JP2020021553A - Electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

To provide: an electrode for a lithium ion secondary battery, hardly affected by moisture even when lithium nickel cobalt aluminum-based oxide is used as a positive electrode active material, and accordingly capable of providing a lithium ion secondary battery good in cycle characteristics; and a lithium ion secondary battery including the electrode for a lithium ion secondary battery.SOLUTION: An electrode for a lithium ion secondary battery includes: a positive electrode active material layer containing lithium nickel cobalt aluminum-based oxide; and a moisture absorbing layer provided on a surface of the positive electrode active material layer, the moisture absorbing layer containing particles A having a specific surface area of 10-30 m/g.SELECTED DRAWING: None

Description

  The present invention relates to a lithium-ion secondary battery electrode and a lithium-ion secondary battery including the lithium-ion secondary battery electrode.

Lithium ion secondary batteries are used as power sources for large stationary power storage devices, power sources for electric vehicles, and the like. In recent years, research into miniaturization and thinning of batteries has been progressing. Generally, a lithium ion secondary battery includes both electrodes (positive electrode and negative electrode) each having an electrode active material layer formed on a surface of a metal foil, and a separator disposed between the both electrodes. The separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution.
The positive electrode of a lithium ion secondary battery generally includes a positive electrode active material layer containing a positive electrode active material and a binder, and the type and composition of each of these components is determined by the cycle characteristics and output of the lithium ion secondary battery. It is known to affect performance such as characteristics. For example, when a lithium nickel cobalt aluminum-based oxide is used as a positive electrode active material, it is known that a high charge / discharge capacity is exhibited, and various developments of lithium ion secondary batteries using the positive electrode active material have been carried out. (For example, Patent Document 1).
However, it is known that nickel-cobalt-aluminum-based oxides are deteriorated by moisture in the air, and the cycle characteristics and the like of a lithium ion secondary battery are deteriorated (Patent Document 2).

JP 2017-208207 A JP 2018-014199 A

As described above, the lithium ion secondary battery including the positive electrode active material layer containing the lithium nickel cobalt aluminum-based oxide has a problem that the cycle performance is reduced due to the influence of moisture, and it is required to solve this problem. I have.
Therefore, the present invention provides a lithium-ion secondary battery that is less susceptible to moisture even when a lithium-nickel-cobalt-aluminum-based oxide is used as a positive electrode active material, thereby providing a lithium-ion secondary battery with good cycle characteristics. It is an object to provide a battery electrode and a lithium ion secondary battery including the lithium ion secondary battery electrode.

As a result of intensive studies, the present inventors have found that the above problems can be solved by providing a specific moisture absorbing layer on the surface of the positive electrode active material layer, and have completed the present invention described below. The gist of the present invention is the following [1] to [9].
[1] A positive electrode active material layer containing a lithium nickel cobalt aluminum-based oxide, and a water absorbing layer provided on the surface of the positive electrode active material layer, wherein the water absorbing layer has a specific surface area of 10 to 30 m ² / An electrode for a lithium ion secondary battery, comprising g particles A.
[2] The electrode for a lithium ion secondary battery according to the above [1], wherein the water absorbing layer contains particles B having a specific surface area of less than 10 m ² / g.
[3] The electrode for a lithium ion secondary battery according to the above [1] or [2], wherein the moisture absorption layer contains a binder.
[4] The electrode for a lithium ion secondary battery according to any one of the above [1] to [3], wherein the particles A are organic particles having a carbonyl group.
[5] The electrode for a lithium ion secondary battery according to any one of [1] to [4], wherein the particles A are a polymethyl urea resin.
[6] The electrode for a lithium ion secondary battery according to any one of [1] to [5], wherein the content of the particles A in the moisture absorbing layer is 15 to 63% by mass.
[7] The electrode for a lithium ion secondary battery according to any one of [1] to [6], wherein the primary particle diameter of the particles A is 0.01 to 0.5 μm.
[8] The electrode for a lithium ion secondary battery according to any one of the above [2] to [7], wherein the primary particle diameter of the particles B is 0.05 to 2 μm.
[9] A lithium ion secondary battery comprising the lithium ion secondary battery electrode according to any one of [1] to [8].

  According to the present invention, even when a lithium nickel cobalt aluminum-based oxide is used as a positive electrode active material, the lithium ion secondary battery can be provided with a low susceptibility to moisture and, as a result, a good lithium ion secondary battery having good cycle characteristics. A battery electrode and a lithium ion secondary battery including the lithium ion secondary battery electrode can be provided.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a lithium ion secondary battery of the present invention.

[Electrode for lithium ion secondary battery]
The electrode for a lithium ion secondary battery of the present invention includes a positive electrode active material layer containing a lithium nickel cobalt aluminum-based oxide, and a moisture absorbing layer provided on a surface of the positive electrode active material layer. The absorption layer contains particles A having a specific surface area of 10 to 30 m ² / g. Since the water absorbing layer has a high water absorbing power, the positive electrode active material layer existing near the water absorbing layer is hardly affected by the water. As a result, the lithium ion secondary battery including the lithium ion secondary battery electrode has good cycle characteristics.

<Moisture absorption layer>
(Particle A)
The water absorbing layer in the electrode for a lithium ion secondary battery of the present invention contains particles A having a specific surface area of 10 to 30 m ² / g. By including the particles A in such a specific surface area range, it is possible to increase the water absorbing power of the water adsorption layer. Preferably the specific surface area of the particles A is 11~28m ² / g, more preferably 12~24m ² / g. The specific surface area can be determined by the BET method, and specifically, can be determined by the BET method using nitrogen gas adsorption.
The average primary particle diameter of the particles A is not particularly limited, but is preferably 0.01 to 0.5 μm, more preferably 0.05 to 0.5 μm, from the viewpoint of increasing the water absorbing power of the water adsorption layer. More preferably, it is 0.1 to 0.5 μm.
The average primary particle diameter of the particles in the present specification is the long diameter of a plurality of particles (for example, 60 particles obtained by subtracting extremely small 20 and extremely large 20 from 100 arbitrarily extracted particles) by electron microscopic observation. Is measured, and the measured value is averaged.

The type of the particles A is not particularly limited, and may be either organic particles or inorganic particles.
Specific organic particles include, for example, urea resin, melamine formaldehyde resin, acrylic resin, acryl-styrene resin, acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate) And particles composed of organic compounds such as polyacetal resin, epoxy resin, polyester resin, phenol resin and melamine resin.
Specific inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), and fluoride. Examples include particles composed of inorganic compounds such as potassium, lithium fluoride, clay, zeolite, and calcium carbonate. The inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide. The particles A may be used alone or in combination.

Among these, the particles A are preferably organic particles from the viewpoint of increasing the water absorbing power of the water adsorption layer. Among the organic particles, organic particles having a carbonyl group are preferable from the viewpoint of further increasing the water absorbing power of the water adsorption layer.
Examples of the organic particles having a carbonyl group include urea resins, acrylic resins, acryl-styrene resins, polyamide resins, polyimide resins, poly (lithium 2-acrylamido-2-methylpropanesulfonate), polyester resins, and the like. Can be
The acrylic resin is, for example, a poly (meth) acrylate obtained by polymerizing a monomer containing a (meth) acrylate. For example, poly (methyl (meth) acrylate), poly (ethyl (meth) acrylate), poly (propyl (meth) acrylate), poly (butyl (meth) acrylate), methyl (meth) acrylate-ethyl (meth) acrylate copolymer And the like. In addition, (meth) acrylic acid means acrylic acid or methacrylic acid.
The acryl-styrene-based resin is an acryl-styrene-based copolymer obtained by polymerizing a monomer mixture containing at least one of (meth) acrylic acid ester and (meth) acrylic acid and a styrene-based monomer. Examples of the acrylic-styrene resin include (meth) acrylic acid-styrene copolymer, methyl (meth) acrylate-styrene copolymer, and ethyl (meth) acrylate-styrene copolymer.
Among the organic particles having a carbonyl group, a urea resin is preferable, and a polymethyl urea resin is particularly preferable, from the viewpoint of further increasing the water absorbing power of the water adsorption layer. Examples of the polymethyl urea resin include “Pergopack M6” manufactured by Albemarle.

  The particles A may form secondary particles in which the primary particles are aggregated. In particular, in the polymethyl urea resin described above, usually, fine particles having a primary particle diameter of 0.01 to 0.5 μm aggregate to form microparticles having an average particle diameter of about 3.5 μm to 6.5 μm. Therefore, it has a high porosity and is excellent in water absorption.

  The content of the particles A in the moisture adsorption layer is preferably from 15 to 63% by mass, more preferably from 20 to 40% by mass, based on the total amount of the moisture adsorption layer.

(Particle B)
The particles contained in the moisture adsorption layer may be only particles A having a specific surface area of 10 to 30 m ² / g, but preferably contain particles B having a specific surface area of less than 10 m ² / g in addition to the particles A. . By using the particles A and the particles B together, the water absorbing power of the water adsorption layer is further improved. Further, by using the particles B, an appropriate gap is formed in the moisture adsorption layer, the resistance of the lithium ion secondary battery electrode including the moisture adsorption layer is reduced, and the output characteristics of the lithium ion secondary battery are reduced. Tends to be good.
Preferably the specific surface area of the particles B is 1~8m ² / g, and more preferably 3 to 6 m ² / g.
The primary particle diameter of the particles B is preferably from 0.05 to 2 μm, more preferably from 0.1 to 1.8 μm, even more preferably from 0.3 to 1.5 μm.

  The type of the particle B is not particularly limited, and the same type as that described for the particle A can be used. Among them, alumina, boehmite, silicon dioxide, silicon nitride, titania and the like are preferable.

The content of the particles B in the moisture adsorption layer is preferably from 5 to 83% by mass, more preferably from 30 to 82% by mass, and more preferably from 40 to 80% by mass, based on the total amount of the moisture adsorption layer. Is even more preferred.
When the particles A and the particles B are used in combination, it is preferable that the content of the particles B in the moisture adsorption layer is larger than that of the particles B from the viewpoint of increasing the water adsorption power. The mass ratio of the particles A and the particles B (the mass of the particles A / the mass of the particles B) is preferably from 0.4 to 1, and more preferably from 0.45 to 0.6.

(binder)
It is preferable that the moisture adsorption layer contains a binder. Although the kind of the binder is not particularly limited, fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA) ), Acrylic resin such as polymethyl 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, carboxymethylcellulose, hydroxyethylcellulose, and polyvinyl alcohol.
The content of the binder in the moisture adsorption layer is preferably from 2 to 80% by mass, more preferably from 8 to 40% by mass, based on the total amount of the moisture adsorption layer.

The thickness of the moisture adsorption layer is not particularly limited, but is preferably 1 to 25 μm, more preferably 2 to 15 μm, and even more preferably 4 to 10 μm. When the value is equal to or more than the lower limit of the above range, the water adsorbing power of the water adsorbing layer is increased, and the performance of the positive electrode active material layer is easily prevented from lowering. When it is at most the upper limit of the above range, the performance as a lithium ion secondary battery such as chargeability will be good.
The moisture adsorption layer may contain any other components other than the particles A, the particles B, and the binder as long as the effects of the present invention are not impaired.

<Positive electrode active material layer>
The positive electrode active material layer in the electrode for a lithium ion secondary battery of the present invention contains a lithium nickel cobalt aluminum-based oxide as a positive electrode active material. By using a lithium nickel cobalt aluminum-based oxide, the charge / discharge capacity of a lithium ion secondary battery can be improved.
The lithium nickel cobalt aluminum oxide is obtained by substituting a part of nickel of lithium nickelate with aluminum and cobalt. Lithium-nickel-cobalt-aluminum-based oxide, by the formula _{Li t Ni 1-x-y} Co x Al y O 2 ( where, 0.95 ≦ t ≦ 1.15,0 <x ≦ 0.3,0 <y ≦ 0.2, x + y ≦ 0.5).
The average particle size of the lithium nickel cobalt aluminum-based oxide is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. The average particle size can be determined by measuring the particle size distribution by laser diffraction.
The content of the lithium nickel cobalt aluminum-based oxide in the positive electrode active material layer is preferably from 50 to 98.5% by mass, more preferably from 60 to 98% by mass, based on the total amount of the positive electrode active material layer.

In the present invention, a lithium nickel cobalt aluminum oxide is used as the positive electrode active material. However, a positive electrode active material other than the lithium nickel cobalt aluminum oxide may be used together as long as the effects of the present invention are not impaired. As the positive electrode active material other than the lithium nickel cobalt aluminum-based oxide, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), olivine type lithium iron phosphate (LiFePO ₄₎ ), NCM (nickel-cobalt-manganese) oxides and the like.
The content of the lithium nickel cobalt aluminum-based oxide based on the total amount of the positive electrode active material is preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

  The positive electrode active material layer preferably contains a conductive auxiliary. The conductive auxiliary agent is not particularly limited, and examples thereof include carbon materials such as Ketjen black, acetylene black, carbon nanotube, and rod-like carbon. The content of the conductive additive is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, based on the total amount of the positive electrode active material layer.

  The positive electrode active material layer preferably contains a positive electrode binder. As the kind of the binder for the positive electrode, the same kind as the binder used in the above-mentioned moisture absorbing layer can be used. The content of the binder in the positive electrode active material layer is preferably 0.1 to 40% by mass, more preferably 0.1 to 10% by mass, and still more preferably 0.1 to 40% by mass, based on the total amount of the positive electrode active material layer. 5 to 5% by mass.

The thickness of the positive electrode active material layer is not particularly limited, but is preferably from 10 to 200 μm, and more preferably from 50 to 150 μm.
The positive electrode active material layer may contain any other components other than the above-described positive electrode active material, conductive auxiliary agent, and binder as long as the effects of the present invention are not impaired.

The electrode for a lithium ion secondary battery of the present invention preferably further includes a positive electrode current collector.
That is, the electrode for a lithium ion secondary battery of the present invention preferably includes a positive electrode current collector, a positive electrode active material layer provided on at least one surface of the positive electrode current collector, and a positive electrode current collector of the positive electrode active material layer. A moisture adsorbing layer provided on a surface opposite to the body side. Examples of the material constituting the positive electrode current collector include metals having conductivity, such as copper, aluminum, titanium, nickel, and stainless steel. Preferably, aluminum or copper, and more preferably, aluminum is used. The positive electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.

<Lithium ion secondary battery>
Hereinafter, the lithium ion secondary battery of the present invention will be described with reference to the drawings, but the present invention is not limited to the drawings.
FIG. 1 is a schematic cross-sectional view showing an embodiment of a lithium ion secondary battery including the lithium ion secondary battery electrode of the present invention. The lithium ion secondary battery 10 includes a lithium ion secondary battery electrode 11 serving as a positive electrode, a negative electrode 12, and a separator 13 disposed between the lithium ion secondary battery electrode 11 and the negative electrode 12.
The electrode 11 for a lithium ion secondary battery includes a positive electrode current collector 11a, a positive electrode active material layer 11b provided on the surface of the positive electrode current collector 11a, and a positive electrode current collector 11a on the opposite side of the positive electrode current collector 11a of the positive electrode active material layer 11b. A moisture adsorption layer 11c provided on the surface.
The negative electrode 12 includes a negative electrode current collector 12a and a negative electrode active material layer 12b provided on a surface of the negative electrode current collector 12a.
The separator 13 is provided between the moisture adsorption layer 11c and the negative electrode active material layer 12b.
The positive electrode active material layer 11b contains a lithium-nickel-cobalt-aluminum-based oxide, and is likely to be deteriorated in cycle characteristics due to the influence of moisture under normal circumstances. However, in the present invention, since the moisture adsorption layer 11c exists near the positive electrode active material layer 11b, the positive electrode active material layer 11b is hardly affected by moisture. Therefore, the lithium ion secondary battery 10 having the positive electrode active material layer 11b has good performance such as cycle characteristics.

Hereinafter, each configuration of the lithium ion secondary battery of the present invention will be described.
(Positive electrode)
As the positive electrode in the lithium ion secondary battery of the present invention, the above-described electrode for a lithium ion secondary battery can be used, and preferably, an electrode for a lithium ion secondary battery including a positive electrode current collector can be used.

(Negative electrode)
The negative electrode in the lithium ion secondary battery of the present invention has a negative electrode active material layer, and preferably has a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector. The negative electrode active material layer typically includes a negative electrode active material and a negative electrode binder. Examples of the negative electrode active material include carbon materials such as graphite and hard carbon, a composite of a tin compound and silicon and carbon, and lithium.
The negative electrode active material is not particularly limited, but preferably has an average particle size of 0.5 to 50 µm, more preferably 1 to 30 µm.
The content of the negative electrode active material in the negative electrode active material layer is preferably from 50 to 98.5% by mass, more preferably from 60 to 98% by mass, based on the total amount of the negative electrode active material layer.

The negative electrode active material layer may contain a conductive auxiliary. As the conductive additive, a material having higher conductivity than the above-described negative electrode active material is used, and specific examples thereof include carbon materials such as Ketjen black, acetylene black, carbon nanotube, and rod-like carbon.
When the negative electrode active material layer contains a conductive auxiliary, the content of the conductive auxiliary is preferably 1 to 30% by mass, and more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferred.

As the kind of the binder for the negative electrode, the same kind as the binder used in the above-described moisture absorbing layer can be used. The content of the binder for the negative electrode in the negative electrode active material layer is preferably 0.1 to 40% by mass, more preferably 0.1 to 10% by mass, and still more preferably 0 to 10% by mass, based on the total amount of the negative electrode active material layer. 0.5 to 5% by mass.
The thickness of the negative electrode active material layer is not particularly limited, but is preferably from 10 to 200 μm, and more preferably from 50 to 150 μm.

  Examples of the material constituting the negative electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable. The negative electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.

(Separator)
The lithium ion secondary battery of the present invention includes a separator disposed between a negative electrode and a positive electrode. The separator effectively prevents a short circuit between the positive electrode and the negative electrode. Further, the separator may hold an electrolyte described later.
Examples of the separator include a porous polymer film, a nonwoven fabric, and a glass fiber. Among these, a porous polymer film is preferable. Examples of the porous polymer film include an olefin-based porous film such as an ethylene-based porous film.

(Electrolytes)
The lithium ion secondary battery of the present invention 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 electrolyte is used as the electrolyte.
Examples of the electrolyte include an electrolyte containing an organic solvent and 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 thereof include polar solvents such as furan, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, and a mixture of two or more of these solvents. Examples of electrolyte salts include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₆ , LiCF ₃ CO ₂ , LiPF ₆ SO ₃ , LiN (SO ₃ CF ₃ ) ₂ , Li (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , a salt containing lithium such as LiN (COCF ₂ CF ₃ ) ₂ , lithium bisoxalate borate (LiB (C ₂ O ₄ ) _{2, and the} like; Examples include complexes such as boron hydride complexes and complex hydrides such as LiBH _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 further containing a polymer compound in the above-mentioned electrolytic solution. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl meth) acrylate. Note that the gel electrolyte may be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode. For example, the electrolyte solution is filled in the battery cell in which the above-described negative electrode, positive electrode, and separator are housed. Further, the electrolyte may be, for example, applied on the negative electrode or the positive electrode and disposed between 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 stacked. In this case, the negative electrode and the positive electrode may be provided alternately along the laminating direction. Further, the separator may be disposed between each negative electrode and each 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 electrode for a lithium ion secondary battery was evaluated by the following evaluation method.
(Measurement of the amount of water adsorbed on the water absorption layer)
The electrode for a lithium ion secondary battery produced in each of Examples and Comparative Examples was cut into a predetermined size (15 mm × 48 mm) and dried at 120 ° C. under vacuum for 8 hours. Then, it left for 24 hours under the environment of the dew point of -40 degreeC--30 degreeC, and measured the water value ((alpha)) of the electrode for lithium ion secondary batteries.
After leaving the electrode for a lithium ion secondary battery for 24 hours in an environment having a dew point of −40 ° C. to −30 ° C., the electrode was further left in the atmosphere (temperature 25 ° C., humidity 60% RH) for 24 hours to obtain a moisture value. (Β) was measured. Next, the difference obtained by subtracting the moisture value (α) from the obtained moisture value (β) was determined as the moisture value (γ).
The moisture value (α) and the moisture value (β) were measured using a Karl Fischer apparatus (“ADP-611” manufactured by Kyoto Electronics Industry Co., Ltd.) at a heating temperature of 200 ° C., a flow gas of nitrogen (N ₂ ), and a flow amount. This is a value obtained when the relative drift value becomes 0.03 μg / s or less under the condition of 200 mL / min.
The water value (γ) is the amount of water absorbed by the positive electrode active material layer and the water absorption layer, and the composition and thickness of the positive electrode active material layer of the lithium ion secondary battery electrode manufactured in each of Examples and Comparative Examples are different. Since they are the same, the moisture value (γ) correlates with the moisture adsorption amount of the moisture adsorption layer.

[Example 1]
(Preparation of composition for positive electrode active material layer)
100 parts by mass of a lithium nickel cobalt aluminum-based oxide having an average particle diameter of 10 μm as a positive electrode active material, 4 parts by mass of acetylene black as a conductive additive, 4 parts by mass of polyvinylidene fluoride (PVdF) as an electrode binder, and N -Methylpyrrolidone (NMP) to obtain a composition for a positive electrode active material layer adjusted to a solid concentration of 60% by mass.
(Preparation of composition for moisture adsorption layer)
Polymethyl urea resin having a specific surface area of 18 m ² / g and an average primary particle diameter of 0.05 μm (polymethyl urea resin “Pergo Pack M6” manufactured by Albemarle Co., Ltd.) as particles A, and polyvinylidene fluoride hexafluoropropylene (PVDF) as a binder -HFP) powder to obtain a mixture. The amount of each component was adjusted such that the composition of the formed moisture adsorption layer was as shown in Table 1. The mixture was mixed with NMP so that the solid content concentration was 30% by mass, gently stirred with a stirrer for 30 minutes, and filtered with a filter having an aperture of 80 μm to obtain a composition for a moisture adsorption layer.
(Manufacture of electrodes for lithium ion secondary batteries)
The composition for a positive electrode active material layer 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 laminate was provided with a positive electrode active material layer on both sides of an aluminum foil by pressing under a pressure of 400 kN / m. The thickness of each of the positive electrode active material layers in the laminate was 45 μm. Next, the composition for a moisture adsorption layer was applied to both surfaces of the positive electrode active material layer of the laminate using a bar coater. By drying the coating film formed by applying the composition for a water adsorption layer at 60 ° C., a water absorption layer having a thickness of 5 μm was formed on both surfaces of the positive electrode active material layer, and the electrode for a lithium ion secondary battery was formed. I got With respect to the lithium ion secondary battery electrode, the amount of water adsorbed on the water absorbing layer was measured. Table 1 shows the results.

[Example 2]
An electrode for a lithium ion secondary battery was obtained in the same manner as in Example 1, except that the preparation of the composition for moisture adsorption was performed as follows. With respect to the lithium ion secondary battery electrode, the amount of water adsorbed on the water absorbing layer was measured. Table 1 shows the results.
(Preparation of composition for moisture adsorption layer)
Polymethyl urea resin having a specific surface area of 18 m ² / g and an average primary particle diameter of 0.05 μm (a polymethyl urea resin “Pergopack M6” manufactured by Albemarle) as particles A, and a specific surface area of 4 m ² / g as particles B Alumina particles (Al ₂ O ₃ ) having an average primary particle diameter of 0.5 μm (manufactured by Sasol) and PVDF-HFP powder as a binder were mixed to obtain a mixture. The amount of each component was adjusted such that the composition of the formed moisture adsorption layer was as shown in Table 1. The mixture was mixed with NMP so that the solid content concentration was 30% by mass, gently stirred with a stirrer for 30 minutes, and filtered with a filter having an aperture of 80 μm to obtain a composition for a moisture adsorption layer.

[Comparative Example 1]
An electrode for a lithium ion secondary battery was obtained in the same manner as in Example 2, except that the particles A were not used in the preparation of the composition for adsorbing moisture. The amount of each component was adjusted such that the composition of the formed moisture adsorption layer was as shown in Table 1. With respect to the lithium ion secondary battery electrode, the amount of water adsorbed on the water absorbing layer was measured. Table 1 shows the results.

From the results of Examples 1 and 2, it was found that the water adsorbing layer of the electrode for a lithium ion secondary battery containing the particles A having a specific surface area in a specific range had a high water absorbing power. On the other hand, from the results of Comparative Example 1, it was found that the water absorbing layer of the electrode for a lithium ion secondary battery containing no particles A had a low water absorbing power.
From these results, the positive electrode active material layer of the electrode for a lithium ion secondary battery of the present invention is hardly affected by moisture, and the lithium ion secondary battery using the electrode for a lithium ion secondary battery has good cycle characteristics. It turned out to be.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 11 Positive electrode 11a Positive electrode current collector 11b Positive electrode active material layer 11c Water absorption layer 12 Negative electrode 12a Negative electrode current collector 12b Negative electrode active material layer 13 Separator

Claims (9)

A positive electrode active material layer containing a lithium nickel cobalt aluminum-based oxide,
A moisture absorbing layer provided on the surface of the positive electrode active material layer,
The electrode for a lithium ion secondary battery, wherein the water absorption layer contains particles A having a specific surface area of 10 to 30 m ² / g. The moisture absorption layer comprises particles B is less than a specific surface area of 10 m 2 / ^g, a lithium ion secondary battery electrode of claim 1.   The electrode for a lithium ion secondary battery according to claim 1, wherein the moisture absorbing layer contains a binder.   The electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the particles A are organic particles having a carbonyl group.   The electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the particles A are a polymethyl urea resin.   The electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the content of the particles A in the moisture absorbing layer is 15 to 63% by mass.   The electrode for a lithium ion secondary battery according to claim 1, wherein a primary particle diameter of the particles A is 0.01 to 0.5 μm.   The electrode for a lithium ion secondary battery according to claim 2, wherein a primary particle diameter of the particles B is 0.05 to 2 μm. A lithium ion secondary battery comprising the electrode for a lithium ion secondary battery according to claim 1.