JPS60253163A - Laminated electrolytic cell - Google Patents

Abstract

PURPOSE:To obtain a method for manufacturing an electrolytic cell which is resistive to industrial use and obtain an electrolytic cell having excellent characteristics by utilizing aggregated carbon fiber for electrode and integrating it with a bipolar plate. CONSTITUTION:A conductive bipolar plate and electrode which is an aggregation of carbon fiber are previously laminated physically and chemically. For example, conductive carbon black of 30wt% and polyethylene powder of 70wt% are uniformly mixed, it is laid within the metal molds and a carbon plastic plate 5 is formed by the hot-press method. Next, the upper cover of metal molds is opened, a falt carbon fiber cloth is laided on the plastic plate 5, it is pressed with a light force. Therefore, an electrode 8 is joined to conductive carbon black plate 5 and it is laminated through spacers 6 and ion exchange films 7.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a laminated electrolytic cell using a novel electrode material, and more specifically, a layered electrolytic cell having a specific crystal structure and surface oxygen content. This invention relates to a stacked electrolytic cell using carbon fiber electrode material which is extremely advantageous for industrial production.

Relationship with conventional technology Since the energy crisis of 1973, energy issues have become widely recognized by all walks of life. At the same time as the development of new energy sources, the development of systems that include energy conversion, storage, transportation, and utilization for effective use of generated energy is also becoming important. Taking storage as an example, in large-scale power generation such as nuclear power and coal-fired power generation, which are expected to account for a large proportion of the power source mix in the future, it is necessary to maintain a constant output and generate power at a constant rate in order to maintain high efficiency. There is a growing demand for power storage technology that can appropriately store surplus power at night and release it during the day when demand increases to respond to fluctuations in demand (load leveling). However, the annual operating rate of major power generation facilities is below 60% and continues to decline.

In addition to pumped-storage power generation, which has been put into practical use but has losses due to power transmission and is subject to restrictions on location, there are other methods for storing power, such as new secondary batteries, flywheels, compressed air, and superconductivity. Various methods are being considered, but electrochemical operation using new batteries is the most promising, and for the time being it is considered the most viable alternative to pumped storage power generation as a solution system that includes transportation. In addition, the new secondary battery can be used with sunlight,
Natural energy such as wind and wave power? There are high expectations that it could be used as a backup device for power generation or as a battery for electric vehicles. As a secondary battery that can be applied to the above purpose,
Lead-acid batteries, sodium-sulfur batteries, lithium-iron sulfide batteries, metal-chloride batteries, redox flow batteries, etc. are currently being developed. Among these new types of secondary batteries, metal-halogen secondary batteries (excluding the negative electrode) and redox flow secondary batteries are battery active materials? It belongs to the so-called regenerative fuel cell, which uses a system in which energy is supplied from the outside and all electrochemical energy changes are performed within the cell itself. Among them, redox flow secondary batteries can be said to belong to the classic type of regenerative fuel cells.

This battery? Since electrochemical reactions, including electrochemical reactions, are generally heterogeneous phase reactions that occur on the surface of electrodes, electrolytic cells are inherently two-dimensional. Therefore, there is a drawback that the amount of reaction per unit volume of the electrode tank is small. Therefore, in order to increase the reaction amount per volume, that is, the current density, the electrochemical reaction field is converted to a 3'rK element, and examples of its application can be found in the above-mentioned regenerative fuel cells, waste water treatment, and electrolytic production of organic compounds. The electrochemical reactions in regenerative fuel cells are usually shown in Figure 1), (bl, (
The best method is to use a flow-through type electrolytic cell having a unipolar three-dimensional battery as shown in c). Figure 1 (al, et al+(c
), 1 is a diaphragm (separator), 2 is an electrolyte flow path,
3 is a current collector, and 4 is a monopolar three-dimensional battery. Especially (bl
The +EL type is a type in which all cells are laminated, and can be said to have a favorable structure from the viewpoint of secondary batteries that make large batteries.

Traditionally, three-dimensional electrodes in regenerative fuel cells have been made of nonwoven fabrics, woven fabrics, or porous carbon made of ordinary carbon fibers due to their electrical conductivity, chemical resistance, and economic efficiency. A board has been used. If the porosity of a porous carbon plate is increased to increase the reaction field noise, the strength of the carbon plate will decrease and it will be easily damaged during lamination, and it is difficult to accurately process thin plates with a thickness of g I II m. Difficult to use. An aggregate of carbon fibers is most preferable. FIG. 2 is a layout diagram of battery materials immediately before assembly of this redox flow secondary battery. The electrode fabric etc. is attached to the inside of the spacer 6 of a certain thickness using an adhesive 10. 1fJfl, there. This gluing is done to prevent short circuits at the inlet and outlet of the liquid, to make it easier to handle when there are 28 layers of electrolytic cells, but it is extremely detailed and takes time, and the adhesive dries or hardens. Time to? In short, it is not a manufacturing process that can withstand industrialization. This is especially a problem when producing a practical battery that is used in a series-stacked form in which all electrolytic cells are made of bipolar plates.

In the present invention, three-dimensional electrodes were studied in order to eliminate all the drawbacks associated with the conventional electrolytic cell assembly, and as a result,
This can be achieved by integrating with the current collector (or bipolar plate).
I found a solution.

Furthermore, the present inventors have also discovered that unless the internal structure, particularly the microcrystalline structure, and the amount of bound oxygen on the fiber surface of the carbonaceous single fibers constituting the electrode are within appropriate ranges, it is unlikely to be an effective electrode material, leading to the present invention. In other words, in conventional redox 70 secondary batteries using carbon fiber (typically iron-chromium redox flow secondary batteries), the oxidation-reduction reaction of chromium ions is slow, and the conductivity of the battery is low. In addition, problems such as the fact that hydrogen is generated during charging and the current efficiency of the battery tends to decrease have been cited as problems.

OBJECTS OF THE INVENTION The present invention relates to the internal structure and surface structure of carbon fibers of carbon fiber electrode materials used in flow-through electrolytic cells, and to providing an entire industrial method for assembling electrolytic cells.

In other words, the present invention has an average <002> plane spacing of 3.70λ or less determined by wide-angle X-ray analysis, and an average crystallite size of 9.70λ in the fcC axis direction. A carbonaceous fiber having a pseudographite microcrystalline structure of ON or higher and having a bonded oxygen atom number on the fcHt#I surface of at least 3% of the carbon atom number required for ESCASC external analysis is used as an electrode material, and is completely bipolar. By integrating it with the plate, we aim to provide an electrolytic cell production system that can withstand industrialization, as well as provide an electrolytic cell with extremely excellent characteristics of t1.7.

The present inventors conducted the following studies on the fiber internal structure and surface structure of a three-dimensional electrode made of carbonaceous fiber used in a flow-through electrolytic cell.

The production and tearing of the electrode for a flow-through type electrolytic cell according to the present invention is carried out, for example, as follows. The raw material fibers used in the present invention include:
It is carbonizable and has the fiber strength, elongation, etc. necessary for producing the target tissue, a specific internal crystal structure described later, and surface II!
Elementary concentration? It is essential to use everything you have.

For example, raw material fibers such as cellulose, acrylic, phenol, and aromatic polyamide fibers can be used. Pitch fibers made entirely of coal and petroleum are eligible raw material fibers, but
Since the fiber strength is weak and it is not necessary to undergo a step to form various aggregated forms, it is preferable to carry out carbonization to a certain extent and then to undergo a ninth step to obtain the desired structure. As for these single fibers, the thinner they are, the larger the outer surface area can be obtained and the more advantageous they are in terms of strength, and those with a denier of 0.5 to 15 deniers are particularly preferred. Next, short single fibers can be used to make non-woven fabrics, and can also be used to create knitted fabrics, woven fabrics, strings, and hybrid fabrics.
A single embroidered fiber? The fibers are bundled and made into warp yarns, preferably in the form of spun yarn or multifilament yarn. Next, use this yarn to create the desired structure, such as spun yarn, woven fabric, knitted fabric, etc. make. Next, the various fiber aggregates are treated with an appropriate flame retardant as necessary to make them flame resistant, usually under an inert atmosphere or an active atmosphere at a temperature of 400°C or less. Let's do it.

Next, carbonization is carried out at 500°C or higher, preferably 1100°C or higher. Is it possible to create a predetermined internal crystal structure through such operations? The carbon fiber aggregate with which it has is a special feature.

The concentration of surface enzyme atoms, which is important in the present invention, can be increased by subjecting the carbon fibers having all the internal crystal structures described above to a total dry oxidation treatment. For example, 1 x i
The treatment is carried out in a nitrogen atmosphere with an oxygen partial pressure of 0''-' torr or higher, so that the weight yield is in the range of 65 to 99%.The treatment temperature is usually preferably 400°C or higher.Low temperature ( For example, at 200 to 300'C), the reactivity of the carbon to be treated decreases, so the oxidation effect cannot be obtained.If the oxidation treatment is carried out in a fully wet manner, there will be problems such as the formation of glabellar compounds and the generation of harmful gases during treatment. Not only is there more, but the cost is nearly 100 times higher, and it cannot be said to be industrially advantageous.

By performing the dry oxidation treatment as described above, many of the edges of the plane perpendicular to the C axis of the pseudographite microcrystals can be exposed on the fiber surface, and 'rI1. All X atoms can be formed. This oxygen atom is generated as a carboxyl group, a phenolic hydroxyl group, a carbonyl group, a quinone group, a lactone group, a free radical oxide, etc., and these reactive groups greatly contribute to the electrode reaction, thereby increasing the electrical conductivity. (Voltage efficiency) f: It can be increased.

As shown above, it was determined from wide-angle X-ray analysis that it has a pseudographite microcrystalline structure in which the (002> plane spacing is less than 3.70λ on average and the crystallite size in the C-axis direction of the housing is more than 9.0λ on average. Moreover, by using carbon fiber as an electrode material in which the number of bonded oxygen atoms on the surface of the ESCASC fiber is at least 3%, preferably 6 to 16% of the number of carbon atoms, the characteristic values of the battery can be improved. Certain current efficiency and conductivity will be significantly improved.

In other words, as described above, wide-angle X-ray analysis (the analysis method is described below) is performed when the two-stranded <002> plane spacing is on average 3.70 A or less and the crystallite size in the p and txc axis directions is on average 9.0 Å.
A carbonaceous fiber with a pseudographite microcrystalline structure? By using it as an electrode material, the amount of hydrogen generated at the negative electrode during charging was suppressed, and the current efficiency was able to be enhanced overall. <0
02> When using carbonaceous material with low crystallinity in which the interplanar spacing exceeds 3.7 OA' and the crystallite size in the C-axis direction is less than 9.0 λ on average, the amount of hydrogen generated at the negative electrode during charging is large. ,′σ.

Liquidity cannot be increased. Although it is not clear why the current efficiency is increased or decreased by using carbon fibers with a specific crystal structure with high crystallinity as electrode materials, as the crystal structure develops, the hydrogen overvoltage increases and charging It is thought that reduction of ROM complex ions sometimes occurs selectively, thereby increasing current efficiency.

On the other hand, carbon atoms with a ratio of the number of bonded oxygen atoms to the number of carbon atoms (hereinafter referred to as 0/C ratio) of 3% or more on the MR fiber surface as determined by ESCA surface analysis (described later in the analysis method) as described above. By using quality fibers in the tIL cedar material, the electrode reaction rate and shear conductivity could be significantly increased.
S W with a fiber surface O/C ratio of less than 3% by CA analysis
When using carbonaceous fibers with a low concentration of 1 element, the electrode reaction rate during discharge is low and the conductivity cannot be increased. Like this carbonaceous lIt fiber with many oxygen atoms bonded to the surface of the VC material fiber? By using it as an electrode material, conductivity,
It is not clear why the voltage efficiency of the replacement n is increased, but the rR atoms on the surface are persistent in the 41 effect during childbirth, desorption of complex ions from carbon fibers, complex exchange reactions, etc. ) Things and thoughts! climb.

The inventors of the present invention then investigated an industrial method for assembling a carbon fiber aggregate having the above-mentioned characteristics into a battery. Current collector plate or bipolar plate for separating and stacking 11
The plate was made by cutting out 7 carbon/graphite sintered bodies.
It was extremely expensive. Therefore, it would be a good idea to replace the conductive glass, which has been popular in many places in recent years, with this case.

Chemical resistance i! Considering this, vinyl chloride resin or polyolefin resin mixed with carbon black or Koji fiber is preferably used. Do we have bipolar plates, separators, electrode materials? Instead of arranging them separately and assembling them as shown in Figure 2, the electrode material is directly joined to the bipolar plate 5 (current collector plate) as shown in Figures 3 (a) and (b) for post-electrolysis. I decided to assemble a tank storage. In this case = W, the carbon plastic bipolar plate is particularly effective and rare. That is, immediately after carbon black and resin powder were mixed and pressed into a plate shape, or after that, the carbon fiber aggregates according to the present invention were thermally bonded directly at a bonding temperature or higher (6 degrees). Compared to the method shown in FIG. 2, in which the electrode material is completely bonded to the separator and then assembled after assembly, this method is much simpler and is industrially more advantageous. The aggregate form of carbon fibers that can be used is preferably Yli cloth or spun yarn as shown in Figure 3-) and (b), but twisted tow-like materials, felt, etc. can also be used without problems. The easiest way to join the conductive bipolar plate and the i-electrode material is to do it thermally without using any additional materials. Can be used.

3rd (2) (a), (bl is an assembly diagram that can be used as a single N, but since the y-tree-like method is the same when stacking, it will be omitted.

Note that the <002> plane spacing (do
ox), crystallite size in the C@ direction (Lc), current efficiency, conductivity, and O/C ratio determined by ESCA are determined by the following method.

■<002> Plane spacing: doot carbon fiber knitted fabric? Powder it in an agate mortar, add about 5 to 10 tons of high-purity silicon powder for X-ray standards as an internal standard substance to the sample, mix it, fill it in a sample cell, and make CuKa.
A wide-angle X-ray diffraction curve is measured using a transmission diffractometer method using a radiation source.

To correct the curve, use the following simple method without making corrections for so-called Lorentz, polarization factors, absorption factors, atomic scattering factors, etc. In other words, the baseline of the peak corresponding to <002> diffraction is subtracted by 1, the real intensity from the baseline is plotted again, and the <002> corrected intensity curve is obtained. obtain. Find the midpoint of the line segment where a line parallel to the angular axis drawn at two-thirds of the beak height of this curve intersects the intensity curve, correct the angle at the midpoint using the total internal standard, and then 6 Double the angle of refraction ・CuKα
According to the following Bragg equation, <002>
Increase the distance between the surfaces.

λ dot−2 θ λ : 1.5418λ 01 Diffraction angle ■Crystallite size in C-axis direction Lc) In the corrected diffraction intensity curve obtained in the previous section, the so-called half-width β gold at the position half the peak height The size of crystallites in the C-axis direction can be determined using

There are various discussions about the shape factor K, but K=0.9
0i was adopted. λ and θ have the same meaning as in the previous section.

■Cell current efficiency Complete construction of the small flow-through type electrolytic cell shown in Figure 2, repeated charging and discharging at various constant current densities, and testing of electrode performance. For the positive electrode, a 4N hydrochloric acid acidic water bath solution with a concentration of ferrous chloride and ferric chloride of 1 M/l each was used, and for the negative electrode, a 4N hydrochloric acid acidic water bath solution with a concentration of 1 M/l of ferrous chloride and ferric chloride was used.
l of 4N hydrochloric acid acidic aqueous solution? Prepared.

The amount of catholyte and anode is in large excess compared to the amount of anode, so that we can focus on the characteristics of the anode. The electrode area is 10 d1, and the liquid flow rate is 5 ml per minute. Current density 16.40 mA/-
I conducted a test with the same value during charging and discharging. In a one-cycle test that begins with charging and ends with discharging, the amount of electricity required for charging is extracted by a constant current discharge at Q1 coulombs, 0.2 V-1, followed by a foot potential discharge at < O, S V. The amount of electricity is Q! Let lQs coulomb,
Calculate the current efficiency using the following formula.

If a reaction other than the reduction of Cr to Cr''+ occurs during charging, for example a side reaction such as reduction of I(), the amount of electricity that can be taken out will decrease and the current efficiency will decrease.

■Cell conductivity The charging rate is the ratio of the amount of electricity taken out in the casing during discharging to the theoretical amount of electricity Qth required to completely reduce Cr"t Cr"+ in the negative electrode liquid. From the slope of the current-to-voltage curve at 50%, the cell resistance (Ω-) and its reciprocal, the cell conductivity (5cIs-1), can be determined.The greater the cell conductivity, the greater the redox reaction of ions at the electrode. The discharge occurs quickly, the discharge potential is high at high current density, and the voltage efficiency of the cell is high, making it an excellent electrode.

The tests in ■ and ■ were carried out at 25°C and 1 hour.

■Measurement of C10 ratio by ESCA The device used to measure the 0/C ratio by ESCA or X-ray electron fractionation method, abbreviated as XPC, is Takashi ESC.
A 750, and all ESCAPAC 760 were used for analysis.

Each specimen was punched into 6 diameters and conductive paste (from υ0
The samples attached to a thermal sample stand were used for analysis.

Before measurement, the sample was heated to 120°C and vacuum degassed for 3 hours or more. WifKα radiation (1253,6eV) was used as the radiation source, and the vacuum level inside the device was 10-' torr at 7t.Measurements were made for the C1g and O1e peaks, and each peak was measured using an ESCAPAC760 (J, H, 5 cofield
Based on the correction method using <)t-correction analysis, each peak area? demand. Obtained 1 and the area is #' for C1s
i1.00, Olg is multiplied by the relative intensity of 2.85, and the area is directly calculated from the surface (oxygen/carbon atomic ratio in %).

The present invention will be explained in detail below using comparative examples and examples, but the present invention is not limited to these examples.

Effects of the Invention The disassembly tank according to the present invention suppresses the amount of hydrogen gas generated during charging, can comfortably improve current efficiency and cell conductivity, and simplifies the entire battery manufacturing process, making it industrially viable. This provides a great deal of practical utility.

Comparative Example 1 A double-sided knitted fabric was produced using a 4-gauge double-sided knitting machine using a 20 count twin yarn made of 2.0 denier B raw cellulose fibers obtained by thoroughly desulfurizing, bleaching, and washing with water. Organize! Hi.

This knitted fabric has a basis weight of 4249/- and an apparent density of 0.
37097 cd, thickness σ1.15 silk, this knitted fabric was scoured, dipped in an aqueous solution of ammonium chloride, squeezed and dried, and the amount of ammonium chloride impregnated was 10 times the dry weight of the fabric. After heating at 270℃ in an inert gas stream for 60 minutes.
After heating for 4 minutes, flame resistance treatment was performed for 4 times, then the temperature was raised to 1600°C at a temperature increase rate of 400 degrees per hour, and held for 30 minutes to complete carbonization. After cooling, 5 strands of carbon fiber H1 knitted fabric A? Obtained. The basis weight of this item is 2709/, t, density 0.26 c
c/I derotz 几.

Further, this product was dispersed at 900° C. in an inert gas with a total oxygen partial pressure of 200 torr to prepare an electrode for a three-dimensional flow type electrolytic cell. X M for such knitted fabric B
The ys analysis result is d6oz = 3-60A s Lc =
'lL8λ,'! 7t O/C ratio tl: 10.2
%Met. ICHI x 10 cm from this fabric
Cut out two square pieces and fix them one by one in silicone resin within the frame of the two spacers shown in Figure 2.
The application of the adhesive was sloppy and hardening took a lot of effort. Using a graphite plate as the current collector plate 5, the solder conductivity and current efficiency were determined by the test method described above.
It is 93.8% and the electrode characteristics are excellent and excellent.

Comparative Example 2 The fabric At-1 obtained in Comparative Example 1 When the battery performance of the entire electrolytic cell assembly was measured in the same manner as in Comparative Example 1, the current efficiency was 90.
%, the conductivity was 0.15S, and the electrode properties were poor.

The doot + IJC of Fabric A was the same as Fabric B, but the 0/C ratio was 2.8%.

Example 1 30% by weight of conductive carbon black and 70Jl-% of powdered polyethylene were uniformly mixed (1. Placed in a mold and used to prepare a carbon plastic plate using a hot press method. Open the top lid of the fabric, place it on a 1 x 10 CM plastic plate of Fabric B prepared in Ratio Example 1, and press it lightly again (-) in Figure 3 (al
An electrode of No. 8 was made by sliding it onto a conductive carbon plastic plate. The specific resistance of the conductive carbon plastic was 0.280 scratches, which was higher than that of graphite, but the electrode characteristics were a current efficiency of 93.4% and a cell conductivity of 1i0.
It showed performance close to that of the 40s Bei-1 and the Fuchi IVC.

Fruiting example 2 A single fiber of 2.0 denier regenerated cellulose hawk fiber is fully grown,
The entire spun yarn of 5,000 denier was made with 3 twisted yarns of 9 strands of 15,000 denier (a yarn similar to a string was made and treated in the same manner as in obtaining fabric B7 of Comparative Example 1), passed through a high temperature of 1800°C, and was oxidized in air. A 6,050 denier carbon fiber spun yarn was bonded to the same carbon plastic plate as in Example 1 by aligning 5 non-parallel lines in the width of the yarn.About 1 point was found in the thickness of the spun yarn. Therefore, the battery was assembled using a spacer with a thickness of 1.3 mm as shown in Figure 3 (bl), and the battery characteristics were measured. It was found that excellent battery characteristics were obtained.The carbon jj & male doot used was 3.64 people + Lc was 10.8 A, and O/C was 11.2%.
Deat t0

[Brief explanation of the drawing]

Figure 1 (b) l, fbl, (c) f'i is a schematic diagram showing a flow-through type electrolytic cell using all three-dimensional electrode materials, and Fig. 2 shows the current efficiency of the three-dimensional electrode material according to the present invention. It is an explanatory diagram of a method that uses both feet. Further VC, Figure 3 (al, (bl) shows the assembly port of the electrolytic cell according to the present invention. 1; diaphragm 2; electrolyte flow path 3; assembly 4; or bipolar temporary 6; spacer 71 ion exchange membrane 8; carbon fiber electrode 9; active material aqueous solution flow path JO; adhesive patent applicant Toyobo Co., Ltd. No. 1121 (a) (b) (C) No. 2121 No. 3121 ( CI) No. (

Claims (1)

[Claims] (1) The conductive bipolar plate and the electrode, which is an aggregate of carbon fibers, are physically or chemically bonded in advance.
A laminated electrolytic cell characterized in that f″L7t is assembled later. (2) The electrode material is d60t≦3.7A, O/C≧3.0
%. Lc≧9. Claim i consisting of OA carbon fiber
The electrolytic cell according to item 11. (31) The electrolytic cell according to claim TL+, wherein the electrode material is a carbon fiber aggregate having a hybrid composition wt of woven, knitted, string, felt, or the like. (4) The conductive bipolar plate is The electrolytic cell according to claim 1, comprising carbon black, carbon fiber, or a mixture thereof and a resin.