JPH0711969B2 - Metal-halogen secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal-halogen secondary battery,
More specifically, it relates to a secondary battery in which a specific porous carbon fiber woven fabric, knitted fabric or the like is applied to the positive electrode.

[Conventional technology] Since the energy crisis of 1973, energy problems have been widely recognized by various layers. At the same time as the development of new energy sources, it is becoming important to develop systems that include the conversion, storage, transportation, and use of energy that effectively uses the energy generated. Taking storage as an example, in large-scale power generation such as nuclear power and coal-fired power, which is expected to occupy a large proportion in the future power supply composition, it is necessary to maintain constant output and perform steady power generation in order to maintain high efficiency. Properly store surplus electricity at night and release it when demand increases during the day,
There is an increasing demand for a power storage technology capable of responding to fluctuations in demand (load leveling). Even now, the annual operating rate of major power generation facilities is below 60% and is continuing to decline. Electric power storage methods have been put into practical use, but there are losses due to power transmission, and in addition to pumped-storage power generation, which places restrictions on locations, various methods such as new secondary batteries, flywheels, compressed air, and superconductivity Is being considered.

[Problems to be Solved by the Invention] Above all, electrochemical operation using a new battery is predominant, and is considered to be the most viable method to replace pumped storage power generation as a solution system including transportation for the time being. Further, the new type secondary battery is expected to be used as a backup device for power generation using natural energy such as sunlight, wind power, and wave power, or as a battery for electric vehicles.

Lead storage batteries, sodium-sulfur batteries, lithium-iron sulfide batteries, metal-halogen batteries, redox flow batteries, etc. have been developed as secondary batteries applicable to the above purpose. Among them, the zinc-halogen battery is a liquid circulation type, it is easy to adjust the battery output, maintenance is easy with a low-temperature operating aqueous solution battery, the battery capacity can be easily adjusted with the liquid tank capacity, and both polarities are active. Substances are abundant in resources and inexpensive, have a high theoretical energy density, and have a simple battery reaction so that the battery configuration is simple and can be made from inexpensive materials. Therefore, development has been rapidly advanced in recent years.

However, there are some problems that must be solved in order to put the metal-halogen battery into practical use. Among them, how to reduce the halogen reduction reaction at the positive electrode (halogen electrode) during discharge, quickly and effectively Whether to proceed or not directly affects the energy efficiency of the battery, which is an important technical issue. Conventionally used as a positive electrode
As an inexpensive example to replace the Pt plate, there is a thin carbon plastic electrode plate or carbon sintered plate in which a mixture of electrically conductive powder carbon and powder resin is heat press molded, but discharge progresses at these electrodes and the positive electrode active material When the concentration of the was lowered, the potential dropped remarkably, and the energy efficiency of the battery remained at a low value. In particular, a marked decrease in potential was observed with high current density discharge.

[Means for Solving the Problems] The inventors of the present invention have arrived at the present invention as a result of intensive research to improve various drawbacks associated with such conventional carbon plastic electrodes and carbon sintered plates.

That is, the present invention provides a porous carbon fiber as a positive electrode, which has a pore volume of 0.1 cc / g or more in the diameter range of 30 to 1000Å and an electric resistivity of a single fiber of 5 × 10 ⁻² Ω · cm or less. A metal having a fiber density of 0.1 g / cc or more and a woven cloth or knitted cloth bonded to the surface of an electrode substrate such as the carbon plastic electrode plate or the carbon sintered plate. −
It is a halogen secondary battery.

[Operation] The reduction reaction of halogen in the carbon plastic electrode or the carbon sintered plate does not proceed because the surface of the electrode is smooth and the actual reaction surface area is small, so that when the halogen concentration decreases, the amount of halogen diffusion and adsorption to the electrode surface It is considered that the amount decreases and so-called polarization occurs. Therefore, the inventors of the present invention, for example, etched the surface of the carbon plastic electrode by various methods to increase the surface area, or produced an electrode using powdered activated carbon instead of powdered carbon, but the effect was small. However, as in the present invention, an electrode in which a woven cloth or knitted cloth made of porous carbon fibers is bonded to the surface of an electrode base material made of, for example, the carbon plastic plate or the carbon sintered plate is prepared, and metal-halogen 2 When the battery was used for the next battery and charged and discharged, the positive electrode potential was extremely high even when the halogen concentration was lowered, and the energy efficiency of the battery was significantly improved. Moreover, the pore volume of 30 to 1000Å is 0.1cc / g.
When a woven fabric or knitted fabric made of porous carbon fiber having a specific resistance of 5 × 10 ⁻² Ω · cm or less and having a fiber density of 0.1 g / cc or more is used, voltage, It was found that excellent current efficiency values were obtained and that the electrode performance was comparable to that of expensive platinum plates. That is, when the distribution of so-called micropores having a diameter of less than 30Å becomes the main, the pore diameter is so small that the diffusion coefficient of the halogen dissolved in the aqueous solution of the metal halide salt is too small to effectively work in the electrode reaction. Further, if the pores having a pore diameter of more than 1000Å are mainly used, the surface area of the entire porous carbon fiber becomes small, which is not preferable. Furthermore, the pore volume in the diameter range of 30 to 1000Å is 0.1cc /
In the case of a sheet-like material made of a porous carbon fiber having less than g, especially a nonwoven fabric, the surface area per unit volume is small and the effect of the present invention cannot be obtained.

The electrical resistivity of monofilament is the same as that of ordinary porous carbon fiber.
It is in the vicinity of 10 ⁻¹ Ω · cm, and it is not preferable to use a sheet-like material made of these single fibers because the internal resistance of the battery becomes high. A battery with extremely high voltage efficiency can be obtained by using a sheet-like material made of porous carbon fiber having a single fiber specific resistance of 5 × 10 ⁻² Ω · cm or less. And the specific resistance of single fiber is 5 × 10 ^-2 Ω ・
It was found that the use of a porous carbon fiber sheet having a size of cm or less increases the reduction reaction rate of halogen on the electrode surface as well as the internal resistance of the battery, increasing the electrode potential is an important advantage that cannot be overlooked. It was Fiber density is 0.1g
If it is less than / cc, there is less contact between fibers, the electrical resistance increases, the internal resistance of the battery increases, and the voltage efficiency decreases, which is not preferable. Furthermore, the fiber density is 0.1 g /
If it is less than cc, fibers are likely to fall off during the production of the electrode, which causes a problem in processing.

The raw material fiber used in the present invention may be carbonizable as long as it is a cellulosic fiber from the viewpoints of easiness of carbonization, easiness of development of porosity, strength and elongation of porous carbon fiber, and the like.
Acrylic, phenolic, petroleum and coal pitch fibers can be used advantageously.

The woven fabric made of porous carbon fibers is a cloth-like product in which porous carbon yarns in which a plurality of porous carbon single fibers are bundled are crossed vertically and horizontally. For example, a spun yarn made of organic material that can be carbonized or a cloth-like product made by crossing filament yarns in the longitudinal and transverse directions is used as a starting material, which is flame-resistant, carbonized, and made porous to be made of porous carbon fiber. It is possible to make a woven cloth, or it is possible to make a cloth by weaving the carbonized or porous yarn. Any woven structure may be used as long as it is commonly used, and for example, plain weave, twill weave, satin weave, satin weave and the like can be selected.

A knitted fabric made of porous carbon fibers means a spun or filament yarn made of a carbonizable raw material organic material as a circular knitted fabric or a warp knitted fabric, for example, double dampey, double cord,
Half, half back, interlock, jacquard,
It means a porous carbon fiber cloth that maintains the original structure obtained by subjecting a cloth having a structure such as mock loading and ribs to flame resistance, carbonization and porosity.

As a method for flameproofing and carbonizing the above-mentioned organic fibers or sheets, an appropriate method must be selected according to the organic matter constituting each fiber. In particular, it is necessary to pay attention to flame resistance as is well known. As a method of imparting porosity, finally, the fiber has a pore volume in the range of 30 to 1000 Å and a pore volume of 0.1 cc /
Any method may be used as long as it has g or more.
A porous carbon fiber cloth may be obtained by flameproofing and carbonizing a yarn or cloth made of porous organic single fibers. Also, as a method of obtaining activated carbon fiber
The activation method at a temperature of 400 to 1000 ° C is effective as the simplest method. The activation method using a metal catalyst described in Japanese Patent Application No. 56-114648 can also be used particularly advantageously for this purpose.

As the etching of the carbon fibers, the method using the oxidizing gas as described above is mentioned, but it goes without saying that other methods can be used both wet and dry.

In order to reduce the internal resistance of the battery and increase the redox reaction rate of halogen at the positive electrode, the electrical resistivity of the single fiber should be 5 × 10 ^-2 Ω · cm or less. 1000
A high temperature treatment of not less than 0 ° C may be performed, or conversely, a carbon fiber group that has been subjected to a high temperature treatment in an inert gas may be made porous.

The pore diameter and the pore volume of the porous carbon fiber in the present invention are in the range of diameter 30 to 300 Å using the adsorption side nitrogen gas adsorption isotherm at the boiling point of liquid nitrogen under normal pressure by using Cranston-Incray (Cranston- InKIey) calculation method, the range of diameter 300-1000Å is measured by mercury porosimetry, and the pore solution of 30-1000Å (hereinafter abbreviated as ▲ TPV ¹⁰⁰⁰ ₃₀ ▼) is calculated by the sum of both. Is. Note that the relationship between the thickness of the multi-molecular adsorption layer (t) and the relative pressure (P / Ps) in nitrogen adsorption is t (Å) = 4.3 [5 / ln (Ps / P)] ^1/3 Frenkel-Halsey ) Was adopted.

The electrical resistivity of the porous carbon fiber was measured as follows.

An appropriate number of sampled monofilaments are lined up, both ends are fixed with a conductive adhesive, electricity is applied, and the resistance R (Ω) of the fiber is determined from the voltage and current values between the adhesives. Also, measure the length L (cm) between the conductive adhesives. When the single fiber is bent, the substantial fiber length is obtained with a microscope or the like. Next, the fibers are removed, and the total cross-sectional area S (cm ² ) in the direction perpendicular to the fiber method is obtained by a microscope, and the electrical resistivity P (Ω · cm) in the fiber direction is calculated by the following formula.

However, the measurement is carried out by performing the same drying as in the previous section in a dry atmosphere at room temperature and a relative humidity of 5% or less.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The invention is not limited to the examples.

[Examples] Comparative Example 1 A mixture of conductive carbon powder and polyolefin resin powder was uniformly mixed so that the amount of the conductive carbon powder was 30% by weight, and a fixed thickness was provided on the bottom of a mold set at 10 ° C higher than the softening point of the resin. Then, it was hot-pressed to prepare a carbon plastic plate having a thickness of 1.0 mm and a size of 10 cm square. This plate was placed in one chamber of a flow-through type electrolytic cell having a cation exchange resin membrane as a separator to serve as a positive electrode, while a 99.99% rolled zinc plate was placed in another chamber to serve as a negative electrode. A certain amount of electrolytic solution of zinc bromide concentration of 3.0 mol / l and potassium chloride concentration of 4.0 mol / l was circulated in the electrolytic cell negative electrode chamber, while zinc bromide and potassium chloride had the same concentration as the negative electrode liquid in the positive electrode chamber. , Circulate an electrolyte solution containing 3.0 mol / l bromine, and carry out a constant flow discharge at a current density of 40 mA / cm ² at room temperature. The bromine concentration in the positive electrode electrolyte solution and an Ag / AgCl electrode with a Luggin capillary are used as reference electrodes. As a result, the unipolar potential of the positive electrode was observed. The results are shown in Table 1. The result of using a platinum plate for the positive electrode is also shown.

A bromine concentration of 2.0 M / l corresponds to the initial stage of discharge, and 0.5 M / l corresponds to the final stage of discharge. It can be seen that the carbon plastic electrode has a large potential drop at the end of discharge.

Comparative Example 2 Several kinds of twill fabrics having different basis weights were prepared using spun yarns having different counts and made of regenerated cellulose fibers having a single fiber of 2.0d. Also, double-sided knitted fabrics were knitted using spun yarns composed of 2.0d regenerated cellulose fibers having different counts as single yarns, and several knitted fabrics having different basis weights were prepared.

These woven fabrics and knitted fabrics are immersed in an aqueous solution of dibasic ammonium phosphate, squeezed, and dried to impregnate the dibasic ammonium phosphate with 10% of the weight of the fiber, and then 270
Heat in an inert gas stream at 30 ° C for 30 minutes, then from 270 ° C to 8 ° C.
It takes about 90 minutes to raise the temperature to 50 ° C, and then it is treated for 30 minutes in a gas flow containing 40% by volume of steam, with a basis weight of 45 to 50 g / cm ²
The resulting porous carbon fiber woven fabric was designated as A, and the knitted fabric was designated as M. Further, the steam activation time was set to 60 minutes, and the woven fabric having the same basis weight as A and M was set to B, and the knitted fabric was set to N. Further, the same treatments as those for obtaining the fabrics A and M are applied to the raw fabrics for obtaining the B and N, and the obtained porous carbon fiber fabric is dipped in an aqueous solution of iron chloride.
Impregnated with iron chloride equivalent to 4.3 and 4.7 wt% as Fe,
After drying, 100 ° C in a nitrogen gas stream containing 40% by volume of steam
More than 850 ℃, hold for 15 minutes, cooled in an inert gas, washed with 1N-HCl solution, washed with water and dried.
The porous carbon fiber woven fabric of 50 g / cm ² was designated as C, and the knitted fabric was designated as P.
The porous carbon fiber cloths A, B, C, M, N, obtained as described above,
P was laid on the bottom of the mold described in Comparative Example 1 and the carbon plastic powder mixture used in Comparative Example 1 was also applied to the same to give a uniform thickness, which was hot pressed to a thickness of 1 mm and a size of 10 cm square. An electrode (positive electrode) in which a porous carbon fiber cloth was bonded to the surface of the carbon plastic plate of was produced.

A discharge experiment of a zinc-bromine battery using these electrodes according to the present invention as a positive electrode was conducted in the same manner as in Comparative Example 1, and the results shown in Table 2 were obtained.

Example 1 The fabrics A, B, C, M, N and P obtained in Comparative Example 2 were heat-treated at 1050 ° C. in an inert gas to give AH, BH, CH and MH, respectively.
Fabrics called NH and PH were obtained. All of the fabrics showed some weight loss and shrinkage, which offset each other and the density remained almost unchanged. There was no change in ▲ TPV ³⁰⁰⁰ ₃₀ ▼. However, the electrical resistivity showed a remarkable decrease. Table 3 shows the results of the same battery test as for the cloth in Comparative Example 2. It can be seen that among the electrodes according to the present invention, the electrode to which the cloth such as BH, CH, PH or the like is bonded has already exceeded the performance of the Pt plate.

Here, by comparing Table 2 (Comparative Example) with Table 3 (Example), it can be summarized as follows. For comparison, those whose pore volume did not satisfy the conditions of the present invention (fabrics A, M, AH, MH) were excluded. That is, the pore volume satisfies the conditions of the present invention, but the single fiber specific resistance does not satisfy the conditions of the present invention (fabric B, C, N, P: hereinafter referred to as Comparative Example group), It was examined how the single fiber specific resistances satisfying the conditions of the present invention (fabric BH, CH, NH, PH: hereinafter referred to as Example group) were improved.

I. Comparative example group Potential average at the beginning of discharge Average potential at end of discharge Rate of potential decrease from the initial stage of discharge to the final stage of discharge II. Example group Potential average at the beginning of discharge Average potential at end of discharge Rate of potential decrease from the initial stage of discharge to the final stage of discharge As is clear from comparison of the above calculation results, the potential at the end of discharge is significantly improved by the invention (0.64 → 0.74).
In addition, the potential reduction rate from the initial stage to the final stage is significantly suppressed (18% → 10%) in the present invention. Therefore, a battery constructed by assembling a number of such excellent electrode base materials is
It is understood that the energy efficiency will be much better.

Comparative Example 3 A non-woven fabric having a weight per unit area of 130 g / m ² was manufactured by a needle punching method using a regenerated cellulose fiber having the same single fiber thickness of 2.0 d and a length of 76 mm used in Example 1 as a raw material, and the same method as in Example 1 was used. After performing the flameproofing treatment and the flameproofing treatment at 850 ° C., steam activation was performed at 850 ° C. for different times to obtain two types of activated carbon fiber nonwoven fabrics S and T having a basis weight of 60 g / m ² and 43 g / m ² . . The nonwoven fabric S is dipped in a solution of magnesium acetate, squeezed and dried to impregnate 3.2% by weight of magnesium acetate corresponding to magnesium acetate, and 100% in a nitrogen gas containing 40% by volume of steam.
C. to 850.degree. C., held for 10 minutes, cooled in a nitrogen stream, washed with acid and washed with water to obtain an activated carbon fiber nonwoven fabric U. A part of the nonwoven fabric U was heat-treated at 1050 ° C. in an inert gas and cooled to obtain a nonwoven fabric U. With respect to the activated carbon fiber nonwoven fabrics T, U, and UH, an electrode plate was produced by the same method as in Comparative Example 2 and a discharge experiment was conducted.

The results are shown in Table 4. Performance is improved compared to carbon plastic electrodes, but the potential is lower. In addition, the number of fibers dropped off was especially large during the production of the electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Fukatsu 2-1-2 Katata, Otsu City, Shiga Prefecture (56) Reference JP-A-59-96662 (JP, A)

Claims (1)

[Claims] 1. A pore volume in the range of 30 to 1000Å in diameter is 0.1c.
c./g or more and the electric resistivity of the single fiber is 5 × 10 ^-2 Ω ・
Includes porous carbon fiber that is less than or equal to cm, and has a fiber density of 0.1 g /
A metal-halogen secondary battery in which a woven fabric or knitted fabric of cc or more is bonded to the surface of an electrode base material for a halogen electrode.