JP2011054325A - Collector for bipolar type secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means capable of restraining transmission of lithium ions inside a collector containing resin. <P>SOLUTION: The collector for a bipolar type secondary battery contains a resin layer having conductivity, wherein the resin layer having the conductivity contains a lithium-content layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current collector for a bipolar secondary battery.

  In recent years, hybrid vehicles (HEV), electric vehicles (EV), and fuel cell vehicles have been manufactured and sold from the viewpoint of environment and fuel consumption, and new developments are continuing. In these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging. As the power supply device, 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. In particular, lithium ion secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charging and discharging, and various developments have been intensively advanced. However, in order to apply to the power sources for driving motors of various automobiles as described above, it is necessary to use a plurality of secondary batteries connected in series in order to ensure a large output.

  However, when a battery is connected via the connection portion, the output is reduced due to the electrical resistance of the connection portion. Further, the battery having the connection portion has a disadvantage in terms of space. That is, the connection portion causes a reduction in the output density and energy density of the battery.

  In order to solve this problem, bipolar secondary batteries such as bipolar lithium ion secondary batteries have been developed. A bipolar secondary battery has a structure in which a plurality of bipolar electrodes, each having a positive electrode active material layer formed on one side of a current collector and a negative electrode active material layer formed on the other side, are stacked via an electrolyte layer or a separator. Have

  The current collector used in such a bipolar secondary battery is preferably made of a material that is lighter and more conductive in order to ensure a higher output density. Therefore, in recent years, a current collector composed of a polymer material to which a conductive filler is added in place of the conventional metal foil has been proposed. For example, Patent Document 1 discloses a current collector including a conductive resin in which metal particles or carbon particles are mixed as a conductive filler in a polymer material.

JP 2006-190649 A

  However, the current collector as described in Patent Document 1 has a lower barrier property against lithium ions in the electrolytic solution than the metal foil current collector. For this reason, when applied to a bipolar lithium ion secondary battery, lithium ions may penetrate into the current collector of the bipolar electrode and the lithium ions may remain occluded inside the current collector. It was. Since the occluded lithium ions are not easily released, the capacity of the battery may be reduced.

  Therefore, an object of the present invention is to provide means for suppressing the permeation of lithium ions into the current collector in a bipolar battery current collector including a conductive resin layer.

  The inventors of the present invention have made extensive studies in view of the above problems. As a result, the present inventors have found that the above object can be achieved by providing a lithium-containing layer in a current collector including a conductive resin layer.

  According to the present invention, lithium is supplied from a lithium-containing layer installed in a current collector including a conductive resin layer to an adjacent resin layer, and a lithium occlusion layer that is a resin layer in which lithium is occluded is formed. The By forming such a lithium occlusion layer, it is possible to suppress the penetration of lithium ions in the electrolyte into the current collector.

It is a schematic sectional drawing which shows the structure of a bipolar lithium ion secondary battery. It is a schematic sectional drawing showing typically the current collector by a 1st embodiment. It is a schematic sectional drawing showing the modification of the electrical power collector of 1st Embodiment. It is the schematic which shows the preferable form of a lithium content layer. It is a schematic sectional drawing showing the bipolar electrode using the electrical power collector of 1st Embodiment. It is a schematic sectional drawing showing the modification of the bipolar electrode using the electrical power collector of 1st Embodiment. It is a perspective view showing the appearance of a bipolar lithium ion secondary battery.

  First, a bipolar lithium ion secondary battery which is a preferred embodiment will be described, but the present invention is not limited to the following embodiment. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  When distinguished by the structure and form of the bipolar battery, it is not particularly limited, such as a stacked (flat) battery or a wound (cylindrical) battery, and can be applied to any conventionally known structure.

  Similarly, there is no particular limitation even when distinguished by the form of electrolyte of the bipolar battery. For example, the present invention can be applied to any of a liquid electrolyte type battery in which a separator is impregnated with a nonaqueous electrolytic solution, a polymer gel electrolyte type battery also called a polymer battery, and a solid polymer electrolyte (all solid electrolyte) type battery. With respect to the polymer gel electrolyte and the solid polymer electrolyte, these can be used alone, or the polymer gel electrolyte or the solid polymer electrolyte can be used by impregnating the separator.

  Moreover, when it sees in the electrode material of a battery, or the metal ion which moves between electrodes, it does not restrict | limit in particular, It can apply to any well-known electrode material. Examples include lithium ion secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, nickel metal hydride secondary batteries, nickel cadmium secondary batteries, nickel metal hydride batteries, and the like, preferably lithium ion secondary batteries. . This is because in the lithium ion secondary battery, the voltage of the cell (single cell layer) is large, high energy density and high output density can be achieved, and it is excellent as a vehicle driving power source or an auxiliary power source.

  FIG. 1 is a schematic cross-sectional view schematically showing the entire structure of a bipolar lithium ion secondary battery 10. The bipolar lithium ion secondary battery 10 shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29.

  As shown in FIG. 1, the power generating element 21 of the bipolar lithium ion secondary battery 10 has a positive electrode active material layer 13 electrically coupled to one surface of the current collector 11, and is opposite to the current collector 11. It has a plurality of bipolar electrodes 23 formed with a negative electrode active material layer 15 electrically coupled to the side surface. Each bipolar electrode 23 is laminated via the electrolyte layer 17 to form the power generation element 21. The electrolyte layer 17 has a configuration in which an electrolyte is held at the center in the surface direction of a separator as a base material. At this time, the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23 face each other through the electrolyte layer 17. The bipolar electrodes 23 and the electrolyte layers 17 are alternately stacked. That is, the electrolyte layer 17 is interposed between the positive electrode active material layer 13 of one bipolar electrode 23 and the negative electrode active material layer 15 of another bipolar electrode 23 adjacent to the one bipolar electrode 23. ing.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar lithium ion secondary battery 10 has a configuration in which the single battery layers 19 are stacked. In addition, for the purpose of preventing liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17, an insulating portion 31 is disposed on the outer peripheral portion of the unit cell layer 19. A positive electrode active material layer 13 is formed only on one side of the positive electrode outermost layer current collector 11 a located in the outermost layer of the power generation element 21. The negative electrode active material layer 15 is formed only on one surface of the outermost current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21. However, the positive electrode active material layer 13 may be formed on both surfaces of the outermost layer current collector 11a on the positive electrode side. Similarly, the negative electrode active material layer 15 may be formed on both surfaces of the outermost layer current collector 11b on the negative electrode side.

  Further, in the bipolar secondary battery 10 shown in FIG. 1, the positive electrode current collector plate 25 is disposed so as to be adjacent to the outermost layer current collector 11 a on the positive electrode side, and this is extended and led out from the battery exterior material 29. . On the other hand, the negative electrode current collector plate 27 is disposed so as to be adjacent to the outermost layer current collector 11 b on the negative electrode side, and is similarly extended and led out from the battery exterior material 29.

  In the bipolar lithium ion secondary battery 10 shown in FIG. 1, an insulating part 31 is usually provided around each single battery layer 19. The insulating part 31 prevents the adjacent current collectors 11 in the battery from coming into contact with each other and a short circuit caused by a slight irregularity at the end of the unit cell layer 19 in the power generation element 21. Is provided. By installing such an insulating part 31, long-term reliability and safety can be ensured, and a high-quality bipolar lithium ion secondary battery 10 can be provided.

  Note that the number of stacks of the unit cell layers 19 is adjusted according to a desired voltage. Further, in the bipolar secondary battery 10, the number of stacking of the single battery layers 19 may be reduced if a sufficient output can be secured even if the thickness of the battery is made as thin as possible. Even in the bipolar lithium ion secondary battery 10, in order to prevent external impact and environmental degradation during use, the power generation element 21 is sealed in the battery exterior material 29 under reduced pressure, and the positive current collector plate 25 and the negative current collector plate It is preferable to adopt a structure in which 27 is taken out of the battery exterior material 29. Hereinafter, main components of the bipolar secondary battery of this embodiment will be described.

  FIG. 2 is a schematic cross-sectional view schematically showing the current collector 11 (first embodiment) of the bipolar lithium ion secondary battery 10. As shown in FIG. 2, the current collector 11 includes a resin layer 2 having conductivity and a lithium-containing layer 3. By supplying lithium from the lithium-containing layer 3 to the resin layer 2 having conductivity, in the resin layer 2 having conductivity, the lithium occlusion layer 4, which is a region having a high lithium concentration, is located in the vicinity of the lithium-containing layer 3. It is formed. By forming the lithium storage layer 4, it is possible to suppress the penetration of lithium ions contained in the electrolyte into the resin layer 2. For this reason, the capacity | capacitance fall of the bipolar battery resulting from the lithium ion in electrolyte solution being occluded inside the resin layer 2 can be suppressed.

  In the bipolar battery, since the electric charge generated on the negative electrode side is directly supplied to the positive electrode on the opposite side of the current collector, the current flows in the stacking direction, but the flow in the plane direction is not necessary. Therefore, in order to improve the current collection efficiency of the current collector, it is effective to use a resin whose conductivity in the perpendicular direction is higher than that in the plane direction.

  In addition, when a resin with a large resistance in the planar direction is used as a current collector, when an internal short circuit occurs in a single battery constituting the bipolar battery, the current collector suppresses the short circuit current, thereby generating heat from the bipolar battery. Can be prevented. Further, if the resin has high thermal conductivity and high heat dissipation, the heat distribution in the planar direction of the current collector can be made uniform, and the thermal expansion in the planar direction can be made uniform. As a result, deterioration of the bipolar battery can be further suppressed.

  As a method for preventing lithium ions in the electrolyte from permeating through the resin layer when using a current collector including a conductive resin layer, a metal foil such as a copper foil having a partition wall (barrier property) function is used. A method of laminating the formed ion blocking layer on the surface of the resin layer is used. However, when a material having a large atomic weight such as copper is used for the bonding surface between the active material layer and the resin layer, the weight of the current collector increases, and the battery capacity per weight can be reduced. By providing the lithium-containing layer 3 in the conductive resin layer 2 as shown in FIG. 2, it is possible to suppress the decrease in battery capacity per weight while suppressing the penetration of lithium ions into the resin layer 2. Can do. For example, as a resin layer having conductivity, a polyimide resin (A4 size, thickness 50 μm) containing 10% by mass of a conductive agent is used, and the weight of a current collector in which a copper foil as an ion blocking layer is laminated is 5 .45 g. Here, the thickness of the copper foil was 2 μm, which is a thickness capable of suppressing the penetration of lithium ions into the resin layer. On the other hand, the weight of the current collector in which the lithium-containing layer was disposed on the polyimide resin (A4 size, thickness 50 μm) containing 10% by mass of the conductive agent was 4.44 g, and the effect of reducing the weight by about 19% was confirmed. . Here, the lithium-containing layer has a flat plate shape, and the thickness is 3 μm, which is a thickness at which a lithium occlusion layer having a sufficient lithium concentration is formed in the resin layer.

  Hereinafter, the conductive resin layer, the lithium-containing layer, and the lithium storage layer constituting the current collector of the present embodiment will be described.

(Conductive resin layer)
The conductive resin layer (resin layer) is a layer containing a polymer material and is not particularly limited as long as it is a conductive layer. Preferably, the resin layer has higher conductivity in the direction perpendicular to the planar direction.

  Specific forms of the resin layer include 1) a form in which the polymer material constituting the resin is a conductive polymer, and 2) a form in which the polymer material constituting the resin is a non-conductive polymer. When a non-conductive polymer is used, conductivity can be imparted to the resin layer by adding a conductive material.

  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. Specifically, polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole, or a mixture thereof is preferable. Polyaniline, polypyrrole, polythiophene, and polyacetylene are more preferable from the viewpoints of electron conductivity and stable use in the battery.

  Examples of non-conductive polymers include olefin resins such as polyethylene (low density polyethylene (LDPE), high density polyethylene (HDPE), linear low density polyethylene (LLDPE), etc.), polypropylene (PP), and polybutylene. , Ethylene-vinyl acetate copolymer (EVA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyether nitrile (PEN), polyimide (PI), polyamide (PA), polyamide Imido (PAI), polytetrafluoroethylene (PTFE), ethylene-propylene rubber, styrene-butadiene rubber (SBR), styrene ethylene butylene styrene block copolymer, polyacrylonitrile (PAN), polymethyl acrylic Rate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), silicones, and the like epoxy resins. Since these materials have low ion conductivity, transmission of lithium ions can be suppressed. Preferred are polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide, ethylene-propylene rubber, styrene-butadiene rubber, and styrene ethylene butylene styrene block copolymer. Especially, since the polyimide is easy to occlude lithium, the effect of this invention is remarkable.

  One of the above polymer materials may be used alone, or two or more thereof may be mixed and used.

  A conductive filler may be added to the polymer material as necessary. In particular, when a non-conductive polymer is used as the polymer material, a conductive filler is essential for imparting conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property.

  The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals It is preferable to contain an alloy or metal oxide containing. These metals are resistant to the potential of the positive electrode or negative electrode formed on the current collector surface. Among these, an alloy containing at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, and Cr is more preferable.

  Specific examples of the alloy include stainless steel (SUS), Inconel (registered trademark), Hastelloy (registered trademark), and other Fe—Cr alloys, Ni—Cr alloys, and the like. By using these alloys, higher potential resistance can be obtained.

  The conductive carbon is not particularly limited, but is at least selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. It is preferable that 1 type is included. These conductive carbons 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 have excellent conductivity. Further, since the density is lower than that of the conductive filler containing the above metal, the current collector can be reduced in weight. Among these, it is more preferable to include at least one selected from the group consisting of carbon nanotubes, carbon nanohorns, ketjen black, carbon nanoballoons, and fullerenes. Since these conductive carbons have a hollow structure, the surface area per mass is large, and the current collector can be further reduced in weight. In addition, electroconductive fillers, such as these metals and electroconductive carbon, can be used individually by 1 type or in combination of 2 or more types.

  The size of the conductive filler is not particularly limited, and fillers of various sizes can be used depending on the size and thickness of the resin layer or the shape of the conductive filler. As an example, the average particle diameter when the conductive filler is granular is preferably about 0.1 to 10 μm from the viewpoint of facilitating molding of the resin layer. In the present specification, “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the conductive filler. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted. The particle diameter and average particle diameter of an active material to be described later can be defined similarly.

  The content of the conductive filler contained in the resin layer is not particularly limited, but is preferably 5 to 35% by mass, more preferably 5 to 25% by mass with respect to the total mass of the polymer material. Preferably it is 5-15 mass%. By adding such an amount of the conductive filler to the polymer material, sufficient conductivity can be imparted to the polymer material while suppressing an increase in the mass of the resin layer.

  The shape of the conductive filler is not particularly limited, and a known shape such as a granular shape, a fibrous shape, a plate shape, a lump shape, a cloth shape, and a mesh shape can be appropriately selected. For example, when it is desired to impart conductivity to a resin over a wide range, it is preferable to use a granular conductive filler. On the other hand, when it is desired to further improve the conductivity in a specific direction in the resin, it is preferable to use a conductive filler having a certain direction in the shape of a fiber or the like.

  In addition to the polymer material and the conductive filler, the resin layer may contain other additives.

  The thickness of the conductive resin layer is not particularly limited, but is preferably 0.1 to 200 μm, more preferably 5 to 150 μm, and still more preferably 10 to 100 μm. When the thickness of the resin layer is 0.1 μm or more, a current collector with high current collection efficiency can be obtained. If the thickness of the resin layer is 200 μm or less, a battery having a high battery capacity per unit volume can be obtained.

(Lithium-containing layer)
The lithium-containing layer has a function of supplying lithium to the conductive resin layer. Thereby, a lithium occlusion layer is formed in the resin layer having conductivity, and entry of lithium ions in the electrolytic solution can be prevented.

  The position where the lithium-containing layer is disposed is not particularly limited. For example, it may be provided on the surface of the conductive resin layer (between the conductive resin layer and the positive electrode active material layer or the negative electrode active material layer), or may be provided inside the conductive resin layer. Or a combination of these may be used. In particular, it is preferable to provide the lithium-containing layer inside a conductive resin layer because a lithium storage layer is efficiently formed inside the conductive resin layer.

  The lithium-containing layer may be a single layer or two or more layers. By providing two or more lithium-containing layers, the lithium concentration in the formed lithium storage layer can be further increased. For example, as shown in FIG. 3, when a plurality of lithium-containing layers are arranged, the resin layer portion 4 a sandwiched between two lithium-containing layers is more lithium than the portion 4 in contact with one lithium-containing layer. A lithium storage layer having a high concentration can be formed. Therefore, the effect of suppressing the penetration of lithium ions in the electrolytic solution into the resin layer can be improved.

  As a material used for the lithium-containing layer, lithium metal, stabilized lithium, or the like can be used. Stabilized lithium is lithium that has been treated with an inert material so as to have higher atmospheric stability than untreated lithium metal, such as lithium powder covered with an outer layer such as lithium carbonate. .

  The form of the lithium-containing layer is not particularly limited, but a thin film is preferable because a stable lithium storage layer can be formed inside the conductive resin layer. Although it does not restrict | limit especially as a shape of the said thin film, As shown in FIG. 4, (a) flat form, (b) mesh shape, (c) granular shape may be used preferably. If it is a shape like FIG. 4, a lithium content layer can be formed easily and the stable lithium occlusion layer can be formed inside the resin layer which has electroconductivity.

  The thickness of the lithium-containing layer is not particularly limited, but is preferably 0.01 to 3.0 μm. If it is the said range, the lithium occlusion layer which has suitable lithium concentration can be formed. In addition, since the lithium-containing layer can be formed inside the conductive resin layer with little variation in film thickness, a stable lithium storage layer can be formed.

  As described above, the conductive resin layer may include a plurality of lithium-containing layers. When there are a plurality of lithium-containing layers, the thicknesses of the layers may be the same or different from each other. Of the plurality of lithium-containing layers, at least one thickness is preferably in the above range, and all lithium-containing layers preferably have a thickness in the above range.

  Although the thickness of the whole electrical power collector is not specifically limited, In order to raise the output density of a battery, it is so preferable that it is thin. In a bipolar battery, the current collector present between the positive electrode active material layer and the negative electrode active material layer may have a high electrical resistance in the planar direction (the direction horizontal to the stacking direction), so the thickness of the current collector It is possible to reduce the thickness. Specifically, the thickness of the entire current collector is preferably 0.1 to 300 μm, and more preferably 0.1 to 200 μm.

  The method for disposing the lithium-containing layer on the conductive resin layer is not particularly limited, and any existing resin thin film or metal thin film deposition technique, lamination technique, bonding technique, or the like can be used as appropriate.

  That is, a method of laminating a conductive resin layer and a lithium-containing layer by thermocompression bonding, or a slurry containing a polymer material or a conductive polymer material in which a conductive material is added to the surface of the lithium-containing layer. A method of applying and drying to form a resin layer may be used. Alternatively, the ion blocking layer may be formed by a technique in which a slurry containing a polymer material to which a conductive material is added, a conductive polymer material, or the like is applied to the surface of the ion blocking layer and dried, followed by thermocompression bonding.

  Preferably, it is produced by coating lithium metal or stabilized lithium on a resin layer having conductivity using a method such as vapor deposition or sputtering. For example, after masking the surface of the conductive resin layer where the lithium-containing layer is not formed, the lithium-containing layer is formed as a thin film at a predetermined position by sputtering. Alternatively, a portion of the lithium metal that does not form a lithium-containing layer can be formed by applying a water-soluble paint to the portion that does not form a lithium-containing layer with a gravure roll or the like, performing a sputter treatment thereon, and then submerging it. Is removed to form a lithium-containing layer. Then, the collector which has a lithium content layer inside can be obtained by forming the resin layer which has electroconductivity further on the surface in which the lithium content layer was formed. A current collector including two or more lithium-containing layers can also be produced by repeating these methods. However, manufacturing methods other than these manufacturing methods may be used. In addition, what is necessary is just to adjust the application | coating position of said masking shape or said water-soluble paint, when producing a mesh-like lithium content layer. The particulate lithium-containing layer can be produced by dispersing lithium metal or stabilized lithium powder on the surface of the resin layer and further forming a resin layer thereon.

  The first embodiment described above has the following effects. That is, by disposing the lithium-containing layer on the conductive resin layer, a lithium occlusion layer in which lithium is occluded in the resin can be formed. Thereby, it can suppress that the lithium ion contained in electrolyte solution penetrate | invades into a resin layer. By using such a current collector, the battery capacity of a bipolar battery using a current collector having a resin layer can be improved. In addition, cycle characteristics (capacity maintenance ratio) can be improved.

(Lithium occlusion layer)
The lithium occlusion layer is a layer in which lithium is occluded in a resin layer, which is formed in a portion of the resin layer adjacent to the lithium-containing layer. The lithium concentration in the lithium occlusion layer is not particularly limited as long as it is a concentration that can suppress the penetration of lithium from the electrolytic solution. In the current collector of the present embodiment, the present inventors form a lithium occlusion layer having a lithium concentration that gradually decreases from the portion in contact with the lithium-containing layer in the stacking direction (thickness direction). It was confirmed. The lithium concentration in the lithium storage layer can be adjusted by controlling the thickness of the lithium-containing layer and the distance between the two lithium-containing layers.

  The lithium occlusion layer is formed by moving at least part of lithium from the lithium-containing layer to the resin layer having conductivity. A method for moving at least a part of lithium is not particularly limited. For example, a voltage of about 1 to 5 V is applied in the thickness direction of the current collector in which the lithium-containing layer is disposed in the resin layer to cause lithium movement. Preferably, a battery is produced using the current collector, and this is charged and discharged. By doing so, lithium can sufficiently move into the resin layer, and a lithium concentration gradient can be formed in the resin layer. Charge / discharge conditions are not particularly limited. For example, at 25 ° C., charging / discharging at 4.3 V-2.5 V and a constant current of 0.5 C is performed 200 cycles.

  FIG. 5 shows the current collector 11 for a bipolar secondary battery described above, the positive electrode active material layer 13 formed on one surface of the current collector, and the negative electrode formed on the other surface of the current collector. 2 is a schematic cross-sectional view of a bipolar secondary battery electrode 23 including an active material layer 15. FIG.

  As shown in FIG. 5, in the current collector 11, the lithium-containing layer 3 is preferably formed in a region closer to the negative electrode active material layer 15 than the center position in the thickness direction of the resin layer 2 having conductivity. Lithium ions in the electrolyte enter into the resin layer mainly from the joint surface between the negative electrode active material layer and the resin layer. Therefore, if the lithium-containing layer 3 is formed on the side close to the negative electrode active material layer 15 as shown in FIG. 5, the lithium occlusion layer 4 can be obtained on the side close to the negative electrode active material layer, and the lithium ions in the electrolytic solution can be obtained. Highly effective in preventing intrusion. Note that when there are a plurality of lithium-containing layers, at least one layer may satisfy the above condition, but it is preferable that all the layers satisfy the above condition.

  In addition, as shown in FIG. 5, when the electrode 23 is viewed from the negative electrode active material layer 15 side, the region where the lithium-containing layer 3 is formed completely covers the region where the negative electrode active material layer 15 is formed. preferable. Lithium ions in the electrolyte enter into the resin layer mainly from the joint surface between the negative electrode active material layer 15 and the resin layer 2. Therefore, if the lithium-containing layer 3 is formed in a region that covers the region of the joint surface between the negative electrode active material layer 15 and the resin layer 2, the lithium storage layer 4 is formed so as to cover the region of the joint surface. And is highly effective in preventing the entry of lithium ions in the electrolyte. Note that when there are a plurality of lithium-containing layers, at least one layer may satisfy the above condition, but it is preferable that all the layers satisfy the above condition.

  FIG. 6 is a schematic view showing a modification of the bipolar electrode described above. In the bipolar electrode 23 shown in FIG. 6, the conductive resin layer 2 has a plurality of lithium-containing layers 3. In the resin layer 2, a lithium storage layer 4 is formed in a region in contact with the lithium-containing layer 3. At this time, as shown in FIG. 6, it is preferable that the thickness of the lithium-containing layer 3 is thicker as it approaches the negative electrode active material layer 15. In order to suppress long-term penetration of lithium ions in the electrolyte into the resin layer, the vicinity of the bonding surface between the negative electrode active material layer 15 and the resin layer 2 needs to have a high lithium concentration in the long term. There is. In order to make the vicinity of the bonding surface between the negative electrode active material layer 15 and the resin layer 2 in a state where the lithium concentration is high in the long term, the first lithium-containing layer 3a counted from the negative electrode active material layer 15 side is long-term. Need to be maintained. Since the lithium-containing layer is thinned over time when the battery is operated, it is preferable that the first lithium-containing layer 3a is as thick as possible, counting from the negative electrode active material layer 15 side. On the other hand, if the plurality of lithium-containing layers are all thickly counted from the negative electrode active material layer 15 side in the same manner as the first lithium-containing layer 3a, the weight of the entire current collector may increase. Therefore, the first lithium-containing layer 3a counted from the negative electrode active material layer 15 side is set to be the thickest and thinned toward the positive electrode active material layer 13 side. In addition, the penetration of lithium ions in the electrolyte into the current collector can be suppressed.

  The bipolar lithium ion secondary battery described above is characterized by the structure of the current collector. Hereinafter, other main components will be described.

(Active material layer)
[Positive electrode (positive electrode active material layer) and negative electrode (negative electrode active material layer)]
The active material layer 13 or 15 contains an active material, and further contains other additives as necessary.

The positive electrode active material layer 13 includes a positive electrode active material. As the positive electrode active material, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Co—Mn) O _2, and lithium-such as those in which a part of these transition metals are substituted with other elements Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. Of course, positive electrode active materials other than those described above may be used.

The negative electrode active material layer 15 includes a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite, soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. . In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in each active material layer 13, 15 is not particularly limited, but is preferably 1 to 20 μm from the viewpoint of increasing the output.

  The positive electrode active material layer 13 and the negative electrode active material layer 15 include a binder.

  Although it does not specifically limit as a binder used for an active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FE) ), Tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) , Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-) TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluoro rubber (VDF-PFP-TFE fluoro rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluoro rubber (VDF-PFMVE-TFE fluoro rubber), vinylidene fluoride-chlorotrifluoroethylene fluoro rubber Examples thereof include vinylidene fluoride-based fluororubber such as (VDF-CTFE-based fluororubber), an epoxy resin, and the like. Among these, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable. These suitable binders are excellent in heat resistance, have a very wide potential window, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

  The amount of the binder contained in the active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. Yes, more preferably 1 to 10% by mass.

  Examples of other additives that can be included in the active material layer include a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer and the negative electrode active material layer is not particularly limited. The mixing ratio can be adjusted by appropriately referring to known knowledge about the non-aqueous solvent secondary battery. The thickness of each active material layer is not particularly limited, and conventionally known knowledge about the battery can be appropriately referred to. For example, the thickness of each active material layer is about 2 to 100 μm.

(Electrolyte layer)
As the electrolyte constituting the electrolyte layer 13, a liquid electrolyte or a polymer electrolyte can be used.

  The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). Further, as the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiBETI, can be similarly employed.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte 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), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

(Outermost layer current collector)
As the material of the outermost layer current collector, for example, a metal or a conductive polymer can be adopted. From the viewpoint of ease of taking out electricity, a metal material is preferably used. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum and copper are preferable from the viewpoints of electron conductivity and battery operating potential.

(Tabs and leads)
A tab may be used for the purpose of taking out the current outside the battery. The tab is electrically connected to the outermost layer current collector or current collector plate, and is taken out of the laminate sheet which is a battery exterior material.

  The material which comprises a tab in particular is not restrict | limited, The well-known highly electroconductive material conventionally used as a tab for lithium ion secondary batteries can be used. As a constituent material of the tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and aluminum, copper, and the like are more preferable from the viewpoint of light weight, corrosion resistance, and high conductivity. Is preferred. Note that the same material may be used for the positive electrode tab and the negative electrode tab, or different materials may be used.

  The positive terminal lead and the negative terminal lead are also used as necessary. As the material of the positive terminal lead and the negative terminal lead, a terminal lead used in a known lithium ion secondary battery can be used. It should be noted that the part taken out from the battery outer packaging material 29 has a heat insulating property so as not to affect the product (for example, automobile parts, particularly electronic devices) by contacting with peripheral devices or wiring and causing leakage. It is preferable to coat with a heat shrinkable tube or the like.

(Battery exterior material)
As the battery exterior material 29, a known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover a power generation element (battery element) can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV.

(Insulation part)
The insulating part 31 prevents a liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17. In addition, the insulating part 31 prevents the adjacent current collectors in the battery from coming into contact with each other or the occurrence of a short circuit due to a slight irregularity at the end of the unit cell layer 19 in the power generation element 21. Is provided.

  The material constituting the insulating portion 31 may have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance at the battery operating temperature, and the like. That's fine. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Among these, polyethylene resin and polypropylene resin are preferably used as the constituent material of the insulating portion 31 from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming property), economy, and the like.

  In addition, said bipolar battery can be manufactured by a conventionally well-known manufacturing method.

<Appearance structure of bipolar battery>
FIG. 7 is a perspective view showing the appearance of a laminated flat bipolar lithium ion secondary battery which is a typical form of a bipolar battery.

  As shown in FIG. 7, the laminated flat lithium ion secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for taking out electric power from both sides thereof. Has been pulled out. The power generation element (battery element) 57 is wrapped by the battery outer packaging material 52 of the lithium ion secondary battery 50, and the periphery thereof is heat-sealed. The power generation element (battery element) 57 includes the positive current collector plate 58 and the negative electrode The current collector plate 59 is sealed in a state of being pulled out. Here, the power generation element (battery element) 57 corresponds to the power generation element (battery element) 21 of the bipolar lithium ion secondary battery 10 shown in FIG. 1 described above. A plurality of single battery layers (single cells) 19 composed of a positive electrode (positive electrode active material layer) 13, an electrolyte layer 17, and a negative electrode (negative electrode active material layer) 15 are laminated.

  The lithium ion battery is not limited to a stacked flat shape. The wound lithium ion battery may have a cylindrical shape, or may be a rectangular flat shape obtained by deforming such a cylindrical shape. In the said cylindrical shape thing, a laminate film may be used for the exterior material, and the conventional cylindrical can (metal can) may be used, for example, It does not restrict | limit. Preferably, the power generation element (battery element) is covered with an aluminum laminate film. With this configuration, weight reduction can be achieved.

  Further, the removal of the current collecting plates 58 and 59 shown in FIG. 7 is not particularly limited. The positive electrode current collector plate 58 and the negative electrode current collector plate 59 may be drawn from the same side, or the positive electrode current collector plate 58 and the negative electrode current collector plate 59 may be divided into a plurality of parts and taken out from each side. It is not limited to the one shown in FIG. Further, in a wound type lithium ion battery, instead of the current collector plate, for example, a terminal may be formed using a cylindrical can (metal can).

  The lithium ion battery is suitable as a power source for driving a vehicle or an auxiliary power source that requires a high volume energy density and a high volume output density as a large capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, etc. Can be used.

2 resin layer having conductivity,
3, 3a lithium-containing layer,
4, 4a lithium storage layer,
10, 50 Bipolar lithium ion secondary battery,
11 Current collector,
11a The outermost layer current collector on the positive electrode side,
11b The outermost layer current collector on the negative electrode side,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21, 57 power generation element,
23 Bipolar electrode,
25, 58 positive current collector,
27, 59 negative electrode current collector plate,
29, 52 Battery exterior material,
31 Insulation part.

Claims (7)

  A current collector for a bipolar secondary battery, comprising a resin layer having conductivity, wherein the resin layer having conductivity comprises a lithium-containing layer.   The current collector for a bipolar secondary battery according to claim 1, wherein the resin layer having conductivity includes polyimide as a polymer material.   The current collector for a bipolar secondary battery according to claim 1, wherein the lithium-containing layer has a thickness of 0.01 to 3.0 μm. The current collector for a bipolar secondary battery according to any one of claims 1 to 3,
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,
The bipolar secondary battery electrode, wherein the lithium-containing layer is formed in a region closer to the negative electrode active material layer than a center position in the thickness direction of the conductive resin layer.   The region in which the lithium-containing layer is formed completely covers the region in which the negative electrode active material layer is formed when the bipolar secondary battery electrode is viewed from the negative electrode active material layer side. Bipolar secondary battery electrode.   6. The bipolar secondary battery according to claim 4, wherein a plurality of the lithium-containing layer layers are laminated via a conductive resin, and the thickness of the lithium-containing layer is thicker as it approaches the negative electrode active material layer. Electrode.   A bipolar secondary battery comprising the electrode for a bipolar secondary battery according to any one of claims 4 to 6.

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