JPH04272652A - Separator for battery - Google Patents

Abstract

PURPOSE:To provide a very excellent separator for a secondary battery using an alkaline electrolyte, i.e., excellent in the retaining property of the electrolyte and wettability, and resisting deterioration due to the electrolyte and electrochemical oxidation and reduction and also excellent in the separating property of both electrodes, ion, transmittivity, particle filtering properties and mechanical strength, etc. CONSTITUTION:A battery separator containing core-sheath combined fiber having alkali-resistant, hydrophilic polyamide resin as its sheath component and alkali-resistant, electrochemical oxidation/reduction resistant resin as its core component.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a separator used in secondary batteries using an alkaline electrolyte such as nickel-cadmium batteries, and more specifically to a separator that has excellent electrolyte retention and wettability, The present invention also relates to a battery separator that has durability against repeated use of charging and discharging.

0002

[Prior Art] Nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, etc. are known as secondary batteries that use alkaline electrolytes. is a nickel-cadmium battery.

[0003] The performance required of the separator for these secondary batteries is that it should be interposed between the positive and negative plates to prevent short circuits between the plates, that it should not impede the flow of ions between the plates, and that it should not interfere with electrolysis. In addition to general requirements such as not allowing fine particles or metals of the active substance eluted into the solution to pass through, and having mechanical strength that is easy to handle, it also has good electrolyte retention properties, good wettability of the electrolyte solution, etc. Examples include resistance to electrolytes and electrochemical oxidation/reduction.

In particular, the most commonly used separators for nickel-cadmium secondary batteries are:
It is a woven or nonwoven fabric made of polyamide fibers such as nylon 6 and nylon 66. These have excellent electrolyte retention properties, which are necessary to obtain high superpower and low internal resistance, and also have excellent wettability, including the electrolyte again after gas permeation when oxygen generated at the positive electrode is consumed at the negative electrode. It also has the characteristic of being stable in a potassium hydroxide aqueous solution, which is a strongly alkaline electrolyte. However, since polyamide fibers lack electrochemical oxidation and reduction resistance, the fibers deteriorate during charging and discharging, causing the separator to lose its shape and cause a short circuit between the electrode plates. ,
The drawback is that the battery life is short.

[0005] In contrast, a method using a woven or nonwoven fabric made of polyolefin fibers such as polypropylene or polyethylene has been proposed. These are stable in electrolytes and are resistant to electrochemical oxidation and reduction, and even after repeated use over long periods of time, the separator will not lose its shape or mechanical strength, resulting in short circuits between the electrode plates. It has the characteristic of not causing However, since polyolefin fibers lack hydrophilicity, they have poor electrolyte retention and poor wettability, resulting in poor battery performance such as electromotive force. Although the wettability has been slightly improved by surfactant treatment, the liquid retention has not been improved.

As an improvement to the above two methods, a separator having a multilayer structure in which a polyamide fiber layer and a polyolefin fiber layer are laminated, or a separator formed by mixing both fibers, etc., have been proposed. These methods aim to improve performance by taking advantage of both the hydrophilic properties of polyamide fibers and the electrochemical oxidation and reduction resistance of polyolefin fibers. However, even with these methods, although battery performance and battery life are slightly improved compared to each alone, electrochemical oxidation and
There is no change in the fact that the polyamide fiber deteriorates due to reduction, and the liquid retention and wettability of the polyolefin fiber are poor, resulting in an average performance as a whole, and it is not a fundamental solution.

[0007] As mentioned above, the liquid retention property of the electrolyte
Until now, there has been no separator for secondary batteries using an alkaline electrolyte that has excellent wettability and does not deteriorate due to electrochemical oxidation/reduction, thus providing a long-life, high-performance battery.

[0008]

[Problems to be Solved by the Invention] The present invention provides a separator that is extremely excellent as a separator for secondary batteries using an alkaline electrolyte, that is, it has excellent liquid retention and wettability for the electrolyte, and has excellent electrolyte and electrochemical properties. The purpose of the present invention is to provide a separator that does not deteriorate due to physical oxidation or reduction and has excellent bipolar separation properties, ion permeability, fine particle filtration properties, mechanical strength, etc.

[0009]

[Means for Solving the Problems] The present invention contains a core-sheath composite fiber in which the sheath component is a polyamide resin and the core component is a resin having alkali resistance and electrochemical oxidation/reduction resistance. This is a battery separator featuring:

When using the core-sheath composite fiber of the present invention,
The alkali-resistant and hydrophilic polyamide resin disposed on the outer layer of the fiber retains a sufficient amount of electrolyte and satisfies wettability. In addition, the resin that has alkali resistance and electrochemical oxidation/reduction resistance placed in the inner layer of the fiber maintains sufficient mechanical strength even during battery reactions.
Even if the resin placed in the outer layer deteriorates and its mechanical strength decreases, the separator as a whole will not lose its shape because it is integrated with the resin placed in the inner layer. has no adverse effect on liquid retention and wettability. Therefore, since the electrolyte has excellent liquid retention and wettability, battery performance such as super power is improved, and the separator does not lose its shape due to the electrolyte and electrochemical oxidation/reduction, resulting in a longer battery life.

[0011]Also, as a composite fiber, it is possible to prepare a fiber by mixing a polyamide resin and a resin having alkali resistance and electrochemical oxidation/reduction resistance in advance and spinning the resulting fiber. If the separator is used, as the resin deteriorates, the resin peels off at the interface, increasing the surface area, making it easier for the deterioration to proceed, and the shape of the separator is likely to collapse, which is not preferable.

[0012] In the present invention, the polyamide resin having alkali resistance and hydrophilicity includes nylon 6 and nylon 6.
6. Polyamide resin such as nylon 610. In addition to polyamide-based resins, saponified ethylene-vinyl acetate copolymers are examples of resins that have alkali resistance and hydrophilicity, but they are inferior to polyamide-based resins in terms of alkali resistance and hydrophilicity, so they are Even as a separator containing the core-sheath composite fiber used as the sheath component, the alkali absorption amount is low and it is unsuitable. Other polymers may be mixed with the polyamide resin used in the present invention, if necessary. What is alkali resistance?
A weight change rate of 30% or less after 7 days of immersion in a 40% by weight sodium hydroxide aqueous solution at 23° C. according to the method described in Japanese Patent No. K-7114. Also, hydrophilicity means
According to the method described in JIS K-7209, 23
A substance with a water absorption rate of 1% or more after being immersed in water at ℃ for 24 hours.

In the present invention, the resins having alkali resistance and electrochemical oxidation/reduction resistance include polyolefin resins such as polyethylene and polypropylene, polytetrafluoroethylene, polytrifluorochloroethylene, polyhexafluoropropylene, and tetrafluoroethylene. It can be selected from fluororesins such as ethylene-hexafluoropropylene copolymer. Electrochemical oxidation/reduction resistance means that the weight loss rate of the resin is 50% by the method described later.
% or less.

[0014] The core-sheath composite fiber in the present invention refers to a fiber obtained by a generally known melt spinning method, covering a core fiber with a molten resin, impregnating it with a resin solution, or the like. Further, in this case, the position of the core portion may be eccentric. Regarding the cross-sectional shape of the fibers, in addition to the usual fiber shapes, there are triangular, pentagonal, octagonal, T-shaped, and
Fibers with irregular cross sections such as L-shape, Y-shape, star-shape, dogbone shape, horseshoe-shape, or uneven cross-section may be used, or hollow fibers such as macaroni-shape, lotus root-shape, sponge-shape, or rice-field shape may be used. In consideration of liquid retention, it is preferable to use fibers with irregular cross-sections such as Y-shape, which are bulky.

The thickness of the fiber is preferably 10 deniers or less, more preferably 10 deniers or less, in order to improve the performance of the separator in terms of polar separation, ion permeability, fine particle filtration, etc., and to reduce the size, thickness, and weight of the separator. It is 5 denier or less. The method for producing the separator in the present invention may be generally known methods such as paper making method, card method, thermal bond method, needle punch method, spunlace method, spunbond method, melt blown method, etc. be selected as appropriate.

[0016] The separator obtained by the above manufacturing method is preferably subjected to hot pressing in order to have practical strength. When the defects in the core-sheath composite fibers are heated and pressurized by heat press processing, the core component breaks through the polyamide resin that is the sheath component, and the core components are thermally fused together, achieving practical strength as a separator. It will be done. The hot press temperature is higher than the melting point of the core components in order to thermally fuse the core components together. In addition, when the sheath component melts, the separator becomes clogged, causing an increase in internal resistance and a decrease in alkali absorption, so the hot pressing temperature is set to be below the melting point of the polyamide resin that is the sheath component. That is, the melting point of the core component is preferably 10° C. or more lower than the melting point of the sheath component.

[0017] In the core-sheath composite fiber, the area ratio of the polyamide resin as the sheath component to the fiber cross section is 15 to 90.
% is preferable. If it is less than 15%, it is not preferable because the entire surface of the core component cannot be covered and the hydrophilicity of the polyamide resin is not utilized. Moreover, if it exceeds 90%, it is not preferable because the core component cannot break through the polyamide resin, which is the sheath component, during hot pressing as described above. The content of composite fibers in the separator in the present invention is generally 50% by weight or more, but in consideration of the purpose of the present invention, it is more preferably 70% by weight or more, still more preferably 90% by weight or more. . In this case, other components include binders such as resin binders or fibrous binders, and other fiber components, but preferably fibers with alkali resistance and electrochemical oxidation/reduction resistance. .

The battery separator of the present invention is applicable not only to nickel-cadmium batteries, but also to nickel-cadmium batteries.
Secondary batteries that use alkaline electrolytes such as silver-zinc batteries, silver-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, and even nickel-hydrogen batteries, or alkaline manganese batteries, mercury batteries, and silver oxide batteries. - Can also be used as a separator for primary batteries that use alkaline electrolytes, such as zinc-air batteries.

The principles, embodiments, and effects of the present invention will be explained in more detail with reference to the following examples, but these examples are merely taken as examples, and these examples do not limit the present invention in any way. It's not a thing. In both Examples and Comparative Examples, each fiber was manufactured by a papermaking method to make a separator. The binder used was 1 denier and the fiber length was 3 mm.
Polyvinyl alcohol fiber binder (manufactured by Kuraray)
VPB105-2×3), each fiber and binder fiber were disintegrated with a beater and mixed and stirred to form a slurry. This was made into paper using a Tappy paper machine to have a basis weight of 80 g/m 2 and dried at 110°C. then 20
Hot press processing was performed at 0°C and 3 kg/cm2.

[0020]

[Example] Example 1 Nylon 6 with an alkali resistance weight change rate of 5.2% and a water absorption rate of 1.5% is placed in the sheath, and an alkali resistance weight change rate of 0% and an electrochemical oxidation/reduction weight loss rate. Using a 2-denier core-sheath composite fiber with 0.1% polypropylene as the core/core + sheath (area ratio) = 1/4, this fiber accounts for 96% by weight and the binder fiber accounts for 4% by weight. The paper was made as follows.

Comparative Example 1 Using the 2-denier nylon 6 fibers used in Example 1, paper was made so that the fibers accounted for 96% by weight and the binder fibers accounted for 4% by weight. Comparative Example 2 Using the 2-denier polypropylene fibers used in Example 1, paper was made so that the fibers accounted for 96% by weight and the binder fibers accounted for 4% by weight. Comparative Example 3 The 2 denier fiber of nylon 6 used in Example 1 was
The paper was made so that the 2-denier fibers of polypropylene used in Example 1 were 48% by weight, and the binder fibers were 4% by weight.

[0022] Regarding the above four types of separators, the alkali liquid absorption amount, liquid absorption rate, and electrochemical oxidation/reduction resistance were measured according to the following methods. (1) A 5 cm x 5 cm sample whose alkali absorption weight was measured was
After being immersed in a potassium hydroxide aqueous solution of % by weight for 30 minutes,
The liquid was drained for 30 seconds, the weight was measured, and the amount of liquid absorbed was calculated using the following formula.

[0023]

[Math 1]

(2) Alkaline absorption speed: A sample of 25 mm x 10 cm is immersed vertically in a 35% by weight potassium hydroxide aqueous solution at 25°C to a depth of 25 mm, and the time required for the alkaline aqueous solution to be absorbed to a height of 25 mm. was measured.

(3) Electrochemical oxidation/reduction weight loss rate The 5 cm x 5 cm sample whose weight was measured was added to a mixed solution of 5 cc of 30 wt% potassium hydroxide aqueous solution and 250 cc of 5 wt% potassium permanganate aqueous solution. It was immersed at 50°C for 1 hour. Next, after washing under running water for 1 hour and air drying, the weight was measured, and the weight loss was calculated using the following formula.

[0026]

[Math 2]

(4) Electrochemical oxidation/reduction paper strength retention rate A sample of 15 mm x 17 cm was tested according to JIS P-8113.
The dry tear length was measured according to . Samples of the same size,
5 to a mixed solution of 5 cc of 30 wt% potassium hydroxide aqueous solution and 250 cc of 5 wt% potassium permanganate aqueous solution.
It was immersed at 0°C for 1 hour. Next, after washing under running water for 1 hour and air drying, the dry tear length was measured in the same manner, and the paper strength retention was calculated using the following formula.

[0028]

[Math 3]

The above results are shown in Table 1.

[0030]

[Table 1]

From the results shown in Table 1, it is clear that the battery separator of the present invention has excellent electrolyte retention and wettability, as well as electrochemical oxidation and reduction resistance.

Claims (1)

[Claims] 1. A battery separator comprising a core-sheath composite fiber in which the sheath component is a polyamide resin and the core component is a resin having alkali resistance and electrochemical oxidation/reduction resistance.