JP2023026032A - Electrode sheet and manufacturing method thereof - Google Patents

Abstract

To provide an electrode which reduces a binder amount required for fixing cathode active material particles, hardly swells with an electrolyte, maintains a space sufficient for Li ion movements and is not deformed even at high temperatures, and a manufacturing method thereof.SOLUTION: The present invention relates to an electrode sheet including: aramid nanofibers of which the average fiber diameter is equal to or less than 100 nm; aramid pulp having a fibril structure; an electrode active material; a conductive assistant agent; and a soluble binder which is soluble in a non-aqueous polar solvent or an electrolytic solution. The electrode active material is held by the aramid nanofibers and the aramid pulp. The content of the aramid nanofibers is 0.05 to 0.9 wt.% with the electrode sheet defined as a reference, the aramid pulp is 0.05 to 0.9 wt.% with the electrode sheet defined as a reference, and the content of the soluble binder is 0.1 to 1.0 wt.% with the electrode sheet defined as a reference.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an electrode sheet and its manufacturing method, and more particularly to an electrode sheet suitable for a positive electrode for a non-aqueous Li-ion secondary battery and its manufacturing method.

Li-ion secondary batteries, which have high energy density and capacity, are expanding their applications to small portable terminals, personal computers, electric vehicles, and the like.
A positive electrode of a Li-ion secondary battery is produced by laminating a sheet of electrode active material such as Li metal oxide having high voltage and capacity to a conductive sheet such as aluminum foil.

In recent years, high-capacity positive electrode active materials have been developed, but since these cause deterioration in performance due to contamination with water, the solvent for forming the slurry for forming the powder sheet is a non-aqueous polar solvent (N-methyl 2 pyrrolidone, etc.) or an electrolyte solution (electrolyte) is used.
Polyvinylidene fluoride (PVdF) is widely used as a soluble binder that dissolves or swells in these solvents.

PVdF is usually dissolved in a non-polar solvent such as N-methyl-2-pyrrolidone (NMP), and is 2 to 3% by weight with respect to the electrode active material, which is a conductive additive carbon black (CB) or carbon nanotube (CNT) carbon material. are appropriately mixed and coated on the collector electrode foil to form a sheet.

Since PVdF is a polymer that is difficult to crystallize, it has a thermal deformation temperature (approximately 90°C) and a melting temperature (approximately 140-170°C). As a result, there is a possibility that the conductive network of LiB will be destroyed and cause a decrease in capacity. In addition, the temperature rises to 200° C. or higher due to abnormal heat generation such as a short circuit, making it difficult to maintain the shape of the electrode.

Although there are various shapes of positive electrode active materials, assuming that they are spheres with the same diameter, the porosity in the closest packing is about 27%, but in reality the porosity is 20 to 25 due to the particle size distribution. %It is estimated to be.

In addition, since the specific gravities of the positive electrode active material and PVdF are usually 4 to 5 g/cc and 1.75 g/cc, respectively, if 2% by weight of PVdF is used, even if it is assumed that the space occupation ratio does not swell, This corresponds to approximately 6%, which occupies 1/3 to 1/4 of the void space.
Furthermore, a large space is used when it swells with electrolyte.

Since charging and discharging are performed by moving Li ions in the electrolytic solution that fills the voids, inhibiting the movement of Li ions by the binder undesirably increases the diffusion resistance.
Moisture is generally a factor that lowers the activity of the positive electrode active material, and it is preferable to dry the electrode at a high temperature.

In order to solve such problems, the present inventors discovered that an electrode with excellent heat resistance can be produced by using an aromatic polyamide fibrid as a binder (see Patent Document 1). Adhesion of the conductive active material was insufficient.

JP 2007-158163 A

The present invention has been made to solve the above problems, and its purpose is to reduce the amount of heat-resistant fiber binder that is insoluble in a non-aqueous polar solvent or electrolyte solution necessary for fixing the positive electrode active material particles, and To provide an electrode which does not easily swell at high temperatures, maintains a sufficient space for Li ion migration, and does not deform even at high temperatures, and a method for manufacturing the same.

As a result of intensive studies, the present inventors have found that aramid nanofibers and aramid pulp having a fibril structure are used as a heat resistant fiber binder that is insoluble in a non-aqueous polar solvent or electrolyte solution. The present inventors have found that it is possible to reduce the amount of binder required to form an active material into a sheet, and that an electrode sheet with low resistance and little deterioration in performance due to repeated charging and discharging can be obtained.

That is, according to the present invention, the objects of the invention are achieved by the following 1 to 6.
1. An electrode containing an aramid nanofiber having an average fiber diameter of 100 nm or less, an aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a soluble binder soluble in a non-aqueous polar solvent or electrolyte solution a sheet,
The electrode active material is held by aramid nanofibers and aramid pulp, the content of aramid nanofibers is 0.05 to 0.9% by weight based on the electrode sheet, and the content of aramid pulp is 0.05% by weight based on the electrode sheet. 05 to 0.9% by weight, and a soluble binder content of 0.1 to 1.0% by weight based on the electrode sheet.
2. 2. The electrode sheet according to the preceding item 1, wherein the aramid nanofibers are made of para-type wholly aromatic polyamide.
3. 2. The electrode sheet according to the preceding item 1, wherein the aramid pulp comprises a para-type wholly aromatic polyamide.
4. 4. The electrode sheet according to any one of the preceding items 1 to 3, wherein the electrode active material contains a Li metal oxide.
5. 5. The electrode sheet according to any one of the preceding items 1 to 4, which is used for the positive electrode of a Li-ion secondary battery.
6. An aramid nanofiber having an average fiber diameter of 100 nm or less, an aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a soluble binder that can be dissolved in a non-aqueous polar solvent or an electrolyte solution, 6. The method for producing an electrode sheet according to any one of the preceding items 1 to 5, wherein the slurry is mixed with a polar solvent or electrolyte solution, coated on an electrode current collector, and pressed if necessary.

The electrode sheet composed of aramid nanofibers and aramid pulp of the present invention has excellent morphological stability even at high temperatures, and the heat-resistant fiber binder that is insoluble in the non-aqueous polar solvent or electrolyte solution that constitutes the electrode is swollen by the electrolyte solution. Since the surface coating of the electrode active material can be reduced with a small amount, the industrial effect achieved is exceptional.

It is an example which showed the structure observation image of the aramid nanofiber of this invention. It is an example which showed the structure observation image which expanded FIG. 1 for average fiber diameter calculation. It is explanatory drawing regarding the calculation method of an average fiber diameter. FIG. 4 is a schematic diagram of an electrode sheet using only aramid pulp as a binder. FIG. 4 is a schematic diagram of an electrode sheet using only aramid nanofibers as a binder. FIG. 2 is a schematic diagram of an electrode sheet using both aramid pulp and aramid nanofibers as a binder.

According to the present invention, an aramid nanofiber having an average fiber diameter of 100 nm or less, an aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a non-aqueous polar solvent or a soluble soluble in an electrolyte solution An electrode sheet containing a binder, wherein an electrode active material is held by aramid nanofibers and aramid pulp, and the content of aramid nanofibers is 0.05 to 0.9% by weight based on the electrode sheet. , the aramid pulp is 0.05 to 0.9% by weight based on the electrode sheet, and the content of the soluble binder is 0.1 to 1.0% by weight based on the electrode sheet. A sheet is provided.

Further, according to the production method of the present invention, an aramid nanofiber having an average fiber diameter of 100 nm or less, an aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a non-aqueous polar solvent or electrolyte solution A soluble binder that can be dissolved is mixed with a non-aqueous polar solvent or an electrolyte solution to form a slurry, which is coated on an electrode current collector and, if necessary, press-treated to stably form an electrode sheet. It is possible to manufacture

In addition, by containing 0.1 to 1.0% by weight of a soluble binder that can be dissolved in a non-aqueous polar solvent or an electrolytic solution, a conductive aid that is easy to fall off from the network structure formed by aramid nanofibers and aramid pulp. It is possible to obtain an electrode with excellent charge-discharge performance by suppressing the falling off of nanoparticles such as , suppressing deformation at high temperatures by greatly reducing the total binder amount and a strong network of heat-resistant nanofibers.

<Aramid (wholly aromatic polyamide)>
Aramid in the present invention is a wholly aromatic polyamide. As the wholly aromatic polyamide, para-type wholly aromatic polyamide (poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide etc.), and meta-type wholly aromatic polyamides (poly-m-phenylene isophthalamide, etc.), and para-type wholly aromatic polyamides are preferred because of their high elasticity and high strength. For example, fibers using para-type wholly aromatic polyamide include poly-p-phenylene terephthalamide fibers (commercially available products are "Twaron (registered trademark)" manufactured by Teijin Limited, "Kevlar (registered trademark)" manufactured by Toray DuPont Co., Ltd. )”, etc.), and coparaphenylene/3,4′-oxydiphenylene terephthalamide fibers (commercially available products such as “Technora (registered trademark)” manufactured by Teijin Limited), and meta-type wholly aromatic polyamides are used. Examples of the fibers include poly-m-phenylene isophthalamide fibers (commercially available products include "Teijin Conex (registered trademark)" manufactured by Teijin Limited and "Nomex (registered trademark)" manufactured by DuPont).

<Aramid nanofiber>
The aramid nanofibers in the present invention have an average fiber diameter of 100 nm or less, preferably 50 nm or less, more preferably 25 nm or less. The lower limit of the average fiber diameter is preferably 1 nm or more, preferably 3 nm or more. Moreover, it is preferable that the aramid nanofibers do not have a fiber diameter of 500 nm or more.

The aramid nanofiber in the present invention preferably has an aspect ratio represented by fiber length/fiber diameter of 10 or more and 1,000 or less, more preferably 10 or more and 500 or less, and still more preferably 10 or more and 100 or less. . If the aspect ratio is less than 10, it is difficult to develop an entangled structure of fibers and to form a fine mesh structure. Therefore, it may be difficult to develop expected characteristics.

The specific surface area of the aramid nanofibers in the present invention is preferably 50 m ² /g or more, more preferably 80 m ² /g or more. The upper limit of the specific surface area is preferably 200 m ² /g or less, more preferably 150 m ² /g or less. If the specific surface area is lower than the above range, a sufficient bonding area with the electrode active material cannot be ensured, and a small amount of the binder does not lead to the expression of good binder properties. On the other hand, if the specific surface area is higher than the above range, the viscosity of the coating liquid is increased, which is undesirable because the coating properties are deteriorated and it becomes difficult to maintain the dispersed state.

Moreover, the aramid nanofiber in the present invention is a wholly aromatic polyamide, preferably a para-type wholly aromatic polyamide. As the para-type wholly aromatic polyamide, poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-amide hydrazide, poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide and the like are preferable and oriented. Poly-p-phenylene terephthalamide fibers having crystallinity (forming domains of liquid crystal structure in the spinning solution) are preferred.

<Production of aramid nanofibers>
The aramid nanofibers used in the present invention are produced by, for example, using a para-type wholly aromatic polyamide fiber or a para-type wholly aromatic polyamide pulp as a raw material, soaking and swelling the fiber in a solvent with high affinity, Furthermore, it is preferable to add a strongly basic substance to break the hydrogen bond, and to produce it as a result. The para-type wholly aromatic polyamide that can be preferably used in the present invention is a polymer in which one or more divalent aromatic groups are linked by amide bonds, and the aromatic group has two or more Aromatic rings may be present and the aromatic rings may be attached directly or through oxygen or sulfur. Also, the hydrogen atom of the divalent aromatic group may be substituted with a halide, a lower alkyl group, or a phenyl group. As the solvent used for producing aramid nanofibers, aprotic polar solvents are preferred, and specific examples include dimethylsulfoxide, dimethylacetamide, N-methyl-2-pyrrolidone and the like. Potassium hydroxide, sodium hydroxide, barium hydroxide, calcium hydroxide, etc., are examples of strongly basic substances used for producing aramid nanofibers.

Specifically, the production of aramid nanofibers in the present invention is carried out by immersing para-type wholly aromatic polyamide (for example, poly-p-phenylene terephthalamide) fibers or pulp in dimethyl sulfoxide adjusted to alkalinity. be able to.

A para-type wholly aromatic polyamide (eg, poly-p-phenylene terephthalamide) is obtained by forming a domain of a liquid crystal structure in a spinning solution, discharging it from a capillary, and washing the spinning solvent with water. After the weak bonds between the liquid crystal domains constituting the fiber are cut by the above-mentioned method under alkaline conditions, the obtained fiber is liberated in a highly compatible solvent, so that the fiber can be cut with high elasticity and high strength. You can get the fiber that has been made. Then, the aramid nanofibers can be isolated by putting the resulting cut fibers into a poor solvent (water, alcohol, acetone, etc.) as a dispersion solvent.

In addition, a para-type whole aromatic polyamide (for example, poly-p-phenylene terephthalamide) fiber having a diameter of 10 to 20 μm is cut into several mm and subjected to a refiner treatment in which mutual shearing is performed in water. Aromatic polyamide (eg, poly-p-phenylene terephthalamide) pulp can be obtained. In such a refiner treatment, the fibers that are finer from the fiber surface due to the shear fracture at the liquid crystal interface are not completely separated and are in a branched state, and the diameter of the finer fibers is 100 to 1000 nm. The diameter is several μm. Refined pulp can also be converted into aramid nanofibers by the above treatment.

As another method for refining the aramid material, instead of the chemical treatment as described above, a method of applying a mechanical shearing force can be considered, but this method partially obtains a fibril structure with a nano-order fiber diameter Stay as long as you can. Therefore, since a non-fibrillated micro-order structure is also included, a homogeneous entangled structure on the nano-order cannot be obtained, and expected physical properties are not exhibited. In the present invention, it is preferable to form an entangled structure with uniformly nanoized fibers instead of partial nanoization.

<Aramid pulp>
The aramid pulp in the present invention has a fibril structure (sometimes called fibrids). Aramid pulp having a fibril structure can be obtained, for example, by a known method described in JP-T-2014-501859. Specifically, for example, a method such as cutting poly-p-phenylene terephthalamide fibers into several millimeters, dispersing them in water, and rubbing them against each other using a refiner to form fibrils may be used. Alternatively, it is also possible to use a structure obtained by spraying and solidifying a para-type aromatic polyamide solution in a poor solvent such as water.

The fibril structure of the aramid pulp in the present invention preferably partially has a fiber diameter exceeding 100 nm, more preferably 300 nm or more. As schematically shown in FIG. 4, the fibril structure is composed of a trunk 2 and branch portions (fibril portions) 3, and either the trunk portion 2 or branch portions 3 have a fiber diameter exceeding the above range. It's fine if you have it. Also, the average fiber length is preferably 1000 μm or less. The lower limit of the average fiber length is preferably 100 μm or more, preferably 500 μm or more.

The specific surface area of the aramid pulp in the present invention is preferably 10 m ² /g or more and 40 m ² /g or less, more preferably 20 m ² /g or more and 30 m ² /g or less.
Thus, by using aramid pulp having a structure larger than that of aramid nanofibers, the stress transmission distance in the network structure formed by the heat-resistant fiber binder insoluble in non-aqueous polar solvents or electrolyte solutions is increased. becomes possible.

<Fibrous binder>
In the present invention, it is important to use aramid nanofibers and aramid pulp together as a fibrous binder.
When only aramid pulp is used as the fibrous binder, it is difficult to secure a sufficient specific surface area necessary for gripping the electrode active material 1, as schematically shown in FIG. In addition, the branched structure of the pulp entraps the solvent in a coating liquid in which aramid pulp is dispersed, resulting in low fluidity and difficulty in uniform coating.

When only aramid nanofibers are used as the fibrous binder, homogeneous coatability and high specific surface area are ensured, as schematically shown in FIG. On the other hand, it is difficult to hold the electrode active material 1 whose particle size is on the order of several tens of micrometers, and as a result, it is difficult to prevent the electrode active material from coming off. It is presumed that this is because the structural size of the aramid nanofibers 4 is smaller than that of the electrode active material, making it difficult to form a long-distance network connecting the electrode active materials. In addition, the coating liquid in which only the aramid nanofibers 4 are dispersed has high liquid fluidity and is excellent in uniform coating properties. Thick coating coatability is lowered.

Based on the above, by using aramid pulp and aramid nanofibers together as a fibrous binder, as schematically shown in FIG. And the branch 3 is expected to exhibit binder performance due to the high specific surface area derived from the aramid nanofibers 4 . In addition, the combined use of aramid pulp and aramid nanofiber is expected to achieve both uniform coatability and thick coatability.

<Electrode active material>
The electrode active material in the present invention is a substance capable of releasing and filling ions such as Li by charging and discharging, and is preferably a Li metal oxide. Specifically, cobalt lithium oxide, manganese Lithium oxide, NMC (nickel-manganese-cobalt) Li oxide, and the like.

<Conductive auxiliary agent>
The conductive aid in the present invention is a conductive substance placed on the surface of the electrode active material and between the electrode active material particles, and is preferably a carbon material in terms of electrochemical stability. Specifically, carbon black (acetylene black, ketjen black, etc.) is preferable, and carbon nanotubes (CNT) and conductive polymers (polyacene, etc.) may be used in combination.

The soluble binder in the present invention is a substance that is soluble in a non-aqueous polar solvent and is not decomposed by the potential difference generated by the electrode active material, and is preferably a heat-resistant polymer that changes little even at high temperatures. Specifically, polyvinylidene fluoride (PVdF ), polyimide, meta-aramid, etc. Among them, polyvinylidene fluoride (PVdF) is particularly preferable.

<Electrode sheet and its manufacture>
The electrode sheet in the present invention comprises the above-described electrode active material, conductive aid, aramid nanofiber, aramid pulp, and soluble binder, and the electrode active material and conductive aid consist of aramid nanofiber, aramid pulp, and soluble binder. and the content of aramid nanofibers is 0.05 to 0.9% by weight, preferably 0.06 to 0.5% by weight, more preferably 0.07, based on the electrode sheet. 0.3% by weight, more preferably 0.08 to 0.2% by weight. Also, the content of aramid pulp is 0.05 to 0.9% by weight, preferably 0.1 to 0.7% by weight, more preferably 0.2 to 0.5% by weight, based on the electrode sheet. %. Further, the content of the soluble binder is 0.1 to 1.0% by weight, preferably 0.2 to 0.9% by weight, more preferably 0.3 to 0.8% by weight, based on the electrode sheet. % by weight.

Aramid nanofibers can generate hydrogen bonds with adjacent nanofibers through amide bonds, which are polymer structures, to form a sheet of the electrode active material and the conductive aid.

If the content of aramid nanofibers and aramid pulp is less than 0.05% by weight, it cannot be formed into a sheet, which is not preferable. On the other hand, if it exceeds 0.9% by weight, the nanofibers and the pulp tend to be unevenly distributed, which is not preferable.

Furthermore, in order to prevent the electrode active material from expanding and contracting due to the movement of Li ions during charging and discharging, and as a result, rubbing between particles occurs, the conductive auxiliary agent may fall off. preferably.

The electrode sheet described above can be produced by the following method. That is, the electrode sheet of the present invention has a weight ratio of aramid nanofiber, aramid pulp and soluble binder of 0.05 to 0.9:0.05 to 0.9:0.1 to 1.0. It can be obtained by adding an electrode active material to a conductive auxiliary agent of 4% by weight or less on a basis, forming a slurry with a non-aqueous polar solvent, coating it on a current collector sheet or film, and drying it.

The sheet obtained by the above method is press-treated using a heated calender roll or the like to reduce voids and increase the density, increase the density of the electrode active material per volume, and increase the secondary battery capacity. Needless to say, it is required that the electrode sheet should not be destroyed by heat and pressure.

More specifically, for example, a para-type wholly aromatic polyamide fiber or a para-type wholly aromatic polyamide pulp is added with a strongly basic substance in an aprotic polar solvent to form nanofibers, and the average fiber diameter is Aramid nanofibers of 100 nm or less, aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a soluble binder that can be dissolved in a non-aqueous polar solvent or electrolyte solution, a non-aqueous polar solvent or electrolyte An electrode sheet can be obtained by mixing the slurry with the solution to form a slurry, coating the electrode current collector with the slurry, and subjecting it to press treatment as necessary.

By this operation, a sheet having a predetermined thickness with no change in active thickness is obtained, and a secondary battery (Li-ion secondary battery) is produced by laminating the sheet with a separator and a negative electrode sheet and injecting an electrolytic solution.
The electrode sheet preferably has an electrical conductivity of 30×10 ⁻³ S/cm or more, more preferably 33×10 ⁻³ S/cm or more, and still more preferably 35×10 ⁻³ S/cm or more. cm or more. Also, the electrolytic solution permeation speed is preferably 230 to 400 sec, more preferably 250 to 400 sec, and still more preferably 300 to 400 sec. Also, both the single cell performances at 25° C. and 70° C. are preferably 95% or more, more preferably 96% or more.

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the scope of the present invention is not limited to the following Examples and Comparative Examples. In addition, each characteristic value in the examples was measured by the following method.

<Average fiber diameter>
The structure of the sample was observed using a scanning electron microscope (manufactured by JEOL Ltd., product board: JSM-6330F). From the image observed at a magnification setting of 50,000 times, select an image area of 1,800 nm to 2,000 nm in width and 1,200 nm to 1,500 nm in length, and divide the image area into 4 vertically and 4 horizontally. A total of 16 grid areas A1-D4 obtained by division are defined, one sample present in each grid area is selected, and the average value of the fiber diameter of the selected sample measured on the image is the average fiber diameter. (See Figures 2 and 3).

<Specific surface area measurement>
The specific surface area of the target sample was measured using an automatic flow-type specific surface area measuring device (Flowsorb manufactured by Shimadzu Corporation). Helium having a known adsorption occupation area was adsorbed on the sample surface at liquid nitrogen temperature, and the specific surface area of the sample was determined from the amount of helium gas adsorbed.

(Coating liquid characteristics)
<Homogeneous Coatability>
The state of the coating liquid (thickness of the coating liquid immediately after coating) immediately after the prepared coating liquid was applied by die coating was visually observed to evaluate whether uniform coating was possible without unevenness.
○: Uniform coating is possible △: Partial unevenness exists, but coating is possible ×: Coating unevenness exists over the entire surface, making it difficult to apply with a die coat

<Thick coatability>
After applying the coating liquid to the predetermined coating area, leave it on a horizontal surface for 10 minutes under normal temperature and pressure environment, and die-coat the prepared coating liquid on a commercially available aluminum foil (clearance: 100 μm). A change over time (area change (area reduction rate)) of the coating liquid applied to the coating area was observed. The evaluation criteria were as follows.
○: Area change (area reduction rate) of coating area is less than 5% △: Area change (area reduction rate) of coating area is 5% or more and less than 20% ×: Area change (area reduction rate) of coating area is 20% or more

(Electrode coatability)
<Deformation during drying>
After applying the coating liquid to the specified coating area, dry it for 20 minutes in a hot plate (100 ° C) and normal pressure environment on a horizontal place, and die-coat the prepared coating liquid on a commercially available aluminum foil (clearance : 100 μm), and the coating liquid applied to the coating area was observed. The evaluation criteria were as follows.
○: Area change of coating area is less than 5% △: Area change of coating area is 5% or more and less than 10% ×: Area change of coating area is 10% or more

<Shaft winding test>
As an index of the workability in the process of rotating and winding the electrodes of cylindrical and rectangular batteries, an electrode sheet (width 10 mm, length 50 mm) was wound around a SUS wire of 4 mmφ, and the presence or absence of cracks and peeling was evaluated.
○: No cracks and peeling △: Cracks and peeling occur partially ×: Cracks and peeling occur entirely

<Powder drop>
The surface of the prepared electrode sheet was gently rubbed with a wiping cloth (Kimwipe), and the stain was judged.
○: No stain removal △: Slightly stained ×: Stained

[Example 1]
<Creation of aramid nanofiber>
Aramid pulp: 10 g (10 g of Twaron 1000 fiber from Teijin Aramid Co., Ltd. cut to 6 mm was boiled and washed in 1000 g of boiling water for 30 minutes, cooled, washed with water and dried).
・ Tokyo Chemical Industry Co., Ltd. dimethyl sulfoxide (DMSO) > 99% 80 g,
・Tokyo Ohka Kogyo Co., Ltd. Potassium hydroxide (KOH) 10g
The above three types were put into a planetary mixer and stirred at 70° C. for 2 hours. After stirring, the aramid pulp lost its shape and gave a translucent red, highly viscous solution.

The resulting translucent red solution containing nanofibers was diluted with 3 times the volume of DMSO and gradually poured into 20 liters of water with stirring to precipitate nanofibers of poly-p-phenylene terephthalamide. At this time, the solution was a reddish-yellow slurry, into which a necessary amount of sulfuric acid was added for KOH neutralization, and poly-p-phenylene terephthalamide nanofibers were collected by filtration.

Subsequently, washing with distilled water or ion-exchanged water and stretching and dehydration were carried out 3 to 5 times to remove the solvent and salt. Distilled water was added to the resulting aqueous solids containing poly-p-phenylene terephthalamide nanofibers so that the solid content concentration was 1%, and a stone mill type pulverizer (Super Mascolloider) manufactured by Masuko Sangyo Co., Ltd. was used to obtain a poly-p-phenylene terephthalamide nanofiber-dispersed aqueous solution. The resulting poly-p-phenylene terephthalamide nanofiber dispersion was diluted with isopropyl alcohol, added dropwise to a preparation, dried, and confirmed to have an average fiber diameter of 20 nm (see FIGS. 1 and 2).

0.25 parts by mass of the above aramid nanofiber and fine aramid pulp (Twaron (registered trademark): 1094 pulp manufactured by Teijin Limited) were treated with a high-pressure homogenizer. A positive electrode active material (Ni ^: Mn:Co=1: 1:1) 95 parts by mass of LiO ₂ and 4 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) were mixed so that the solid content concentration was 70%, and the mixture was mixed at 2000 rpm using a thin-film swirling high-speed mixer (Filmix). After dispersing for 5 minutes, an electrode slurry was prepared.

A film was formed on a commercially available aluminum foil using a die coat, and dried on a hot plate (100° C.) for 20 minutes.
The dried electrode sheet was press-treated with a metal roll calender (treatment temperature: 60° C., treatment line pressure: 2 kN/cm) to obtain a coated electrode sheet.
The obtained electrode sheet was punched into a predetermined size of 50 mm×50 mm and dried at 170° C. for 10 hours to obtain an evaluation electrode. The obtained evaluation electrode sheet was evaluated according to the evaluation method described above.

[Example 2]
0.25 parts by mass of aramid nanofiber, aramid spray solidified body (a product obtained by spraying and solidifying an aramid polymer solution in a poor solvent. Specific surface area: 26 m ² /g), 0.5 parts by mass of PVdF, 4 parts by mass of acetylene black , and an electrode sheet was prepared and evaluated in the same manner as in Example 1, except that the positive electrode active material was changed to 95 parts by mass.

[Comparative Example 1]
An electrode sheet was prepared and evaluated in the same manner as in Example 1 except that PVdF was changed to 1.0 parts by mass, 4 parts by mass of acetylene black, and 95 parts by mass of the positive electrode active material.

[Comparative Example 2]
An electrode sheet was prepared and evaluated in the same manner as in Example 1 except that 0.5 parts by mass of aramid nanofiber, 0.5 parts by mass of PVdF, 4 parts by mass of acetylene black, and 95 parts by mass of the positive electrode active material were used. .

[Comparative Example 3]
An electrode sheet was prepared and evaluated in the same manner as in Example 1 except that 0.5 parts by mass of fine aramid pulp, 0.5 parts by mass of PVdF, 4 parts by mass of acetylene black, and 95 parts by mass of the positive electrode active material were used. rice field.

[Comparative Example 4]
An electrode sheet was prepared and evaluated in the same manner as in Example 1 except that 0.5 parts by mass of the aramid spray solidified body, 0.5 parts by mass of PVdF, 4 parts by mass of acetylene black, and 95 parts by mass of the positive electrode active material were used. rice field.

The electrode sheet of the present invention is an electrode sheet suitable for positive electrodes for non-aqueous Li-ion secondary batteries.

1 electrode active material 2 aramid pulp (trunk portion)
3 Aramid pulp (fibril part)
4 Aramid nanofiber

Claims (6)

An electrode containing an aramid nanofiber having an average fiber diameter of 100 nm or less, an aramid pulp having a fibril structure, an electrode active material, a conductive aid, and a soluble binder soluble in a non-aqueous polar solvent or electrolyte solution a sheet,
The electrode active material is held by aramid nanofibers and aramid pulp, the content of aramid nanofibers is 0.05 to 0.9% by weight based on the electrode sheet, and the content of aramid pulp is 0.05% by weight based on the electrode sheet. 05 to 0.9% by weight, and a soluble binder content of 0.1 to 1.0% by weight based on the electrode sheet. 2. The electrode sheet according to claim 1, wherein said aramid nanofibers are made of para-type wholly aromatic polyamide. 2. The electrode sheet according to claim 1, wherein said aramid pulp comprises a para-type wholly aromatic polyamide. The electrode sheet according to any one of claims 1 to 3, wherein the electrode active material contains Li metal oxide. The electrode sheet according to any one of claims 1 to 4, which is an electrode sheet used for a positive electrode of a Li-ion secondary battery. Aramid nanofibers with an average fiber diameter of 100 nm or less, aramid pulp having a fibril structure, electrode active materials, conductive aids, non-aqueous polar solvents or soluble binders soluble in electrolyte solutions, non-aqueous polar solvents or electrolyte solutions 6. The method for producing an electrode sheet according to any one of claims 1 to 5, wherein a slurry is obtained by mixing the slurry, coating the slurry on an electrode current collector, and pressing if necessary.

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