JPH07105927A - Battery separator - Google Patents

Abstract

PURPOSE:To provide a battery separator having a very high effect, which excels in the anti-alkaline property compared with a conventional polyamide separator, presents good lasting of the wettability, and permits constructing a long life battery. CONSTITUTION:A separator concerned for a battery is formed by laminating a synthetic fiber non-woven fabric chiefly containing polyolefin resin and a synthetic fiber non-woven cloth of anti-alkaline property, wherein a thermoplastic, hydrophilic resin is included in the polyolefin resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator used in a sealed type secondary battery, and particularly has a good affinity with an electrolytic solution and a short circuit caused by elution of an active material during use. The present invention relates to a battery separator having excellent prevention performance.

[0002]

2. Description of the Related Art Nonwoven fabrics made of synthetic fibers such as polyamide and polyolefin are used as conventional battery separators. These separators are mainly required to have electrolytic solution resistance, electrolytic solution retention, oxidation resistance, short circuit prevention, etc. Polyamide nonwoven fabrics, which are generally used in many cases, are excellent in electrolyte retention, but there is a problem that they are poor in electrolyte resistance and oxidation resistance especially at high temperatures. On the other hand, polyolefin nonwoven fabrics such as polyethylene and polypropylene are excellent in electrolytic solution resistance and oxidation resistance and are ideal for extending the battery life, but since the surface is hydrophobic, it has no affinity with the electrolytic solution. However, there is a problem with respect to electrolyte retention, and it is used only in some batteries. Therefore, in order to solve these drawbacks, JP-A-53-621 has been proposed.
Japanese Patent No. 38 proposes a battery separator obtained by subjecting a wet polyolefin nonwoven fabric to corona discharge treatment and surfactant treatment. Further, JP-A-60-9056 discloses a battery separator in which a polypropylene ultrafine fiber nonwoven fabric having an average fineness of 0.01 to 0.5 denier and an alkali resistant synthetic fiber nonwoven fabric are laminated and then treated with a surfactant. Is proposed.

[0003]

However, in the battery separator described in JP-A-53-62138, the duration of hydrophilicity becomes longer as compared with the method in which the surfactant is post-treated. However, the surfactant adhering to the surface cannot be removed, causing uneven distribution of the electrolytic solution, and it is impossible to significantly improve the battery life due to internal discharge. Further, in the battery separator described in JP-A-60-9056, in the initial stage when the surfactant adhering to the surface works effectively, the ultrafine fiber non-woven fabric is structurally dense, so that the electrolyte retention property is low. Although good, it is difficult to re-penetrate the electrolyte solution due to the denseness of the structure as the surfactant adhering to the surface comes off, and it is impossible to significantly improve the battery life.

[0004]

In order to solve the above problems, the present invention provides a battery separator constituted by laminating and integrating a synthetic fiber nonwoven fabric containing a polyolefin resin as a main component and an alkali resistant synthetic fiber nonwoven fabric. A thermoplastic hydrophilic resin is blended with the polyolefin resin. That is, the present invention is a synthetic fiber non-woven fabric obtained by spinning a blend resin containing a polyolefin resin excellent in electrolytic solution resistance and oxidation resistance and a thermoplastic hydrophilic resin excellent in long-term hydrophilicity by, for example, a melt blow method. And an alkali-resistant synthetic fiber non-woven fabric, which are laminated and integrated.

As the polyolefin resin, for example, homopolymers or copolymers of ethylene, propylene, 4-methyl-1-pentene and the like can be used. These polymers may be used alone or in admixture of two or more. From the viewpoint of spinnability, the heat flow property may be such that the melt flow rate is 10 g / 10 min or more, preferably 30 g / min or more.

Polyalkylene oxide (hereinafter abbreviated as PAO) is suitable as the thermoplastic hydrophilic resin, and examples thereof include polyethylene oxide, polypropylene oxide, and random or block copolymers of ethylene oxide / propylene oxide. . You may use these PAO individually or in mixture of 2 or more types. The average molecular weight of PAO is 10 to 50.
The range of 0,000, particularly 20 to 1,000,000 is preferable. Outside of this range, there are disadvantages such as poor compatibility with the polyolefin resin as the main material and poor spinnability. If the molecular weight is extremely low,
Solubility in the electrolyte is too large, and it becomes difficult to maintain long-term hydrophilicity. Further, the blending amount of the thermoplastic hydrophilic resin is preferably in the range of 2 to 20% by weight in the synthetic fiber containing a polyolefin resin as a main component from the viewpoint of compatibility with the polyolefin resin and spinnability.

It is preferable that synthetic fibers made of a blended resin containing the above-mentioned polyolefin resin as a main component and a thermoplastic hydrophilic resin blended therein are manufactured as ultrafine fibers by a melt blow method and formed into an ultrafine synthetic fiber nonwoven fabric.

It is also possible to add a conventional surfactant to the synthetic fiber containing the polyolefin resin as a main component. The ionicity of the surfactant used here is not particularly limited, but a nonionic surfactant containing no metal ion or the like is suitable from the viewpoint of the self-discharge characteristics of the battery. Further, the content of the surfactant is preferably in the range of 0 to 6% by weight in the synthetic fiber containing the polyolefin resin as the main component because the melted resin in the extruder does not slip when the spinning raw material is prepared and the production is easy.

The average fiber diameter of the synthetic fiber containing the polyolefin resin as a main component is 12 μm from the viewpoint of electrolyte retention.
The following is preferable, and the range of 1 to 10 μm is particularly preferable. Further, the basis weight is preferably in the range of ^{20 to} 80 g / m ² in order to secure the electrolyte retaining property and the liquid retaining property.

As the alkali-resistant synthetic fiber, a polyethylene-polypropylene (hereinafter abbreviated as PP-PE) composite fiber nonwoven fabric or a nonwoven fabric made of vinylon fiber is preferable. When a PP-PE composite fiber nonwoven fabric is used, a polyethylene component having a lower melting point than polypropylene, which is the main component of the meltblown nonwoven fabric, serves as an adhesive, so that the laminated integration can be achieved without impairing the good characteristics of the meltblown layer made of ultrafine fibers. It is possible. Further, in the vinylon non-woven fabric, by utilizing the property of hot water solubility, it is possible to bond at a temperature lower than the melting point of the polypropylene component of the melt blown non-woven fabric, so that the laminated integration can be achieved without impairing the good properties of the melt blown layer. It is possible. The fiber diameter of the alkali-resistant synthetic fiber to be used is not particularly limited, but in order to ensure short-circuit prevention performance due to cracks, burrs, etc. of the electrode plate that occurs during assembly, the fiber diameter should be in the range of 1-10 denier preferable.

Further, by carrying out a surface modification treatment such as a normal corona discharge or a plasma discharge after the lamination and integration, it is possible to further improve the sustainability of wettability.

[0012]

According to the battery separator of the present invention, the wettability of the electrolytic solution can be maintained for a long period of time as compared with conventional polypropylene separators and polyamide nonwoven fabric separators whose surface is treated with a surfactant. It has a long life and is mainly composed of a chemically stable material, so that it has excellent self-discharge characteristics. That is, according to the battery separator of the present invention, by kneading a thermoplastic hydrophilic resin, which has a molecular weight considerably higher than that of a surfactant and is hardly dissolved in water, into the polyolefin resin which is the main component of the blended resin, the conventional technique As described above, the surfactant attached to the separator surface does not fall off, and even when the thermoplastic hydrophilic resin on the separator surface is lost, the thermoplastic hydrophilic resin can be replenished from the inside of the separator. Therefore, as compared with the conventional technique, the wettability with the electrolytic solution is prolonged. Furthermore, since the main component of the blended resin is a polyolefin resin with excellent electrolyte resistance, it does not generate nitrate ions that easily promote self-discharge unlike polyamide nonwoven fabric separators, and exhibits excellent effects on self-discharge characteristics. To do. Also,
When synthetic fibers composed mainly of a polyolefin resin are made into ultrafine fibers, since the specific surface area is large and the structure is dense, it is difficult to release the once retained electrolyte.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples. In this embodiment, the polyolefin resin is JIS
Melt flow rate specified in K7210 is 80g / 1
Using 0 min polypropylene (hereinafter abbreviated as PP),
Polyethylene oxide (Alcox R-1000, manufactured by Meisei Chemical Co., Ltd.) was used as the thermoplastic hydrophilic resin. A polyoxyethylene nonionic surfactant was used as the surfactant. These materials were melted and kneaded by a different-direction twin-screw extruder, and then pelletized, and used as spinning raw materials to produce the following separators.

(Example 1) A blend resin composed of 98% PP resin and 2% thermoplastic hydrophilic resin was prepared.
At a melting temperature of 300 ℃, the die (orifice diameter 0.3m
m, bitches 1 mm apart) and a gas discharge slit having a width of 0.25 mm on both sides thereof is used to set the gas temperature to 3
The fiber was spun under the conditions of 20 ° C. and a gas pressure of 2 kg / cm ² , and was collected on a cotton collecting conveyor net that moved at a constant speed at a distance of 35 cm from the die. The resulting blended PP meltblown nonwoven fabric (average fiber diameter 8 μm) and PP-PE core-sheath composite fiber nonwoven fabric (1.5 denier 70%, 2 denier 30)
% Of mixed fiber) was laminated and integrated by a heat laminator under the condition of a roll temperature of 120 ° C. to obtain a separator.

(Example 2) PP resin 90 was used as the blend resin.
%, And a thermoplastic hydrophilic resin 10%, a separator was obtained in the same manner as in Example 1.

(Example 3) PP resin 80 was used as the blend resin.
%, And a thermoplastic hydrophilic resin 20%, a separator was obtained in the same manner as in Example 1.

(Example 4) PP resin 9 was used as the blend resin.
3.5%, thermoplastic hydrophilic resin 5%, surfactant 1.5
A separator was obtained in the same manner as in Example 1 except that the separator was made of a composition of 10%.

(Example 5) The separator obtained in Example 4 was further subjected to discharge treatment under the condition of 5 m / min by a corona discharge treatment device having two electrodes (4 on both sides) on each side to form a separator. Got

(Comparative Example 1) A web was formed in the same manner as in Example 1 except that the blend resin was a composition of only PP resin, and 1.2% of a surfactant was attached by post-impregnation treatment. A separator was obtained.

Comparative Example 2 PP resin 98 was used as the blend resin.
%, And a nonionic surfactant of 2% was used to obtain a separator in the same manner as in Example 1.

Next, the characteristics of each of the obtained separators were tested and evaluated. The test method and evaluation method according to this example are as follows. (Compatibility with PP) The raw material pellets were sliced into a thin film, dyed, and then observed with a transmission electron microscope to observe the dispersed state of the blended material. And × indicates that the hydrophilic material is in the form of large particles and dispersed non-uniformly, and ◎, 〇, △, ×
Was evaluated in 4 steps in this order. (Spinnability) Depending on the generation status of the unfibridated material generated during spinning, ◎ indicates that there is no unfibridated material at all, and × indicates that the unfibridated material frequently occurs and the nonwoven fabric cannot be used. It was evaluated in four stages in the order of ◯, △, ×. (Liquid absorption rate A) Width 2 from the obtained separator in the flow direction
A sample of 5 mm x 200 mm in length is taken and hanged so that the lower end of the sample is immersed in 30% potassium hydroxide aqueous solution by 5 mm, and the height of the potassium hydroxide aqueous solution sucked up by capillary action is absorbed for 30 minutes. It was speed. (Liquid absorption rate B) The separator was immersed in a 30% aqueous potassium hydroxide solution at 80 ° C for 10 days, washed until the washing liquid became neutral, dried at 80 ° C, and then the same as in the liquid absorption rate A method. The measurement was carried out by the method.

[0022]

[Table 1]

From the results shown in Table 1, it can be seen that the separators of the examples using the blended resin in which the polyolefin resin is mixed with the thermoplastic hydrophilic resin have a markedly improved long-term hydrophilicity as compared with the separator of the comparative example. . Example 4
As described above, the separator in which the blending amount of the thermoplastic hydrophilic resin in the blended resin is significantly reduced by using the surfactant together,
The wettability was good and the resin spinnability was also good. Further, as in Example 5, by performing corona discharge treatment as a post-treatment, a separator having better wettability persistence was obtained. On the other hand, as in the comparative example, in the case of blending the surfactant alone and in the post-treatment, although the initial liquid absorption rate A may be higher than that in the examples, the immersion in the electrolytic solution showing an improvement in the sustainability of the wettability. The liquid absorption speed B after that is poor penetration. When the alkali weight loss of Example 1 and Comparative Example 2 were compared, the values were 0.4% and 0.8%, respectively, and even if the surfactant and the thermoplastic hydrophilic resin were blended in the same amount, As can be seen from the fact that the activator has a larger alkali weight loss, the surfactant is easily eluted at the same time when the activator is immersed in the electrolytic solution, and the wettability is significantly lowered.
The alkali weight loss is calculated by calculating the weight loss rate after immersion in a 31% potassium hydroxide aqueous solution at 80 ° C. for 1 week according to the following formula. Alkali weight loss (%) = 100− (weight after immersion / weight before immersion) × 100

Next, the separator of Example 5 and a conventional polyamide non-woven fabric separator were assembled in a usual AA size sealed cylindrical nickel-hydrogen battery to prepare test batteries a and b. These batteries a and b are at an ambient temperature of 20 ° C,
A charging / discharging cycle test was carried out in which 150% was charged at a charging current of 1 CmA and discharged at a discharging current of 1 CmA. The battery life is the discharge capacity of 70% of the initial capacity.
When it reached%, it was judged as the life. FIG. 1 shows a curve of discharge capacity retention rate by a charge / discharge cycle test. As shown in FIG. 1, the polyamide separator of the comparative example has a life of 400 cycles, while the separator of the present invention has a life of 55 cycles.
The life was extended to about 40% with 0 cycles, which was a long life.

[0025]

As described above, according to the present invention,
It is possible to provide a battery separator having excellent alkali resistance, excellent wettability sustainability, and capable of constituting a long-life battery, as compared with a conventional polyamide separator, and having an extremely high effect.

[Brief description of drawings]

FIG. 1 is a curve showing the discharge capacity retention rate of a separator of the present invention and a conventional polyamide separator in a charge / discharge cycle test.

Claims (6)

[Claims] 1. A separator for a battery, which is formed by laminating and integrating a synthetic fiber non-woven fabric containing a polyolefin resin as a main component and an alkali-resistant synthetic fiber non-woven fabric, characterized in that a thermoplastic hydrophilic resin is blended with the polyolefin resin. Battery separator for. 2. The battery separator according to claim 1, wherein the thermoplastic hydrophilic resin is polyalkylene oxide. 3. The battery separator according to claim 1, wherein the blending amount of the thermoplastic hydrophilic resin in the synthetic fiber containing the polyolefin resin as a main component is 2 to 20% by weight. . 4. The battery separator according to claim 1, wherein the synthetic fiber containing the polyolefin resin as a main component is obtained by a melt blow method. 5. The battery separator according to claim 1, wherein the synthetic fiber containing the polyolefin resin as a main component is mixed with a surfactant. 6. The battery separator according to claim 1, which is subjected to a surface modification treatment after the lamination and integration.