JP4812447B2 - Nickel metal hydride storage battery - Google Patents

Description

  The present invention relates to a nickel metal hydride storage battery.

Although nickel-metal hydride storage batteries have a wide range of uses, nickel-metal hydride storage batteries are applied to power sources for hybrid vehicles and electric vehicles because of their high output. Increasing the output of the nickel-metal hydride storage battery has been performed, for example, by increasing the facing area between the positive electrode plate and the negative electrode plate while reducing the thickness of the positive electrode plate, the negative electrode plate, and the separator.
On the other hand, in a nickel metal hydride storage battery, self-discharge characteristics are also important, and it is known that a separator is sulfonated as a means for preventing self-discharge.

  However, the sulfonated separator is more susceptible to damage due to damage to the fibers constituting the separator as compared to a separator subjected to other hydrophilic treatment such as fluorine gas treatment. For this reason, in a cylindrical nickel-metal hydride storage battery using a sulfonated separator, the positive electrode plate and the negative electrode plate may be in direct contact with each other by breaking the separator.

  Moreover, the separator which carried out the sulfonation process is inferior to a liquid absorptivity compared with the separator which performed the other hydrophilic treatment. In particular, in a high-power application battery, it is necessary to secure an ion movement path (conduction path) between the positive electrode plate and the negative electrode plate, and the liquid is infiltrated into the separator by vacuum injection. In this regard, the separator treated with fluorine gas is excellent in liquid absorbency and hydrophilicity, and in the nickel metal hydride storage battery using the separator treated with fluorine gas, the liquid permeation is possible even after pouring due to its own liquid absorbency. As a result, a sufficient conduction path is ensured and high output is achieved. In addition, plasma treatment, surfactant treatment, and the like can provide the same effects as the fluorine gas treatment.

Therefore, a cylindrical nickel-metal hydride storage battery using two types of separators has been proposed from the relationship between suppression of self-discharge, short-circuit resistance, and output characteristics (Patent Document 1).
In the battery of Patent Document 1, one of the two types of separators is subjected to, for example, fluorine gas treatment to ensure strength, and the other separator is subjected to sulfonation treatment. And the separator which performed the fluorine gas process is arrange | positioned on the outer side of a positive electrode plate, and the separator which carried out the sulfonation process is arrange | positioned on the inner side of a positive electrode plate.
JP 2004-31293 A

  However, in the nickel-metal hydride storage battery of Patent Document 1, when the area of the electrode plate is increased beyond a certain area, there is a problem that the output is decreased. In particular, one of the two types of separators is subjected to fluorine gas treatment, for example, to ensure strength, and the other separator is subjected to sulfonation treatment, and the internal pressure of the battery is increased. In order to prevent this, it becomes prominent when the negative electrode plate contains a water-insoluble polymer binder.

  The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a nickel-metal hydride storage battery in which the output does not decrease even if the area of the electrode plate is increased beyond a certain level. There is to do.

In the course of various studies to achieve the above-mentioned object, the present inventors have clarified the cause of the above-mentioned problem and succeeded in solving the problem and have arrived at the present invention.
More specifically, the present inventors disassembled the charged / discharged battery and observed the negative electrode plate. When the area of the negative electrode plate increased beyond a certain area, there was a region where the electrolyte solution was insufficiently penetrated. It was found to occur. When the area of the negative electrode plate increases beyond a certain area due to the presence of such a region, the alkaline electrolyte is unevenly distributed between the positive electrode plate and the negative electrode plate, and the increased negative electrode plate The area was not used effectively, and high output was impeded.

  The inventors further investigated the uneven distribution of the alkaline electrolyte and investigated the following causes. That is, the non-uniform distribution of the alkaline electrolyte is present in the gap as the gap between the electrode plate and the separator is reduced and dispersed as the positive electrode plate, the negative electrode plate and the separator are made thinner and larger. In addition to the localization of the alkaline electrolyte, it is necessary to improve the density of the separator as the thickness is reduced, and the absorption of the electrolyte has become difficult as a result. The sulfonated separator and the fluorine gas It was thought that the alkaline electrolyte was localized in the separator because of the difference in liquid absorption of the treated separator. In particular, the localization of the alkaline electrolyte in the gap between the negative electrode plate and the separator becomes more prominent when the negative electrode plate contains a water-insoluble polymer binder based on the water repellency of the binder. I thought.

Accordingly, the inventors have developed means for uniformly distributing the alkaline electrolyte between the positive electrode plate and the negative electrode plate, and have arrived at the present invention.
According to the present invention, in a nickel metal hydride battery including a spiral electrode group housed together with an alkaline electrolyte in a container, the electrode group includes a water-absorbing alloy particle and a water-insoluble material that binds the hydrogen-absorbing alloy particle. A negative electrode plate containing a polymer binder and having an effective surface area per unit capacity of 70 cm ² / Ah or more, a positive electrode plate wound in a spiral with the negative electrode plate, and containing nickel hydroxide as a positive electrode active material; A first separator made of a non-woven polyolefin fiber, disposed between the outer surface of the positive electrode plate and the inner surface of the negative electrode plate, and disposed between the inner surface of the positive electrode plate and the outer surface of the negative electrode plate; A second separator made of a nonwoven fabric of fibers, and one nonwoven fabric of the first separator and the second separator has a fluorine gas treatment, a plasma treatment, and a surfactant treatment. Provided is a nickel-metal hydride storage battery that is subjected to at least one hydrophilization treatment selected from the above, and the other nonwoven fabric is subjected to one of sulfonation treatment, plasma treatment, and surfactant treatment. (Claim 1).

As a preferred embodiment, the nonwoven fabric of the first separator is subjected to at least one hydrophilic treatment selected from the fluorine gas treatment, plasma treatment and surfactant treatment, and the nonwoven fabric of the second separator is subjected to the sulfonation treatment. And one of the plasma treatment and the surfactant treatment (Claim 2).
As a preferred aspect, the second separator is subjected to the plasma treatment after the sulfonation treatment (Claim 3).

In a preferred embodiment, the second separator has a liquid absorption height of a potassium hydroxide aqueous solution in a range of 5 mm or more and 120 mm or less in 30 minutes (Claim 4).
As a preferred embodiment, the second separator has a liquid absorption height of a potassium hydroxide aqueous solution in a range of 5 mm or more and 60 mm or less in 30 minutes (Claim 5).

In the nickel metal hydride storage battery according to claim 1 of the present invention, one of plasma treatment and surfactant is applied to the nonwoven fabric of the other separator in addition to the sulfonation treatment. For this reason, the hydrophilicity of the other separator is increased, the liquid absorbency of the alkaline electrolyte is improved, and the alkaline electrolyte is distributed substantially uniformly inside the separator even if the separator is highly dense. In addition, due to the increased hydrophilicity, the alkaline electrolyte is distributed substantially uniformly in the gap between the negative electrode plate and the other separator even if the negative electrode plate contains a water-repellent water-insoluble polymer binder. To do. Therefore, in this battery, even if the effective surface area per unit capacity of the negative electrode plate exceeds 70 cm ² / Ah, the alkaline electrolyte is uniformly distributed in the entire region where the positive electrode plate and the negative electrode plate face each other. As a result, the battery reaction proceeds uniformly and high output is achieved.

  In the nickel-metal hydride storage battery according to claim 2, the non-woven fabric of the second separator disposed between the inner surface of the positive electrode plate and the outer surface of the negative electrode plate is subjected to sulfonation treatment, and the outer surface of the positive electrode plate and the inner surface of the negative electrode plate The first separator disposed between the two has higher strength than the second separator. Thus, by using a higher strength separator as the first separator, in this nickel metal hydride storage battery, occurrence of an internal short circuit is prevented.

  In the nickel-metal hydride storage battery according to claim 3, the second separator is subjected to plasma treatment after sulfonation treatment. In the surfactant treatment, the surfactant is only attached and dried, and there is a high possibility that it will fall off. In the plasma treatment, an element corresponding to the plasma gas type is introduced into the second separator and introduced. Since the element is bonded to the fiber of the second separator, this element does not adversely affect the battery characteristics in the long term.

In the nickel metal hydride storage battery of claim 4, the liquid absorption height of the potassium hydroxide aqueous solution of the second separator is in the range of 5 mm to 120 mm in 30 minutes. When the liquid absorption height is within this range, the alkaline electrolyte is uniformly and reliably distributed in the entire region where the positive electrode plate and the negative electrode plate face each other.
That is, in the nickel metal hydride storage battery, in order for the second separator to uniformly absorb the alkaline electrolyte based on its liquid absorbency, the liquid absorption height needs to be 5 mm or more in 30 minutes.

  In addition, when the plasma treatment is performed so that the liquid absorption height falls within a range of 120 mm or less in 30 minutes, the dielectric breakdown does not occur in the second separator due to the plasma treatment, and the internal short circuit of the battery is prevented. On the other hand, if the second separator is treated with a surfactant so as to fall within the range of 120 mm or less at a liquid absorption height of 30 minutes, the influence of impurities on battery performance can be reduced, and further, the separator is dried after the treatment. Time is also shortened.

In the nickel metal hydride storage battery of claim 5, the liquid absorption height of the potassium hydroxide aqueous solution of the second separator is in the range of 5 mm to 60 mm in 30 minutes.
In this battery, when the surfactant treatment is applied to the second separator, when the insulation between the positive and negative electrodes is inspected before the injection, the resistance decreases due to moisture absorbed by the surfactant (pseudo short). Is erroneously determined to be poor insulation.

  On the other hand, when the second separator is subjected to plasma processing, the processing time of the plasma processing is shortened and productivity is improved.

FIG. 1 shows a nickel metal hydride storage battery according to an embodiment of the present invention.
This battery includes a cylindrical outer can 2 with a bottom, and a spiral electrode group 4 is accommodated in the outer can 2 together with an alkaline electrolyte (not shown). The alkaline electrolyte is a caustic aqueous solution containing potassium hydroxide (KOH) as a main solute. The alkaline electrolyte may further contain one or both of lithium hydroxide (LiOH) and sodium hydroxide (NaOH).

The electrode group 4 is formed by spirally winding a strip-like positive electrode plate 6, a negative electrode plate 8, a first separator 10 a and a second separator 10 b, and the first separator 10 a includes the outer surface of the positive electrode plate 6 and the negative electrode plate 8. The second separator 10 b is positioned between the inner surface of the positive electrode plate 6 and the outer surface of the negative electrode plate 8.
A circular lid plate 16 having a gas vent hole 14 in the center is disposed in the open end of the outer can 2 via a ring-shaped insulating gasket 12. The insulating gasket 12 and the cover plate 16 are fixed by the opening edge of the caulked outer can 2.

A positive electrode current collector 17 and a positive electrode lead 18 are disposed between the positive electrode plate 6 of the electrode group 4 and the inner surface of the cover plate 16 to electrically connect them. On the other hand, a negative electrode current collector 20 that electrically connects between the negative electrode plate 8 of the electrode group 4 and the bottom surface of the outer can 2 is disposed.
A valve body 22 is arranged on the outer surface of the cover plate 16 so as to close the gas vent hole 14, and a cylindrical positive electrode terminal 24 with a flange is attached so as to surround the valve body 22. A compression coil spring 26 is disposed between the back surface of the valve body 22 and the end wall of the positive electrode terminal 24, and the compression coil spring 26 presses the valve body against the lid plate with a predetermined urging force.

Hereinafter, the positive electrode plate 6, the negative electrode plate 8, the first separator 10a, and the second separator 10b will be described in detail.
The positive electrode plate 6 is a sintered nickel electrode, and has a porous nickel sintered substrate as a positive electrode substrate. A positive electrode mixture is supported in the pores of the nickel sintered substrate, and the positive electrode mixture contains nickel hydroxide as a positive electrode active material and cobalt hydroxide as a conductive agent.

The negative electrode plate 8 is a hydrogen storage alloy electrode, and has, for example, a punching metal as the negative electrode substrate. The punching metal is filled with a negative electrode mixture in its through-holes, and a layered negative electrode mixture is held on both sides thereof. When the surface area of the negative electrode mixture layer on both surfaces of the negative electrode plate 8 is X and the capacity of the negative electrode plate is Y, the ratio of the surface area X to the capacity Y (effective surface area per unit capacity) X / Y is 70 cm ² / Ah or more It is.

The negative electrode mixture includes hydrogen storage alloy particles, a binder, and, if necessary, a conductive agent. The hydrogen storage alloy particles are made of, for example, an AB ₅ type or AB _3.5 type hydrogen storage alloy, and can electrochemically store and release hydrogen as a negative electrode active material. The capacity Y of the negative electrode plate 8 is obtained from the product of the hydrogen storage amount per unit mass of the alloy and the alloy mass of the negative electrode plate 8 when the temperature is 40 ° C. and the hydrogen equilibrium pressure is 1 MPa.

For example, carbon powder can be used as the conductive agent.
The binder is made of a water-insoluble polymer and is selected from, for example, SBR (styrene butadiene latex), PTFE (polytetrafluoroethylene), acrylic ester, methacrylic ester, aromatic olefin, conjugated diene, and olefin. 1 type, or 2 or more types selected from a copolymer containing 2 or more types can be used. As the binder, a water-soluble thickener may be used in combination with a water-insoluble polymer binder as necessary. For example, CMC (carboxymethyl cellulose), PVA (polyvinyl alcohol), PEO (polyethylene) One or two or more selected from ethylene oxide) and polyacrylates may be used.

The first separator 10a and the second separator 10b are obtained by subjecting a nonwoven fabric mainly made of polyolefin synthetic resin fibers to a hydrophilic treatment.
Specifically, the nonwoven fabric is produced by using a polyolefin synthetic resin fiber as a material, for example, by a dry method, a wet method, a spunbond method, a melt blow method, and the like, and as the polyolefin synthetic resin fiber, for example, polyethylene, polypropylene, etc. A synthetic resin can be used.

As for the fiber structure, a single structure or a core-sheath type composite structure fiber can be used. In the case of a core-sheath type fiber, the surface of the core material made of polyolefin synthetic resin is different from the core material. Covered with a sheath material of polyolefin-based synthetic resin.
The first separator 10a and the second separator 10b differ in the hydrophilic treatment applied to the nonwoven fabric. In the first separator 10a, the nonwoven fabric is subjected to fluorine gas treatment, plasma treatment, and surfactant treatment. At least one selected hydrophilic treatment is performed. In other words, in the first separator 10a, the nonwoven fabric is subjected to a hydrophilic treatment other than the sulfonation treatment.

The fluorine gas treatment is performed, for example, by treating the nonwoven fabric with a mixed gas obtained by further adding oxygen gas, carbon dioxide gas, sulfur dioxide gas or the like to fluorine gas diluted with an inert gas. The fluorine gas treatment introduces hydrophilic groups such as OH, COOH, SO ₃ H into the nonwoven fabric fibers.
In the surfactant treatment, the nonwoven fabric is dipped in a solution in which the surfactant is dissolved and then dried. Examples of the surfactant that can be used include saturated carboxylates such as fatty acid salts, alkyl ethoxy carboxylates, acylated amino acid salts, sulfate ester salts, sulfonates, and the like. In the surfactant treatment, the surfactant is adsorbed on the fibers of the nonwoven fabric, and the hydrophilicity is improved.

The plasma treatment is performed by converting oxygen gas into plasma to generate oxygen radicals and treating the nonwoven fabric with the oxygen radicals. By the plasma treatment, hydrophilic functional groups such as OH and COOH groups are introduced into the nonwoven fabric fibers.
Among the above hydrophilization treatments, fluorine gas treatment is preferable because the resulting separator is excellent in liquid absorbency and long-term stability.

  On the other hand, after the sulfonation treatment, the nonwoven fabric of the second separator 10b is subjected to one of a surfactant treatment and a plasma treatment, and preferably, a plasma treatment is performed. The treatment conditions for the surfactant treatment and the plasma treatment are preferably set so that the absorption height H of the potassium hydroxide aqueous solution of the second separator 10b falls within the range of 5 mm to 120 mm in 30 minutes. More preferably, it is in the range of 5 mm or more and 60 mm or less.

Here, the liquid absorption height H is measured as follows.
The sample obtained by cutting the second separator into a strip shape was placed vertically so that only the lower end of the sample was immersed in the aqueous potassium hydroxide solution, and the height at which the aqueous potassium hydroxide solution rose within the sample in 30 minutes (liquid absorption) Height H) is measured with respect to the water surface. The concentration of potassium hydroxide used for the measurement is 30% by mass.

The sulfonation treatment is performed by treating the nonwoven fabric with an acid containing a sulfate group such as sulfuric acid or fuming sulfuric acid. The functional group resulting from S, such as a sulfone group (—SO ₃ H), is introduced into the nonwoven fabric fibers by the sulfonation treatment.
Note that the surfactant treatment and plasma treatment methods are the same as in the case of the first separator 10a, and thus the description thereof is omitted.

The above-described nickel metal hydride storage battery has an effective surface area per unit capacity of the negative electrode plate 8 of 70 cm ² / Ah or more, and the negative electrode plate 8 is thin and large. In addition, this battery has a high output because the alkaline electrolyte is uniformly distributed between the positive electrode plate 6 and the negative electrode plate 8. The reason is as follows.
In the nickel metal hydride storage battery described above, one of plasma treatment and surfactant is applied to the nonwoven fabric of the second separator 10b in addition to the sulfonation treatment. For this reason, the hydrophilicity of the second separator 10b is increased, the liquid absorbency of the alkaline electrolyte is improved, and the denseness of the second separator 10b is high. The liquid is absorbed as time passes, and the alkaline electrolyte is distributed substantially uniformly therein.

Further, since the hydrophilicity of the second separator 10b is increased, even if the negative electrode plate 8 contains a water-repellent water-insoluble polymer binder, the gap between the negative electrode plate 8 and the second separator 10b is increased. Alkaline electrolyte is distributed substantially uniformly.
Therefore, in this battery, even if the effective surface area per unit capacity of the negative electrode plate 8 exceeds 70 cm ² / Ah, the alkaline electrolyte is uniformly distributed in the entire region where the positive electrode plate 6 and the negative electrode plate 8 face each other. As a result, the battery reaction proceeds uniformly and high output is achieved.

And in this battery, when the liquid absorption height H of the potassium hydroxide aqueous solution of the second separator 10b is in the range of 5 mm or more in 30 minutes, it is alkaline in the entire region where the positive electrode plate 6 and the negative electrode plate 8 face each other. The electrolyte is reliably distributed uniformly.
In addition, when the plasma treatment is performed on the second separator 10b after the sulfonation treatment, the plasma treatment only introduces a polar group corresponding to the plasma gas type into the second separator 10b. The battery characteristics are not adversely affected.

  When the plasma treatment is performed on the second separator 10b so that the liquid absorption height H falls within the range of 5 mm to 120 mm within 30 minutes, the dielectric breakdown does not occur in the second separator 10b due to the plasma treatment, The internal short circuit of the battery is prevented, and when the surfactant treatment is applied to the second separator 10b so that the liquid absorption height H falls within the range of 120 mm or less in 30 minutes, the influence of impurities can be reduced and the treatment can be reduced. Later separator drying time can also be shortened.

Further, when the plasma treatment is performed on the second separator 10b so that the liquid absorption height H falls within the range of 60 mm or less in 30 minutes, the treatment time of the plasma treatment is shortened and the productivity is improved.
On the other hand, when the surfactant treatment is applied to the second separator 10b so that the liquid absorption height H falls within the range of 60 mm or less in 30 minutes, the surfactant in the second separator 10b is used. However, in the long run, it is prevented from affecting the battery characteristics as an impurity, and when inspecting the insulation between the positive and negative electrodes before injecting the battery, the resistance decreases due to moisture absorbed by the surfactant (pseudo short) ) Is mistakenly determined to be an insulation failure.

Example 1
1. Preparation of negative electrode plate The metal raw materials were weighed and mixed so that the composition was Nd _0.9 Mg _0.1 (Ni _0.9 Co _0.03 Al _0.07 ) _3.5, and this mixture was mixed with a high frequency melting furnace. The ingot was obtained by dissolution. This ingot was heated in an argon atmosphere at a temperature of 1000 ° C. for 10 hours to adjust the crystal structure of the ingot. Thereafter, the ingot was mechanically pulverized in an inert atmosphere, and particles entering between 400 mesh and 200 mesh were sieved to obtain rare earth-Mg-Ni hydrogen storage alloy particles having the above composition. The obtained rare earth-Mg—Ni-based hydrogen storage alloy particles had an average particle diameter of 25 μm corresponding to 50% weight integral measured using a laser diffraction / scattering particle size distribution analyzer.

To 100 parts by mass of the obtained alloy particles, 0.5 parts by mass of SBR (styrene butadiene latex), 0.3 parts by mass of CMC (carboxymethylcellulose) and an appropriate amount of pure water are added and kneaded as a water-insoluble polymer binder. A slurry was prepared. Then, the nickel punching sheet coated with the negative electrode slurry is rolled and cut after drying at room temperature, and the effective surface area, that is, the surface area of the two negative electrode mixture layers held on both surfaces of the negative electrode plate A negative electrode plate having a sum (vertical × horizontal × 2 surfaces) of 990 cm ² was produced.
The obtained negative electrode plate was occluded with hydrogen until the temperature reached 40 ° C. and the hydrogen equilibrium pressure became 1.0 MPa, and the negative electrode capacity determined from the hydrogen occlusion amount at this time was 13.5 Ah.

2. Production of Positive Electrode Plate A porous nickel sintered substrate having a porosity of about 85% was immersed in a mixed aqueous solution having a specific gravity of 1.75 containing nickel nitrate and cobalt nitrate. By this immersion, the sintered substrate holding the nickel salt and cobalt salt in the pores is immersed in a 25% by mass aqueous sodium hydroxide (NaOH) solution, and the nickel salt and cobalt salt are respectively nickel hydroxide and hydroxide. Converted to cobalt. Thereafter, the sodium hydroxide aqueous solution was removed from the sintered substrate by washing thoroughly with water, and after drying, nickel hydroxide and cobalt hydroxide were held in the pores of the porous nickel sintered substrate.

The porous nickel sintered substrate is subjected to the filling process consisting of the above-mentioned immersion in a mixed aqueous solution, immersion in a sodium hydroxide aqueous solution, washing and drying steps 6 times, and then dried at room temperature and then cut into a predetermined size. Then, a sintered nickel electrode having a packing density of nickel hydroxide and cobalt hydroxide in the pores of 2.5 g / cm ³ was produced.
In the obtained sintered nickel electrode, the effective surface area, that is, the sum of the areas filled with the positive electrode mixture on both sides of the electrode (length × width × 2 surfaces) was 920 cm ² .

3. Production of first and second separators (1) Production of non-woven fabric Using a core-sheath composite fiber having a thermal adhesive property in which the core material is made of polypropylene and the sheath material is made of low-melting polyethylene, and high-strength polypropylene fiber, A nonwoven fabric having a basis weight of 50 g / m ² was produced by a wet method with a drying temperature of about 135 ° C.
(2) Hydrophilization treatment of the first separator (fluorine gas treatment)
The obtained nonwoven fabric was treated with a mixed gas of fluorine gas and sulfur dioxide gas diluted with nitrogen gas to modify the surface and impart hydrophilicity.

(3) Hydrophilization treatment of the second separator (sulfonation treatment + surfactant treatment)
The obtained non-woven fabric was immersed in fuming sulfuric acid to give a sulfone group and to give hydrophilicity. The ratio of sulfur atoms to carbon atoms (S / C) in the nonwoven fabric after the sulfonation treatment was a ratio of 2.3 sulfur atoms to 1000 carbon atoms.
Then, the sulfonated nonwoven fabric was dipped in a solution containing sodium carboxylate as a surfactant and dried to adsorb the surfactant to the nonwoven fabric fibers.
(4) Thickness adjustment of 1st and 2nd separator The thickness of the 1st and 2nd separator which carried out the hydrophilic treatment was adjusted to 0.13 mm by passing between a pair of heating rolls, respectively.

4). Assembling of the Nickel Metal Hydride Battery The obtained positive electrode plate, negative electrode plate, first separator and second separator were wound to produce a spiral electrode group.
At this time, the first separator is positioned between the outer surface of the positive electrode plate and the inner surface of the negative electrode plate, the second separator is positioned between the inner surface of the positive electrode plate and the outer surface of the negative electrode plate, and the outer diameter of the electrode group Was wound to 31mm. In addition, the end of the nickel sintered substrate that is the substrate of the positive electrode plate protrudes from one end of the electrode group, and the end of the punching metal that is the substrate of the negative electrode plate protrudes from the other end. did.

For this electrode group, a disk-shaped positive electrode current collector having a large number of openings is welded to a nickel sintered substrate protruding at one end thereof, and a large number of openings are formed in a punching metal protruding at the other end. A disc-shaped negative electrode current collector having the following was welded.
Thereafter, a cylindrical body as a positive electrode lead was further welded to the positive electrode current collector. More specifically, the cylindrical body is formed by obliquely cutting off both ends of a pipe having an oval cross section (for example, made of nickel and having a thickness of 0.3 mm). The cylindrical body was disposed on the diameter of the positive electrode current collector, and the bottom of the cylindrical body was spot welded to the positive electrode current collector.

After welding the positive electrode lead, the electrode group was housed in the outer can and the negative electrode current collector was welded to the bottom surface of the outer can. Thereafter, an aqueous potassium hydroxide solution having a concentration of 30% by mass as an electrolytic solution was poured into the outer can under reduced pressure, and a separately prepared sealing body was welded to the upper bottom of the cylindrical body. The sealing body includes a lid plate, an insulating gasket, a valve body, a compression coil spring, and a positive electrode terminal, and the lid plate was welded to the upper bottom of the cylindrical body.
Then, the sealing body is pressed against the electrode group with a punch to compress and deform the cylindrical body, and the opening edge of the outer can is crimped inward to produce a cylindrical nickel-metal hydride storage battery with a nominal capacity of 6.0 Ah. did.

Example 2
A battery of Example 2 was assembled in the same manner as in Example 1 except that the concentration of the solution used for the surfactant treatment was increased.
Example 3
A battery of Example 3 was assembled in the same manner as in Example 2 except that the concentration of the solution used for the surfactant treatment was increased.

Example 4
A battery of Example 4 was assembled in the same manner as in Example 1 except that the sulfonated nonwoven fabric was passed between the electrodes of the plasma device and treated with oxygen plasma instead of the surfactant treatment.
Example 5
A battery of Example 5 was assembled in the same manner as in Example 4 except that the current value of the plasma treatment was increased.
Example 6
A battery of Example 6 was assembled in the same manner as in Example 5 except that the current value of the plasma treatment was increased.

Comparative Example 1
A battery of Comparative Example 1 was assembled in the same manner as in Example 1 except that the surfactant treatment was not performed.
Comparative Example 2
As shown in Table 1, the effective surface areas of the positive electrode plate and the negative electrode plate were reduced, and the comparison was made in the same manner as in Comparative Example 1 except that the basis weight and thickness of the first and second separators were changed. The battery of Example 2 was assembled.
In Comparative Example 1 and Comparative Example 2, the active material filling amount of the positive electrode plate and the negative electrode capacity of the negative electrode plate are the same.

5. Evaluation method (1) Liquid permeability of separator (liquid absorption height H)
The liquid absorption height H was measured as follows as an index of the liquid permeability (liquid absorption) of the aqueous potassium hydroxide solution in the first and second separators of Examples 1 to 6 and Comparative Examples 1 and 2.
A sample obtained by cutting the first and second separators before winding into a strip shape is placed vertically so that only the lower end of the sample is immersed in the aqueous potassium hydroxide solution. The raised height (liquid absorption height H) was measured with reference to the water surface. The results are shown in Table 1. The concentration of potassium hydroxide used for the measurement is 30% by mass.

(2) Area ratio of discoloration region on negative electrode plate Each of the batteries of Examples 1 to 6 and Comparative Examples 1 and 2 was charged to a charging depth of 120% with a charging current of 1 It in an environment where the temperature was 25 ° C. Thereafter, after a rest time of 1 hour, each battery was left (aged) for 24 hours in an environment of 70 ° C. Subsequently, each battery was discharged to a final voltage of 0.3 V with a discharge current of 1 It again in an environment where the temperature was 25 ° C. Then, the above-described charging / discharging cycle comprising charging, resting, leaving, and discharging steps was further repeated twice.

  Thus, each battery having the charge / discharge cycle repeated three times was disassembled, the negative electrode plate was taken out, and the penetration state of the alkaline electrolyte into the negative electrode plate was examined. As a result, in Examples 1, 2, 4, 5, 6 and Comparative Example 1, there was a region where the alkaline electrolyte solution did not sufficiently permeate, and in this region, the discoloration considered to be due to oxidation of the hydrogen storage alloy occurred. Admitted. Then, about the negative electrode plate by which the color-change area | region was confirmed, the ratio of the area of the color-change area with respect to the total surface area was investigated. The results are shown in Table 1. The area of the discoloration region was calculated as the product of the length and width measured.

6). Evaluation Results (1) As is apparent from Table 1, Examples 1 to 6 in which the surfactant treatment or plasma treatment was performed on the second separator were compared with Comparative Example 1 in which these treatments were not performed. The area ratio was small, and the permeability of the alkaline electrolyte to the negative electrode plate was excellent.
(2) From Examples 1 to 3, it can be seen that the higher the concentration of the solution used for the surfactant treatment, the higher the liquid absorption height H and the lower the ratio of the discolored area.
(3) From Examples 4 to 6, it can be seen that the larger the current value of the plasma treatment, the higher the liquid absorption height H and the lower the ratio of the discolored area.
(4) In Comparative Example 2, no discoloration region was generated even though neither the surfactant treatment nor the plasma treatment was applied to the second separator. This is because in Comparative Example 2, the effective surface area of the negative electrode plate is small and the basis weight and thickness of the first and second separators are large compared to Comparative Example 1, so that the alkaline electrolyte is uniformly distributed between the electrode plates. It is thought that it was because.

On the other hand, although not shown in Table 1, the output of the battery of Comparative Example 2 was small because the effective surface area of the electrode plate was lower than that of Examples 1-6. From this, it can be seen that in a battery having a large effective surface area per unit capacity in the negative electrode plate, high output can be achieved by subjecting the second separator to surfactant treatment or plasma treatment.
The present invention is not limited to the above-described embodiment and examples, and various modifications can be made. For example, in one embodiment, the positive electrode plate 6 is a sintered nickel electrode, but a non-sintered nickel electrode may be used.

  In one embodiment, the nonwoven fabric of the first separator 10a is subjected to at least one hydrophilization treatment selected from fluorine gas treatment, plasma treatment, and surfactant treatment, and the nonwoven fabric of the second separator 10b is applied to the nonwoven fabric of the second separator 10b. Although the sulfonation treatment and one of the surfactant treatment and the plasma treatment are performed, the reverse may be possible. However, in order to prevent an internal short circuit, the nonwoven fabric of the first separator 10a is subjected to at least one hydrophilization treatment selected from fluorine gas treatment, plasma treatment, and surfactant treatment, and the second separator 10b. The non-woven fabric is preferably subjected to sulfonation treatment and one of surfactant treatment and plasma treatment.

It is sectional drawing which shows the nickel hydride storage battery of one Embodiment of this invention.

Explanation of symbols

2 Exterior can 4 Electrode group 6 Positive electrode plate 8 Negative electrode plate
10a First separator
10b Second separator

Claims (5)

In a nickel metal hydride battery comprising a spiral electrode group housed together with an alkaline electrolyte in a container,
The electrode group includes:
A negative electrode plate comprising hydrogen storage alloy particles and a water-insoluble polymer binder that binds the hydrogen storage alloy particles, and an effective surface area per unit volume of 70 cm ² / Ah or more;
A positive electrode plate that is spirally wound together with the negative electrode plate and contains nickel hydroxide as a positive electrode active material;
A first separator that is disposed between an outer surface of the positive electrode plate and an inner surface of the negative electrode plate and is made of a nonwoven fabric of polyolefin-based fibers;
The second separator is disposed between the inner surface of the positive electrode plate and the outer surface of the negative electrode plate, and is made of a nonwoven fabric of polyolefin fibers,
One nonwoven fabric of the first separator and the second separator is subjected to at least one hydrophilic treatment selected from fluorine gas treatment, plasma treatment and surfactant treatment, and the other nonwoven fabric is sulfonated. One of the treatment, the plasma treatment, and the surfactant treatment is performed. The nonwoven fabric of the first separator is subjected to at least one hydrophilization treatment selected from the fluorine gas treatment, plasma treatment and surfactant treatment,
The nickel hydride storage battery according to claim 1, wherein the non-woven fabric of the second separator is subjected to one of the sulfonation treatment, the plasma treatment, and the surfactant treatment.   The nickel hydride storage battery according to claim 2, wherein the second separator is subjected to the plasma treatment after the sulfonation treatment.   3. The nickel-metal hydride storage battery according to claim 2, wherein the second separator has a potassium hydroxide aqueous solution absorption height in a range of 5 mm to 120 mm in 30 minutes.   5. The nickel-metal hydride storage battery according to claim 4, wherein the second separator has a potassium hydroxide aqueous solution absorption height in a range of 5 mm to 60 mm in 30 minutes.

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