JP2010244943A - Bipolar secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for giving a shutting down function that suppresses heat shrinkage of a separator caused by heat bonding during the manufacturing of a battery and shutting off the transfer of lithium ions between electrodes, when the temperature of the battery becomes a high temperature during the operation of the battery. <P>SOLUTION: A bipolar secondary battery has a power generating element formed by laminating a bipolar electrode having a current collector; a positive active material layer formed on one surface of the current collector; and a negative active material layer formed on the other surface of the current collector and the separator and is formed by jointing the periphery of the bipolar electrode and the periphery of the separator via a sealing part. The separator has a main material which is a porous membrane containing resin and temperature-responsive polymer gel having phase transition temperature conducting phase transition from a swelling state to a shrinking state, accompanying the rise in the temperature, and the sealing part and the separator are bonded by heating at the temperature or lower of phase transition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bipolar secondary battery. In particular, the present invention has a shutdown function that can suppress the thermal contraction of the separator due to heat adhesion at the time of battery manufacture, and shuts off the movement of lithium ions between the electrodes when the battery becomes hot during battery operation. The present invention relates to 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 is a power generator in which a positive electrode active material layer is formed on one surface of a current collector and a plurality of bipolar electrodes having a negative electrode active material layer formed on the other surface are stacked via an electrolyte layer. Has an element. In other words, the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer form one single cell layer, and a plurality of the single cell layers are stacked with the current collector interposed therebetween.

  As the electrolyte layer, a layer in which a liquid electrolyte or a gel electrolyte is held by a separator is used from the viewpoint that high battery performance can be exhibited. The separator has a form of a microporous film having a large number of holes in the stacking direction of the bipolar secondary battery in order to enable movement of lithium ions between the electrodes.

  In addition, in a bipolar secondary battery having such a structure, in order to prevent the electrolyte from leaking outside from the single cell layer and coming into contact with the electrolyte of other single cell layers, causing a liquid junction, A seal portion is disposed so as to surround the outer peripheral portion of the unit cell layer. At this time, the seal portion and the separator are bonded by heating.

  However, it has been pointed out that the separator shrinks due to the heat at the time of heat bonding, and the battery is distorted or an internal short circuit occurs. Therefore, in Patent Document 1, an attempt is made to solve this problem by a method of selecting a material having a thermal contraction rate of the separator of 5% or less at the heat bonding temperature between the separator and the seal portion.

  By the way, in order to use a battery safely, the separator which has a shutdown function which stops a charge / discharge reaction when a battery becomes high temperature during a charge / discharge reaction is developed. The shutdown function blocks the movement of lithium ions between the electrodes. When the battery reaches a high temperature, the resin constituting the separator is melted to shut down the holes.

JP 2007-250405 A

  However, as in Patent Document 1 described above, when a material having high heat resistance is selected as the separator material, there is a problem that the shutdown function does not work effectively or the shutdown function itself is not provided.

  Accordingly, the present invention provides a bipolar device having a shutdown function that suppresses thermal contraction of the separator due to heat adhesion during battery manufacture, and blocks lithium ion movement between electrodes when the battery becomes hot during battery operation. An object is to provide a type secondary battery.

  The present inventors have intensively studied to solve the above problems. And, by covering the surface of the pores of the main material (conventional separator) which is a microporous film with a temperature-responsive polymer gel, the bipolar type has a shutdown function and suppresses thermal shrinkage during heat bonding The present inventors have found that a secondary battery can be obtained and completed the present invention.

  That is, the bipolar secondary battery of the present invention has a power generation element in which a bipolar electrode and a separator are stacked. The bipolar electrode includes a current collector, 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. The peripheral part of a bipolar electrode and a separator is joined via a seal part. And a separator contains the main material which is a microporous film containing resin, and a temperature-responsive polymer gel. The temperature-responsive polymer gel has a phase transition temperature that undergoes a phase transition from a swollen state to a contracted state as the temperature rises. The seal part and the separator are bonded by heating at a temperature below the phase transition temperature.

  According to the present invention, at the time of heat-bonding between the separator and the seal portion, the temperature-responsive polymer gel is in the swollen state on the surface of the pore because it is not higher than the phase transition temperature. At this time, even if a stress that causes thermal contraction of the separator occurs, the temperature-responsive polymer gel in a swollen state existing on the surface of the pores can relieve the stress and effectively suppress the thermal contraction of the separator. . Further, when the temperature reaches the phase transition temperature or higher during battery operation, the temperature-responsive polymer gel contracts in the pores to close the pores, thereby blocking the movement of lithium ions between the electrodes. Therefore, it is possible to provide a bipolar battery excellent in reliability that can reduce internal short circuit and battery distortion due to thermal contraction of the separator and has a shutdown function.

1 is a schematic cross-sectional view schematically showing the overall structure of a bipolar lithium ion secondary battery according to an embodiment of the present invention. It is the cross-sectional schematic which represented typically the separator which has a polyimide as the main material based on one Embodiment of this invention. 2A is a schematic cross-sectional view in the surface direction of the separator, and FIG. 2B is a schematic cross-sectional view in the thickness direction of the separator. It is the cross-sectional schematic which represented typically the separator which uses polyethylene as the main material based on one Embodiment of this invention. 3A is a schematic cross-sectional view in the surface direction of the separator, and FIG. 3B is a schematic cross-sectional view in the thickness direction of the separator. 4A and 4B are external views schematically showing an assembled battery according to an embodiment of the present invention, in which FIG. 4A is a plan view of the assembled battery, FIG. 4B 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 lithium ion 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 secondary battery having a power generation element in which a bipolar electrode and a separator are laminated. The bipolar electrode includes a current collector, 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. The peripheral part of a bipolar electrode and a separator is joined via a seal part. And a separator contains the main material which is a microporous film containing resin, and a temperature-responsive polymer gel. The temperature-responsive polymer gel has a phase transition temperature that undergoes a phase transition from a swollen state to a contracted state as the temperature rises. The seal part and the separator are bonded by heating at a temperature below the phase transition temperature.

  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. In addition, 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. The seal portion 31 is formed by placing a seal material between the peripheral portion of the current collector 11 and the separator in the electrolyte layer 17 and heat-bonding.

  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 is made of a conductive material, and active material layers are arranged on both sides thereof to constitute an electrode. The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

  There are no particular limitations on the material constituting the current collector, and for example, a metal or a resin in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material may be employed. Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. 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, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  Examples of the conductive polymer material 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.

  Examples of non-conductive polymer materials include 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), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only 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. 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. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

(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 by 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 store 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.

  Note that the particle diameter and shape of the negative electrode active material are not particularly limited, and can take the same form as the above-described positive electrode active material, and thus detailed description thereof is omitted here.

  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, water 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 functions as a lithium ion transfer medium between the electrodes. The electrolyte layer of this embodiment is formed by holding a liquid electrolyte or a gel electrolyte on a separator.

(Separator)
The separator according to the present embodiment includes a main material that is a microporous film containing a resin and a temperature-responsive polymer gel.

  If the material which comprises a main material contains resin, there will be no restriction | limiting in particular, The material used for the conventional separator can be used suitably. Examples of the resin include polyolefins such as polyethylene (PE) and polypropylene (PP), polyimide, aramid, and polyester. Among these, a polyolefin having a low melting point as a thermoplastic resin is excellent in that shutdown occurs at a relatively low temperature stage even when the battery becomes high temperature. On the other hand, since polyimide, aramid, and the like, which are thermosetting resins, are excellent in heat resistance, thermal shrinkage can be more effectively suppressed during heat bonding between the separator and the seal portion. These materials may be used alone or in combination of two or more. An example of a combination of two or more resins includes a laminate having a three-layer structure of PP / PE / PP. In this mode, shutdown occurs when the battery temperature reaches 130 ° C., which is the melting point of PE. Even if the battery temperature continues to rise after shutdown, meltdown does not occur until the melting point of PP reaches 170 ° C., so that it is possible to prevent the entire surface from being short-circuited.

  The main material has the form of a microporous membrane having pores. The holes are preferably formed anisotropically only in the direction of the thickness of the main material, thereby preventing electrolyte leakage. The pore diameter is not particularly limited, but is preferably 1 μm or less (usually a pore diameter of about 10 nm), and its porosity is preferably 20 to 80%. The thickness of the main material is not particularly limited, but is usually 5 to 200 μm, preferably 10 to 100 μm.

  The temperature-responsive polymer gel is a gel state in which a solvent contained in an electrolyte described later penetrates into a temperature-responsive polymer material. The temperature-responsive polymer gel according to this embodiment undergoes a phase transition from a swollen state to a contracted state at the phase transition temperature as the temperature rises from a low temperature to a high temperature. This phase transition is reversible, and even when the temperature decreases from a high temperature to a low temperature, the phase transition occurs from the contracted state to the swollen state at the phase transition temperature.

  As temperature-responsive polymer materials having such properties, for example, N-substituted (meth) acrylamide polymers or copolymers, polyethers, and alkyl celluloses are known, and these are not limited. Can be used.

  Examples of the N-substituted (meth) acrylamide include N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, and N-cyclopropyl. (Meth) acrylamide, Nt-butyl (meth) acrylamide, N, N-ethylmethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-2-hydroxyethyl-N-methyl (meth) acrylamide N-2-hydroxyethyl-N-ethyl (meth) acrylamide, N-2-hydroxyethyl-Nn-propyl (meth) acrylamide, N-2-hydroxyethyl-N-isopropyl (meth) acrylamide, N- 2-hydroxyethyl-Nt-butyl (meth) acryl Amide, N-2-hydroxyethoxyethyl (meth) acrylamide, N-2-hydroxyethyl-1,1-dimethyl (meth) acrylamide, N-2-methoxyethyl (meth) acrylamide, N-2-ethoxyethyl (meth) ) Acrylamide, N-3-methoxypropyl (meth) acrylamide, N-3-ethoxypropyl (meth) acrylamide, N-3-isopropoxypropyl (meth) acrylamide, N-3-n-propoxypropyl (meth) acrylamide, Nn-butoxypropyl (meth) acrylamide, N-isobutoxypropyl (meth) acrylamide, N-2-ethylhexyloxypropyl (meth) acrylamide, N-3- (2-methoxyethoxy) propyl (meth) acrylamide, N -Furfuryl (medium ) Acrylamide, N-tetrahydrofurfuryl (meth) acrylamide, N-1-methyl-2-methoxyethyl (meth) acrylamide, N-1-methoxymethylpropyl (meth) acrylamide, N-3-methylthiopropyl (meth) acrylamide , N-3-morpholinopropyl (meth) acrylamide, N- (2,2-dimethoxyethyl) -N-methyl (meth) acrylamide, N- (1,3-dioxolan-2-ylmethyl) -N-methyl (meta ) Acrylamide, N-8-acryloyl-1,4-dioxa-8-azaspiro [4.5] decane, N-acryloylmorpholine, N-acryloyl-2,6-dimethylmorpholine, N-2-methoxyethyl-N- Methyl (meth) acrylamide, N-2-methoxyethyl-N-eth Ru (meth) acrylamide, N-2-methoxyethyl-Nn-propyl (meth) acrylamide, N-2-methoxyethyl-N-isopropyl (meth) acrylamide, N-2-methoxyethyl-Nt-butyl (Meth) acrylamide, N, N-di (2-methoxyethyl) (meth) acrylamide and the like can be mentioned.

  Examples of the polyethers include block copolymers containing polyethylene oxide and polypropylene oxide such as Pluronic (registered trademark) and Tetronic (registered trademark).

  Examples of the alkyl cellulose include methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methyl cellulose.

  Among such temperature-responsive polymer materials, those having a phase transition temperature of 60 to 120 ° C are preferable, and those having a phase transition temperature of 80 to 100 ° C are more preferable. Examples of the compound having a phase transition temperature in such a range include poly (N-ethylacrylamide), poly (N-ethylmethacrylamide), and poly (N, N-diethylacrylamide).

  The number average molecular weight of the temperature-responsive polymer material is not particularly limited as long as the temperature-responsive polymer material has a phase transition temperature in a desired temperature range, but is generally 3000 to 25000. , Preferably 8000 to 15000. In the temperature-responsive polymer material, the phase transition temperature decreases as the molecular weight increases. Therefore, a temperature-responsive polymer material having a higher phase transition temperature can be obtained even by using a polymer composed of the same monomer by increasing the polymerization time and increasing the concentration of the reaction solution.

  The preferable form of the separator which concerns on this form is shown in FIG. 2 and FIG. FIG. 2 is a schematic cross-sectional view schematically showing a separator mainly composed of polyimide. FIG. 3 is a schematic cross-sectional view schematically showing a separator mainly made of polyethylene. 2A and 3A represent cross-sectional schematic views in the plane direction of the separator, and FIGS. 2B and 3B represent cross-sectional schematic views in the thickness direction of the separator.

  According to FIG. 2, the separator 50i is formed by coating the surface of the hole of the main material 51i made of polyimide with a temperature-responsive polymer gel 53i made of poly (N-ethylacrylamide). Under a low temperature (110 ° C.), the temperature-responsive polymer gel 53i is in a swollen state, and thus covers the surface of the hole over a wide range. And if it exceeds a phase transition temperature and becomes high temperature (130 degreeC), the temperature-responsive polymer gel 53i will be in a contracted state. As a result, the temperature-responsive polymer gel 53i that has spread on the surface of the pores aggregates to close the pores. Since polyimide is a material that does not easily heat shrink, the shrinkage of the holes is small. Therefore, the main material 51i alone does not function as a shutdown function even at high temperatures, but the shutdown function can be exhibited by allowing the temperature-responsive polymer gel to be present in the pores.

  On the other hand, according to FIG. 3, the separator 50e is formed by coating the surface of the hole of the main material 51e made of polyethylene with a temperature-responsive polymer gel 53e made of poly (N-ethylacrylamide). Under a low temperature (110 ° C.), the temperature-responsive polymer gel 53e is in a swollen state, and thus covers the surface of the hole over a wide range. Since polyethylene is a thermoplastic resin having a melting point at a relatively low temperature (130 ° C.), when the temperature rises to around 100 ° C., a part of the main material 51e melts and the holes start to shrink. However, since the phase transition temperature of poly (N-ethylacrylamide) is 120 ° C., the temperature-responsive polymer gel 53e maintains a swollen state at 110 ° C. Therefore, the hole made of polyethylene contracts, and the stress that the entire separator 50e tends to contract can be relaxed. When the temperature further rises and exceeds the phase transition temperature and reaches a high temperature (130 ° C.), the melting of the main material 51e proceeds and the temperature-responsive polymer gel 53e enters a contracted state. Then, the holes are closed by melting of the main material 51e and aggregation of the temperature-responsive polymer gel 53e.

  As shown in FIGS. 2 and 3, the bipolar secondary battery of this embodiment is formed by bonding the seal portion and the separator by heating at or below the phase transition temperature of the temperature-responsive polymer gel. The adhesion temperature at this time is preferably 10 ° C. or more lower than the phase transition temperature. Thereby, the thermal contraction of the separator at the time of battery manufacture can be suppressed effectively. In this specification, the value of the hot press is used as the bonding temperature.

Moreover, since the surface and the surface of the hole of the main material are coated with the temperature-responsive polymer gel, as shown in FIGS. 2 and 3, the separator and the seal portion are bonded by heating. Shrinkage of the separator can be effectively suppressed. Further, when the battery becomes high temperature, the shutdown function can be satisfactorily exhibited. Furthermore, in order to make these effects remarkable, it is preferable that the temperature-responsive polymer gel covers 60 to 90% of the entire surface area of the pores, and 70 to 85%. Is more preferable. In the present specification, the value measured by neutralization titration is used as the coating area of the temperature-responsive polymer gel on the surface of the hole. When the temperature-responsive polymer material is made of poly (N-substituted (meth) acrylamide), specifically, it can be determined by the following method. First, a separator sample in which the coating area of the temperature-responsive polymer gel is changed is prepared. The covering area can be adjusted by changing the polymerization time as in the examples described later. Next, the amide bond contained in the temperature-responsive polymer gel of each separator sample is hydrolyzed with prescribed sodium hydroxide. Then, this is titrated with a prescribed hydrochloric acid to obtain a titer. The obtained results are plotted on the vertical axis and the titration amount on the horizontal axis, and a calibration curve is created. And a coating area is calculated | required from the titration amount of an unknown separator sample.
Moreover, it is preferable that the mass ratio of the temperature-responsive material with respect to the total mass of resin contained in the main material is 40-70 mass%, and it is more preferable that it is 50-60 mass%.

  The method for coating the surface of the pores with the temperature-responsive polymer gel is not particularly limited, and examples thereof include a method in which the pores of the separator are coated with a monomer solution that is a raw material for the temperature-responsive polymer material. By immersing the obtained separator in the electrolyte, the solvent in the electrolyte penetrates into the temperature-responsive polymer material, and becomes a temperature-responsive polymer gel in a swollen state. As another method, there is a method in which a temperature-responsive polymer material (powder) polymerized in advance is applied to the holes by a vacuum impregnation method and then immersed in an electrolyte to form a gel.

(Electrolytes)
There is no restriction | limiting in particular in the electrolyte which comprises an electrolyte layer, A liquid electrolyte and a gel electrolyte can be used suitably.

  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 and 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 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.

  The matrix polymer of gel 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. In addition, the said electrolyte may be contained in the active material layer of an electrode.

[Seal part]
The seal portion (insulating 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, acrylic resin, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber, nylon resin, etc. can be used. Among these, polyethylene resin, polypropylene resin, and acrylic resin are preferably used as the constituent material of the seal portion 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 this embodiment, a laminate film that is excellent in high output and cooling performance and can be suitably used for a battery for large equipment such as for EV and HEV is desirable.

<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.

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

  As shown in FIG. 3, the assembled battery 300 according to the present embodiment forms a small assembled battery 250 that can be attached and detached by connecting a plurality of bipolar secondary batteries of the present embodiment 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 4A is a plan view of the assembled battery, FIG. 4A is a front view, and FIG. 4C is a side view. The small assembled battery 250 that can be attached / detached has 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 according to the present embodiment is characterized by mounting the lithium ion battery according to the present embodiment or a combination battery formed by combining a plurality of these. In this embodiment, since a battery having a long life and excellent long-term reliability and output characteristics can be configured, it is possible to configure a plug-in hybrid electric vehicle having a long EV travel distance and an electric vehicle having a long charge travel distance when such a battery is mounted. . In other words, the lithium ion battery of this embodiment 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 embodiment or a combination battery formed by combining a plurality of these is a vehicle, for example, a hybrid vehicle, a fuel cell vehicle, an electric vehicle (for automobiles, all four-wheel vehicles (passenger cars, trucks, buses and other commercial vehicles, 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. 5 is a conceptual diagram of a vehicle equipped with the assembled battery of this embodiment. As shown in FIG. 5, in order to mount the assembled battery 300 on a vehicle such as the electric vehicle 400, the battery pack 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle. The electric vehicle 400 using the assembled battery 300 as described above has high durability and can provide sufficient output even when used for a long period of time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance. A vehicle equipped with the assembled battery of this embodiment 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.

[Example 1]
<Preparation of electrolyte>
LiPF ₆ as a lithium salt is dissolved at a concentration of 1.0 M in a PC-EC mixed solvent in which propylene carbonate (PC) and ethylene carbonate (EC) are mixed at 1: 1 (volume ratio) to prepare an electrolytic solution. did. 90% by mass of the obtained electrolytic solution, 10% by mass of a mixture of hexafluoropropylene (HFP) and polyvinylidene fluoride (PVDF) (HFP: PVDF = 90: 10 (mass ratio)) as a host polymer, viscosity adjusting solvent A suitable amount of dimethyl carbonate (DMC) was mixed to prepare an electrolyte.

<Production of bipolar electrode>
85% by mass of LiMn ₂ O ₄ as a positive electrode active material, 5% by mass of acetylene black as a conductive additive, 10% by mass of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of N-methylpyrrolidone (NMP) as a viscosity adjusting solvent ) To prepare a positive electrode active material slurry.

  90% by mass of hard carbon as a negative electrode active material, 10% by mass of PVDF as a binder, and NMP as a viscosity adjusting solvent were mixed to prepare a negative electrode active material slurry.

  Stainless steel (SUS) was prepared as a current collector. Then, the prepared positive electrode active material slurry was applied to one surface of the current collector and dried. Moreover, the negative electrode active material slurry was apply | coated to the other surface of the electrical power collector, and it was made to dry. By pressing this, a laminate in which a positive electrode active material layer (thickness: 36 μm) was formed on one surface of the current collector and a negative electrode active material layer (thickness: 30 μm) was formed on 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 450 × 300 (mm) and formed on the outer periphery of 20 mm from the outer edge and the positive 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. And the electrolyte obtained above was apply | coated to the positive electrode active material layer and the negative electrode active material layer, and the bipolar electrode which the gel electrolyte was infiltrated was produced by drying DMC.

<Preparation of separator>
90 parts by mass of N-ethylmethacrylamide as a monomer used as a raw material for the temperature-responsive polymer material and 7 parts by mass of N, N′-methylenebisacrylamide as a crosslinking agent are dissolved in water, and the solution is made of polyimide. The separator main material (thickness: 20 μm, average pore diameter: 70 nm, porosity: 60%) was impregnated and pulled up. This separator was immersed in paraffin oil and replaced with nitrogen gas. Then, 3 parts by mass of azobisisobutyronitrile was added as an initiator, and polymerization was carried out at room temperature for 3 hours while stirring to produce a separator in which the main material was coated with a temperature-responsive polymer material.

<Production of bipolar secondary battery>
12 mm wide seal portions (acrylic resin) were disposed on the four sides of the current collector exposed portion of the surface of the bipolar electrode obtained above where the positive electrode active material layer was formed. Next, the 435 × 285 (mm) separator obtained above was disposed so as to cover the bipolar electrode on the side where the positive electrode active material layer was formed. Thereafter, a seal portion (acrylic resin) was disposed on the separator corresponding to the exposed portion of the current collector, and the negative electrode surface of the bipolar electrode was stacked thereon. Thus, 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 Six bipolar electrodes were laminated via a separator in the order of the type electrode (negative electrode active material layer / current collector / positive electrode active material layer). The seal part was pressed from above and below (0.2 MPa, 160 ° C., 5 seconds) to fuse the current collector, seal part, and separator.

The obtained power generation element was sandwiched between aluminum tabs for current extraction (130 mm × 80 mm, thickness 100 μm), and vacuum sealed using an aluminum laminate film as an exterior material. This was hot-pressed at a surface pressure of 1 kg / cm ² for 1 hour using a hot press machine to cure the uncured seal portion and complete a bipolar secondary battery. The hot press temperature (adhesion temperature) is as shown in Table 1 below.

[Example 2]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 1 except that the polymerization time was 4.5 hours.

[Example 3]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 1 except that the polymerization time was 6 hours.

[Example 4]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 1 except that N-ethylacrylamide was used as a monomer as a raw material for the temperature-responsive polymer material.

[Example 5]
In <Production of Separator>, a separator was produced in the same manner as in Example 4 except that the polymerization time was 4.5 hours.

[Example 6]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 4 except that the polymerization time was 6 hours.

[Example 7]
<Manufacture of separator> In the same manner as in Example 1, except that a separator main material (thickness: 20 μm, average pore diameter: 70 nm, porosity: 60%) made of aramid was used. Produced.

[Example 8]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 7 except that the polymerization time was 4.5 hours.

[Example 9]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 7 except that the polymerization time was 6 hours.

[Example 10]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 7 except that N-ethylacrylamide was used as a monomer as a raw material for the temperature-responsive polymer material.

[Example 11]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 7 except that the polymerization time was 4.5 hours.

[Example 12]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 7 except that the polymerization time was 6 hours.

[Example 13]
In <Preparation of Separator>, the same method as in Example 1 except that a separator main material made of polyethylene (PE) (thickness: 20 μm, average pore diameter: 70 nm, porosity: 60%) was used. A separator was prepared.

[Example 14]
In <Preparation of Separator>, the same method as in Example 1 except that a separator main material made of polyethylene (PE) (thickness: 20 μm, average pore diameter: 70 nm, porosity: 60%) was used. A separator was prepared.

[Example 15]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 13 except that N-ethylacrylamide was used as a raw material for the temperature-responsive polymer material and the polymerization time was 6 hours. .

[Example 16]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 13 except that the polymerization time was 1 hour.

[Example 17]
<Separator production> A separator was produced in the same manner as in Example 13 except that the polymerization time was 2.8 hours.

[Example 18]
In <Preparation of Separator>, a separator was prepared in the same manner as in Example 13 except that the polymerization time was 6.1 hours.

[Comparative Example 1]
As the separator, only a separator main material made of PE that was not coated with a temperature-responsive polymer material was used.

[Comparative Example 2]
As the separator, only a separator main material made of aramid and not coated with a temperature-responsive polymer material was used.

[Comparative Example 3]
Example 1 except that N, N-diethylacrylamide was used as a raw material for the temperature-responsive polymer material, the separator polymerization time was 4 hours, and a separator main material made of polyethylene (PE) was used. A separator was prepared in the same manner as described above. The phase transition temperature of poly (N, N-diethylacrylamide) was 60 ° C., and the hot press temperature (adhesion temperature) was set to 80 ° C., which is higher than this.

(Evaluation of internal short circuit during initial charging)
Each bipolar secondary battery produced above is charged to 21.0 V by a constant current method (CC, current: 0.5 mA) in an atmosphere of 25 ° C., and then charged by a constant voltage method (CV, 21 V). The battery was charged for 10 hours. At this time, the number of batteries in which an internal short circuit occurred among the 10 batteries was examined. The results are shown in Table 1.

(Internal resistance measurement test)
Each bipolar secondary battery produced above is charged to 21.0 V by a constant current method (CC, current: 0.5 mA) in an atmosphere of 25 ° C., and then charged by a constant voltage method (CV, 21 V). The battery was charged for 10 hours. Thereafter, the cell voltage was discharged to 14 V with a constant current (CC, current: 1 C), and the internal resistance after the discharge was measured in an atmosphere at 25 ° C.

  Next, after heating the battery to 130 ° C., which is higher than the phase transition temperature of the temperature-responsive polymer material used in each of the examples and comparative examples, the internal resistance was also measured. And the internal resistance after heating to 130 degreeC when the internal resistance in 25 degreeC was set to 1 was calculated | required. The results are shown in Table 1.

  From the results of Table 1, in Examples 1 to 18, which were heat-bonded at a temperature lower than the phase transition temperature of the temperature-responsive polymer gel, the thermal contraction of the separator was suppressed, and an internal short circuit during initial charging did not occur. This is because, when the separator and the seal portion are heated and bonded, the temperature-responsive polymer gel coated on the surface of the pores of the separator exists in a swollen state, so that the stress when the separator is thermally contracted is relieved. it was thought.

  Moreover, the internal resistance after setting battery temperature to 130 degreeC showed the value from Examples 1-18 higher than Comparative Examples 1-3. This is thought to be because the shutdown function worked well because the gel in the pores contracted and closed the pores when the battery temperature became higher than the phase transition temperature of the temperature-responsive polymer gel. It was. In Comparative Example 3, it was considered that the shutdown effect was lowered because the temperature-responsive polymer gel had already contracted during the heat-bonding of the separator and the seal portion.

10 Bipolar secondary battery,
11 Current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
11a The outermost layer current collector on the positive electrode side,
11b The outermost layer current collector on the negative electrode side,
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,
50i, 50e separator,
51i, 51e Main material,
53i, 53e temperature-responsive polymer gel,
250 small battery pack,
300 battery packs,
310 connection jig,
400 vehicles.

Claims (7)

A current collector,
A positive electrode active material layer formed on one surface of the current collector;
A bipolar electrode having a negative electrode active material layer formed on the other surface of the current collector, and a separator having a power generation element formed by lamination,
A bipolar secondary battery in which a peripheral portion of the bipolar electrode and the separator is joined via a seal portion,
The separator is a main material that is a microporous film containing a resin;
A temperature-responsive polymer gel having a phase transition temperature that transitions from a swollen state to a contracted state as the temperature rises,
The bipolar secondary battery, wherein the seal part and the separator are bonded by heating at or below the phase transition temperature. The surface of the pores present in the main material is coated with the thermoresponsive polymer gel,
The bipolar secondary battery according to claim 1, wherein an area covered with the thermoresponsive polymer gel is 60 to 90% of the entire surface area of the pores.   The bipolar secondary battery according to claim 1 or 2, wherein the temperature-responsive polymer gel contains poly (N-substituted (meth) acrylamide).   The bipolar secondary battery according to any one of claims 1 to 3, wherein the main material includes at least one thermoplastic resin selected from the group consisting of polyethylene and polypropylene.   The bipolar secondary battery according to any one of claims 1 to 3, wherein the main material includes at least one thermosetting resin selected from the group consisting of polyimide and aramid.   An assembled battery comprising a plurality of the bipolar secondary batteries according to any one of claims 1 to 5 electrically connected.   A vehicle on which the bipolar secondary battery according to any one of claims 1 to 5 or the assembled battery according to claim 6 is mounted as a power source for driving a motor.