WO2018164094A1

WO2018164094A1 - Collector for electricity storage devices, method for producing same, and coating liquid used in production of same

Info

Publication number: WO2018164094A1
Application number: PCT/JP2018/008486
Authority: WO
Inventors: 彬史武田; 中村　武志; 仁横内
Original assignee: 昭和電工株式会社
Priority date: 2017-03-07
Filing date: 2018-03-06
Publication date: 2018-09-13
Also published as: TW201843870A; JP2020074261A

Abstract

[Problem] To provide: a collector for electricity storage devices, which is used in order to supply a coating liquid that has improved dispersibility of a powder carbon material such as carbon fine particles and to obtain an electricity storage device that has a low resistance; and a method for producing this collector for electricity storage devices. [Solution] A collector for electricity storage devices, which is obtained by forming a coating layer on one surface or both surfaces of a sheet-like conductive substrate, and which is characterized in that: the coating layer contains a powder carbon material, a polymer that contains vinylidene fluoride as a monomer unit, and a vinyl polymer containing no fluorine; the vinyl polymer containing no fluorine is a homopolymer that contains N-vinyl acetamide or the like as a monomer unit, or a copolymer; the content ratio of the vinyl polymer containing no fluorine in the coating layer is 0.099-5.0% by mass; and the content ratio of the powder carbon material in the coating layer is 15.0-65.0% by mass.

Description

Current collector for power storage device, method for producing the same, and coating liquid used for the production

The present invention relates to a current collector for an electricity storage device, a method for producing the current collector, and a coating solution used for the production. More specifically, the present invention relates to a current collector for an electricity storage device provided with a resin layer containing a powdery carbon material on the surface of a metal foil, a method for producing the same, and a coating liquid used for the production.
In addition, in this invention, an electrical storage device means a lithium ion secondary battery in a storage battery, and an electric double layer capacitor and a lithium ion capacitor in an electrochemical capacitor.

In recent years, lithium ion secondary batteries, electric double layer capacitors, redox flow batteries and the like have attracted high attention as power storage devices. Lithium ion secondary batteries are used as power sources for notebook computers, mobile phones, electric tools, electronic / communication devices, etc. in terms of miniaturization and weight reduction. Recently, lithium ion secondary batteries are also used in electric vehicles and hybrid vehicles from the viewpoint of application to environmental vehicles. Electric double layer capacitors also have the potential to replace batteries due to their remarkably high storage capacity, and are attracting high attention such as backup power supplies, automobile idling stop systems, and large storage systems such as ESS. Further, redox flow batteries are being put into practical use as large-scale power facilities of 1000 kW class from the viewpoint of high cycle life.

The lithium ion secondary battery, the electric double layer capacitor, and the redox flow battery each have a configuration similar to each other. One of these similar configurations is an electrode. Reducing the resistance of the electrode is a common problem for lithium ion secondary batteries, electric double layer capacitors, and redox flow batteries, and various studies are being conducted.

For example, a lithium ion secondary battery includes a positive electrode using a metal oxide such as lithium cobaltate as a positive electrode active material, a negative electrode using a carbon material such as graphite as a negative electrode active material, and an electrolytic solution using carbonates as a solvent. Become. In a lithium ion secondary battery, charging and discharging are performed by moving lithium ions between a positive electrode and a negative electrode.
The positive electrode is obtained by applying a slurry containing a positive electrode active material and a binder to the surface of a positive electrode current collector such as an aluminum foil, drying it, and then cutting it into an appropriate size. The negative electrode is obtained by applying a slurry containing a negative electrode active material and a binder to the surface of a negative electrode current collector such as a copper foil, drying it, and then cutting it into an appropriate size. Generally, an organic solvent-based slurry using polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or the like as a binder is used for the positive electrode, and styrene butadiene rubber (SBR) as a binder for the negative electrode. In general, an aqueous slurry using an acrylic resin or the like is used.

By the way, in recent years, attempts have been made to increase the voltage by using a high-voltage active material in response to a request for increasing the capacity of the electricity storage device. For example, in a lithium ion secondary battery, an attempt has been made to achieve high capacity by charging at a voltage of 4.2 V or higher using a positive electrode active material having a high nickel ratio. Furthermore, as a means for achieving low resistance and long life of the electricity storage device, using a carbon coated foil in which carbon fine particles are coated with a binder resin on an aluminum foil used as a current collector for an electrode, The resistance of the electrical storage device itself is reduced by reducing the resistance of the interface. However, when the voltage is increased, the voltage exceeds the withstand voltage of binder resins (acrylic resins, polysaccharide resins, etc.) used for general carbon-coated foils. There's a problem. Functional degradation means that the resistance at the interface between the electrode and the current collector is increased, and the adhesion between the electrode and the current collector is decreased. As a result, normal charging / discharging of the electricity storage device cannot be performed, and all of the characteristics that are important performance indicators of the secondary battery, such as an increase in the internal resistance of the battery, a decrease in the capacity, and a shortened life, are affected. Become.

As a means for solving such a problem, it is conceivable to apply PVDF having a high withstand voltage as a binder resin used for the carbon coat foil of the current collector for the electricity storage device. For example, Patent Documents 1 to 4 describe PVDF as a binder, and these power storage devices are expected to improve the capacity by increasing the voltage.

Patent Document 1 discloses a current collector having a conductive resin layer on at least one surface of a conductive base material, the resin layer including a fluororesin and conductive particles, and having a thickness of 0.3 to A current collector that is 20 μm is disclosed. It has been shown that PVDF and acrylic acid-modified PVDF are preferable as the fluororesin. It is described that a lithium ion battery using this current collector can be provided with a shutdown function and high high-rate characteristics.
In Patent Document 2, a conductive layer is interposed between a current collector and an electrode mixture layer in at least one of a positive electrode and a negative electrode of a non-aqueous secondary battery, and the conductive layer includes a conductive material and a binder. And the conductive layer is disclosed to have a mass ratio (α crystal / β crystal) of α to β crystals of PVDF based on a nuclear magnetic resonance spectrum of 0.35 to 0.56. . It is described that with this configuration, when the temperature rises due to overcharging or the like, the internal resistance of the battery can be increased to suppress overheating of the battery.
In Patent Document 3, a conductive intermediate layer containing conductive particles and a thermoplastic polymer is interposed between an electrode active material layer and a current collector in an electrode for a secondary battery, and there are several thermoplastic polymers. It is disclosed that the average molecular weight is from 630,000 to less than 1 million, and PVDF is preferred as the thermoplastic polymer. It is described that, by this configuration, the stability and cycle characteristics of the conductive intermediate layer in the secondary battery electrode are enhanced, and the shutdown effect of the conductive intermediate layer is exhibited well.
In Patent Document 4, a positive electrode in which a positive electrode active material layer in which a first binder is contained in an active material is formed on the surface of a positive electrode current collector, and the first binder on the surface of a negative electrode current collector. In a lithium ion polymer secondary battery comprising a negative electrode on which a negative electrode active material layer in which a second binder same as or different from the agent is contained in an active material is formed, a positive electrode current collector, a positive electrode active material layer, A first adhesion layer, a second adhesion layer between the negative electrode current collector and the negative electrode active material layer, wherein the first and second adhesion layers are formed of the third binder and the conductive material. A lithium ion polymer secondary battery that includes both of them and the third binder is a polymer compound obtained by modifying the first binder or the second binder with a modifying substance is shown. PVDF is cited as an example of the first binder and the second binder, and the first adhesive layer or the second adhesive layer contains graphite, modified PVDF, and 0.1 to 20% by mass of a dispersant. The dispersant includes an acidic polymer dispersant, a basic polymer dispersant, or a neutral polymer dispersant. As a result, the adhesion between the current collector and the active material layer is increased, it is excellent in long-term storage and cycle characteristics without being dissolved in the electrolyte, and even when hydrofluoric acid is generated inside the battery, the adhesion layer is It has been disclosed that it becomes a protective layer and corrosion of the current collector can be suppressed.
Patent Document 5 discloses a nonaqueous electrolyte secondary battery having a positive electrode having a positive electrode mixture layer containing a positive electrode active material and a positive electrode current collector, a negative electrode, a nonaqueous electrolyte, and a separator. The metal foil and the conductive layer containing carbon fine particles formed on the surface of the metal foil, and the positive electrode mixture layer is formed on the positive electrode current collector, and the gap of the positive electrode mixture layer A non-aqueous electrolyte secondary battery having a rate of 25 to 40% is shown. With this configuration, a non-aqueous electrolyte secondary battery having good load characteristics that enables charging / discharging with a large current is provided. Is disclosed.

International Publication No. 2013/151046 Japanese Patent No. 5553165 Japanese Patent No. 5578370 Japanese Patent No. 3982221 JP2015-88465A

PVDF is generally known as a binder used for an electrode such as a lithium ion secondary battery, but the dispersibility of carbon fine particles in a slurry containing carbon fine particles and PVDF as a conductive auxiliary agent is very poor, This is particularly noticeable when the particle size of the carbon fine particles used is small, such as a carbon-coated foil. If the dispersibility of the carbon fine particles is poor, the slurry cannot be uniformly applied onto the substrate, resulting in uneven coating and a portion having poor conductivity, which is not preferable. In addition, when trying to apply the slurry thinly and uniformly with a gravure printing machine, streaky omissions (portions where the substrate is exposed in streaks) may occur or the cells of the gravure printing plate may be clogged. . That is, there are many problems in properly applying PVDF as a binder to a carbon coated foil.
As one solution to the problem, it is effective to add an additive such as a dispersant to improve the dispersibility. The amount added is also important. If too much is added, the viscosity of the slurry will increase. If the amount added is too small, the effect of improving dispersibility will not be obtained, and detailed examination is required before use. However, Patent Document 1 does not describe any additive. Patent Document 2 describes that any component other than PVDF can be contained, and a polymer other than PVDF is cited as an example, but details thereof are not described. In Patent Document 3, various additives such as a dispersant and a thickener are mixed as necessary when conductive particles and a thermoplastic polymer, which are materials of the conductive intermediate layer, are mixed in a solvent. Is described, but details are not described. In Patent Document 4, there are descriptions of an acidic polymer dispersant, a basic polymer dispersant, a neutral polymer dispersant, and the like as the dispersant, but no specific detailed study has been made. Patent Document 5 mentions polyvinylidene fluoride as a binder and polyvinylpyrrolidone as a dispersing material, but specific details have not been studied. Patent Document 5 mentions polyvinylidene fluoride as a binder and polyvinylpyrrolidone as a dispersing material, but specific details have not been studied.

The present invention is a coating liquid for producing a current collector for a power storage device in which a carbon coat layer is formed on one side or both sides of a conductive substrate, and dispersion of a powdery carbon material such as carbon fine particles in the liquid It is an object of the present invention to supply a coating liquid with improved properties, and to provide a current collector for a power storage device for obtaining a low resistance power storage device and a method for manufacturing the same.

As a result of intensive studies to achieve the above object, the present inventors have added a specific vinyl polymer to the coating liquid, and the addition amount is set to a specific range. It has been found that the dispersibility of the powdery carbon material is improved, and the resistance of the electricity storage device using the current collector produced using this coating liquid is lowered, and the present invention has been completed.
That is, the present invention provides the following means in order to solve the above problems.

[1] A current collector for an electricity storage device in which a coating layer is formed on one side or both sides of a sheet-like conductive substrate,
The coating layer includes a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer,
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
A current collector for an electricity storage device, wherein the content of the fluorine-free vinyl polymer in the coating layer is 0.099 to 5.0 mass%.
[2] The current collector for an electricity storage device as described in 1 above, wherein the content of the powdery carbon material in the coating layer is 15.0 to 65.0 mass%.
[3] The current collector for an electricity storage device according to 1 or 2, wherein the basis weight of the coating layer per one surface of the conductive substrate is 0.1 to 5.0 g / m ² .
[4] An electrode for a lithium ion secondary battery comprising the current collector for an electricity storage device according to any one of 1 to 3 above.
[5] A lithium ion secondary battery comprising the current collector for an electricity storage device according to any one of 1 to 3 above.
[6] A step of preparing a coating liquid in which a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer are dissolved or dispersed in a solvent,
A step of applying the prepared coating solution to one or both sides of a sheet-like conductive substrate, and a step of drying the applied coating solution;
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating solution is 2 to 15% by mass,
The mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 0.099 to 5.0 mass%. A method for producing a current collector for an electricity storage device, comprising:
[7] The method for producing a current collector for an electricity storage device as described in 6 above, wherein the solvent is water or N-methyl-2-pyrrolidone.
[8] A coating liquid containing a powdery carbon material in a solvent, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer,
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating solution is 2 to 15% by mass,
The mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 0.099 to 5.0 mass%. The coating liquid for manufacturing the electrical power collector for electrical storage devices characterized by being.
[9] The coating solution for producing the current collector for an electricity storage device as described in 8 above, wherein the solvent is water or N-methyl-2-pyrrolidone.

The current collector for the electricity storage device according to the present invention has low resistance. Moreover, the coating liquid for forming the coating layer of the current collector for the electricity storage device according to the present invention has improved dispersibility of the powdery carbon material in the coating liquid. When the coating liquid according to the present invention is used, uniform coating is possible, and provision of a low-resistance electricity storage device can be realized.

When the method for producing a current collector for an electricity storage device according to the present invention is used, a coating liquid in which a powdery carbon material, a polymer containing vinylidene fluoride, and a fluorine-free vinyl polymer are dissolved or dispersed in a solvent is used. Therefore, a general coating method can be selected, and the current collector can be easily produced.

3 is a photograph showing the results of observing the dispersibility of the coating liquid of Example 1-1. The photograph which shows the result of having observed the dispersibility of the coating liquid of Example 1-6. 3 is a photograph showing the results of observing the dispersibility of the coating liquid of Comparative Example 1-1. In the gravure coat test of Example 10, the photograph which shows the external appearance of the gravure roll part with favorable coating property without agglomerate generation | occurrence | production. In the gravure coat test of the comparative example 10, the photograph which shows the external appearance of the gravure roll part with a bad coating property by aggregate generation | occurrence | production.

Hereinafter, a power storage device current collector, a manufacturing method thereof, and a coating solution for manufacturing the current collector according to a preferred embodiment of the present invention will be described in detail. The materials, specifications, and the like exemplified in the following description are merely examples, and the present invention is not limited to them, and can be appropriately modified and implemented without changing the gist thereof.

[Current collector for power storage devices]
In the current collector for a power storage device according to a preferred embodiment of the present invention, a coating layer is formed on one side or both sides of a sheet-like conductive substrate. The coating layer includes a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit (hereinafter, also simply referred to as “polymer containing vinylidene fluoride”), and a fluorine-free vinyl polymer.

(Conductive substrate)
The material of the sheet-like conductive substrate of the current collector for the electricity storage device is not particularly limited as long as it is a metal, and a foil-like substrate is preferably used because of its excellent processability. For example, in a current collector of a lithium ion secondary battery, an aluminum foil is used for the positive electrode current collector and a copper foil is used for the negative electrode current collector.
There is no restriction | limiting in particular in the material of aluminum foil, Preferably it is aluminum alloy foil which contains 95 mass% or more of pure aluminum foil or aluminum. A1085 material is mentioned as an example of pure aluminum foil, A3003 material (Mn addition type | system | group) is mentioned as an example of aluminum alloy foil.
There is no restriction | limiting in particular in the material of copper foil, Preferably it is the electrolytic copper foil by which the surface was rust-proofed. In addition, the base material used for an electrical storage device can be selected, As such a base material, nickel foil, titanium foil, stainless steel foil etc. are mentioned, for example.
The substrate is not particularly limited by the thickness, but from the viewpoint of miniaturization and handling properties of the electricity storage device, it is usually preferably 3 μm to 100 μm thick. When performing the roll-to-roll manufacturing method, the thickness is 5 μm to 50 μm. Are preferably used.
The shape of the substrate may be a foil with no holes, or may be a foil with holes such as a two-dimensional mesh foil, a three-dimensional net-like foil, or a punching metal foil.
The surface of the substrate may be subjected to a known surface treatment, and examples of the treatment method include mechanical surface treatment, etching, chemical conversion treatment, anodization, wash primer, corona discharge, glow discharge and the like. .

(Coating layer)
A coating layer containing a powdery carbon material, a polymer containing vinylidene fluoride, and a fluorine-free vinyl polymer is formed on one or both sides of the sheet-like conductive substrate.
The thickness of the coating layer is preferably from 0.1 μm to 15.0 μm, more preferably from 0.2 μm to 10.0 μm, and even more preferably from 0.3 μm to 5.0 μm. A thickness of the coating layer of 0.1 μm or more is preferable because the conductivity between the conductive base material and the electrode active material can be secured by the powdery carbon material. On the other hand, if the thickness is 15.0 μm or less, the increase in electric resistance due to the layer thickness does not increase, and it is also preferable from the viewpoint of productivity.

The weight per unit area of the coating layer (coating weight per unit area) is preferably 0.1 to 5.0 g / m ² , and preferably 0.3 to 3.0 g / m ^2. Is more preferable. When the basis weight of the coating layer is 0.1 g / m ² or more, the conductivity between the conductive substrate and the electrode active material can be secured by the powdery carbon material. If the weight per unit area of the coating layer is 5.0 g / m ² or less, the resistance value can be reduced to about 1/10 or less compared to the case where the coating layer is not formed on the conductive substrate, It is also preferable from the viewpoint of productivity. In addition, when a coating layer is formed on both surfaces of a conductive substrate, the basis weight is approximately twice the above. Different basis weights may be used on the front surface and the back surface.

(Powdered carbon material)
The powdered carbon material is not particularly limited as long as it serves to impart conductivity to the coating layer, but carbon nanofibers, carbon fibers such as carbon nanotubes, carbon black, and carbon fine particles such as graphite fine particles are preferable. . Examples of carbon black include acetylene black, furnace black, and ketjen black. In particular, from the viewpoint of conductivity to the coating layer, the electrical resistivity of the powder measured in accordance with JIS K 1469: 2003 is 1 × 10 ⁻¹ Ω · cm or less with 100% green compact. A thing is preferable and it can use it combining the said thing as needed.

The carbon fine particles used as the powdery carbon material are not particularly limited in the particle diameter of the primary particles, but are preferably 10 to 100 nm. The primary particle size of the carbon fine particles is obtained by measuring 100 to 1000 primary particle sizes using an electron microscope and arithmetically averaging them. In the case of a spherical shape, the diameter is converted to a sphere.
The shape of the carbon fine particles is not particularly limited, but it is preferable that the particles are linked in a beaded manner so that many conductive paths are formed and are uniformly dispersed on the conductive substrate. This is because the electron conductive carbon fine particles share the movement of electrons between the active material of the electrode and the base material, and it is preferable that the contact area between the coating layer and the active material is large. Furthermore, it is preferable that the carbon fine particles are aggregated and have a small number of islands. This is because when the aggregation is small, the thickness of the coating layer is uniform, and the thickness of the electricity storage device can be designed uniformly without variation. For this purpose, the surface roughness Ra of the surface irregularities of the coating layer is preferably 1 μm or less.

The content of the powdery carbon material in the coating layer is preferably 15.0 to 65.0% by mass, more preferably 17.5 to 62.5% by mass, and 20.0 to 60.%. The content is more preferably 0% by mass, even more preferably 20.0-50.0% by mass, and particularly preferably 25.0-35.0% by mass.
If the content of the powdery carbon material in the coating layer is 15.0% by mass or more, preferably 20.0% by mass or more, sufficient conductivity can be exhibited. Further, if the content of the powdery carbon material is 65.0% by mass or less, preferably 50.0% by mass or less, the binder is sufficiently present so that the powdery carbon materials and the conductive substrate and the coating layer are present. Can be maintained.

(Polymer containing vinylidene fluoride)
A polymer containing vinylidene fluoride as a monomer unit is contained in the coating layer as a binder. The molecular weight of the polymer containing vinylidene fluoride and the type of polymer are not particularly limited. Polymers containing vinylidene fluoride as monomer units are polyvinylidene fluoride (PVDF), which is a homopolymer of vinylidene fluoride (VDF), or a copolymer having monomer units of vinylidene fluoride and a different fluorine compound. is there. Examples of such a copolymer include vinylidene fluoride and a monomer compound shown below, that is, tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), hydrofluoroether (HFE), and the like. Binary copolymers can be mentioned. Further, copolymer with perfluoroalkoxyalkane (PFA) (substantially VDF-TFE-perfluoroalkyl vinyl ether terpolymer), copolymer with ethylene-tetrafluoroethylene copolymer (ETFE) Examples thereof include a combination (substantially VDF-ethylene-TFE terpolymer) and VDF-TFE-HFP terpolymer.

In addition, it is preferable to use a polymer containing vinylidene fluoride at least partially modified with acid. Acid modification means that a newly added acid is added to an unsaturated bond portion at a defluorinated portion in a polymer containing vinylidene fluoride. Defluorination can be performed by heating a polymer containing vinylidene fluoride. The newly added acid is an acid such as an organic acid. The polymer containing the acid-modified vinylidene fluoride is improved in adhesion to the metal foil by the added acid.

Acids and acid derivatives to be modified include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, monomethyl maleate, monoethyl maleate, maleic anhydride Acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinic acid, methacryloyloxyethyl succinic acid, acryloyloxyethyl phthalic acid, methacryloyloxyethyl phthalic acid, trifluoroacrylic acid, trifluoromethyl Acrylic acid, 1,1-bis (acryloyloxymethyl) ethyl isocyanate, 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, etc. can be used. . Among these, from the viewpoint of adhesion to the metal foil, a PVDF binder obtained by modifying a part of PVDF with monomethyl maleate, maleic anhydride, methyl acrylate, or methyl methacrylate can be preferably used.

The content of the polymer containing vinylidene fluoride in the coating layer is preferably 35.0 to 85.0% by mass, more preferably 37.5 to 82.5% by mass, and 40.0 to More preferably, it is 80.0% by mass, and even more preferably 50.0-80.0% by mass. In a particularly preferred embodiment, the value of (mass of powdered carbon material) / (mass of polymer containing vinylidene fluoride) is 20/80 to 40/60, preferably 25/75 to 35/65. .
If the content of the polymer containing vinylidene fluoride in the coating layer is 35.0% by mass or more, preferably 50.0% by mass or more, adhesion to the conductive substrate is ensured, and carbon from the coating layer is obtained. Dropping of fine particles can be prevented. If the content of the polymer containing vinylidene fluoride is 85.0% by mass or less, preferably 80.0% by mass or less, the proportion of the powdery carbon material is sufficient and high conductivity can be maintained.

(Fluorine-free vinyl polymer)
The fluorine-free vinyl polymer is selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. It is a homopolymer as a monomer unit or a copolymer containing one or more selected from the above group as a monomer unit.
Each derivative (monomer unit) is a part of hydrogen of the original compound (monomer unit) before derivatization, as long as the characteristics of the fluorine-free vinyl polymer according to the present invention are not impaired. Those substituted with alkyl groups, alkoxy groups, hydroxyl groups, carboxy groups, amino groups, etc., and those in which a part of the original compound (monomer unit) is modified by acetylation, acetalization, etherification, esterification, etc. It can be used suitably.
The weight average molecular weight of the fluorine-free vinyl polymer is preferably 50,000 to 1,500,000, more preferably 100,000 to 900,000. The molecular weight can be determined as a value converted to a standard sample such as pullulan using gel permeation chromatography. When the weight average molecular weight is in the above range, the dispersibility of the powdered carbon material is good in the coating solution of the fluorine-free vinyl polymer described later, and prevents thickening and aggregation of carbon fine particles during coating. be able to. These fluorine-free vinyl polymers are presumably adsorbed to the surface of the powdery carbon material and suppress the aggregation of the powdery carbon materials due to electrostatic repulsion and steric hindrance. .

The content of the fluorine-free vinyl polymer in the coating layer is 0.099 to 5.0% by mass, preferably 0.2 to 4.0% by mass, more preferably 0.3 to 3.0% by mass. preferable.
When the content of the fluorine-free vinyl polymer in the coating layer is in the range of 0.099 to 5.0% by mass, the dispersibility of the powdery carbon material in the coating liquid for producing the coating layer Therefore, a uniform coating layer can be formed. When the content of the fluorine-free vinyl polymer is less than 0.099% by mass, the dispersibility of the powdery carbon material in the coating liquid deteriorates and aggregates are generated. It becomes a sea-island shape and hinders precise thickness control during electrode layer coating. If the content of the fluorine-free vinyl polymer exceeds 5.0% by mass, the resistance value of the electricity storage device increases, which is not preferable. The cause of the increase in resistance is not clear, but vinylidene fluoride tends to come into contact with carbon particles and conductive substrates at points, whereas fluorine-free vinyl compounds are easier to coat the surfaces of carbon particles. For this reason, it is presumed that the electrical contact between the carbon particles and between the carbon particles and the conductive base material deteriorates and the resistance value increases.

The content of the fluorine-free vinyl polymer in the coating layer is measured by pyrolysis gas chromatography mass spectrometry (GC / MS). The coating liquid or coating foil containing the fluorine-free vinyl polymer is set to a pyrolysis temperature of 550 ° C. and a flow rate in the column of 1 mL / min, and the obtained chromatogram and mass spectrum are compared with known data. Thus, the vinyl compound is identified. A calibration curve for obtaining the content of the fluorine-free vinyl polymer from the peak area of the identified peak is, for example, 3 in which the content of the fluorine-free vinyl compound is 0.1, 1.0, 5.0 mass%. Create by measuring points.

In addition, the coating layer may contain other resin components in addition to the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer. The other resin may be any resin. For example, a resin compound in which a polysaccharide polymer or a derivative thereof is crosslinked with a crosslinking agent can be used. In addition, polyacrylic resin, polyolefin resin, polyether resin, polyamide, polyimide, polyamideimide, epoxy resin, and the like may be used.

[Coating solution for producing current collector for electricity storage device]
A current collector coating solution for an electricity storage device according to a preferred embodiment of the present invention is obtained by dissolving or dispersing a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer in a solvent. is doing.

As the solvent, either an organic solvent-based solvent or an aqueous solvent can be used. The organic solvent-based solvent is not particularly limited, and examples thereof include methanol, ethanol, isopropanol, hexane, acetone, N-methyl-2-pyrrolidone (NMP), and the like. Alternatively, two or more kinds can be used in combination. Of these, water or N-methyl-2-pyrrolidone is preferably used.
It is preferable to use water as the solvent because the coating liquid can be produced at low cost with little environmental load.
Moreover, as an organic solvent, what evaporates below the temperature of the heat processing after application | coating is desirable. Specifically, those having a boiling point of 100 to 220 ° C. at normal pressure are preferred. When an organic solvent having such a boiling point is used, since the concentration of the coating liquid hardly changes during the coating operation, a coating layer having a predetermined thickness is easily obtained. Further, the solvent can be sufficiently removed by heat treatment. N-methyl-2-pyrrolidone is preferred as the organic solvent having the above boiling point.

In the coating solution, the powdered carbon material, the polymer containing vinylidene fluoride, and the fluorine-free vinyl polymer do not need to be dissolved in the solvent, and may be dispersed in the solvent. For example, when an aqueous solvent is used, a polymer containing vinylidene fluoride generally does not dissolve, but the coating solution is a slurry in which a polymer containing vinylidene fluoride is suspended in the solvent. Good.

The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating solution is 2 to 15% by mass, preferably 5 to 15% by mass, preferably 7 to 15 mass% is more preferable.
The mass ratio of the powdery carbon material to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride, and the fluorine-free vinyl polymer contained in the coating liquid is 15.0 to 65.0% by mass. It is preferably 17.5 to 62.5% by mass, more preferably 20.0 to 60.0% by mass, further preferably 20.0 to 50.0% by mass. Even more preferred is 25.0-35.0% by weight. When the mass ratio of the powdery carbon material is 15.0 mass% or more, preferably 20.0 mass% or more, a coating layer exhibiting sufficient conductivity can be formed. Moreover, if the said mass ratio of a powdery carbon material is 65.0 mass% or less, Preferably it is 50.0 mass% or less, since a binder exists enough, powder carbon materials and a conductive base material and coating | cover A coating layer that maintains the adhesion of the layers can be formed.
The mass ratio of the polymer containing vinylidene fluoride to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride, and the fluorine-free vinyl polymer contained in the coating solution is 35.0 to 85. It is preferably 0% by mass, more preferably 37.5 to 82.5% by mass, still more preferably 40.0 to 80.0% by mass, and 50.0 to 80.0% by mass. Is more preferable. In a particularly preferred embodiment, the value of (mass of powdered carbon material) / (mass of polymer containing vinylidene fluoride) is preferably 20/80 to 40/60, more preferably 25/75 to 35 / 65. If the mass ratio of the polymer containing vinylidene fluoride is 35.0 mass% or more, preferably 50.0 mass% or more, adhesion to the conductive substrate is ensured, and the carbon fine particles from the coating layer It is possible to form a coating layer that can prevent falling off. Moreover, if the said mass ratio of the polymer containing a vinylidene fluoride is 85.0 mass% or less, Preferably it is 80.0 mass% or less, the ratio of a powdery carbon material is enough and can maintain high electroconductivity. A coating layer can be formed.
Further, the mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer contained in the coating liquid is 0.099-5. 0% by mass, preferably 0.2 to 4.0% by mass, and more preferably 0.3 to 3.0% by mass. When the mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is in the range of 0.099 to 5.0% by mass. A slurry with good dispersibility of the powdery carbon material is obtained, and a uniform coating layer can be formed. When the mass ratio of the fluorine-free vinyl polymer is less than 0.099% by mass, the dispersibility of the powdery carbon material is deteriorated and aggregates are generated, resulting in poor coatability. On the other hand, when the mass ratio of the fluorine-free vinyl polymer exceeds 5.0% by mass, the viscosity of the slurry increases, so that the coating property is deteriorated, and the resistance value of the electricity storage device is not preferable. .

The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating liquid is in the above range, and the powdery carbon material and the fluorine contained in the coating liquid are in the above range. When the mass ratio of the fluorine-free vinyl polymer to the total mass of the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is within the above range, the dispersibility of the powdery carbon material is good and the liquid The viscosity becomes appropriate, a general coating method can be selected, and a current collector for an electricity storage device can be easily produced. At this time, the viscosity of the coating liquid at the coating temperature is preferably 50 to 3000 mPa · s, more preferably 50 to 1000 mPa · s, and even more preferably 50 to 300 mPa · s. preferable. If the viscosity of the coating liquid is 3000 mPa · s or less, coating on the substrate can be easily performed. Moreover, if the viscosity of a coating liquid is 50 mPa * s or more, sufficient film thickness can be formed on a base material.
Viscosity is measured using a B-type viscometer, and a rotor and rotation speed suitable for the viscosity range to be measured are selected. For example, when measuring the viscosity of a coating solution of about several hundred mPa · s, no. Two rotors are used, the rotation speed is 60 rpm, and the measurement temperature is 20 to 25 degrees.

[Method for producing current collector for power storage device]
The method for producing a current collector for an electricity storage device according to the present invention includes a coating liquid in which a powdered carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer are dissolved or dispersed. , A step of applying the prepared coating solution to one or both sides of the sheet-like conductive substrate, and a step of drying the applied coating solution. As the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer, those described above can be used.

The method of applying the coating solution to one or both sides of the conductive substrate is not particularly limited, but a general coating method such as gravure coating, die coating, bar coating, spin coating, nip coating, etc. should be used. Can do.

The applied coating solution is dried to form a coating layer on the substrate. Drying is preferably performed at a temperature of 50 ° C. or higher in order to sufficiently evaporate the solvent.
When the coating liquid has a thermosetting resin component, it is preferable to cure the resin component. When a thermosetting resin is contained, it is more preferable to dry at a temperature higher than the curing temperature (crosslinking reaction temperature) of the resin. The coating liquid may contain a catalyst, a polymerization agent, a crosslinking agent and the like that promote such a curing reaction.

[electrode]
A lithium ion secondary battery using the current collector for an electricity storage device according to the present invention will be described as an example. Although the current collector for an electricity storage device of the present invention is expected to exhibit an effect when applied to an electrode using a positive electrode active material of high voltage specification, it is not limited to a specific positive electrode current collector, You may use for a collector. Since the effect of reducing the interfacial resistance between the current collector and the electrode can be obtained with either the positive electrode or the negative electrode, a low-resistance electricity storage device can be obtained.

The positive electrode is formed by applying and drying a slurry in which a positive electrode active material, a positive electrode conductive additive and a binder are dissolved or dispersed in a solvent on the current storage device current collector of the present invention. Here, as the binder, PVDF or the like that can be dissolved in an organic solvent-based solvent is generally used. Further, an aqueous slurry containing SBR, acrylic resin, or the like can also be used.

A well-known thing can be used for a positive electrode active material and the conductive support agent for positive electrodes.
Examples of the positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), and a part of Co in lithium cobaltate by Mn and Ni. ternary lithium substituted compound _{_{(Li (Co x Mn y Ni}} z) O 2), a part of Ni of lithium nickelate was replaced by Co and _{_{Al (Li (Ni x Co y}} Al z) O 2), An olivine system (LiFePO ₄ , LiMnPO ₄ ) or the like is preferable. As the conductive additive for the positive electrode, for example, carbon black such as acetylene black, furnace black, ketjen black, vapor grown carbon fiber, fine graphite powder and the like are suitable.

The negative electrode is formed by applying and drying a slurry in which a negative electrode active material, a negative electrode conductive additive and a binder are dissolved or dispersed in a solvent on the current collector for the electricity storage device of the present invention. Here, as the binder, PVDF or the like is generally used in the organic solvent, and SBR or acrylic resin or the like is generally used in the aqueous solvent.

A well-known thing can be used for a negative electrode active material and the conductive support agent for negative electrodes.
As the negative electrode active material, for example, a graphite system such as natural graphite or artificial graphite, an alloy system containing an element of silicon or tin, a titanium-containing oxide system such as lithium titanate, or a mixed system thereof is preferably used. . As the conductive additive for the negative electrode, for example, carbon black such as acetylene black, furnace black, ketjen black, vapor grown carbon fiber, and the like are preferably used.

[Lithium ion secondary battery]
The lithium ion secondary battery which concerns on 1 aspect of this invention is equipped with said electrode. The electrode has a coating layer formed on a conductive substrate to form a current collector, and has an electrode active material layer containing a positive electrode active material or a negative electrode active material, a conductive additive and a binder on the coating layer, The positive electrode and the negative electrode are joined via a separator, and the inside is further filled with an electrolytic solution, and an exterior material is provided.

As the electrolytic solution, separator, and exterior material, which are constituent elements of the electricity storage device other than the electrodes, known materials can be used. The electrolytic solution is not limited to a liquid, and a gel or solid electrolyte can also be used. As the separator, for example, a film of polypropylene, polyethylene or the like is preferably used.

A lithium ion secondary battery can be discharged by connecting a load such as a motor or a light source to the positive electrode and the negative electrode, and can be charged by connecting a power source.

When the current collector provided with the coating layer of the present invention on the surface of the conductive base material is used for the electrode of the lithium ion secondary battery, the resistance value of the electrode is lowered as compared with the case of the conventional current collector. Can do. That is, it is possible to reduce the internal resistance of the lithium ion secondary battery. In addition, by using the current collector for an electricity storage device of the present invention, a high voltage charging of a lithium ion secondary battery to which a high voltage active material is applied is possible, and a high capacity lithium ion secondary battery is realized. Can do.

[Evaluation of coating solution]
<Dispersibility of powdery carbon material>
Specifically, the evaluation of the dispersibility of the powdered carbon material in the coating liquid was carried out by dropping 5 mL of the coating liquid on the wall surface of a 50 mL glass test tube held vertically. The state was observed with the naked eye. When the aggregate was not observed on the wall surface, it was determined that the dispersibility was good, and when the aggregate was observed, it was determined that the dispersibility was poor.

[Evaluation of lithium ion secondary battery]
<Preparation of positive electrode sheet>
90 parts by mass of LiFePO ₄ (manufactured by Alees, M121) as a positive electrode active material, ₅ parts by mass of conductive carbon black (manufactured by Imerys, SUPER P) as a conductive additive, and polyvinylidene fluoride (manufactured by Arkema, HSV-900 as a binder) ) N-methyl-2-pyrrolidone was added to 5 parts by mass while stirring and mixing to prepare a slurry dispersion. The prepared dispersion was applied onto a current collector used in the following Examples and Comparative Examples using a doctor blade having a clearance of 200 μm, dried, and pressure-molded to obtain a positive electrode sheet.
<Preparation of negative electrode sheet>
95 parts by weight of artificial graphite (manufactured by Showa Denko KK, SCMG (registered trademark) -AR) as a negative electrode active material, 1 part by weight of conductive carbon black (manufactured by Imerys, SUPER P) as a conductive auxiliary agent, and styrene butadiene rubber as a binder (Nippon ZEON Co., Ltd., BM-400B) 3 parts by mass (in terms of solid content), carboxymethylcellulose (Daicel Finechem Co., Ltd., # 1380) as a thickener 1 part by mass (in terms of solid content) The mixture was stirred and mixed to prepare a slurry dispersion. The prepared dispersion was applied onto a copper foil having a thickness of 20 μm with a doctor blade having a clearance of 200 μm, dried, and pressure-molded to obtain a negative electrode sheet.
<Production of laminate cell for evaluation>
The positive electrode sheet and the negative electrode sheet prepared as described above were overlapped with a polypropylene separator (Celgard, Cellguard 2500) interposed therebetween. It was put in an aluminum laminate packaging material, an electrolyte solution was injected, and heat sealing was performed in a vacuum to obtain a laminate cell for evaluation.
As the electrolytic solution, a solution in which LiPF ₆ was dissolved at 1 mol / L as an electrolyte and vinylene carbonate was added at 1% by mass as an additive in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7 was used. .
As described above, a cell having a rated capacity of 100 mAh (1C = 100 mA) was produced.
<Evaluation of direct current internal resistance (DC-IR) of battery>
The direct current internal resistance (DC-IR) of the battery is adjusted to 50% depth of charge (SOC) after initial charge / discharge of the cell, and then discharged at 5 points between 0.1C and 2C for 5 seconds each under a room temperature environment. Then, the amount of voltage change before and after that was measured with a charge / discharge device (TOSCAT-3000, manufactured by Toyo System Co., Ltd.). The DC internal resistance was calculated as the average value of the voltage change amount / current value at five points.

Example 1-1
In order to prepare a coating liquid for producing a current collector, PVDF aqueous dispersion (weight average molecular weight (Mw): 730,000, acid-modified: acrylic acid) is used as a binder (polymer containing vinylidene fluoride) as a solid content. 70 parts by mass in terms of conversion, 30 parts by mass of acetylene black (Denka Co., Ltd., Denka Black (registered trademark), HS-100) having a primary particle size of 48 nm as a powdery carbon material, and a fluorine-free vinyl polymer 0.1 parts by mass of poly-N-vinylacetamide (PNVA (registered trademark), manufactured by Showa Denko KK) was prepared. Table 1 shows the amount (parts by mass) of the powdered carbon material, the polymer containing vinylidene fluoride, and the fluorine-free vinyl polymer and the content (% by mass) in the coating layer (Tables 2 and 3). The same applies to.
First, acetylene black, PNVA (registered trademark) and an appropriate amount of pure water were mixed, and the mixture was mixed at 4000 rpm for 30 minutes using a disperser type stirrer (manufactured by Nippon Seiki Co., Ltd., Excel Auto Homogenizer). PVDF aqueous dispersion was added, and pure water was further added so that the solid content concentration was 7% by mass. The mixed solution was mixed at 500 rpm for 3 minutes using the above-mentioned disperser type stirrer to obtain a coating solution.
When the dispersibility of acetylene black in the obtained coating liquid was evaluated, no aggregates were observed and the dispersibility was good (FIG. 1).
Next, an aluminum foil having a material ALN30 and a thickness of 15 μm was prepared, and a coating solution was applied thereon using an applicator. Then, it dried for 5 minutes with the 80 degreeC dryer, and obtained the electrical power collector. The basis weight was 0.52 g / m ² .
Using the obtained current collector, a secondary battery was produced by the above method and the internal resistance was determined to be 300 mΩ (Table 1).

(Examples 1-2 to 6)
A coating liquid was prepared in the same manner as in Example 1-1 except that the amount of PNVA added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass, respectively. Evaluation was made to produce a secondary battery, and the internal resistance was evaluated. The evaluation results are shown in Table 1. Further, the observation result of the dispersibility of the coating liquid of Example 1-6 is shown in FIG. 2, and no agglomerates were observed, and the dispersibility was good.

(Comparative Examples 1-1 to 3)
Except that the addition amount of PNVA was 0, 6 and 10 parts by mass, respectively, a coating solution was prepared and dispersibility was evaluated in the same manner as in Example 1-1, and a secondary battery was prepared to reduce internal resistance. evaluated. Here, the addition amount of 0 parts by mass means that no addition is performed (the same applies hereinafter). The evaluation results are shown in Table 1. Further, the observation result of the dispersibility of the coating liquid of Comparative Example 1-1 is shown in FIG. 3. As a result, aggregates were observed and the dispersibility was poor.

Example 2-1
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 1-1 except that polyvinyl alcohol (PVA, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used instead of PNVA. The internal resistance was evaluated. The evaluation results are shown in Table 1.

(Examples 2-2 to 6)
A coating liquid was prepared in the same manner as in Example 2-1 except that the amount of PVA added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass, respectively. Evaluation was made to produce a secondary battery, and the internal resistance was evaluated. The evaluation results are shown in Table 1.

(Comparative Examples 2-1 to 3)
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 2-1, except that the amount of PVA added was 0, 6 and 10 parts by mass, respectively, and a secondary battery was prepared and internal resistance was evaluated. did. The evaluation results are shown in Table 1.

Example 3-1
As binder, 70 parts by mass of PVDF powder (Mw = 630,000, acid-modified: acrylic acid), 30 parts by mass of acetylene black (Denka Co., Ltd., Denka Black (registered trademark), HS-100) having a primary particle size of 49 nm, polyvinyl 0.1 parts by mass of pyrrolidone (PVP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was prepared, and N-methyl-2-pyrrolidone (NMP) was added thereto so that the solid concentration was 7% by mass. The mixed solution was mixed at 4000 rpm for 30 minutes using a disposable type stirrer (manufactured by Nippon Seiki Co., Ltd., Excel Auto Homogenizer) to obtain a coating solution. Otherwise, the dispersibility was evaluated in the same manner as in Example 1-1, and a secondary battery was fabricated and the internal resistance was evaluated. The evaluation results are shown in Table 1.

(Examples 3-2 to 6)
A coating liquid was prepared in the same manner as in Example 3-1, except that the amount of PVP added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass. Evaluation was made to produce a secondary battery, and the internal resistance was evaluated. The evaluation results are shown in Table 1.

(Comparative Examples 3-1 to 3)
Except that the addition amount of PVP was 0, 6 and 10 parts by mass, a coating solution was prepared and dispersibility was evaluated in the same manner as in Example 3-1, and a secondary battery was manufactured and internal resistance was evaluated. did. The evaluation results are shown in Table 1.

Example 4-1
Instead of PVDF powder (Mw = 630,000, acid-modified: acrylic acid), PVDF powder (Mw = 1.200, acid-modified: acrylic acid) is used as a binder, and polyvinyl acetate (PVAc, Nippon Acetate) is used instead of PVP. A coating liquid was prepared and dispersibility was evaluated in the same manner as in Example 3-1, except that Poval Co., Ltd. was used, and a secondary battery was manufactured and internal resistance was evaluated. The evaluation results are shown in Table 2.

(Examples 4-2 to 6)
A coating solution was prepared and evaluated for dispersibility in the same manner as in Example 4-1, except that the amount of PVAc added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass. Then, a secondary battery was produced and the internal resistance was evaluated. The evaluation results are shown in Table 2.

(Comparative Examples 4-1 to 3)
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 4-1, except that the amount of PVAc added was 0, 6 and 10 parts by mass. A secondary battery was prepared and internal resistance was evaluated. The evaluation results are shown in Table 2.

Example 5-1
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 1-1 except that ethylene-vinyl acetate copolymer (EVA, manufactured by Mitsubishi Chemical Corporation) was used instead of PNVA. The internal resistance was evaluated. The evaluation results are shown in Table 2.

(Examples 5-2 to 6)
A coating solution was prepared and the dispersibility was evaluated in the same manner as in Example 5-1, except that the amount of EVA added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass. Then, a secondary battery was produced and the internal resistance was evaluated. The evaluation results are shown in Table 2.

(Comparative Examples 5-1 to 3)
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 5-1, except that the amount of EVA added was 0, 6 and 10 parts by mass. A secondary battery was prepared and internal resistance was evaluated. . The evaluation results are shown in Table 2.

Example 6-1
A coating solution was prepared in the same manner as in Example 4-1, except that a (vinyl alcohol-vinyl pyrrolidone) copolymer (P (VA-VP), manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used instead of PVP. Then, the dispersibility was evaluated, and a secondary battery was produced to evaluate the internal resistance. The evaluation results are shown in Table 2.

(Examples 6-2 to 6)
A coating solution was prepared in the same manner as in Example 6-1 except that the amount of P (VA-VP) added was 0.3, 0.5, 1.0, 3.0, and 5.0 parts by mass. Then, the dispersibility was evaluated, and a secondary battery was produced to evaluate the internal resistance. The evaluation results are shown in Table 2.

(Comparative Examples 6-1 to 3)
A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 6-1, except that the addition amount of P (VA-VP) was changed to 0, 6 and 10 parts by mass. The internal resistance was evaluated. The evaluation results are shown in Table 2.

(Comparative Examples 7-1 to 9)
Polyethylene glycol (PEO, manufactured by NOF Corporation) is used instead of PVAc, and the amount added is 0, 0.1, 0.3, 0.5, 1.0, 3.0, 5.0, 6 A coating solution was prepared and dispersibility was evaluated in the same manner as in Example 4 except that the amount was 0.0 and 10.0 parts by mass. A secondary battery was manufactured and internal resistance was evaluated. The evaluation results are shown in Table 3.

(Comparative Examples 8-1 to 9)
A secondary battery was prepared by preparing a coating solution and evaluating dispersibility in the same manner as Comparative Examples 7-1 to 9 except that polyacrylic acid (PAA, manufactured by Toa Gosei Co., Ltd.) was used instead of PEO. The internal resistance was evaluated. The evaluation results are shown in Table 3.

(Comparative Examples 9-1 to 9)
Implementation was performed except that HS-100 and PVDF aqueous dispersion were used as a polymer containing a powdery carbon material and VDF, respectively, 10, 70 or 90 parts by mass, and 90, 30 or 10 parts by mass in terms of solid content. In the same manner as in Examples 1-1, 1-4, and 1-6, a coating solution was prepared to evaluate dispersibility, and a secondary battery was manufactured to evaluate internal resistance. The evaluation results are shown in Table 4.

[Possibility of application to gravure coating]
(Example 10)
The coating liquid of Example 1-1 was placed in a liquid reservoir (pan) of a gravure coater (manufactured by Nakajima Seiki Engineering Co., Ltd. (currently Union Tech Co., Ltd.)), and the gravure roll was rotated at a constant speed. The aluminum foil was brought into contact with the gravure roll, and coating was performed by conveying the aluminum foil in the direction opposite to the rotation direction. At this time, no generation of streaks was observed in the un-engraved part (corresponding to the part where the coating layer was not formed) and the engraving part (corresponding to the part where the coating layer was formed) of the gravure roll (FIG. 4). This shows that this coating liquid has good dispersibility of carbon black and can be applied to gravure coating.
(Comparative Example 10)
A coating solution prepared in the same manner as in Example 1-1 except that the amount of poly-N-vinylacetamide added was changed to 0.05 parts by mass (content in the coating layer: 0.050% by mass) The gravure coater was placed in a liquid reservoir and the gravure roll was rotated at a constant speed in the same manner as in Example 9. At this time (a state in which the aluminum foil was not in contact with the gravure roll), generation of streaks was observed in the unengraved portion of the gravure roll (FIG. 5).
The generation of the streaks is presumed to be due to the fact that the dispersibility of acetylene black deteriorates due to the small amount of poly-N-vinylacetamide added, and aggregates are formed. In addition, although the generation of streaks was not observed in the engraving part of the gravure roll, this was caused by agglomerates entering a minute depression (portion where the coating liquid was retained) existing in the engraving part. This is thought to be because it became difficult to observe the occurrence of streaks visually. This shows that this coating liquid cannot be applied to gravure coating.

Claims

A current collector for an electricity storage device in which a coating layer is formed on one or both sides of a sheet-like conductive substrate,
The coating layer includes a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer,
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
The content of the fluorine-free vinyl polymer in the coating layer is 0.099 to 5.0% by mass,
A current collector for an electricity storage device, wherein the content of the powdery carbon material in the coating layer is 15.0 to 65.0 mass%.
The current collector for an electricity storage device according to claim 1, wherein a weight per unit area of the coating layer per surface of the conductive substrate is 0.1 to 5.0 g / m 2 .
An electrode for a lithium ion secondary battery comprising the current collector for an electricity storage device according to claim 1 or 2.
A lithium ion secondary battery comprising the current collector for an electricity storage device according to claim 1 or 2.
A step of preparing a coating liquid in which a powdery carbon material, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer are dissolved or dispersed in a solvent;
A step of applying the prepared coating solution to one or both sides of a sheet-like conductive substrate, and a step of drying the applied coating solution;
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating solution is 2 to 15% by mass,
The mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 0.099 to 5.0 mass%. Yes,
The mass ratio of the powdery carbon material to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 15.0 to 65.0% by mass. A method for producing a current collector for an electricity storage device.
The method for producing a current collector for an electricity storage device according to claim 5, wherein the solvent is water or N-methyl-2-pyrrolidone.
A coating liquid containing a powdery carbon material in a solvent, a polymer containing vinylidene fluoride as a monomer unit, and a fluorine-free vinyl polymer,
The fluorine-free vinyl polymer is one selected from the group consisting of N-vinylacetamide and N-vinylacetamide derivatives, vinyl alcohol and vinyl alcohol derivatives, vinyl pyrrolidone and vinyl pyrrolidone derivatives, and vinyl acetate and vinyl acetate derivatives. Is a homopolymer having a monomer unit, or a copolymer containing one or more selected from the above group as a monomer unit,
The total content of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer in the coating solution is 2 to 15% by mass,
The mass ratio of the fluorine-free vinyl polymer to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 0.099 to 5.0 mass%. Yes,
The mass ratio of the powdery carbon material to the total mass of the powdery carbon material, the polymer containing vinylidene fluoride and the fluorine-free vinyl polymer is 15.0 to 65.0% by mass. A coating liquid for producing a current collector for an electricity storage device.
The coating solution for producing a current collector for an electricity storage device according to claim 7, wherein the solvent is water or N-methyl-2-pyrrolidone.