JP2001023599A - Battery separator and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide superior affinity to electrolytic solution and suppress lowering of the battery performance when used for a long time by impregnating a specific ratio of epoxy denaturated polyvinyl alcohol composed of epoxy group containing vinyl alcohol and vinylester, and polyethylene glycol group containing the respective elements to a base material mainly composed of polyolefin resin. SOLUTION: Among base materials are unwoven and woven fabrics such as span bond mainly composed of fibers such as polypropylene. Epoxy group containing vinyl alcohol impregnated therein includes elements expressed by formula I-IV (where, R1-R4 and R6 are H or alkyl group, R5 is alkyl group, n1 and n2 are 1 and 2, and n3 is 4-50) respectively containing 0.01-10 mol%, 70-99.98 mol%, 0-29 mol%, and 0.01-10 mol%. The impregnation ratio of the epoxy group containing vinyl alcohol to the base material 100 pts.wt. is 1-20 pts.wt. It can be industrially manufactured at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for an alkaline secondary battery such as a nickel cadmium battery, a nickel hydride battery and a nickel zinc battery.

[0002]

2. Description of the Related Art At present, various types of primary batteries, secondary batteries, and fuel cells are used for portable devices, mobile devices, stationary devices, spare devices, and independent power sources. When these batteries are broken down into components, most batteries have a positive electrode, a negative electrode,
It consists of electrolytes, separators, containers and the like. Of course, the role played by the electrodes is great in order to improve the characteristics of the battery, and it is necessary to improve the positive electrode and the negative electrode, as well as the importance of the separator. .

[0003] The important role of the separator in the battery is to firstly separate the positive electrode and the negative electrode to prevent an electrical short circuit, and secondly to prevent the passage of ions in the electrolyte. . In the alkaline secondary battery targeted by the present invention, since the electrolyte is a strong alkali, it must be a material having alkali resistance. For this reason, nonwoven fabrics and woven fabrics made of polyamide with alkali resistance and hydrophilicity are most often used.However, polyamide has alkali resistance at room temperature, but is inferior in alkali resistance at high temperatures and for a long period of time. In the secondary battery is performed, a short circuit may occur due to a decrease in strength,
The measures were required. Of course, such a tendency is more remarkable in natural fibers and cellulosics.

[0004] Therefore, nonwoven fabrics and woven fabrics made of an olefin resin having a higher alkali resistance than polyamide, particularly polyethylene or polypropylene, have been studied. These separators do not decrease in strength even at high temperatures or for long-term use, and can be said to be preferable as separators for extending the life of batteries. However, these polyethylene and polypropylene separators have a problem that their affinity with an alkaline electrolyte is extremely poor and their retention is also poor.

[0005] In order to overcome these problems and to use a nonwoven fabric made of a polyolefin resin as an alkaline battery separator, Japanese Patent Publication No. 6-101323 discloses a method of introducing a sulfone group into a polyolefin resin.
3-503074, JP-T-6-505756 discloses UV
Various methods have been proposed, such as graft polymerization of a vinyl monomer by irradiation. The present inventors have already found that an epoxy-modified polyvinyl alcohol can be impregnated into a nonwoven fabric or woven fabric of a polyolefin resin to obtain an affinity for an electrolytic solution and a retention property (Japanese Patent Application No. 8-27374).
No. 8). However, even in the case of this formulation, the hydrophilicity gradually decreased with repeated charging / discharging for a long period of time, and it was found that the battery performance was reduced due to this.Therefore, further improvement of the epoxy-modified polyvinyl alcohol was studied. I was

[0006]

SUMMARY OF THE INVENTION The present invention improves the hydrophilicity of a nonwoven or woven base material containing an olefin resin as a main constituent material to obtain a separator having a good affinity for an electrolytic solution. That the primary purpose is to
When used as a battery separator, a second object is to obtain a separator capable of minimizing deterioration in battery performance even when used for a long time. Another object of the present invention is to obtain a separator having the above-mentioned characteristics that can be industrially manufactured at low cost.

[0007]

Means for Solving the Problems A first invention of the present invention is:
A non-woven fabric or a woven fabric having a polyolefin resin as a main constituent material is used in an amount of 0.01 to 10 mol% of an epoxy group-containing structural unit represented by the general formula (1), and a vinyl alcohol represented by the general formula (2) Structural unit 70 to 99.98 mol%, vinyl ester structural unit 0 represented by general formula (3)
1 to 20 parts by weight of an epoxy-modified polyvinyl alcohol composed of 0.01 to 29 mol% and a structural unit of the general formula (4) having a polyethylene glycol group in an amount of 0.01 to 10 mol% per 100 parts by weight of the base material. The present invention relates to a battery separator characterized by the following.

[0008]

Embedded image

In a second aspect of the present invention, a styrene-based thermoplastic resin is added to 100 parts by weight of a nonwoven or woven base material mainly composed of a polyolefin-based resin.
The present invention relates to a battery separator impregnated with 1 to 20 parts by weight of the epoxy-modified polyvinyl alcohol (hereinafter referred to as epoxy-modified PVA) described in the first aspect. A third invention of the present invention relates to a battery using the battery separator described in the first or second invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An epoxy group-containing structural unit represented by the following general formula (1) is a structural unit (1), and a vinyl alcohol structural unit represented by a general formula (2) is a structural unit (2).
The vinyl ester structural unit represented by the general formula (3) may be referred to as a structural unit (3), and the structural unit of the general formula (4) having a polyethylene glycol group may be referred to as a structural unit (4). In the present invention, the structural units (1), (2),
The epoxy-modified PVA composed of (3) and (4) undergoes epoxy cross-linking by heating to form a polyvinyl alcohol having a network structure. Therefore, a sheet-like material containing this epoxy-modified PVA and containing a polyolefin-based resin as a main component is not easily attacked by an alkaline electrolyte such as potassium hydroxide. As a result, it can be used for a long period of time without a decrease in sheet strength and a deterioration in hydrophilicity. Further, since the separator of the present invention is excellent in heat resistance by being crosslinked with epoxy, it can be used as a separator for an alkaline secondary battery.

In the epoxy-modified polyvinyl alcohol comprising the structural units (1), (2) and (3),
When it is contained in a sheet containing a polyolefin-based resin as a main component, it undergoes epoxy crosslinking by heating to form a polyvinyl alcohol having a network structure, and the sheet is less likely to be attacked by an alkaline electrolyte such as potassium hydroxide. However, when the epoxy-modified polyvinyl alcohol is subjected to epoxy crosslinking, the epoxy-modified polyvinyl alcohol becomes too hard, and there is also a problem that the liquid retaining property gradually decreases during long-term use. For this reason, further improvements have been required.

When the structural unit of the general formula (4) having a polyethylene glycol group is introduced into the epoxy-modified polyvinyl alcohol having the structural units (1), (2) and (3), the polyvinyl alcohol film becomes partially amorphous. The membrane itself becomes softer and structurally,
Liquid retention is improved. Further, since the polyethylene glycol group is a hydrophilic group, the liquid retaining property is improved in terms of chemical properties.

The preferred amount for copolymerizing the structural unit of the general formula (4) having a polyethylene glycol group is from 0.01 to 1 of the structural unit of the general formula (1).
0 mol%, structural units 70 to 9 represented by general formula (2)
9.98 mol%, structural unit 0 represented by general formula (3)
The content is 0.01 to 10 mol%, preferably 0.1 to 5 mol%, based on 29 mol%. When the amount of the structural unit of the general formula (4) is less than 0.01 mol%,
The effect of improving the liquid retaining property does not appear. On the other hand, when the content exceeds 10 mol%, the epoxy crosslinking is inhibited, so that the resistance to an alkaline electrolyte decreases. N ₃ of the structural unit (4) is preferably 4 to 50, and more preferably 4 to 20. If it is less than 4, the effect of improving the liquid retaining property does not appear. If it exceeds 50, the epoxy crosslinking is inhibited, so that the resistance to an alkaline electrolyte decreases. The alkyl group of R _{6 in} the structural unit (4) is not particularly limited.

Incidentally, the structural units (1), (2),
Examples of the epoxy-modified polyvinyl alcohol comprising (3) include vinyl alcohol (hereinafter abbreviated as VA), allyl glycidyl ether copolymer, VA, methallyl glycidyl ether copolymer, and VA • 1- (3-butenyloxy)-
2,3-epoxypropane copolymer, VA · 1-allyloxy-3,4-epoxybutane copolymer, VA · 1-
Allyloxy-4,5-epoxypentane copolymer, V
A • 1-allyloxy-3,4-epoxy-3-methylbutane copolymer, VA • 1-allyloxy-3,4-epoxypentane copolymer, VA • 1-allyloxy-
3,4-epoxy-3-methylpentane copolymer, VA
1-allyloxy-4,5-epoxy-4-methylpentane copolymer, VA.1-allyloxy-4,5-epoxyhexane copolymer, VA.1-allyloxy-
4,5-epoxy-4-methylhexane copolymer, VA
-Methallyl-methyl glycidyl ether copolymer, V
A. methallyl-dimethyl glycidyl ether copolymer and a copolymer having a vinyl ester unit (for example, a vinyl acetate unit) as the third copolymer unit are exemplified.

Although the composition of the epoxy-modified polyvinyl alcohol can be variously changed depending on the purpose, the structural unit (2) has a vinyl alcohol unit of 99.99 to 70 mol% and the structural unit (3)
And the epoxy group-containing monomer unit of the structural unit (1) is selected from the range of 0.01 to 10 mol%. The content of the epoxy group-containing monomer unit is 0.01
If it is less than 10 mol%, the effect of modification is small, and if it exceeds 10 mol%, the aqueous solution viscosity of the modified PVA increases with time. Further, when the content of the vinyl ester unit in the modified PVA exceeds 29 mol%, the water solubility decreases, which is not preferable.

Although the degree of polymerization of the epoxy-modified PVA of the present invention is appropriately selected according to the application, it is in the range of 200 to 3500, that is, the number average molecular weight is 8000 to 220,000. When the number average molecular weight exceeds 220,000, the viscosity of the aqueous PVA solution is so high that handling is difficult and gelation is liable to occur. On the other hand, if it is less than 8000, water resistance, strength, oil and fat resistance, and organic solvent resistance are low, which is not preferable.

As the base material of the separator, various dry nonwoven fabrics such as spunbond, meltblown, spunlace, card or airlay, which are mainly composed of fibers of polyolefin resin, wet nonwoven fabric, or a woven fabric produced by weaving warp and weft yarns. There is no particular limitation on the cloth or the like. Further, a laminated or laminated type thereof may be used. Above all, in consideration of sheet strength in an alkaline electrolyte, a spun bond or a lamination or lamination type of a spun bond and something is preferable.

The fiber of the polyolefin resin used for the substrate is not particularly limited either, but may be a single fiber of polyethylene, polypropylene, a copolymer of polypropylene and polyethylene, or a side-by-side type or a core-sheath type composite made of these resins. Fibers can also be used.

The epoxy-modified PV of the present invention is applied to a nonwoven fabric or woven fabric of a fiber containing a polyolefin resin as a main constituent material.
As a method for containing A, there are various coating methods such as a roll coater, a blade coater, a bar coater, and an impregnated coater. Among them, an impregnated coater is preferably used in order to make it almost uniformly contained in the entire substrate.

The epoxy-modified PVA of the present invention for a substrate
As the impregnation amount increases, the hydrophilicity increases, but when the air permeability, which is a characteristic of nonwoven fabrics and woven fabrics, decreases, the flexibility, which is a characteristic of nonwoven fabrics and woven fabrics, is lost, and the winding suitability of the separator is poor. . As a result of examination, a good range for the impregnation amount is 0.5 to 10 g / m ² , preferably 0.5 to 5 g / m ² . If the impregnation amount is less than 0.5 g / m ² , the hydrophilicity is poor, and if it exceeds 10 g / m ² , the stiffness becomes too strong and flexibility is lost.

It has been found that it is effective to introduce a styrene-based thermoplastic resin into the substrate and then introduce the epoxy-modified PVA to further strengthen the bond with the substrate. Since the styrene-based thermoplastic resin functions as an anchoring agent, a strong bond between the polyolefin-based resin and the styrene-based thermoplastic resin, and between the styrene-based thermoplastic resin and the epoxy-modified PVA, enables the alkaline electrolyte such as potassium hydroxide to be more strongly bonded. It is possible to obtain a separator that is hardly attacked.

Examples of the styrene-based thermoplastic resin that can be introduced include styrene-ethylene-butylene-styrene block copolymer (abbreviated as SEBS), styrene-ethylene-propylene-styrene block copolymer (abbreviated as SEPS), and styrene- Examples include isoprene-styrene block copolymer (abbreviated as SIS) and styrene-butadiene-styrene block copolymer (abbreviated as SBS). The amount of the styrene-based thermoplastic resin is 1 to 20 parts by weight based on 100 parts by weight of the base material. When the amount is less than 1 part by weight, the anchor effect cannot be obtained, and when the amount is more than 20 parts by weight, the voids of the base material become too small, so that the air permeability and the liquid retaining property are reduced.

As a method for introducing the styrene-based thermoplastic resin, a solution in which the styrene-based thermoplastic resin is dissolved in an organic solvent such as toluene or xylene in a polyolefin-based nonwoven fabric or woven fabric, or an aqueous emulsion solution of the styrene-based thermoplastic resin is used. And the like.

[0024]

EXAMPLES Examples of the separator of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1 An epoxy-modified PVA (DR-0389, manufactured by Denki Kagaku Kogyo Co., Ltd.) composed of the structural units (1), (2), (3) and (4) was dissolved in a 1% by weight aqueous solution in an uncrosslinked state. I got On the other hand, a basis weight of 46 g / m ² made of polypropylene resin and a thickness of 18
A spunbond nonwoven fabric having a thickness of 0 μm and a fineness of 1.3 d was obtained. First, 3000 cm ³ of a 2% by weight aqueous solution of the above-mentioned epoxy-modified PVA is poured into a stainless steel vat having a depth of 5 cm and a length of 36 cm × width of 25 cm,
Submerge the 30cm x 25cm spunbond into it,
Leave for a minute. Thereafter, the spun bond is taken out and sandwiched between two rubber roll presses, and epoxy-modified PV
A was squeezed, impregnated with 1.5 g / m ² of solid content, and then cooled to 130 ° C.
Was dried with a hot air dryer for 5 minutes to thermally crosslink the epoxy-modified PVA to obtain a battery separator.

Example 2 An epoxy-modified PVA (DR-0379, manufactured by Denki Kagaku Kogyo Co., Ltd.) composed of the structural units (1), (2), (3) and (4) was dissolved in a 2% by weight aqueous solution in an uncrosslinked state. I got On the other hand, a basis weight of 46 g / m ² made of polypropylene resin and a thickness of 18
A spunbond nonwoven fabric having a thickness of 0 μm and a fineness of 1.3 d was obtained. Further, a styrene-based thermoplastic resin (Clayton G-1652; manufactured by Shell) was dissolved in toluene to obtain a 6% by weight solution. First, 3,000 cm ³ of the above 6% by weight solvent solution was poured into a stainless steel vat having a depth of 5 cm and a length of 36 cm × width of 25 cm.
The above-mentioned spun bond of 0 cm × 25 cm was sunk, then the spun bond was taken out and sandwiched between two rubber roll presses, and the styrene-based thermoplastic resin was squeezed, and the solid content was 7 g.
/ M ² . Further, the above-mentioned 2% by weight aqueous solution of the epoxy-modified PVA is poured into the stainless steel vat, the spun bond is sunk, and left for 5 minutes. Thereafter, the spun bond was taken out, sandwiched in the previous press, the epoxy-modified PVA was squeezed, impregnated with 2.5 g / m ² of solid content, dried with a hot air drier at 130 ° C. for 5 minutes, and the epoxy-modified PVA was heated. Crosslinking was performed to obtain a battery separator.

Comparative Example 1 In Example 1, instead of using DR-0389,
Example 1 was repeated except that an epoxy-modified polyvinyl alcohol (W-100, manufactured by Denki Kagaku Kogyo Co., Ltd.) composed of the above structural units (1), (2) and (3) was used. Similarly, a battery separator impregnated with a solid content of 3.0 g / m ² was obtained. Table 1 shows the results of evaluating the above three types of battery separators by the following test methods.
Shown in

Test Method (1) A sample having a basis weight of 10 cm × 10 cm was collected,
Weigh the number to the nearest digit. Basis weight (g / m ² ) = Sample weight × 100 (2) Thickness Measure at 10 places with a micrometer, and let the average value be the thickness. (3) Retention rate A sample of 10 cm x 10 cm is collected and weighed to four decimal places. (W1) Next, the sample is immersed in 30% KOH, and after 2 minutes, the sample is pulled up, the liquid is cut for 2 minutes, and the weight is measured. (W2) Retention rate (%) = (W2−W1) / W1 × 100 250% or more is required as a suitable battery separator. (4) Alkali resistance under high temperature conditions A sample of 10 cm × 10 cm is collected and weighed to four decimal places. (W1) Next, the sample is immersed in 30% KOH at 60 ° C., and after 100 hours, the sample is pulled up. Thereafter, KOH is cut off with water, dried under vacuum, and the weight is measured. (W2) Retention rate (%) = (W1−W2) / W1 × 100 250% or more is required as a suitable battery separator. Each separator is soaked in a 30% KOH aqueous solution at 80 ° C., taken out after 100 hours, and washed with water. Measure the weight change of the separator. (5) Reduction in capacity due to self-discharge The wet nonwoven fabric thus obtained was assembled into an AA size sealed nickel-metal hydride battery (nominal capacity 1100 mAH) to make 10 pieces, and after the characteristics were stabilized, 0.3 CmA, 15
It was charged at 0% and discharged at 45 ° C. for 2 hours. Table 1 shows the average of the remaining capacity (%) after 4 weeks. (6) Measurement of battery internal pressure Ten pieces were assembled in an AA size sealed nickel-metal hydride battery (nominal capacity: 1100 mAH) created in the same manner, and after the characteristics were stabilized, 45 ° C., charge 0.25 CmA, discharge 1
After charging and discharging for 500 cycles with CmA, 20 ° C, 1 Cm
Table 1 shows the internal pressure of the battery 60 minutes after charging with A.

[0029]

[Table 1]

[0030]

According to the present invention, it is possible to obtain a separator having a good affinity for an electrolytic solution when used in a battery, and a separator which does not deteriorate the battery performance even when used for a long time. Further, it is possible to obtain a separator having the above characteristics that can be industrially manufactured at low cost.

Claims (3)

[Claims] 1. An epoxy group-containing structural unit represented by the general formula (1) in an amount of 0.01 to 10 mol% in a nonwoven fabric or a woven fabric containing a polyolefin resin as a main constituent material, a general formula (2) A vinyl alcohol structural unit represented by the formula:
Epoxy-modified polyvinyl consisting of 9.98 mol%, 0 to 29 mol% of a vinyl ester structural unit represented by the general formula (3), and 0.01 to 10 mol% of a structural unit of the general formula (4) having a polyethylene glycol group. A battery separator characterized by impregnating an alcohol with 1 to 20 parts by weight based on 100 parts by weight of a base material. Embedded image 2. The epoxy-modified polyvinyl alcohol according to claim 1, wherein 1 to 20 parts by weight of a styrene-based thermoplastic resin is used with respect to 100 parts by weight of a nonwoven or woven fabric base material mainly composed of a polyolefin-based resin. 1 to 20 parts by weight of a battery separator. 3. A battery using the battery separator according to claim 1.