JP2002319401A - Hydrogen storage alloy electrode paste, hydrogen storage alloy electrode and hydride secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydride secondary battery in which conductivity of the hydrogen storage alloy electrode is improved and charging and discharging cycle characteristics are superior. SOLUTION: As an active substance of the hydrogen storage alloy, carbon black water dispersion that is dispersed with carbon black using a sulfonic acid group contained-polymer and an emulsion that is dispersed with a binder by using an emulsifying agent are contained and a hydrogen storage alloy electrode paste is prepared. And by applying the hydrogen storage alloy electrode paste on a conductive base material, and drying, a hydrogen storage alloy electrode is manufactured. And using the hydrogen storage alloy electrode as an anode, a hydride secondary battery such as a nickel hydrogen storage battery and an air battery are constructed. It is desirable that poly-N- vinylacetamide is contained as an thickener in the above hydrogen storage alloy electrode paste, and as the above sulfonic acid group contained-polymer, naphthalenesulfonic acid formalin condensate is desirable, and as a binder, a copolymer of styrene and 2-ethylhexylacrylate is desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a paste for a hydrogen storage alloy electrode using a hydrogen storage alloy as an active material, and a paste obtained by applying the paste for a hydrogen storage alloy electrode to a conductive substrate and drying the paste. The present invention relates to a hydride secondary battery represented by a nickel-metal hydride storage battery using an occlusion alloy electrode and the hydrogen storage alloy electrode as a negative electrode.

[0002]

2. Description of the Related Art Nickel-metal hydride storage batteries, which are the most in demand among alkaline storage batteries, use a hydrogen storage alloy capable of storing and releasing hydrogen reversibly as an active material of a negative electrode. , A positive electrode using nickel hydroxide as an active material, a separator, and an alkaline electrolyte.

In the above nickel-metal hydride storage battery, the active material of the hydrogen storage alloy electrode constituting the negative electrode is La or a rare earth hydrogen storage element composed of an element selected from misch metal (Mm), Ni, Co, Mn and Al. Alloys and Laves hydrogen storage alloys composed of Zr, Ni, V and Mn are well known, but rare earth hydrogen storage alloy powders are generally widely used. Then, the hydrogen storage alloy electrode is prepared by dispersing the powder of the hydrogen storage alloy in a solvent together with a conductive agent and a polymer binder in a solvent to prepare an electrode paste, and applying the electrode paste to a conductive base material, Manufactured by drying.

As a conductive agent in such a hydrogen storage alloy electrode, carbon black having a three-dimensional chain structure formed by secondary aggregation of carbon particles having a particle size of 10 to 30 nm and having a large surface area is used. By doing so, it is known that the conductivity of the hydrogen storage alloy electrode is improved, and as a result, the gas absorption reaction rate of the hydrogen storage alloy powder is increased and the cycle characteristics are improved. The carbon black is used in a state of being dispersed in water when preparing a paste for an electrode.

However, when the carbon black is dispersed in the paste, the following problems occur. That is, in preparing the paste for the electrode, a binder is used together with the conductive agent.
Generally, a polymer synthesized by emulsion polymerization is used, and is added in the form of an emulsion when preparing a paste for an electrode. However, since carbon black has a large surface area and is lipophilic, when mixed with the above-mentioned binder emulsion, the emulsifier used for emulsification is liberated and adsorbed on the carbon black to cause emulsion destruction. Then, aggregation of the binder occurs. As a result, the binder is no longer used effectively,
In addition, the dispersion state of carbon black also deteriorates, and the effect of imparting conductivity cannot be sufficiently exhibited.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, improves the dispersion state of carbon black and a binder, improves the conductivity of a hydrogen storage alloy electrode, and improves the conductivity. An object is to provide a hydride secondary battery having excellent discharge cycle characteristics.

[0007]

According to the present invention, an aqueous carbon black dispersion is prepared by dispersing carbon black for imparting conductivity using a sulfonic acid group-containing polymer. The object has been achieved by mixing a hydrogen storage alloy as an active material and an emulsion containing a binder to prepare a paste for a hydrogen storage alloy electrode. That is,
When the carbon black is dispersed in the sulfonic acid group-containing polymer, the sulfonic acid group-containing polymer covers the surface of the carbon black, so that it is difficult to bond with the emulsifier, and as a result, the release of the emulsifier from the binder emulsion is prevented. Thus, the dispersed state of the carbon black and the binder is improved, and as a result, a hydride secondary battery having excellent charge / discharge cycle characteristics can be obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon black used in the present invention is not particularly limited, but has an average primary particle diameter of about 10
having a structure in which carbon particles of 40 nm to 40 nm are secondarily aggregated in a chain shape, and having a specific surface area of 700 to 1500 m ² / g, DB
It is preferable that the oil absorption of P (the volume of pores in carbon black having a constant weight is replaced by linseed oil and the volume is used as an index of the structure) is 300 to 600 mL / 100 g. Carbon black having such a structure is excellent as a conductive agent, and can exhibit excellent conductivity-imparting action even at a low addition amount.

[0009] The carbon black is not particularly limited with respect to the method for producing it, and is obtained, for example, by burning a hydrocarbon such as petroleum.

Since the carbon black has a low density and a large specific surface area, it is difficult to disperse it in water by a simple method. Therefore, in the present invention, a sulfonic acid group-containing polymer is used as a dispersant, whereby a carbon black aqueous dispersion having a high carbon black concentration and excellent storage stability is obtained.

The compounding amount of carbon black is preferably 0.5 to 25 parts by weight based on 100 parts by weight of the aqueous dispersion. As described above, by setting the blending amount of carbon black to 0.5 parts by weight or more in 100 parts by weight of the aqueous dispersion, a sufficient amount of carbon black to be attached is ensured, and 25 parts by weight or less. This makes it possible to maintain fluidity and prevent difficulties in handling.

In the present invention, a polymer containing a sulfonic acid group is used as a dispersant used to disperse the carbon black. The polymer containing a sulfonic acid group is a polymer compound containing a sulfonic acid group. And has surface activity, and specific examples thereof include, for example, naphthalene sulfonic acid formalin condensate, polystyrene sulfonate, polystyrene sulfonate copolymer, polyacrylic acid copolymer, polydicyclo Examples include, but are not limited to, pentadiene sulfonates, polyaliphatic diene sulfonates, and the like.

The amount of the sulfonic acid group-containing polymer is as follows:
0.1% by weight in 100 parts by weight of the aqueous carbon black dispersion.
It is preferably from 0.01 to 15 parts by weight, particularly preferably from 0.02 to 12 parts by weight. By setting the amount of the sulfonic acid group-containing polymer to 0.01 parts by weight or more in 100 parts by weight of the carbon black aqueous dispersion as described above, the effect as a dispersant is sufficiently exhibited, and When the amount of the sulfonic acid group-containing polymer is too small, the performance of the carbon black can be prevented from deteriorating due to too much sulfonic acid group-containing polymer.

The amount of the carbon black itself is not particularly limited, but is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 1 part by weight, per 100 parts by weight of the hydrogen storage alloy as the active material. Parts by weight are preferred. That is,
By setting the amount of carbon black to be 0.05 parts by weight or more with respect to 100 parts by weight of the hydrogen storage alloy, sufficient conductivity is imparted. Thus, the required capacity can be secured by preventing the capacity from decreasing due to the above.

In preparing the paste for an electrode of the present invention, an emulsion in which a binder is dispersed with an emulsifier is contained, and the binder is used to satisfactorily bind the hydrogen storage alloy and the hydrogen storage alloy with the conductive base material. It is for binding, and in the present invention, as the binder, a rubber-based polymer synthesized by emulsion polymerization is preferable, and therefore, the binder is used in the form of an emulsion dispersed with an emulsifier. For example, a copolymer synthesized by emulsion polymerization using styrene and 2-ethylhexyl acrylate as main components, particularly a copolymer having a copolymerization ratio of 35 mol% of a styrene unit and 65 mol% of 2-ethylhexyl acrylate is preferable.

In the present invention, the amount of the binder used is not particularly limited, but is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the hydrogen storage alloy as the active material. ~ 1 part by weight is preferred. That is, as described above, the amount of binder used is
By adjusting the content to 0.05 part by weight or more with respect to 00 parts by weight, sufficient binding property is exhibited. Can be maintained in an appropriate range.

In the present invention, as the hydrogen storage alloy,
For example, AB_FiveType hydrogen storage alloy, AB_TwoType hydrogen storage
Gold, A_TwoB-type hydrogen storage alloy, solid-solution V-based hydrogen storage alloy
Although various types can be used, in particular, La is 35% by weight or less.
The rare earth elements Mm (Misch metal) and Ni, Co
And Mn are preferable. Where Mm
35% by weight of La in rare earth elements expressed as
% Or more, a small amount selected from Ce, Pr, Nd and Sm.
It is preferable that the composition is at least a mixture with one kind of element.
However, the Co content, which greatly affects the alloy cost,
For lowering, the ratio of La is 60% by weight or more.
Is more preferable, and La alone may be used. Also,
In order to increase the corrosion resistance of the hydrogen storage alloy to the electrolyte,
At least one selected from Y, Yb, Er and Mg
Is preferable, and among them, hydrogen
Suppresses the pulverization of the storage alloy and reduces the ignition of the hydrogen storage alloy
Mg, which has the effect of lowering energy, is
From the viewpoint of ensuring safety in the process. this
The content ratio of these elements is rare earth element Mm (however,
Does not include Y, Yb, Er)
It is preferable to be in the range of 0.015 to 0.1. sand
That is, the ratio to Mm is set to 0.015 or more in atomic ratio.
Good corrosion resistance is given by
Lower temperature discharge characteristics.
Can be. Further, from the viewpoint of suppressing pulverization, Al is not contained.
Preferably, the composition is particularly MmNi_xCo_yMn
_zAl_sM _t(Where M is Y, Yb, Er and Mg
Represents at least one element selected from the group consisting of
x, y, z, s, and t are respectively 3.8 ≦ x ≦ 4.
4, 0.2 ≦ y ≦ 0.7, 0.1 ≦ z ≦ 0.5, 0.1
≦ s ≦ 0.4, 0.015 ≦ t ≦ 0.1)
Hydrogen storage alloys are preferred.

Further, in preparing the paste for a hydrogen storage alloy electrode of the present invention, it is preferable to add a thickener. As the thickener, polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose and the like are generally known. In the present invention, poly-N-vinylacetamide or N-vinylacetamide and other monomers described later are particularly used. Are preferred. That is, in a paste for a hydrogen storage alloy electrode containing a hydrogen storage alloy as an active material, a change in paste viscosity or a decrease in fluidity due to the catalytic action of the hydrogen storage alloy, or a change in the pH of the paste over time, etc. Although it is easy to occur, the inclusion of a copolymer of poly-N-vinylacetamide or N-vinylacetamide with another monomer can improve the quality stability of the paste, so that hydrogen absorption with little variation in quality can be achieved. An alloy electrode can be obtained. As the other monomer to be copolymerized with the N-vinylacetamide, for example, an ethylenically unsaturated monomer, in particular, acrylic acid or acrylate is used.

The paste for a hydrogen storage alloy electrode according to the present invention comprises:
The hydrogen storage alloy powder described above, an aqueous dispersion of carbon black, an emulsion in which a binder is dispersed with an emulsifier, and, if necessary, a copolymer of poly-N-vinylacetamide or N-vinylacetamide with another monomer, etc. It is prepared by mixing with a thickening agent consisting of

The paste for hydrogen-absorbing alloy electrode is applied to a conductive substrate made of a punching metal, a metal foam, or the like, dried and, if necessary, subjected to a rolling treatment to obtain hydrogen. An occlusion alloy electrode can be obtained.

The above hydrogen storage alloy electrode can be used as a negative electrode of a hydride secondary battery such as a nickel hydride storage battery and an air battery. That is, the hydride secondary battery of the present invention is configured to include the negative electrode, the positive electrode, and the electrolyte, each including the above-described hydrogen storage alloy electrode.

When the hydride secondary battery is a nickel-metal hydride battery, a nickel electrode is used as the positive electrode, and an alkaline electrolyte is used as the electrolyte.

In the configuration of the nickel-metal hydride storage battery,
The nickel electrode used as the positive electrode is one using nickel hydroxide as an active material, and the nickel hydroxide is
In order to reduce the impedance of the battery, it is preferable to have a compound containing cobalt on the surface, or to use a mixture of cobalt or a compound containing cobalt. As the alkaline electrolyte, an aqueous alkaline solution such as an aqueous potassium hydroxide solution or an aqueous sodium hydroxide solution is used.

When the hydride secondary battery is an air battery, an air electrode is used as a positive electrode, and an alkaline electrolyte or an ion exchange resin is used as an electrolyte.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples. In the following,% is% by weight unless otherwise specified.

Example 1 Ketjen Black ECP (Ketjen Black International) was used as carbon black for imparting conductivity, and a naphthalenesulfonic acid formalin condensate (molecular weight 7,000) was used as a sulfonic acid group-containing polymer. The Ketjen black ECP, the naphthalene sulfonic acid formalin condensate, and water were mixed and stirred at a weight ratio of 3: 1: 96 to prepare a carbon black aqueous dispersion. The Ketjen Black ECP used in preparing the aqueous carbon black dispersion liquid belongs to furnace black and has an average primary particle diameter of 34%.
nm, specific surface area 1300 m ² / g, DBP oil absorption 5
00 mL / 100 g, and has a structure in which the primary particles are secondary aggregated.

Next, the composition is MmNi _4.27 Co _0.4 Mn.
_0.38 Al _0.3 Mg _0.044 (The composition of the rare earth element in Mm is La: 80%, Ce: 12%, Pr + Nd: 8%
100 parts by weight of a hydrogen storage alloy powder represented by the following formula), 10 parts by weight of the carbon black-water dispersion, 10 parts by weight of a 5% aqueous solution of poly-N-vinylacetamide, and 42.5% of styrene. A paste for a hydrogen storage alloy electrode was prepared by mixing 1.3 parts by weight of a 2-ethylhexyl acrylate copolymer. The weight average molecular weight of the poly-N-vinylacetamide used in preparing the paste was 3,000,000, and styrene-2-
The ethylhexyl acrylate copolymer is composed of 35 mol% of styrene units and 65 mol% of 2-ethylhexyl acrylate units.

A punching metal having a thickness of 56 μm is used as the conductive substrate, and the paste is applied to both surfaces of the conductive substrate by a continuous coating method so that the total thickness after drying becomes 0.6 mm. After drying at 70 ° C., a rolling treatment was performed to obtain a sheet. This sheet was cut into a predetermined size (36 mm wide × 69 mm long) to obtain a hydrogen storage alloy electrode.

The positive electrode is made of nickel hydroxide coated with cobalt hydroxide particles on the surface of the particles (2% of zinc forms a solid solution, 1% of cobalt forms a solid solution, and cobalt hydroxide particles cover the surface of the nickel hydroxide particles). Is 5% of nickel hydroxide) as an active material, and a mixture obtained by adding 4 parts by weight of cobalt oxide powder to 100 parts by weight of this nickel hydroxide powder is used as a conductive material comprising a nickel foam. Paste type nickel electrode (36 mm width x 4 length)
8 mm x thickness 0.62 mm) was immersed in an alkaline aqueous solution (an alkaline aqueous solution containing 30% potassium hydroxide and 2% lithium hydroxide) heated to 80 ° C for 2 hours, taken out and dried, It was used after washing and drying.

The above-mentioned hydrogen-absorbing alloy electrode is used as a negative electrode, and the nickel electrode after the above-mentioned treatment is used as a positive electrode. And put the spiral electrode body in a single 4 size electrode can, and add an alkaline electrolyte [1 liter (L) of 30% aqueous potassium hydroxide solution]
And 17 g of lithium hydroxide powder and 33 g of zinc oxide powder were dissolved therein, and the mixture was sealed to assemble a hydride secondary battery of a nickel-metal hydride storage battery type.

The battery thus manufactured was heated at 60 ° C. for 1 hour.
After holding for 7 hours, and after cooling, the battery was charged at 295 mA for 2.5 hours, discharged at 380 mA (discharge termination voltage: 1 V), and then activated again at 60 ° C. for 17 hours.

Here, the structure of the hydride secondary battery will be described with reference to FIG. 1. 1 is a positive electrode composed of the above nickel electrode, and 2 is a negative electrode composed of the above hydrogen storage alloy electrode. In FIG. 1, the positive electrode 1 and the negative electrode 2 are not shown in detail, but are shown as having a single structure with the base material and the like omitted. Then, the positive electrode 1 and the negative electrode 2 are overlapped with a separator 3 interposed therebetween, spirally wound and inserted into the battery can 5 as a spiral electrode body 4, and an insulator 14 is disposed on an upper portion thereof. . An insulator 13 is provided on the bottom of the battery can 5 before the electrode body 4 is inserted.

The annular gasket 6 is made of nylon 66, and the battery lid 7 is composed of a terminal plate 8, a sealing plate 9, a metal spring 10 and a valve body 11 arranged in an internal space formed by the terminal plate 8, a sealing plate 9, and a battery can. The opening 5 is sealed with the battery cover 7 or the like. That is, after the electrode body 4, the insulators 13, 14 and the like are inserted into the battery can 5, an annular groove 5a having a bottom protruding inwardly is formed near the opening end of the battery can 5, and the groove is formed. The annular gasket 6 and the battery lid 7 are arranged in the opening of the battery can 5 by supporting the lower portion of the annular gasket 6 with the inner peripheral side protruding portion of the battery can 5, and the portion of the battery can 5 from the groove 5 a toward the inside is inward. The opening of the battery can 5 is closed by tightening. The terminal plate 8 is provided with a gas discharge port 8a, the sealing plate 9 is provided with a gas detection port 9a, and a metal spring 10 and a valve body 11 are arranged between the terminal plate 8 and the sealing plate 9. ing. And
The outer peripheral portion of the sealing plate 9 is bent so that the outer peripheral portion of the terminal plate 8 is sandwiched between the terminal plate 8 and the sealing plate 9.

Under normal circumstances, this battery is a metal spring 1
Since the valve body 11 closes the gas detection port 9a by the pressing force of 0, the inside of the battery is kept in a sealed state, but when gas is generated inside the battery and the pressure inside the battery rises abnormally. , The metal spring 10 contracts to form a gap between the valve body 11 and the gas detection port 9a, and gas inside the battery is discharged to the outside of the battery through the gas detection port 9a and the gas discharge port 8a. As a result, when the battery internal pressure decreases and the battery internal pressure returns to normal, the metal spring 10 is restored to the original state,
The pressing force causes the valve body 11 to close the gas detection port 9a again to keep the inside of the battery in a sealed structure.

The positive electrode lead body 12 is made of a nickel ribbon, one end of which is spot-welded to an exposed portion of the base material at the outermost periphery of the positive electrode 1, and the other end is spot-welded to the lower end of the sealing plate 9. And the terminal plate 8 is connected to the sealing plate 9.
And can function as a positive electrode terminal. The base material is exposed on the outer surface of the outermost peripheral portion of the negative electrode 2, and the base material contacts the inner wall of the battery can 5, whereby the battery can 5 functions as a negative electrode terminal.

Comparative Example 1 The same Ketjen Black ECP and water as in Example 1 were mixed and stirred at a weight ratio of 3:97 to prepare an aqueous carbon black dispersion. Then, a hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that this aqueous carbon black dispersion was used, and a nickel hydride storage battery type hydride secondary battery was assembled and activated.

The batteries of Example 1 and Comparative Example 1 were replaced with 16
Charge at 0 mA for 6 hours, and after 1 hour pause, 1 at 130 mA
The battery was discharged to V to determine the standard capacity. Table 1 shows the results. After the measurement of the standard capacity, the battery was similarly charged at 160 mA for 6 hours, and after a pause of 1 hour, 6500 mA (10 C).
At 0.9 V to determine the discharge capacity. The results are shown in Table 1 under the item name of 10C capacity.

[0038]

[Table 1]

As shown in Table 1, the battery of Example 1 had a larger standard capacity and 10 C capacity than the battery of Comparative Example 1, and the difference was particularly remarkable at 10 C capacity.
The battery of Example 2 had a large discharge capacity even at a high-rate discharge of 10 C, and was excellent in high-rate discharge characteristics.

Next, the batteries of Example 1 and Comparative Example 1 were charged at 650 mA (terminated at −ΔV = 10 mV).
After resting for 20 minutes, discharge at 650 mA (final voltage: 1)
V) The charge / discharge cycle was repeated, and the internal resistance (AC 1 kHz), discharge capacity and weight reduction of the battery were examined every 100 cycles. The results are shown in Tables 2, 3, and 4, respectively.

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

As shown in Tables 2 to 4, the battery of Example 1 had a smaller increase in internal resistance with an increase in the number of cycles and a smaller discharge even when the number of cycles increased, as compared with the battery of Comparative Example 1. The capacity was large, the weight loss with the increase in the number of cycles was small, and the charge / discharge cycle characteristics were excellent.

That is, as is clear from the results shown in Tables 1 to 4, the battery of Example 1 of the present invention had excellent high-rate characteristics and charge / discharge cycle characteristics. this is,
In the present invention, the use of a sulfonic acid group-containing polymer as a dispersant improves the dispersibility of carbon black and a binder, thereby improving high-rate discharge characteristics and regenerating an enzyme generated from the positive electrode side during a cycle. Bonding and hydrogen storage reactions will be performed quickly,
It is considered that the weight loss during the cycle was suppressed, and as a result, the increase in the internal resistance and the capacity were suppressed, and the charge / discharge cycle characteristics were improved.

[0046]

As described above, according to the present invention, it is possible to provide a hydride secondary battery in which the conductivity of the hydrogen storage alloy electrode is improved and the charge / discharge cycle characteristics are excellent.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a hydride secondary battery according to the present invention.

[Explanation of symbols]

 1 positive electrode 2 negative electrode 3 separator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/24 H01M 4/24 J 4/26 4/26 J 10/30 10/30 Z F term (reference 4J002 AB013 BC072 BC101 BE023 BG011 BK001 BL011 CC291 CH023 DA036 GQ02 HA07 5H028 AA02 BB05 BB06 EE06 5H050 AA07 AA12 BA14 CA04 CB16 DA03 DA11 DA14 EA23 GA02 GA10

Claims (7)

[Claims] 1. A paste for a hydrogen storage alloy electrode using a hydrogen storage alloy as an active material, wherein an aqueous dispersion of carbon black in which carbon black is dispersed using a sulfonic acid group-containing polymer and a binder are dispersed in an emulsifier. A paste for a hydrogen-absorbing alloy electrode, comprising: 2. The paste for a hydrogen storage alloy electrode according to claim 1, wherein the sulfonic acid group-containing polymer is a naphthalenesulfonic acid formalin condensate. 3. The paste for a hydrogen storage alloy electrode according to claim 1, wherein the binder is a copolymer containing styrene and 2-ethylhexyl acrylate as main components. 4. The hydrogen storage alloy electrode according to claim 1, wherein the thickener comprises poly-N-vinylacetamide or a copolymer of N-vinylacetamide and another monomer. Paste. 5. A hydrogen storage alloy electrode obtained by applying the paste for a hydrogen storage alloy electrode according to claim 1 to a conductive base material and drying the paste. 6. A hydride secondary battery comprising a negative electrode comprising the hydrogen storage alloy electrode according to claim 5, a positive electrode, and an electrolyte. 7. The hydride secondary battery according to claim 6, wherein the positive electrode comprises a nickel electrode and the electrolyte comprises an alkaline electrolyte.