Electroconductive particles, electroconductive material, connection structure, and current collector

Abstract

The present invention provides electroconductive particles which, when used for electrical connection between pieces of metal foil: 1) can increase the dispersibility of the electroconductive particles; 2) can suppress breakage of the metal foil; 3) can reduce initial connection resistance; and 4) can enhance conduction reliability.　The electroconductive particles according to the present invention are used for electrically connecting between pieces of metal foil. The particles each comprise a base material particle and an electroconductive part disposed on the surface of the base material particle. When the electroconductive particles are compressed by 20%, the compressive elastic modulus is 1000 N / mm2 to 25000 N / mm2.

Description

Conductive particles, conductive materials, connection structures, and current collectors

[0001] The present invention relates to conductive particles used for electrically connecting metal foils and uses thereof. The present invention also relates to a conductive material, a connection structure, and a current collector using the conductive particles.

[0002] In recent years, the automotive industry has been promoting the development of electric vehicles (BEVs) and hybrid electric vehicles (HEVs) from the viewpoint of environmental protection. As secondary batteries for driving motors used in electric vehicles (BEVs) and hybrid electric vehicles (HEVs), lithium-ion secondary batteries, which can achieve high energy density and power density, have been attracting attention.

[0003] In order to achieve even higher energy density and power density in lithium ion secondary batteries, bipolar batteries in which a positive electrode active material and a negative electrode active material are respectively disposed on both sides of a plurality of current collectors are being considered.

[0004] Patent Document 1 listed below discloses a bipolar battery including a current collector, an electrode (positive electrode) electrically coupled to one surface of the current collector, an electrode (negative electrode) electrically coupled to the other surface of the current collector, and an electrolyte layer disposed between the electrodes, the current collector containing a polymer material. Patent Document 1 also describes that the current collector contains conductive particles, and that metal particles or carbon particles are used as the conductive particles.

[0005] Patent Document 2 below discloses a conductive laminate sheet including a metal layer and a conductive resin layer laminated on at least one side of the metal layer. In the conductive laminate sheet, the conductive resin layer contains a resin, a conductive material, and polyvinylpyrrolidone, and the content ratio of the polyvinylpyrrolidone per 100 parts by mass of the conductive material is 100 parts by mass or more and 300 parts by mass or less. Patent Document 2 also describes that carbon black is preferred as the conductive material.

[0006] JP 2006-190649 A JP 2014-167849 A

[0007] Current collectors such as those described in Patent Documents 1 and 2 can increase output density to a certain extent. However, in connection structures and current collectors using metal particles or carbon particles as conductive particles (conductive materials) as described in Patent Documents 1 and 2, the metal foil in the current collector may break, and the metal particles or carbon particles in the connection portion (conductive resin layer) may settle or aggregate. This may prevent the metal particles or carbon particles from being uniformly dispersed. As a result, the initial connection resistance between the metal foil of the resulting connection structure and current collector may be high, and the connection resistance may be high (resulting in low conductivity reliability) after a conductivity reliability test under a high-temperature, high-humidity environment.

[0008] An object of the present invention is to provide conductive particles and uses thereof that, when used for electrical connection between metal foils, can 1) improve the dispersibility of the conductive particles, 2) suppress damage to the metal foil, 3) reduce initial connection resistance, and 4) improve conduction reliability. Another object of the present invention is to provide a conductive material, a connection structure, and a current collector that use the conductive particles.

[0009] This specification discloses the following conductive particles and their uses, conductive materials, connection structures, and current collectors.

[0010] Item 1. A conductive particle used to electrically connect metal foils, comprising a base particle and a conductive portion disposed on the surface of the base particle, wherein the compressive modulus of elasticity when the conductive particle is compressed by 20% is 1000 N / mm ２ More than 25000N / mm ２ Conductive particles, which are:

[0011] Item 2. The conductive particles according to Item 1, wherein the base particles are resin particles.

[0012] Item 3. The conductive particles according to Item 1 or 2, wherein the specific gravity of the conductive particles is 1.0 or more and 4.5 or less.

[0013] Item 4. The conductive particles according to any one of Items 1 to 3, wherein the conductive particles have a volume resistivity of 0.0030 Ω·m or less.

[0014] Item 5. The conductive particle according to any one of Items 1 to 4, wherein the conductive portion contains nickel.

[0015] Item 6. The conductive particle according to any one of Items 1 to 5, wherein the conductive portion contains a rust inhibitor.

[0016] Item 7. The conductive particles according to any one of Items 1 to 6, wherein the base particle has an average circularity of 0.85 or more and 1.00 or less.

[0017] Item 8. The conductive particles according to any one of Items 1 to 7, wherein the variation in circularity of the base particle is 0.04 or less.

[0018] Item 9. A conductive material comprising the conductive particles according to any one of items 1 to 8 and a binder resin.

[0019] Item 10. A connection structure comprising a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, wherein a material of the connection portion contains the conductive particles according to any one of Items 1 to 8, and the first metal foil and the second metal foil are electrically connected by the conductive particles.

[0020] Item 11. The connection structure according to Item 10, wherein the thickness of each of the first metal foil and the second metal foil is 100 μm or less.

[0021] Item 12. The connection structure according to Item 10 or 11, wherein the first metal foil and the second metal foil each contain gold, silver, copper, tin, aluminum, nickel, titanium, or stainless steel.

[0022] Item 13. A current collector for use in a battery, comprising a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, wherein a material of the connection portion contains the conductive particles according to any one of Items 1 to 8, and the first metal foil and the second metal foil are electrically connected by the conductive particles.

[0023] Item 14. The current collector according to Item 13, which is used in a bipolar battery.

[0024] Item 15. The current collector according to Item 13 or 14, wherein the current collector is wound into a roll.

[0025] Item 16. Use of the conductive particles according to any one of Items 1 to 8 in a current collector included in a battery including a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, for electrically connecting the first metal foil and the second metal foil.

[0026] Item 17. The use according to Item 16, wherein the battery is a bipolar battery.

[0027] The conductive particles according to the present invention are conductive particles used for electrically connecting metal foils. The conductive particles according to the present invention include a base particle and a conductive portion disposed on the surface of the base particle. The conductive particles according to the present invention have a compressive modulus of elasticity of 1000 N / mm when compressed by 20%. ２ More than 25000N / mm ２ The conductive particles according to the present invention have the above-described configuration, and therefore, when used for electrical connection between metal foils, 1) the dispersibility of the conductive particles can be improved, 2) damage to the metal foil can be suppressed, 3) the initial connection resistance can be reduced, and 4) the conduction reliability can be improved.

[0028] Fig. 1 is a cross-sectional view schematically showing a conductive particle according to a first embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing a conductive particle according to a second embodiment of the present invention. Fig. 3 is a cross-sectional view schematically showing a conductive particle according to a third embodiment of the present invention. Fig. 4 is a cross-sectional view schematically showing a connection structure (current collector) using the conductive particle shown in Fig. 1. Fig. 5 is a cross-sectional view schematically showing a bipolar battery using the connection structure (current collector) shown in Fig. 4.

[0029] The present invention will be described in detail below.

[0030] (Conductive Particles) The conductive particles according to the present invention are conductive particles used for electrically connecting metal foils. The conductive particles according to the present invention include a base particle and a conductive portion disposed on the surface of the base particle. The conductive particles according to the present invention have a compressive modulus of elasticity of 1000 N / mm when compressed by 20%. ２ More than 25000N / mm２ The following is the result.

[0031] When conventional conductive particles (particularly metal particles or carbon particles) are used for electrical connection between metal foils, the metal foil may be torn or the metal particles or carbon particles may not be sufficiently dispersed in the connection. Specifically, when metal particles are used for electrical connection between metal foils, the metal foil may be damaged due to the hardness of the metal particles, or the metal particles may settle due to their high specific gravity, preventing uniform dispersion in the connection. Furthermore, when carbon particles are used for electrical connection between metal foils, the carbon particles may aggregate and prevent uniform dispersion in the connection. In these cases, the initial connection resistance between the metal foils of the resulting connection structure and current collector may be high, or the connection resistance may be high (resulting in low conductivity reliability) after a conductivity reliability test under a high-temperature, high-humidity environment.

[0032] The conductive particles according to the present invention have the above-mentioned configuration, and therefore, when used for electrical connection between metal foils, 1) the dispersibility of the conductive particles can be improved, 2) damage to the metal foil can be suppressed, 3) the initial connection resistance can be reduced, and 4) the conductivity reliability can be improved.

[0033] The compressive elastic modulus (20% K value) when the conductive particles are compressed by 20% is 1000 N / mm ２ More than 25000N / mm ２ The 20% K value of the conductive particles is preferably 1200 N / mm ２ More preferably, 1500 N / mm ２ More preferably, 1600 N / mm ２ More preferably, 1700 N / mm ２ or more, most preferably 1800 N / mm ２ or more, preferably 23,000 N / mm ２ or less, more preferably 22000 N / mm ２ or less, more preferably 21000 N / mm ２ Below, particularly preferably 20,000 N / mm ２or less. If the 20% K value of the conductive particles is equal to or greater than the lower limit, when metal foils are connected using the conductive particles, the dispersibility of the conductive particles can be further improved, the contact area between the conductive particles and the metal foil becomes appropriate, the initial connection resistance can be further reduced, and the conduction reliability can be further improved. If the 20% K value of the conductive particles is equal to or less than the upper limit, when metal foils are connected using the conductive particles, the breakdown of the metal foil can be more effectively suppressed, the initial connection resistance can be further reduced, and the conduction reliability can be further improved.

[0034] The compressive elastic modulus (10% K value) when the conductive particles are compressed by 10% is preferably 100 N / mm ２ More preferably, 150 N / mm ２ More preferably, 200 N / mm ２ More preferably, 250 N / mm ２ or more, preferably 30,000 N / mm ２ or less, more preferably 28000 N / mm ２ or less, more preferably 26000 N / mm ２ Below, particularly preferably 24000 N / mm ２ When the 10% K value of the conductive particles is equal to or greater than the lower limit, the conductive particles can be in adequate contact with the metal foil when connecting metal foils using the conductive particles, thereby further reducing the initial connection resistance. When the 10% K value of the conductive particles is equal to or less than the upper limit, the destruction of the metal foil can be more effectively suppressed when connecting metal foils using the conductive particles.

[0035] The compressive elastic modulus (30% K value) when the conductive particles are compressed by 30% is preferably 200 N / mm ２ More preferably, 300 N / mm ２ More preferably, 400 N / mm ２ More preferably, 500 N / mm ２ or more, preferably 40,000 N / mm ２ or less, more preferably 35,000 N / mm ２ or less, more preferably 30,000 N / mm ２Below, particularly preferably 25000 N / mm ２ When the 30% K value of the conductive particles is equal to or greater than the lower limit, the contact area between the conductive particles and the metal foil becomes appropriate when metal foils are connected using the conductive particles, and the initial connection resistance can be further reduced. When the 30% K value of the conductive particles is equal to or less than the upper limit, the damage to the metal foil can be more effectively suppressed when metal foils are connected using the conductive particles.

[0036] In the conductive particles, the ratio of the compressive modulus when compressed by 10% (10% K value) to the compressive modulus when compressed by 20% (20% K value) (10% K value / 20% K value) is preferably 1.00 or more, more preferably 1.05 or more, even more preferably 1.10 or more, and is preferably 1.20 or less, more preferably 1.15 or less, even more preferably 1.13 or less. When the ratio (10% K value / 20% K value) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the effects of the present invention can be more effectively exhibited.

[0037] In the conductive particles, the ratio of the compressive modulus when compressed 20% (20% K value) to the compressive modulus when compressed 30% (30% K value) (20% K value / 30% K value) is preferably 1.00 or more, more preferably 1.05 or more, even more preferably 1.10 or more, and is preferably 1.60 or less, more preferably 1.50 or less, and even more preferably 1.40 or less. When the ratio (20% K value / 30% K value) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the effects of the present invention can be more effectively exhibited.

[0038] The 10% K value, 20% K value, and 30% K value of the conductive particles can be measured as follows.

[0039] Using a micro-compression tester, the conductive particles are compressed with a smooth cylindrical indenter end face (diameter 50 μm, made of diamond) under conditions of 25°C and a maximum test load of 90 mN for 30 seconds. The load value (N) and compression displacement (mm) at this time are measured. From the obtained measured values, the compressive elastic modulus can be calculated using the following formula. As the micro-compression tester, for example, a Fischerscope H-100 manufactured by Fischer can be used.

[0040] K value (N / mm ２ ) = (3 / 2 １／２ ) F.S. －３／２ ・R －１／２ F: Load value (N) when the conductive particle is compressed and deformed by 10%, 20%, or 30%; S: Compression displacement (mm) when the conductive particle is compressed and deformed by 10%, 20%, or 30%; R: Radius of the conductive particle (mm).

[0041] Methods for controlling the 10% K value, the 20% K value, and the 30% K value within preferred ranges include the following: A method for adjusting physical properties by adjusting the monomer type, monomer molecular weight, crosslinking agent, polymerization temperature, polymerization time, etc. of the base particle A method for adjusting hardness by adjusting the metal type, alloy type, thickness, etc. of the conductive portion

[0042] From the viewpoint of further improving the effects of the present invention, the compression recovery rate of the conductive particles is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more, and is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

[0043] The compression recovery rate can be measured as follows.

[0044] Conductive particles are scattered on a sample stage. For each scattered conductive particle, a micro-compression tester is used, and a load (reversed load value) is applied at 25°C toward the center of the conductive particle with the smooth end face of a cylindrical indenter (diameter 100 μm, made of diamond) until the conductive particle is compressed and deformed by 40%. The load is then released to the origin load value (0.40 mN). The load-compression displacement during this period is measured, and the compression recovery rate can be calculated using the following formula. The loading rate is 0.33 mN / sec. As the micro-compression tester, for example, a Fischerscope H-100 manufactured by Fischer is used.

[0045] Compression recovery rate (%) = [L2 / L1] x 100 L1: Compression displacement from the load value for origin when applying a load to the reverse load value L2: Unloading displacement from the reverse load value when releasing the load to the load value for origin

[0046] The specific gravity of the conductive particles is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and preferably 4.5 or less, more preferably 3.5 or less, even more preferably 3.0 or less. When the specific gravity of the conductive particles is above the lower limit, the conductive particles do not float in the connection part, and the conductive particles can be appropriately dispersed. When the specific gravity of the conductive particles is below the upper limit, the conductive particles are prevented from settling in the connection part, and the conductive particles can be uniformly dispersed by a simple operation.

[0047] The specific gravity of the conductive particles can be measured using a specific gravity measuring device, such as the "AccuPic Series" manufactured by Shimadzu Corporation.

[0048] The volume resistivity of the conductive particles is preferably 0.0030 Ω·m or less, more preferably 0.0020 Ω·m or less, and even more preferably 0.0015 Ω·m or less. When the volume resistivity of the conductive particles is below the upper limit, even a small amount of conductive particles can provide good electrical connection between metal foils, thereby suppressing excessive heat generation due to resistance. The lower limit of the volume resistivity of the conductive particles is not particularly limited. The volume resistivity of the conductive particles may be 0.0001 Ω·m or more, 0.0003 Ω·m or more, or 0.0005 Ω·m or more.

[0049] The volume resistivity of the conductive particles can be measured using, for example, a powder resistivity measurement system, such as the "Powder Resistivity Measurement System MCP Series" manufactured by Mitsubishi Chemical Analytech Co., Ltd.

[0050] The particle diameter of the conductive particles is preferably 0.5 μm or more, more preferably 1.0 μm or more, and preferably 500 μm or less, more preferably 300 μm or less, even more preferably 100 μm or less, and particularly preferably 30 μm or less. When the particle diameter of the conductive particles is above the above lower limit and below the above upper limit, when metal foils are connected using the conductive particles, the contact area between the conductive particles and the metal foil is sufficiently large, and agglomerated conductive particles are less likely to be formed when forming the conductive part. In addition, the gap between the metal foils connected via the conductive particles is not too large, and the conductive part is less likely to peel off from the surface of the base particle. In addition, when the particle diameter of the conductive particles is above the above lower limit and below the above upper limit, the conductive particles can be suitably used for conductive material applications.

[0051] The particle diameter of the conductive particles is preferably an average particle diameter, and more preferably a number average particle diameter. The particle diameter of the conductive particles can be determined, for example, by observing 50 random conductive particles with an electron microscope or optical microscope and calculating the average particle diameter of each conductive particle, or by performing laser diffraction particle size distribution measurement. In observation with an electron microscope or optical microscope, the particle diameter of each conductive particle is determined as the particle diameter in equivalent circle diameter. In observation with an electron microscope or optical microscope, the average particle diameter in equivalent circle diameter of 50 random conductive particles is approximately equal to the average particle diameter in equivalent sphere diameter. In laser diffraction particle size distribution measurement, the particle diameter of each conductive particle is determined as the particle diameter in equivalent sphere diameter. The particle diameter of the conductive particles is preferably calculated by laser diffraction particle size distribution measurement.

[0052] The conductive particles are preferably used for electrical connection between metal foils. The conductive particles are conductive particles for connecting metal foils. The conductive particles are preferably not used in anisotropic conductive materials.

[0053] The present invention will be specifically described below with reference to the drawings.

[0054] FIG. 1 is a cross-sectional view schematically showing a conductive particle according to a first embodiment of the present invention.

[0055] The conductive particle 1 shown in Fig. 1 has a base particle 2 and a conductive portion 3. The conductive portion 3 is disposed on the surface of the base particle 2. In the first embodiment, the conductive portion 3 is in contact with the surface of the base particle 2. The conductive particle 1 is a coated particle in which the surface of the base particle 2 is coated with the conductive portion 3. In the conductive particle 1, the conductive portion 3 is a single-layer conductive portion (conductive layer).

[0056] Unlike conductive particles 11 and 21 described later, conductive particle 1 does not have a core substance. Conductive particle 1 does not have protrusions on its surface, and there are no protrusions on the outer surface of conductive portion 3. Conductive particle 1 is spherical.

[0057] Thus, the conductive particles according to the present invention may not have protrusions on the surface, may not have protrusions on the outer surface of the conductive portion, and may be spherical.

[0058] FIG. 2 is a cross-sectional view schematically showing a conductive particle according to a second embodiment of the present invention.

[0059] 2 includes a base particle 2, a conductive portion 12, and a plurality of core materials 13. The conductive portion 12 is disposed on the surface of the base particle 2 so as to be in contact with the base particle 2. In the conductive particle 11, the conductive portion 12 is a single-layer conductive portion (conductive layer).

[0060] The conductive particle 11 has a plurality of protrusions 11a on its surface. The conductive portion 12 has a plurality of protrusions 12a on its outer surface. A plurality of core materials 13 are arranged on the surface of the base particle 2. The plurality of core materials 13 are embedded in the conductive portion 12. The core materials 13 are arranged inside the protrusions 11a, 12a. The conductive portion 12 covers the plurality of core materials 13. The outer surface of the conductive portion 12 is raised by the plurality of core materials 13, forming the protrusions 11a, 12a.

[0061] FIG. 3 is a cross-sectional view schematically showing a conductive particle according to a third embodiment of the present invention.

[0062] 3 includes a base particle 2, a conductive portion 22, and a plurality of core materials 13. The conductive portion 22 as a whole includes a first conductive portion 22A on the base particle 2 side and a second conductive portion 22B on the opposite side to the base particle 2 side.

[0063] The only difference between the conductive particle 11 and the conductive particle 21 is the conductive portion. That is, the conductive particle 11 has a single-layer conductive portion 12, whereas the conductive particle 21 has a two-layer structure of a first conductive portion 22A and a second conductive portion 22B. The first conductive portion 22A and the second conductive portion 22B are formed as separate conductive portions.

[0064] The first conductive portion 22A is disposed on the surface of the base particle 2. The first conductive portion 22A is disposed between the base particle 2 and the second conductive portion 22B. The first conductive portion 22A is in contact with the base particle 2. Therefore, the first conductive portion 22A is disposed on the surface of the base particle 2, and the second conductive portion 22B is disposed on the surface of the first conductive portion 22A. The conductive particle 21 has a plurality of protrusions 21a on its surface. The conductive portion 22 has a plurality of protrusions 22a on its outer surface. The first conductive portion 22A has a plurality of protrusions 22Aa on its outer surface. The second conductive portion 22B has a plurality of protrusions 22Ba on its outer surface. In the conductive particle 21, the conductive portion 22 is a two-layer conductive portion (conductive layer).

[0065] The conductive particles are preferably used in current collectors (use of the conductive particles in current collectors). The conductive particles are preferably used in batteries (use of the conductive particles in batteries). The conductive particles are preferably used in current collectors included in batteries (use of the conductive particles in current collectors included in batteries). The conductive particles are preferably used in bipolar batteries (use of the conductive particles in bipolar batteries) and more preferably used in bipolar batteries for automobiles (use of the conductive particles in bipolar batteries). The conductive particles are preferably used in current collectors included in batteries, particularly preferably used in current collectors included in bipolar batteries, and most preferably used in current collectors included in bipolar batteries for automobiles. In these preferred embodiments, the current collector is preferably a current collector included in a battery including a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil. The conductive particles are preferably used to electrically connect the first metal foil and the second metal foil (use of the conductive particles to electrically connect the first metal foil and the second metal foil).

[0066] Other details of the conductive particles will be described below. In the following description, "(meth)acrylic" means either or both of "acrylic" and "methacrylic", and "(meth)acrylate" means either or both of "acrylate" and "methacrylate".

[0067] [Base particle] Examples of the base particle include resin particles, inorganic particles excluding metal particles, organic-inorganic hybrid particles, and metal particles. The base particle may be a core-shell particle having a core and a shell disposed on the surface of the core. The core may be an organic core. The shell may be an inorganic shell. In order to obtain better effects of the present invention, the base particle is preferably a resin particle or an organic-inorganic hybrid particle, and more preferably a resin particle.

[0068] The base particles are preferably resin particles formed from a resin. When electrically connecting metal foils using the conductive particles, the conductive particles are placed on a first metal foil, and then a second metal foil is laminated on the surface of the conductive particles opposite the first metal foil, thereby compressing the conductive particles. If the base particles are resin particles, the conductive particles are easily deformed during lamination, increasing the contact area between the conductive particles and the metal foil. This can further reduce the initial connection resistance between the metal foils, and can further reduce the connection resistance after a continuity test under a high-temperature, high-humidity environment (further increasing the continuity reliability).

[0069] As the resin material of the resin particles, various organic substances can be suitably used.As the resin material of the resin particles, can be enumerated: polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene, polybutadiene and other polyolefin resins; acrylic resins such as polymethyl methacrylate and polymethyl acrylate; polyalkylene terephthalate, polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, phenol resin, melamine resin, benzoguanamine resin, urea resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamideimide, polyetheretherketone, polyethersulfone, and the polymer obtained by polymerizing one or more of various polymerizable monomers having ethylenic unsaturated groups. Since the hardness of the base particle can be easily controlled within a suitable range, it is preferable that the resin for forming the resin particles is a polymer obtained by polymerizing one or more polymerizable monomers having multiple ethylenically unsaturated groups.

[0070] When the resin particles are obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, the polymerizable monomer having an ethylenically unsaturated group may be a non-crosslinkable monomer or a crosslinkable monomer.

[0071] Examples of the non-crosslinkable monomer include styrene-based monomers such as styrene and α-methylstyrene; carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. alkyl (meth)acrylate compounds such as methyl (meth)acrylate; oxygen atom-containing (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate, and glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; and halogen-containing monomers such as trifluoromethyl (meth)acrylate, pentafluoroethyl (meth)acrylate, vinyl chloride, vinyl fluoride, and chlorostyrene.

[0072] Examples of the crosslinkable monomer include tetramethylolmethane tetra(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol tri(meth)acrylate, glycerol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, and (poly)propylene glycol di(meth)acrylate. Examples of suitable monomers include polyfunctional (meth)acrylate compounds such as pyrene glycol di(meth)acrylate, (poly)tetramethylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate; and silane-containing monomers such as triallyl (iso)cyanurate, triallyl trimellitate, divinylbenzene, diallyl phthalate, diallyl acrylamide, diallyl ether, γ-(meth)acryloxypropyltrimethoxysilane, trimethoxysilylstyrene, and vinyltrimethoxysilane.

[0073] The resin particles can be obtained by polymerizing the polymerizable monomer having an ethylenically unsaturated group by a known method, such as a suspension polymerization method in the presence of a radical polymerization initiator, or a method in which non-crosslinked seed particles are used to swell and polymerize the monomer together with the radical polymerization initiator.

[0074] When the base particle is an inorganic particle other than a metal particle or an organic-inorganic hybrid particle, the inorganic material of the base particle can be silica, carbon black, etc. The inorganic material is preferably not a metal. The particles formed by silica are not particularly limited, but can be, for example, particles obtained by hydrolyzing a silicon compound having two or more hydrolyzable alkoxysilyl groups to form crosslinked polymer particles, and then optionally baking the particles. The organic-inorganic hybrid particles can be, for example, organic-inorganic hybrid particles formed by crosslinked alkoxysilyl polymer and acrylic resin.

[0075] When the base particles are metal particles, examples of the metal particles include silver, copper, nickel, silicon, gold, titanium, etc. However, the base particles are preferably not metal particles, and are preferably not copper particles.

[0076] The material of the base particle preferably contains a crosslinkable monomer. In this case, the effects of the present invention can be more effectively exhibited. In order to more effectively exhibit the effects of the present invention, the crosslinkable monomer preferably contains divinylbenzene, polytetramethylene glycol diacrylate, or vinyltrimethoxysilane, and more preferably is divinylbenzene, polytetramethylene glycol diacrylate, or vinyltrimethoxysilane.

[0077] The total content of the crosslinkable monomers in 100% by weight of the material of the base particle is preferably 3% by weight or more, more preferably 5% by weight or more, even more preferably 10% by weight or more, particularly preferably 80% by weight or more, and is preferably 100% by weight or less, more preferably 95% by weight or less, and even more preferably 90% by weight or less. When the content of the crosslinkable monomers is equal to or more than the above lower limit and equal to or less than the above upper limit, the effects of the present invention can be more effectively exhibited.

[0078] The compressive modulus of elasticity (10% K value) when the base particle is compressed by 10% is preferably 100 N / mm ２ More preferably, 150 N / mm ２ More preferably, 200 N / mm ２ More preferably, 250 N / mm ２ When the 10% K value of the base particle is equal to or greater than the lower limit, the hardness of the resulting conductive particles can be improved, and when metal foils are connected using the conductive particles, the contact area between the conductive particles and the metal foil becomes appropriate, thereby further reducing the initial connection resistance. The 10% K value of the base particle is preferably 40,000 N / mm ２ or less, more preferably 35,000 N / mm ２ or less, more preferably 30,000 N / mm ２ Below, particularly preferably 25000 N / mm ２ or less. If the 10% K value of the base particle is the above upper limit or less, when metal foils are connected using the obtained conductive particles, the contact area between the conductive particles and the metal foil becomes large, so that the initial connection resistance between the metal foils can be further reduced, and the connection resistance after a continuity test under a high-temperature, high-humidity environment can be further reduced (conductivity reliability can be further increased). The range of the 10% K value of the base particle can be set by appropriately selecting the above lower limit and upper limit.

[0079] The compressive modulus of elasticity (20% K value) when the base particle is compressed by 20% is preferably 200 N / mm ２ More preferably, 400 N / mm ２ More preferably, 600 N / mm ２ More preferably, 800 N / mm２ When the 20% K value of the base particle is equal to or greater than the lower limit, the hardness of the resulting conductive particles can be improved, and when metal foils are connected using the conductive particles, the contact area between the conductive particles and the metal foil becomes appropriate, thereby further reducing the initial connection resistance. The 20% K value of the base particle is preferably 40,000 N / mm ２ or less, more preferably 35,000 N / mm ２ or less, more preferably 30,000 N / mm ２ Below, particularly preferably 25000 N / mm ２ or less. If the 20% K value of the base particle is the above upper limit or less, when metal foils are connected using the obtained conductive particles, the contact area between the conductive particles and the metal foil becomes large, so that the initial connection resistance between the metal foils can be further reduced, and the connection resistance after a conductivity test in a high-temperature, high-humidity environment can be further reduced (conductivity reliability can be further increased). The range of the 20% K value of the base particle can be set by appropriately selecting the above lower limit and upper limit.

[0080] The compressive elastic modulus value (30% K value) when the base particle is compressed by 30% is preferably 300 N / mm ２ More preferably, 500 N / mm ２ More preferably, 700 N / mm ２ More preferably, 900 N / mm ２ When the 30% K value of the base particle is equal to or greater than the lower limit, the hardness of the resulting conductive particles can be improved, and when metal foils are connected using the conductive particles, the contact area between the conductive particles and the metal foil becomes appropriate, thereby further reducing the initial connection resistance. The 30% K value of the base particle is preferably 40,000 N / mm ２ or less, more preferably 35,000 N / mm ２ or less, more preferably 30,000 N / mm ２ Below, particularly preferably 25000 N / mm ２or less. If the 30% K value of the base particle is the above upper limit or less, when metal foils are connected using the obtained conductive particles, the contact area between the conductive particles and the metal foil becomes large, so that the initial connection resistance between the metal foils can be further reduced, and the connection resistance after a conductivity test under a high-temperature, high-humidity environment can be further reduced (conductivity reliability can be further increased). The range of the 30% K value of the base particle can be set by appropriately selecting the above lower limit and upper limit.

[0081] The particle diameter of the base particle is preferably 0.1 μm or more, more preferably 1.0 μm or more, even more preferably 1.5 μm or more, particularly preferably 2.0 μm or more. The particle diameter of the base particle is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 50 μm or less, even more preferably 30 μm or less, particularly preferably 10 μm or less, and most preferably 5.0 μm or less. When the particle diameter of the base particle is above the lower limit, when metal foils are connected using the obtained conductive particles, the contact area between the conductive particles and the metal foil is increased, so that the initial connection resistance between the metal foils can be further reduced, and the connection resistance after a conductivity test under a high-temperature and high-humidity environment can be further reduced (conductivity reliability can be further improved). Furthermore, when a conductive portion is formed on the surface of the base particle by electroless plating, aggregation is less likely to occur, and aggregated conductive particles are less likely to be formed. When the particle diameter of the base particle is below the upper limit, the conductive particles are easily compressed sufficiently, the connection resistance between the metal foils is further reduced, and the gap between the metal foils is further reduced.

[0082] The particle diameter of the base particles refers to the number average particle diameter. The particle diameter of the base particles is determined using a particle size distribution measuring device or the like. The particle diameter of the base particles is preferably determined by observing 50 random base particles with an electron microscope or optical microscope and calculating the average value. When observed with an electron microscope or optical microscope, the particle diameter of each base particle is determined as the particle diameter in equivalent circle diameter. When observed with an electron microscope or optical microscope, the average particle diameter in equivalent circle diameter of 50 random base particles is approximately equal to the average particle diameter in equivalent sphere diameter. When observed with a particle size distribution measuring device, the particle diameter of each base particle is determined as the particle diameter in equivalent sphere diameter. The particle diameter of the base particles is preferably calculated using a particle size distribution measuring device. When measuring the particle diameter of the base particles in the conductive particles, it can be measured, for example, as follows.

[0083] The conductive particles were added to Kulzer's Technovit 4000 so that the content was 30% by weight, and dispersed to prepare an embedding resin for conductive particle inspection. An ion milling device (Hitachi High-Technologies Corporation's IM4000) was used to cut out a cross section of the conductive particles dispersed in the embedding resin, passing through the vicinity of the center of the base particle. Then, using a field emission scanning electron microscope (FE-SEM Hitachi High-Technologies Corporation's S-4800) and an EDX device (HORIBA's X-MaxN80), the image magnification was set to 6000x, and 50 conductive particles were randomly selected. The base particle of each conductive particle was observed, and SEM images and element mapping images were obtained. The particle diameter of the base particle in each conductive particle was measured, and the arithmetic average was used to determine the particle diameter of the base particle.

[0084] The average circularity of the base particles is preferably 0.85 or more, more preferably 0.89 or more, even more preferably 0.90 or more, particularly preferably 0.91 or more, and preferably 1.00 or less. When the average circularity of the base particles is equal to or more than the above lower limit and equal to or less than the above upper limit, the effects of the present invention can be more effectively exhibited.

[0085] The average circularity of the base particles can be determined by determining the circularity of a plurality of base particles using the method described below and averaging the obtained circularity values. Among the element mapping images obtained by the method for measuring the average particle diameter of the base particles described above, a mapping image of the main elements constituting the base particles is prepared. The mapping image of the main elements is analyzed using image processing software Image J Fiji (open source software, version information ImageJ 2.14.0 / 1.54f, Java 1.8.0_322 (64-bit)). The analysis procedure is, for example, as follows. 1) Duplicate, 2) Subtract Background, 3) Auto Threshold, 4) Fill Holes, 5) Shape Smoothing, 6) Open, 7) Watershed, 8) Analyze Particles. In each step, 2) in Subtract Background, set Rolling Ball Radius to an appropriate value according to the size of the particles in the image, 3) in Auto Threshold, set Method to Otsu, 5) in Shape Smoothing, set relative_proportion_fds to 8, 6) in Open, set iterations to 1 count, and 8) in Analyze Particles, set size to an appropriate value according to the size of the particles in the image. The analysis calculates the area, perimeter, circularity, etc. of the particles. The circularity is calculated using the following formula:

[0086] Circularity = 4π × (area) ÷ (perimeter) ２

[0087] Methods for increasing the average circularity of the base particles include the following: 1) A method for producing base particles with an appropriate stirring force (such as a method for suppressing division and aggregation during production of base particles), 2) A method for producing base particles in an appropriate interfacial environment (such as a method for appropriately selecting a hydrophilic material and a hydrophobic material), and 3) A method for increasing the swelling ratio during production of base particles (such as a method for solidifying particles after sufficient swelling).

[0088] The variation in circularity of the base particle is preferably 0 or more, preferably 0.05 or less, more preferably 0.04 or less, and even more preferably 0.03 or less. When the variation in circularity of the base particle is equal to or more than the above lower limit and equal to or less than the above upper limit, the effects of the present invention can be more effectively exhibited.

[0089] The variation in circularity of the base particles is the standard deviation of the circularity, and is calculated by the following formula.

[0090]

[0091] Methods for decreasing the circularity of the base particles include the methods mentioned above for increasing the average circularity of the base particles.

[0092] [Conductive Part] The metal for forming the conductive part is not particularly limited. Examples of the metal include gold, silver, palladium, copper, platinum, zinc, iron, tin, lead, ruthenium, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, thallium, germanium, cadmium, silicon, and alloys thereof. The metal may be tin-doped indium oxide (ITO) or solder. When connecting metal foils using conductive particles, from the viewpoint of further reducing the initial connection resistance and further improving the conduction reliability, the metal is preferably tin, nickel, palladium, copper, silver, gold, or an alloy containing tin, and more preferably nickel.

[0093] As in the conductive particles 1 and 11 shown in FIGS. 1 and 2, the conductive portion may be formed of a single layer. As in the conductive particle 21 shown in FIG. 3, the conductive portion may be formed of multiple layers. The conductive portion may have a single-layer structure or a laminated structure of two or more layers. When the conductive portion is formed of multiple layers, the outermost layer is preferably a gold layer, a silver layer, a nickel layer, a palladium layer, a ruthenium layer, a tin layer, or a copper layer, and more preferably a gold layer, a silver layer, or a nickel layer. When the outermost layer is one of these preferred conductive layers, when metal foils are connected using the conductive particles, the initial connection resistance can be further reduced and the conduction reliability can be further improved. Furthermore, when the outermost layer is a precious metal layer, corrosion resistance is further improved.

[0094] The method for forming the conductive portion on the surface of the base particle is not particularly limited. Examples of the method for forming the conductive portion include electroless plating, electroplating, physical vapor deposition, and coating the surface of the base particle with a metal powder or a paste containing a metal powder and a binder. Since the formation of the conductive portion is simple, the method for forming the conductive portion is preferably electroless plating. Examples of the physical vapor deposition method include vacuum deposition, ion plating, and ion sputtering.

[0095] The thickness of the conductive part (thickness of the entire conductive part) is preferably 10 nm or more, more preferably 100 nm or more, even more preferably 120 nm or more, and preferably 1000 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, particularly preferably 250 nm or less, and most preferably 200 nm or less. The thickness of the conductive part is the thickness of the entire conductive layer when the conductive part is multilayered. When the thickness of the conductive part is equal to or greater than the above lower limit and equal to or less than the above upper limit, sufficient conductivity is obtained, and the conductive particles do not become too hard, so that the conductive particles deform sufficiently when connecting between metal foils.

[0096] When the conductive portion is formed of multiple layers, the thickness of the outermost conductive layer is preferably 1 nm or more, more preferably 10 nm or more, and preferably 500 nm or less, more preferably 200 nm or less. When the thickness of the outermost conductive layer is equal to or greater than the lower limit and equal to or less than the upper limit, corrosion resistance is sufficiently increased and the connection resistance between the metal foils is further reduced. Furthermore, when the outermost layer is a gold layer, the thinner the gold layer, the lower the cost.

[0097] The thickness of the conductive portion can be measured by observing the cross section of the conductive particle using, for example, a transmission electron microscope (TEM).

[0098] From the viewpoint of effectively increasing conductivity, the conductive portion preferably contains nickel. From the viewpoint of effectively increasing conductivity, the conductive particles preferably have a conductive portion containing nickel. The nickel content of 100% by weight of the nickel-containing conductive portion is preferably 50% by weight or more, more preferably 65% ​​by weight or more, even more preferably 70% by weight or more, even more preferably 75% by weight or more, even more preferably 80% by weight or more, particularly preferably 85% by weight or more, and most preferably 90% by weight or more. The nickel content of 100% by weight of the nickel-containing conductive portion is preferably 100% by weight (total amount) or less, and may be 99% by weight or less, or may be 95% by weight or less. When the nickel content is above the lower limit, the connection resistance between the metal foils is further reduced. Furthermore, when there is little oxide film on the surface of the metal foil or the conductive portion, the higher the nickel content, the lower the connection resistance between the metal foils tends to be. The range of the nickel content of 100% by weight of the nickel-containing conductive portion can be set by appropriately selecting the lower limit and the upper limit.

[0099] The metal content of the conductive portion can be measured using various known analytical methods. Examples of methods for measuring the metal content of the conductive portion include absorption spectrometry and spectral analysis. In the absorption spectrometry, a flame absorption spectrophotometer, an electric heating furnace absorption spectrophotometer, etc. can be used. Examples of the spectral analysis include plasma emission spectrometry and plasma ion source mass spectrometry.

[0100] The average content of metals contained in the conductive portion can be measured using, for example, an ICP optical emission analyzer. Examples of commercially available ICP optical emission analyzers include the "ICP optical emission analyzer" manufactured by HORIBA.

[0101] The conductive portion may contain phosphorus or boron in addition to nickel. The conductive portion may also contain a metal other than nickel. When the conductive portion contains multiple metals, the multiple metals may be alloyed.

[0102] In 100% by weight of the conductive portion containing nickel and phosphorus or boron, the content of phosphorus or boron is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and preferably 10% by weight or less, more preferably 5% by weight or less. When the content of phosphorus or boron is equal to or more than the above lower limit and equal to or less than the above upper limit, when used for electrical connection between metal foils, the initial connection resistance can be further reduced and the conduction reliability can be further improved.

[0103] From the viewpoint of further enhancing the reliability of conduction when used for electrical connection between metal foils, the conductive portion preferably contains a rust inhibitor. From the viewpoint of further enhancing the reliability of conduction when used for electrical connection between metal foils, the conductive portion preferably has been subjected to rust prevention treatment.

[0104] Examples of the rust inhibitor include sulfonic acid-based rust inhibitors, carboxylic acid-based rust inhibitors, and phosphate ester-based rust inhibitors. The rust inhibitors may be used alone or in combination of two or more.

[0105] From the viewpoint of further improving the reliability of conduction when used for electrical connection between metal foils, the rust inhibitor preferably contains a sulfonic acid-based rust inhibitor or a phosphate ester-based rust inhibitor, and more preferably contains a phosphate ester-based rust inhibitor. From the viewpoint of further improving the reliability of conduction when used for electrical connection between metal foils, the conductive portion is preferably treated for rust prevention with a sulfonic acid-based rust inhibitor or a phosphate ester-based rust inhibitor, and more preferably treated for rust prevention with a phosphate ester-based rust inhibitor.

[0106] [Core Material] From the viewpoint of further reducing the connection resistance and further increasing the conduction reliability, it is preferable that the conductive particles have a plurality of protrusions on the outer surface of the conductive portion. Furthermore, it is preferable that the conductive particles have a plurality of core materials that raise the outer surface of the conductive portion so as to form a plurality of the protrusions within the conductive portion. The conductive particles do not need to have protrusions on the outer surface of the conductive layer.

[0107] By embedding the core material in the conductive part, it is easy to form a plurality of protrusions on the outer surface of the conductive part, although it is not necessary to use a core material to form protrusions on the surface of the conductive particle and the surface of the conductive part.

[0108] Examples of methods for forming the protrusions include the following: A method in which a core substance is attached to the surface of a base particle, and then a conductive portion is formed by electroless plating. A method in which a conductive portion is formed on the surface of a base particle by electroless plating, and then a core substance is attached, and then a conductive portion is formed by electroless plating. A method in which a core substance is added during the process of forming a conductive portion on the surface of a base particle by electroless plating.

[0109] Examples of the material for the core substance include conductive and non-conductive substances. Examples of the conductive substance include conductive non-metals such as metals, metal oxides, and graphite, and conductive polymers. Examples of the conductive polymer include polyacetylene. Examples of the non-conductive substance include silica, alumina, tungsten carbide, titanium oxide, barium titanate, and zirconia. As the metal for the core substance, any of the metals listed as the materials for the conductive material can be used as appropriate.

[0110] Examples of materials for the core substance include barium titanate (Mohs hardness 4.5), nickel (Mohs hardness 5), silica (silicon dioxide, Mohs hardness 6-7), titanium oxide (Mohs hardness 7), zirconia (Mohs hardness 8-9), alumina (Mohs hardness 9), tungsten carbide (Mohs hardness 9), and diamond (Mohs hardness 10). The inorganic particles are preferably nickel, silica, titanium oxide, zirconia, alumina, tungsten carbide, or diamond, and more preferably silica, titanium oxide, zirconia, alumina, tungsten carbide, or diamond. The inorganic particles are further preferably titanium oxide, zirconia, alumina, tungsten carbide, or diamond, and particularly preferably zirconia, alumina, tungsten carbide, or diamond. The Mohs hardness of the core substance material is preferably 4 or higher, more preferably 6 or higher, even more preferably 7 or higher, and particularly preferably 7.5 or higher. When the Mohs hardness of the core material is equal to or higher than the lower limit, the 10% K value, 20% K value, and 30% K value of the conductive particles can be easily controlled within suitable ranges.

[0111] The shape of the core material is not particularly limited. The core material is preferably in the form of a mass. Examples of the core material include a particulate mass, an aggregate mass formed by aggregating a plurality of microparticles, and an amorphous mass.

[0112] The average particle size of the core material is preferably 0.001 μm or more, more preferably 0.05 μm or more, and is preferably 0.9 μm or less, more preferably 0.2 μm or less. When the average particle size of the core material is equal to or greater than the lower limit and equal to or less than the upper limit, the connection resistance between the metal foils is effectively reduced.

[0113] The average particle size of the core material is preferably a number average particle size, which can be determined by observing 50 random core materials under an electron microscope or an optical microscope and calculating the average value.

[0114] The number of the protrusions per conductive particle is preferably 3 or more, more preferably 5 or more. The upper limit of the number of the protrusions is not particularly limited. The upper limit of the number of the protrusions can be appropriately selected taking into account the particle diameter of the conductive particles, etc.

[0115] From the viewpoint of further reducing the initial connection resistance and further increasing the electrical conductivity reliability when connecting metal foils using conductive particles, the surface area of ​​the portion where the protrusions are located is preferably 10% or more, more preferably 30% or more, and preferably 95% or less, more preferably 90% or less, of the total surface area (100%) of the conductive particles.

[0116] The average height of the plurality of protrusions is preferably 0.001 μm or more, more preferably 0.05 μm or more, and is preferably 0.9 μm or less, more preferably 0.5 μm or less. When the average height of the protrusions is equal to or greater than the lower limit and equal to or less than the upper limit, the connection resistance between the metal foils is effectively reduced.

[0117] [Insulating material] The conductive particles may or may not include an insulating material disposed on the surface of the conductive portion. From the viewpoint of more effectively exhibiting the effects of the present invention, it is preferable that the conductive particles do not include an insulating material.

[0118] Examples of the insulating material include polyolefins, (meth)acrylate polymers, (meth)acrylate copolymers, block polymers, thermoplastic resins, crosslinked thermoplastic resins, thermosetting resins, and water-soluble resins.

[0119] (Conductive Material) The conductive material according to the present invention includes the conductive particles described above and a binder resin. The conductive particles are preferably dispersed in the binder resin and used as a conductive material. The conductive material is preferably a conductive material for connecting metal foils. The conductive particles and the conductive material are preferably used for electrical connection between metal foils. The conductive particles and the conductive material are preferably used for electrical connection between metal foils of a connection structure and a current collector, respectively. The conductive material is different from an anisotropic conductive material.

[0120] Preferably, the conductive material does not contain conductive particles having a particle diameter of 2.0 to 5.0 times the average particle diameter of the conductive particles, or contains 0.1 wt% or less of conductive particles having a particle diameter of 2.0 to 5.0 times the average particle diameter of the conductive particles, relative to 100 wt% of the conductive particles in the conductive material. In this case, when connecting metal foils using the conductive material, the initial connection resistance can be further reduced, and the conduction reliability can be further improved.

[0121] The content of conductive particles having a particle diameter of 2.0 to 5.0 times the average particle diameter of the conductive particles, based on 100% by weight of the conductive particles in the conductive material, is preferably 0.1% by weight or less, more preferably 0.01% by weight or less, even more preferably 0.001% by weight or less, and most preferably 0% by weight. Most preferably, the conductive material does not contain conductive particles having a particle diameter of 2.0 to 5.0 times the average particle diameter of the conductive particles. In these cases, when metal foils are connected using the conductive material, the initial connection resistance can be further reduced and the conductivity reliability can be further improved.

[0122] The binder resin is not particularly limited. The binder resin preferably contains a thermoplastic component (thermoplastic compound) or a curable component, and more preferably contains a curable component. Examples of the curable component include a photocurable component and a thermosetting component. The photocurable component preferably contains a photocurable compound and a photopolymerization initiator. The thermosetting component preferably contains a thermosetting compound and a thermosetting agent. Examples of the binder resin include vinyl resins, thermoplastic resins, curable resins, thermoplastic block copolymers, and elastomers. Only one type of the binder resin may be used, or two or more types may be used in combination.

[0123] Examples of the vinyl resin include vinyl acetate resin, acrylic resin, and styrene resin. Examples of the thermoplastic resin include polyolefin resin, ethylene-vinyl acetate copolymer, and polyamide resin. Examples of the curable resin include epoxy resin, urethane resin, polyimide resin, and unsaturated polyester resin. The curable resin may be a room temperature curable resin, a thermosetting resin, a photocurable resin, or a moisture curable resin. Examples of the thermoplastic block copolymer include a styrene-butadiene-styrene block copolymer, a styrene-isoprene-styrene block copolymer, a hydrogenated styrene-butadiene-styrene block copolymer, and a hydrogenated styrene-isoprene-styrene block copolymer. Examples of the elastomer include a styrene-butadiene copolymer rubber and an acrylonitrile-styrene block copolymer rubber.

[0124] The conductive material and the binder resin preferably contain a thermoplastic component or a thermosetting component. The conductive material and the binder resin may contain a thermoplastic component or a thermosetting component. The conductive material and the binder resin preferably contain a thermosetting component. The thermosetting component preferably contains a heat-curable curable compound and a heat curing agent. The heat curing agent is preferably a thermal cationic curing initiator. The heat-curable curable compound and the heat curing agent are used in an appropriate blend ratio so that the binder resin cures. If the binder resin contains a thermal cationic curing initiator, acid is likely to be contained in the cured product. However, by using the conductive particles according to the present invention, when connecting metal foils using a conductive material, the initial connection resistance can be further reduced and the conductivity reliability can be further improved.

[0125] The conductive material may contain various additives such as a filler, an extender, a softener, a plasticizer, a polymerization catalyst, a curing catalyst, a colorant, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a lubricant, an antistatic agent, and a flame retardant.

[0126] The conductive material can be used as a conductive paste, a conductive film, or the like. When the conductive material is a conductive film, a film not containing conductive particles may be laminated on a conductive film containing conductive particles. The conductive paste is preferably a conductive paste for connecting metal foils. The conductive paste is different from an anisotropic conductive paste. The conductive film is preferably a conductive film for connecting metal foils. The conductive film is different from an anisotropic conductive film.

[0127] The content of the binder resin in 100% by weight of the conductive material is preferably 10% by weight or more, more preferably 30% by weight or more, even more preferably 50% by weight or more, particularly preferably 70% by weight or more, and is preferably 99.99% by weight or less, more preferably 99.9% by weight or less. When the content of the binder resin is equal to or more than the lower limit and equal to or less than the upper limit, the conductive particles are efficiently arranged between the metal foils, and the electrical conductivity reliability between the metal foils is further improved.

[0128] The content of the conductive particles in 100% by weight of the conductive material is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and is preferably 80% by weight or less, more preferably 60% by weight or less, even more preferably 40% by weight or less, particularly preferably 20% by weight or less, and most preferably 10% by weight or less. When the content of the conductive particles is equal to or more than the lower limit and equal to or less than the upper limit, the electrical conductivity reliability between the metal foils is further improved.

[0129] (Connection Structure) A connection structure can be obtained by connecting metal foils using the conductive particles or a conductive material containing the conductive particles and a binder resin.

[0130] The connection structure according to the present invention comprises a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, the material of the connection portion containing the conductive particles described above. In the connection structure, the first metal foil and the second metal foil are electrically connected by the conductive particles. Because the connection structure according to the present invention has the above configuration, 1) the dispersibility of the conductive particles in the connection portion can be improved, 2) damage to the metal foil can be suppressed, 3) initial connection resistance can be reduced, and 4) conduction reliability can be improved.

[0131] The connection structure is preferably used as a current collector. The connection structure is preferably used in a battery. The connection structure is preferably used in a bipolar battery, and more preferably used in a bipolar battery for an automobile. The connection structure is preferably used as a current collector included in a battery, particularly preferably used as a current collector included in a bipolar battery, and most preferably used as a current collector included in a bipolar battery for an automobile.

[0132] FIG. 4 is a cross-sectional view that schematically shows a connection structure (current collector) that uses the conductive particles shown in FIG.

[0133] The connection structure (current collector) 51 shown in Figure 4 includes a first metal foil 52, a second metal foil 53, and a connection portion 54 connecting the first metal foil 52 and the second metal foil 53. The connection portion 54 is formed by curing a connection portion material containing conductive particles 1. Note that in Figure 4, the conductive particles 1 are shown schematically for convenience of illustration. Instead of the conductive particles 1, conductive particles 11, 21, etc. may be used. In the connection structure 51, the first metal foil 52 and the second metal foil 53 are electrically connected by one or more conductive particles 1.

[0134] The method for manufacturing the connection structure (current collector) preferably includes the following steps (1) to (4): (1) a first arranging step of arranging a connection portion material on a surface of a first metal foil; (2) a drying step of drying the connection portion material; (3) a second arranging step of arranging a second metal foil on the surface of the connection portion material opposite to the first metal foil; and (4) a connecting step of heating the connection portion material to form a connection portion and electrically connecting the first metal foil and the second metal foil by the conductive particles in the connection portion.

[0135] In the method for manufacturing a connection structure, the material of the connection portion contains the conductive particles described above. The material of the connection portion may be the conductive material described above.

[0136] In the first disposing step, the method for disposing the material for the connection portions is not particularly limited, and examples of the method for disposing the material for the connection portions include roll coating, gravure coating, spin coating, and bar coating.

[0137] In the drying step, methods for drying the material of the connection portion include natural drying, freeze drying, heat drying, etc. In the drying step, the material of the connection portion is preferably dried by heat drying.

[0138] In the drying step, when the material of the connection portion is dried by heating, the heating temperature is preferably 30° C. or higher, more preferably 50° C. or higher, and preferably 450° C. or lower, more preferably 350° C. or lower. In the drying step, when the material of the connection portion is dried by heating, the heating time is preferably 0.1 minute or longer, more preferably 1 minute or longer, and preferably 200 minutes or shorter, more preferably 100 minutes or shorter.

[0139] In the connecting step, if the material of the connecting portion contains a thermosetting component, it is preferable to heat the material of the connecting portion to a temperature equal to or higher than the hardening temperature of the thermosetting component, so that the connecting portion connecting the first metal foil and the second metal foil can be formed from the material of the connecting portion.

[0140] The heating temperature in the connecting step is preferably 100° C. or higher, more preferably 150° C. or higher, and preferably 400° C. or lower, more preferably 300° C. or lower, and even more preferably 250° C. or lower. When the heating temperature in the connecting step is equal to or higher than the lower limit and equal to or lower than the upper limit, good electrical connection between the metal foils can be achieved.

[0141] The heating time in the connecting step is not particularly limited, and may be 2 seconds or more, 15 seconds or less, 10 seconds or less, 9 seconds or less, or 7 seconds or less.

[0142] In this embodiment, it is preferable that no pressure is applied in the second arranging step and the connecting step. In this case, the weight of the second metal foil is added to the material of the connecting portion. Therefore, damage to the metal foil can be suppressed when the connecting portion is formed.

[0143] In this way, the connection structure (current collector) 51 shown in FIG. 4 is obtained. The second arrangement step and the connection step may be performed consecutively. After the second arrangement step, the resulting laminate of the first metal foil, the connection portion material, and the second metal foil may be moved to a heating section, and the connection step may be performed. To perform the heating, the laminate may be placed on a heating member, or the laminate may be placed in a heated space.

[0144] Examples of metals used for the metal foil include gold, silver, palladium, copper, platinum, zinc, iron, tin, lead, ruthenium, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, thallium, germanium, cadmium, silicon, and alloys thereof. The metal used for the metal foil may be stainless steel, tin-doped indium oxide (ITO), or solder.

[0145] From the viewpoint of further reducing the initial connection resistance and further increasing the electrical conductivity reliability, the metal used for the metal foil is preferably gold, silver, copper, tin, aluminum, nickel, titanium, or stainless steel, and more preferably copper or aluminum. From the viewpoint of further reducing the initial connection resistance and further increasing the electrical conductivity reliability, the first metal foil and the second metal foil each preferably contain gold, silver, copper, tin, aluminum, nickel, titanium, or stainless steel, and more preferably copper or aluminum. The metals used for the first and second metal foils may be the same or different.

[0146] In the method for manufacturing the connection structure, it is preferable that the first metal foil and the second metal foil are long, and that the connection structure is manufactured by transporting the long first metal foil and the long second metal foil by a roll-to-roll method in the first arranging step, the drying step, the second arranging step, and the connecting step. In this case, a long connection structure can be manufactured, and the manufacturing efficiency of the connection structure can be further improved.

[0147] When a roll-to-roll method is used, the transport speed of the first metal foil and the second metal foil is not particularly limited.

[0148] The shapes of the first metal foil and the second metal foil are not particularly limited. From the viewpoint of manufacturing the connection structure by a roll-to-roll method, the first metal foil and the second metal foil are preferably long. The lengths of the first metal foil and the second metal foil are not particularly limited. The lengths of the first metal foil and the second metal foil may be 1 m or more, 10 m or more, 5000 m or less, or 1000 m or less.

[0149] The thickness of the first metal foil and the second metal foil is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, and is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 50 μm or less. When the thickness of the first metal foil and the second metal foil is equal to or greater than the lower limit, damage to the metal foil can be further suppressed. When the thickness of the first metal foil and the second metal foil is equal to or less than the upper limit, the connection structure can be made lighter, and when the connection structure is used as a current collector in a battery, the battery can be made lighter. The thickness of the first metal foil and the second metal foil may be the same or different.

[0150] The thickness of the connection portion is preferably 1 μm or more, more preferably 2 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. When the thickness of the connection portion is equal to or more than the above lower limit and equal to or less than the above upper limit, the adhesive strength between the metal foils can be improved, and the electrical connection between the metal foils can be improved.

[0151] (Current Collector) The current collector according to the present invention is a current collector used in a battery. The current collector according to the present invention is included in a battery and is a part of the battery. The current collector according to the present invention comprises a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, and the material of the connection portion contains the conductive particles described above. In the current collector, the first metal foil and the second metal foil are electrically connected by the conductive particles. Since the current collector according to the present invention has the above configuration, 1) the dispersibility of the conductive particles in the connection portion can be improved, 2) damage to the metal foil can be suppressed, 3) initial connection resistance can be reduced, and 4) conduction reliability can be improved.

[0152] The current collector is preferably the connection structure described above, and preferably has the structure of connection structure (current collector) 51 shown in FIG.

[0153] The current collector (connection structure) may be cut to a predetermined size as needed, or may be used as cut. In the current collector (connection structure), it is preferable that the long metal foils are electrically connected by the conductive particles. After the long metal foils are electrically connected by the conductive particles to form the long current collector, the long current collector (connection structure) may be cut.

[0154] The current collector (connection structure) may be laminated as needed. The current collector (connection structure) may be cut to a predetermined size and then laminated as needed. The current collector (connection structure) may be laminated in two or more layers, or in three or more layers, or in 20 or less layers, or in 10 or less layers.

[0155] The current collector is preferably used in bipolar batteries. The current collector is particularly preferably used in bipolar batteries for automobiles. The current collector is particularly preferably used in bipolar batteries for electric vehicles (BEVs) and hybrid electric vehicles (HEVs).

[0156] FIG. 5 is a cross-sectional view that schematically shows a bipolar battery that uses the connection structure (current collector) shown in FIG.

[0157] 5 includes a positive electrode 62, a connection structure (current collector) 51, a negative electrode 63, and an electrolyte layer 64. The connection structure (current collector) 51 includes a first metal foil 52, a second metal foil 53, and a connection portion 54 connecting the first metal foil 52 and the second metal foil 53. The connection portion 54 is formed by curing a material for the connection portion that includes conductive particles 1.

[0158] The bipolar battery 61 includes a connection structure (current collector) 51 as a current collector.

[0159] In the bipolar battery 61, a plurality of positive electrodes 62, a plurality of connection structures (current collectors) 51, a plurality of negative electrodes 63, and a plurality of electrolyte layers 64 are stacked in the thickness direction.

[0160] In the bipolar battery 61, a positive electrode 62, an electrolyte layer 64 laminated on the positive electrode 62, and a negative electrode 63 laminated on the electrolyte layer 64 (i.e., the negative electrode 63 disposed on the surface of the electrolyte layer 64 opposite to the positive electrode 62) constitute one unit cell layer. In the bipolar battery 61, a plurality of unit cell layers are laminated. A current collector 51 is disposed between adjacent unit cell layers.

[0161] The positive electrode includes a positive electrode active material, and the material of the positive electrode may include the binder resin described above.

[0162] Examples of the positive electrode active material include lithium compounds. Examples of the lithium compounds include lithium-transition metal composite oxides (lithium-based composite oxides), lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. Examples of the lithium-transition metal composite oxides (lithium-based composite oxides) include LiCoO ２ , LiNiO ２ , and Li(Ni—Co—Mn)O ２ etc.

[0163] The negative electrode includes a negative electrode active material, and the material of the negative electrode may include the binder resin described above.

[0164] The negative electrode active material may be a carbon active material, a lithium-transition metal composite oxide (e.g., Li ４ Ti ５ O １２ ), metal active materials, and lithium alloy-based negative electrode active materials, etc. Examples of the carbon active material include graphite, soft carbon, and hard carbon.

[0165] The electrolyte layer includes an electrolyte, such as a liquid electrolyte or a solid electrolyte.

[0166] In the liquid electrolyte, a supporting salt is generally dissolved in an organic solvent. Examples of the supporting salt include lithium salts. Examples of the organic solvent include carbonates. Examples of the carbonates include ethylene carbonate (EC) and propylene carbonate (PC).

[0167] Examples of the solid electrolyte include a gel electrolyte containing an electrolytic solution and a true solid electrolyte containing no electrolytic solution.

[0168] In the gel electrolyte, the liquid electrolyte is generally dispersed in a matrix polymer containing an ion-conductive polymer.

[0169] When the electrolyte layer contains a liquid electrolyte or a gel electrolyte, the electrolyte layer preferably includes a separator, such as a porous membrane made of a polyolefin such as polyethylene or polypropylene.

[0170] In the true solid electrolyte, the supporting salt is generally dissolved in the matrix polymer, and the true solid electrolyte does not contain an organic solvent.

[0171] The bipolar battery is preferably a bipolar lithium ion secondary battery.

[0172] The current collector may be wound into a roll. The current collector may be in the form of a roll body wound into a roll.

[0173] When the current collector is wound in a roll, the current collector (connection structure) is preferably produced by a roll-to-roll method.

[0174] In the roll body, the length of the current collector wound into a roll is not particularly limited, and may be 1 m or more, 10 m or more, or 5000 m or less, or 1000 m or less.

[0175] In the roll body, the width of the current collector wound into a roll shape is not particularly limited, and the length of the current collector may be 0.3 m or more, or 0.5 m or more, or 10 m or less, or 5 m or less.

[0176] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0177] The following materials were prepared:

[0178] (Base particles) Base particle A: resin particle (prepared according to Synthesis Example 1 below; average particle diameter 3.0 μm; average circularity and circularity variation varied depending on the lot; shown in the table) Base particle B: resin particle (same material as base particle A; average particle diameter 2.5 μm; average circularity and circularity variation varied depending on the lot; shown in the table) Base particle C: resin particle (same material as base particle A; different particle diameter, average circularity and circularity variation from base particle A; average particle diameter 10.0 μm; average circularity 0.92; circularity variation 0.04) Base particle D: resin particle (prepared according to Synthesis Example 2 below; average particle diameter 3.0 μm; average circularity and circularity variation varied depending on the lot; shown in the table) Base particle E: resin particle (prepared according to Synthesis Example 3 below; average particle diameter 3.0 μm; average circularity and circularity variation varied depending on the lot; shown in the table)

[0179] Synthesis Example 1 30 parts by weight of divinylbenzene and 70 parts by weight of polytetramethylene glycol diacrylate were stirred to obtain a monomer mixture. 2000 parts by weight of a 2.5 wt% aqueous solution of polyvinyl alcohol with a molecular weight of approximately 2000 dissolved in pure water was placed in a reaction vessel. The obtained monomer mixture was added thereto and stirred to adjust the particle size of the monomer droplets to a predetermined particle size. Next, the mixture was heated at 90°C for 9 hours to polymerize the monomer droplets, thereby obtaining particles. The obtained particles were washed several times with hot water and acetone, and then classified to recover the resin particles, thereby obtaining base particle A.

[0180] Synthesis Example 2: 300 g of a 0.13 wt % aqueous ammonia solution was placed in a 500 mL reaction vessel equipped with a stirrer and a thermometer. Next, a mixture of 4.1 g of methyltrimethoxysilane, 19.2 g of vinyltrimethoxysilane, and 0.7 g of silicone alkoxy oligomer ("X-41-1053" manufactured by Shin-Etsu Chemical Co., Ltd.) was slowly added to the aqueous ammonia solution in the reaction vessel. After the hydrolysis and condensation reactions were allowed to proceed with stirring, 2.4 mL of a 25 wt % aqueous ammonia solution was added, and the particles were isolated from the aqueous ammonia solution. The resulting particles were then subjected to a 25 wt % aqueous ammonia treatment under an oxygen partial pressure of 10－１７ The mixture was calcined at 350° C. and 1000 atm for 2 hours to obtain base particles D.

[0181] Synthesis Example 3: 7.5 parts by weight of isobornyl acrylate, 85 parts by weight of polytetramethylene glycol diacrylate, and 7.5 parts by weight of cyclohexyl methacrylate were stirred to obtain a monomer mixture. 2000 parts by weight of a 2.5 wt% aqueous solution of polyvinyl alcohol with a molecular weight of approximately 2000 dissolved in pure water was placed in a reaction vessel. The obtained monomer mixture was added thereto and stirred to adjust the particle size so that the monomer droplets had a predetermined particle size. Next, the mixture was heated at 90°C for 9 hours to polymerize the monomer droplets, thereby obtaining particles. The obtained particles were washed several times with hot water and acetone, and then classified to recover the resin particles, thereby obtaining base particle E.

[0182] (Carbon filler) "Denka Black" manufactured by Denka Company Ltd. (particle diameter 3.0 μm, average circularity 0.30, circularity variation 0.20) (Nickel particles) "Nickel fine powder" manufactured by Kojundo Chemical Co., Ltd. (particle diameter 3.0 μm, average circularity 0.75, circularity variation 0.15)

[0183] Example 1 A suspension was obtained by adding and dispersing base particles A in 500 parts by weight of distilled water. A nickel-phosphorus alloy plating solution (pH 6.5) containing 200 g / L of nickel sulfate, 85 g / L of sodium hypophosphite, 30 g / L of sodium citrate, 50 ppm of thallium nitrate, and 20 ppm of bismuth nitrate was also prepared. While stirring the resulting suspension at 60°C, the nickel-phosphorus alloy plating solution was gradually added dropwise to the suspension to perform electroless nickel-phosphorus plating. The suspension was then filtered to remove the particles, which were then washed with water and dried to obtain conductive particles having a nickel-phosphorus conductive layer on the surface of the base particles A and protrusions on the surface. The resulting conductive particles were then dispersed for 10 minutes in an ethanol solution containing 1 wt% 2-ethylhexyl azide phosphate (a rust inhibitor), filtered to remove the particles, and dried to perform a rust prevention treatment.

[0184] Example 2 Conductive particles were obtained in the same manner as in Example 1, except that no rust prevention treatment was carried out.

[0185] Example 3 Conductive particles were obtained in the same manner as in Example 1, except that the thickness of the conductive portion was changed.

[0186] Example 4 Conductive particles were obtained in the same manner as in Example 1, except that the nickel-phosphorus alloy plating solution was changed to a nickel-boron plating solution (pH 8.5) containing 0.35 mol / L of nickel sulfate, 1.38 mol / L of dimethylamine borane, and 0.5 mol / L of sodium citrate.

[0187] Example 5 Conductive particles were obtained in the same manner as in Example 1, except that the nickel-phosphorus alloy plating solution was changed to a pure nickel plating solution (pH 6.5) containing 200 g / L of nickel sulfate, 50 g / L of hydrazine hydrate, 30 g / L of sodium citrate, 50 ppm of thallium nitrate, and 20 ppm of bismuth nitrate.

[0188] (Example 6) Conductive particles were obtained in the same manner as in Example 4, except that a gold plating layer (thickness 20 nm) was formed on the outer surface of the nickel-boron conductive layer (thickness 80 nm) when producing the conductive particles.

[0189] Example 7 Conductive particles were obtained in the same manner as in Example 1, except that the nickel-phosphorus alloy plating solution was changed to a silver plating solution (pH 8.0) containing 200 g / L of silver nitrate and 50 g / L of hydroquinone, and the thickness of the conductive portion was changed.

[0190] Example 8 Conductive particles were obtained in the same manner as in Example 1, except that base particle A was changed to base particle D.

[0191] Example 9 Conductive particles were obtained in the same manner as in Example 1, except that the base particle A was changed to the base particle D and the thickness of the conductive portion was changed.

[0192] Example 10 Conductive particles were obtained in the same manner as in Example 1, except that base particle A was changed to base particle B.

[0193] Example 11 Conductive particles were obtained in the same manner as in Example 1, except that base particle A was changed to base particle C.

[0194] Example 12 Conductive particles were obtained in the same manner as in Example 1, except that base particle A was changed to base particle E.

[0195] Comparative Example 1 Conductive particles were obtained in the same manner as in Example 1, except that the base particle A was changed to a carbon filler and the conductive portion was not formed.

[0196] Comparative Example 2 Conductive particles were obtained in the same manner as in Example 1, except that the base particles A were changed to nickel particles and the conductive portion was not formed.

[0197] Comparative Example 3 Conductive particles were obtained in the same manner as in Example 1, except that the base particle A was changed to the base particle D and the thickness of the conductive portion was changed.

[0198] Comparative Example 4 Conductive particles were obtained in the same manner as in Example 1, except that the base particle A was changed to the base particle E and the thickness of the conductive portion was changed.

[0199] (Evaluation) (1) Specific Gravity The specific gravity of the obtained conductive particles was measured using a specific gravity measuring device ("AccuPic Series" manufactured by Shimadzu Corporation) according to the method described above.

[0200] (2) Volume Resistivity Value The volume resistivity value of the obtained conductive particles was measured by the method described above using a powder resistivity measurement system ("Powder Resistivity Measurement System MCP Series" manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0201] (3) Compressive modulus (20% K value) when conductive particles are compressed by 20% The 20% K value of the obtained conductive particles was measured using a microcompression tester (Fisherscope H-100 manufactured by Fischer) according to the method described above.

[0202] (4) Dispersibility of Conductive Particles The obtained conductive particles were added to Mitsui Chemicals' "Structbond XN-5A" so that the content was 10 wt %, and dispersed to prepare a conductive material. The obtained conductive material was applied to a glass slide, and 100 conductive particles were observed using a microscope, and the number of conductive particles that had settled or aggregated was counted. The dispersibility of the conductive particles was evaluated according to the following criteria.

[0203] [Evaluation criteria for dispersibility of conductive particles] ○○○: The number of conductive particles that have settled or aggregated is less than 3. ○○: The number of conductive particles that have settled or aggregated is 3 or more but less than 5. ○: The number of conductive particles that have settled or aggregated is 5 or more but less than 10. ×: The number of conductive particles that have settled or aggregated is 10 or more.

[0204] (5) Suppression of Metal Foil Breakage The obtained conductive particles were added to Mitsui Chemicals' "Structbond XN-5A" so that the content was 10 wt % and dispersed to prepare a conductive material (connection material). Copper foil (width 1 m x length 1 m x thickness 10 μm) was prepared as the first metal foil, and aluminum foil (width 1 m x length 1 m x thickness 30 μm) was prepared as the second metal foil. A conductive material was placed on the surface of the first metal foil (copper foil) to a thickness of 3 μm by roll coating. Then, a second metal foil (aluminum foil) was placed on the surface of the conductive material opposite the first metal foil, and heated at 150 ° C. for 20 minutes to harden the conductive material and form a connection. The first metal foil and the second metal foil were electrically connected by the conductive particles in the connection to obtain a connection structure (current collector). The first metal foil and the second metal foil of the obtained connection structure were observed to confirm the presence or absence of breakage of the metal foil. The ability to prevent the metal foil from breaking was evaluated according to the following criteria.

[0205] [Evaluation criteria for suppression of metal foil breakage] ◯: No breaks or blistering in the entire metal foil. ○: No breaks in the entire metal foil, but blistering in part of the metal foil. ×: Breaks in at least part of the metal foil.

[0206] (6) Initial connection resistance (5) Suppression of metal foil breakage The connection resistance A between the metal foils of the connection structure (current collector) obtained in (5) Suppression of metal foil breakage was measured by a four-terminal method. The initial connection resistance was evaluated according to the following criteria.

[0207] [Evaluation criteria for initial connection resistance] ○○○: Connection resistance A is 2.0Ω or less ○○: Connection resistance A is greater than 2.0Ω and less than 3.0Ω ○: Connection resistance A is greater than 3.0Ω and less than 5.0Ω ×: Connection resistance A exceeds 5.0Ω

[0208] (7) Conduction reliability (6) After the evaluation of the initial connection resistance, the connection structure (current collector) was left at 85°C and 85% humidity for 500 hours to conduct a conduction reliability test under a high temperature and high humidity environment. After the conduction reliability test, the connection resistance B between the metal foils of the connection structure was measured using a four-terminal method. The conduction reliability was evaluated according to the following criteria.

[0209] [Evaluation criteria for conduction reliability] ○○○: Connection resistance B is 2.0Ω or less. ○○: Connection resistance B is greater than 2.0Ω and less than 3.0Ω. ○: Connection resistance B is greater than 3.0Ω and less than 5.0Ω. ×: Connection resistance B exceeds 5.0Ω.

[0210] The composition of the conductive particles and the results are shown in Tables 1 to 4 below.

[0211]

[0212]

[0213]

[0214]

[0215] DESCRIPTION OF SYMBOLS 1...Conductive particle 2...Base particle 3...Conductive portion 11...Conductive particle 11a...Protrusion 12...Conductive portion 12a...Protrusion 13...Core material 21...Conductive particle 21a...Protrusion 22...Conductive portion 22a...Protrusion 22A...First conductive portion 22Aa...Protrusion 22B...Second conductive portion 22Ba...Protrusion 51...Connection structure (current collector) 52...First metal foil 53...Second metal foil 54...Connection portion 61...Bipolar battery 62...Positive electrode 63...Negative electrode 64...Electrolyte layer

Claims

1. A conductive particle used to electrically connect metal foils, comprising a base particle and a conductive portion disposed on the surface of the base particle, and having a compressive elastic modulus of 1000 N / mm when the conductive particle is compressed by 20%. ２ More than 25000N / mm ２ The conductive particles are as follows:

2. The conductive particle according to claim 1, wherein the base particle is a resin particle.

3. The conductive particles according to claim 1 or 2, wherein the specific gravity of the conductive particles is 1.0 or more and 4.5 or less.

4. The conductive particles according to any one of claims 1 to 3, wherein the volume resistivity of the conductive particles is 0.0030 Ω·m or less.

5. The conductive particle according to any one of claims 1 to 4, wherein the conductive portion contains nickel.

6. The conductive particle according to any one of claims 1 to 5, wherein the conductive portion contains a rust inhibitor.

7. The conductive particle according to any one of claims 1 to 6, wherein the average circularity of the base particle is 0.85 or more and 1.00 or less.

8. The conductive particle according to any one of claims 1 to 7, wherein the variation in circularity of the base particle is 0.04 or less.

9. A conductive material comprising the conductive particles according to any one of claims 1 to 8 and a binder resin.

10. A connection structure comprising a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, wherein the material of the connection portion contains the conductive particles described in any one of claims 1 to 8, and the first metal foil and the second metal foil are electrically connected by the conductive particles.

11. The connection structure according to claim 10, wherein the thickness of the first metal foil and the second metal foil is 100 μm or less.

12. The connection structure according to claim 10 or 11, wherein the first metal foil and the second metal foil each contain gold, silver, copper, tin, aluminum, nickel, titanium, or stainless steel.

13. A current collector for use in a battery, comprising: a first metal foil; a second metal foil; and a connection portion connecting said first metal foil and said second metal foil, wherein a material of said connection portion contains the conductive particles according to any one of claims 1 to 8, and said first metal foil and said second metal foil are electrically connected by said conductive particles.

14. The current collector according to claim 13, which is used in a bipolar battery.

15. The current collector according to claim 13 or 14, wherein the current collector is wound into a roll.

16. Use of the conductive particles according to any one of claims 1 to 8 in a current collector included in a battery comprising a first metal foil, a second metal foil, and a connection portion connecting the first metal foil and the second metal foil, for electrically connecting the first metal foil and the second metal foil.

17. The use according to claim 16, wherein the battery is a bipolar battery.

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