阅读说明：本技术 导电性碳材料分散液 (Conductive carbon material dispersion liquid ) 是由 畑中辰也 矢岛麻里 境田康志 于 2019-03-19 设计创作，主要内容包括：下述导电性碳材料分散液适于在锂离子二次电池等储能器件的电极集电体上所形成的底涂层的制作,该导电性碳材料分散液包含导电性碳材料、阳离子性分散剂和溶剂,不含阴离子性化合物,阳离子性分散剂例如为双氰胺/二亚乙基三胺缩合物、聚乙撑亚胺等不具有阴离子性官能团的阳离子性聚合物。(A conductive carbon material dispersion liquid containing a conductive carbon material, a cationic dispersant such as a dicyandiamide/diethylenetriamine condensate, a cationic polymer having no anionic functional group such as polyethyleneimine, and a solvent, and not containing an anionic compound is suitable for producing an undercoat layer formed on an electrode current collector of an energy storage device such as a lithium ion secondary battery.)

1. A conductive carbon material dispersion liquid is characterized by containing a conductive carbon material, a cationic dispersant having no anionic functional group, and a solvent, and being free of anionic compounds.

2. The conductive carbon material dispersion liquid according to claim 1, wherein the cationic dispersant contains 1 or 2 or more species selected from the group consisting of cationic polymers using dicyandiamide as a monomer, cationic polymers using diethylenetriamine as a monomer, cationic polymers using dicyandiamide and diethylenetriamine as monomers, and cationic polymers using ethyleneimine as a monomer.

3. The conductive carbon material dispersion liquid according to claim 2, wherein the cationic dispersant comprises a cationic polymer obtained by using ethyleneimine as a monomer.

4. The conductive carbon material dispersion liquid according to claim 2, wherein the cationic dispersant comprises a cationic polymer obtained by using dicyandiamide as a monomer.

5. The conductive carbon material dispersion liquid according to claim 2, wherein the cationic dispersant comprises a cationic polymer obtained by using diethylenetriamine as a monomer.

6. The conductive carbon material dispersion liquid according to claim 2, wherein the cationic dispersant comprises a cationic polymer obtained using dicyandiamide and diethylenetriamine as monomers.

7. The conductive carbon material dispersion liquid according to any one of claims 1 to 6, wherein the conductive carbon material comprises carbon nanotubes.

8. The conductive carbon material dispersion liquid according to any one of claims 1 to 7, wherein the solvent contains water.

9. The conductive carbon material dispersion liquid according to any one of claims 1 to 8, wherein the solid content is 20% by mass or less.

10. The conductive carbon material dispersion liquid according to claim 9, wherein the solid content is 10% by mass or less.

11. The conductive carbon material dispersion liquid according to claim 10, wherein the solid content is 5% by mass or less.

12. The conductive carbon material dispersion liquid according to any one of claims 1 to 11, which is used for forming an undercoat layer.

13. A conductive thin film obtained from the conductive carbon material dispersion liquid according to any one of claims 1 to 11.

14. The conductive film according to claim 13, wherein the weight per unit area is 5000mg/m²The following.

15. The conductive film according to claim 14, wherein the weight per unit area is 1000mg/m²The following.

16. The conductive film according to claim 15, wherein the weight per unit area is 500mg/m²The following.

17. The conductive film according to claim 16, wherein the weight per unit area is 300mg/m²The following.

18. A composite current collector for an electrode of an energy storage device, comprising the conductive thin film according to any one of claims 13 to 17.

19. An electrode for an energy storage device, comprising the composite current collector for an electrode of an energy storage device according to claim 18.

20. An energy storage device comprising an electrode for an energy storage device according to claim 19.

21. The energy storage device of claim 20, which is a lithium ion secondary battery.

Technical Field

The present invention relates to a conductive carbon material dispersion liquid.

Background

With the demand for reduction in size, weight, and functionality of portable electronic devices such as smartphones, digital cameras, and portable game machines, development of high-performance batteries has been actively performed in recent years, and the demand for rechargeable batteries that can be repeatedly used by charging has been greatly increased.

Among them, lithium ion secondary batteries are currently the most intensively developed because they have high energy density and high voltage and do not have memory effect during charge and discharge.

In addition, in recent years, electric vehicles have been actively developed in response to environmental problems, and secondary batteries as power sources thereof are increasingly required to have higher performance.

Further, the lithium ion secondary battery has the following structure: a positive electrode and a negative electrode capable of storing and discharging lithium and a separator interposed therebetween are housed in a container, and an electrolytic solution (a gel-like or all-solid-state electrolyte instead of a liquid electrolytic solution in the case of a lithium ion polymer secondary battery) is filled therein.

The positive electrode and the negative electrode are generally manufactured by applying a composition containing an active material capable of occluding and releasing lithium, a conductive material mainly composed of a carbon material, and a polymer binder onto a current collector such as a copper foil or an aluminum foil. The binder is used for binding an active material and a conductive material, and further binding them to a metal foil, and fluorine-based resins such as polyvinylidene fluoride (PVdF) which are soluble in N-methylpyrrolidone (NMP), and aqueous dispersions of olefin-based polymers are commercially available.

However, the above binder is insufficient in adhesion to the current collector, and causes peeling and falling off of a part of the active material or the conductive material from the current collector, a minute short circuit, and fluctuation in battery capacity in the production process such as cutting and winding of the electrode.

Further, there is a problem that, even after long-term use, the volume change of the electrode material layer due to the volume change caused by the swelling of the binder by the electrolyte solution and the lithium storage and release of the active material increases the contact resistance between the electrode material layer and the current collector, or the battery capacity deteriorates due to the separation and detachment of part of the active material and the conductive material from the current collector, and further there is a problem in terms of safety.

As an attempt to solve the above problems, a method has been developed in which an electrically conductive undercoat layer is provided between the current collector and the electrode material layer as a technique for reducing the resistance of the battery by improving the adhesion between the current collector and the electrode material layer and reducing the contact resistance.

For example, patent document 1 discloses a technique of disposing a conductive layer containing carbon as a conductive filler as an undercoat layer between a current collector and an electrode material layer, and patent documents 2 and 3 disclose the same technique, in which a composite current collector (hereinafter also referred to as a composite current collector) including an undercoat layer is used, whereby contact resistance between the current collector and the electrode material layer can be reduced, a decrease in capacity during high-rate discharge can be suppressed, and deterioration of a battery can be suppressed.

Further, patent documents 4 and 5 disclose an undercoat layer using carbon nanotubes (hereinafter also abbreviated as CNTs) as a conductive filler.

Among conductive carbon materials, CNTs used in patent documents 4 and 5 are conductive carbon materials having particularly excellent conductivity, but are insoluble in a solvent, and thus it is difficult to form a coating film. Therefore, in recent years, an example in which CNTs are dispersed using a dispersant has been reported (patent document 6).

On the other hand, the cationic polymer exhibits high adhesion force by strongly performing electrostatic interaction with the anionic polymer.

Patent document 7 reports an example of using a cationic polymer as a dispersant for carbon nanotubes, and in the technique of this document, a diallylamine-based cationic polymer, an anionic surfactant, and a nonionic surfactant must be used in combination.

In addition, in patent document 8, a dispersant having a cationic amine head is used, but the dispersant is a zwitterion and requires a second polymer component when further dispersing carbon nanotubes.

In the techniques of patent documents 7 and 8, since the number of required insulating components increases, there is a problem that the development of the conductivity expected for the CNT is hindered, and since the composition contains a cationic component and an anionic component, a strong electrostatic interaction with another anionic material cannot be expected in a neutralized state.

From these points of view, a technique capable of stably dispersing the conductive carbon material in the dispersion medium only with the cationic polymer is desired.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a conductive carbon material dispersion liquid using only a cationic polymer as a dispersant for a conductive carbon material.

Means for solving the problems

The present inventors have made extensive studies to achieve the above object and, as a result, have found a composition in which a conductive carbon material such as CNT can be dispersed using a dispersant containing a cationic polymer having no anionic functional group, and have completed the present invention.

Namely, the present invention provides:

1. a conductive carbon material dispersion liquid which is characterized by containing a conductive carbon material, a cationic dispersant having no anionic functional group, and a solvent, and being free of anionic compounds;

2.1A conductive carbon material dispersion liquid, wherein the cationic dispersant contains 1 or 2 or more species selected from the group consisting of cationic polymers using dicyandiamide as a monomer, cationic polymers using diethylenetriamine as a monomer, cationic polymers using dicyandiamide and diethylenetriamine as monomers, and cationic polymers using ethyleneimine as a monomer;

3.2 the conductive carbon material dispersion liquid according to any one of claims 3 to 2, wherein the cationic dispersant contains a cationic polymer obtained by using ethyleneimine as a monomer;

4.2 the conductive carbon material dispersion liquid according to any one of claims 4 to 2, wherein the cationic dispersant comprises a cationic polymer obtained by using dicyandiamide as a monomer;

5.2A conductive carbon material dispersion liquid, wherein the cationic dispersant comprises a cationic polymer obtained by using diethylenetriamine as a monomer;

6.2A conductive carbon material dispersion liquid, wherein the cationic dispersant comprises a cationic polymer obtained by using dicyandiamide and diethylenetriamine as monomers;

7.1 to 6, wherein the conductive carbon material comprises carbon nanotubes;

8.1 to 7, wherein the solvent contains water;

9.1 to 8, wherein the solid content is 20% by mass or less;

10.9A conductive carbon material dispersion liquid containing 10 mass% or less of solid matter;

11.10 the conductive carbon material dispersion liquid, wherein the solid content is 5 mass% or less;

12.1 to 11, which is used for forming an undercoat layer;

13. a conductive thin film obtained from the conductive carbon material dispersion liquid of any one of 1 to 11;

14.13 the electroconductive thin film, wherein the weight per unit area is 5000mg/m²The following;

15.14 the electroconductive thin film, wherein the weight per unit area is 1000mg/m²The following;

16.15 the electroconductive thin film, wherein the weight per unit area is 500mg/m²The following;

17.16 the conductive film, wherein the weight per unit area is 300mg/m²The following;

18. a composite current collector for an electrode of an energy storage device, comprising a conductive thin film of any one of 13 to 17;

19. an electrode for an energy storage device, comprising the composite current collector for an electrode of an energy storage device of 18;

20. an energy storage device including the electrode for an energy storage device of 19;

21.20, which is a lithium ion secondary battery.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a conductive carbon material such as CNT can be dispersed using only a cationic polymer as a dispersant.

The conductive carbon material dispersion is suitable for producing an undercoat layer formed on an electrode collector of an energy storage device such as a lithium ion secondary battery, and by using an electrode having an undercoat layer produced from the dispersion of the present invention, it is possible to provide a low-resistance energy storage device and a simple and efficient production method therefor.

Drawings

Fig. 1 is a schematic cross-sectional view of a carbon nanotube having a constricted portion used in the present invention.

Detailed Description

The present invention will be described in more detail below.

The conductive carbon material dispersion liquid according to the present invention contains a conductive carbon material, a cationic dispersant having no anionic functional group, and a solvent, and does not contain an anionic compound.

Specific examples of the conductive carbon material used in the dispersion liquid of the present invention can be appropriately selected from known carbon materials such as carbon black, ketjen black, acetylene black, carbon whiskers, Carbon Nanotubes (CNTs), carbon fibers, natural graphite, and artificial graphite, and in the present invention, a conductive carbon material containing carbon black and/or CNTs is particularly preferably used, and a conductive carbon material containing carbon black alone or CNT alone is more preferably used.

CNTs are generally produced by arc discharge, Chemical Vapor Deposition (CVD), laser ablation, and the like, and CNTs used in the present invention can be obtained by any method. The CNT includes a single-layer CNT (hereinafter abbreviated as SWCNT) in which 1 carbon film (graphene sheet) is wound in a cylindrical shape, a 2-layer CNT (hereinafter abbreviated as DWCNT) in which 2 graphene sheets are wound in a concentric shape, and a multi-layer CNT (hereinafter abbreviated as MWCNT) in which a plurality of graphene sheets are wound in a concentric shape. From the viewpoint of cost, multilayer CNTs having a diameter of 2nm or more are particularly preferable, and from the viewpoint of being thin-filmable, multilayer CNTs having a diameter of 500nm or less are particularly preferable, multilayer CNTs having a diameter of 100nm or less are more preferable, multilayer CNTs having a diameter of 50nm or less are even more preferable, and multilayer CNTs having a diameter of 30nm or less are most preferable. The diameter of the CNT can be measured by observing, for example, a thin film obtained by drying a product in which the CNT is dispersed in a solvent, with a transmission electron microscope.

In addition, when SWCNT, DWCNT, or MWCNT is produced by the above method, there are cases where catalyst metals such as nickel, iron, cobalt, and yttrium remain, and therefore purification for removing these impurities is necessary. For the removal of impurities, it is effective to perform ultrasonic treatment simultaneously with acid treatment using nitric acid, sulfuric acid, or the like. However, since the n-conjugated system constituting the CNT is broken by acid treatment with nitric acid, sulfuric acid, or the like, and there is a possibility that the original properties of the CNT are impaired, it is preferably purified and used under appropriate conditions.

In particular, as the CNT used in the present invention, it is preferable to use a CNT which is easily dispersed in a dispersion liquid in order to exert an effect of reducing the battery resistance when the dispersion liquid is used as a coating film to form an undercoat layer. Such CNTs are preferably those having a large number of crystal discontinuities that can be easily cut with small energy.

From such a viewpoint, the CNT used in the composition of the present invention preferably has a constricted portion. The CNT having the constricted portion has a parallel portion and a constricted portion having a tube outer diameter of 90% or less with respect to the tube outer diameter of the parallel portion in the wall of the CNT.

The constriction is a portion produced by changing the growth direction of the CNT, and therefore has a crystal discontinuity portion, which is a fracture-prone portion that can be easily cut with a small machine.

A schematic cross-sectional view of a CNT having a parallel portion 1 and a constricted portion 3 is shown in fig. 1.

The parallel portion 1 is a portion where the wall can be recognized as 2 parallel straight lines or 2 parallel curved lines as shown in fig. 1. In the parallel portion 1, the distance between the outer walls of the walls in the normal direction of the parallel lines is the tube outer diameter 2 of the parallel portion 1.

On the other hand, the constricted portion 3 is a portion whose both ends are connected to the parallel portion 1 and whose wall distance is closer to the parallel portion 1, and more specifically, a portion having a tube outer diameter 4 of 90% or less with respect to the tube outer diameter 2 of the parallel portion 1. The outside diameter 4 of the constricted portion 3 is the distance between the outer walls at the portion of the constricted portion 3 where the walls constituting the outer walls are closest to each other. As shown in fig. 1, a discontinuous crystalline portion exists in the numerous constricted portions 3.

The shape of the wall and the outer diameter of the CNT can be observed with a transmission electron microscope or the like. Specifically, a 0.5% dispersion of CNTs was prepared, the dispersion was placed on a sample stage and dried, and the constricted portion was confirmed by using an image photographed at 5 ten thousand times with a transmission electron microscope.

The CNT is prepared by preparing a 0.1% dispersion of CNT, placing the dispersion on a sample table to dry, dividing an image taken by a transmission electron microscope at 2 ten thousand times into regions of 100nm square, and when a region of 300 regions in which the proportion of CNT in the region of 100nm square is 10-80% is selected, the proportion of a site prone to break (the proportion of a site prone to break) in the entire area is determined from the proportion of a region of 300 regions in which at least 1 part of a constricted portion is present in 1 region. When the area occupied by CNTs in a region is 10% or less, the amount of CNTs present is too small, and thus measurement is difficult. In addition, when the area occupied by CNTs in a region is 80% or more, since the number of CNTs occupied in a region is increased, it is difficult to overlap CNTs and to distinguish parallel portions from constricted portions, and accurate measurement becomes difficult.

The CNT used in the present invention has a ratio of the easy-to-break site of 60% or more. When the proportion of the easily breakable portion is less than 60%, the CNT is difficult to disperse, and when excessive mechanical energy is applied to disperse the CNT, the crystal structure of the graphite mesh surface is broken, and the properties such as conductivity, which are the features of the CNT, are degraded. In order to obtain higher dispersibility, the ratio of the easily breakable portion is preferably 70% or more.

Specific examples of CNTs that can be used in the present invention include CNTs having a contracted structure disclosed in International publication No. 2016/076393 and Japanese patent application laid-open No. 2017-206413, TC series such as TC-2010, TC-2020 and TC-3210L, TC-1210LN (manufactured by Korea Industrial Co., Ltd.), CNT based on the super growth method (manufactured by national research and development Act., New energy and Industrial Technology Integrated development Act.), eDIPS-CNT (manufactured by national research and development Act., New energy and Industrial Technology Integrated development Act.), SWNT series ((manufactured by Nippon City Nano carbon Co., Ltd.) (trade name), VGCF series (manufactured by Showa electric engineering Co., Ltd.) (trade name), FloTube series (manufactured by CNano Technology Co., Ltd.) (trade name), AMC (manufactured by Yuyao Highun K., Baytubes (trade name; manufactured by Bayer corporation), GRAPHISTRENGTH (trade name; manufactured by アルケマ corporation), MWNT7 (trade name; manufactured by Gekko Kagaku Kogyo Co., Ltd.), ハイペリオン CNT (trade name; manufactured by Hypesprion Catalysis International Co., Ltd.), and the like.

In the conductive carbon material dispersion liquid of the present invention, a cationic dispersant having no anionic functional group is used as the dispersant. In the present invention, "having no anionic functional group" means a form of a salt (for example, hydrochloride salt of amine) containing a cation and a counter anion of a cationic dispersant, which has no anionic functional group in a molecule, that is, which does not have a zwitterionic structure.

The cationic dispersant is not particularly limited as long as it does not have an anionic functional group, and can be suitably selected from known cationic polymers not having an anionic functional group, and from the viewpoint of more excellent dispersibility of the carbon material, it preferably contains 1 or 2 or more species selected from among cationic polymers synthesized using dicyandiamide as a monomer, cationic polymers synthesized using diethylenetriamine as a monomer, cationic polymers synthesized using dicyandiamide and diethylenetriamine as monomers, and cationic polymers synthesized using ethyleneimine as a monomer, and more preferably contains 1 or 2 or more species selected from among cationic polymers synthesized using dicyandiamide and diethylenetriamine as monomers and cationic polymers synthesized using ethyleneimine as a monomer, more preferably, the resin composition contains 1 or 2 or more kinds selected from dicyandiamide-diethylenetriamine condensates and polyethyleneimines which are cationic polymers synthesized using ethyleneimines as monomers.

Further, each of the cationic polymers may be a copolymer using a monomer component other than the monomer components.

The cationic polymer can be synthesized by a known method, or a commercially available product can be used.

Examples of such commercially available products include ユニセンス series manufactured by センカ, エポミン (polyethyleneimine) SP-003, SP-006, SP-012, SP-018, SP-020, P-1000, ポリメント (aminoethylated acrylic polymers) NK-100PM, NM-200PM, NK-350, and NK-380 manufactured by Japanese catalyst.

As the ユニセンス series, ユニセンス KHP10P (dicyandiamide-diethylenetriamine condensate hydrochloride) can be preferably used.

In the present invention, the mixing ratio of the conductive carbon material such as CNT and the cationic dispersant is not particularly limited, and can be 1,000: 1-1: about 100.

The concentration of the dispersant in the dispersion is not particularly limited as long as it can disperse the conductive carbon material such as CNT in the solvent, and is preferably about 0.001 to 30% by mass, more preferably about 0.002 to 20% by mass in the dispersion.

Further, the concentration of the conductive carbon material such as CNT in the dispersion liquid varies depending on the weight per unit area of the intended conductive film (undercoat layer), required mechanical properties, electrical properties, thermal properties, and the like, and in the case of using CNT, as long as at least a part thereof can be dispersed in isolation, the concentration is arbitrary, and is preferably about 0.0001 to 30 mass%, more preferably about 0.001 to 20 mass%, and still more preferably about 0.001 to 10 mass% in the dispersion liquid.

The solvent is not particularly limited as long as it is a solvent conventionally used for preparation of a conductive composition, and examples thereof include water; ethers such as Tetrahydrofuran (THF), diethyl ether, and 1, 2-Dimethoxyethane (DME); halogenated hydrocarbons such as dichloromethane, chloroform, and 1, 2-dichloroethane; amides such as N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP); ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, isopropanol, n-butanol, t-butanol, and n-propanol; aliphatic hydrocarbons such as n-heptane, n-hexane, and cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and propylene glycol monomethyl ether; glycols such as ethylene glycol and propylene glycol. These solvents can be used alone in 1 or more than 2 kinds of mixed use.

In particular, water, NMP, DMF, THF, methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol are preferable in terms of the ratio of isolated dispersion of CNTs being increased. In addition, from the viewpoint of improving coatability, it is preferable to include methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol. In addition, water is preferably contained from the viewpoint of cost reduction. These solvents can be used alone in 1 kind or in a mixture of 2 or more kinds for the purpose of increasing the ratio of isolated dispersion, improving coatability and reducing cost. When a mixed solvent of water and an alcohol is used, the mixing ratio is not particularly limited, and the ratio of water: alcohol 1: 1-10: about 1.

In the conductive carbon material dispersion liquid of the present invention, a polymer that does not contain an anionic functional group and serves as a matrix can be added. Examples of the base polymer include fluorine-based resins such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer [ P (VDF-HFP) ], and vinylidene fluoride-chlorotrifluoroethylene copolymer [ P (VDF-CTFE) ]; polyolefin resins such as polyvinyl pyrrolidone, ethylene-propylene-diene terpolymer, PE (polyethylene), PP (polypropylene), EVA (ethylene-vinyl acetate copolymer), and EEA (ethylene-ethyl acrylate copolymer); polystyrene resins such AS PS (polystyrene), HIPS (high impact polystyrene), AS (acrylonitrile-styrene copolymer), ABS (acrylonitrile-butadiene-styrene copolymer), MS (methyl methacrylate-styrene copolymer), and styrene-butadiene rubber; a polycarbonate resin; vinyl chloride resin; a polyamide resin; a polyimide resin; (meth) acrylic resins such as PMMA (polymethyl methacrylate); polyester resins such as PET (polyethylene terephthalate), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, PLA (polylactic acid), poly-3-hydroxybutyric acid, polycaprolactone, polybutylene succinate, and polyethylene glycol succinate/adipate; a polyphenylene ether resin; a modified polyphenylene ether resin; a polyacetal resin; polysulfone resin; polyphenylene sulfide resin; a polyvinyl alcohol resin; polyglycolic acid; modified starch; cellulose acetate, carboxymethyl cellulose, cellulose triacetate; chitin, chitosan; thermoplastic resins such as lignin, polyaniline, and emeraldine base (emeraldine base) which is a semi-oxide thereof; a polythiophene; polypyrrole; a polyphenylene vinylene group; a polyphenylene group; conductive polymers such as polyacetylene, and further epoxy resins; a urethane acrylate; a phenolic resin; a melamine resin; urea resin; the conductive carbon material dispersion liquid of the present invention preferably uses water as a solvent, and therefore, as the matrix polymer, a water-soluble matrix polymer such as a water-soluble cellulose ether, polyvinyl alcohol, or polyethylene glycol is also preferable.

The base polymer can also be obtained as a commercially available product, and examples of such commercially available products include METOLOSESH series (hydroxypropyl methylcellulose, available from shin-Etsu chemical industries, Ltd.), METOLOSE SE series (hydroxyethyl methylcellulose, available from shin-Etsu chemical industries, Ltd.), JC-25 (completely saponified polyvinyl alcohol, available from Nippon vinegar ビ. ポバール, available from Nippon vinegar ビ. ポバール, available from JP-03 (partially saponified polyvinyl alcohol, available from Nippon vinegar ビ. ポバール, available from Nippon vinegar Co., Ltd.), and the like.

The content of the matrix polymer is not particularly limited, and is preferably about 0.0001 to 99% by mass, and more preferably about 0.001 to 90% by mass in the dispersion.

Further, the conductive carbon material dispersion liquid of the present invention may contain a crosslinking agent containing no anionic functional group. The crosslinking agent is preferably dissolved in the solvent used.

Examples of the crosslinking agent include ketones, alkyl halides, acrylamides, epoxy compounds, cyanamide compounds, ureas, acids, acid anhydrides, acid halides, compounds having a functional group such as an isothiocyanate group, an isocyanate group or an aldehyde group, compounds having a hydroxyl group (dehydration condensation), a mercapto group (disulfide bond), an ester group (claisen condensation), a silanol group (dehydration condensation), a vinyl group or an acryloyl group which are reactive with an amino group, and the like.

Specific examples of the crosslinking agent include polyfunctional acrylates, tetraalkoxysilanes, monomers or polymers having a blocked isocyanate group, and the like, which exhibit crosslinking reactivity in the presence of an acid catalyst.

Such crosslinking agents are also available as commercial products. Examples of commercially available products include a-9300 (Ethoxylated isocyanuric acid triacrylate, manufactured by shinkamura chemical industries, Ltd.), a-GLY-9E (Ethoxylated glycerol triacrylate (EO9mol), Ethoxylated glycerinat (EO9mol), manufactured by shinkamura chemical industries, Ltd.), a-TMMT (pentaerythritol tetraacrylate, manufactured by shinkamura chemical industries, Ltd.), tetraalkoxysilane (manufactured by tokyo chemical industries, Ltd.), tetraethoxysilane (manufactured by tokyo chemical industries, Ltd.), and polymers having blocked isocyanate groups such as エラストロン series E-37, H-3, H38, BAP, NEW BAP-15, C-52, F-29, W-11P, MF-9 and MF-25K (manufactured by first Industrial pharmaceutical Co., Ltd.), and the like.

The amount of these crosslinking agents to be added varies depending on the solvent to be used, the base material to be used, the desired viscosity, the desired shape of the film, and the like, and is 0.001 to 80% by mass, preferably 0.01 to 50% by mass, and more preferably 0.05 to 40% by mass based on the cationic dispersant.

As described above, the conductive carbon material dispersion liquid of the present invention does not contain an anionic compound having an anionic functional group. Therefore, even when a base polymer or a crosslinking agent is used, an anionic compound having an anionic functional group is not used.

The method for preparing the conductive carbon material dispersion liquid of the present invention is not particularly limited, and the conductive carbon material, the cationic dispersant, the solvent, and the matrix polymer, the crosslinking agent, and the like used as needed may be mixed in an arbitrary order to prepare the dispersion liquid.

In this case, the mixture is preferably subjected to a dispersion treatment, and the dispersion ratio of the conductive carbon material such as CNT can be further increased by this treatment. Examples of the dispersion treatment include mechanical treatment, wet treatment using a ball mill, a bead mill, a jet mill, or the like, and ultrasonic treatment using a bath type or a probe type ultrasonic instrument, and particularly, wet treatment using a jet mill and ultrasonic treatment are preferable.

The time of the dispersion treatment is arbitrary, and is preferably about 1 minute to 10 hours, more preferably about 5 minutes to 5 hours. In this case, heat treatment may be performed as necessary.

When an arbitrary component such as a matrix polymer is used, these may be added after preparing a mixture containing a cationic dispersant, a conductive carbon material and a solvent.

The solid content concentration of the conductive carbon material dispersion liquid in the present invention is not particularly limited, but considering the use for forming an undercoat layer, etc., it is preferably 20% by mass or less, more preferably 10% by mass or less, and still more preferably 5% by mass or less.

The lower limit is arbitrary, and from the viewpoint of practical use, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more.

The solid content is the total amount of components other than the solvent constituting the conductive carbon material dispersion liquid.

The conductive carbon material dispersion liquid described above is applied to a substrate, and dried naturally or by heating, thereby producing a conductive thin film. In this case, if the current collector of the energy storage device is used as the substrate, the conductive thin film to be produced can function as the undercoat layer.

The weight per unit area of the conductive thin film is not particularly limited, but is preferably 5000mg/m in consideration of reduction in internal resistance of the device when used as an undercoat layer²Below, more preferably 1000mg/m²Hereinafter, 500mg/m is more preferable²Below, more preferably 300mg/m²The following.

On the other hand, the lower limit of the weight per unit area is not particularly limited, and the function of the undercoat layer is secured, if consideration is given toThe battery having excellent characteristics can be obtained with good performance, and the concentration of the electrolyte is preferably 1mg/m²Above, more preferably 5mg/m²The above, more preferably 10mg/m²Above, more preferably 15mg/m²The above.

The weight per unit area of the conductive thin film is the area (m) of the conductive thin film²) When the conductive thin film is formed in a pattern, the ratio of the mass (mg) of the conductive thin film(s) in (e) is the area of the conductive thin film alone and does not include the area of the substrate exposed between the conductive thin films formed in the pattern.

The mass of the conductive thin film can be calculated, for example, by cutting a test piece of an appropriate size from a substrate on which the conductive thin film is formed, measuring the mass W0 thereof, then measuring the mass W1 of the conductive thin film peeled from the test piece, and calculating from the difference (W0 to W1), or by measuring the mass W2 of the substrate in advance, then measuring the mass W3 of the substrate on which the conductive thin film is formed, and calculating from the difference (W3 to W2).

Examples of the method for peeling off the conductive film include a method in which the conductive film is immersed in a solvent in which the conductive film dissolves or swells, and a method in which the conductive film is wiped off with a cloth or the like.

In addition, the thickness of the conductive thin film is preferably 1nm to 10 μm, more preferably 1nm to 1 μm, and still more preferably 1 to 500nm, in view of reducing the internal resistance of the resulting device.

The thickness of the conductive thin film can be determined from the exposed portion of the conductive thin film in the cross section by, for example, cutting a test piece of an appropriate size from a substrate on which the conductive thin film is formed, tearing the test piece by hand, and exposing the cross section, and observing the test piece with a microscope such as a Scanning Electron Microscope (SEM).

The weight per unit area and the film thickness can be adjusted by a known method. For example, when the conductive thin film is formed by coating, the solid content concentration of the conductive carbon material dispersion liquid, the number of coating times, the gap between the coating liquid inlets of the coater, and the like can be changed to adjust the thickness.

When the weight per unit area and the film thickness are to be increased, the solid content concentration is increased, the number of applications is increased, or the gap is increased. When the weight per unit area and the film thickness are to be reduced, the solid content concentration is reduced, the number of applications is reduced, or the gap is reduced.

As the current collector, a current collector conventionally used as a current collector of an electrode for an energy storage device can be used. For example, copper, aluminum, titanium, stainless steel, nickel, gold, silver, an alloy thereof, a carbon material, a metal oxide, a conductive polymer, or the like can be used, and when welding such as ultrasonic welding is applied to produce an electrode structure, a metal foil made of copper, aluminum, titanium, stainless steel, or an alloy thereof is preferably used.

The thickness of the current collector is not particularly limited, but in the present invention, it is preferably 1 to 100 μm.

Examples of the method for applying the conductive carbon material dispersion include spin coating, dip coating, flow coating, ink jet coating, casting, spray coating, bar coating, gravure coating, slit coating, roll coating, offset printing (フレキソ printing), transfer printing, brush coating, blade coating, air knife coating, and die coating.

The temperature for the heat drying is also arbitrary, and is preferably about 50 to 200 ℃, more preferably about 80 to 150 ℃.

The electrode for an energy storage device of the present invention can be produced by forming an electrode material layer on the conductive thin film (undercoat layer).

Examples of the energy storage device in the present invention include various energy storage devices such as an electric double layer capacitor, a lithium secondary battery, a lithium ion secondary battery, a proton polymer battery, a nickel metal hydride battery, an aluminum solid capacitor, an electrolytic capacitor, and a lead storage battery, and the undercoat foil of the present invention can be suitably used particularly for an electric double layer capacitor and a lithium ion secondary battery.

Among them, various active materials that have been conventionally used in electrodes for energy storage devices can be used as the active material.

For example, in the case of a lithium secondary battery or a lithium ion secondary battery, a chalcogen compound capable of adsorbing and desorbing lithium ions, a chalcogen compound containing lithium ions, a polyanion-based compound, a sulfur simple substance, a compound thereof, and the like can be used as the positive electrode active material.

Examples of such a chalcogen compound capable of adsorbing and desorbing lithium ions include FeS₂、TiS₂、MoS₂、V₂O₆、V₆O₁₃、MnO₂And the like.

Examples of the lithium ion-containing chalcogenide compound include LiCoO₂、LiMnO₂、LiMn₂O₄、LiMo₂O₄、LiV₃O₈、LiNiO₂、Li_xNi_yM_1-yO₂(wherein M represents at least one metal element selected from the group consisting of Co, Mn, Ti, Cr, V, Al, Sn, Pb and Zn, x is 0.05 ≦ 1.10, and y is 0.5 ≦ 1.0).

The polyanionic compound includes, for example, LiFePO₄And the like.

Examples of the sulfur compound include Li₂S, erythrosine, and the like.

On the other hand, as the negative electrode active material constituting the negative electrode, a simple substance of at least one element selected from the group consisting of elements belonging to groups 4 to 15 of the periodic table, an alkali metal alloy, a lithium ion occluding/releasing substance, an oxide, a sulfide, a nitride, or a carbon material capable of reversibly occluding/releasing a lithium ion can be used.

Examples of the alkali metal include Li, Na, and K, and examples of the alkali metal alloy include Li-Al, Li-Mg, Li-Al-Ni, Na-Hg, and Na-Zn.

Examples of the simple substance of at least one element selected from the group consisting of elements belonging to groups 4 to 15 of the periodic table, which adsorbs/desorbs lithium ions, include silicon, tin, aluminum, zinc, and arsenic.

Examples of the oxide include oxidation of stannic oxideSubstance (SnSiO)₃) Lithium bismuth oxide (Li)₃BiO₄) Lithium zinc oxide (Li)₂ZnO₂) Lithium titanium oxide (Li)₄Ti₅O₁₂) Titanium oxide, and the like.

Examples of the sulfide include lithium iron sulfide (Li)_xFeS₂(0 ≦ x ≦ 3)), lithium copper sulfide (Li)_xCuS (0 ≦ x ≦ 3)), and the like.

The nitride includes a transition metal nitride containing lithium, specifically, Li_xM_yN (M ≦ Co, Ni, Cu, 0 ≦ x ≦ 3, 0 ≦ y ≦ 0.5), lithium iron nitride (Li ≦ x ≦ 3), lithium iron nitride (Li ≦ y ≦ 0.5)₃FeN₄) And the like.

Examples of the carbon material capable of reversibly occluding and releasing lithium ions include graphite, carbon black, coke, glassy carbon, carbon fiber, carbon nanotube, and a sintered body thereof.

In the case of an electric double layer capacitor, a carbonaceous material can be used as the active material.

Examples of the carbonaceous material include activated carbon, and for example, activated carbon obtained by carbonizing a phenol resin and then activating the carbonized phenol resin is exemplified.

The electrode mixture layer can be formed by applying an electrode paste prepared by mixing the above-described active material, the binder polymer described below, and a solvent used as needed, onto the undercoat layer, and drying the electrode paste naturally or by heating.

The binder polymer can be appropriately selected from known materials and used, and examples thereof include conductive polymers such as polyvinylidene fluoride (PVdF), polyvinyl pyrrolidone, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer [ P (VDF-HFP) ], vinylidene fluoride-chlorotrifluoroethylene copolymer [ P (VDF-CTFE) ], polyvinyl alcohol, polyimide, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyaniline, and the like.

The amount of the binder polymer to be added is preferably 0.1 to 20 parts by mass, and particularly preferably 1 to 10 parts by mass, based on 100 parts by mass of the active material.

The solvent may be suitably selected from the solvents exemplified in the dispersion liquid, and NMP is preferable in the case of a water-insoluble binder such as PVdF, and water is preferable in the case of a water-soluble binder such as PAA.

Further, the electrode paste may contain a conductive material. Examples of the conductive material include carbon black, ketjen black, acetylene black, carbon whiskers, carbon fibers, natural graphite, artificial graphite, titanium oxide, ruthenium oxide, aluminum, nickel, and the like.

Examples of the method for applying the electrode paste include the same methods as those for the dispersion liquid described above.

The temperature at the time of heating and drying is also arbitrary, and is preferably about 50 to 400 ℃, and more preferably about 80 to 150 ℃.

The electrodes may be pressed as desired. The pressing method can be a commonly used method, and particularly, a press method and a roll method are preferable. The pressing pressure in the roll-to-roll method is not particularly limited, but is preferably 0.2 to 3 tons/cm.

The energy storage device according to the present invention includes the above-described electrode for an energy storage device, and more specifically, includes at least a pair of positive and negative electrodes, a spacer and an electrolyte interposed between the positive and negative electrodes, and at least one of the positive and negative electrodes is formed of the above-described electrode for an energy storage device.

Since this energy storage device has a feature in that the electrode for an energy storage device is used as an electrode, a spacer, an electrolyte, and the like, which are other device constituent members, can be appropriately selected from known materials and used.

Examples of the spacer include a cellulose spacer and a polyolefin spacer.

The electrolyte may be any of a liquid and a solid, and may be any of an aqueous system and a nonaqueous system.

Examples of the nonaqueous electrolyte include a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous organic solvent.

Examples of the electrolyte salt include lithium salts such as lithium tetrafluoroborate, lithium hexafluorophosphate, lithium perchlorate and lithium trifluoromethanesulfonate; quaternary ammonium salts such as tetramethylammonium hexafluorophosphate, tetraethylammonium hexafluorophosphate, tetrapropylammonium hexafluorophosphate, methyltriethylammonium hexafluorophosphate, tetraethylammonium tetrafluoroborate and tetraethylammonium perchlorate, and lithium imides such as lithium bis (trifluoromethanesulfonyl) imide and lithium bis (fluorosulfonyl) imide.

Examples of the nonaqueous organic solvent include alkylene carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate; dialkyl carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; nitriles such as acetonitrile, and amides such as dimethylformamide.

The form of the energy storage device is not particularly limited, and conventionally known cells of various forms such as a cylindrical form, a flat wound rectangular form, a laminated rectangular form, a coin form, a flat wound laminated form, and a laminated form can be used.

When the present invention is applied to a coin type, the electrode for an energy storage device of the present invention may be punched into a predetermined disk shape and used.

For example, a lithium ion secondary battery can be manufactured by providing one electrode on a cap of a coin cell to which a gasket and a spacer are welded, overlapping the spacer of the same shape impregnated with an electrolyte thereon, further overlapping the electrode for an energy storage device of the present invention with an electrode laminate layer from above, placing a case and a gasket, and sealing with a coin cell battery caulking machine.

In the case of application to a laminate type, an electrode structure may be used in which a portion (welded portion) of an electrode having an electrode material layer formed on a part or the entire surface of the undercoat layer, where the electrode material layer is not formed, is welded to the metal pole piece. Furthermore, when the portions where the undercoat layer is formed and the electrode material layer is not formed are welded, the weight per unit area of the undercoat layer on the average surface of the current collector is preferably 0.1g/m²Hereinafter, more preferably 0.09g/m²It is more preferably less than 0.05g/m²。

In this case, the electrode constituting the electrode structure may be one sheet or a plurality of sheets, and in general, a plurality of sheets are used for both the positive and negative electrodes.

In this case, the separator is preferably interposed between the positive electrode and the negative electrode.

The metal pole piece may be welded to the welded portion of the outermost electrode of the plurality of electrodes, or may be welded to the welded portion of any adjacent 2 electrodes of the plurality of electrodes with the metal pole piece interposed therebetween.

The material of the metal pole piece is not particularly limited as long as it is a material generally used in an energy storage device, and examples thereof include metals such as nickel, aluminum, titanium, and copper; alloys such as stainless steel, nickel alloy, aluminum alloy, titanium alloy, and copper alloy, and the like, preferably include at least one metal selected from aluminum, copper, and nickel in consideration of welding efficiency.

The shape of the metal pole piece is preferably foil-shaped, and the thickness thereof is preferably about 0.05 to 1 mm.

As the welding method, a known method for welding between metals can be used, and specific examples thereof include TIG welding, spot welding, laser welding, ultrasonic welding, and the like, and it is preferable to join the electrode and the metal pole piece by ultrasonic welding.

Examples of the ultrasonic welding method include a method in which a plurality of electrodes are disposed between an anvil and a horn, a metal pole piece is disposed at a welded portion, and ultrasonic waves are applied to the electrodes to weld the electrodes together; firstly welding the electrodes, and then welding the metal pole pieces.

In the present invention, in all methods, not only the metal pole piece and the electrode are welded at the welding portion, but also the plurality of electrodes are ultrasonically welded to each other.

The pressure, frequency, output, processing time, and the like at the time of welding are not particularly limited, and may be appropriately set in consideration of the material used, the presence or absence of an undercoat layer, the weight per unit area, and the like.

The electrode structure produced as described above is housed in a laminate bag, and after the electrolyte solution is injected, a laminate unit is obtained by heat sealing.