers.

[Conventional technology]

In recent years, development of electrodes using activated carbon fibers with large specific surface areas has been carried out. The electrodes of Koori et al. are used as electrode plates for fuel cells (JP-A No. 59-46762, JP-A-58
-100364 ), polarizability wLt for electric double-headed no-kahashita! ! ii (JP 5B-206116, JP 59
-4114), secondary battery electrode (JP 59-15797
4, Japanese Unexamined Patent Publication No. 59-163765), and a counter electrode for electrochemical display devices (Japanese Unexamined Patent Publication No. 59-143130).

Activated carbon fibers having a large specific surface area of 100 to 3000 l'g are extremely useful as various electrode materials because of their large contact area with solutions. For example, in the case of an electric double non-capacitor that uses activated carbon fiber as a polarizable electrode, a large amount of doping is possible due to its large specific surface area, which makes it possible to create a capacitor with high energy output. has.

[Problem that the invention seeks to solve]

However, electrodes using such useful activated carbon fibers also have a low packing density. 711 had the disadvantage of high resistance. For this reason, there have been disadvantages in that the volumes of the various batteries become large and the internal resistance of the various batteries becomes large.

There was a strong desire among those in the industry to improve the chargeability and reduce the resistance of electrodes made of activated carbon fibers. For example, as a method for increasing the conductivity of a W electrode, a method has already been proposed in which a conductivity improving layer is supported on activated carbon fibers. Furthermore, as a method of increasing the packing density, an electrode in which general activated carbon powder is solidified with a Teflon binder has already been reported (Japanese Patent Application Laid-Open No. 178713/1983) However, even when this method is used, the electrode performance is was not sufficient.

[Means for solving problems]

The present inventors conducted extensive studies in view of the above objectives, and found that carbon powder obtained by pulverizing carbon fibers was mixed with active carbon obtained by pulverizing activated carbon fibers, and Teflon, etc. Activated carbon obtained by binding using a binder of 1! ! :fM has discovered that high filling of the a-electrode and high 4-electrification can be achieved at the same time without losing any of the useful properties of conventional activated carbon electrodes.

The activated carbon fiber used in the present invention is a carbon fiber that has particularly excellent adsorption ability, and generally has a specific surface area of 100:4 or more. The preferred specific surface area is 500r
It is preferable to use IVg or more, especially 140 otrl1g or more.

The activated carbon electrode 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. Further, in this case, it is particularly preferable to use activated carbon having an Ip/I□ of 0.3 or less and mainly having a non-grade structure.

Here, IP is the maximum value of the intensity above the tangent line drawn at both ends of the diffraction peak on the (002) plane of the X-ray diffraction intensity curve, and lo is the maximum intensity value at the diffraction angle 2θ indicating the IP. This is the X-ray intensity remaining after subtracting the air scattering intensity from the measured diffraction intensity. 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. 6l-23
8951).

However, although the performance per unit weight of this activated carbon is quite excellent, the performance per unit volume is still not sufficient, and at the same time as the density of activated carbon electrodes has been increased, the conductivity of activated carbon electrodes has also been improved. It was strongly requested.

Raw materials for the activated carbon fibers used in the present invention include synthetic organic polymers or pitch. The synthetic organic polymer includes purely synthetic polymers such as polyvinyl alcohol, phenol resin, polyacrylonitrile, etc., as well as semi-synthetic polymers such as cellulose derivatives.

The diameter of the activated carbon fiber used in the present invention is not particularly limited, but it is preferable to use a diameter of 1 μm or more and 30 μm or less since an electrode with good performance can be obtained.

In the present invention, the means for obtaining a fine powder of activated carbon fibers is not particularly limited, and pulverization using a ball mill is preferable since a homogeneous sample can be obtained.

Grinding is preferably carried out using a ball mill for several hours.

In the present invention, the aspect ratio of the fiber after pulverization is preferably 3 or more and 100 or less, particularly preferably 5 or more and 50 or less.

Taikai's 'II! It was necessary to mix conductive material and carbon fiber in 1- to the association that thirsts for prisoners. Since the electrical conductivity of activated carbon fibers is less than 100 (l·α) −1, when a binder is added to the activated carbon fibers and solidified, the electrical conductivity decreases considerably. Therefore, it was necessary to mix other conductive materials to improve conductivity. Various conductive materials can be used for this purpose, such as thin metal wires and carbon powder.According to the research of the present inventors, it is best to use carbon powder obtained by crushing carbon fibers as the conductive material. It was recognized that this method is good because the improvement effect is extremely large. For example, when thin metal wires are used, the specific gravity of the crushed activated carbon fibers is very different, making it extremely difficult to mix them uniformly and the thin metal wires clumping together, resulting in little improvement in conductivity. Ta. The method of mixing carbon powder to improve the conductivity of an electrode requires mixing a considerably large amount of carbon powder, which is at least 1096 times the weight of the electrode, and a significant improvement in conductivity cannot be expected, so it is not practical. The above was not a very good method.

The carbon fiber used in the present invention is not particularly limited, and is a material with high conductivity, generally 100 (l cm)-'
As mentioned above, it preferably has an electrical conductivity of 101 (l·cm)-' or more. It is particularly preferable to use pitch-based carbon fibers because of their high conductivity. Pitch-based carbon fibers with an electrical conductivity of about 102(l·α)-1 are easily available. These carbon fibers could be easily powdered using techniques such as a ball mill, as in the case of activated carbon fibers. The size and shape of the carbon fiber powder to be used is not particularly limited, but it is preferable to use one having the same size as the activated carbon fibers, since this allows for uniform mixing and a large effect on conductivity. That is, the carbon fiber powder has an aspect ratio of 3 or more and 100
Below, preferably 5 or more and 50 or less, average diameter 1 to 30
pm, the electric type 4 degree is more than lOo(l·an)-', and the specific surface area is less than 100 l'g. The amount of carbon fiber powder to be mixed is not particularly limited, but it is usually 1 to 20% by weight, particularly preferably 4 to 8% by weight, based on the activated carbon fiber powder. Even if more than this is mixed, the conductivity of the electrode will hardly improve.

In the present invention, various polymeric resins such as polyethylene, polypropylene, etc. are used as the binder, but it is particularly preferable to use a Teflon binder (aqueous or alcoholic desversion). The amount of the binder added is preferably 5% by weight or more and 20% by weight or less based on the activated carbon fiber powder.

The invention! The electrode has achieved high density and high conductivity at the same time, and is extremely useful as a positive electrode for various kinds of batteries, especially secondary batteries. An example of its use as a secondary battery will be described below.

Examples of electrolytes for secondary batteries made using the electrode of the present invention include salts of cations and anions such as metal cations, quaternary ammonium ions, carbonium cations, oxonium cations, and pyridinium cations. can. The anion used here is αu4
-1BF4-18bF6-1sb (support)6-1Δ5F6
-1P top '6-1 total '2-, etc. can be mentioned. Particularly preferred anions are ClO4- or BF4-. Specific auxiliary electrolytes include LiCj+04, L
iBF4, LiA! l'F6, NaBF4, NaCJO
4J3u4N; CI! 04, KBF4, (06)15
)30BF4, NH4HF2, LiI, Liar, etc., but are not limited to these.

The organic solvent used as the electrolyte of the secondary battery is an organic non-aqueous solvent, and is preferably aprotic and has a high dielectric constant. Specific examples include, but are not limited to, propylene carbonate, r-butyrolactone, dimethyl sulfoxide, dimethyl formamide, acetonitrile, ethylene carbonate, tetrahydrofuran, dimethoxyethane, and dichloroethane.

These organic solvents may be used alone or as a mixed solvent of two or more.

The concentration of the electrolyte varies depending on the type of negative electrode or positive electrode used, the type of electrolyte, the type of organic solvent, etc., so it cannot be specified unconditionally, but it is usually 0.001 to 10 mol/l.
is within the range of

Oxygen and moisture present in the electrolyte or solvent may degrade battery performance, so it is desirable to sufficiently purify the material in advance using conventional methods.

The metal used as the negative electrode of the present invention is not particularly limited, but alkali metals, alkaline earth metals, metals of Group 3 and Group 4 of the periodic table, etc. are preferable, such as Li, N
a, KlBb, Cs%Be, Mg, Ca, Sr
, Ba1Sc, Y%La, Ti, Zr, AI,
Pb, Bi, KgSNi, etc. can be used. Alternatively, alloys of the above metals, such as Li-Mg alloys,
Examples include AI-hetg gold alloy, Li-k1g alloy, Li-a1 alloy, l, 1-Pb alloy, and the like. It is also possible to use conductive polymers such as carbon fibers, activated carbon fibers, polyacetylene, polyphenylene, etc., on which the above metals are supported.

Among the above-mentioned metals and alloys, lithium-based metals are particularly preferably used in view of high voltage and weight reduction of the battery. Examples of materials containing lithium-based metals include, in addition to metallic lithium, alloys containing metallic lithium or materials in which metallic lithium is supported on the surface.

In the present invention, if necessary, a porous membrane made of synthetic resin such as polyethylene, polypropylene, Teflon, etc. or natural fiber may be used as a diaphragm between the two electrodes. It is also preferable that the battery be sealed to prevent oxygen and moisture from entering the battery from the outside world.

Although the example of a secondary battery has been described above, it can also be used as a capacitor by using a similar electrolyte and using the activated carbon electrodes of the present invention for both electrodes.

〔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 1800 d, number of filaments 10
0Of, strength 10.5 g/d, elongation 7%) was used. Next, as a dehydration/carbonizing agent (8M4)2
1000g of each 509 of MO4 and (NH4)2KPO4
This aqueous solution was heated to 60°, the woven fabric was immersed in it for 5 minutes, and then the liquid was squeezed with a mangle and heated to 105°C.
and dried for 3 minutes. The acceptance rate of dehydrating agent is 109 by gravimetric method.
It was 6. The woven fabric with this dehydrating agent attached was heated to 210℃ for 3
50.0 per la width of the woven fabric when heated for 0 minutes. The shrinkage rate of the fiber was controlled by applying a low tension of 4096 g. Rough carbonization conditions of 330℃ x 10 minutes and that?
During heating in two steps at +400° C. for 20 minutes, a low tension of 30Q per ICm width of the woven fabric was applied, and the shrinkage rate of the fiber was set to 6096 when viewed from the starting PVA fiber. Note that the weight R1m fraction at that time was 55%. 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 B E 'l' method using N2 gas was 2300 mm. The X-ray diffraction intensity curve of this activated carbon fiber was measured using a rotating anisotropic X-ray diffraction instrument (Type) IAD-rA manufactured by Rigaku Denki. The measurement conditions were 40 kV 100 mA, CuK-a line (λ=
1.5418A), slit 1/2.0.15m++
+, set meal speed 1°/min, full scale 800
Measured by transmission method at cps. It was found that it should exist near 2θ or 25'' (Ip/Io
= o, o7).

The rough and fine internal structure was examined using solid-state high-resolution NMIt. Data points measured by MAS GATE method are 8, sampling points are 1.5
Measurements were conducted under the following conditions: 10,000 scans
Since a curve having a peak around 40 PPM was obtained, it was confirmed that the structure was centered on a phenyl group skeleton. No C-H absorption was observed in the surface reflection infrared, and it was confirmed that carbonization was almost complete. Further, the apparent specific gravity of this activated carbon fiber was 0.2.

Example 1 The 11 activated carbon fibers obtained in Synthesis Example 1 were ground for 24 hours using a ball mill to obtain powdered activated carbon fibers.

The particle size distribution was 99.6% below 350 mesh.

When observed using a scanning microscope, the activated carbon fiber powder had an average diameter of about 10 μm''C and an aspect ratio of about 15.The specific surface area of this powder was about 23 ood/cm.
g, and the conductivity is approximately 5 x 10-'(l・cIn)-
1 is Buddha.

The carbon fibers used were pitch-based carbon fibers (manufactured by Union Carbide) with an electrical conductivity of about 102 (l·cm)-'. This carbon fiber was pulverized using a ball mill under exactly the same conditions as above. The particle size distribution was below 350 mesh or 99.4%. The average diameter of this carbon fiber powder is 15μ, and the aspect ratio is about 20.
Met.

The powdered activated carbon fibers and powdered carbon fibers thus obtained were molded using a Teflon binder as a binder. The powdered activated carbon fiber used was 80% (weight%), the powdered carbon fiber was 6%, and the Teflon binder was 1496 (the Teflon binder was an aqueous dispersion of Teflon. The weight of the Teflon binder included was the dry weight). 170℃ after mixing each
Compression molding was performed to obtain a sheet with a thickness of about iMn. The electrical resistance of this sheet was 3×10'LΩ·cm)-'. Further, the apparent specific gravity was 0.6, which was greatly improved.

Comparative Example 1 A sheet having a thickness of approximately 1 mm was obtained in the same manner as in Example 1 by mixing 86% of the powdered activated carbon fiber obtained in Example 1 and 14% of the Teflon binder. The conductivity of this sheet is 6X
10-2 (l·cm)-', which was significantly lower than when powdered carbon fiber was mixed.

Comparative Example 2 70% of the powdered activated carbon fiber obtained in Example 1, 15% of Teflon binder, and 15% of conductive carbon powder [Ketsutun Black EC; manufactured by Lion] were mixed to produce the same as Example 1. Pressure molding was performed in the same manner.

The conductivity of the obtained sheet was 8 x 10-' (l・on
)-', which was significantly lower than when powdered carbon fiber was used.

Comparative Example 3 Stainless fiber [NASLON; ■Made by Nippon Seisen] 31rr
A thin metal wire was obtained by cutting into a length of m. 60% of the powdered activated carbon fiber obtained in Example 1, 259% of the above metal wire
6. 15% Teflon binder was added and mixed. Rough pressure molding was performed to obtain a sheet. The electrical conductivity of the obtained sheet is 5
×10° (l·cm)-', and the effect was not as great as when powdered carbon fiber was mixed. When observed under a microscope, the activated carbon fiber and the thin metal wire were found to be phase separated.

The most effective way to increase the conductivity of electrodes made of powdered activated carbon fibers was to mix powdered carbon fibers.

Usage example 1 The sheet with a thickness of about 1+++m obtained in Example 1 was cut into a sheet with a diameter of 1
It was punched out into a disk shape of α. A secondary battery using this as a positive electrode and metallic lithium as a negative electrode 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 rrtn.

The 11EN solution was prepared by dissolving lithium perchlorate in propylene carbonate at a concentration of IM/7.

Nickel expanded metal was used as the current collecting electrode on the positive electrode side. The output density of this secondary battery was measured at an open circuit voltage of 3V and was found to be 9 kW/&p. In addition, a lithium secondary battery was manufactured using the sample obtained in the comparative example, and the output density was determined, and the results are shown in Table 1.

The examples showed extremely low power densities, but the other power densities were greatly reduced.

Example 2 Commercially available activated carbon fiber (specific surface area approximately 2500rrVg, I
P/Io=0.4) was ground for 24 hours using a ball mill to obtain powdered activated carbon fibers. The particle size distribution was 99.596 below 350 mesh. When observed using a scanning electron microscope, the powdered activated carbon fibers had an average diameter of approximately 15 μm.
m, and the 7 spectral ratio was approximately 10. An electrode was produced in exactly the same manner as in Example 1 using the oven.

Comparative Examples 4 to 6 Electrodes were produced in exactly the same manner as Comparative Examples 1 to 3, except that the powdered activated carbon fiber obtained in Example 2 was used.

Usage Example 2 Usage Example 1 using the electrodes of Example 2 and Comparative Example 4.5.6
A lithium secondary battery was produced in the same manner as above. Table 2 shows the electrical conductivity of each electrode and the output density of a lithium secondary battery using the electrode.

The examples showed extremely superior output densities, while the other output densities were greatly reduced.

〔Effect of the invention〕

1 of the present invention! The electrode is extremely useful industrially as an electrical device for double-layer capacitors or lithium secondary batteries because it can simultaneously improve packing density and high conductivity.

Claims (1)

[Claims] (1) Mainly the aspect ratio is 3 or more and 100 or less,
Specific surface area is 100m^2/g or more, average diameter is 1 to 30
Micron powder fibrous carbon powder and aspect ratio of 3 to 1
00 or less, the specific surface area is less than 100 m^2/g, the average diameter is 1 to 30 μm, and the electrical conductivity is 10^0 (l・c
m) An electrode formed from a mixture with finely powdered fibrous carbon powder having a particle size of ^-^1 or more.