JP2002063889A - Nickel hydride secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydride secondary battery which can realize high capacity and long service life. SOLUTION: A separator with a hydrophilic part is formed at a part of its fine porous membrane surface being made of polyolefin with an average pore size of 0.01 to 1 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel-metal hydride secondary battery.

[0002]

2. Description of the Related Art In recent years, nickel-metal hydride secondary batteries have been used as power supplies for electric and electronic devices such as personal computers and mobile phones. As their needs have increased, demands for higher capacity and longer life have increased. It is getting.

As a means for achieving high capacity, it is effective to reduce the thickness of the separator and increase the amount of the electrode active material filled in the battery.

However, there is a problem in reducing the thickness of the conventional separator.

That is, as a conventional separator, a nonwoven fabric having a thickness of about 120 to 150 μm subjected to a hydrophilization treatment is used. The short-circuit easily occurs due to the burr of the electrode or the active material dropped from the electrode due to the size of the hole diameter of the electrode. Furthermore, nonwoven fabrics have quality problems such as increased unevenness in thickness and basis weight, which may adversely affect battery performance.

On the other hand, the above problem can be solved by using a microporous membrane which has a small pore size, is dense, has a high strength even if the thickness is less than 100 μm, and can realize a uniform thickness and basis weight. .

However, when a microporous membrane is used as a separator, another problem newly arises. That is, the microporous membrane has a problem that water retention is low and cycle life is short. In addition, there is also a problem that the permeability of oxygen gas generated in the positive electrode at the time of overcharging is low, the recombination reaction in the negative electrode is hindered, the internal pressure of the sealed battery tends to increase, and liquid leakage easily occurs. Therefore, in order to use the microporous membrane as a separator, it is necessary to make further improvements.

[0008]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a nickel-metal hydride secondary battery in which the problems of the prior art are improved and a high capacity and long life can be realized.

[0009]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned problems of the prior art, and as a result, achieved the above object by using a microporous membrane having specific properties as a separator. They have found that they can do this and have finally completed the present invention.

That is, the present invention relates to the following nickel-metal hydride secondary battery.

1. A nickel-hydrogen secondary battery using a separator in which a hydrophilic portion is provided on a part of the surface of a microporous polyolefin membrane having an average pore diameter of 0.01 to 1 μm.

2. 2. The nickel-hydrogen secondary battery according to claim 1, wherein the area of the hydrophilic part of the separator is 40 to 95% of the membrane surface area.

3. Separator thickness is 10 to 100 μm
3. The nickel-metal hydride secondary battery according to the above item 1 or 2.

4. 4. The nickel-metal hydride secondary battery according to any one of the above items 1 to 3, wherein the hydrophilic portion has at least one hydrophilic group of a sulfone group and a carboxyl group.

[0015] 5. 5. The nickel hydrogen according to any one of the above items 1 to 4, wherein a nickel positive electrode obtained by applying a paste containing nickel hydroxide powder whose particle surface is coated with cobalt hydroxide to a two-dimensional current collector is used. Rechargeable battery.

6. 6. The nickel-metal hydride secondary battery according to claim 5, wherein the thickness of the positive electrode is 0.1 to 0.6 mm.

[7] 7. The nickel-hydrogen secondary battery according to any one of the above items 1 to 6, using a negative electrode in which the hydrogen storage alloy is fixed to a two-dimensional current collector.

[8] The nickel-metal hydride secondary battery according to claim 7, wherein the thickness of the negative electrode is 0.1 to 0.6 mm.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The nickel-hydrogen secondary battery of the present invention is characterized in that a microporous polyolefin membrane having an average pore diameter of 0.01 to 1 μm is provided with a separator having a hydrophilic portion provided on a part of the membrane surface. I do. Hereinafter, the separator and the nickel-hydrogen secondary battery using the separator will be described in order. (1) Separator The polyolefin microporous membrane itself is not particularly limited, and a microporous membrane made of polyethylene, polypropylene, polymethylpentene, or the like can be used. These can also use a commercial item or the thing obtained by the well-known manufacturing method.

The separator of the present invention uses a polyolefin microporous membrane in which a hydrophilic portion is provided on a part of the membrane surface.

The hydrophilic portion in the separator of the battery of the present invention is a portion (region) having a hydrophilic group. The type of the hydrophilic group is not particularly limited, and examples thereof include a sulfone group, a carboxyl group, a hydroxyl group, and an amide group. These may be one kind or two or more kinds. In the present invention, at least one of a sulfone group and a carboxyl group is particularly preferable.

In the present invention, the “membrane surface” of the microporous polyolefin membrane means both the outer surface of the microporous membrane and the surface of the inner wall of pores (voids) following the outer surface. In the present invention,
The film surface portion (remaining portion) other than the hydrophilic portion is substantially composed of a hydrophobic portion. Therefore, in the above microporous membrane,
The hydrophilic part plays a role of retaining the electrolyte, and the hydrophobic part plays a role of permeating the gas generated at the electrode during overcharging.

The area of the hydrophilic portion is made to be a part of the film surface. That is, it is sufficient to have a hydrophilic part and a hydrophobic part. In the present invention, in particular, the area of the hydrophilic part is usually about 40 to 95% of the membrane surface area, preferably 70 to 90%.
And If it is less than 40%, the liquid retention amount of the separator decreases, and as a result, the film resistance increases, and the discharge characteristics may decrease. If it exceeds 95%, the gas permeability may be reduced because the hydrophobic portion becomes too small.

In the present invention, the "area of the hydrophilic portion"
The term “ratio (%)” refers to a ratio of the hydrophilic portion in the plan view of the polyolefin microporous membrane when the area of the polyolefin microporous membrane in the plan view of the polyolefin microporous membrane is 100% as shown in FIG. The measuring method is based on a hydrophilized separator (a plan view 10c).
m × width 10 cm × thickness) was determined by determining the area of the colored portion after immersion for 1 hour. That is, it was calculated by the area W (%) of the hydrophilic part = 100 × (W / 100).

The shapes of the hydrophilic portion and the hydrophobic portion are not particularly limited, and can be set arbitrarily. In particular, it is preferable that the hydrophilic portion and the hydrophobic portion are finely and uniformly distributed. For example, a shape in which circular hydrophobic portions having a diameter of 5 mm or less are uniformly distributed in the hydrophilic portion, and a shape in which lattice-like hydrophobic portions having a width of 5 mm or less are distributed in the hydrophilic portion can be exemplified.

The average pore size of the polyolefin microporous membrane is as follows:
Usually about 0.01 to 1 μm, preferably 0.05 to 0.
The thickness may be set to 5 μm. If the average pore size is less than 0.01 μm, gas permeability may be reduced even if it has a hydrophobic part. If the thickness is larger than 1 μm, a short circuit may occur due to the dropped electrode active material or the burr of the electrode.

The thickness of the polyolefin microporous membrane is not particularly limited, and can be appropriately set according to the average pore diameter, desired characteristics, and the like. Usually about 10-100 μm,
Preferably, the thickness is 30 to 90 μm. By setting within this range, film strength, film resistance, and the like can be more appropriately controlled.

The method for producing the separator is not particularly limited, and a film obtained by a known method may be used, and a part of this film may be subjected to a hydrophilic treatment. For example, Japanese Patent Application Laid-Open
Based on a microporous polyolefin membrane obtained by a method disclosed in Japanese Patent No. 21050, JP-A-6-93130, etc., a part of the surface of the polyolefin microporous membrane may be subjected to a hydrophilic treatment.

The method of the hydrophilic treatment is not particularly limited as long as a hydrophilic group (preferably at least one of a sulfone group and a carboxyl group) can be provided to the porous membrane. For example, the porous membrane is partially coated with a hydrophilic resin having a highly hydrophilic group such as a sulfone group and a carboxyl group,
Alternatively, the separator can be obtained by partially performing a sulfonation reaction with a mixed gas of fluorine and sulfurous acid or a graft reaction of a hydrophilic monomer such as acrylic acid. (2) Nickel hydrogen secondary battery The battery of the present invention can employ known battery components, except for using the separator. Preferably, a battery using nickel hydroxide as the positive electrode active material, a hydrogen storage alloy as the negative electrode active material, and an alkaline aqueous solution as the electrolytic solution can be employed, and other components may be in any form.

For example, for the positive electrode, a sheet-like electrode obtained by impregnating a three-dimensional current collector such as a foamed nickel base with a paste containing nickel hydroxide and press-molding the same is preferable in achieving high capacity of the battery of the present invention. . More preferably, a nickel positive electrode obtained by applying a paste containing nickel hydroxide powder whose particle surface is coated with cobalt hydroxide to a two-dimensional current collector is used. By adopting such a configuration, in particular,
Burrs and the like hardly occur at the time of winding, and the separator can be further thinned (for example, the separator thickness is 50 μm or less), so that the capacity can be further increased or the size can be further reduced. That is, by adopting the separator in combination with the nickel positive electrode, more excellent battery characteristics can be obtained.

The thickness of the positive electrode is not particularly limited, but is usually preferably about 0.1 to 0.6 mm. Within this range, high capacity, high output discharge characteristics and the like can be obtained more reliably.

As the two-dimensional current collector used in the positive electrode, a known current collector such as a nickel-plated perforated steel sheet, nickel mesh, expanded metal, nickel foil, or the like can be used. As the cobalt hydroxide for coating the surface of the nickel hydroxide powder particles, a low crystalline α-type having excellent electronic conductivity is preferable. Further, as a binder for applying this to a two-dimensional current collector, a known binder can be used, for example, polytetrafluoroethylene (PTFE),
Polyvinylidene fluoride, styrene-butadiene rubber and the like can be suitably used. As the conductive additive, for example, nickel flake having a large surface area and softening treatment can be suitably used.

The negative electrode is preferably one in which a hydrogen storage alloy is fixed to a two-dimensional current collector such as a nickel-plated perforated steel plate. In this case, the thickness of the negative electrode is preferably about 0.1 to 0.6 mm. Within this range, high capacity, high output discharge characteristics, and the like can be obtained more reliably. As the two-dimensional current collector, the same one as that used in the positive electrode can be used.

The form of the battery of the present invention is not particularly limited, and any known form can be adopted. In particular, in the battery of the present invention, a closed cylinder, a square or the like is most suitable for increasing the capacity.

In the nickel-hydrogen secondary battery of the present invention, since the separator has good gas permeability, the internal pressure of the battery is hardly increased, and the separator can be made thinner, so that the electrode active material can be filled more. , A large increase in capacity can be realized.

More surprisingly, the battery of the present invention
The cycle life is longer than before. In conventional nonwoven fabric separators, it is thought that the electrolyte leakage of the separator causes cycle deterioration.However, the separator having a partially hydrophilic portion has a relatively small pore size, so that the electrolyte retention ability is low. This is because, even when charge and discharge are repeated, leakage of the electrolytic solution is suppressed or prevented.

[0037]

According to the present invention, it is possible to provide a high capacity and long life nickel-metal hydride secondary battery by using a separator provided with a hydrophilic part on a part of the surface of a polyolefin porous membrane. Can be.

[0038]

The present invention will now be described in more detail with reference to examples and comparative examples. Note that the scope of the present invention is not limited to these examples.

Production Example 1 (Production of Separator) Three types of samples A to C were produced as separators.

22% by weight of finely divided silica and 44% by weight of dioctyl phthalate were mixed with a Henschel mixer, and 34% by weight of a polyethylene resin having a viscosity average molecular weight of 300,000 was added thereto, followed by mixing with a Henschel mixer again. This mixture was formed into a flat film having a thickness of 160 μm by a film manufacturing apparatus in which a T-die having a width of 450 mm was attached to a 30 mmφ twin screw extruder.

The formed film was immersed in methylene chloride for 10 minutes to extract dioctyl phthalate and then dried.
Further, this was immersed in 25% caustic soda at 60 ° C. for 60 minutes to extract finely divided silica, washed with water and dried. This film was stretched 2 to 5 times vertically and 1.1 to 2 times horizontally at 110 ° C. using a biaxial stretching machine to obtain a microporous polyethylene film having a predetermined film thickness, porosity and pore diameter.

Using the obtained polyethylene microporous membrane,
A copolymer of 60 mol% of isoprene and 40 mol% of styrene, wherein the introduction ratio of sulfone groups is 15 mol% based on isoprene.
Isopropanol was added to an aqueous latex solution obtained by finely dispersing the sulfonated copolymer of
The solution added by weight% was applied by a gravure printing method, and the solvent was evaporated to form a hydrophilic portion.

At this time, in the samples A and C, the shape of the remaining hydrophobic portion was an island having a diameter of 3 mm, and the area of the entire hydrophobic portion was 20% of the whole. In sample B, the entire surface of the film was subjected to a hydrophilic treatment. Table 1 shows the physical properties of each sample.

[0044]

[Table 1]

Each physical property in Table 1 was measured as follows. (1) Film thickness It was measured with a dial gauge (“PEACOCK No. 25” manufactured by Ozaki Seisakusho). (2) Porosity Measured using a mercury porosimeter. (3) Average pore size It was measured using a mercury polysimeter. Using a device "Bore Sizer 9320 type (manufactured by Shimadzu Corporation)", a sample weight of 0.02 to 0.04 mg was subjected to vacuum degassing as a pretreatment for 5 minutes, and then measured from 2.0 psia. From the obtained pore distribution data, the point (mode system) having the largest press-fit volume was defined as the average pore diameter.

Example 1 7 parts by weight of cobalt oxide, 3 parts by weight of an aqueous solution of carboxymethyl cellulose (solids concentration 10% by weight), and polytetrafluoroethylene dispersant solution (solids concentration 60 parts by weight) per 100 parts by weight of nickel hydroxide powder %) 3 parts by weight and 23 parts by weight of water were mixed to obtain a paste mixture. This paste mixture is applied and filled on a nickel foam base material,
After drying at 80 ° C. for 1 hour, compression molding was performed at a pressure of 1 ton / cm ² . Thereafter, the sheet was cut into a predetermined size to obtain a positive electrode sheet.

Rare earth hydrogen storage alloy (MmNi _3.5 Co _0.8
A1 _0.4 Mn _0.3 ) Aqueous carboxymethylcellulose solution (solids concentration 10% by weight) per 100 parts by weight of powder
5 parts by weight of a polytetrafluoroethylene dispersant solution (solid content concentration: 60% by weight) and 23 parts by weight of water were mixed to obtain a paste mixture. The paste mixture was applied to a nickel-plated perforated steel sheet, filled and dried at 80 ° C. for 1 hour, and then compression molded at a pressure of 1 ton / cm ² . Thereafter, the sheet was cut into a predetermined size to obtain a negative electrode sheet.

The positive electrode sheet and the negative electrode sheet were combined with each other for a negative electrode capacity:
It was wound through a separator A so that the positive electrode capacity was 1.5: 1, and was placed in a subC-sized battery can. This was mixed with an electrolyte (1 liter of a 30 wt% KOH aqueous solution and LiOH 1
7 g of an alkaline aqueous solution). The positive electrode tab was spot-welded to the sealing body with the reversible valve provided with the resin packing, and the outermost peripheral portion of the negative electrode was brought into contact with the side surface of the can, followed by sealing. Then, this was stored at 45 ° C. for 14 hours, and charged at 0.2 C with respect to the theoretical capacity for 6 hours.
Discharged to 0.9 V at C. This charge / discharge cycle was repeated until the discharge capacity became constant, thereby producing a nickel-metal hydride battery.

Further, the number of cycles until charging and discharging were performed in a cycle of charging 1 C (−ΔV = 5 mV) and discharging 1 C (0.9 V cut) until the discharge capacity was reduced to 500 mAh was evaluated. Table 2 shows the results.

Comparative Example 1 A battery was prepared in the same manner as in Example 1 except that a sulfonated nonwoven fabric having a thickness of 150 μm (porosity: 60%, average pore diameter: 20 μm) was used as a separator. At this time, since the volume of the separator was larger than that of Example 1, the amount of the electrode active material packed was about 17% less. The battery characteristics of this battery were examined in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 2 A battery was manufactured in the same manner as in Example 1 except that the separator B was used, and the battery characteristics were examined in the same manner as in Example 1. However, since the separator had no hydrophobic portion, the internal pressure of the battery increased from the time of initial charging, and the electrolyte leaked.

Comparative Example 3 A battery was prepared in the same manner as in Example 1 except that a 80 μm-thick sulfonated nonwoven fabric (porosity: 60%, average pore diameter: 15 μm) was used as a separator. I tried to examine the battery characteristics. However, this battery had many short-circuit failures and could not be tested.

Example 2 Nickel hydroxide powder having a particle surface coated with cobalt hydroxide was used as an electrode active material, and this was treated with a long diameter of 50 to 100.
The powder was mixed with the flaky nickel powder having a small diameter of 1 μm and a short diameter of 1 to 10 μm at a weight ratio of 5: 1. Thereafter, a polytetrafluoroethylene solution as a binder is added and mixed in a solid content of 2.4 parts by weight with respect to 100 parts by weight of the above nickel hydroxide powder, and the resulting mixture is kneaded and then stretched using a roller. As a result, a sheet-like molded product was obtained.

The obtained sheet-like molded product was placed on both sides of a nickel-plated perforated steel plate and pressed and formed at a pressure of 5 ton / cm ² for 1 minute using a flat plate press.
A nickel positive electrode was manufactured.

A battery was prepared in the same manner as in Example 1 except that the above positive electrode and the microporous membrane separator C were used. As a result, about 7% more electrode active material than in Example 1 could be packed. The battery characteristics of this battery were examined in the same manner as in Example 1. Table 2 shows the results.

Example 3 A battery was prepared in the same manner as in Example 2 except that the microporous membrane separator A was used as the separator. The battery characteristics of this battery were examined in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 4 A battery was produced in the same manner as in Example 2 except that a 30 μm-thick sulfonated nonwoven fabric (porosity: 50%, average pore diameter: 10 μm) was used as a separator. I tried to examine the battery characteristics. However, this battery was severely short-circuited and could not be used as a battery.

[0058]

[Table 2]

From the results shown in Table 2, it can be seen that the battery of the present invention having the separator provided with a hydrophilic portion on a part of the membrane surface can exhibit excellent characteristics.

In particular, in Example 2 using a nickel positive electrode obtained by applying a paste containing nickel hydroxide powder whose surface is coated with cobalt hydroxide to a two-dimensional current collector, the separator thickness is as thin as 30 μm. It can be seen that a separator can be used, and a more excellent discharge capacity than in Example 1 can be obtained. That is, a particularly excellent effect is obtained in a combination of a nickel positive electrode obtained by applying a paste containing nickel hydroxide powder having a particle surface coated with cobalt hydroxide to a two-dimensional current collector and a separator having a separator thickness of 50 μm or less. It can be seen that it can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a polyolefin microporous membrane.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/30 H01M 10/30 Z (72) Inventor Takafumi Sansui 515 Kojimacho, Moriyama-shi, Shiga Asahi Kasei Kogyo Co., Ltd. In-house (72) Inventor Tetsuo Sakai 1-81-31 Midorioka, Ikeda-shi, Osaka Industrial Technology Institute Inside Osaka Institute of Industrial Technology (72) Inventor Nobuhiro Kuriyama 1-81-31 Midorioka, Ikeda-shi, Osaka Industrial Technology F-term in the Osaka Institute of Industrial Technology (reference) 5H021 AA06 BB09 BB12 EE04 EE17 EE18 EE34 HH03 HH04 5H028 AA01 AA05 EE01 EE05 EE10 HH06 5H050 AA07 AA08 BA14 CA03 CA30 CB17 DA02 DA03 DA04

Claims (8)

[Claims] 1. A nickel-hydrogen secondary battery comprising a microporous polyolefin membrane having an average pore diameter of 0.01 to 1 .mu.m, wherein a separator having a hydrophilic portion provided on a part of the membrane surface is used. 2. The separator according to claim 1, wherein the area of the hydrophilic portion is 4% of the membrane surface area.
The nickel-metal hydride secondary battery according to claim 1, wherein the content is 0 to 95%. 3. The nickel-metal hydride secondary battery according to claim 1, wherein the thickness of the separator is 10 to 100 μm. 4. The nickel-hydrogen secondary battery according to claim 1, wherein the hydrophilic portion has at least one hydrophilic group of a sulfone group and a carboxyl group. 5. The nickel positive electrode according to claim 1, wherein a paste containing nickel hydroxide powder whose surface is coated with cobalt hydroxide is applied to a two-dimensional current collector. Nickel-metal hydride secondary battery. 6. The nickel-metal hydride secondary battery according to claim 5, wherein the thickness of the positive electrode is 0.1 to 0.6 mm. 7. The nickel-hydrogen secondary battery according to claim 1, wherein a negative electrode in which the hydrogen storage alloy is fixed to a two-dimensional current collector is used. 8. The nickel-hydrogen secondary battery according to claim 7, wherein the thickness of the negative electrode is 0.1 to 0.6 mm.