JP2020126733A - Electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

To provide an electrode for a lithium ion secondary battery, capable of ensuring high charge/discharge capacity while ensuring insulation and also capable of charging/discharging at high speed.SOLUTION: An electrode 10 for a lithium ion secondary battery includes an electrode active material layer 11 and an insulation layer 12 provided on a surface of the electrode active material layer 11. The insulation layer 12 contains inorganic particles and a binder, and the inorganic particles include first inorganic particles having a relative permittivity of 80 or more and second inorganic particles having a relative permittivity of less than 80.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lithium ion secondary battery electrode having an insulating layer, and a lithium ion secondary battery.

BACKGROUND OF THE INVENTION Lithium ion secondary batteries are used as large-sized stationary power sources for power storage, power sources for electric vehicles, and the like, and in recent years, research into making batteries smaller and thinner has progressed. A lithium ion secondary battery is generally provided with both electrodes in which an electrode active material layer is formed on the surface of a metal foil and a separator arranged between both electrodes. The separator plays a role of preventing a short circuit between both electrodes and holding an electrolytic solution.

Conventionally, a lithium ion secondary battery, for example, to have a good short-circuit suppressing function, even when the separator is contracted, also, in order to ensure the insulation between the electrodes instead of the separator, the electrode active material layer It is considered that a porous insulating layer is provided on the surface. For example, in Patent Document 1, the insulating layer is a coat layer in which inorganic particles are connected and fixed by a binder polymer, and inorganic particles having a dielectric constant of 10 or more are used.

Japanese Patent Publication No. 2007-520867

However, it is difficult for a lithium-ion secondary battery having a conventional insulating layer to improve the charge/discharge capacity, especially at a high rate of about 5 C, while ensuring insulation, and it is difficult to perform high-speed charge/discharge. Is.

Therefore, the present invention provides an electrode for a lithium-ion secondary battery capable of ensuring high charge/discharge capacity and high-speed charge/discharge while ensuring insulation, and a lithium-ion secondary battery including the electrode. This is an issue.

As a result of earnest studies, the inventors of the present invention have solved the above problems by using first inorganic particles having a high dielectric constant and second inorganic particles having a low dielectric constant as the inorganic particles used in the insulating layer. The inventors have found that they can be solved and completed the following invention. The gist of the present invention is the following [1] to [13].
[1] An electrode active material layer, and an insulating layer provided on the surface of the electrode active material layer,
The insulating layer contains inorganic particles and a binder,
An electrode for a lithium ion secondary battery, wherein the inorganic particles include first inorganic particles having a relative dielectric constant of 80 or more and second inorganic particles having a relative dielectric constant of less than 80.
[2] The electrode for a lithium ion secondary battery according to the above [1], wherein the electrode active material layer is a positive electrode active material layer.
[3] The electrode for a lithium ion secondary battery according to the above [1] or [2], wherein the insulating layer has a thickness of 15 to 50 μm.
[4] The above-mentioned [1] to [3], wherein the first inorganic particles are at least one selected from the group consisting of barium titanate particles, strontium titanate particles, bismuth tantalate particles, and bismuth titanate particles. ] The electrode for lithium ion secondary batteries of any one of these.
[5] The electrode for a lithium ion secondary battery according to the above [4], wherein the first inorganic particles are barium titanate particles.
[6] The electrode for a lithium ion secondary battery according to any one of the above [1] to [5], wherein the first inorganic particles have a relative dielectric constant of 900 or more.
[7] The electrode for a lithium ion secondary battery according to any one of the above [1] to [6], wherein the first inorganic particles have an average particle size of 50 to 500 nm.
[8] The electrode for a lithium-ion secondary battery according to any one of the above [1] to [7], wherein the second inorganic particles are at least one selected from alumina and boehmite.
[9] The lithium ion secondary battery electrode according to any one of the above [1] to [8], wherein the second inorganic particles have an average particle diameter of 100 to 1500 nm.
[10] The electrode for a lithium ion secondary battery according to any one of the above [1] to [9], wherein the binder is polyvinylidene fluoride (PVdF).
[11] The electrode for a lithium ion secondary battery according to any one of the above [1] to [10], wherein the insulating layer has a porous structure and the porosity is 50 to 80%.
[12] A lithium ion secondary battery including the electrode for a lithium ion secondary battery according to any one of [1] to [11] above.
[13] The lithium ion secondary battery according to the above [12], which comprises a positive electrode and a negative electrode, and the positive electrode is the electrode for the lithium ion secondary battery.

According to the present invention, it is possible to provide an electrode for a lithium ion secondary battery, which is capable of ensuring high charge/discharge capacity while ensuring insulation properties and performing high-speed charge/discharge.

It is a schematic sectional drawing which shows one Embodiment of the electrode for lithium ion secondary batteries of this invention.

<Lithium-ion secondary battery electrode>
Hereinafter, the lithium-ion secondary battery electrode of the present invention will be described in detail.
As shown in FIG. 1, the lithium-ion secondary battery electrode 10 includes an electrode active material layer 11 and an insulating layer 12 provided on the surface of the electrode active material layer 11. In addition, in the lithium-ion secondary battery electrode 10, the electrode active material layer 11 is usually laminated on the electrode current collector 13.
The electrode active material layer 11 may be laminated on both surfaces of the electrode current collector 13, and in that case, the insulating layer 12 may be provided on the surface of each electrode active material layer 11. By providing the insulating layers 12 on both surfaces of the lithium-ion secondary battery electrode 10 in this manner, even when a plurality of negative electrodes and positive electrodes are laminated to form a multilayer structure, a short circuit between each positive electrode and each negative electrode is effectively prevented. it can.
In the present invention, the lithium ion secondary battery electrode 10 may be either a negative electrode or a positive electrode, but is preferably a positive electrode.

[Insulation layer]
The insulating layer 12 contains inorganic particles and a binder (hereinafter, also referred to as “binder for insulating layer”). The insulating layer 12 is a layer formed by binding inorganic particles with an insulating layer binder, and has a porous structure.

(Inorganic particles)
The inorganic particles in the insulating layer 12 are insulating particles, and include first inorganic particles having a relative dielectric constant of 80 or more and second inorganic particles having a relative dielectric constant of less than 80. In the present invention, as described above, by using the first inorganic particles having a high relative dielectric constant and the second inorganic particles having a low relative dielectric constant in combination, the charge/discharge capacity, particularly the charge/discharge capacity at a high rate is increased. Therefore, high-speed charging/discharging becomes possible. Although the principle is not clear, the polarization assist effect of the first inorganic particles having a high relative permittivity increases the charge/discharge capacity by the insulating layer containing the first and second inorganic particles, enabling high-speed charge/discharge. It is estimated that

The first inorganic particles are not particularly limited as long as they have a relative dielectric constant of 80 or more, and examples thereof include inorganic particles having a perovskite structure. Inorganic particles having a perovskite structure are likely to be polarized and have a high relative dielectric constant. Inorganic particles having a perovskite structure are typically complex oxides.
The relative permittivity of the first inorganic particles is preferably 200 or more, more preferably 500 or more, further preferably 900 or more, and most preferably 1000 or more, from the viewpoint of enabling high-speed charge/discharge. The relative dielectric constant of the first inorganic particles is not particularly limited, but is, for example, 10000 or less, preferably 5000 or less, and more preferably 3000 or less.
The relative dielectric constant of the first inorganic particles can be adjusted by appropriately selecting the material forming the inorganic particles, but can also be adjusted by the particle size and the like.
The relative dielectric constant of the inorganic particles can be measured at the measurement temperature (23° C.), for example, by the coaxial probe method.

Specific examples of the first inorganic particles include barium titanate particles, strontium titanate particles, bismuth tantalate particles, and bismuth titanate particles. The first inorganic particles may be used alone or in combination of two or more. Among the above, the first inorganic particles are preferably barium titanate particles from the viewpoint of improving charge/discharge characteristics and insulating properties.

The average particle size of the first inorganic particles is preferably 50 to 500 nm. By setting the average particles within these ranges, it becomes easy to adjust the porosity of the insulating layer within a desired range, and it becomes easy to improve charge/discharge characteristics and insulating properties. For example, even within the range of thickness described below. Sufficient insulation can be secured. The average particle size of the first inorganic particles is more preferably 100 nm or more, further preferably 150 nm or more, more preferably 350 nm or less, further preferably 250 nm or less.
The average particle size means the particle size (D50) at a volume cumulative of 50% in the particle size distribution of the electrode active material obtained by the laser diffraction/scattering method.

The second inorganic particles are not particularly limited as long as the relative dielectric constant is less than 80, and inorganic particles generally used for the insulating layer can be used. The relative dielectric constant of the second inorganic particles is preferably 40 or less, more preferably 20 or less, still more preferably 15 or less from the viewpoint of improving battery characteristics such as charge/discharge characteristics, and for example, 2 or more, preferably Is 5 or more, more preferably 7 or more.
The relative dielectric constant of the second inorganic particles can be adjusted by appropriately selecting the material forming the inorganic particles, but can also be adjusted by the particle size and the like.

Specific examples of the second inorganic particles include alumina, boehmite, silicon dioxide, silicon nitride, zirconia, zinc oxide, boron nitride, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), Examples thereof include lithium fluoride, clay, zeolite, calcium carbonate and the like. The second inorganic particles may be used alone or in combination of two or more.
Among the above, the second inorganic particles are preferably alumina and boehmite, and more preferably alumina, from the viewpoint of improving battery characteristics such as charge/discharge characteristics and insulating properties.

The average particle size of the second inorganic particles is preferably 100 to 1500 nm, and is typically larger than the average particle size of the first inorganic particles. By setting the average particle diameter within these ranges, it becomes easier to adjust the porosity of the insulating layer within a desired range, and it becomes easier to improve the charge/discharge characteristics and the insulating properties. Also, by changing the average particle size of the first inorganic particles, the inorganic particles are densely packed, and it becomes easy to adjust the thickness and the voids. The average particle size of the second inorganic particles is more preferably 200 nm or more, further preferably 360 nm or more, more preferably 1000 nm or less, further preferably 750 nm or less.

In the insulating layer, the volume ratio of the first inorganic particles and the second inorganic particles (first inorganic particles/second inorganic particles) is preferably 1/9 to 9/1, more preferably 2/8. -8/2, more preferably 3/7-7/3. By setting the volume ratio of the first and second inorganic particles within the above range, it becomes easy to increase the charge/discharge capacity.

The content of the inorganic particles in the insulating layer 12 is preferably 45 to 92 vol% based on the total amount of the insulating layer. When the content of the inorganic particles is within the above range, it becomes easy to form a uniform porous structure in the insulating layer 12, and it is possible to achieve both appropriate insulating properties and high charge/discharge characteristics. From these viewpoints, the content of the inorganic particles is more preferably 60 to 87% by volume, further preferably 65 to 84% by volume.

(Binder for insulating layer)
The binder for the insulating layer is polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), fluorine-containing resin such as polytetrafluoroethylene (PTFE), polymethyl acrylate (PMA), poly Acrylic resin such as methyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber, poly(meth)acrylic acid, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol and the like. These binders may be used alone or in combination of two or more. In addition, carboxymethyl cellulose and the like may be used in the form of salt such as sodium salt.
Of these, fluorine-containing resins are preferable, and polyvinylidene fluoride is more preferable.

The content of the insulating layer binder contained in the insulating layer 12 is preferably 8 to 55% by volume based on the total amount of the insulating layer. When the content of the binder for the insulating layer is within the above range, a uniform porous structure can be formed in the insulating layer, so that both appropriate insulation and high charge/discharge capacity can be achieved. From these viewpoints, the content of the binder for the insulating layer is more preferably 13 to 40% by volume, still more preferably 16 to 35% by volume.
The insulating layer may contain other optional components other than the inorganic particles and the binder for the insulating layer, as long as the effects of the present invention are not impaired. However, in the total volume of the insulating layer, the total content of the inorganic particles and the binder for the insulating layer is preferably 90% by volume or more, and more preferably 95% by volume or more.

The thickness of the insulating layer 12 is preferably 15 to 50 μm. By setting the thickness of the insulating layer 12 within the above range, the coverage of the electrode active material layer 11 with the insulating layer 12 is improved, and the short-circuit suppressing effect is improved. Further, the resistance increase due to the insulating layer 12 is suppressed, and various battery characteristics such as charge/discharge characteristics are improved. From these viewpoints, the thickness of the insulating layer 12 is more preferably 20 to 40 μm, further preferably 25 to 35 μm.

The insulating layer 12 has a porous structure as described above, but the porosity thereof is preferably 50 to 80%. By setting the porosity to 80% or less, the coverage of the electrode active material layer 11 with the insulating layer 12 is increased, and the short-circuit suppressing effect is improved. By setting the porosity to 50% or more, the resistance increase due to the insulating layer 12 is suppressed, and the battery characteristics such as charge/discharge characteristics are improved. From the viewpoint of short-circuit suppressing effect and charge/discharge characteristics, the porosity of the insulating layer is more preferably 55 to 75%, further preferably 63 to 73%.

[Electrode active material layer]
The electrode active material layer typically includes an electrode active material and an electrode binder. When the electrode is the positive electrode, the electrode active material becomes the positive electrode active material, and the electrode active material layer becomes the positive electrode active material layer. On the other hand, when the electrode is the negative electrode, the electrode active material becomes the negative electrode active material and the electrode active material layer becomes the negative electrode active material layer. The electrode active material layer is preferably a positive electrode active material layer.

(Cathode active material)
Examples of the positive electrode active material used in the positive electrode active material layer include lithium metal oxide compounds. Examples of the lithium metal oxide compound include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ). Further, olivine-type lithium iron phosphate (LiFePO ₄ ) or the like may be used as the positive electrode active material. Further, as the positive electrode active material, one using a plurality of metals other than lithium may be used, and NCM (nickel cobalt manganese)-based oxide, NCA (nickel cobalt aluminum-based) oxide, etc. called ternary system may be used. May be used. As the positive electrode active material, these materials may be used alone or in combination of two or more.

(Negative electrode active material)
Examples of the negative electrode active material used in the negative electrode active material layer include graphite, carbon materials such as hard carbon, composites of tin compounds and silicon and carbon, lithium, and the like. Among these, carbon materials are preferable, and graphite is preferable. More preferable. As the negative electrode active material, the above substances may be used alone or in combination of two or more.

(Average particle size of electrode active material)
The average particle size of the electrode active material is not particularly limited, but is preferably 0.5 to 50 μm, more preferably 1 to 30 μm, and further preferably 5 to 25 μm.

(Content of electrode active material)
The content of the electrode active material in the electrode active material layer is preferably 60 to 99% by mass, more preferably 80 to 99% by mass, and even more preferably 90 to 98% by mass, based on the total amount of the electrode active material layer.

(Binder for electrodes)
Specific examples of the binder for electrodes include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), fluorine-containing resins such as polytetrafluoroethylene (PTFE), polymethyl acrylate (PMA). ), acrylic resin such as polymethylmethacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) , Polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber (SBR), poly(meth)acrylic acid, carboxymethyl cellulose (CMC), hydroxyethyl cellulose, polyvinyl alcohol and the like. These binders may be used alone or in combination of two or more. In addition, carboxymethyl cellulose and the like may be used in the form of salt such as sodium salt.
Of these, fluorine-containing resins are preferable, and polyvinylidene fluoride is more preferable.
The content of the binder in the electrode active material layer is, based on the total amount of the electrode active material layer, preferably 0.5% by mass or more, more preferably 0.5 to 20% by mass, and 1.0 to 10% by mass. Mass% is more preferable.

(Conductive agent)
The electrode active material layer may further include a conductive additive. The conductive additive is preferably used when the electrode active material layer is the positive electrode active material layer. A material having higher conductivity than the above-mentioned electrode active material is used as the conduction aid, and specific examples thereof include carbon materials such as Ketjen black, acetylene black (AB), carbon nanotubes, and rod-shaped carbon. The conductive additive may be used alone or in combination of two or more. When a conductive auxiliary agent is contained in the electrode active material layer, the content of the conductive auxiliary agent is preferably 0.5 to 15 mass% based on the total amount of the electrode active material layer, and 1.0 to 9 mass%. % Is more preferable.

The electrode active material layer may contain an optional component other than the electrode active material, the conductive additive, and the binder within a range that does not impair the effects of the present invention. However, in the total mass of the electrode active material layer, the total content of the electrode active material, the conductive additive, and the binder is preferably 90% by mass or more, and more preferably 95% by mass or more.
The thickness of each electrode active material layer 11 is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 80 μm.

[Electrode current collector]
Examples of the material forming the electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, when the electrode current collector is the positive electrode current collector, aluminum, titanium, nickel and stainless steel are preferable, and aluminum is more preferable. When the electrode current collector is the negative electrode current collector, copper, titanium, nickel and stainless steel are preferable, and copper is more preferable. The electrode current collector is generally composed of a metal foil, and the thickness thereof is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 20 μm. When the thickness of the electrode current collector is 1 to 50 μm, handling of the electrode current collector is facilitated and reduction in energy density can be suppressed.

<Method for manufacturing electrode for lithium-ion secondary battery>
Next, one embodiment of a method for manufacturing an electrode for a lithium ion secondary battery will be described in detail. In the method for manufacturing an electrode for a lithium ion secondary battery of the present invention, first, an electrode active material layer is formed, and then an insulating layer is formed on the surface of the electrode active material layer.

(Formation of electrode active material layer)
In forming the electrode active material layer, first, an electrode active material layer composition containing an electrode active material, an electrode binder, and a solvent is prepared. The composition for an electrode active material layer may contain other components such as a conductive additive which is blended as necessary. The electrode active material, the electrode binder, the conductive auxiliary agent and the like are as described above. The composition for electrode active material layer becomes a slurry.

Water or an organic solvent is used as the solvent in the electrode active material layer composition. Specific examples of the organic solvent include one or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Of these, N-methylpyrrolidone is preferred.
The solid content concentration of the composition for an electrode active material layer is preferably 5 to 75% by mass, more preferably 20 to 65% by mass.

The electrode active material layer may be formed by a known method using the composition for electrode active material layer, for example, the composition for electrode active material layer is applied onto an electrode current collector and dried. Can be formed by
Further, the electrode active material layer may be formed by applying the composition for an electrode active material layer onto a base material other than the electrode current collector and drying the composition. Examples of the base material other than the electrode current collector include known release sheets. The electrode active material layer formed on the base material is preferably formed by forming an insulating layer on the electrode active material layer, then peeling the electrode active material layer from the base material, and transferring it onto the electrode current collector.
The electrode active material layer formed on the electrode current collector or the substrate is preferably pressure-pressed. By pressing under pressure, the electrode density can be increased. The pressure press may be a roll press or the like.

(Formation of insulating layer)
The insulating layer composition used for forming the insulating layer contains inorganic particles, an insulating layer binder, and a solvent. The composition for an insulating layer may contain other optional components blended as necessary. The details of the inorganic particles, the binder for the insulating layer, and the like are as described above. The insulating layer composition becomes a slurry. Water or an organic solvent may be used as the solvent, and the details of the organic solvent are as described in the coating liquid for the electrode active material layer. The solid concentration of the insulating layer composition is preferably 5 to 75% by mass, more preferably 15 to 50% by mass.

The insulating layer can be formed by applying the composition for an insulating layer on the electrode active material layer and drying the composition. The method for applying the composition for an insulating layer to the surface of the electrode active material layer is not particularly limited, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, and screen printing. Law etc. are mentioned.
The drying temperature is not particularly limited as long as the solvent can be removed, but is, for example, 40 to 120°C, preferably 50 to 90°C. The drying time is not particularly limited, but is, for example, 30 seconds to 20 minutes.

<Lithium-ion secondary battery>
The lithium ion secondary battery of the present invention has a lithium ion secondary battery electrode having the above-mentioned insulating layer. Specifically, the lithium-ion secondary battery of the present invention includes a positive electrode and a negative electrode that are arranged so as to face each other, and at least one of the negative electrode and the positive electrode has the above-described insulating layer. Although it serves as a battery electrode, it is preferable that at least the positive electrode is a lithium ion secondary battery electrode having the above-mentioned insulating layer. In the lithium ion secondary battery electrode (negative electrode or positive electrode), an insulating layer may be provided on the surface facing the other electrode (positive electrode or negative electrode).

The lithium-ion secondary battery of the present invention may further include a separator arranged between the positive electrode and the negative electrode. By providing the separator, a short circuit between the positive electrode and the negative electrode can be prevented more effectively. Moreover, the separator may hold an electrolyte described below. The insulating layer provided on the positive electrode or the negative electrode may or may not be in contact with the separator, but is preferably in contact with the separator.
Examples of the separator include a porous polymer film, a non-woven fabric, glass fiber and the like. Among these, the porous polymer film is preferable. Examples of the porous polymer film include olefin-based porous films. The separator may be heated by heat generated when the lithium-ion secondary battery is driven to cause thermal contraction. However, even when such thermal contraction occurs, the insulating layer is provided to easily suppress a short circuit.
Further, in the lithium ion secondary battery of the present invention, the separator may be omitted. Even if the separator is omitted, the insulation between the negative electrode and the positive electrode may be ensured by the insulating layer provided on at least one of the negative electrode and the positive electrode.

The lithium ion secondary battery may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated. In this case, the negative electrodes and the positive electrodes may be provided alternately along the stacking direction. When a separator is used, the separator may be arranged between each negative electrode and each positive electrode.
In the lithium ion secondary battery, the above-described negative electrode and positive electrode, or the negative electrode, positive electrode, and separator are housed in a battery cell. The battery cell may be any of square type, cylindrical type, laminated type and the like.

The lithium ion secondary battery includes an electrolyte. The electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used. For example, an electrolytic solution is used as the electrolyte.
Examples of the electrolytic solution include an organic solvent and an electrolytic solution containing an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, and tetrohydra. Examples include polar solvents such as furan, 2-methyltetrahydrofuran, dioxolane, and methyl acetate, or a mixture of two or more kinds of these solvents. As the electrolyte salt, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ CO ₂ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ CF ₂ CF ₃ ) ₂ , LiN(COCF ₃ ). ₂ and a salt containing lithium such as LiN(COCF ₂ CF ₃ ) ₂ and lithium bisoxalate borate (LiB(C ₂ O ₄ ) ₂ ). Organic acid lithium salt-boron trifluoride complex, LiBH. Examples thereof include complexes such as complex hydrides such as _4. These salts or complexes may be used alone or in a mixture of two or more.
Further, the electrolyte may be a gel electrolyte containing a polymer compound in the electrolytic solution. Examples of the polymer compound include a fluoropolymer such as polyvinylidene fluoride and a polyacrylic polymer such as poly(meth)acrylate. The gel electrolyte may be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode, and for example, the electrolyte is filled in the battery cell in which the negative electrode and the positive electrode described above, or the negative electrode, the positive electrode, and the separator are housed inside. Further, the electrolyte may be applied, for example, on the negative electrode or the positive electrode and arranged between the negative electrode and the positive electrode.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The obtained lithium ion secondary battery was evaluated by the following evaluation methods.
(Evaluation of insulation)
Charging/discharging during the second charging/discharging performed under the same conditions where the voltage does not change (voltage drop is 0.1 V or less) after full charging in the first charging/discharging in a thermostatic chamber adjusted to 25°C. When the efficiency was 99% or more, the insulating property was evaluated as "A" because there was no micro short circuit. On the other hand, if the voltage drop after full charge during the first charge/discharge is greater than 0.1 V, or if the charge/discharge efficiency during the second charge/discharge is less than 99%, it is considered that there is a micro short circuit and the insulation property is reduced. It was evaluated as "B".

(Charge/discharge characteristics)
The batteries obtained in Examples and Comparative Examples were cycled at charge/discharge rates of 0.5 C and 5 C to measure the charge/discharge capacity.

The physical properties of the obtained lithium-ion secondary battery electrode were measured by the following measuring methods.
(Porosity)
The cross section of the lithium-ion secondary battery electrode on which the insulating layer was formed was exposed by the ion milling method. Next, the exposed cross section of the lithium-ion secondary battery electrode is observed with a FE-SEM (field emission scanning electron microscope) at a magnification that allows the entire insulating layer to be observed, and an image of the insulating layer is obtained. It was The magnification was 5000 to 25000 times. Next, the obtained image was binarized using image analysis software “Image J” so that the real part of the insulating layer was displayed in black and the void part of the insulating layer was displayed in white. And the ratio of the area of the white part was measured. The ratio of the area of this white portion is the porosity (%) of the insulating layer.
(Thickness of insulating layer)
The thickness of the insulating layer was measured as an average of 5 points from the above SEM image.

[Example 1]
(Preparation of positive electrode)
100 parts by mass of NCA-based oxide (average particle size 10 μm) as a positive electrode active material, 2 parts by mass of acetylene black as a conductive aid, 2 parts by mass of polyvinylidene fluoride as a binder for electrodes, and N-methyl as a solvent. Pyrrolidone was mixed to obtain a slurry for a positive electrode active material layer adjusted to a solid content concentration of 60% by mass. This positive electrode active material layer slurry was applied on both sides of a 15 μm thick aluminum foil as a positive electrode current collector, preliminarily dried, and then vacuum dried at 120° C. Then, the positive electrode current collector coated with the positive electrode active material layer slurry on both sides was pressed with a roller at a linear pressure of 400 kN/m, and further punched into 100 mm×200 mm square electrode dimensions, and the positive electrode active material was applied to both sides. It was a positive electrode having a layer. Among the dimensions, the area coated with the positive electrode active material was 100 mm×180 mm. The thickness of the positive electrode active material layer formed on both sides was 50 μm on each side.

(Preparation of negative electrode)
100 parts by mass of graphite (average particle size 10 μm) as a negative electrode active material, 1.5 parts by mass of sodium salt of carboxymethyl cellulose (CMC) as a binder for electrodes, 1.5 parts by mass of styrene-butadiene rubber (SBR), and solvent Was mixed with water to obtain a slurry for negative electrode active material layer adjusted to a solid content of 50% by mass. This negative electrode active material layer slurry was applied to both surfaces of a 12 μm thick copper foil as a negative electrode current collector and vacuum dried at 100° C. After that, the negative electrode current collector coated with the slurry for the negative electrode active material layer on both sides was pressed by a roller with a linear pressure of 500 kN/m, and further punched into 110 mm×210 mm square of the electrode size, and the negative electrode active material was formed on both sides. It was a negative electrode having a layer. Among the dimensions, the area coated with the negative electrode active material was 110 mm×190 mm. The thickness of the negative electrode active material layer formed on both sides was 50 μm on each side.

(Preparation of electrolyte)
LiPF ₆ as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3:7 (EC:DEC) to a concentration of 1 mol/liter to prepare an electrolyte solution. Prepared.

(Formation of insulating layer)
Polyvinylidene fluoride solution (manufactured by Kureha Co., Ltd., product name: L#1710, 10 mass% solution, solvent: NMP), barium titanate particles as the first inorganic particles (Fuji Film Wako Pure Chemical Industries, Ltd., average particle size) Diameter 200 nm (adjusted by ball milling and classification), relative dielectric constant 1000), and alumina particles as second inorganic particles (manufactured by Nippon Light Metal Co., Ltd., product name: low soda alumina, average particle diameter 500 nm, relative dielectric constant 10). ) Was added so as to be the volume% in Table 1, and mixed and dispersed while applying a medium shearing force to obtain a slurry. NMP was further added to this slurry so that the solid content concentration was 30% by mass, and the mixture was gently stirred with a stirrer for 30 minutes to obtain an insulating layer slurry.
The insulating layer slurry is applied to the surface of each positive electrode active material layer of the positive electrode with a bar coater, and the coating film is dried at 60° C. for 10 minutes to form an insulating layer on the surface of each positive electrode active material layer. Then, the opposite side was similarly coated to obtain a positive electrode having insulating layers on both sides.

(Manufacture of batteries)
Ten negative electrodes obtained above, nine positive electrodes having an insulating layer, and eighteen separators were laminated to obtain a laminate. Here, the negative electrodes and the positive electrodes were alternately arranged, and the separator was disposed between each negative electrode and the positive electrode. A polyethylene porous film was used as the separator.
The exposed end portions of the positive electrode current collectors of the respective positive electrodes were collectively bonded by ultrasonic welding, and terminal tabs protruding to the outside were bonded. Similarly, the end portions of the exposed portion of the negative electrode current collector of each negative electrode were collectively joined by ultrasonic welding and the terminal tabs protruding to the outside were joined.
Next, the laminate was sandwiched between aluminum laminated films, the terminal tabs were projected to the outside, and three sides were sealed by laminating. The electrolyte solution obtained above was injected from one side left unsealed and vacuum-sealed to manufacture a laminated cell.

[Comparative Example 1]
The same procedure as in Example 1 was performed, except that the second inorganic particles were not mixed with the insulating layer slurry and the volume% of the first inorganic particles was adjusted to be in Table 1. In Comparative Example 1, the same first inorganic particles as in Example 1 were used.

[Comparative Examples 2 and 3]
The same procedure as in Example 1 was performed except that the first inorganic particles were not mixed with the insulating layer slurry and the volume% of the second inorganic particles was adjusted to be in Table 1. In Comparative Example 2, the same second inorganic particles as in Example 1 were used, and in Comparative Example 3, alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name: low soda alumina, average) were used as the second inorganic particles. A particle size of 200 nm and a relative dielectric constant of 10) were used.

As shown in the above examples, by using the first inorganic particles having a high relative permittivity and the second inorganic particles having a low relative permittivity for the insulating layer, 0.5 C while ensuring the insulating property, A high charge/discharge capacity was secured at 5 C, and high-speed charge/discharge could be performed with the high capacity. On the other hand, in Comparative Examples 1 to 3, since the insulating layer did not contain both the first and second inorganic particles, the charge and discharge capacities at 0.5C and 5C were lower than those in Example 1 and were high. It was not possible to charge and discharge at high speed.

10 Electrode for Lithium Ion Secondary Battery 11 Electrode Active Material Layer 12 Insulation Layer 13 Electrode Current Collector

Claims (13)

An electrode active material layer, and an insulating layer provided on the surface of the electrode active material layer,
The insulating layer contains inorganic particles and a binder,
An electrode for a lithium ion secondary battery, wherein the inorganic particles include first inorganic particles having a relative dielectric constant of 80 or more and second inorganic particles having a relative dielectric constant of less than 80. The electrode for a lithium ion secondary battery according to claim 1, wherein the electrode active material layer is a positive electrode active material layer. The thickness of the said insulating layer is 15-50 micrometers, The electrode for lithium ion secondary batteries of Claim 1 or 2. 4. The first inorganic particles are at least one kind selected from the group consisting of barium titanate particles, strontium titanate particles, bismuth tantalate particles, and bismuth titanate particles. The electrode for a lithium-ion secondary battery according to 1. The electrode for a lithium ion secondary battery according to claim 4, wherein the first inorganic particles are barium titanate particles. The electrode for a lithium ion secondary battery according to claim 1, wherein a relative dielectric constant of the first inorganic particles is 900 or more. The average particle diameter of the said 1st inorganic particle is 50-500 nm, The electrode for lithium ion secondary batteries of any one of Claims 1-6. The electrode for a lithium ion secondary battery according to claim 1, wherein the second inorganic particles are at least one selected from alumina and boehmite. The average particle diameter of the said 2nd inorganic particle is 100-1500 nm, The electrode for lithium ion secondary batteries of any one of Claims 1-8. The said binder is polyvinylidene fluoride (PVdF), The electrode for lithium ion secondary batteries of any one of Claims 1-9. The electrode for a lithium ion secondary battery according to claim 1, wherein the insulating layer has a porous structure and the porosity is 50 to 80%. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to claim 1. The lithium ion secondary battery according to claim 12, comprising a positive electrode and a negative electrode, the positive electrode being the electrode for the lithium ion secondary battery.