JP2010073421A - Bipolar electrode and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bipolar electrode capable of preventing liquid junction originating from a minute crack of a current collector in a bipolar type secondary battery using the current collector including a polymer material. <P>SOLUTION: The bipolar electrode comprises a current collector consisting of at least two layers containing a polymer material, a positive electrode active material layer formed on one face of the current collector, and a negative electrode active material layer formed on the other face of the current collector. Its manufacturing method is also provided. It is preferable that the current collector is of two layers, and it is further preferable that a conductive paste is interposed between the two layers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bipolar electrode, and more particularly to a bipolar electrode applicable to a bipolar lithium ion secondary battery suitable for mounting on a vehicle and a method for manufacturing the same.

  In recent years, in order to cope with air pollution and global warming, reduction of carbon dioxide emissions has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done. This is because in these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging.

  As the secondary battery for driving the motor, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. Among them, lithium ion secondary batteries are attracting attention because they have the highest theoretical energy among all the batteries and have high durability against repeated charging and discharging, and are currently being developed rapidly. . Among such lithium ion secondary batteries, bipolar lithium ion secondary batteries generally apply a positive electrode active material or the like to one surface of a current collector, and apply the negative electrode active material or the like to the other surface of the current collector. A plurality of bipolar electrodes coated on is used. The bipolar secondary battery has a configuration in which such bipolar electrodes are connected via an electrolyte layer and stored in a battery case.

Conventionally, in a lithium ion secondary battery, a metal foil has been used as a current collector. In recent years, a conductive current collector containing a resin instead of a metal foil has been proposed (see, for example, Patent Document 1). Such a resin current collector is lighter than a metal foil and is expected to improve battery output.
JP-A 61-285664

  However, a current collector made of a resin such as a polymer material may cause micro cracks, and this crack causes a liquid junction of the electrolyte in the electrode, resulting in a decrease in battery performance. . Therefore, an object of the present invention is to provide a means that can prevent battery performance degradation even if cracks occur in a current collector using a polymer material.

  That is, the present invention is a bipolar electrode including a current collector made of only at least two layers containing a polymer material, a positive electrode active material layer formed on one surface of the current collector, and the current collector And a negative electrode active material layer formed on the other surface of the body. Furthermore, the present invention also provides a method for manufacturing the bipolar electrode. That is, in the production method, first, at least two layers containing a polymer material are prepared, and a slurry containing a positive electrode active material is applied to one side of the first layer containing the polymer material, dried, and pressed. And a step of forming a positive electrode active material layer. Next, a slurry containing a negative electrode active material is applied to one side of the second layer containing a polymer material, dried, and pressed to form a negative electrode active material layer. Finally, the method includes a step of overlapping the surface of the first layer on which the positive electrode active material layer is not formed and the surface of the second layer on which the negative electrode active material layer is not formed.

  According to the present invention, since the position of the crack generated in each layer of the current collector does not coincide with the contact surface of each layer, the crack does not penetrate in the thickness direction of the current collector. As a result, even when a current collector containing a polymer material is used, a bipolar electrode that can prevent a liquid junction caused by a minute crack caused by pressing during production can be provided.

  Hereinafter, the present invention will be described in detail. First, a basic configuration of a bipolar lithium ion secondary battery using the bipolar electrode of the present invention will be described with reference to the drawings.

[Battery overall structure]
FIG. 1 shows a flat (stacked) lithium ion secondary battery (hereinafter simply referred to as a bipolar lithium ion secondary battery), which is a typical embodiment of a lithium ion secondary battery using the bipolar electrode of the present invention. FIG. 2 is a schematic cross-sectional view schematically showing the entire structure of a secondary battery.

  As shown in FIG. 1, the bipolar lithium ion secondary battery 10 of the present embodiment has a substantially rectangular power generation element (battery element) 17 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 22. Has a structured. As shown in FIG. 1, the power generation element 17 of the bipolar secondary battery 10 of the present embodiment has an electrolyte layer 15 sandwiched between two or more bipolar electrodes 14, and the positive electrode active of adjacent bipolar electrodes 14. The material layer 12 and the negative electrode active material layer 13 are opposed to each other with the electrolyte layer 15 interposed therebetween. Here, the bipolar electrode 14 has a structure in which the positive electrode active material layer 12 is provided on one surface of the current collector 11 and the negative electrode active material layer 13 is provided on the other surface. That is, in the bipolar secondary battery 10, the bipolar electrode 14 having the positive electrode active material layer 12 on one surface of the current collector 11 and the negative electrode active material layer 13 on the other surface is provided with the electrolyte layer 15. A power generation element (battery element) 17 having a structure in which a plurality of layers are stacked via a battery is provided.

  The adjacent positive electrode active material layer 12, electrolyte layer 15 and negative electrode active material layer 13 constitute a single cell layer 16. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 16 are laminated. In addition, an insulating layer 23 is disposed on the periphery of the unit cell layer 16 in order to prevent a liquid junction due to leakage of the electrolyte from the electrolyte layer 15. By providing the insulating layer 23, the adjacent current collectors 11 can be insulated from each other, and a short circuit due to contact between the adjacent electrodes (the positive electrode active material layer 12 and the negative electrode active material layer 13) can be prevented.

  Note that the positive electrode 14a and the negative electrode 14b located in the outermost layer of the power generation element (battery element) 17 may not have a bipolar electrode structure. For example, a structure in which the positive electrode active material layer 12 or the negative electrode active material layer 13 only on one side necessary for the current collectors 11a and 11b (or terminal plates) may be arranged. Specifically, as shown in FIG. 1, a positive electrode active material layer 12 is formed only on one side of the positive electrode side outermost layer current collector 11 a located in the outermost layer of a power generation element (battery element) 17. You may do it. Similarly, a negative electrode active material layer 13 may be formed only on one side of the outermost current collector 11 b on the negative electrode side located in the outermost layer of the power generation element (battery element) 17. In the bipolar lithium ion secondary battery 10, the positive electrode tab 18 and the negative electrode tab 19 are provided on the positive electrode side outermost layer current collector 11 a and the negative electrode side outermost layer current collector 11 b at both the upper and lower ends, respectively. 20 and the negative terminal lead 21 are joined together. However, the positive electrode side outermost layer current collector 11 a may be extended to form the positive electrode tab 18, and may be derived from a laminate sheet that is the battery exterior material 22. Similarly, the negative electrode side outermost layer current collector 11 b may be extended to form a negative electrode tab 19, which may be similarly derived from a laminate sheet that is the battery outer packaging material 22.

  In the bipolar lithium ion secondary battery 10, the power generation element (battery element; laminated body) 17 is sealed in the battery outer packaging material 22 under reduced pressure, and the positive electrode tab 18 and the negative electrode tab 19 are taken out of the battery outer packaging material 22. It is better to have a structure. This is because such a structure can prevent external impact and environmental degradation during use. The basic configuration of the bipolar lithium ion secondary battery 10 can be said to be a configuration in which a plurality of stacked unit cell layers 16 are connected in series. In the bipolar electrode of the present invention used in the bipolar secondary battery as described above, the current collector is composed of at least two layers containing a polymer material. The present inventors have found that in a bipolar secondary battery using a current collector made of a polymer material, minute cracks generated in the pressing process at the time of manufacturing an electrode cause the battery performance to deteriorate. In the manufacture of an electrode, usually, a paste containing a positive electrode active material or the like is applied to one surface of a current collector, a paste containing a negative electrode active material or the like is applied to the other surface, and then the current collector is applied. Pressing the body. The same applies when a polymer material is used for the current collector. As described above, a current collector made of a polymer material may be cracked by pressing. However, the present inventors have found that the current collector can be composed of at least two layers made of a polymer material, and by overlapping these layers, liquid junction of the electrolyte due to cracks can be prevented. Even if cracks have occurred in each of the at least two layers constituting the current collector, it has been found that if it does not penetrate the thickness direction of the current collector, liquid junction can be prevented and the present invention has been completed. It is a thing.

  The mechanism by which this current collector prevents liquid junction due to cracks is schematically shown in FIGS. 2A and 2B in comparison with the case of a conventional single layer. FIG. 2A shows a case where the current collector 31 has one layer, and FIG. 2B shows a case where the current collector 35 of the present invention has a layer 34 containing a polymer material stacked in two layers. 2A and 2B, the left side shows before the pressing process, and the right side shows after the pressing process. The upper layers of the current collectors 31 and 35 are the positive electrode active material layers 32 and 36, and the lower layers are the negative electrode active material layers 33 and 37. In the case where the current collector 31 is a single layer, if a crack A enters, it penetrates up and down and causes a liquid junction. On the other hand, when the current collector 35 is composed of two layers, even if a crack A enters each layer 34 containing the polymer material, if the position is different, the current collector is caused by the presence of another layer. It is possible to prevent cracks from penetrating up and down. Since the possibility that the cracks of the layers containing the polymer material coincide is extremely low, such a laminated structure is effective in preventing liquid junction. If the current collector is laminated in three or more layers, the effect of preventing liquid junction is further enhanced. However, since the size of the entire bipolar secondary battery is increased by increasing the number of stacked layers, the number of layers of the current collector should be appropriately selected according to the application. Preferably, the number of layers containing the polymeric material is 2-5, more preferably 2-3, and most preferably 2. By configuring the current collector with a layer containing the two polymer materials, not only the entire current collector becomes the thinnest, but also sufficient liquid junction prevention can be achieved.

  The current collector structure of the present invention is particularly effective in preventing liquid junctions in the case of a current collector in which a conductive filler is mixed with a non-conductive polymer material. As shown in FIG. 3, the current collector made of the polymer material extends in the horizontal direction by pressing. At this time, since the elastic modulus is different between the polymer material and the conductive filler, the conductive filler is less likely to be stretched than the polymer material during pressing. This is because cracks are likely to occur at locations where the filler concentration is non-uniform due to aggregation of the filler. According to the present invention, even if a current collector containing a conductive filler is used and a crack is generated by pressing, it can be prevented from causing a decrease in battery performance.

  Next, each member of the bipolar lithium ion secondary battery as described above and the bipolar electrode of the present invention used therefor will be described.

[Current collector]
The polymer material itself constituting the current collector used for the bipolar electrode of the present invention does not necessarily have conductivity, but in order to fulfill the function as the current collector, the current collector as a whole It has electrical conductivity.

  When the current collector includes a polymer material that does not have conductivity, it naturally includes a conductive filler (conductive particles). The conductive filler is selected from materials that are conductive and have no conductivity with respect to the ions used as the charge transfer medium. The conductive filler is selected from materials that can withstand the applied positive electrode potential and negative electrode potential. Specific examples include aluminum particles, SUS particles, carbon particles, silver particles, gold particles, copper particles, and titanium particles, but are not limited thereto. Alloy particles may be used. The conductive filler is not limited to the above-described form, and carbon nanotubes or the like can be used, and what is put into practical use as a so-called filler-based conductive resin composition can be used. Among these, carbon fine particles are particularly preferable as used in Examples described later. This is because carbon particles such as carbon black and graphite have a very wide potential window, are stable in a wide range with respect to both the positive electrode potential and the negative electrode potential, and are excellent in conductivity. Also, since the carbon particles are very light, the increase in mass is minimized.

  The distribution of the conductive filler in the current collector may not be uniform, and the particle distribution may be changed inside the current collector. A plurality of conductive particles may be used, and the distribution of the conductive particles may be changed inside the current collector. For example, a preferable conductive filler may be properly used in a portion in contact with the positive electrode and a portion in contact with the negative electrode. As the conductive filler used on the positive electrode side, aluminum particles, SUS particles, and carbon particles are preferable, and carbon particles are particularly preferable. As the conductive filler used for the negative electrode, silver particles, gold particles, copper particles, titanium particles, SUS particles, and carbon particles are preferable, and carbon particles are particularly preferable. Furthermore, since carbon particles are often used as a conductive aid for electrodes, even if they come into contact with these conductive aids, the contact resistance is very low because of the same material. When carbon particles are used as the conductive filler, it is possible to reduce the compatibility of the electrolyte by applying a hydrophobic treatment to the surface of the carbon, making it difficult for the electrolyte to penetrate into the current collector holes. is there.

  Although the preferable magnitude | size of an electroconductive filler is not restrict | limited in particular, Preferably it is 0.1-50 micrometers, More preferably, it is 1-20 micrometers, More preferably, it is 1-3 micrometers. Furthermore, the shape of the conductive filler is not particularly limited, and may be fibrous, plate-like, or massive.

  In addition to the conductive filler, the current collector includes a polymer material that binds the conductive filler. By using a polymer material as the constituent material of the current collector, the binding property of the conductive filler can be increased and the reliability of the battery can be increased. The polymer material is selected from materials that can withstand the applied positive electrode potential and negative electrode potential.

  The polymer material not having conductivity is preferably polyethylene, polypropylene, polyethylene terephthalate, polyacrylonitrile, polyether nitrile, polymethyl acrylate, polymethyl methacrylate, polyamide, polyimide, cellulose, carboxymethyl cellulose, ethylene-vinyl acetate. Polymer, polyvinyl chloride, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and its hydrogenated product, styrene / isoprene -Thermoplastic polymers such as styrene block copolymers and their hydrogenated products, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol 1, 3-butylene glycol, polyvinyl alcohol, polyvinyl propynal, polyvinyl butyral, polyacrylamide, polyethylene glycol, polypropylene glycol, polybutylene glycol and other hydroxyl group-containing compounds, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), fluoropolymers such as ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride Do-hexafluoropropylene fluorine rubber (VDF-HFP fluorine rubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene Fluoro rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine Vinylidene fluoride such as rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber (VDF-CTFE fluoro rubber), etc. And fluorocarbon rubber. These polymer materials may be used alone or in combination of two or more.

  These polymer materials have a very wide potential window, are stable in a wide range with respect to both the positive electrode potential and the negative electrode potential, and can improve the adhesion to the active material layer. More preferably, polypropylene is used as the polymer material. The reason why polypropylene is preferable is that it is stable with respect to the electrolytic solution and has a small thermal expansion coefficient.

  The distribution of the polymer material in the current collector may not be uniform, and the distribution of the polymer material may change within the current collector. A plurality of polymer materials may be used, and the distribution of the polymer material may be changed inside the current collector. For example, a preferable polymer material may be properly used for a portion in contact with the positive electrode and a portion in contact with the negative electrode. The current collector may contain other materials as necessary.

  The ratio of the polymer material and the conductive particles in the current collector is not particularly limited, but is preferably 5 to 35 vol%, more preferably 5 to 25 vol%, based on the total of the polymer material and the conductive filler. More preferably, 5 to 15 vol% of conductive filler is present. By allowing a sufficient amount of the conductive filler to be present, the conductivity of the current collector can be sufficiently ensured.

  The thickness of the current collector is not particularly limited, but it is preferable that the current collector is thin from the viewpoint of increasing the output density of the battery. In a bipolar battery, the current collector present between the positive electrode and the negative electrode may have a high electrical resistance in the direction parallel to the stacking direction. Therefore, if an anisotropic conductive film is selected, the thickness of the current collector can be reduced. It is possible to make it thinner. Specifically, the thickness of the current collector is preferably 1 to 100 μm, more preferably 1 to 50 μm, and still more preferably 5 to 30 μm. In the present invention, the current collector is formed by laminating two or more layers. Here, the thickness indicates the thickness of each layer to be laminated.

  The presence of the conductive filler in the current collector is not always necessary, and the polymer itself may have conductivity. That is, a film made of a conductive polymer (also referred to as “conductive polymer” in this specification) can be used as a current collector.

  The conductive polymer is selected from materials that are conductive and have no conductivity with respect to ions used as charge transfer media. These conductive polymers are considered to be conductive because the conjugated polyene system forms an energy band. As a typical example, a polyene-based conductive polymer that has been put into practical use in an electrolytic capacitor or the like can be used. Specific examples include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole, or a mixture thereof.

  The resistance value in the current collector is not particularly limited, but preferably the conductive polymer is used so that the resistance value in the current collector portion is 1/100 or less of the resistance value of the entire battery. It is desirable to select.

[Active material layer]
An active material layer is formed on the current collector. The active material layer is a layer containing an active material that plays a central role in the charge / discharge reaction. When the electrode is used as a positive electrode, the active material layer includes a positive electrode active material. On the other hand, when the electrode is used as a negative electrode, the active material layer includes a negative electrode active material.

As the positive electrode active material, a lithium-transition metal composite oxide is preferable, and examples thereof include a Li—Mn composite oxide such as LiMn ₂ O ₄ and a Li—Ni composite oxide such as LiNiO ₂ . In some cases, two or more positive electrode active materials may be used in combination.

  A carbon material is preferable as the negative electrode active material. Examples of the carbon material include graphite-based carbon materials (graphite) such as natural graphite, artificial graphite, and expanded graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. More preferably, graphite such as natural graphite, artificial graphite, and expanded graphite. As natural graphite, for example, scaly graphite, massive graphite and the like can be used. As the artificial graphite, massive graphite, vapor-grown graphite, flaky graphite, and fibrous graphite can be used. Among these, particularly preferable materials are flake graphite and massive graphite. The use of flaky graphite or massive graphite is particularly advantageous for reasons such as high packing density. In some cases, two or more negative electrode active materials may be used in combination.

  The average particle diameter of the active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 50 μm, and further preferably 1 to 20 μm. However, forms outside these ranges can also be employed. In this application, the average particle diameter of the active material is a value measured by laser diffraction particle size distribution measurement (laser diffraction scattering method).

  Moreover, the content of the active material in the active material layer is preferably 70 to 98% by mass, more preferably 80 to 98% by mass with respect to the total mass of the active material layer. If the content of the active material is within the above range, it is preferable because the energy density can be increased.

  In the electrode of the present invention, the thickness of the active material layer (the thickness of one surface of the coating layer) is preferably 20 to 500 μm, more preferably 20 to 300 μm, and further preferably 20 to 150 μm.

  The active material layer may contain other materials, for example, a binder, a conductive additive, a supporting salt (lithium salt), and the like. The compounding ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

  The binder contained in the active material layer includes polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polytetrafluoroethylene (PTFE). Styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or mixtures thereof.

  A conductive assistant means the additive mix | blended in order to improve electroconductivity. Examples of the conductive assistant include carbon powder such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). As the supporting salt, those contained in the electrolytic solution can be used similarly.

[Conductive paste layer]
In the bipolar electrode of the present invention, the current collector is composed of at least two layers containing a polymer material, and it is preferable to further include a conductive paste layer between the layers. If the current collector is a laminate of a plurality of layers, contact resistance is generated at the interface between the layers, which may affect the performance of the battery. However, the contact resistance can be reduced by applying the conductive paste in advance to the surface of the current collector to be overlaid and pasting it together. Furthermore, since the conductive paste usually contains a binder, if a layer containing two polymer materials is overlapped before the conductive paste is applied and dried, this also serves as an adhesive. Therefore, the mechanical strength of the stacked current collector can be improved.

  As the conductive paste, any of metal oxide-based conductive pastes including zinc oxide, indium oxide, titanium oxide, etc., and carbon-based conductive pastes including carbon black, carbon nanotubes, graphite, etc. can be preferably used. . The thickness of the conductive paste layer is preferably 5 to 100 μm, more preferably 5 to 40 μm, and still more preferably 5 to 20 μm. When the current collector is composed of three or more layers, it is desirable to interpose a conductive paste layer between each layer, but the effect of reducing contact resistance can be obtained even if it is not necessarily present between all layers. .

[Electrolyte layer]
As the electrolyte constituting the electrolyte layer, a porous film separator containing an electrolytic solution or a gel electrolyte can be used. The electrolytic solution is in a form in which a lithium salt as a supporting salt is dissolved in an organic solvent.

  Any organic solvent can be used as long as it can sufficiently dissolve the supporting salt as described above. For example, cyclic carbonates such as propylene carbonate and ethylene carbonate; chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1 Selected from among ethers such as 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; esters such as methyl propionate; amides such as dimethylformamide; methyl acetate and methyl formate The thing using the plasticizer (organic solvent), such as an aprotic solvent, which mixed 1 type or 2 types or more from at least can be used. These organic solvents may be used alone or in combination of two or more.

  Among these, in the present invention, carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC) are preferable.

Conventionally known salts can be used as the supporting salt. Specific examples include Li (C ₂ F ₅ SO ₂ ) ₂ N (LiBETI), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N and the like.

  Moreover, as a specific form of a separator, the microporous film which consists of polyolefin, such as polyethylene and a polypropylene, is mentioned, for example.

  The gel electrolyte has a configuration in which an electrolytic solution is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and vinylidene fluoride-hexafluoropropylene (VDF-HEP). And poly (methyl methacrylate (PMMA), copolymers thereof, etc. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

[Insulation layer]
Insulating layer (sealing part) prevents bipolar current collectors in a bipolar lithium-ion secondary battery from coming into contact with each other and short-circuiting due to slight unevenness at the end of the laminated electrode. In order to do so, it is arranged at the periphery of the cell layer. As the sealing material constituting the insulating layer, it should have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing property), heat resistance at the battery operating temperature, etc. That's fine. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Of these, urethane resins and epoxy resins are preferred from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming properties), economy, and the like.

[tab]
The material of the tab (positive electrode tab and negative electrode tab) can be aluminum, copper, nickel, stainless steel, alloys thereof, or the like. These are not particularly limited, and known materials conventionally used as tabs can be used.

[Battery exterior materials]
As the battery exterior material, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element (battery element) using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

  [Assembly Battery] The present invention also provides an assembled battery using the above bipolar secondary battery.

  The assembled battery of the present invention is constituted by connecting a plurality of bipolar secondary batteries of the present invention. Specifically, at least two or more are used to be serialized or parallelized or both. Capacitance and voltage can be freely adjusted by paralleling in series.

  4 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. 4C is an assembled battery. FIG.

  As shown in FIG. 4, an assembled battery 300 according to the present invention forms a small assembled battery 250 in which a plurality of bipolar secondary batteries of the present invention are connected in series or in parallel to be detachable. The battery pack 300 may further include a plurality of detachable small battery packs 250 connected in series or in parallel. The small assembled battery 250 that can be attached and detached is connected to each other using an electrical connection means such as a bus bar, and the assembled battery 250 is stacked in a plurality of stages using a connection jig 310.

[vehicle]
The present invention also provides a vehicle equipped with the battery or the assembled battery.

  The vehicle of the present invention is equipped with the bipolar secondary battery of the present invention or an assembled battery formed by combining a plurality of these. The bipolar secondary battery of the present invention or an assembled battery formed by combining a plurality of these is used as a power source for driving a vehicle. The bipolar secondary battery or the assembled battery of the present invention is used in a vehicle such as a hybrid vehicle, a fuel cell vehicle, and an electric vehicle (for example, a four-wheeled vehicle (a commercial vehicle such as a passenger car, a truck, a bus, a light vehicle)). In addition, because it is used for motorcycles (including motorcycles and tricycles), it becomes a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  FIG. 5 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention. As shown in FIG. 5, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of the present invention can be widely applied to a hybrid vehicle, a fuel cell vehicle and the like in addition to an electric vehicle as shown in FIG.

  Then, the manufacturing method of the bipolar electrode of this invention and a bipolar secondary battery is demonstrated.

[Production method]
The bipolar electrode manufacturing method of the present invention includes a step of preparing at least two layers containing a polymer material, and applying a slurry containing a positive electrode active material to one side of the layer containing the first polymer material, followed by drying. A step of forming a positive electrode active material layer by pressing, a step of applying a slurry containing a negative electrode active material on one side of the layer containing the second polymer material, drying, and pressing to form a negative electrode active material layer And a step of overlapping a surface of the layer containing the first polymer material where the positive electrode active material layer is not formed and a surface of the layer containing the second polymer material where the negative electrode active material layer is not formed And including.

  The flow of this bipolar electrode manufacturing method will be described with reference to the drawings. As shown in FIG. 6A, first, at least two layers 40 containing a polymer material constituting the current collector 43 are prepared. A slurry containing a positive electrode material constituting the positive electrode active material layer 41 or a negative electrode material constituting the negative electrode active material layer 42 is applied thereon, and dried to form a positive electrode active material layer 41 and a negative electrode active material layer in two layers. 42 is formed. Next, as illustrated in FIG. 6B, the layer 40 including the polymer material including the positive electrode active material layer 41 and the layer 40 including the polymer material including the negative electrode active material layer 42 are separately pressed. After that, as shown in FIG. 6 (c), the surfaces of the layer 40 including the two polymer materials on which the positive electrode active material layer 41 or the negative electrode active material layer 42 are not formed are overlapped, and the current collector 43 is formed. It consists of two layers and is a bipolar electrode. In the case where the current collector includes three or more layers, only a layer containing a separately pressed polymer material may be appropriately sandwiched between layers containing a polymer material provided with an active material layer. Next, as shown in FIG. 6D, the separator 44 is placed on the bipolar electrode. At this time, the separator, the positive electrode, and the negative electrode are impregnated with an electrolyte such as an electrolytic solution or a gel electrolyte so as to form an electrolyte layer. As the outermost layer, a current collector including only the positive electrode active material layer 41 or the negative electrode active material layer 42 is laminated. A tab 45 is attached to the outermost layer of the laminated body as shown in FIG. 6 (e), and the gap between the laminated current collector and the separator is sealed with a sealing material 46. Finally, as shown in FIG. 6F, the whole is covered with a battery exterior material 47 such as a laminate film to complete a bipolar secondary battery.

  FIG. 7 shows an example in which a conductive paste layer is further provided before the current collector is overlaid. As shown in FIG. 7C, the positive electrode active material layer 51 or the negative electrode active material layer 52 is formed on the layer 50 including at least two polymer materials constituting the current collector 54, and shown in FIG. 7B. Press like so. Thereafter, a conductive paste is applied to the surface of the layer 50 containing a polymer material on which the positive electrode active material layer 51 or the negative electrode active material layer 52 is not formed, and a conductive paste layer 53 is formed. As shown in FIG. 7D, the current collector 54 is formed by superimposing the coated surfaces of the conductive paste. In this case, the current collector 54 is configured with the conductive paste layer 53 sandwiched between the layers 50 containing the polymer material. FIG. 7C illustrates an example in which the conductive paste is applied to both the layer 50 including the polymer material including the positive electrode active material layer 51 and the layer 50 including the polymer material including the negative electrode active material layer 52. However, either one of the conductive pastes may be applied. When the current collector is composed of three or more layers containing a polymer material, applying a paste so that a conductive paste layer is formed in all layers between layers containing a polymer material, preferable. This is because the effect of reducing the contact resistance in the current collector is increased. However, there may be an interlayer where no conductive paste layer is interposed. The embodiment of FIG. 7 is the same as that shown in FIG. 6 except that a step of forming a conductive paste layer is added, and further includes a separator 55, a tab 56, a seal material 57, and a battery exterior material 58.

  Hereinafter, the bipolar electrode of the present invention and the method for manufacturing a bipolar secondary battery using the same will be described in more detail.

(1) Manufacture of a layer containing a polymer material constituting a current collector When a layer containing a polymer material constituting a current collector is produced, a coating method can be used. For example, there is a technique in which a slurry containing a polymer material and a conductive filler or a conductive polymer is prepared and applied onto a PET film or the like and cured. Since the specific forms of the polymer material and the conductive filler used for the preparation of the slurry are as described above, the description thereof is omitted here. The application method is not particularly limited, and for example, a conventional application method using an applicator or a coater can be applied. Furthermore, what was formed and formed into a desired shape by thin film manufacturing techniques, such as a doctor blade system, a spray coat, a screen printing system, and an inkjet system, can also be utilized. Also, as used in the examples described later, a current collector can be formed by randomly compressing a mixture of a conductive filler and a polymer material in the thickness direction by thermocompression processing. The formed sheet is commercially available (for example, Hitachi Chemical Co., Ltd., Fujikura Corporation).

(2) Formation of Positive Electrode Active Material Layer The positive electrode active material is usually obtained as a slurry (positive electrode slurry) and applied to one surface of the current collector.

  The positive electrode slurry is a solution containing a positive electrode active material. As other components, a conductive additive, a binder, a polymerization initiator, an electrolyte raw material (polymer or matrix polymer for solid electrolyte, electrolyte, etc.), a supporting salt (lithium salt), a slurry viscosity adjusting solvent, and the like are optionally included. That is, the positive electrode slurry is prepared by mixing a positive electrode active material, a conductive auxiliary agent, an electrolyte raw material, a supporting salt (lithium salt), a slurry viscosity adjusting solvent, a polymerization initiator, and other materials that are arbitrarily mixed at a predetermined ratio. Can be produced.

  First, the above materials are mixed in a solvent to prepare an active material slurry. The binder can be mixed in the active material slurry by a method in which the binder is mixed with a solid content such as an active material in a powder state and then a solvent is added and mixed. Or you may mix in an active material slurry by the method of dissolving in a small amount of solvent previously, and adding to the mixture containing an active material and a solvent.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge can be referred to as appropriate. As an example of the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used.

  Subsequently, the prepared active material slurry is applied to one surface of the layer containing the polymer material constituting the current collector to form a coating film. The application means for applying the active material slurry is not particularly limited, and generally used means such as an applicator and a self-propelled coater may be employed. However, a thin layer can be formed by using screen printing, an ink jet method, a doctor blade method, or a combination thereof as the application means.

  Thereafter, the coating film formed on the surface of the layer containing the polymer material is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the application amount of the active material slurry and the volatilization rate of the solvent of the slurry. Depending on the positive electrode slurry, the cross-linking reaction of the binder may be advanced to increase the mechanical strength of the polymer solid electrolyte. For drying, a vacuum dryer or the like can be used. The drying conditions are determined according to the applied positive electrode slurry and cannot be uniquely defined, but are usually 40 to 150 ° C. and 5 minutes to 20 hours.

(3) Formation of negative electrode active material layer A negative electrode active material (negative electrode slurry) is applied to one surface of a layer containing a polymer material different from the one formed with the positive electrode active material layer. The negative electrode slurry is a solution containing a negative electrode active material. As other components, a conductive additive, a binder, a polymerization initiator, a polymer or matrix polymer for solid electrolyte, an electrolytic solution, a supporting salt (lithium salt), a slurry viscosity adjusting solvent, and the like are optionally included. About the raw material used and addition amount, it is as having mentioned above.

  The negative electrode slurry is applied on the current collector in the same manner as in the case of forming the positive electrode active material layer. Thereafter, the layer containing the polymer material coated with the negative electrode slurry is dried to remove the solvent contained therein. At the same time, depending on the slurry for the negative electrode, the cross-linking reaction of the binder may be advanced to increase the mechanical strength of the polymer gel electrolyte. The drying is the same as in the case of forming the positive electrode active material layer.

(4) Pressing step The layer containing the polymer material in which the positive electrode active material layer is formed by the above procedure and the layer containing the polymer material in which the negative electrode active material layer is formed are respectively surface smoothness and thickness uniformity. The press operation is performed so as to improve the thickness and to obtain a desired film thickness. In the present invention, the current collector is composed of at least two layers, but it is extremely desirable because liquid junction due to cracks can be more effectively prevented by separately pressing the layers containing the respective polymer materials. As described above, the occurrence of cracks penetrating from the positive electrode active material layer to the negative electrode active material layer causes a liquid junction and causes a defective battery. This is because the possibility of matching the positions of the cracks in each of the two or more layers of the current collector becomes very low by separately performing the pressing process.

  The press operation may be either a cold press roll method or a hot press roll method. In the case of a hot-rolling method, if an electrolyte supporting salt or a polymerizable polymer is contained in the active material layer, it is desirable to carry out at a temperature below which they decompose. The press pressure is preferably 20 to 100 t / m, more preferably 30 to 80 t / m, and even more preferably 40 to 70 t / m in linear pressure. However, conditions such as the pressing pressure and time vary depending on the material and the desired film thickness, and are not particularly limited to this range.

The roll press machine is not particularly limited, and a conventionally known roll press machine such as a calendar roll can be appropriately used. However, other conventionally known press devices and press techniques such as a flat plate press may be used as appropriate.

(5) Conductive paste layer formation and current collector lamination An active material layer is formed of a layer including a polymer material in which a positive electrode active material layer is formed and a layer including a polymer material in which a negative electrode active material is formed. Bipolar electrodes are formed by superimposing the unexposed surfaces. When the current collector is composed of three or more layers, only a layer containing a separately pressed polymer material is inserted between those surfaces where no active material is formed.

  At this time, it is preferable that a conductive paste layer is formed by applying a conductive paste to the overlapping surfaces before stacking two or more layers containing a polymer material. The application method is not particularly limited, and generally used means such as an applicator, a self-propelled coater, and a doctor blade can be adopted. At this time, at least one of the surface of the first layer containing the polymer material where the positive electrode active material layer is not formed and the surface of the second layer containing the polymer material where the negative electrode active material layer is not formed is conductive. A paste layer is formed. That is, the conductive paste may be applied to both sides of the layer containing the polymer material to be superposed, or only one side.

  After applying the conductive paste, the layers containing the polymer material may be stacked after drying and may be bonded together before drying. However, when the layers are stacked before being dried, the conductive paste also serves as an adhesive, which is more preferable because the mechanical strength of the current collector is increased. A preferable thickness when applying the conductive paste is 5 to 100 μm, more preferably 5 to 40 μm, and still more preferably 5 to 20 μm.

(6) Formation of electrolyte layer When a polymer solid electrolyte layer is used, for example, by curing a solution prepared by dissolving a polymer solid electrolyte raw material polymer, lithium salt, etc. in a solvent such as NMP. Manufactured. In the case of using the polymer gel electrolyte layer, for example, as a raw material for the polymer gel electrolyte, a pregel solution composed of a matrix polymer and an electrolytic solution, a lithium salt, a polymerization initiator and the like is simultaneously heated and dried in an inert atmosphere. It is produced by polymerizing (accelerating the crosslinking reaction). Further, when using a polymer gel electrolyte layer in which a polymer gel electrolyte is held in a nonwoven fabric separator, for example, as a raw material for the polymer gel electrolyte, a matrix polymer and an electrolytic solution, a lithium salt, a polymerization initiator are used in the separator. It is produced by impregnating a pregel solution composed of, etc., and polymerizing (accelerating the crosslinking reaction) simultaneously with heat drying in an inert atmosphere.

  When using a solid polymer electrolyte layer in which a solid polymer electrolyte is held in a nonwoven fabric separator, for example, as a raw material for the polymer solid electrolyte, a matrix polymer and an electrolytic solution, a lithium salt, a polymerization initiator, etc. It is produced by impregnating a solution obtained by dissolving in a viscosity modifier and polymerizing (accelerating the crosslinking reaction) simultaneously with heat drying in an inert atmosphere. Further, when using a liquid electrolyte layer in which an electrolyte is held in a separator, the separator may be impregnated with the electrolyte. For example, after laminating the separator and the bipolar electrode before impregnation with the electrolyte, May be impregnated in each separator.

  For example, the prepared solution or pregel solution is applied onto the bipolar electrode (positive electrode active material layer and / or negative electrode active material layer), and an electrolyte layer having a predetermined thickness or a part thereof (electrolyte layer thickness) About half of the electrolyte membrane). Thereafter, the electrode on which the electrolyte layer is laminated is cured or heated and dried in an inert atmosphere at the same time as polymerization (accelerating the crosslinking reaction) to increase the mechanical strength of the electrolyte and form the electrolyte layer (complete) ).

  Alternatively, an electrolyte layer laminated between the electrodes or a part thereof (an electrolyte membrane having about half the electrolyte layer thickness) is prepared. The polymer gel electrolyte layer in which the polymer gel electrolyte is held in the electrolyte layer or separator is formed by applying the above solution or pregel solution on a suitable film such as a PET film, and simultaneously curing or heating and drying in an inert atmosphere. Produced by polymerization (accelerating the crosslinking reaction), or impregnated with the above solution or pregel solution into a suitable nonwoven fabric separator such as PP, and polymerized (crosslinking reaction) simultaneously with curing or heat drying in an inert atmosphere. Manufactured).

  For curing or heat drying, a vacuum dryer (vacuum oven) or the like can be used. The conditions for heat drying are determined according to the solution or the pregel solution and cannot be uniquely defined, but are usually 30 to 110 ° C. and 0.5 to 12 hours.

  The thickness of the electrolyte layer can be controlled using a spacer or the like. In the case of using a photopolymerization initiator, it is poured into a light transmissive gap, irradiated with ultraviolet rays using an ultraviolet irradiation device capable of drying and photopolymerization, and the polymer in the electrolyte layer is photopolymerized to carry out a crosslinking reaction. It is good to advance and form a film. However, it is needless to say that the method is not limited to this. Depending on the type of polymerization initiator, radiation polymerization, electron beam polymerization, thermal polymerization, etc. are used properly.

  In addition, since the film used above may be heated to about 80 ° C. in the production process, it has sufficient heat resistance at the temperature and has no reactivity with the solution or the pregel solution, and the production process. For example, polyethylene terephthalate (PET) or polypropylene film can be used, but it should not be limited to these.

  The width of the electrolyte layer is often slightly smaller than the current collector size of the bipolar electrode.

  About the composition component of the said solution or pregel solution, its compounding quantity, etc., it should be suitably determined according to the intended purpose.

  The separator impregnated with the electrolytic solution can be produced by various conventionally known manufacturing methods, for example, a method in which the separator impregnated with the electrolytic solution is sandwiched between bipolar electrodes, a vacuum injection method, or the like. Therefore, detailed description is omitted below.

(7) Lamination of Bipolar Electrode and Electrolyte Layer The bipolar electrode and electrolyte layer produced as described above are sufficiently heated and dried under high vacuum. Thereafter, a plurality of each may be cut into an appropriate size as desired. A predetermined number of these bipolar electrodes and electrolyte layers are overlapped to produce a bipolar secondary battery body (electrode laminate).

  The number of stacked electrode stacks is determined in consideration of battery characteristics required for the bipolar secondary battery. Moreover, the electrode which formed only the positive electrode layer on the electrical power collector is arrange | positioned at the outermost layer by the side of a positive electrode. In the outermost layer on the negative electrode side, an electrode in which only the negative electrode layer is formed on the current collector is disposed. In the step of obtaining a bipolar secondary battery by laminating a bipolar electrode and an electrolyte layer, it is preferable to carry out in an inert atmosphere from the viewpoint of preventing moisture and the like from entering the battery. For example, the bipolar battery may be manufactured under an argon atmosphere or a nitrogen atmosphere.

(8) Formation of insulating layer In this invention, an epoxy resin (precursor solution) etc. are apply | coated by the predetermined width around the electrode formation part of an electrode laminated body, for example. At this time, the voltage detection tab, the electrode terminal plate, the electrode lead, the electrode tab, or the current collector portion to which these need to be connected are masked in advance using a releasable masking material or the like. Thereafter, an epoxy resin or the like is cured to form an insulating layer, and then the masking material is peeled off.

(9) Connection of terminal plate, electrode lead and tab (terminal) The positive electrode tab and the negative electrode tab are joined (electrically connected) to the outermost current collectors of the bipolar battery body (battery laminate), respectively. . As a method for joining the tabs, ultrasonic welding or the like having a low joining temperature can be preferably used. However, the method is not limited to this, and a conventionally known joining method can be appropriately used.

(10) Packing (battery completion)
Finally, in order to prevent external impact and environmental degradation, the entire battery stack is sealed with a battery exterior material such as an aluminum laminate film to complete a bipolar battery. At the time of sealing, one end of the positive electrode tab and the negative electrode tab is taken out of the battery.

  The structure of the bipolar secondary battery of the present invention is not particularly limited, and when distinguished by form and structure, any conventionally known one such as a stacked (flat) battery or a wound (cylindrical) battery can be used. The present invention can also be applied to other forms and structures.

  Hereinafter, the present invention will be described through examples and comparative examples. However, the present invention is not limited to these examples.

<Example 1>
Manufacture of a layer containing a polymer material constituting a current collector As a current collector material, a polymer material having 80 vol% of polypropylene, 20 vol% of carbon fine particles having an average particle diameter of 0.8 μm and a film thickness of 20 μm as a conductive filler is used. Used (off-the-shelf). Two sheets were prepared in order to laminate these to form a current collector.

  Further, two of the current collectors to be laminated were the outermost layers using stainless steel foil, and only one of the positive electrode active material layer and the negative electrode active material layer described below was formed.

Production of Positive Electrode Active Material Layer 85% by mass of LiMn ₂ O ₄ was used as the positive electrode active material, 5% by mass of acetylene black was used as the conductive additive, and 10% by mass of polyvinylidene fluoride (PVdF) was used as the binder. In addition, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was used as a solvent for viscosity adjustment.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, PVdF was added and sufficiently dissolved in the NMP solvent. Thereafter, the positive electrode active material and the conductive auxiliary agent were added little by little to make it familiar with the solvent in which PVdF was dissolved. When all of the positive electrode active material and the conductive additive were added, the viscosity was adjusted by adding a solvent as appropriate.

The slurry obtained above was applied to one side of a layer containing a polymer material constituting a current collector using a coating apparatus. Subsequently, the thickness of the positive electrode active material layer was adjusted using a doctor blade having a constant thickness, and dried at 100 ° C. on a hot stirrer. The obtained positive electrode active material layer had a thickness of 15 μm and a density of 2.5 g / cm ³ .

Production of Negative Electrode Active Material Layer 85% by mass of Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, 5% by mass of acetylene black as a conductive additive, 10% by mass of PVdF as a binder, and an appropriate amount of NMP as a solvent were used.

  First, high purity anhydrous NMP was charged into a dispersing mixer. Next, PVdF was added and sufficiently dissolved in the NMP solvent. Thereafter, the negative electrode active material and the conductive auxiliary agent were added little by little to make it familiar with the solvent in which PVdF was dissolved. When all of the negative electrode active material and the conductive additive were added, a solvent was added as appropriate to adjust the viscosity.

The slurry obtained above was applied to one side of a layer containing another polymer material different from the one in which the positive electrode active material layer was formed, using a coating apparatus. Subsequently, the thickness of the negative electrode active material layer was adjusted using a doctor blade having a constant thickness, and dried at 100 ° C. on a hot stirrer to obtain a negative electrode. The obtained negative electrode active material layer had a thickness of 15 μm and a density of 1.5 g / cm ³ .

Pressing Step The layer containing the polymer material formed with the positive electrode active material layer produced as described above was pressed at a pressing pressure of 50 t / m using a roll press machine. Similarly, a layer containing a polymer material on which a negative electrode active material layer was separately formed was pressed at a pressing pressure of 50 t / m using a roll press.

Formation of conductive paste layer Carbon paste is formed as a conductive paste to a thickness of 10 μm on the surface of the two layers containing the polymer material produced as described above, on which the positive electrode active material layer and the negative electrode active material layer are not formed. Applied. The carbon paste contained graphite, carbon black, phenol resin, and butyl carbitol (trade name “Bunny Height” manufactured by Nippon Graphite Co., Ltd.). Before the carbon paste was dried, the surfaces of the two layers containing the polymer material coated with the carbon paste were overlapped to form a current collector to obtain a bipolar electrode.

  The thickness of the current collector of the obtained bipolar electrode was 40 μm as a whole. In the completed bipolar electrode, the current collector had an electrode portion and a peripheral margin of 10 mm on the surface, and the size of the current collector was 140 × 90 mm. The positive and negative electrodes were the same size.

Formation of Electrolyte Layer The following materials were mixed at a predetermined ratio to form a gel electrolyte layer.

Propylene carbonate and ethylene carbonate were used as the solvent at a mass ratio of 1/1, and 1M LiPF ₆ (90% by mass) was used as the solute. As the matrix polymer, a (VdF-HFP) copolymer of hexafluoropropylene and vinylidene fluoride containing 10% by mass of hexafluoropropylene was used. Dimethyl carbonate (DMC) was used as a viscosity adjusting solvent, and these were mixed to prepare a solution containing a gel polymer electrolyte.

  This electrolyte was applied to the surfaces of the positive electrode active material layer and the negative electrode active material layer using a coating apparatus, the gel polymer electrolyte solution was immersed therein, and the DMC was dried. Further, the gel electrolyte solution was applied and immersed on both sides of a 20 μm thick porous film separator made of polypropylene, and the DMC was dried. The size of the separator was 130 mm × 80 mm. In this example, the layer formed on the active material layer and the separator together form a gel polymer electrolyte layer.

Assembly process On the stainless steel foil current collector formed with only the positive electrode active material layer, a gel polymer electrolyte solution was applied in the same manner as described above, and a separator was placed thereon. On top of that, the above bipolar electrode and separator were laminated. Finally, the gel polymer electrolyte was applied in the same manner as above onto the negative electrode active material layer of the stainless steel foil current collector in which only the negative electrode active material layer was formed, and then the negative electrode active material layer was laminated downward on the separator. . Further, a polyethylene film having a width of 10 mm was placed on the seal margin of each current collector as a sealing material. In this way, a bipolar secondary battery was constructed.

  This bipolar secondary battery is subjected to a hot press machine at 0.2 MPa and 160 ° C. for 5 seconds to eliminate the interface between the electrolyte layer and the bipolar electrode, and further heated for about 1 hour to seal with a sealing material. Went. Al plates with a current of 130 × 80 mm and a thickness of 100 μm were arranged between the upper and lower surfaces of the bipolar electrode thus obtained and sandwiched. The Al plate was further provided with a current extraction terminal having a width of 30 × 50 mm. This bipolar battery was vacuum-sealed with an aluminum laminate film so that the current extraction terminal was exposed to complete a bipolar secondary battery. In this way, 20 bipolar secondary batteries were produced. Twenty bipolar secondary batteries were evaluated as described later.

<Example 2>
In this example, a bipolar electrode and 20 pieces of the bipolar electrode were formed in the same manner as in the example except that the conductive paste layer was not provided between the layers including the polymer material constituting the two-layer current collector of the bipolar electrode. A bipolar secondary battery was produced. These bipolar secondary batteries were used and evaluated as described later in the same manner as in Example 1.

<Comparative example>
One layer containing a polymer material having a thickness of 40 μm was prepared as a current collector, and a positive electrode active material layer was formed on one surface of the current collector of the one layer and a negative electrode active material layer was formed on the other surface and pressed. A bipolar electrode was produced in the same manner as in Example 1 except that. Since the current collector is one layer, no conductive paste layer was provided. Using this bipolar electrode, 20 bipolar secondary batteries were produced in the same manner as in Example 1.

<Evaluation>
The performance of the bipolar secondary batteries obtained in Examples 1 and 2 and the comparative example was evaluated as follows. First, each battery was charged at a constant current of up to 8.2 V at a current of 0.5 mA, then charged at a constant voltage, and charged together for 10 hours. Thereafter, the battery was discharged at 1 mA for 5 seconds, and the internal resistance of the battery was calculated from the voltage change at this time. The results are shown in Table 1 below. The batteries of each example and comparative example use 20 samples, and the numerical values shown in Table 1 are average values of the 20 samples. The internal resistance value is a relative value when the comparative example is 100.

  These batteries were left in an atmosphere of 60 ° C., and the voltage drop was measured. A sample whose voltage dropped to 7.5 V or less when left for 1 week was regarded as defective. The obtained results are shown in Table 1 together with the internal resistance values.

  The proportion of defects for one week after standing was 7 samples out of 20 in the comparative example, but none of Examples 1 and 2 showed a voltage drop even after one week. In a conventional battery using a metal foil as a current collector, such a voltage drop is hardly seen. As described above, this voltage drop is presumed to be a result of a liquid junction caused by a minute crack generated in the current collector containing the polymer material. Therefore, it can be said that the bipolar electrode of the present invention effectively prevents the influence of such a minute crack.

  Moreover, it turns out that the internal resistance of Example 1 is a little high from the measurement result of the internal resistance of a battery. This is thought to be because contact resistance was generated at the interface due to the current collector having two layers, but the current collector had a practically no problem as compared with the comparative example having one layer. Furthermore, in Example 1 provided with the conductive paste layer, the contact resistance is greatly reduced, and it can be seen that the performance of the current collector of the comparative example is almost the same as that of a single layer.

1 is a schematic cross-sectional view schematically showing the overall structure of a bipolar lithium ion secondary battery according to an embodiment of the present invention. It is the figure which showed typically the state which pressed the current collector of 1 layer. It is the figure which showed typically the state which pressed the 2 layer electrical power collector. It is the figure which showed typically the change of the shape when a collector is pressed. It is an external view of one Embodiment of the assembled battery of this invention, Comprising: FIG. 5A is a top view, FIG. 5B is a front view, FIG. 5C is a side view. It is a conceptual diagram of the vehicle carrying the assembled battery of this invention. It is the schematic which shows the process of manufacturing the bipolar secondary battery by one Embodiment of this invention. It is the schematic which shows the process of manufacturing the bipolar secondary battery by one Embodiment of this invention.

Explanation of symbols

10 Bipolar lithium ion secondary battery,
11, 11a, 11b, 31, 35, 43, 54 current collector,
12, 32, 36, 41, 51 positive electrode active material layer,
13, 33, 37, 42, 52 negative electrode active material layer,
14 Bipolar electrode 14a Positive electrode 14b Negative electrode 15 Electrolyte layer,
16 cell layer,
17 Power generation element (battery element; laminate),
18 positive electrode tab,
19 negative electrode tab,
20 positive terminal lead,
21 negative terminal lead,
22, 47, 58 Battery exterior material 23 Insulating layers 34, 40, 50 Layers containing a polymer material,
44, 55 Separator 45, 56 Tab 46, 57 Sealing material 53 Conductive paste layer 250 Small assembled battery,
300 battery packs,
310 connection jig,
400 electric car,
A crack.

Claims (9)

A current collector consisting of at least two layers containing a polymer material;
A positive electrode active material layer formed on one surface of the current collector;
A negative electrode active material layer formed on the other surface of the current collector;
Including bipolar electrode.   The bipolar electrode according to claim 1, wherein the number of layers of at least two layers containing the polymer material is two.   The bipolar electrode according to claim 1, wherein the at least two layers containing the polymer material further contain a conductive filler.   The bipolar electrode according to claim 1, further comprising a conductive paste layer between at least two layers containing the polymer material.   A bipolar secondary battery using the bipolar electrode according to claim 1.   An assembled battery in which a plurality of bipolar secondary batteries according to claim 5 are connected.   A vehicle equipped with the bipolar secondary battery according to claim 5 or the assembled battery according to claim 6 as a driving power source. Providing at least two layers comprising a polymeric material;
Applying a slurry containing a positive electrode active material to one side of the first layer containing a polymer material, drying and pressing to form a positive electrode active material layer;
Applying a slurry containing a negative electrode active material to one side of the second layer containing a polymer material, drying and pressing to form a negative electrode active material layer;
A step of overlapping a surface of the first layer not forming the positive electrode active material layer and a surface of the second layer not forming the negative electrode active material layer;
A method for manufacturing a bipolar electrode including:   The step of overlapping forms a conductive paste layer on at least one of the surface of the first layer where the positive electrode active material layer is not formed and the surface of the second layer where the negative electrode active material layer is not formed. The manufacturing method of the bipolar electrode of Claim 8 containing this.

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