JP2023180729A - Solid electrolyte supporting sheet - Google Patents

Abstract

To provide a nonwoven fabric with excellent heat resistance, lightweight, thin film, high porosity, and uniformity, and a solid electrolyte supporting sheet.SOLUTION: A solid electrolyte supporting sheet is a wet-laid nonwoven fabric consisting of binder fibers (A) and non-binder fibers (B), the wet nonwoven fabric has a basis weight of 1 to 10 g/m2, a thickness of 5 to 30 μm, and a porosity of 60% or more, the binder fiber (A) has an average fiber diameter of 1 to 9 μm and an aspect ratio of 200 to 1500, and the non-binder fibers (B) have an average fiber diameter of 0.1 to 9 μm and an aspect ratio of 200 to 1500.SELECTED DRAWING: None

Description

The present invention relates to a solid electrolyte supporting sheet.

In recent years, all-solid-state batteries have attracted attention as the next generation technology for lithium-ion batteries. Conventional lithium-ion batteries use an organic solvent-based electrolyte, while all-solid-state batteries use a solid electrolyte. Conventional organic solvent-based electrolytes are highly flammable and pose a risk of ignition, and there is also the problem that the charging and discharging performance of lithium ion batteries changes greatly depending on temperature.
On the other hand, all-solid-state batteries use a nonflammable solid electrolyte, so there is little risk of ignition, and they have high electrochemical stability, so they can be expected to exhibit stable performance over a wide temperature range.

As solid electrolytes, sulfide electrolytes are mainly used because they have excellent lithium ion conductivity. This solid electrolyte is generally formed by dispersing the solid electrolyte and a binder in a solvent to create a slurry liquid, and then coating the slurry liquid to form a solid electrolyte layer.
However, with this production method, the strength of the solid electrolyte layer is low, resulting in poor handling properties. Handlability can be improved by increasing the film thickness, but since the lithium ion conductivity in the electrolyte depends on the thickness of the electrolyte layer, the solid electrolyte layer must be made thinner.

Therefore, in order to achieve both handleability and lithium ion conductivity, it has been proposed to use a nonwoven fabric made of a combination of polypropylene fibers or polyethylene fibers and fibrillated heat-resistant fibers as a support sheet for the solid electrolyte layer (Patent Document 1).

However, polypropylene and polyethylene, which are the materials constituting the nonwoven fabric, have a melting point of 120 to 160°C and have low heat resistance, so there is a risk that the solid electrolyte layer will change shape when exposed to high temperatures. Solid electrolyte supporting sheets require thermal stability in order to exhibit stable battery performance over a wide temperature range.

By the way, fibrillated heat-resistant fibers are usually obtained by subjecting heat-resistant fibers having a large fiber diameter to a pre-refining treatment such as beating with a refiner or a beater. In this pre-refining process, there is a risk that metal foreign matter may be mixed in, and furthermore, it is difficult to make the fiber diameter and cut length uniform. A nonwoven fabric obtained using nonuniform fibers causes nonuniformity in the thickness, voids, and pore diameter of the solid electrolyte layer.

JP2020-24860A

The present invention has been made in view of the above background. An object of the present invention is to provide a sheet for supporting a solid electrolyte that has excellent heat resistance, is lightweight, thin, and has high voids and uniformity.

That is, the present invention is a solid electrolyte-supporting sheet that is a wet-laid nonwoven fabric made of binder fibers (A) and non-binder fibers (B), and the wet-laid nonwoven fabric has a basis weight of 1 to 10 g/m ² , a thickness of 5 to 30 μm, and The porosity is 60% or more, the binder fiber (A) has an average fiber diameter of 1 to 9 μm and an aspect ratio of 200 to 1500, and the non-binder fiber (B) has an average fiber diameter of 0.1 to 9 μm and an aspect ratio. 200 to 1500.

According to the present invention, it is possible to provide a sheet for supporting a solid electrolyte that has excellent heat resistance, is lightweight and thin, and has high voids and uniformity.

The present invention will be explained in detail below.

[Solid electrolyte supporting sheet]
The wet-laid nonwoven fabric of the solid electrolyte supporting sheet of the present invention consists of binder fibers (A) and non-binder fibers (B).
The binder fibers (A) have an average fiber diameter of 1 to 9 μm and an aspect ratio of 200 to 1500, and the non-binder fibers (B) have an average fiber diameter of 0.1 to 9 μm and an aspect ratio of 200 to 1500. be.

In the present invention, by adopting this configuration, it is possible to obtain a solid electrolyte-supporting sheet that is a lightweight thin film and a uniform nonwoven fabric with high voids.
When a solid electrolyte is supported by such a uniform nonwoven structure, it is possible to suppress unevenness of the solid electrolyte, uneven thickness, and poor contact at the electrode interface.
Uniformity of structure is important for a solid electrolyte-supporting sheet because unevenness of the solid electrolyte and poor contact at the electrode interface can cause shortened battery life and increased resistance.

[Binder fiber (A)]
The binder fiber (A) is a short fiber having an average fiber diameter of 1 to 9 μm and an aspect ratio of 200 to 1,500. The binder fiber (A) is a heat-fusible fiber, and for example, a core-sheath type composite fiber or an undrawn fiber can be used.

The average fiber diameter of the binder fiber (A) is 1 to 9 μm, preferably 3 to 9 μm. If the average fiber diameter of the binder fibers is less than 1 μm, the nonwoven fabric may lack rigidity and strength, and if it exceeds 9 μm, it may be difficult to form a thin film or the nonwoven fabric may be prone to uneven thickness.

The binder fiber (A) has an aspect ratio of 200 to 1,500, preferably 300 to 1,000. If it is less than 200, it may be difficult to form a fiber network of the nonwoven fabric, resulting in poor paper-making properties, and if it exceeds 1,500, there is a risk that the fibers may become entangled or aggregate.

[Core-sheath type composite fiber]
As a core-sheath type composite fiber, a binder component polymer (for example, amorphous copolymer polyester) that is fused at a temperature of 80 to 170°C and exhibits an adhesive effect is arranged in the sheath part, and the melting point is lower than that of these polymers. A core-sheath type composite fiber in which another polymer (for example, polyester such as polyethylene terephthalate, polytrimethylene terephthalate, or polybutylene terephthalate) having a temperature of 20° C. or higher is arranged in the core is preferred.

The core-sheath type conjugate fiber can be one in which the binder component forms all or part of the surface of a single fiber, and may be an eccentric core-sheath type conjugate fiber or a side-by-side type conjugate fiber.

[Undrawn fiber]
As the undrawn fibers, undrawn fibers of an organic polymer are used, preferably undrawn polyester fibers and/or undrawn polyphenylene sulfide fibers. It is preferable that the undrawn fiber has a birefringence Δn of 0.05 or less.
These undrawn fibers are undrawn fibers spun at a spinning speed of, for example, 800 to 1200 m/min, preferably 900 to 1150 m/min.

Examples of the polyester of the undrawn polyester fiber include polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. From the viewpoint of productivity and water dispersibility, polyethylene terephthalate and polytrimethylene terephthalate are preferably used.

A polymer having phenylene sulfide as a repeating unit is used as the polyphenylene sulfide of the undrawn polyphenylene sulfide fiber. Examples of the phenylene sulfide include p-phenylene sulfide, m-phenylene sulfide, o-phenylene sulfide, phenylene sulfide sulfone, phenylene sulfide ketone, phenylene sulfide ether, diphenylene sulfide, substituent-containing phenylene sulfide, and branched structure-containing phenylene sulfide. Preferred is p-phenylene sulfide.

In this case, p-phenylene sulfide preferably occupies 70 mol% or more, more preferably 90 mol% or more, particularly preferably 100 mol% of the repeating units. That is, poly(p-phenylene sulfide) is most preferred.

[Non-binder fiber (B)]
The non-binder fibers (B) are short fibers with an average fiber diameter of 0.1 to 9 μm and an aspect ratio of 200 to 1,500. If the average fiber diameter of the non-binder fibers (B) is less than 0.1 μm, not only will it be difficult to disperse them, but they may also pass through the mesh in the papermaking process, making it difficult to form a nonwoven fabric. On the other hand, if it exceeds 9 μm, the nonwoven fabric may become non-uniform, and when making a lightweight nonwoven fabric, the fiber network may become weak due to the small number of constituent fibers, making it difficult to form a sheet. If the aspect ratio of the non-binder fibers (B) is less than 200, it may be difficult to form a fiber network of the nonwoven fabric, resulting in poor paper-making properties, and if it exceeds 1,500, there is a risk that entanglement or aggregation of fibers may occur.

Examples of non-binder fibers (B) include polyester fibers, polyphenylene sulfide fibers, polyamide fibers, and polyolefin fibers. Polyester fibers have a melting point of, for example, 260 to 270°C, and are excellent in heat resistance, solvent resistance, and hydrolyzability, and are highly reliable as separators and separator base materials.

Examples of polyesters forming polyester fibers include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), and polyethylene naphthalate. The polyester may be a copolymerized polyester.

The non-binder fiber (B) preferably consists of a non-binder fiber (B1) and/or a non-binder fiber (B2), and the non-binder fiber (B1) has an average fiber diameter of 2 to 9 μm and an aspect ratio of 200 to 1500. The short fiber and non-binder fiber (B2) is a single fiber with an average fiber diameter of 0.1 to 1 μm and an aspect ratio of 200 to 1500.

The non-binder fiber (B2) preferably accounts for 5 to 60% by weight of the wet-laid nonwoven fabric from the viewpoint of paper-making properties, strength and dimensional stability of the nonwoven fabric.
Examples of the non-binder fibers (B1) and (B2) include polyester fibers, polyphenylene sulfide fibers, polyamide fibers, and polyolefin fibers, among which polyester fibers and/or polyphenylsulfone fibers are preferred.

Both the non-binder fiber (B1) and the non-binder fiber (B2) can be obtained by cutting commercially available continuous fibers into predetermined fiber lengths with a guillotine cutter.
In the solid electrolyte supporting sheet of the present invention, the non-binder fibers (B) may be composed of non-binder fibers (B1) and non-binder fibers (B2).

[Wet-processed nonwoven fabric]
The wet nonwoven fabric of the solid electrolyte supporting sheet of the present invention has a basis weight of 1 to 10 g/m ² , a thickness of 5 to 30 μm, and a porosity of 60% or more. By setting the basis weight, thickness, and porosity of the wet-laid nonwoven fabric within these ranges, it is possible to obtain a nonwoven fabric with low resistance by having a structure that is lightweight and thin but has high porosity.

[Weight]
The wet nonwoven fabric of the solid electrolyte supporting sheet has a basis weight of 1 to 10 g/m ² . If the basis weight is less than 1 g/m ² , the fiber network may be weak and sheet formation may be difficult. On the other hand, if it exceeds 10 g/m ² , there is a risk that the resistance will increase and there are disadvantages in making the battery more compact.

[Thickness]
The thickness of the wet-laid nonwoven fabric is 5 to 30 μm. If the thickness is less than 5 μm, the strength of the nonwoven fabric may be insufficient and it may be difficult to form a sheet, and if it exceeds 30 μm, the resistance may increase.

[Porosity]
The porosity of the wet nonwoven fabric of the solid electrolyte supporting sheet is 60% or more. If it is less than 60%, the amount of solid electrolyte retained will decrease because the nonwoven fabric has few voids, which may lead to a shortened lifespan and increased resistance.

[Gurley air permeability]
The Gurley air permeability of the wet nonwoven fabric of the solid electrolyte supporting sheet is preferably 0.5 seconds/100 cc or less. If the Gurley air permeability exceeds 0.5 sec/100 cc, the density is too high for a solid electrolyte supporting sheet, which may increase the resistance, which is not preferable.

[Tensile strength]
The tensile strength in the MD direction of the wet nonwoven fabric of the solid electrolyte supporting sheet is preferably 0.3 N/15 mm or more. Tensile strength indicates the toughness of the solid electrolyte-supporting sheet, and a certain level of toughness is required to prevent the solid electrolyte-supporting sheet from tearing or splitting during the nonwoven fabric manufacturing process or the composite process with solid electrolytes. Yes, the larger the value, the better. If the tensile strength is less than 0.3 N/15 mm, the nonwoven fabric is likely to tear, which is not preferable.

[Heat shrinkage rate]
The heat shrinkage rate of the wet nonwoven fabric of the solid electrolyte supporting sheet after being left at 180° C. for 1 hour is preferably 10% or less in both the MD direction and the CD direction. Thermal shrinkage rate is determined from the viewpoint of heat resistance, so that when the battery becomes high temperature, the solid electrolyte supporting sheet does not undergo shape changes such as tearing of the solid electrolyte layer due to shape changes due to contraction or melting of the solid electrolyte supporting sheet. It is necessary that the material itself has high thermal stability and heat resistance. If the thermal shrinkage rate exceeds 10%, it is not preferable because it tends to cause shape changes at high temperatures.

[Water retention rate]
The water retention rate of the wet nonwoven fabric of the solid electrolyte supporting sheet is preferably 300% by weight or more, as determined by a water retention test. If it is less than 300% by weight, it is not preferable because the liquid absorption property becomes poor in the compounding process with the electrolyte.
In the composite process of solid electrolyte and solid electrolyte support sheet, the solid electrolyte support sheet quickly absorbs the solid electrolyte slurry and has high water retention, which improves the efficiency of the process, suppresses the defect rate, and improves performance. (lower resistance and longer life).

In the water retention test, distilled water was used instead of the solid electrolyte slurry, and the solid electrolyte support sheet was immersed in distilled water for 1 minute, then taken out, water was allowed to drip for 1 minute, and the solid electrolyte support sheet was tested before and after the test. Calculate the water retention rate from the weight change. The higher the water retention rate, the greater the amount of distilled water retained inside the solid electrolyte supporting sheet, which is preferable because the water retention is excellent.
Since the solid electrolyte-supporting sheet of the present invention has the above-described structure, it is possible to obtain a solid electrolyte-supporting sheet that has excellent heat resistance, is lightweight and thin, and has high voids and uniformity.

〔Production method〕
The wet-laid nonwoven fabric of the solid electrolyte-supporting sheet of the present invention can be produced by heat treatment after paper making using an ordinary Fourdrinier paper machine, short wire paper machine, circular wire paper machine, or multilayer paper making using a combination of these machines. can be manufactured.
The heat treatment can be performed by performing a heat treatment using a Yankee dryer or an air-through dryer after paper-making the wet nonwoven fabric. The temperature of the heat treatment is, for example, 80 to 200° C., and the time is, for example, 10 to 600 seconds.

After the heat treatment, a calendar treatment may be further performed using a metal/metal roller, a metal/paper roller, or a metal/elastic roller. When the wet-laid nonwoven fabric has a multilayer structure, it is preferable to obtain the wet-laid nonwoven fabric and then adhere a plurality of wet-laid nonwoven fabrics using a calendar machine or the like.
Note that when undrawn fibers are used as binder fibers, thermocompression bonding is required after heat treatment after papermaking in the production of wet-laid nonwoven fabrics. In this thermocompression bonding step, it is preferable to perform calendering and/or embossing treatment.

The present invention will be explained below with reference to Examples.

1. Raw Materials The following fibers were used in the Examples and Comparative Examples.
(1) Examples 1 and 2
・Non-binder fiber: Polyester fiber (average fiber diameter 3.1 μm, average fiber length 3.0 mm) “Tepils TA04PN SD 0.1 dtex 3 mm” manufactured by Teijin Frontier
・Binder fiber: Polyester binder fiber (average fiber diameter 4.3 μm, average fiber length 3.0 mm) “Tepils TK08PN SD 0.2 dtex 3 mm” manufactured by Teijin Frontier

(2) Example 3
・Non-binder fiber: Polyester fiber (average fiber diameter 7.5 μm, average fiber length 5.0 mm) “Tepils TA04N SD0.6 dtex 5 mm” manufactured by Teijin Frontier
・Binder fiber: Polyester binder fiber (average fiber diameter 4.3 μm, average fiber length 3.0 mm) “Tepils TK08PN SD 0.2 dtex 3 mm” manufactured by Teijin Frontier

(3) Example 4
・Non-binder fiber: Polyester fiber (average fiber diameter 700 nm, average fiber length 0.5 mm) "Nano Front" manufactured by Teijin Frontier
・Non-binder fiber: Polyester fiber (average fiber diameter 3.1 μm, average fiber length 3.0 mm) “Tepils TA04PN SD 0.1 dtex 3 mm” manufactured by Teijin Frontier
・Binder fiber: Polyester binder fiber (fiber diameter 4.3 μm, cut length 3.0 mm) “Tepils TK08PN SD 0.2 dtex 3 mm” manufactured by Teijin Frontier

(4) Example 5
・Non-binder fiber: Polyester fiber nanofiber (average fiber diameter 700 nm, average fiber length 0.5 mm) "Nano Front" manufactured by Teijin Frontier
・Binder fiber: Polyester binder fiber (average fiber diameter 4.3 μm, average fiber length 3.0 mm) “Tepils TK08PN SD 0.2 dtex 3 mm” manufactured by Teijin Frontier

2. Measurement and Evaluation The physical properties in the examples were measured and evaluated by the following methods.
(1) Fiber diameter and average fiber diameter Measurements were made by taking photographs of fiber cross sections at a magnification of 1,000 to 30,000 times using a transmission electron microscope TEM (with a length measurement function). The diameter of the circumscribed circle in the cross section of a single fiber was used as the fiber diameter. The average value of n number 5 was taken as the average fiber diameter.

(2) Fiber Length and Average Fiber Length The fiber length was measured using a scanning electron microscope (SEM) at a magnification of 10 to 500 times with the fibers lying on a substrate. At that time, the fiber length was measured using the length measurement function of the SEM. The average value of n number 5 was taken as the average fiber length.

(3) Aspect ratio Calculated from the average fiber diameter and average fiber length using the following formula. However, d is the average fiber diameter (μm), and l is the average fiber length (mm).
Aspect ratio = l/(d/1000)

(4) Fabric weight Measured based on JIS P8124 (method for measuring metric basis weight of paper).

(5) Thickness The thickness was measured based on JIS P8118 (method for measuring thickness and density of paper and paperboard). Measurement was performed using 5 samples at a measurement load of 75 g/cm ² and the average value was determined.

(6) Density Density was calculated from the basis weight and thickness of the nonwoven fabric using the following formula. However, W is the basis weight (g/m ² ), and L is the thickness (mm).
Density (g/cm ³ )=(W/10000)/(L/10)

(7) Porosity It was calculated from the density of the nonwoven fabric and the resin density of the constituent fibers using the following formula. D is the density (g/cm ³ ), and R is the resin density (g/cm ³ ). Here, R is the density of the polyester resin, and was calculated using R=1.36.
Porosity (%) = 100 - {(D/R) x 100}

(8) Gurley air permeability It was carried out based on JIS P8117 (air permeability test method for paper and paperboard). At this time, the air permeability of 16 nonwoven fabric samples was measured and multiplied by 1/16 to calculate the Gurley air permeability of each sample.

(9) Tensile strength Measured based on JIS P8113 (Tensile strength and test method of paper and paperboard). The MD tensile strength is the tensile strength in the MD direction.

(10) Heat shrinkage rate A nonwoven fabric sample of MD 100 mm x CD 100 mm was left standing in a dryer at 180° C. for 1 hour. The heat shrinkage rate was calculated from the length of the nonwoven fabric sample in the MD direction and the CD direction.

(11) Water retention rate The water retention rate of the nonwoven fabric was measured in the following manner based on JIS L1913 (general nonwoven fabric testing method). That is, the weight of a nonwoven fabric sample (100 mm x 100 mm) was measured, and the sample was immersed in distilled water for 1 minute. Thereafter, the nonwoven fabric sample was taken out, water was dripped on it for 1 minute, and then the weight was measured. The water retention rate was calculated from the weight change of the nonwoven fabric sample before and after the test using the following formula. m ₁ is the weight before the test (mg), and m ₂ is the weight after the test (mg).
Water retention rate (%) = {(m ₂ - m ₁ )/m ₁ }×100

(12) Paper-making properties The paper-making properties of each composition were evaluated when paper was made at the target weight. Those that were able to form a sheet were marked as "〇", and those that could not be formed as a sheet were marked as "x".

[Example 1]
50% by weight of polyester fibers (average fiber diameter 3.1 μm, average fiber length 3.0mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0mm) as binder fibers. %, a nonwoven fabric was produced by a wet papermaking method, dried at 120° C. in a Yankee dryer, and adjusted to a predetermined basis weight and thickness to obtain a solid electrolyte-supporting sheet as a wet nonwoven fabric. The evaluation results are shown in Tables 1 and 2.

The obtained solid electrolyte supporting sheet has a basis weight of 3.1 g/m ² and a thickness of 9.0 μm, and although it is a lightweight and thin film, it has a high porosity of 74.5%, and has a Gurley permeability. The temperature was small and the resistance was low. It also had excellent water retention, and uneven distribution of distilled water within the solid electrolyte supporting sheet was suppressed. Furthermore, since it was composed only of polyester fibers, the heat shrinkage rate at 180° C. was small, and it had excellent heat resistance.

[Example 2]
Wet-laid non-woven fabrics having different basis weights and thicknesses were produced in the same manner as in Example 1 to obtain solid electrolyte-supporting sheets which were wet-laid non-woven fabrics. The evaluation results are shown in Tables 1 and 2. As in Example 1, the sheet for supporting a solid electrolyte was a wet nonwoven fabric with excellent nonwoven fabric uniformity, low resistance, water retention, and heat resistance.

[Example 3]
50% by weight of polyester fibers (average fiber diameter 7.5 μm, average fiber length 5.0 mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0 mm) as binder fibers. A nonwoven fabric was prepared by a wet paper making method using % and dried at 120° C. in a Yankee dryer, and adjusted to a predetermined basis weight and thickness to obtain a solid electrolyte supporting sheet as a wet nonwoven fabric. The evaluation results are shown in Tables 1 and 2. By increasing the fiber diameter of the non-binder fibers, the fibers had high porosity, low resistance, and excellent water retention.

[Example 4]
10% by weight of polyester fiber (average fiber diameter 700 nm, average fiber length 0.5 mm) as a non-binder fiber, and 40 weight % polyester fiber (average fiber diameter 3.1 μm, average fiber length 3.0 mm) as another non-binder fiber. % and 50% by weight of polyester binder fibers (fiber diameter 4.3 μm, cut length 3.0 mm) as binder fibers, a nonwoven fabric was produced by a wet papermaking method, dried at 120 ° C. with a Yankee dryer, and then A solid electrolyte supporting sheet, which is a wet-laid nonwoven fabric, was obtained by adjusting the basis weight and thickness to . The evaluation results are shown in Tables 1 and 2.

By using non-binder fibers with small fiber diameters, the fiber network could be strengthened and the weight could be further reduced. It also had excellent water retention.

[Example 5]
50% by weight of polyester fiber nanofibers (average fiber diameter 700 nm, average fiber length 0.5 mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0 mm) as binder fibers. % by weight, a nonwoven fabric was produced by a wet papermaking method, dried at 120° C. in a Yankee dryer, and adjusted to a predetermined basis weight and thickness to obtain a solid electrolyte supporting sheet as a wet nonwoven fabric. The evaluation results are shown in Tables 1 and 2. By adding fibers with a small fiber diameter, the fiber network can be strengthened and the weight can be further reduced. In addition, it has excellent water retention due to the specific surface area effect of nanofibers.

[Comparative example 1]
50% by weight of polyester fibers (average fiber diameter 3.1 μm, average fiber length 3.0mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0mm) as binder fibers. %, a non-woven fabric is produced by a wet paper-making method, and after drying at 120°C in a Yankee dryer, the non-woven fabric is further calendered and adjusted to a predetermined area weight and thickness to produce a wet non-woven fabric for supporting solid electrolytes. Got a sheet. The evaluation results are shown in Tables 1 and 2. Since the porosity of the nonwoven fabric is low, water retention is low, and there is a risk that the solid electrolyte may be insufficiently filled or unevenly distributed, leading to increased resistance.

[Comparative example 2]
50% by weight of polyester fibers (average fiber diameter 700 nm, average fiber length 0.5 mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0 mm) as binder fibers. A non-woven fabric was produced by a wet paper-making method, dried in a Yankee dryer at 120°C, and further calender heat-treated to adjust to a predetermined area weight and thickness to obtain a solid electrolyte-supporting sheet as a wet non-woven fabric. . The evaluation results are shown in Tables 1 and 2.

Since the porosity of the nonwoven fabric is low, water retention is low, which may cause insufficient filling of the solid electrolyte, uneven distribution, and increased resistance. Furthermore, since the content of nanofibers is high and the porosity is low, the nonwoven fabric becomes dense and has a high Gurley air permeability. Therefore, the resistance of the sheet for supporting a solid electrolyte is high.

[Comparative example 3]
50% by weight of polyester fibers (average fiber diameter 12.6 μm, average fiber length 5.0 mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 3.0 mm) as binder fibers. %, a nonwoven fabric was produced by a wet papermaking method, dried at 120° C. in a Yankee dryer, and adjusted to a predetermined basis weight and thickness to obtain a solid electrolyte-supporting sheet as a wet nonwoven fabric. The evaluation results are shown in Tables 1 and 2. Since the diameter of the fibers constituting the nonwoven fabric is large, the thickness becomes thick, which may cause an increase in resistance.

[Comparative example 4]
An attempt was made to produce a nonwoven fabric with a basis weight of 5 g/m ² using the same method as in Comparative Example 3. A wet-laid nonwoven fabric could not be formed due to the weak fiber network.

[Comparative example 5]
50% by weight of polyester fibers (average fiber diameter 3.1 μm, average fiber length 0.4 mm) as non-binder fibers, and 50% by weight polyester binder fibers (average fiber diameter 4.3 μm, average fiber length 0.4 mm) as binder fibers. %, an attempt was made to produce a nonwoven fabric with a basis weight of 5 g/m ² by a wet papermaking method. However, it was not possible to form a wet-laid nonwoven fabric because the fiber network was weak.

The solid electrolyte supporting sheet of the present invention can be used as a member of a battery.

Claims (8)

A solid electrolyte supporting sheet which is a wet-laid nonwoven fabric made of binder fibers (A) and non-binder fibers (B), and the wet-laid nonwoven fabric has a basis weight of 1 to 10 g/m ² , a thickness of 5 to 30 μm, and a porosity of 60% or more. The binder fiber (A) has an average fiber diameter of 1 to 9 μm and an aspect ratio of 200 to 1500, and the non-binder fiber (B) has an average fiber diameter of 0.1 to 9 μm and an aspect ratio of 200 to 1500. A sheet for supporting a solid electrolyte, characterized by the following. The non-binder fiber (B) consists of a non-binder fiber (B1) and/or a non-binder fiber (B2), the non-binder fiber (B1) has an average fiber diameter of 2 to 9 μm and an aspect ratio of 200 to 1500, The solid electrolyte supporting sheet according to claim 1, wherein the non-binder fiber (B2) has an average fiber diameter of 0.1 to 1 μm and an aspect ratio of 200 to 1500. The sheet for supporting a solid electrolyte according to claim 2, wherein the non-binder fiber (B2) accounts for 5 to 60% by weight of the wet-laid nonwoven fabric. The sheet for supporting a solid electrolyte according to claim 2, wherein the non-binder fibers (B1) and the non-binder fibers (B2) are both polyester fibers and/or polyphenylsulfone fibers. The sheet for supporting a solid electrolyte according to claim 1, having a Gurley air permeability of 0.5 seconds/100 cc or less. The solid electrolyte supporting sheet according to claim 1, having a tensile strength in the MD direction of 0.3 N/15 mm or more. The sheet for supporting a solid electrolyte according to claim 1, having a heat shrinkage rate of 10% or less in both the MD direction and the CD direction after being left at 180° C. for 1 hour. The sheet for supporting a solid electrolyte according to claim 1, having a water retention rate of 300% by weight or more as determined by a water retention test.