JP5417867B2 - Bipolar secondary battery - Google Patents

Description

  The present invention relates to a bipolar secondary battery, and an assembled battery and a vehicle using the battery. In particular, the present invention relates to a bipolar secondary battery capable of preventing a reduction in battery capacity, and an assembled battery and a vehicle using the 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 plurality of bipolar electrodes in which a positive electrode active material layer is formed on one surface of a current collector and a negative electrode active material layer is formed on the other surface through an electrolyte layer and a separator. It has a power generation element.

  The current collector used in such a bipolar secondary battery is preferably made of a lighter material from the viewpoint of improving the power density per unit mass of the battery. Therefore, in recent years, a current collector composed of a resin or a conductive polymer material to which a conductive filler is added in place of a conventional metal foil has been proposed. For example, Patent Document 1 discloses a current collector made of a resin having conductivity in which metal powder is mixed as a conductive filler in a resin.

JP-A 61-285664

  However, when the current collector containing the resin as described above is used in a bipolar secondary battery, the resin in the current collector swells due to the solvent contained in the electrolytic solution. That is, a part of the electrolytic solution can be held in the resin. For this reason, there has been a problem that the electrolyte capacity serving as a lithium ion transfer medium is insufficient between the electrodes, and the battery capacity is reduced.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a bipolar secondary battery that can prevent a reduction in battery capacity.

  The present inventors have intensively studied to solve the above problems. As a result, it has been found that a shortage of the electrolyte solution between the electrodes can be prevented by using a specific combination of the resin contained in the current collector and the solvent contained in the electrolyte solution. Furthermore, as a result of examining the combination of the resin and the solvent in detail, by making the difference between the solubility parameter of the resin and the solubility parameter of the solvent into a specific range, the penetration of the electrolyte into the current collector is effectively performed. The present inventors have found that it is suppressed and have completed the present invention.

That is, the bipolar lithium ion secondary battery of the present invention has a power generation element in which a bipolar electrode and an electrolyte layer containing a supporting salt and a solvent are laminated. A bipolar electrode is formed on a current collector including a resin layer having conductivity based on a resin, a positive electrode active material layer formed on one surface of the current collector, and the other surface of the current collector. A negative electrode active material layer. And the solubility parameter (SP ₁ ) of the resin forming the base material of any one resin layer included in the current collector is 1.9 or more larger than the solubility parameter (SP ₂ ) of the solvent.

  According to the present invention, the penetration of the electrolytic solution into the current collector can be effectively suppressed. Thereby, since electrolyte solution is fully hold | maintained between electrodes, the reduction | decrease in battery capacity can be prevented.

1 is a schematic cross-sectional view schematically showing a bipolar secondary battery according to an embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a preferred embodiment of a current collector according to the present invention. FIG. 3A is an external view schematically showing an assembled battery according to an embodiment of the present invention, in which FIG. 3A is a plan view of the assembled battery, FIG. 3B is a front view of the assembled battery, and FIG. It is a side view. It is a conceptual diagram of the vehicle carrying the bipolar secondary battery or assembled battery of this invention.

Hereinafter, preferred embodiments of the present invention will be described. The present embodiment relates to a bipolar electrode having a power generation element formed by laminating an electrolyte layer containing a supporting salt and a solvent. A bipolar electrode is formed on a current collector including a resin layer having conductivity based on a resin, a positive electrode active material layer formed on one surface of the current collector, and the other surface of the current collector. A negative electrode active material layer. The absolute value of the difference between the solubility parameter (SP ₁ ) of the resin forming the base material of any one resin layer included in the current collector and the solubility parameter (SP ₂ ) of the solvent is 1.9 or more. It is.

  Hereinafter, the present embodiment will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments. 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.

<Bipolar type secondary battery>
FIG. 1 is a cross-sectional view schematically showing the overall structure of a bipolar secondary battery according to an embodiment of the present invention. The bipolar secondary battery 10 of this embodiment 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 laminate film 29 that is a battery exterior material. .

  As shown in FIG. 1, in the power generation element 21 of the bipolar secondary battery 10 of the present embodiment, a positive electrode active material layer 13 that is electrically coupled to one surface of the current collector 11 is formed. And a plurality of bipolar electrodes 23 having a negative electrode active material layer 15 electrically coupled to the opposite 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 secondary battery 10 has a configuration in which the single battery layers 19 are stacked. Further, for the purpose of preventing liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17, a seal portion (insulating layer) 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, a positive electrode current collector plate 25 is disposed so as to be adjacent to the outermost layer current collector 11a on the positive electrode side, and this is extended to form a laminate film 29 which is a battery exterior material. Derived. On the other hand, the negative electrode current collector plate 27 is disposed so as to be adjacent to the outermost layer current collector 11b on the negative electrode side, and similarly, this is extended and led out from the laminate film 29 which is an exterior of the battery.

  In the bipolar secondary battery 10 shown in FIG. 1, a seal portion 31 is usually provided around each single cell layer 19. The purpose of the seal portion 31 is to prevent 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 a seal portion 31, long-term reliability and safety are ensured, and a high-quality bipolar 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 secondary battery 10, in order to prevent external impact and environmental degradation during use, the power generation element 21 is sealed under reduced pressure in a laminate film 29 that is a battery exterior material, and the positive electrode current collector plate 25 and the negative electrode current collector 25. A structure in which the electric plate 27 is taken out of the laminate film 29 is preferable. Hereinafter, main components of the bipolar secondary battery of this embodiment will be described.

[Bipolar electrode]
The bipolar electrode has a current collector and an active material layer formed on the surface of the current collector. More specifically, a positive electrode active material layer is formed on one surface of one current collector, and a negative electrode active material layer is formed on the other surface. The active material layer includes a positive electrode active material or a negative electrode active material, and further includes other additives as necessary.

(Current collector)
The current collector has a function of mediating transfer of electrons from one surface in contact with the positive electrode active material layer to the other surface in contact with the negative electrode active material layer. The current collector according to this embodiment essentially includes at least one conductive resin layer, and may further include other layers as necessary.

  The conductive resin layer is an essential component for the current collector of this embodiment, and can contribute to weight reduction of the current collector as well as functioning as an electron transfer medium. The resin layer may include a base material made of resin and other members such as a conductive filler as necessary.

  There is no restriction | limiting in particular in resin used for a base material, A conventionally well-known nonelectroconductive polymer material or a conductive polymer material can be used without a restriction | limiting. Preferred non-conductive polymer materials include, for example, polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA) , Polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance. Examples of preferable conductive polymer materials include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector. These non-conductive polymer materials or conductive polymer materials may be used alone or in a combination of two or more.

  In order to ensure the conductivity of the resin layer, a conductive filler may be added to the substrate as necessary. In particular, when the resin is composed only of a non-conductive polymer, a conductive filler is inevitably necessary to impart 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. For example, Al is resistant to the positive electrode potential, Ni and Cu are resistant to the negative electrode potential, and Ti and Pt are resistant to the potentials of both electrodes. 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 one 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 to contain. 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. 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 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.

  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. In particular, when the resin includes a conductive polymer material and sufficient conductivity can be secured, it is not always necessary to add a conductive filler. However, when the resin is made of only a nonconductive polymer material, it is essential to add a conductive filler in order to impart conductivity. In this case, the content of the conductive filler is preferably 5 to 35% by mass, more preferably 5 to 25% by mass, and further preferably 5 to 5% by mass with respect to the total mass of the non-conductive polymer material. 15% by mass. By adding such an amount of conductive filler to the resin, sufficient conductivity can be imparted to the non-conductive polymer material while suppressing an increase in the mass of the resin layer.

  The form of dispersion of the conductive filler in the resin layer is not particularly limited, and may be a form that is uniformly dispersed in the resin that is the base material, or may be partially localized and dispersed. Of course. When it is desired to impart conductivity uniformly throughout the resin layer, the conductive filler is preferably dispersed uniformly throughout the resin.

  The thickness of one layer of the resin layer having conductivity is preferably 1 to 200 μm, more preferably 10 to 100 μm, and still more preferably 10 to 50 μm. When the thickness of the resin layer is in such a range, the resistance in the thickness direction can be suppressed sufficiently low. Therefore, it is possible to increase the output density of the battery by reducing the weight while securing the conductivity of the current collector. Furthermore, the life characteristics can be improved and the vibration resistance can be improved by reducing the liquid junction.

  The form of the current collector is not particularly limited as long as it includes at least one conductive resin layer, and can take various forms. For example, in addition to the resin layer, a laminate including other layers as necessary may be used. Examples of other layers other than the resin layer include a metal layer and an adhesive layer, but are not limited thereto.

  An example of a preferred form of the current collector is shown in FIG. In FIG. 2, for example, as shown in (a), one type of conductive resin layer 1a may form a current collector alone, or as shown in (b) to (i) The form which laminated | stacked the resin layer (1a, 1b, 1c) which has the above electroconductivity may be sufficient. By laminating a plurality of resin layers in this manner, even if a minute crack occurs in each resin layer, the position of the crack does not match, so that a liquid junction can be prevented. Moreover, you may have the metal layer 2 containing metals, such as aluminum, nickel, or copper, or these alloys other than a resin layer like (e)-(i). By including such a metal layer, liquid junction between the positive electrode active material layer and the negative electrode active material layer in the bipolar electrode due to ion permeation in the resin layer can be prevented, and long-term reliability with improved lifetime characteristics Bipolar secondary batteries with excellent performance can be constructed. In addition, as a method of laminating the resin layer and the metal layer, a method of depositing metal on the resin layer, a method of fusing resin on the metal foil, and the like can be mentioned. Further, when the current collector is formed by laminating two or more resin layers or metal layers as in (d) and (f) to (i), the contact resistance at the interface between the layers is reduced or the adhesion is performed. From the viewpoint of preventing peeling of the surface, the two layers may be bonded via the adhesive layer 3. Examples of the material used for such an adhesive layer include metal oxide-based conductive pastes including zinc oxide, indium oxide, and titanium oxide; and carbon-based conductive pastes including carbon black, carbon nanotubes, and graphite. Preferably used.

  The thickness of the current collector is preferably thinner in order to increase the output density of the battery by reducing the weight. In a bipolar secondary battery, the current collector existing between the positive electrode active material layer and the negative electrode active material layer of the bipolar electrode may have a high electric resistance in the horizontal direction in the stacking direction. It is possible to reduce the thickness. Specifically, the thickness of the current collector is preferably 1 to 200 μm, more preferably 5 to 150 μm, and still more preferably 10 to 100 μm. By having such a thickness, it is possible to construct a battery having excellent output characteristics and excellent long-term reliability.

(Positive electrode active material layer)
The positive electrode active material layer includes a positive electrode active material. The positive electrode active material has a composition that occludes ions during discharging and releases ions during charging. A preferable example is a lithium-transition metal composite oxide that is a composite oxide of a transition metal and lithium. Specifically, Li · Co-based composite oxide such as LiCoO _2, Li · Ni-based composite oxide such as LiNiO _2, Li · Mn-based composite oxide such as spinel LiMn ₂ O _4, Li · such LiFeO ₂ Fe-based composite oxides and those obtained by replacing some of these transition metals with other elements can be used. These lithium-transition metal composite oxides are excellent in reactivity and cycle characteristics, and are low-cost materials. Therefore, it is possible to form a battery having excellent output characteristics by using these materials for electrodes. In addition, examples of the positive electrode active material include transition metal oxides such as LiFePO ₄ and lithium phosphate compounds and sulfuric acid compounds; transition metal oxides such as V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO ₃ , and sulfides. Materials; PbO ₂ , AgO, NiOOH, etc. can also be used. The positive electrode active material may be used alone or in the form of a mixture of two or more.

  The average particle diameter of the positive electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm, from the viewpoint of increasing the capacity, reactivity, and cycle durability of the positive electrode active material. Within such a range, the secondary battery can suppress an increase in the internal resistance of the battery during charging and discharging under high output conditions, and can extract a sufficient current. When the positive electrode active material is secondary particles, it can be said that the average particle diameter of the primary particles constituting the secondary particles is preferably in the range of 10 nm to 1 μm. It is not limited to. However, it goes without saying that, depending on the manufacturing method, the positive electrode active material may not be a secondary particle formed by aggregation, agglomeration, or the like. As the particle diameter of the positive electrode active material and the particle diameter of the primary particles, a median diameter obtained using a laser diffraction method can be used. The shape of the positive electrode active material varies depending on the type and manufacturing method, and examples thereof include a spherical shape (powdered shape), a plate shape, a needle shape, a column shape, and a square shape, but are not limited thereto. Any shape can be used without any problems. Preferably, an optimal shape that can improve battery characteristics such as charge / discharge characteristics is appropriately selected.

(Negative electrode active material layer)
The negative electrode active material layer includes a negative electrode active material. The negative electrode active material has a composition capable of releasing ions during discharge and storing ions during charging. The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium. Examples of the negative electrode active material include metals such as Si and Sn, TiO, Ti ₂ O ₃ , TiO ₂ , or Metal oxides such as SiO ₂ , SiO, SnO ₂ , complex oxides of lithium and transition metals such as Li _4/3 Ti _5/3 O ₄ or Li ₇ MnN, Li—Pb alloys, Li—Al alloys , Li, or carbon materials such as natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or hard carbon. Moreover, it is preferable that a negative electrode active material contains the element alloyed with lithium. By using an element that forms an alloy with lithium, it is possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a conventional carbon-based material. The negative electrode active material may be used alone or in the form of a mixture of two or more.

  The element alloying with lithium is not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like. Among these, from the viewpoint of configuring a battery having excellent capacity and energy density, at least one selected from the group consisting of carbon materials and / or Si, Ge, Sn, Pb, Al, In, and Zn. It is preferable to include an element, and it is particularly preferable to include an element of a carbon material, Si, or Sn. These may be used alone or in combination of two or more.

  The average particle size of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the capacity, reactivity, and cycle durability of the negative electrode active material. Within such a range, the secondary battery can suppress an increase in the internal resistance of the battery during charging and discharging under high output conditions, and can extract a sufficient current. In addition, when the negative electrode active material is secondary particles, it can be said that the average particle diameter of primary particles constituting the secondary particles is desirably in the range of 10 nm to 1 μm. It is not limited to. However, it goes without saying that, depending on the manufacturing method, the negative electrode active material may not be a secondary particle formed by aggregation, lump or the like. As the particle diameter of the negative electrode active material and the particle diameter of the primary particles, a median diameter obtained by using a laser diffraction method can be used. The shape of the negative electrode active material varies depending on the type and manufacturing method, and examples thereof include a spherical shape (powdered shape), a plate shape, a needle shape, a column shape, and a square shape, but are not limited thereto. Any shape can be used without any problems. Preferably, an optimal shape that can improve battery characteristics such as charge / discharge characteristics is appropriately selected.

  The active material layer may contain other materials if necessary. For example, a conductive aid, a binder, and the like can be included. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

  A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive aid include carbon powders such as acetylene black, carbon black, ketjen black, and graphite, various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark), expanded graphite, and the like. However, it goes without saying that the conductive aid is not limited to these.

  Examples of the binder include polyvinylidene fluoride (PVdF), polyimide, PTFE, SBR, and a synthetic rubber binder. However, it goes without saying that the binder is not limited to these. When the binder and the matrix polymer used as the gel electrolyte are the same, it is not necessary to use a binder.

  The compounding ratio of the components contained in the active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. The thickness of the active material layer is not particularly limited, and conventionally known knowledge about the lithium ion secondary battery can be appropriately referred to. As an example, the thickness of the active material layer is preferably about 10 to 100 μm, and more preferably 20 to 50 μm. If the active material layer is about 10 μm or more, the battery capacity can be sufficiently secured. On the other hand, if the active material layer is about 100 μm or less, it is possible to suppress the occurrence of the problem of an increase in internal resistance due to the difficulty in diffusing lithium ions in the electrode deep part (current collector side).

  The method for forming the positive electrode active material layer (or the negative electrode active material layer) on the current collector surface is not particularly limited, and known methods can be used in the same manner. For example, as described above, a positive electrode active material (or a negative electrode active material) and, if necessary, an electrolyte salt for increasing ion conductivity, a conductive auxiliary agent for increasing electron conductivity, and a binder are appropriately used. A positive electrode active material slurry (or a negative electrode active material slurry) is prepared by dispersing and dissolving in a solvent. This is applied onto a current collector, dried to remove the solvent, and then pressed to form a positive electrode active material layer (or negative electrode active material layer) on the current collector. In this case, the solvent is not particularly limited, and N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide, cyclohexane, hexane and the like can be used. When adopting polyvinylidene fluoride (PVdF) as a binder, NMP is preferably used as a solvent.

  In the above method, the positive electrode active material slurry (or the negative electrode active material slurry) is applied onto the current collector, dried, and then pressed. At this time, the porosity of the positive electrode active material layer (or the negative electrode active material layer) can be controlled by adjusting the pressing conditions.

  Specific means and press conditions for the press treatment are not particularly limited, and can be appropriately adjusted so that the porosity of the positive electrode active material layer (or the negative electrode active material layer) after the press treatment becomes a desired value. Specific examples of the press process include a hot press machine and a calendar roll press machine. Also, the pressing conditions (temperature, pressure, etc.) are not particularly limited, and conventionally known knowledge can be referred to as appropriate.

[Electrolyte layer]
The electrolyte layer has a function as a medium when lithium ions move between the electrodes. In this embodiment, the electrolyte constituting the electrolyte layer is not particularly limited as long as it contains a solvent as the electrolytic solution, and conventionally known liquid electrolytes and polymer gel electrolytes can be appropriately employed.

  The liquid electrolyte is obtained by dissolving a lithium salt as a supporting salt in a solvent. Examples of the solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), and methyl formate (MF). 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) , And γ-butyrolactone (GBL). These solvents may be used alone or as a mixture of two or more.

As the supporting salt (lithium salt) is not particularly _{limited, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiSbF 6, LiAlCl 4, Li 2 B 10 Cl 10, LiI, LiBr, LiCl Inorganic acid anion salts such as LiAlCl, LiHF ₂ , LiSCN, LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiBOB (lithium bisoxide borate), LiBETI (lithium bis (perfluoroethylenesulfonylimide); And organic acid anion salts such as Li (C ₂ F ₅ SO ₂ ) ₂ N). These electrolyte salts may be used alone or in the form of a mixture of two or more.

  On the other hand, the polymer gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer having lithium ion conductivity. Examples of the matrix polymer having lithium ion conductivity include a polymer having polyethylene oxide in the main chain or side chain (PEO), a polymer having polypropylene oxide in the main chain or side chain (PPO), polyethylene glycol (PEG), poly Acrylonitrile (PAN), polymethacrylic acid ester, polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP), polyacrylonitrile (PAN), poly (methyl acrylate) (PMA), poly (Methyl methacrylate) (PMMA) etc. are mentioned. In addition, mixtures of the above-described polymers, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used. Among these, it is desirable to use PEO, PPO and their copolymers, PVdF, PVdF-HFP. In such a matrix polymer, an electrolyte salt such as a lithium salt can be well dissolved. In addition, the matrix polymer can exhibit excellent mechanical strength by forming a crosslinked structure.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a polymer gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include, for example, a polyolefin resin such as a microporous polyethylene film, a microporous polypropylene film, and a microporous ethylene-propylene copolymer film, and a porous film or nonwoven fabric such as aramid, polyimide, and cellulose, These laminated bodies etc. are mentioned. These have the effect that the reactivity with the electrolyte (electrolytic solution) can be kept low. In addition, a composite resin film in which a polyolefin-based resin nonwoven fabric or a polyolefin-based resin porous film is used as a reinforcing material layer, and the reinforcing material layer is filled with a vinylidene fluoride resin compound may be used.

Bipolar secondary battery of this embodiment, the solubility parameters of the resin forming the base material of any one of the resin layer included in the current collector and (SP _1), the solubility parameter of the solvent contained in the electrolytic solution (SP ₂ The absolute value of the difference from) is 1.9 or more. By combining a resin and a solvent in which the absolute value of the solubility parameter difference is within such a range, the electrolyte containing the solvent can be prevented from penetrating into the current collector containing the resin. That is, it is possible to prevent the electrolytic solution from separating from the electrolyte layer, and to solve the conventional problem that the electrolytic solution between the electrodes is insufficient.

The solubility parameter (SP value) is generally used as a measure of the solubility of a binary solution or solvent-solute. It is empirically known that the solubility increases as the difference between the solubility parameter values of the two components decreases. In the present specification, the value obtained by using the atomic group contribution method (Van Keveren method) is adopted as the solubility parameter (SP ₁ ) of the resin. Further, the value of the solubility parameter (SP ₂ ) of the solvent adopts the Hansen solubility parameter.

As described above, the resin in this embodiment may be a single type of non-conductive polymer material or conductive polymer material, or a mixture of two or more types. When the mixture of the latter two or more polymer materials is used, the mixed form may have the following two forms. The first mixed form is a case where two or more polymer materials are mixed at the molecular level. The resin solubility parameter (SP ₁ ) in this case employs the sum of values obtained by multiplying the solubility parameter of each polymer material by each content ratio (w / w), that is, a value calculated by the following equation.

In the above formula, A _k (A ₁ , A ₂ ... A _m ) represents the solubility parameter of each polymer material, and X _k (X ₁ , X ₂ ... X _m ) represents each polymer for the entire resin. It represents the content ratio (w / w) of the material, and m represents the number of types of single polymer materials to be mixed.

On the other hand, the second mixed form is a case where the polymer material as the subcomponent is localized (for example, scattered) in the polymer material as the main component. Here, “main component” means that it is contained in an amount exceeding 50% by mass, preferably 60% by mass or more, based on the entire resin. In such a form, the value of the solubility parameter (SP ₁ ) of the resin adopts the value of the solubility parameter of the polymer material as the main component. Note that when the “polymer material as the main component” is formed by mixing two or more types of polymer materials at the molecular level, the value calculated from the definition of the first mixed form is “high value as the main component”. It becomes the solubility parameter of “molecular material”. Then, according to the definition of the second mixing form, the value of the solubility parameter becomes the solubility parameter of the resin.

As above-mentioned, the solvent in this form may use a single solvent individually by 1 type, and may be used as a mixture which combined 2 or more types. The solubility parameter (SP ₂ ) of the solvent when the latter two or more single solvents are combined is the sum of the values obtained by multiplying the solubility parameter of each single solvent by each content ratio (w / w), The value calculated by the following formula is adopted.

In the above formula, B ₁ (B ₁ , B ₂ ... B _n ) represents the solubility parameter of each single solvent, and Y ₁ (Y ₁ , Y ₂ ... Y _n ) represents each single solvent relative to the whole solvent. It represents the content ratio (w / w) of the solvent, and n represents the number of single solvents to be mixed.

  When the current collector includes two or more resin layers and each resin layer is based on a different resin material, the absolute value of the difference between the solubility parameter of each resin and the solubility parameter of the solvent is the most. The large value should just be 1.9 or more.

Furthermore, in order to reduce the penetration of the solvent into the resin and suppress the battery capacity reduction, the resin solubility parameter (SP ₁ ) should be 1.9 or more larger than the solvent solubility parameter (SP ₂ ). Is preferred. In the case where the current collector includes two or more resin layers and each resin layer is based on a different resin material, the difference between the largest value of SP ₁ of each resin and the SP ₂ of the solvent is It shall be calculated.

  In this embodiment, the combination of the resin and the solvent is not particularly limited as long as the difference in solubility parameter is within the above range. An example of a preferable combination is a combination of a resin containing at least one selected from the group consisting of polyimide, polyethylene terephthalate, polyamide, and polyacrylonitrile and a solvent containing dimethyl carbonate.

[Seal part]
The seal portion (insulating layer) layer has a function of preventing contact between current collectors and a short circuit at the end of the single cell layer. As a material constituting the seal portion, any material having insulating properties, sealability against falling off of solid electrolyte, sealability against moisture permeation from the outside (sealing property), heat resistance under battery operating temperature, etc. Good. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Of these, polyethylene resin and polypropylene resin are preferably used as the constituent material of the insulating layer from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming property), economy, and the like.

[Battery exterior materials]
As the battery exterior material, a conventionally known metal can case can be used, and a bag-like case using a laminate film containing aluminum that can cover the power generation element 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. In the present invention, it is desirable to use a laminate film that is excellent in high output and cooling performance and can be suitably used for batteries for large equipment such as EV and HEV.

<Battery assembly>
An assembled battery can be obtained by electrically connecting a plurality of bipolar secondary batteries of this embodiment in series or in parallel. Thus, it becomes possible to adjust a capacity | capacitance and a voltage freely by parallelizing a some battery in series or in parallel.

  FIG. 3 is an external view of a typical embodiment of the assembled battery according to the present invention, FIG. 3A is a plan view of the assembled battery, FIG. 3B is a front view of the assembled battery, and FIG. 3C is an assembled battery. FIG.

  As shown in FIG. 3, an assembled battery 300 according to the present invention forms a small assembled battery 250 that can be attached and detached by connecting a plurality of bipolar secondary batteries of the present invention in series or in parallel. A large capacity and large output suitable for a vehicle driving power source and an auxiliary power source that require a high volume energy density and a high volume output density by connecting a plurality of these detachable small assembled batteries 250 in series or in parallel. It is also possible to form an assembled battery 300 having 3A is a plan view of the assembled battery, FIG. 3A is a front view, and FIG. 3C is a side view. The small assembled battery 250 that can be attached and detached is provided with an electrical connection means such as a bus bar. The assembled battery 250 is stacked in a plurality of stages using the connection jig 310. How many bipolar secondary batteries are connected to produce the assembled battery 250, and how many assembled batteries 250 are laminated to produce the assembled battery 300 depends on the vehicle (electric vehicle) to be mounted. It may be determined according to the battery capacity and output.

<Vehicle>
The vehicle of the present invention is characterized in that the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these is mounted. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . In other words, the lithium ion battery of the present invention or an assembled battery formed by combining a plurality of these can be used as a power source for driving a vehicle. The lithium ion battery of the present invention or an assembled battery obtained by combining a plurality of these batteries is a vehicle, for example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (all automobiles such as automobiles, commercial vehicles such as passenger cars, trucks, and buses, This is because it can be used for motorcycles (including motorcycles) and tricycles (in addition to mini vehicles, etc.)) to provide a long-life and highly reliable vehicle. 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. 4 is a conceptual diagram of a vehicle equipped with the assembled battery of the present invention. As shown in FIG. 4, 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.

  The effect of this invention is demonstrated using a following example and a comparative example. However, the technical scope of the present invention is not limited only to the following examples. In the following, first, evaluation of penetration of the electrolyte into the current collector using various resins was performed. Then, a bipolar secondary battery was prepared using various current collectors, and the discharge capacity retention rate was measured.

<Evaluation of penetration of electrolyte into current collector>
Two current collectors each having a thickness of 100 μm cut into 10 cm squares were sealed using a thick gusset policyler (FT-230) in a dry atmosphere. Then, 5 cc of a solvent was added from the remaining one side that was not sealed, and this one side was sealed, thereby producing a bag containing an electrolyte solution constituted by a current collector. The produced bags were evenly arranged, the weight was measured after a certain time, and the residual ratio of the solvent was calculated. The combinations of resins and solvents used are shown in Table 1.

Table than one result, the solubility parameter of the resin (SP ₁₎ and the solubility parameter of the solvent (SP ₂₎ Preparation absolute value is 1.9 or more of the difference between 1 4,6～ 8, Reference Example 5 The solvent remaining rate after 3 days was 100%. On the other hand, in Comparative Production Examples 1 to 4 in which the difference in absolute value was less than 1.9, the residual ratio of the solvent after 3 days was remarkably low. The low residual ratio of the solvent in Comparative Production Examples 1 to 4 means that the solvent penetrates into the resin and the solvent volatilizes outside the bag, thereby reducing the amount of solvent in the bag. On the contrary, in Production Examples 1 to 4 , 6 to 8 and Reference Production Example 5 , it was considered that the solvent hardly volatilizes because the solvent hardly penetrates into the resin.

<Evaluation of discharge capacity retention rate of bipolar secondary battery>
(Production of bipolar electrode)
A positive electrode layer slurry was prepared using acetylene black (AB) (conducting aid), polyvinylidene fluoride (PVDF) (binder), an average particle size of 5 μm lithium nickel oxide based active material (LiNiO 2) and NMP. The compounding ratio of each component is lithium nickel oxide active material: AB: PVDF = 86: 6: 8 (mass ratio). Moreover, the slurry for negative electrode layers was produced using acetylene black (AB), polyvinylidene fluoride (PVdF), hard carbon, and NMP. The compounding ratio of each component is hard carbon: AB: PVDF = 85: 5: 10 (mass ratio).

  A current collector (thickness: 100 μm) including a conductive resin layer containing carbon black as a conductive filler was prepared. When the current collector was composed of a plurality of layers, the thickness of each layer was adjusted to 5 μm or more and the total thickness was adjusted to 100 μm. When carbon black is used as the conductive filler, about 3 to 40% by mass of carbon particles is added to the total of the polymer material and the conductive filler so as to obtain an appropriate volume resistivity. Table 2 shows the form of the current collector in each example and comparative example. The prepared positive electrode active material slurry was applied to one surface of the current collector and dried to form a positive electrode active material layer having a thickness of 30 μm. In addition, a negative electrode active material slurry was applied to the other surface of the current collector and dried to form a negative electrode active material layer having a thickness of 20 μm. Thus, the laminated body which formed the positive electrode active material layer in the one surface of the electrical power collector, and formed the negative electrode active material layer in the other surface was obtained.

  The obtained positive electrode active material layer / current collector / negative electrode active material layer laminate was cut into a size of 160 × 130 (mm) and formed on the outer periphery of 10 mm from the outer edge and the negative electrode active material layer and the negative electrode active material By peeling off the layer, the surface of the conductive resin layer as a current collector was exposed. As a result, a bipolar electrode was obtained in which each active material layer surface was 140 × 110 (mm) and the conductive resin layer on the outer peripheral portion 10 mm from the outer edge was exposed.

(Production of bipolar secondary battery)
Three-layer structure product in which a sheet for sealing (PP / PEN / PP is laminated) on the exposed resin layer exposed portion (electrode uncoated portion) of the surface of the obtained bipolar electrode on which the positive electrode active material layer is formed ) Was placed. Next, a 170 × 140 (mm) resin separator (a microporous membrane manufactured by Ube Industries) was disposed so as to cover all the bipolar electrodes on the side where the positive electrode active material layer was formed. Then, the sheet | seat for sealing was arrange | positioned on the separator corresponding to an electrode non-application part, and the negative electrode surface was piled up from it on it. Thus, a bipolar electrode (negative electrode active material layer / current collector / positive electrode active material layer) / separator / bipolar electrode (negative electrode active material layer / current collector / positive electrode active material layer)... Separator / bipolar A bipolar electrode in which 12 cell layers are laminated by laminating and sealing 13 bipolar electrodes via a separator in the order of the type electrode (negative electrode active material layer / current collector / positive electrode active material layer). A type secondary battery structure was produced.

As an electrolytic solution, a solution was prepared by dissolving LiPF _{6 as a} lithium salt in diethylene carbonate (DEC) or propylene carbonate (PC) at a concentration of 1.0M. And the electrolyte layer was formed by impregnating said bipolar secondary battery structure in electrolyte solution, and making it hold | maintain on the separator distribute | arranged between bipolar electrodes.

  After forming the electrolyte layer in this way, four bipolar secondary battery structures are stacked in series, sandwiched between aluminum tabs for current extraction, and vacuum sealed using an aluminum laminate film as an exterior material, 48 series bipolar secondary battery modules were prepared.

(Charge / discharge cycle)
Each bipolar secondary battery manufactured by the above method is charged to 200 V by a constant current method (CC, current: 5C) in an atmosphere at 25 ° C., and is allowed to rest for 10 minutes. Then, the constant current (CC, current: 5C), the battery was discharged to 120V and rested for 10 minutes after the discharge. This charging / discharging process was made into 1 cycle, the charging / discharging test of 10 cycles was done, and discharge capacity retention was investigated. The results are shown in Table 2 below. In Table 2, “discharge capacity retention ratio” represents the ratio of the discharge capacity at the 10th cycle to the discharge capacity at the 1st cycle (expressed as a percentage).

From Table 2, the absolute value of 1.9 or more is example of the difference between the solubility parameter of the resin (SP ₁₎ and the solubility parameter of the solvent (SP ₂₎ 1, 3 to 5, Reference Example 2 (Production Example 1, 6-8, the corresponding) reference production example 5, the discharge capacity retention after 10 cycles was excellent and 70%. On the other hand, in Comparative Examples 1 and 2 (corresponding to Comparative Production Examples 1 and 3) in which the difference in absolute value was 1.9 or less, the discharge capacity retention rate was remarkably low. From the above results, in Examples 1, 3 to 5, and Reference Example 2 , the penetration of the solvent into the resin is effectively suppressed, so that the reduction of the discharge capacity caused by the lack of electrolyte between the electrodes is suppressed. It was thought that

1a, 1b, 1c conductive resin layer,
2 metal layers,
3 Adhesive layer,
10 Bipolar 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 power generation elements,
23 Bipolar electrode,
25 positive current collector,
27 negative current collector,
29 Laminated film,
31 seal part,
250 small battery pack,
300 battery packs,
310 connection jig,
400 vehicles.

Claims (3)

A current collector comprising a resin layer having conductivity based on a resin;
A bipolar electrode having a positive electrode active material layer formed on one surface of the current collector, and a negative electrode active material layer formed on the other surface of the current collector;
A bipolar lithium ion secondary battery having a power generation element formed by laminating an electrolyte layer containing a supporting salt and a solvent,
Bipolar lithium ion in which the solubility parameter (SP ₁ ) of the resin forming the base material of any one resin layer included in the current collector is 1.9 or more larger than the solubility parameter (SP ₂ ) of the solvent Secondary battery. The bipolar lithium ion secondary battery according to claim 1, wherein the current collector includes a plurality of the resin layers. The resin includes at least one selected from the group consisting of polyimide, polyethylene terephthalate, polyamide, and polyacrylonitrile,
The bipolar lithium ion secondary battery according to claim 1, wherein the solvent includes dimethyl carbonate.

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