JP2003157897A - Supporter for solid electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a supporter for solid electrolyte capable of enhancing electric conductivity after supporting a solid electrolyte. SOLUTION: This supporter for solid electrolyte includes a polyvinylidene fluoride resin in nonwoven fabric in a powder state, and is 50% to 80% in porosity. Superfine fiber having a fiber diameter of 4 μm or less is included as a nonwoven fabric constitutive material. The nonwoven fabric maintains a form by fusion or press-fitting of the constitutive material. A pulpy material is included as the nonwoven fabric constitutive material. The thickness of the supporter is desirably 30 μm or less. This supporter can be suitably used as a supporter of the solid electrolyte of a lithium ion polymer battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a support for a solid electrolyte.

[0002]

2. Description of the Related Art Recently, a non-aqueous secondary battery using a solid electrolyte composed of a polymer and a non-aqueous solvent is capable of preventing leakage of the non-aqueous solvent and improving safety. Further, the battery itself is thin and free. Since it can be made into various shapes, development is being actively conducted. However, such a solid electrolyte is insufficient in mechanical strength, and it is difficult to handle it alone and it is difficult to put it into practical use.

Under such a background, a support for supplementing the mechanical strength of the solid electrolyte has been proposed. For example,
A microporous membrane separator made of polyethylene, which is used in a battery using a nonaqueous solvent as an electrolytic solution (for example, a lithium ion battery), is used as a support for a solid electrolyte, or a nonwoven fabric made of a synthetic polyolefin fiber. It is known to use as a support (JP-A-9-227).
24, etc.). Solid electrolytes using these supports were excellent in mechanical strength and were capable of efficiently assembling batteries, but when the support and the solid electrolyte were integrated, the electric conductivity was It turned out to be low.

Further, a support prepared by impregnating a support with a solution of polyvinylidene fluoride resin having a high ability to retain a non-aqueous solvent in an organic solvent or by adhering a polyvinylidene fluoride resin film to the support is integrated. This method is known as a method for improving ionic conductivity. However, although the support in which these polyvinylidene fluoride resins are composited shows high electric conductivity if the non-aqueous solvent is used alone, when it is integrated with the solid electrolyte, the electric conductivity becomes extremely low. There was a problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the drawbacks of the prior art and to provide a solid electrolyte support capable of increasing the electric conductivity after supporting the solid electrolyte.

[0006]

According to the present invention, the above-mentioned problem is characterized in that "a nonwoven fabric contains a polyvinylidene fluoride resin in a powder state and has a porosity of 50% or more and 80% or less. It is possible to solve the problem with a solid electrolyte support (hereinafter, simply referred to as “support”). That is, the support using the conventional polyvinylidene fluoride resin, because the polyvinylidene fluoride resin is in a state of closing the voids of the support, it was not possible to support a sufficient amount of solid electrolyte The support of the present invention contains the polyvinylidene fluoride resin in the form of powder, and the polyvinylidene fluoride resin does not block the voids of the support, and the void ratio is 50% or more and 80% or less. Since it is a large amount, it is possible to support a sufficient amount of the solid electrolyte and thus has excellent ionic conductivity, and since the polyvinylidene fluoride resin can gel and retain the non-aqueous solvent, the solid electrolyte after supporting the solid electrolyte It is possible to increase the electric conductivity.

When the non-woven fabric component contains ultrafine fibers having a fiber diameter of 4 μm or less, the thickness of the support can be reduced, so that the electric conductivity after supporting the solid electrolyte can be further increased.

When the non-woven fabric maintains its shape by fusing or crimping the constituent materials, the non-woven fabric is not filled with voids in order to maintain the non-woven fabric shape and has many voids. The subsequent electrical conductivity can be increased.

[0009] When the pulp-like material is contained as the non-woven fabric constituent, the polyvinylidene fluoride resin is excellently retained, so that the amount of the non-woven fabric constituent can be reduced and the voids can be further increased. The electric conductivity after supporting the solid electrolyte can be increased.

When the thickness of the support is 30 μm or less, the electric conductivity after supporting the solid electrolyte can be further increased.

The support of the present invention can be preferably used as a support for a solid electrolyte of a lithium ion polymer battery.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The non-woven fabric constituting the support of the present invention serves to supplement the mechanical strength of the solid electrolyte, and
It is preferable not to disturb the electrical conductivity as much as possible. Therefore, it is preferable that the non-woven fabric constituent material contains ultrafine fibers and / or pulp-like material so that the support has a small thickness and the constituent material is uniformly dispersed.

The former ultrafine fibers have a fiber diameter of 4 μm.
The following ultrafine fibers are preferable. The finer the fiber diameter, the thinner the support can be, and the higher the homogeneity of the ultrafine fibers, and the powder used for the electrode plate when used for lithium ion polymer batteries. Can be prevented from entering. On the other hand, the lower limit is not particularly limited, but it is preferably about 1 μm so that the strength as a support can be maintained.

The fiber diameter in the present invention means the diameter of the fiber when the cross-sectional shape of the fiber is circular, and the diameter when converted to a circular cross-section when the cross-sectional shape of the fiber is non-circular. Say.

The fiber length of the ultrafine fibers is not particularly limited, but is preferably 5 mm or less, more preferably 3 mm or less so that the distribution of the open pore diameter of the support can be made small. The lower limit of the fiber length of the ultrafine fibers is not particularly limited, but about 0.1 mm is suitable.

Although such ultrafine fibers may be composed of any resin component, for example, a polyester resin such as polyethylene terephthalate, which has an excellent affinity for the non-aqueous solvent forming the solid electrolyte, or a solid Examples thereof include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene that are not easily attacked by the non-aqueous solvent that constitutes the electrolyte, or mixtures or composites thereof.

Further, the non-woven fabric may contain two or more kinds of ultrafine fibers differing in fiber diameter, resin component, or fusion property or pressure bonding property. For example, it is preferable to include two types of ultrafine fibers that differ in terms of fusion-bonding property or pressure-bonding property because the nonwoven fabric form can be maintained by fusing or pressure-bonding one of the ultrafine fibers.

When such ultrafine fibers do not contain a pulp-like substance as described below, it is preferably contained in the non-woven fabric in an amount of 30 mass% or more, and in an amount of 40 mass% or more, in order to obtain the above effect. Is more preferable, it is more preferable that the content is 50 mass% or more, and it is most preferable that the fine fiber is 100%. In addition, when it contains a pulp-like material as described below, it is preferably contained in the nonwoven fabric in an amount of 10 mass% or more, more preferably 20 mass% or more, and more preferably 30 mass% so as to have excellent effects. % Or more is more preferable. On the other hand, it is preferably 60 mass% or less from the viewpoint of the balance with the pulp-like material, and 50 mass%
It is more preferably s% or less, further preferably 40 mass% or less.

Such ultrafine fibers having a fiber diameter of 4 μm or less can be produced, for example, by removing sea components of sea-island type fibers to generate ultrafine fibers composed of island components, or by spinning by superdraw method. It can be manufactured.

On the other hand, it is preferable that the nonwoven fabric component contains a pulp-like material. This pulp-like material can have a thin support and is excellent in uniform dispersibility, and when used for a lithium ion polymer battery, it can prevent the powder used for the electrode plate from entering. Further, since it is excellent in the retention of the polyvinylidene fluoride resin due to the fibrils of the pulp-like material, the amount of the non-woven fabric constituent material can be reduced,
Since the number of voids can be further increased, the electric conductivity after supporting the solid electrolyte can be increased. Furthermore, since the pulp-like material is also entangled between the fibrils, it is also excellent in shape-retaining property, so that it is also easy to handle.

The pulp-like material of the present invention is preferably composed of a synthetic resin so that the strength of the support does not decrease when it comes into contact with a non-aqueous solvent, and more specifically, polyethylene, polypropylene and the like. Polyolefin resin,
Examples include meta-type or para-type wholly aromatic polyamide resins and polyimide resins.

The pulp-like material is preferably contained in the non-woven fabric in an amount of 40 mass% or more, and more preferably in an amount of 50 mass% or more, so that the above-mentioned performance is excellent. On the other hand, although the pulp-like material is excellent in the above-mentioned performance, if it is too much, the nonwoven fabric structure tends to be too dense and the electric conductivity tends to be deteriorated.
It is preferably s% or less, and more preferably 80 mass% or less.

The non-woven fabric of the present invention can contain thick fibers thicker than the ultrafine fibers in addition to the ultrafine fibers or pulp-like material as described above. By including such thick fibers, the strength of the support can be improved.

Since the thick fibers have a larger fiber diameter than the above-mentioned ultrafine fibers, the fiber diameter exceeds 4 μm. The larger the fiber diameter, the more the strength of the support can be improved. It is more preferably 5 μm or more. On the other hand, if the fiber diameter of the thick fiber is too large, the thickness of the support tends to be thick and the electric conductivity tends to deteriorate, so that it is preferably 10 μm or less, more preferably 8 μm or less. .

The fiber length of this thick fiber is not particularly limited, but is preferably 1 to 10 mm, more preferably 3 to 5 mm so that it can be uniformly dispersed.

Such thick fibers may be composed of any resin component, but like the ultrafine fibers, polyester resins such as polyethylene terephthalate, polyolefin resins such as polyethylene, polypropylene and polymethylpentene, Alternatively, it may be composed of a mixture or composite of these. Among these, core-sheath type thick fibers having polyethylene as a sheath component and polypropylene as a core component are preferable because they can be fused with other non-woven fabric constituent materials to improve the strength of the support.

In addition, when thick fibers that can be bound by pressure, such as unstretched polyethylene terephthalate thick fibers, are included, it is possible to improve the strength of the support by pressure bonding with other non-woven fabric constituent materials. Is.

Further, the thick fiber may also contain two or more types of thick fibers which differ in fiber diameter, resin component, or fusion property or pressure bonding property.

Regardless of whether or not such thick fibers contain a pulp-like material, the content in the non-woven fabric is 2 so as not to interfere with the action of the ultrafine fibers or pulp-like material as described above.
It is preferably 0 mass% or less, and 15 mass%
The following is more preferable. In some cases, the non-woven fabric does not contain thick fibers.

The nonwoven fabric of the present invention is preferably composed of, for example, the ultrafine fibers, pulp-like material or thick fibers as described above, and the nonwoven fabric maintains its shape by fusing or crimping the constituent materials. Is preferred. When the non-woven fabric form is maintained by fusing or pressure bonding of the constituent materials in this manner, many voids are not filled in the non-woven fabric in order to maintain the non-woven fabric form and there are many voids. Can be supported, and the electric conductivity after supporting the solid electrolyte can be increased. For example, when the constituent materials are bound with each other by an emulsion or suspension binder, a film is formed by the binder and the voids of the non-woven fabric tend to be closed, but the non-woven fabric of the present invention is formed by fusing or press-bonding the constituent materials. Since it maintains, there are many voids. When the pulp-like material is fused or pressure-bonded, it tends to form a film to close the voids. Therefore, it is preferable that the pulp-like material is fused or pressure-bonded with ultrafine fibers and / or thick fibers.

The phrase "maintaining the form" means having a strength that does not hinder the support of the solid electrolyte.

The support of the present invention can be used in such a nonwoven fabric.
Since it contains polyvinylidene fluoride in powder form,
The voids of the support are not closed by the polyvinylidene fluoride resin, and since the polyvinylidene fluoride resin can gel and retain the non-aqueous solvent, it is possible to increase the electrical conductivity after supporting the solid electrolyte. it can.

The particle size of the polyvinylidene fluoride resin powder is not particularly limited, but the smaller the particle size, the more it can be dispersed throughout the support, and the more uniform the ion conductivity after supporting the solid electrolyte. The particle size is preferably 4 μm or less, and more preferably 2 μm or less, since the properties are improved and the battery performance is improved. The lower limit is not particularly limited, but is preferably 1 μm for adhesion to the surface of the non-woven fabric component by Van der Waals force. The "particle diameter" means an average particle diameter, and this average particle diameter can be measured by a laser diffraction / scattering method.

Further, the content of the polyvinylidene fluoride resin powder in the support is preferably 5 mass% or more of the whole support so that the ionic conductivity can be enhanced. On the other hand, if it exceeds 10 mass% of the whole support, the retention of the polyvinylidene fluoride resin powder by the non-woven fabric constituent becomes poor, so it is preferably 10 mass% or less.

The term "comprising the polyvinylidene fluoride resin in the form of powder" means that the polyvinylidene fluoride resin exists in a discontinuous state with the nonwoven fabric constituent material, or is continuous to some extent, but not completely. It refers to a state in which there is a large or small gap between the polyvinylidene fluoride resin and the non-woven fabric constituent, which existed in a discontinuous state. Examples of such a state include a state where the polyvinylidene fluoride resin is physically attached to the non-woven fabric constituent material (for example, van der Waals force), and a void where the polyvinylidene fluoride resin is formed by the non-woven fabric constituent material. The state of being held can be mentioned. As described above, when the polyvinylidene fluoride resin is in the powder state, since the support has voids, it is possible to support many solid electrolytes when integrated with the solid electrolytes. It has excellent ionic conductivity.

As described above, the support of the present invention contains polyvinylidene fluoride in the form of powder in the non-woven fabric and has a porosity of 50% to 80%.
Since the amount of the solid electrolyte that can be supported can be increased while maintaining the shape retention as the support, excellent electrical conductivity can be obtained. A more preferable porosity is 55
% Or more, more preferably 60% or more. Further, the porosity is more preferably 75% or less, further preferably 70% or less.

The "porosity" (P) of the present invention means a value obtained from the following equation. Porosity (P) = {1-W / (T * d)} * 100 Here, W means a basis weight (g / m < ² >), T means the thickness (micrometer) of a support body, and d. Is the density (g /
cm ³ ). In addition, when two or more kinds of the support-constituting materials are present, the density of the support-constituting material means the mass average of the respective support-constituting materials. In addition, "Basis weight" is JIS P
8124 (Paper and paperboard-Basis weight measurement method) means the basis weight based on the method specified, and "thickness" means JIS B 750.
2 means a value measured by the method defined in 2, that is, a value measured by an outer micrometer under a load of 5 N, and "density" means a value measured by the method defined in JIS K7112.

The thickness of the support of the present invention is preferably 30 μm or less, and preferably 25 μm or less so that the ion migration distance is short, the internal resistance can be lowered, and the electric conductivity can be increased. Is more preferable. The lower limit is not particularly limited, but 10 μm in order not to impair the reinforcing effect of the solid electrolyte as a support and to prevent the amount of the solid electrolyte that can be supported from becoming too small.
It is preferably m, and more preferably 15 μm. When the support of the present invention is used for a lithium ion polymer battery, if the support has such a thickness, it is possible to prevent a minute short circuit due to invasion of the powder active material.

The support of the present invention contains a polyvinylidene fluoride resin in the form of powder in a nonwoven fabric and has a porosity of 5
As long as the support is 0% or more and 80% or less, it may be produced by any method, and is not particularly limited,
For example, when a non-woven fabric is produced by a wet method, a polyvinylidene fluoride resin powder may be combined together to form a fibrous web, and then a pressure may be applied to obtain a desired porosity. In addition, when the non-woven fabric component includes a material that can be fused or pressure-bonded, it is preferable that the material is heated at the same time as the pressure is applied or is heated prior to the pressure to be fused or pressure-bonded. The pressure bonding condition and the heating condition can be appropriately set by repeating the experiment.

As another method for producing the support, a fiber web containing a polyvinylidene fluoride resin powder is formed by the method disclosed in Japanese Patent Application No. 2000-370965, and then, in the same manner as the above method, It can be manufactured by pressurizing or heating and pressurizing so as to obtain a desired porosity. That is, for example, (1) polyvinylidene fluoride powder, (2) ultrafine fiber aggregate, aggregate of splittable fibers that can be divided into ultrafine fibers by the action of compressed gas, aggregate of pulp-like substances, action of compressed gas A non-woven fabric constituent material selected from a group of separating fibers capable of being fibrillated into a pulp-like material, a thick fiber group, and the polyfluoride by jetting the material into a gas by the action of a compressed gas. The vinylidene powder and the ultrafine fibers generated from the nonwoven fabric constituent material, pulp-like material, or thick fibers are dispersed, and these are accumulated to form a fiber web containing polyvinylidene fluoride resin powder, and then the method described above. Exactly the same as above, it can be manufactured by pressurizing or heating and pressurizing so as to obtain a desired porosity. According to this method, since almost no polyvinylidene fluoride powder is dropped off when the fiber web is formed,
The fiber web can be manufactured as designed, and as a result, the support can be manufactured. Further, even if the aggregate of the pulp-like material or the aggregate of the fibrillating fibers capable of being fibrillated by the action of the compressed gas is used as the non-woven fabric constituent material, the pulp-like material is efficiently generated. The fibrils of this pulp-like material have the effect of excellent retention of the polyvinylidene fluoride powder. Furthermore, since the polyvinylidene fluoride powder and the non-woven fabric constituent material are uniformly mixed, they have excellent electric conductivity, and for example, when used for a lithium ion polymer battery, they have excellent high-rate charge / discharge characteristics and battery life. Can be expected to be longer.

When the solid electrolyte is supported by using the support of the present invention, it can be made to have excellent electric conductivity, so that it can be effectively used as a support for a gel-like solid electrolyte for a lithium ion polymer battery. In many cases, 80% or more of this gelled solid electrolyte is composed of a non-aqueous solvent, but the support of the present invention has a high porosity and is excellent in the retention of the non-aqueous solvent containing polyvinylidene fluoride powder. Therefore, it is also effective in preventing liquid leakage.

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

[0043]

Example 1 Polyethylene terephthalate extra fine fibers (fineness = 0.1 dtex, fiber diameter = 3 μm, fiber length = 3 mm) of 30 mass%, polyethylene terephthalate unstretchable crimpable thick fibers (fineness = 0.2 dtex,
Fiber diameter = 5 μm, fiber length = 3 mm, softening temperature = 231
10% by mass, 10% by mass of para-aromatic polyamide pulp (fiber length = 0.38 mm) and 10% by mass of polyvinylidene fluoride resin powder (average particle size = 1 μm).
A slurry containing mass% was prepared.

Then, the prepared slurry was fed to a short-net inclined paper machine to make a paper, and then dried by a Yankee dryer set to a surface temperature of 180 ° C. to produce a fiber web.

Next, this fiber web is subjected to a heat calendering process (pressure = 500 N / cm, temperature = 180 ° C.) to press-bond the polyethylene terephthalate unstretchable crimpable thick fibers to form a nonwoven fabric and at the same time polyvinylidene fluoride resin powder. Support containing (Basis weight = 12 g /
m ² , thickness = 20 μm, porosity = 65%).
The non-woven fabric constituting this support was one capable of supporting the solid electrolyte as described later, and maintained its form by pressure bonding. Further, the support is a state in which polyvinylidene fluoride resin powder is sandwiched between the fiber surface, pulp surface, fiber and pulp, sandwiched between pulp, or sandwiched between fibers (powder state). ), Which had an appropriate void.

(Comparative Example 1) 40 mass% of polyethylene terephthalate ultrafine fibers (fineness = 0.1 dtex, fiber diameter = 3 µm, fiber length = 3 mm), polyethylene terephthalate unstretched crimpable thick fibers (fineness = 0.2 dte)
x, fiber diameter = 5 μm, fiber length = 3 mm, softening temperature = 23
A slurry was prepared in which 10 mass% of 1 ° C.) and 50 mass% of para-aromatic polyamide pulp (fiber length = 0.38 mm) were blended.

Next, the prepared slurry was fed to a short-net inclined paper machine to make a paper, and then dried by a Yankee dryer set to a surface temperature of 180 ° C. to produce a fiber web.

Next, this fiber web was subjected to a heat calendering treatment under the same conditions as in Example 1 to press thick polyethylene non-stretchable crimpable polyethylene terephthalate crimped fibers, and a base material for a support (unit weight = 10 g / m ² , thickness =). 18 μm, porosity = 60
%) Was produced.

Then, 5 g / m ² of polyvinylidene fluoride resin powder (average particle size = 1 μm) was pressed into the base material for the support with fingers to fill it, and the support (area weight = 15 g /
m ² , thickness = 16 μm, porosity = 38%).
In addition, the support contained polyvinylidene fluoride resin powder in a state (filled state) filled in the voids formed by the fibers and the pulp, and was in a state with few voids.

(Comparative Example 2) A base material for a support produced in the same manner as in Comparative Example 1 (area weight = 10 g / m ² , thickness = 18 μm).
m, porosity = 60%) with a 10% methyl ethyl ketone solution of polyvinylidene fluoride resin so that the amount of the solution is twice the mass of the substrate for the support (that is, 20 g / m ² amount). After that, the solvent was dried and removed by a vacuum dryer to obtain a support (area weight = 12 g / m ² , thickness = 15 μm,
Porosity = 45%) was produced. In this support,
The polyvinylidene fluoride resin was present as a film.

(Measurement of Electric Conductivity) The polymer substance and the non-aqueous solvent were mixed at a mass ratio of 10:90 at room temperature to prepare a gel electrolyte solution. Incidentally, as the polymer substance,
A copolymer of ethylene oxide and propylene oxide (registered trademark: Elekcel TA-140; manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is used, and the non-aqueous solvent is propylene carbonate and gamma-butyrolactone in a weight ratio of 1: 1.
In the solvent mixed with, so that the concentration becomes 1 mol / L,
A solvent in which LiBF ₄ was dissolved was used.

Next, this gel electrolyte solution was uniformly applied to each of the supports prepared in Example 1 and Comparative Examples 1 and 2 to form a gel electrolyte layer having a thickness of about 5 μm on the surface of the support, The solid electrolyte was supported.

Next, the support supporting this solid electrolyte was placed in a test cell for measuring electric conductivity, and was made into a circular (diameter = 20 mm) stainless steel (SUS3).
04) After sandwiched between the electrodes made, the test cell was filled with the same non-aqueous solvent as described above, and then pressure (0.2 MPa / cm ² ) was applied between the electrodes to support the solid electrolyte. The electrical conductivity in the depth direction was measured based on the AC impedance method. That is, AUTOLAB PGS
The locus of complex impedance measured by TAT30 (manufactured by ECO CHEMI) was analyzed by the Cole-Cole plot method, and the electric conductivity (unit = S / cm) was obtained. An electric conductivity of 1 × 10 ⁻³ S / cm or more is suitable for practical use. The results are shown in Table 1.
As is clear from Table 1, it was found that the solid electrolyte supported by the support of the present invention has high electric conductivity and is excellent in practicality.

[0054]

[Table 1]

[0055]

The support for solid electrolyte of the present invention is capable of increasing the electric conductivity after supporting the solid electrolyte. Therefore, it can be suitably used for a lithium ion polymer battery.

Claims (6)

[Claims] 1. A non-woven fabric containing polyvinylidene fluoride resin in the form of powder, and having a porosity of 50% or more and 80%.
A support for a solid electrolyte, characterized in that: 2. The support for a solid electrolyte according to claim 1, wherein the nonwoven fabric constituent material contains ultrafine fibers having a fiber diameter of 4 μm or less. 3. The support for a solid electrolyte according to claim 1, wherein the non-woven fabric maintains its shape by fusing or pressure-bonding the constituent materials. 4. The support for a solid electrolyte according to claim 1, wherein the nonwoven fabric constituent material contains a pulp-like material. 5. The support for solid electrolyte according to claim 1, wherein the support has a thickness of 30 μm or less. 6. The support for a solid electrolyte according to claim 1, which is used for a lithium ion polymer battery.