JPWO2011001892A1 - Hydrogen storage alloy electrode and nickel metal hydride battery - Google Patents

Abstract

A hydrogen storage alloy electrode having a hydrogen storage alloy layer with excellent water repellency, capable of suppressing an increase in battery internal pressure, and providing a nickel hydrogen secondary battery excellent in cycle characteristics and load characteristics, and having a weight average molecular weight of A hydrogen storage alloy having a hydrogen storage alloy layer (I) comprising 1200 chlorotrifluoroethylene polymer (a), a binder (b) and hydrogen storage alloy particles (c) on a conductive support (II) An electrode and a nickel metal hydride secondary battery are provided.

Description

  The present invention relates to a hydrogen storage alloy electrode of a nickel metal hydride battery and a nickel metal hydride battery.

  In a nickel metal hydride battery, a layer containing hydrogen storage alloy particles that store hydrogen obtained by electrolyzing an alkaline aqueous solution at the time of charging is formed on the negative electrode current collector, and the stored hydrogen is released during discharge and is oxidized to water. The following reaction occurs.

  As a problem of such a nickel metal hydride battery, it is important to suppress an increase in the internal pressure of the battery that is increased by hydrogen gas generated at the negative electrode and oxygen gas generated at the positive electrode, and also inhibits hydrogen gas release by water generated during discharge. Therefore, it is also important to prevent the battery capacity, cycle characteristics, load characteristics, and the like from being reduced.

  Therefore, by making the surface of the hydrogen storage alloy particles water repellent, the surface of the hydrogen storage alloy particles is brought into a three-phase interface state of solid (alloy layer) -liquid (water or aqueous alkali solution) -gas (hydrogen gas), It has been proposed to improve the problem.

  In Patent Documents 1 and 2, a dispersion of solid fluororesin particles hardly soluble in an organic solvent such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer (FEP) is used. There has been proposed a method of applying to a hydrogen storage alloy layer and interspersing the surface of the hydrogen storage alloy particles with water-repellent fluororesin particles.

  In Patent Document 3, a solution in which a perfluoropolyether having hydrolyzable silyl groups (hydrosilyl groups) at both ends is dissolved in a fluorine-based solvent as a water repellent is applied to the hydrogen storage alloy layer, and the water repellent layer stores hydrogen. A method for coating the surface of alloy particles has been proposed.

  In Patent Documents 4 to 5, fluorine of a fluororesin polymer (perfluorobutenyl vinyl ether polymer, perfluoroallyl vinyl ether polymer or tetrafluoroethylene / perfluoro-2,2-dimethyl-1,3-dioxole copolymer). There has been proposed a method in which a solution of a system solvent is applied (or sprayed) to a hydrogen storage alloy layer, and a water repellent layer is formed (spotted) on the surface of the hydrogen storage alloy particles.

  Patent Document 6 proposes forming a three-phase interface state on the surface of the hydrogen storage alloy particles by fluorinating part or all of the carbon present on the surface of the carbon-containing hydrogen storage alloy particles.

  In Patent Document 7, as a paste for forming a hydrogen storage alloy layer, a perfluoropolyether having two or more specific unsaturated group-containing fluorine-containing amide compounds and two or more hydrosilyl groups is cured with respect to the hydrogen storage alloy particles. The hydrogen storage alloy layer forming material which mix | blended 5 weight% or less of the curable composition containing the platinum catalyst for this is described.

Japanese Patent Laid-Open No. 02-250260 Japanese Patent Laid-Open No. 02-291665 JP 09-097605 A Japanese Patent Laid-Open No. 10-012228 Japanese Patent Laid-Open No. 10-060361 JP 08-315814 A Japanese Patent Laid-Open No. 08-162101

  However, in the method of dispersing water-repellent fluororesin particles on the surface of the hydrogen storage alloy particles (Patent Documents 1 and 2), a process for forming a hardly soluble fluororesin particle layer on the surface of the hydrogen storage alloy particles is required. Moreover, there is a problem that it is difficult to uniformly apply the fluororesin particles.

  In Patent Documents 3 to 5 using a fluorinated ether polymer as a water repellent, it is necessary to use a fluorinated solvent as the organic solvent. However, the fluorinated solvent has a high global warming potential (GWP), and should not be used if possible. desirable.

  Further, in Patent Document 6 in which part or all of carbon existing on the surface of carbon-containing hydrogen storage alloy particles is fluorinated, an alloy other than carbon may be fluorinated together with carbon. Therefore, problems such as capacity reduction remain.

  Patent Document 7 is an invention in which a specific perfluoropolyether is blended as a water repellent agent in a paste for forming a hydrogen storage alloy layer, rather than a form of forming a water repellent layer after forming a hydrogen storage alloy layer. In addition to the need for a platinum catalyst as a catalyst, the presence of the hydrophilic amide group of the amide compound tends to reduce the water-repellent effect.

  The present invention has been completed as a result of studying an environment-friendly material that can be easily applied to form a hydrogen storage alloy layer having excellent water repellency.

  That is, in the present invention, the hydrogen storage alloy layer (I) containing the chlorotrifluoroethylene polymer (a) having a weight average molecular weight of 500 to 1200, the binder (b), and the hydrogen storage alloy particles (c) is electrically conductive. The present invention relates to a hydrogen storage alloy electrode on a support (II).

  The hydrogen storage alloy layer (I) is formed using a paste for forming a hydrogen storage alloy layer containing a low molecular weight CTFE polymer (a), a binder (b), and hydrogen storage alloy particles (c). Alternatively, it may be formed by applying the low molecular weight CTFE polymer (a) to the hydrogen storage alloy layer containing the binder (b) and the hydrogen storage alloy particles (c).

  The present invention also relates to a nickel-metal hydride secondary battery having the hydrogen storage alloy electrode of the present invention as a negative electrode and including a positive electrode and an alkaline electrolyte.

  According to the hydrogen storage alloy electrode of the present invention, a nickel hydrogen secondary battery having a hydrogen storage alloy layer excellent in water repellency, capable of suppressing an increase in battery internal pressure, and excellent in cycle characteristics and load characteristics is provided. be able to.

  The hydrogen storage alloy electrode of the present invention comprises a hydrogen storage alloy layer (I) containing a low molecular weight CTFE polymer (a), a binder (b), and hydrogen storage alloy particles (c) as a conductive support (II). Have on.

  Hereinafter, each element will be described.

(I) Hydrogen Storage Alloy Layer In the present invention, the hydrogen storage alloy layer (I) includes a low molecular weight CTFE polymer (a), a binder (b), and hydrogen storage alloy particles (c).

(A) Low molecular weight CTFE polymer The low molecular weight CTFE polymer used by this invention has fluidity | liquidity at working temperature (25 degreeC). For that purpose, the weight average molecular weight needs to be in the range of 500-1200. If the weight average molecular weight exceeds 1200, fluidity is almost lost at 25 ° C., and uniform dispersion to the hydrogen storage alloy layer becomes difficult, which is not preferable. On the other hand, if it is less than 500, the fluidity becomes so high that it cannot be fixed uniformly on the particles, which is not preferable. In particular, it is preferably 1100 or less, more preferably 700 or more from the viewpoint of fluidity and easy uniform dispersion.

  Focusing on fluidity, for example, the viscosity (25 ° C.) is preferably 100 Pa · s or less, more preferably 60 Pa · s or less, from the viewpoint of good workability of mixing or coating. The lower limit is preferably 0.01 Pa · s or more, and more preferably 0.7 Pa · s or more from the viewpoint that it can be uniformly fixed on the particles.

  The CTFE polymer may be a homopolymer of CTFE or a copolymer with other monomers.

  Examples of commercially available CTFE homopolymers include Daifoil S-10 (weight average molecular weight: about 900), Daifroyl S-20 (weight average molecular weight: 1000), and Daifoil S-3 (weight average) manufactured by Daikin Industries, Ltd. Molecular weight: 700), Difroyl S-50 (weight average molecular weight: 1100), Halocarbon 27 Oil, Halocarbon 56 Oil, Halocarbon 95 Oil, Halocarbon 200 Oil, Halocarbon 400 Oil, HalocarbonHIL Can be illustrated.

  The low molecular weight CTFE polymer used in the present invention has good affinity with nickel, which is a component of the hydrogen storage alloy, and can impart water repellency to the hydrogen storage alloy particles for a long time.

(B) Binder As the binder (b) used in the present invention, a known material conventionally used for forming a hydrogen storage alloy layer of a nickel metal hydride secondary battery, for example, JP-A-2002-15731 The binder described in the above can be employed.

  Specifically, for example, cellulose-based binders such as methylcellulose and carboxymethylcellulose; hydrophilic synthetic resin-based binders such as polyvinyl alcohol and polyethylene oxide; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and the like Examples include fluororesin binders; hydrocarbon binders such as polypropylene, polyethylene, and polystyrene; rubber binders such as styrene-butadiene rubber (SBR).

  Among these, when a non-fluorinated binder is used, the water repellent effect of the low molecular weight CTFE polymer is remarkably exhibited. In the case of using a fluororesin binder, the fluororesin itself has water repellency, but the addition of a low molecular weight CTFE polymer makes it easier to express water repellency on the electrode surface.

(C) Hydrogen storage alloy particles As the hydrogen storage alloy used in the present invention, known materials conventionally used for forming a hydrogen storage alloy layer of a nickel hydrogen secondary battery, for example, Japanese Patent Application Laid-Open No. 02-291665, Alloys described in Japanese Unexamined Patent Publication No. 2008-210554 can be employed.

Specifically, for example, AB ₅ type misch metal (Mm) which is called is called a alloy or AB ₂ type whose main raw material Ti-Zr-Mn-V, Ti-Zr-Cr-Fe, Examples thereof include Ti—Cr—V and Ti—Cr—V called BCC type. Among these, a misch metal-based hydrogen storage alloy is preferable from the viewpoint of good battery characteristics such as cycle characteristics.

A Misch metal-based hydrogen storage alloy (AB ₅ type) is a mixture in which a part of La of a LaNi _5- based alloy having a CaCu ₅ structure is replaced with a rare earth metal element such as Ce, Pr, and Nd. / La / Nd / other rare earth metal elements (= 45/30/5/20% by weight). Further, Mm, Ni, Co, Al, and Mn alloyed at a molar ratio of Mm / Ni / Co / Al / Mn of 1.0 / 3.3 / 0.9 / 0.2 / 0.6 Those alloyed with 1.0 / 4.1 / 0.3 / 0.35 / 0.3 and those alloyed with 1.0 / 3.4 / 0.8 / 0.2 / 0.6 Are known.

  The hydrogen storage alloy is used in the form of particles (powder). The particle size is usually about 40 to 300 μm.

  The contents of the low molecular weight CTFE polymer (a), the binder (b), and the hydrogen storage alloy particles (c) in the hydrogen storage alloy layer (I) used in the present invention are as follows in the hydrogen storage alloy layer (I) ( The same applies hereinafter), low molecular weight CTFE polymer (a) 0.1 to 5.0% by mass, binder (b) 0.5 to 5.0% by mass and hydrogen storage alloy particles (c) 90 to 97% by mass. % Is preferred. In addition, the total amount of the low molecular weight CTFE polymer (a) and the binder (b) is preferably 5% by mass or less, and more preferably 0.6 to 4.0% by mass from the viewpoint of improving battery characteristics.

  The low molecular weight CTFE polymer (a) is preferably 5.0% by mass or less, more preferably 1.0% by mass or less from the viewpoint of good cycle characteristics and load characteristics, and uniformly covers the electrode surface. From the point that can be achieved, it is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more.

  The binder (b) varies depending on the type and molecular weight thereof, but generally it is preferably 5.0% by mass or less, more preferably 3.0% by mass or less from the viewpoint of good battery characteristics, and adhesion. From the viewpoint of good properties, it is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more.

(II) Conductive support As the conductive support (current collector) used in the present invention, a support of a known material conventionally used for a hydrogen storage alloy electrode (negative electrode) of a nickel hydrogen secondary battery, For example, the support body described in Unexamined-Japanese-Patent No. 2002-260646 etc. can be employ | adopted.

  Specific examples include three-dimensional conductive supports such as fibrous nickel and foamed nickel; two-dimensional conductive supports such as punching metal, expanded metal, and metal net.

  The hydrogen storage alloy electrode of the present invention can be produced by forming the hydrogen storage alloy layer (I) on the conductive support (II) by various methods.

For example, (1) a paste is prepared by mixing a predetermined amount of a low molecular weight CTFE polymer (a), a binder (b), and hydrogen storage alloy particles (c) in the absence of a solvent. Method of applying or crimping;
(2) A binder (b) and hydrogen storage alloy particles (c) are mixed using a solvent to prepare a paste, which is applied to a conductive support or pressed to form a hydrogen storage alloy layer, Next, a method of applying a low molecular weight CTFE polymer (a) to the hydrogen storage alloy layer;
(3) The binder (b) and the hydrogen storage alloy particles (c) are mixed using a solvent to prepare a paste, and a hydrogen storage alloy sheet is formed by a casting method or a compression molding method. A method of applying or impregnating the low molecular weight CTFE polymer (a) to the occlusion alloy sheet and then sticking it to the conductive support;
Etc. can be adopted.

  Among these methods, the method (1) is preferable because the low molecular weight CTFE polymer (a) can be uniformly coated on the hydrogen storage alloy particles (c).

  The present invention also relates to a nickel-metal hydride secondary battery using the hydrogen storage alloy electrode of the present invention as a negative electrode and including a positive electrode and an alkaline electrolyte. The nickel metal hydride secondary battery of the present invention is the same as the conventional nickel metal hydride secondary battery, except that the hydrogen storage alloy electrode of the present invention is used as the negative electrode. In addition to the positive electrode and the alkaline electrolyte, the separator, the negative electrode can, etc. Conventionally known structures and materials can be used.

  Specifically, for example, a nickel electrode filled with nickel hydroxide is generally used. This nickel electrode can be produced by filling foam nickel with a paste mainly composed of nickel hydroxide powder having a cobalt oxyhydroxide layer formed on the surface thereof.

  Examples of the alkaline electrolyte include an aqueous potassium hydroxide solution, sodium hydroxide, lithium hydroxide, or a mixed solution thereof.

  The nickel metal hydride secondary battery of the present invention contains a low molecular weight CTFE polymer having excellent water repellency and good affinity for nickel in the hydrogen storage alloy layer, so that a good solid-liquid-gas-3 phase is obtained. An interface state is formed, and hydrogen gas can be smoothly occluded / released, so that an increase in battery internal pressure can be suppressed. As a result, battery characteristics such as cycle characteristics and load characteristics are improved.

  EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

  The measurement method employed in the present invention is as follows.

(Weight average molecular weight)
Measurement is performed using GPC (gel permeation chromatography: HLC-8320GPC manufactured by Tosoh Corporation).

(Kinematic viscosity)
Measurement is performed in accordance with JIS K 6893. Actually, it is measured with a B type viscometer (model number: BLBH) manufactured by Tokyo Keiki Co., Ltd. using a No. 2 rotor under the conditions of 60 rpm, 25 ° C., and 2 minutes.

(Water contact angle)
Using an automatic contact angle measuring device DSA100S (manufactured by Kyowa Interface Science Co., Ltd.), 0.5 μL of pure water is dropped on the electrode and the contact angle after 8 seconds is measured.

Example 1
(1) Production of hydrogen storage alloy powder MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 (Molar ratio is Mm / Ni / Co / Al / Mn = 1.0 / 3.4 / 0.8 / 0.2 / 0.6 Each of the commercially available metal elements Mm, Ni, Co, Al, and Mn was weighed and mixed at a predetermined ratio. The mixture was poured into a high-frequency melting furnace and dissolved, and then poured into a mold and cooled to prepare a hydrogen storage alloy lump (ingot) made of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 . This lump of hydrogen storage alloy was coarsely pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became about 50 μm to prepare a hydrogen storage alloy powder. In addition, the average particle diameter of the obtained hydrogen storage alloy powder is a value measured by a laser diffraction method.

(2) Production of Hydrogen Storage Alloy Electrode A PTFE dispersion (D-210C manufactured by Daikin Industries, Ltd. (solid content 61.0%)) as a binder was added to 98 parts by mass of the produced hydrogen storage alloy powder. 0.5 parts by mass (in terms of solid content), 0.5 part by mass of low molecular weight CTFE polymer (Daikin S-20 manufactured by Daikin Industries, Ltd., weight average molecular weight 1000) was added, and pure water was added and kneaded to hydrogen. A slurry for forming an occlusion alloy layer (active material slurry) was prepared. This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode). The negative electrode was subjected to energy dispersive X-ray fluorescence (EDX) analysis, and the distribution of fluorine atoms and chlorine atoms was found to show that CTFE was uniformly attached to the surface of the hydrogen storage alloy.

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 107.4 degrees.

Example 2
The mixture was kneaded in the same manner as in Example 1 except that a low molecular weight CTFE polymer having a weight average molecular weight of about 900 (Daifloil S-10 manufactured by Daikin Industries, Ltd.) was used as the low molecular weight CTFE polymer. A paste for forming an occlusion alloy layer was prepared and applied to a nickel-plated punching metal, followed by drying in a 90 ° C. constant temperature bath until moisture disappeared to produce a hydrogen occlusion alloy electrode (negative electrode).

When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 104.5 degrees.

Example 3
A dispersion of PTFE as a binder (D-210C manufactured by Daikin Industries, Ltd.) was added to 98.5 parts by mass of the hydrogen storage alloy powder composed of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 prepared in step (1) of Example 1. 1.5 parts by mass of (solid content 61.0%) was added, and pure water was further added and kneaded to prepare a hydrogen storage alloy layer forming slurry (active material slurry). This slurry for forming a hydrogen storage alloy layer was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until there was no water.

  Next, the obtained hydrogen storage alloy electrode is uniformly formed so that a low molecular weight CTFE polymer (Daifloil S-20 manufactured by Daikin Industries, Ltd.) has a thickness of about 2 μm (corresponding to about 1.0% in terms of mass). Then, drying was performed again in a constant temperature bath at 90 ° C. until the water disappeared, and a hydrogen storage alloy electrode (negative electrode) was produced. Further, when the coated negative electrode was subjected to EDX analysis and the distribution of fluorine atoms and chlorine atoms was observed, it was found that CTFE was uniformly attached to the surface of the hydrogen storage alloy.

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 106.8 degrees.

Example 4
To 97.9 parts by mass of the hydrogen storage alloy powder composed of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 prepared in step (1) of Example 1, SBR aqueous emulsion (TRD2001 manufactured by JSR Co., Ltd. (solid content 48) was used as a binder. 0.0%)) 1.5 parts by mass (in terms of solid content), 0.5 parts by mass of low molecular weight CTFE polymer (Daikin Industries S-20, Daikin Industries, Ltd.), carboxymethyl cellulose (CMC) as a thickener 0.1 parts by mass, and pure water was added and kneaded to prepare a hydrogen storage alloy layer forming slurry (active material slurry). This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 108.0 degrees.

Example 5
A dispersion of PTFE as a binder (D-210C manufactured by Daikin Industries, Ltd.) was added to 98.4 parts by mass of the hydrogen storage alloy powder made of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 produced in the step (1) of Example 1. 1.5 parts by mass (solid content 61.0%)), 0.1 part by mass of low molecular weight CTFE polymer (Daikin Industries S-20, Daikin Industries Co., Ltd.), and pure water In addition, the slurry for forming a hydrogen storage alloy layer (active material slurry) was prepared by kneading. This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 103.0 degrees.

Example 6
A dispersion of PTFE (D-210C manufactured by Daikin Industries, Ltd.) as a binder was added to 93.5 parts by mass of the hydrogen storage alloy powder made of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 produced in the step (1) of Example 1. (Solid content 61.0%)) is added in an amount of 1.5 parts by mass (in terms of solid content), 5.0 parts by mass of low molecular weight CTFE polymer (Daikin Industries S-20, Daikin Industries, Ltd.), and pure water. And kneaded to prepare a slurry for forming a hydrogen storage alloy layer (active material slurry). This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 107.0 degrees.

Example 7
The mixture was kneaded in the same manner as in Example 1 except that a low molecular weight CTFE polymer having a weight average molecular weight of about 700 (Daiflo Industries S-3 manufactured by Daikin Industries, Ltd.) was used as the low molecular weight CTFE polymer. An alloy layer forming paste was prepared, applied to nickel-plated punching metal, and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 105.4 degrees.

Example 8
The mixture was kneaded in the same manner as in Example 1 except that a low molecular weight CTFE polymer having a weight average molecular weight of about 1100 (Daifloil S-50 manufactured by Daikin Industries, Ltd.) was used as the low molecular weight CTFE polymer. An alloy layer forming paste was prepared, applied to nickel-plated punching metal, and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 107.0 degrees.

Example 9
98.4 parts by mass of hydrogen storage alloy powder made of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 prepared in step (1) of Example 1, 1.1 parts by mass of carboxymethyl cellulose (CMC) as a binder, low molecular weight 0.5 parts by mass of CTFE polymer (Daifloil S-20 manufactured by Daikin Industries, Ltd.) was added, and pure water was added and kneaded to prepare a hydrogen storage alloy layer forming slurry (active material slurry). This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 106.5 degrees.

Comparative Example 1
A dispersion of PTFE as a binder (D-210C manufactured by Daikin Industries, Ltd.) was added to 98.5 parts by mass of the hydrogen storage alloy powder made of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 prepared in the step (1) of Example 1. (Solid content 61.0%)) was added in an amount of 1.5 parts by mass (solid content), and pure water was further added and kneaded to prepare a hydrogen storage alloy layer forming slurry (active material slurry). This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 63.5 degrees.

Comparative Example 2
A dispersion of PTFE as a binder (D-210C manufactured by Daikin Industries, Ltd.) was added to 98.5 parts by mass of the hydrogen storage alloy powder composed of MmNi _3.4 Co _0.8 Al _0.2 Mn _0.6 prepared in step (1) of Example 1. 1.5 parts by mass of (solid content 61.0%) was added, and pure water was further added and kneaded to prepare a hydrogen storage alloy layer forming slurry (active material slurry). This slurry for forming a hydrogen storage alloy layer was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until there was no water.

  Next, PTFE dispersion (D-210C manufactured by Daikin Industries, Ltd.) was uniformly applied to the obtained hydrogen storage alloy electrode so as to have a thickness of about 2 μm (corresponding to about 1.0% in terms of mass). Then, it dried again until there was no water in a 90 degreeC thermostat, and produced the hydrogen storage alloy electrode (negative electrode). Moreover, when the distribution of fluorine was confirmed by EDX analysis for the coated negative electrode, it was found that there was a part where PTFE was partially agglomerated and it was not uniformly coated.

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 105.0 degrees.

Comparative Example 3
A mixture for kneading the hydrogen storage alloy layer was prepared by kneading the mixture in the same manner as in Example 1 except that a CTFE polymer having a weight average molecular weight of 300 was used as the CTFE polymer. This hydrogen storage alloy layer forming slurry was applied to a nickel-plated punching metal and dried in a constant temperature bath at 90 ° C. until moisture disappeared to prepare a hydrogen storage alloy electrode (negative electrode).

  When the contact angle with water on the surface of the hydrogen storage alloy layer of the obtained hydrogen storage alloy electrode was examined, it was 64.0 degrees.

Comparative Example 4
A mixture for kneading the hydrogen storage alloy layer was prepared by kneading the mixture in the same manner as in Example 1 except that a CTFE polymer having a weight average molecular weight of 1300 was used as the CTFE polymer. However, the kneading operation did not proceed smoothly and could not be uniformly mixed at room temperature.

Example 10
The hydrogen storage alloy electrode of the present invention produced in Example 1 was cut into a size of 330 mm × 30 mm to form a negative electrode, a fired nickel plate (270 mm × 30 mm) as a positive electrode, and a thickness of 130 μm as a separator between the positive electrode and the negative electrode After being wound in a spiral shape with a polypropylene nonwoven fabric subjected to the hydrophilic treatment, it was accommodated in a battery can having a size of SUBC (diameter 22.5 mm, total length 43 mm). Next, a 6N-potassium hydroxide aqueous solution was filled in the battery can and then sealed to prepare a nickel metal hydride secondary battery of the present invention.

  The cycle characteristics and load characteristics of this nickel metal hydride secondary battery were examined as follows. The results are shown in Table 1.

(Load characteristics)
After charging at a current value of 1 C for 1.5 hours, the discharge capacity when discharged to a final voltage of 1.0 V at a current value of 3.0 C is measured. The evaluation is performed using an index with the discharge capacity of Comparative Example 5 as 100.

(Cycle characteristics)
A charge / discharge cycle in which the battery is charged at a current value of 1 C for 1.5 hours and then discharged to a final voltage of 1.0 V at a current value of 1 C while measuring the discharge capacity is defined as one cycle. The number of cycles until the discharge capacity becomes 80% or less of the initial discharge capacity is counted, and the evaluation is performed using an index with the number of cycles of Comparative Example 5 as 100.

Examples 11-18 and Comparative Examples 5-7
A nickel-metal hydride secondary battery was produced in the same manner as in Example 10 except that the hydrogen storage alloy electrodes produced in Examples 2 to 9 and Comparative Examples 1 to 3 were used, and the cycle characteristics and load characteristics were examined. The results are shown in Table 1.

  From the results of Table 1, it can be seen that all the examples are clearly improved in both load characteristics and cycle characteristics as compared with Comparative Examples 5 and 6. In Comparative Example 6 in which a PTFE dispersion was later applied to the electrode, since some of the hydrogen storage alloy particles were not uniformly covered, the water repellency became poor as a whole, and the low molecular weight CTFE weight was low. It is considered that the load characteristics and the cycle characteristics were not improved as compared with Example 12 in which the combined dispersion was later applied to the electrodes. Moreover, it seems that the low-polymerized product CTFE having an average molecular weight of about 300 as in Comparative Example 7 was not effective because it could not be uniformly fixed on the particles.

Claims (4)

A hydrogen storage alloy layer (I) containing a chlorotrifluoroethylene polymer (a) having a weight average molecular weight of 500 to 1200, a binder (b), and hydrogen storage alloy particles (c) is used as a conductive support (II). A hydrogen storage alloy electrode on top. The hydrogen storage alloy layer (I) includes a chlorotrifluoroethylene polymer (a) having a weight average molecular weight of 500 to 1200, a binder (b), and hydrogen storage alloy particles (c). The hydrogen storage alloy electrode according to claim 1, which is formed using a paste. A chlorotrifluoroethylene polymer (a) having a weight average molecular weight of 500 to 1200 is added to the hydrogen storage alloy layer in which the hydrogen storage alloy layer (I) includes the binder (b) and the hydrogen storage alloy particles (c). The hydrogen storage alloy electrode according to claim 1, which is formed by coating. A nickel metal hydride secondary battery comprising the hydrogen storage alloy electrode according to any one of claims 1 to 3 as a negative electrode, and a positive electrode and an alkaline electrolyte.