Current collector for bipolar secondary batteries and bipolar secondary batteries

Abstract

A current collector and a bipolar secondary battery are provided, which enable more reliable formation of conductive pathways and suppress pinhole defects. A current collector for a bipolar secondary battery comprises a conductive filler and a resin binder, wherein the conductive filler has at least one morphology selected from spike-like, structural, and spherical morphologies, and the D of the conductive filler... 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the current collector.

Description

Technical Field

[0001] This manual relates to current collectors for bipolar secondary batteries and bipolar secondary batteries themselves. Background Technology

[0002] Sometimes, resin-containing current collectors, which include conductive particles and resin binders, are used as current collectors in secondary batteries such as lithium-ion secondary batteries. For example, a technique has been disclosed to suppress in-plane conductivity by setting the particle size of the conductive particles to 0.5 to 2 times the thickness of the current collector and setting the thickness of the resin-containing current collector to 1 to 500 μm (Japanese Patent Application Laid-Open No. 2012-150896). Summary of the Invention

[0003] However, if the conductive particles are too small, they become embedded within the current collector, failing to adequately ensure a conductive path. Furthermore, even if the particle size is twice the thickness of the current collector layer, the distribution of particle size means that sufficient conductive paths cannot be guaranteed by conductive filler penetrating the current collector. On the other hand, it is believed that if the conductive particles are too large, pinholes will form within the current collector.

[0004] This specification provides a current collector and a bipolar secondary battery that can more reliably form a conductive path and suppress pinhole defects.

[0005] According to this specification, a current collector for a bipolar secondary battery is provided. The current collector includes a conductive resin layer comprising a conductive filler and a resin binder.

[0006] The conductive filler has at least one morphology selected from spike-like, structural, and spherical shapes, and the D of the conductive filler 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the conductive resin layer.

[0007] In addition, according to this specification, a bipolar secondary battery is provided, which has a bipolar electrode having the above-described current collector.

[0008] Based on the above current collector, the conductive filler has a predetermined D 90 The conductive filler morphology allows it to reliably penetrate the conductive resin layer, protruding beyond the thickness of the conductive resin matrix. This ensures a conductive path in the thickness direction of both the conductive resin layer and the current collector. Consequently, low resistance in the thickness direction of the current collector can be achieved. Simultaneously, pinhole formation in the conductive resin layer can be suppressed. Attached Figure Description

[0009] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings, wherein the same reference numerals denote the same elements.

[0010] Figure 1 This is a diagram illustrating the general structure of a bipolar secondary battery.

[0011] Figure 2 This is a diagram illustrating the general structure of a collector.

[0012] Figure 3 This is a diagram illustrating an example of a collector.

[0013] Figure 4A This is a microscopic photograph showing the spiked Ni powder (sample 1) used in the embodiments.

[0014] Figure 4B This is a microscopic photograph of Ni powder (sample 2) with a structural morphology used in the embodiments.

[0015] Figure 5A This is a diagram showing the evaluation units (sample and comparative sample) in the embodiments.

[0016] Figure 5B This is a diagram showing the evaluation unit (comparative example) in the embodiment. Detailed Implementation

[0017] This specification discloses a current collector for a bipolar secondary battery and a bipolar secondary battery. Here, one embodiment of the current collector includes a conductive resin layer comprising a conductive filler and a resin binder. The conductive filler has at least one morphology selected from a spike-like morphology, a structural morphology, and a spherical morphology, and the D of the conductive filler... 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the conductive resin layer.

[0018] In another embodiment of the current collector, the D of the conductive filler 90 The particle size can also be more than 2.0 times and less than 5.2 times the thickness of the matrix.

[0019] In another embodiment of the current collector, the thickness of the substrate may be greater than 8 μm and less than 25 μm.

[0020] In another embodiment of the current collector, the D of the conductive filler 90 The particle size can also be above 16μm and below 75μm.

[0021] In another embodiment of the current collector, the conductive filler may also have a spike-like or structural form.

[0022] The bipolar secondary battery disclosed in this specification is not particularly limited; for example, it may be a lithium-ion bipolar secondary battery or a solid-state battery. Furthermore, although there are no particular limitations, it may be used, for example, in vehicles.

[0023] In this specification, the terms "above" and "below" to refer to numerical values ​​include the concepts of "above" and "greater than," and "below" and "less than." When a predetermined numerical value is defined as a threshold, a useful numerical range can be formed even if it is above that value, exceeding that value. Similarly, a useful numerical range can be formed even if it is below that value, being less than that value.

[0024] Furthermore, as long as the secondary battery is bipolar, there is no particular limitation on the shape of the cell. A bipolar secondary battery is a battery obtained by stacking multiple bipolar electrodes, with a positive electrode active material layer formed on one side of the current collector and a negative electrode active material layer formed on the other side, in series, separated by a separator containing an electrolyte.

[0025] The following is a detailed description of the current collector (hereinafter referred to as current collector) 4 and the secondary battery 100 of the bipolar secondary battery disclosed in this specification. Figure 1 This represents the cross-section of secondary battery 100. Figure 2 The cross-sectional structure of collector 4 is shown in magnified view.

[0026] like Figure 1 As shown, the secondary battery 100 is constructed by stacking multiple bipolar electrodes 2 separated by a separator 12. The bipolar electrodes 2 are formed by fixing a negative electrode active material layer 6 and a positive electrode active material layer 8 to a current collector 4. End current collectors 16a and 16b are formed at the ends of the secondary battery 100 and are connected to the outside. In addition, the outer periphery of the secondary battery 100 is insulated by an insulating sealing material 14. As an insulating sealing material, a known insulating sealing material can be used.

[0027] Current collector and conductive resin layer

[0028] like Figure 2 As shown, the current collector 4 includes a conductive resin layer 10 containing a resin binder 20 and a conductive filler 22. The conductive resin layer 10 is a film. The resin binder 20 forms a matrix (hereinafter referred to as matrix) 24 on which the conductive resin layer 10 is formed. The conductive filler 22 is dispersed and held in the matrix 24.

[0029] In addition to the resin binder 20, the matrix 24 may also contain other components such as dispersants, crosslinking accelerators, and plasticizers. From the viewpoint of electrical stability, the total content of other components relative to the total mass of the conductive resin layer 10 is preferably 0.001% by mass or more and 5% by mass or less, and more preferably 0.001% by mass or more and 3% by mass or less.

[0030] Resin adhesives

[0031] As for the resin adhesive 20, there are no particular limitations, and various resins can be used. Examples include olefin resins such as polyethylene, polypropylene, and polymethylpentene; acrylic resins such as poly(meth)acrylic acid and poly(meth)acrylate; fluoropolymers of polytetrafluoroethylene; and halogenated vinyl resins; thermosetting resins such as epoxy resins, vinyl ester resins, unsaturated polyester resins, phenolic resins, and melamine resins; and polyaniline, polypyrrole, polythiophene, polyacetylene, poly(p-phenylene) polymers, polyphenylene acetylene, polyacrylonitrile, and poly... Known conductive polymers such as diazoles are used. One type of resin can be used alone, or two or more can be used in combination. While there are no particular limitations, non-conductive resins are preferred for forming conductive pathways in the thickness direction of the conductive filler. From the viewpoint of electrical stability, olefin-based resins such as polyethylene, polypropylene, and polymethylpentene are preferred. Additionally, acrylic resins are sometimes preferred.

[0032] conductive filler

[0033] The conductive filler 22 can include metallic materials or alloys such as nickel, aluminum, stainless steel, platinum, gold, silver, copper, and titanium; graphite, carbon black (acetylene black, furnace black, Ketjen black (registered trademark)); carbon nanotubes, carbon nanofibers, carbon nanohorns, diamond-like carbon, glassy carbon, and other carbon materials; and metallic compound materials such as metal carbides, metal nitrides, and metal oxides. One type or two or more can be used in combination. For example, in the current collector 4, metallic materials such as nickel or nickel alloys are effective from a conductivity point of view.

[0034] The shape of the conductive filler 22 is not particularly limited and can take various forms. For example, it can take the form of spikes, structures, spheres, needles, etc. Spikes refer to particles that have multiple spike-like protrusions continuously or aggregated on the surface. In addition, the spiked particles as a whole generally have an amorphous to spherical shape. Spiked particles with nickel as the main component can be purchased, for example, as Vale's Type 123.

[0035] A structural morphology refers to a structure formed by the fusion of multiple primary particles. Structures based on primary particle connections can be categorized into filamentous (chain-like) and grape-like forms. Particles with nickel as the primary component in structural morphologies (filamentous, etc.) are available, for example, from Vale.

[0036] From the viewpoint of forming conductive pathways in the thickness direction of the conductive resin layer 10, the conductive filler 22 preferably has a shape other than a flake-like shape. That is, a portion of the conductive filler 22 may also have a flake-like shape, but the main particle shape is preferably other than a flake-like shape. In the case of a flake-like shape, there is a tendency that it is difficult to adopt a through-type structure in the conductive resin layer 10.

[0037] The conductive filler 22 preferably has a spike-like shape, a structural shape, or a spherical shape. Because the conductive filler 22 has a spike-like shape, it is easy to penetrate along the thickness T direction of the conductive resin layer 10 due to its amorphous to spherical shape, and the number of contact points in the conductive path is greater due to the protrusions. When it has a structural shape, it is easy to adopt a slender shape such as filaments as a whole, which is preferable as it tends to easily penetrate the conductive resin layer 10. Furthermore, when it has a spherical shape, it is also easy to penetrate the conductive resin layer 10, which is preferable as it provides a larger exposed surface area of ​​the conductive resin layer 10. The particle size of the conductive filler 22 will be described later.

[0038] D of conductive filler 90 Particle size

[0039] The conductive filler 22 can have a D ratio of more than 1.7 times and less than 5.2 times the thickness T (μm) of the matrix 24. 90 (μm). If D 90 If the ratio X to the thickness T of the substrate 24 is less than 1.7, it becomes difficult to penetrate the conductive resin layer 10 in the thickness direction, and the resistance in the thickness direction tends to increase. Furthermore, if the ratio X is 5.2 or greater, the frequency of pinhole formation increases, and the conductive resin layer 10 tends to become discontinuous. Therefore, by setting the ratio X within this range, the frequency of pinhole formation can be suppressed, and the resistance in the thickness direction of the secondary battery 100 can be reduced.

[0040] The ratio X can be, for example, 2.0 times or more, 2.1 times or more, 2.5 times or more, or 2.8 times or more. Furthermore, the ratio X can be, for example, 5.1 times or less, 5.0 times or less, 4.0 times or less, 3.8 times or less, or 3.0 times or less. The range of ratio X can be further appropriately combined with lower and upper limits within the range of 1.7 times or more and less than 5.2 times. The range of ratio X can be, for example, 2.0 times or more and less than 5.1 times, 2.0 times or more and less than 5.0 times, 2.0 times or more and less than 4.0 times, 2.0 times or more and less than 3.0 times, 2.1 times or more and less than 5.0 times, 2.1 times or more and less than 4.0 times, or 2.1 times or more and less than 3.8 times, etc.

[0041] Furthermore, as described above, the conductive filler 22 preferably has a spike-like shape, a structural shape (filamentous, etc.), or a spherical shape. If it is a spike-like shape, the resistance in the thickness direction can be suppressed even without increasing the ratio X. Therefore, the frequency of pinhole formation can be effectively reduced. Additionally, if it is a structural shape, the resistance in the thickness direction can be suppressed in this shape. When the conductive filler 22 has a spike-like shape, the ratio X can be 2.0 times or more and 5.0 times or less, 2.0 times or more and 4.0 times or less, 2.0 times or more and 3.0 times or less, or 2.0 times or more and 2.5 times or less. When it has a structural shape, the ratio X can be 2.0 times or more and 4.0 times or less, or 2.0 times or more and 3.0 times or less.

[0042] D of conductive filler 22 90 Particle size is the particle size D in the particle size distribution based on volume. 90 The following particle proportions determine the particle size at 90%. D 90 The particle size distribution can be measured using a laser diffraction / scattering particle size distribution measuring device.

[0043] D of conductive filler 22 90 There are no special limitations; for example, it can be 16μm or larger and 75μm or smaller, 16μm or larger and 60μm or smaller, 16μm or larger and 45μm or smaller, 16μm or larger and 30μm or smaller, etc.

[0044] The thickness T of the matrix 24 is the thickness of the matrix 24 itself within the conductive resin layer 10, excluding any protrusions based on the conductive filler 22. Thickness T is the average thickness measured at 10 points on a cross-section cut along the thickness direction of the conductive resin layer 10 using an energy-dispersive X-ray spectrometer (EDX). These 10 points are any locations where the conductive filler 22 is not observed and the matrix 24, which disperses and holds the conductive filler 22, is the only visible component.

[0045] The thickness T of the matrix 24 of the conductive resin layer 10 is not particularly limited, but if the D of the conductive filler 22 is taken into account... 90 For example, the thickness T is 1 μm or more and 100 μm or less. This thickness T is, for example, 3 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, and 8 μm or more. Alternatively, this thickness T is, for example, 80 μm or less, 60 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, and 15 μm or less. The thickness T of the matrix 24 is within the range of 1 μm or more and 100 μm or less, and the lower and upper limits can be further appropriately combined to set, for example, 8 μm or more and 25 μm or less, 8 μm or more and 20 μm or less, and 8 μm or more and 15 μm or less.

[0046] The content of conductive filler 22 and resin binder 20 in the conductive resin layer 10 is not particularly limited. For example, relative to the total mass of conductive filler 22 and resin binder 20, conductive filler 22 may be 5% by mass or more (resin binder 20 may be 95% by mass or less), 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more. Alternatively, conductive filler 22 may be 40% by mass or less, 35% by mass or less, or 30% by mass or less. The range of conductive filler 22 content can be set by appropriately combining their lower and upper limits. For example, it may be 5% by mass or more and 15% by mass or less, 6% by mass or more and 14% by mass or less, 8% by mass or more and 12% by mass or less, etc. Furthermore, the total mass of the conductive filler 22 and the resin adhesive 20 is not particularly limited relative to the total mass of the conductive resin layer 10, but is 95% or more and 100% or less, 97% or more and 100% or less, 98% or more and 100% or less, or 99% or more and 100% or less.

[0047] The current collector 4 may only have a conductive resin layer 10. Additionally, as... Figure 3 As shown, the current collector 4 may also have a metal layer 30 on at least one side of the conductive resin layer 10. Figure 3In the example shown, the conductive resin layer 10 is used as the current collector layer on the negative electrode side. In this case, a metal layer 30 may be provided on the surface of the conductive resin layer 10 opposite to the positive electrode active material layer 8. The metal layer 30 may use a known metal as the current collector on the positive electrode side. The metal layer 30 may contain, for example, aluminum, typically aluminum or aluminum alloy foil. Although not shown, when the conductive resin layer 10 is used as the current collector layer on the positive electrode side, a metal layer 30 may be provided on the surface of the conductive resin layer 10 opposite to the negative electrode active material layer 6. In this case, the metal layer 30 may use a known metal as the current collector on the negative electrode side. For example, it may contain copper or nickel, typically copper foil or nickel foil. The thickness of the metal layer 30 as a metal foil is not particularly limited, for example, it may be 5 μm or more and 100 μm or less, or 20 μm or more and 40 μm or less.

[0048] Furthermore, the metal layer 30 can also be obtained by film formation methods such as physical evaporation (vacuum evaporation, ion plating, and sputtering), chemical evaporation, and deposition. When the metal layer 30 is formed based on physical evaporation or the like, the thickness of the metal layer 30 is not particularly limited, for example, it can be set to be 5 nm or more and 200 nm or less.

[0049] Depending on the requirements, in addition to the conductive resin layer 10, the current collector 4 may also have a carbon coating 32 between it and the negative electrode active material layer 6 and / or the positive electrode active material layer 8. The carbon coating 32 comprises carbon materials such as acetylene black, carbon black, and graphite, which are electronically conductive. The carbon coating 32 can improve the adhesion between the current collector 4 and the active material layers 6 and 8. The carbon coating 32 is provided in contact with the active material layers 6 and 8. When the current collector 4 has a metal layer 30, the metal layer 30 is provided on the surface opposite to the active material layers 6 and 8. The main component of the carbon coating 32 is carbon material, and the carbon material is bonded together by resins such as the described resin adhesive. The carbon coating 32 is, for example, 0.1 μm or more and 5 μm or less.

[0050] Method for manufacturing current collectors

[0051] The method for manufacturing the current collector 4 disclosed in this specification includes: preparing a conductive resin composition containing a conductive filler 22 and a resin binder 20, and using the conductive resin composition to form a film-like conductive resin layer 10.

[0052] In this manufacturing method, the conductive filler 22 has a D ratio X of at least 1.7 times and less than 5.2 times the thickness T of the matrix 24 of the conductive resin layer 10 in the current collector 4 to be manufactured. 90 Value. According to this method, a current collector 4 for a bipolar secondary battery can be obtained that maintains a low resistance level in the thickness direction of the conductive resin layer 10 and the current collector 4. Regarding the thicknesses T and D of the resin binder 20, conductive filler 22, and matrix 24... 90Compared to X, the conductive resin layer 10 can be appropriately applied using the various methods described above.

[0053] The conductive resin composition can be prepared by mixing a resin binder (or its raw material) 20 and a conductive filler 22. In addition, the conductive resin composition may, as needed, contain additives such as dispersants and solvents.

[0054] The conductive resin layer 10 is molded into a desired film shape with a matrix 24 of a predetermined thickness T. When manufacturing the conductive resin layer 10, those skilled in the art can adjust the thickness of the matrix 24 of the conductive resin layer 10 to the desired thickness T through appropriate experiments or calculations, depending on the composition of the conductive resin layer 10 used. Preparation D 90 A conductive resin composition is prepared by using conductive filler 22 with a ratio X of the thickness T of the matrix 24 within a predetermined range.

[0055] There are no particular limitations on the molding method; any known film molding method for manufacturing a film-like conductive resin layer 10 can be used. From the viewpoint of efficiently manufacturing the conductive resin layer 10, for example, a known film molding method can be appropriately used. From the viewpoint of efficiently manufacturing a film-like conductive resin layer 10, for example, molding methods such as casting with coating, extrusion molding, etc., can be employed.

[0056] When using an extrusion molding method, a thermal load is applied to the conductive filler 22. Therefore, metallic materials such as metals or alloys, or carbon materials, are preferably used as the conductive filler 22. Furthermore, to overcome the shear force during extrusion and ensure the conductive filler 22 penetrates along the thickness direction, a spike-like or structural form is preferred. The conductive filler 22 with a spike-like form has an amorphous to spherical shape, and has multiple spike-like protrusions continuously or aggregated on its surface. Therefore, it is advantageous in that pinholes are less likely to form under the shear force during extrusion molding, and it is easy to form conductive pathways in the thickness direction even with a relatively small diameter.

[0057] When the current collector 4 is formed using the conductive resin layer 10 as a single monomer, the current collector 4 can be directly obtained by obtaining the conductive resin layer 10. Alternatively, when the current collector 4 is formed using the conductive resin layer 10 and the metal layer 30, an extrusion lamination method can be used, in which the conductive resin layer 10 is laminated onto the metal foil serving as the metal layer 30 during extrusion molding. According to the extrusion lamination method, a current collector 4 having both the conductive resin layer 10 and the metal layer 30 can be obtained efficiently.

[0058] When the current collector 4 has a carbon coating 32, in addition to carbon materials and resin binders, a composition containing a dispersion medium such as NMP can be applied to the metal layer 30 and / or the conductive resin layer 10 as needed, and then applied by appropriate drying.

[0059] Secondary batteries and their manufacturing methods

[0060] The secondary battery disclosed in this specification is a bipolar secondary battery 100, which can include a bipolar electrode 2 having a current collector 4 as disclosed in this specification. According to this secondary battery 100, by using the current collector 4, the resistance in the thickness direction is maintained at a low level. Therefore, a secondary battery 100 that is advantageous from the viewpoint of cost and battery characteristics is provided.

[0061] The secondary battery 100 includes a bipolar electrode 2 on one side of the current collector 4, having a negative electrode active material layer 6 formed thereon, and a positive electrode active material layer 8 formed thereon on the other side. Furthermore, the secondary battery 100 may, as needed, include a carbon coating 32 positioned opposite the negative electrode active material layer 6 and / or the positive electrode active material layer 8 of the current collector 4. Additionally, the secondary battery 100 has a structure in which multiple bipolar electrodes 2 are stacked in series across a separator 12.

[0062] This secondary battery 100 can be manufactured by anyone skilled in the art using appropriate and well-known methods. There are no limitations on the negative electrode active material layer 6, the positive electrode active material layer 8, and the separator 12; well-known materials can be used for them. Additionally, according to this specification, a bipolar electrode 2 having a current collector 4 is also provided.

[0063] As can be seen from the above description, the following methods are included in this specification.

[0064] [1] A current collector for a bipolar secondary battery, comprising a conductive resin layer including a resin binder and a conductive filler.

[0065] The conductive filler has at least one morphology selected from spike-like morphology, structural morphology, and spherical morphology.

[0066] The conductive filler's D 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the conductive resin layer.

[0067] [2] According to the current collector described in [1], the D of the conductive filler 90 The particle size is more than 2.0 times and less than 5.0 times the thickness of the matrix, preferably more than 2.0 times and less than 4.0 times, and more than 2.0 times and less than 3.0 times.

[0068] [3] According to the current collector of [1] or [2], the thickness of the substrate is 8 μm or more and 25 μm or less, preferably 8 μm or more and 20 μm or less, and more preferably 8 μm or more and 15 μm or less.

[0069] [4] The current collector according to any one of [1] to [3], wherein the D of the conductive filler 90 The particle size is 16 μm or more and 75 μm or less, preferably 16 μm or more and 60 μm or less, and more preferably 16 μm or more and 45 μm or less.

[0070] [5] The current collector according to any one of [1] to [4], wherein the conductive filler has the spike-like shape or the structural shape.

[0071] [6] A bipolar secondary battery comprising a bipolar electrode having a current collector as described in any one of [1] to [5].

[0072] [7] A method for manufacturing a current collector for a bipolar secondary battery, comprising the following steps:

[0073] Prepare a conductive resin composition comprising a resin binder and a conductive filler; and

[0074] The current collector is preferably formed by extrusion molding using the aforementioned current collector composition.

[0075] The conductive filler's D 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the conductive resin layer to be manufactured.

[0076] [8] A bipolar electrode having a current collector as described in any one of [1] to [5].

[0077] [9] A method for manufacturing a bipolar secondary battery, wherein the current collector described in any one of [1] to [5] is used to manufacture the bipolar secondary battery.

[0078] Hereinafter, embodiments are described to illustrate the disclosure of this specification in more detail. Therefore, the following embodiments are used to illustrate the disclosure of this specification and are not intended to limit its scope.

[0079] Example 1

[0080] In this embodiment, various conductive resin compositions were prepared, and current collectors (samples 1-5, comparative sample 1-10) with conductive resin layers integrated on Al foil were fabricated. The resistance values ​​in the through-direction of these current collectors were evaluated. Furthermore, Ni powder with the morphology and particle size distribution shown in Table 1 was used as the conductive filler in each conductive resin composition. In addition, adhesive polypropylene (for extrusion lamination) was used as the resin binder. The resin binder and conductive filler were fed into a biaxial extrusion mixer at a mass ratio of 90:10. The mixture was kneaded at 240°C to obtain a conductive resin composition. Then, the conductive resin composition was heated to 280°C using an extrusion lamination apparatus and directly laminated onto an Al foil (40 μm thick). Figure 4A and Figure 4B Microscopic images show Ni powder with a spike-like morphology in sample 1 and Ni powder with a structural body-like morphology in sample 2. The particle size distribution of the conductive filler used was determined by measuring the particle size distribution on a volume basis using a laser diffraction / scattering particle size distribution measuring device.

[0081] Furthermore, the pulverized materials 1-3 are prepared into a Ni powder using a pulverizer at a predetermined pressure, and the graded materials 1-3 are prepared into a Ni powder using a rotary classifier at a predetermined speed.

[0082] For these various current collectors, the resistance value in the thickness direction was measured. The resistance value (mΩ) was measured by clamping the current collector with electrodes of 20 mm diameter on both sides in the thickness direction, multiplying it by the electrode area, and dividing by the film thickness to calculate the volume resistivity. Furthermore, regarding the thickness T of the conductive resin layer matrix, the laminated cross-section cut in the thickness direction of the current collector was observed using SEM with EDX. The average thickness was obtained by measuring 10 points at arbitrary locations where Ni powder was not observed. The measurement results are shown in Table 1. Additionally, the appearance of each current collector was observed, and the frequency of pinhole formation was evaluated (A: Excellent, B: Good, C: Average, D: Poor). The results are also shown in Table 1.

[0083] Table 1

[0084]

[0085] As shown in Table 1, it can be seen that when the filler morphology is spike-like, structural, or spherical, D... 90 If the thickness T is 1.7 or greater, the volume resistivity in the thickness direction is below 1000, and the pinhole generation frequency is not a problem (samples 1-5). On the other hand, it can be seen that if D... 90 When the thickness T reaches 5.2, pinholes will occur at a high frequency even if the volume resistivity is low (Comparative Example 10).

[0086] If D 90As the thickness T decreases, the volume resistivity increases (comparative examples 1-9). This is especially true in the case of a flaky morphology, even with D... 90 / The thickness T is 2.4, and the volume resistivity also increases (comparative sample 3).

[0087] In particular, it can be seen that when the conductive filler has a spike-like or structural body-like morphology, D 90 The indicator that the thickness T is 2.0 or above is valid.

[0088] Example 2

[0089] In this embodiment, a coin-shaped unit with a unipolar structure was fabricated using the current collector (sample 1, sample 2, and comparative sample 4) prepared in Example 1, and the IV resistance was measured. The ratio of the IV resistance to the bonding foil (conventional bipolar current collector) used as a control example is shown in Table 2.

[0090] Furthermore, the structure of the unit used for evaluation is shown in Figure 5A and Figure 5B For the current collector with Al foil modulated in Example 1, a carbon coating, a negative electrode active material layer, and a positive electrode active material layer are sequentially formed and integrated with the separator layer to form a modulation evaluation unit. The modulation and formation of each layer are shown below.

[0091] carbon coating

[0092] Acetylene black and PVDF (mass ratio 90:10) were mixed with N-methylpyrrolidone (NMP) to form a coating solution with a solid content of 30%. The solution was then applied to the conductive resin layer side of the current collector using a dressing applicator at a concentration of 1 mg / cm². 2 Apply the coating and let it dry.

[0093] Negative electrode active material layer

[0094] A negative electrode paste was prepared by mixing amorphous carbon-coated graphite (as the active material), carboxymethyl cellulose (CMC) (as a thickener), and styrene-butadiene rubber (SBR) (as a binder) at a mass ratio of 97:0.7:2.3. The paste was then applied to the carbon coating using a dressing apparatus at a concentration of 22.6 mg / cm³. 2 The prepared negative electrode paste was coated with a specific amount of material and dried, then rolled to achieve the desired negative electrode density (1.2 g / cm³). 2 The negative electrode layer of ).

[0095] Positive electrode active material layer

[0096] Lithium nickel cobalt manganese oxide (NCM) as the active material, acetylene black as the conductive additive, and PVDF as the binder were mixed at a mass ratio of 95:2.5:2.5 to prepare the positive electrode paste. The paste was then applied to the carbon coating using a dressing applicator at a concentration of 38 mg / cm³. 2The prepared positive electrode paste was applied to an Al foil (12 μm thick) and dried, then rolled to achieve the desired positive electrode density (3.0 g / cm³). 2 The positive electrode layer.

[0097] Furthermore, in the comparative example, a Cu foil (10 μm) was integrated on an Al foil (40 μm thick) with an adhesive layer (3 μm) in between, and a carbon coating was formed on the surface of the Cu foil. Otherwise, the process was carried out in the same manner as described above.

[0098] Table 2

[0099]

[0100] As shown in Table 2, in the cells using the current collectors of samples 1 and 2, the IV resistivity was the same as when using the laminated foil. On the other hand, in the cells using the current collector of comparative example sample 4, the IV resistivity deteriorated significantly.

[0101] Therefore, it can be concluded that, based on the D of the conductive filler 90 The conductive resin layer and current collector with controlled thickness T can maintain a low resistance in the thickness direction, resulting in low resistance when forming a secondary battery.

Claims

1. A current collector for a bipolar secondary battery, comprising a conductive filler and a resin binder. The conductive filler has at least one morphology selected from spike-like morphology, structural morphology, and spherical morphology. The conductive filler's D 90 The particle size is more than 1.7 times and less than 5.2 times the thickness of the matrix in which the conductive filler is dispersed and maintained in the current collector.

2. The current collector for a bipolar secondary battery according to claim 1, The conductive filler's D 90 The particle size is more than 2.0 times and less than 5.0 times the thickness of the matrix.

3. The current collector for a bipolar secondary battery according to claim 1, The thickness of the matrix is ​​greater than 8 μm and less than 25 μm.

4. The current collector for a bipolar secondary battery according to claim 3. The conductive filler of the D 90 The particle size is greater than 16μm and less than 75μm.

5. The current collector for a bipolar secondary battery according to claim 1, The conductive filler has the spike-like morphology or the structural body morphology.

6. A bipolar secondary battery, It has a bipolar electrode having a current collector as described in any one of claims 1 to 5.

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