JPH0982304A - Method for manufacturing nickel-hydrogen secondary battery - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a method for producing a nickel-hydrogen secondary battery, which has improved self-discharge characteristics during high temperature storage and improved charge-discharge cycle life by improving a separator. To do. In a method for manufacturing a nickel-hydrogen secondary battery, which comprises a positive electrode containing a nickel compound, a negative electrode containing a hydrogen storage alloy, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. The separator is produced by irradiating a sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a nickel-hydrogen secondary battery having an improved separator.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery has a structure in which an electrode group made by interposing a separator between a positive electrode containing a nickel compound and a negative electrode containing a hydrogen storage alloy is housed in a container together with an alkaline electrolyte. Have. The secondary battery is voltage-compatible with a nickel-cadmium secondary battery having a negative electrode containing a cadmium compound instead of the hydrogen storage alloy, and has a higher capacity than the nickel-cadmium secondary battery. Have characteristics.

Although such a nickel-hydrogen secondary battery has a higher capacity than the nickel-cadmium secondary battery, it basically has the same structure as the nickel-cadmium secondary battery and is stored in a charged state at a high temperature. There is a problem with the self-discharge characteristics when the above is done.

Self-discharge of the nickel-cadmium secondary battery during high-temperature storage is caused by (1) impurities (eg, nitrate ion, nitrite ion, etc.) generated by oxidative decomposition of the separator.
N, which is the charge product of the positive electrode that occurs due to (ammonia)
It occurs due to two factors, iOOH reduction reaction and (2) NiOOH autolysis reaction. Of these, the above (2)
NiOOH self-decomposition reaction is
Since it is slower than the reduction reaction of H, it is considered that the main cause of the self-discharge reaction during high temperature storage is the reduction reaction of NiOOH described in (1) above.

The above-mentioned oxidative decomposition of the separator is particularly remarkable when a nonwoven fabric made of polyamide fiber widely used in nickel-cadmium secondary batteries is used as a separator from the viewpoint of hydrophilicity, and polyamide-based synthetic resin fiber The impurities generated by the oxidative decomposition are Ni of the positive electrode.
OOH is reduced to promote self-discharge reaction.

From the above, in the nickel-cadmium secondary battery, it is attempted to use a polyolefin fiber which is basically hydrophobic, though it has better oxidation resistance than the polyamide fiber, after being subjected to a hydrophilic treatment. ing.

On the other hand, unlike the nickel-cadmium secondary battery, the nickel-hydrogen secondary battery uses a hydrogen storage alloy for the negative electrode to achieve a higher capacity than the nickel-cadmium secondary battery. The hydrogen storage alloy of the negative electrode is
Hydrogen gas can be stored and released depending on temperature and pressure. Utilizing this property of reversibly occluding and releasing hydrogen gas, it occludes and releases hydrogen gas electrochemically instead of temperature and pressure, making it a secondary battery with a higher capacity than nickel-cadmium secondary batteries. Has been realized. The equilibrium pressure and the amount of hydrogen storage at each temperature of the hydrogen storage alloy are determined according to its composition. The equilibrium pressure and the amount of hydrogen storage slightly vary depending on the composition of the hydrogen storage alloy, but generally the equilibrium pressure increases as the temperature increases, and the amount of hydrogen storage decreases. For this reason, the hydrogen storage amount of the hydrogen storage alloy is reduced, so that the hydrogen gas that cannot be stored in the hydrogen storage alloy is released.

In a nickel-hydrogen secondary battery using the hydrogen storage alloy having the above-mentioned properties as a negative electrode, the storage capacity of hydrogen decreases due to an increase in the equilibrium pressure of the hydrogen storage alloy during high temperature storage, and hydrogen gas absorbs hydrogen. A phenomenon occurs that could not occur in a nickel-cadmium secondary battery, in which the alloy is released and fills the battery. Since the generated hydrogen gas exists in the battery at a high concentration, a reaction for reducing NiOOH of the positive electrode occurs. Therefore, in order to improve the self-discharge characteristics during storage at high temperature in a nickel-hydrogen secondary battery,
The above-mentioned two causes that became apparent when the self-discharge characteristics of the nickel-cadmium secondary battery were improved, namely, (1) reduction reaction of NiOOH, which is a charge product of the positive electrode due to impurities generated by oxidative decomposition of the separator, and , (2)
Besides self-decomposition reaction of NiOOH, which could not occur in nickel-cadmium secondary battery (3) NiO by hydrogen gas inevitably released from hydrogen storage alloy during high temperature storage
It is also necessary to solve the problem of OH reduction reaction. In order to solve such a problem, it is necessary to take measures to prevent hydrogen gas inevitably generated from the negative electrode including the hydrogen storage alloy during high-temperature storage from reaching the paste-type positive electrode.

As the separator of the nickel-hydrogen secondary battery, there is conventionally known a nonwoven fabric made of polyolefin fiber which is irradiated with an energy beam to graft-copolymerize a vinyl monomer having a hydrophilic group. As the energy beam, ultraviolet rays, ionizing radiation such as electron beams and X-rays are used. The use of ultraviolet rays as the energy beam is useful because the energy beam irradiation can be performed by a simple operation. According to this method, a polyolefin fiber nonwoven fabric is irradiated with ultraviolet rays to generate carbon radicals in the nonwoven fabric, and a vinyl monomer having a hydrophilic group is graft-copolymerized with the radicals to obtain a separator.

However, the separator prepared by graft copolymerization using ultraviolet rays as the energy beam described above is inferior in hydrophilicity and has a small amount of retained electrolytic solution.
In a secondary battery including such a separator, the hydrogen gas inevitably generated from the hydrogen storage alloy of the negative electrode during high temperature storage permeates the separator and reduces the NiOOH of the positive electrode, so that the high temperature storage property is significantly deteriorated. .

Further, the secondary battery provided with the separator has a problem that charge / discharge cycle characteristics are inferior. In particular, in the secondary battery, when a paste type positive electrode or a paste type hydrogen storage alloy negative electrode is used to increase the filling amount of the active material, the electrolytic solution in the separator is a binder contained in the positive electrode or the negative electrode. As the water-absorbing agent is absorbed by the agent, the amount of the electrolyte retained in the separator decreases as the charge-discharge cycle progresses, the internal resistance of the secondary battery increases, and the charge-discharge cycle life is significantly increased. Fall to.
Further, when nickel hydroxide is used as an active material of the paste-type positive electrode, the positive electrode tends to expand as the charge / discharge cycle progresses and absorb the alkaline electrolyte in the separator, which further causes the above-mentioned problems. It will be noticeable.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a nickel-hydrogen secondary battery, which has improved self-discharge characteristics during high temperature storage and improved charge / discharge cycle life by improving a separator. It is the one we are trying to provide.

[0013]

A method of manufacturing a nickel-hydrogen secondary battery according to the present invention comprises a positive electrode containing a nickel compound, a negative electrode containing a hydrogen storage alloy, and a separator interposed between the positive electrode and the negative electrode. And a method for producing a nickel-hydrogen secondary battery including an alkaline electrolyte, wherein a polyolefin-based synthetic resin fiber sheet material containing no light stabilizer is irradiated with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group. It is characterized in that a separator is produced by the above.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a nickel-hydrogen secondary battery (cylindrical nickel-hydrogen secondary battery) manufactured by the method according to the present invention will be described below with reference to FIG. As shown in FIG. 1, an electrode group 5 made by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is housed in a bottomed cylindrical container 1. The negative electrode 4
Are arranged at the outermost periphery of the electrode group 5 and are in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. Circular sealing plate 7 having a hole 6 in the center
Are arranged in the upper opening of the container 1. The ring-shaped insulating gasket 8 is arranged in a compressed state between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening by caulking to reduce the diameter of the upper opening of the container 1 to the inside of the container 1. The sealing plate 7 is airtightly fixed. The positive electrode lead 9 has one end connected to the positive electrode 2 and the other end connected to the lower surface of the sealing plate 7. The hat-shaped positive electrode terminal 10 is mounted on the sealing plate 7 so as to cover the hole 6. The rubber safety valve 11 is provided with the sealing plate 7.
Is arranged so as to close the hole 6 in a space surrounded by the positive electrode terminal 10.

Next, the positive electrode 2, the negative electrode 4, and the separator 3
The alkaline electrolyte will be described. 1) Positive electrode 2 The positive electrode 2 contains a nickel compound.

The positive electrode preferably has a structure in which a current collector is filled with the paste containing the nickel compound. The positive electrode, for example, after preparing a paste containing the nickel compound, a conductive material, a binder, and water, fill the current collector with the paste, dried it, if necessary It is produced by applying pressure molding.

As the nickel compound, nickel hydroxide, nickel hydroxide in which zinc and cobalt are coprecipitated,
Nickel oxide etc. can be mentioned. Among them, it is preferable to use nickel hydroxide in which zinc and cobalt are coprecipitated.

The conductive material is made of one or more selected from cobalt compounds and metallic cobalt. Examples of the cobalt compound include cobalt hydroxide (Co (OH) ₂ ) and cobalt monoxide (CoO). In particular, it is preferable to use cobalt hydroxide, cobalt monoxide, or a conductive material containing both cobalt hydroxide and cobalt monoxide.

Examples of the binder include hydrophobic polymers such as polytetrafluoroethylene (PTFE), polyethylene and polypropylene, such as carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) such as poly. Examples thereof include polyacrylic acid salts such as sodium acrylate (SPA), hydrophilic polymers such as polyvinyl alcohol (PVA) and polyethylene oxide, and rubber-based polymers such as latex.

As the current collector, for example, nickel,
Examples thereof include a net-like, sponge-like, fibrous, or felt-like porous metal body formed of a metal such as stainless steel or an alkali resistant material such as a resin plated with nickel. 2) Negative Electrode 4 This negative electrode 4 contains a hydrogen storage alloy.

The negative electrode preferably has a structure in which a conductive substrate is filled with a paste containing a hydrogen storage alloy. For the negative electrode, for example, a paste containing the hydrogen storage alloy, a conductive material, a binder, and water is prepared, the conductive substrate is filled with the paste, dried, and then pressure-molded if necessary. It is manufactured by

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. . For example, LaNi ₅ , MmN
i ₅ (Mm; misch metal composed of a mixture of lanthanum elements such as La, Ce, Pr, Nd and Sm), LmN
i ₅ (Lm; lanthanum-enriched misch metal), or a part of these Ni, Al, Mn, Co, Ti, C
u-, Zn-, Zr-, Cr-, B-substituted multi-elements, TiNi-based, TiFe-based, ZrN
Examples thereof include i type and MgNi type. Especially,
Formula LmNi _x Mn _y A _z (However, A is Al, Co
At least one metal selected from the atomic ratios x, y, z
Represents a total value of 4.8 ≦ x + y + z ≦ 5.4), and the negative electrode containing the rare earth-based hydrogen storage alloy can suppress pulverization due to the progress of charge / discharge cycles, and the secondary battery It is preferable because the charge / discharge cycle life of can be improved.

Examples of the conductive material include carbon black. As the binder, the same binder as described above for the positive electrode can be used.

Examples of the conductive substrate include two-dimensional substrates such as punched metal, expanded metal, perforated rigid plate, and nickel net, and three-dimensional substrates such as felt-like metal porous bodies and sponge-like metal substrates. Can be mentioned. 3) Separator 3 This separator 3 is produced by irradiating a sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group. The polyolefin synthetic resin fiber sheet-like material containing no light stabilizer can be prepared from, for example, a polyolefin synthetic resin fiber to which no light stabilizer is added.

Specifically, the separator can be produced by the following methods (a) to (c). (A) After immersing a sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer in a solution containing a vinyl monomer having a hydrophilic group, the sheet material is irradiated with ultraviolet rays to graft-copolymerize the vinyl monomer. By doing so, a separator is produced.

(B) The sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer is irradiated with ultraviolet rays, and then the sheet material is dipped in a solution containing a vinyl monomer having a hydrophilic group. A separator is produced by graft-copolymerizing the vinyl monomer with.

(C) A sheet material made of a polyolefin-based synthetic resin fiber not containing a light stabilizer, which is dipped in a solution containing a vinyl monomer having a hydrophilic group, is irradiated with ultraviolet rays to expose the vinyl monomer to the sheet material. A separator is produced by graft copolymerization.

Among them, the method (a) is preferable because the loss of carbon radicals generated by ultraviolet irradiation is small and the graft copolymerization ratio is easily controlled.
As the polyolefin-based synthetic resin fiber, a polyolefin fiber, a core-sheath structure composite fiber in which a polyolefin fiber different from the polyolefin fiber is coated on the surface of a core material made of the polyolefin fiber, and different polyolefin fibers are joined in a circular shape. A composite fiber having a divided structure can be used. Examples of the polyolefin include polyethylene and polypropylene.

Examples of the sheet-like material containing the polyolefin-based synthetic resin fiber include a non-woven fabric made of the above-mentioned polyolefin-based synthetic resin fiber, a woven fabric made of the same fiber, or a composite sheet obtained by combining these non-woven fabrics and a woven fabric. be able to. The nonwoven fabric is, for example, a dry method,
It is produced by a wet method, a spun bond method, a melt blow method or the like. Among these methods, the spunbond method and the meltblown method are advantageous in terms of preventing a short circuit between the positive electrode and the negative electrode because a nonwoven fabric having a small fiber diameter can be produced. The non-woven fabric has a fiber diameter of 0.1 to 15 from the viewpoint of increasing the density and preventing a short circuit between the positive electrode and the negative electrode.
It is preferably made of a polyolefin synthetic resin fiber of μm. Further, the separator made of the composite sheet,
Dense and high tensile strength.

As the vinyl monomer having a hydrophilic group, for example, acrylic acid, methacrylic acid, esters of acrylic acid or methacrylic acid, vinyl pyridine, vinylpyrrolidone, styrenesulfonic acid, styrene and the like are directly reacted with an acid or a base. And a functional group capable of forming a salt, or a functional group capable of forming a salt by being hydrolyzed after being graft-copolymerized. Among them, acrylic acid is suitable as the vinyl monomer.

The graft copolymerization ratio of the vinyl monomer having a hydrophilic group onto the sheet is 0.2 to 2 in terms of potassium ion exchange amount determined by titration described below.
It is preferably 0 meq / g (milli-equivalent per gramme). The amount of ion exchange is 0.2 meq / g
If the amount is less than the range, the liquid retaining property of the separator may be deteriorated. On the other hand, if the amount of ion exchange exceeds 2.0 meq / g, the operating voltage may decrease when the secondary battery is discharged with a large current. More preferable ion exchange amount is
It is 0.7-1.4 meq / g.

(Titration method) First, 0.5 to 1 g of a sample (for example, a non-woven fabric made of polyolefin fiber graft-copolymerized with acrylic acid) was placed in a 100 ml polyethylene wide-mouthed bottle, and 100 ml of 1N-HCl solution was added, If the sample is floating, submerge it completely,
Store in a 60 ° C. thermostat for 1 hour. Subsequently, the sample is transferred to a beaker containing 200 ml of ion-exchanged water, stirred with a glass rod, and washed until the pH of the washing solution becomes 6 to 7 while replacing the ion-exchanged water. The sample is drained, spread on a stainless steel vat, and dried in a dryer at 100 ° C. for 1 hour. After cooling, weigh the sample 0.1 mg
And transfer to a 100 ml polyethylene jar.
110g ± 0.01g of these 0.01N-KOH solutions
Add. On the other hand, 100 ml as a blank sample
0.01N-KOH solution in a polyethylene wide-mouth bottle
Collect 10 g ± 0.01 g. Subsequently, these jars are placed in a thermostat at 60 ° C., shaken gently every 30 minutes, and stored for 2 hours. After gently shaking each of the jars, each sample is taken out and allowed to cool to room temperature. Approximately 100 g of the test solution after cooling is weighed to 0.01 g in a 200 ml conical beaker, and neutralized by phenolphthalein as an indicator with a 0.1 N HCl solution. The blank test solution is titrated by the same operation. By such a titration, the amount of potassium ion exchange is calculated by the following equation (1).

[0033]

[Equation 1]

The thickness of the separator 3 is 0.15 mm.
It is preferable to set the range to 0.3 mm. Basis weight of the separator 3 should preferably be in the range of ^{30g / m 2 ~70g / m 2} . The basis weight is 30 g / m ²
If it is less than the above, the strength of the separator 3 may be reduced. On the other hand, if the basis weight exceeds 70 g / m ² , the battery capacity may decrease. More preferred basis weight is in the range of ^{40g / m 2 ~60g / m 2} . 4) Alkaline Electrolyte Solution Examples of the alkaline electrolyte solution include an aqueous solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH).
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

According to the method for producing a nickel-hydrogen secondary battery of the present invention, a sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer is irradiated with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group. By doing so, a separator is produced. The secondary battery incorporating the separator can achieve improvement in high temperature storage characteristics and long life.

That is, a polyolefin-based synthetic resin fiber, which is a material for a sheet, is usually made of a weathering stabilizer such as an antioxidant or a light stabilizer in order to suppress auto-oxidative deterioration caused by heat or light energy. Has been added. Of these weather resistance stabilizers, light stabilizers absorb ultraviolet rays and convert them into heat, kinetic and light energy (phosphorescence, fluorescence) that is harmless to polyolefin-based synthetic resin fibers and release them to the outside, or they are generated by ultraviolet rays. It has a function of suppressing autoxidative deterioration by trapping the generated radicals and stopping further radical chain reaction. As this light stabilizer, hindered amine (HALS: Hindered Amine Light Stabiliz-er), which has a high radical scavenging effect, is widely used for styrene synthetic resin, polyurethane, etc. in addition to polyolefin synthetic resin fiber. Although the amount of the light stabilizer added varies depending on the type of resin, it is usually several hundreds.
Is about several thousand ppm. When an attempt is made to graft-copolymerize a vinyl monomer having a hydrophilic group by irradiating a sheet material made of a polyolefin-based synthetic resin fiber containing such a light stabilizer with ultraviolet rays, the light stabilizer stops the chain reaction of carbon radicals. Therefore, the vinyl monomer is partially graft-copolymerized with the sheet-like material, the graft copolymerization ratio is low, and the hydrophilicity of the separator is lowered.

When a polyolefin-based synthetic resin fiber sheet-like material containing no light stabilizer as in the present invention is irradiated with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group, a chain reaction of carbon radicals is promptly conducted. To occur,
It is possible to uniformly and sufficiently graft-copolymerize the vinyl monomer on the sheet with a small irradiation amount of ultraviolet rays, and improve the hydrophilicity of the separator without degrading the fibers by ultraviolet rays. Further, the auto-oxidative deterioration of the separator made of a polyolefin synthetic resin fiber sheet-like material containing no light stabilizer can be suppressed by an antioxidant, and depending on the case, there is a problem even without the antioxidant. There is no. Therefore, when a separator made by graft-copolymerizing a vinyl monomer having a hydrophilic group by irradiating the sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer described above with ultraviolet rays is incorporated into a secondary battery, The separator can hold a large amount of electrolytic solution, and an electrolytic solution film can be formed on the surface including gaps between fibers. This electrolyte membrane hinders the permeation of hydrogen gas, which is inevitably generated from the hydrogen storage alloy of the negative electrode when the nickel-hydrogen secondary battery is stored at high temperature, so that the self-discharge characteristics can be improved. Further, since the separator has an excellent electrolytic solution holding property for a long period of time, it is possible to suppress an increase in internal resistance due to the progress of the charging / discharging cycle of the secondary battery, and improve the charging / discharging cycle life. be able to.

[0038]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Example 1) <Preparation of paste-type negative electrode> Commercially available lanthanum-enriched misch metal Lm and Ni, Co, Mn, and Al were used in a high-frequency furnace to produce LmNi _4.0 Co _0.4 Mn _0.3 Al.
_A hydrogen storage alloy having a composition of _0.3 was prepared. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. 0.5 parts by weight of sodium polyacrylate, 0.125 parts by weight of carboxymethylcellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity 1.5,
A paste was prepared by mixing 2.5 parts by weight (solid content 60 wt%) and 1.0 part by weight of carbon powder as a conductive material together with 50 parts by weight of water. This paste was applied to a punched metal, dried, and then pressure-molded to produce a paste-type negative electrode.

<Preparation of paste type positive electrode> 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder were mixed with 0.3 parts by weight of carboxymethyl cellulose and polytetrafluoro with respect to the nickel hydroxide powder. A paste was prepared by adding 0.5 parts by weight of a suspension of ethylene (specific gravity: 1.5, solid content: 60% by weight) in terms of solid content, adding 45 parts by weight of pure water thereto and kneading. Subsequently, after this paste was filled in a nickel-plated fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by roller pressing to produce a paste-type positive electrode.

<Preparation of Separator> Polypropylene resin containing no light stabilizer was formed by a spunbond method into long fibers having a fiber diameter of 10 μm, and the basis weight was 50 g / m ^2.
Thus, a nonwoven fabric having a thickness of 0.20 mm was produced. After immersing the non-woven fabric in an acrylic acid aqueous solution, it was irradiated with ultraviolet rays to graft-copolymerize an acrylic acid monomer. The nonwoven fabric was washed to remove unreacted acrylic acid, and then dried to produce a separator. The graft copolymerization ratio of the acrylic acid monomer of the obtained separator was measured by the titration method described above. As a result, the ion exchange amount of potassium was 0.8 meq / g. Further, after the separator is immersed in an aqueous solution of a fiber identification indicator to dye acrylic acid in the separator, the surface of the separator is observed, and the surface is uniformly dyed, and the acrylic acid monomer is present in the nonwoven fabric. It was confirmed that the graft copolymerization was carried out uniformly.

Next, the separator was interposed between the negative electrode and the positive electrode and spirally wound to form an electrode group. Such an electrode group and 7N KOH and 1N Li
An AA-size cylindrical nickel-metal hydride secondary battery having the above-described structure shown in FIG. 1 was assembled by storing the electrolyte solution composed of OH in a bottomed cylindrical container.

(Example 2) A nonwoven fabric having a fiber diameter of 1 μm and a basis weight of 50 g / m ² and a thickness of 0.20 mm was prepared from a polypropylene resin containing no light stabilizer by a melt blow method. In the same manner as in Example 1, this nonwoven fabric was immersed in an aqueous solution of acrylic acid and irradiated with ultraviolet rays to graft-copolymerize an acrylic acid monomer to prepare a separator. As a result of measuring the graft copolymerization ratio of the acrylic acid monomer of the obtained separator by the titration method described above, the ion exchange amount of potassium was 0.8 meq / g. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the surface was uniformly dyed, and the acrylic acid monomer was uniformly graft-copolymerized on the nonwoven fabric. I confirmed that.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

Comparative Example 1 500 ppm as a light stabilizer
The polypropylene resin containing the hindered amine of is made of long fibers having a fiber diameter of 10 μm by using the spunbond method.
A nonwoven fabric having a basis weight of 50 g / m ² and a thickness of 0.20 mm was prepared. In the same manner as in Example 1, this nonwoven fabric was immersed in an aqueous solution of acrylic acid and irradiated with ultraviolet rays to graft-copolymerize an acrylic acid monomer to prepare a separator. The graft copolymerization ratio of the acrylic acid monomer of the obtained separator was measured by the titration method described above, and as a result, the ion exchange amount of potassium was 0.1 meq /
g. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the dyeing state of the surface was uneven and uneven, and the acrylic acid monomer was partially present in the nonwoven fabric. It was confirmed that the copolymer was graft-copolymerized with.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

The obtained secondary batteries of Examples 1 and 2 and Comparative Example 1 were charged at 1 CmA to 150% and then charged to 1C.
The charging / discharging cycle of discharging until the battery voltage reached 1.0 V at mA was repeated 3 times. Then 150 at 1 CmA
After being stored in a constant temperature bath at 45 ° C. for 14 days in a state where the battery was fully charged, the battery was discharged at 1 CmA until the battery voltage reached 1.0 V, and the discharge capacity (remaining capacity) was measured. Charge 150% at 1 CmA before storing for 14 days in a 45 ° C thermostat, and
When the discharge capacity when the battery voltage is discharged to 1.0 V with CmA is C _0, and the discharge capacity after storage for 14 days in a constant temperature bath at 45 ° C. is the residual capacity C _R , the capacity residual rate is calculated from the following formula. I asked.

Capacity Remaining Ratio (%) = ( _CR / _C0 ) × 100 FIG. 2 shows the relationship between the number of days of storage in each secondary battery and the capacity remaining ratio obtained from the above formula. As is apparent from FIG. 2, the secondary batteries of Examples 1 and 2 of the present invention have improved self-discharge characteristics during high temperature storage as compared with the secondary battery of Comparative Example 1. In the separator used in the secondary batteries of Examples 1 and 2, since a sufficient amount of acrylic acid monomer was uniformly graft-copolymerized, an electrolytic solution film should be formed on the entire surface including gaps between fibers. You can Therefore, it is possible to prevent the hydrogen gas generated from the paste-type negative electrode containing the hydrogen storage alloy from moving to the positive electrode during high temperature storage. Therefore, the reduction reaction of the positive electrode with hydrogen gas can be suppressed, and the self-discharge characteristics during high temperature storage can be improved.

Further, with respect to the obtained secondary batteries of Examples 1 and 2 and Comparative Example 1, a charging / discharging cycle was repeated in which after charging 150% at 1 CmA, the battery was discharged at 1 CmA until the battery voltage reached 1.0V. 1 CmA for each cycle
Then, the discharge capacity was calculated from the time until the battery voltage reached 1.0V.

The results of the charge / discharge cycle characteristic test are shown in FIG.
Shown in The discharge capacity ratio on the vertical axis of FIG. 3 is the discharge capacity in the subsequent cycles of the secondary batteries of Examples 1 and 2 and Comparative Example 1, with the discharge capacity of the first cycle of Example 1 being 100. . The cycle number ratio on the horizontal axis of FIG. 3 is such that the discharge capacity of the secondary battery of Example 1 is 8 times the discharge capacity of the first cycle.
Assuming that the number of cycles reaching 0% is 100, Examples 1-2
The cycle number of Comparative Example 1 is shown.

As is apparent from FIG. 3, the secondary batteries of Examples 1 and 2 of the present invention have a longer charge / discharge cycle life than the secondary battery of Comparative Example 1. This is from Example 1
This is because the separator used in No. 2 has an excellent electrolytic solution retention property for a long period of time and can suppress an increase in internal resistance due to exhaustion of the electrolytic solution.

(Example 3) A polypropylene resin containing no light stabilizer was prepared by a spunbond method to have a fiber diameter of 10 μm.
A non-woven fabric made of the long fibers of No. 1 having a basis weight of 50 g / m ² and a thickness of 0.20 mm was produced. After irradiating the nonwoven fabric with ultraviolet rays, it was immersed in an acrylic acid aqueous solution to graft-copolymerize an acrylic acid monomer. The nonwoven fabric was washed to remove unreacted acrylic acid, and then dried to produce a separator. The graft copolymerization ratio of the acrylic acid monomer of the obtained separator was measured by the titration method described above. As a result, the ion exchange amount of potassium was 0.8 meq / g. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the surface was uniformly dyed, and the acrylic acid monomer was uniformly graft-copolymerized on the nonwoven fabric. I confirmed that.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

Comparative Example 2 500 ppm as a light stabilizer
The polypropylene resin containing the hindered amine of is made of long fibers having a fiber diameter of 10 μm by using the spunbond method.
A nonwoven fabric having a basis weight of 50 g / m ² and a thickness of 0.20 mm was prepared. This non-woven fabric was irradiated with ultraviolet rays and immersed in an acrylic acid aqueous solution in the same manner as in Example 3 to graft-copolymerize an acrylic acid monomer to prepare a separator. The graft copolymerization ratio of the acrylic acid monomer of the obtained separator was measured by the titration method described above, and as a result, the ion exchange amount of potassium was 0.05 meq.
/ G. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the dyeing state of the surface was uneven and uneven, and the acrylic acid monomer was partially present in the nonwoven fabric. It was confirmed that the copolymer was graft-copolymerized with.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

With respect to the obtained secondary batteries of Example 3 and Comparative Example 2, the capacity remaining rate after storage for 14 days in a constant temperature bath at 45 ° C. was determined by the same method as described above, and Example 3 was obtained. Also, although the discharge capacity C ₀ when the battery voltage was discharged to 1.0 V at 1 CmA in Comparative Example 2 was the same, the remaining capacity ratio of the secondary battery in Example 3 was 65%. The secondary battery of Comparative Example 2 has a capacity remaining ratio of 35.
%Met.

Further, with respect to the obtained secondary batteries of Example 3 and Comparative Example 2, a charge / discharge cycle characteristic test was conducted by the same method as described above. As a result, although the discharge capacities of the first cycle of Example 3 and Comparative Example 2 were the same, the number of cycles in which the discharge capacity of the secondary battery of Example 3 reached 80% of the discharge capacity of the first cycle was calculated. When set to 100, the number of cycles in which the discharge capacity of the secondary battery of Comparative Example 2 reached 80% of the discharge capacity in the first cycle was 65.

(Example 4) A polypropylene resin containing no light stabilizer was prepared by the spunbond method to have a fiber diameter of 10 μm.
A non-woven fabric made of the long fibers of No. 1 having a basis weight of 50 g / m ² and a thickness of 0.20 mm was produced. The nonwoven fabric dipped in the acrylic acid aqueous solution was irradiated with ultraviolet rays to graft-copolymerize the acrylic acid monomer. The nonwoven fabric was washed to remove unreacted acrylic acid, and then dried to produce a separator. The graft copolymerization ratio of the acrylic acid monomer of the obtained separator was measured by the titration method described above. As a result, the ion exchange amount of potassium was 0.8 meq / g. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the surface was uniformly dyed, and the acrylic acid monomer was uniformly graft-copolymerized on the nonwoven fabric. I confirmed that.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

(Comparative Example 3) 500 ppm as a light stabilizer
The polypropylene resin containing the hindered amine of is made of long fibers having a fiber diameter of 10 μm by using the spunbond method.
A nonwoven fabric having a basis weight of 50 g / m ² and a thickness of 0.20 mm was prepared. A separator was produced by graft-copolymerizing an acrylic acid monomer to this nonwoven fabric in the same manner as in Example 4. As a result of measuring the graft copolymerization ratio of the acrylic acid monomer of the obtained separator by the titration method described above, the ion exchange amount of potassium was 0.1.
meq / g. Further, after the acrylic acid in the separator was dyed by the same method as described above, the surface of the separator was observed, and the dyeing state of the surface was uneven and uneven, and the acrylic acid monomer was partially present in the nonwoven fabric. It was confirmed that the copolymer was graft-copolymerized with.

Then, the same separator as in Example 1 was interposed between the negative electrode and the positive electrode and wound in a spiral shape to prepare an electrode group. Such an electrode group was housed in a cylindrical container with a bottom together with an electrolytic solution having the same composition as in Example 1, and the above-described FIG.
An AA size cylindrical nickel-hydrogen secondary battery having the structure shown in was assembled.

With respect to the obtained secondary batteries of Example 4 and Comparative Example 3, the capacity remaining rate after storage for 14 days in a constant temperature bath at 45 ° C. was determined by the same method as described above. Also, although the discharge capacity C ₀ when the battery voltage was discharged to 1.0 V at 1 CmA in Comparative Example 3 was the same, the capacity remaining ratio of the secondary battery in Example 4 was 70%, whereas The residual capacity of the secondary battery of Comparative Example 3 was 50.
%Met.

Further, the obtained secondary batteries of Example 4 and Comparative Example 3 were subjected to a charge / discharge cycle characteristic test by the same method as described above. As a result, although the discharge capacities of the first cycle of Example 4 and Comparative Example 3 were the same, the number of cycles in which the discharge capacity of the secondary battery of Example 4 reached 80% of the discharge capacity of the first cycle was calculated. When set to 100, the number of cycles in which the discharge capacity of the secondary battery of Comparative Example 3 reached 80% of the discharge capacity in the first cycle was 70.

In addition, although the example applied to the cylindrical nickel-hydrogen secondary battery has been described in the above-mentioned embodiment, the battery shape is not limited to this, and the separator is interposed between the strip-shaped positive electrode and the negative electrode. Then, it can be similarly applied to a prismatic nickel-hydrogen secondary battery provided with electrode groups that are alternately stacked.

[0064]

As described in detail above, according to the present invention, it is possible to provide a method for manufacturing a nickel-hydrogen secondary battery which has improved self-discharge characteristics during high temperature storage and has a long life.

[Brief description of drawings]

FIG. 1 is a perspective view showing a nickel-hydrogen secondary battery of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the number of days of storage at high temperature and the capacity remaining ratio in the nickel-hydrogen secondary batteries of Examples 1 and 2 and Comparative Example 1 of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the cycle number ratio and the discharge capacity ratio in the nickel-hydrogen secondary batteries of Examples 1 and 2 and Comparative Example 1 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 2 ... positive electrode, 3 ... separator, 4 ... negative electrode, 7 ...
Sealing plate, 8 ... insulating gasket.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohito Teraoka 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Toshiba Battery Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a nickel-hydrogen secondary battery comprising a positive electrode containing a nickel compound, a negative electrode containing a hydrogen storage alloy, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. A nickel-hydrogen secondary battery characterized in that a separator is produced by irradiating a sheet material made of a polyolefin-based synthetic resin fiber containing no light stabilizer with ultraviolet rays to graft-copolymerize a vinyl monomer having a hydrophilic group. Manufacturing method.