JP5181422B2 - Bipolar secondary battery - Google Patents

Description

  The present invention relates to a bipolar secondary battery, an assembled battery in which a plurality of the bipolar secondary batteries are connected, and a vehicle equipped with these batteries.

  In recent years, reduction of carbon dioxide emissions has been strongly desired for environmental protection. In the automobile industry, there are high expectations for the reduction of carbon dioxide emissions by introducing electric vehicles, hybrid electric vehicles, fuel cell vehicles, hybrid fuel cell vehicles, etc., and secondary batteries for motor drive that hold the key to their practical application. The development of As a secondary battery, attention is focused on a lithium ion secondary battery that can achieve high energy density and high output density. 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 unit cell layers connected in series in order to ensure a large output. Such a battery is called a bipolar type, and is expected to achieve a high energy density and a high output density.

  Among these, a bipolar secondary battery using a solid polymer electrolyte that does not contain a solution in the electrolyte layer has been proposed. According to this, since there is no solution (electrolyte) in the battery, there is no risk of liquid leakage or gas generation, high reliability, and a bipolar secondary battery that does not require a hermetic seal structurally is provided. It can be done. However, the ionic conductivity of the polymer solid electrolyte is lower than that of the polymer gel electrolyte, which will be described later, and the battery output density and energy density are not sufficient in a normal use environment, and the practical use stage has not yet been reached. Therefore, further improvement in ionic conductivity is awaited.

  On the other hand, a bipolar secondary battery using a polymer electrolyte containing an electrolytic solution in an electrolyte layer has been proposed. If a polymer electrolyte containing an electrolytic solution, that is, a polymer gel electrolyte is used for the electrolyte layer, the ion conductivity is excellent and the battery output density and energy density can be sufficiently obtained. It is expected as the closest bipolar secondary battery.

When a polymer gel electrolyte is used as the electrolyte, there arises a problem that the electrolyte solution oozes out from the electrolyte portion and comes into contact with electrodes or electrolyte layers of other unit cell layers, causing a liquid junction (short circuit). For this reason, normally, in a bipolar battery, a sealing member is disposed on a current collector of the bipolar electrode so as to surround a single battery composed of a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and a liquid junction (For example, refer to Patent Document 1).
JP 2004-158343 A

  However, when the bipolar battery as described above is used, for example, as a power source for driving a motor of an electric vehicle or a hybrid vehicle, the sealing performance of the seal member is lowered, and various problems may occur. That is, when used as an in-vehicle power source, the battery temperature may rise to about 60 ° C., but particularly in a current collector, a large amount of Joule heat is generated as a large current flows, and the current collector In some cases, the body temperature may exceed the softening point of the constituent material of the seal member. On the other hand, in a situation where the battery temperature rises, the pressure inside the battery often increases, and the thermal expansion coefficients of the constituent materials of the current collector and the seal member are generally different. These various factors, combined with the softening of the sealing member as described above, particularly reduce the sealing performance between the current collector and the sealing member. To occur). When the sealing performance is thus lowered, the electrolyte inside the battery leaks out, and there is a risk that a liquid junction will occur between adjacent unit cells. In addition, moisture penetrates from the outside to the inside of the battery, causing the electrolyte solution to decompose and deteriorate.

  In addition, as a method of improving the sealing performance by the sealing member, for example, a method of increasing the sealing area by the sealing member can be considered, but this leads to an increase in the size of the battery and causes a decrease in the volume energy density of the battery. Not realistic.

  Accordingly, an object of the present invention is to provide means for improving the sealing performance of a sealing member while minimizing the decrease in the volume energy density of the battery in a bipolar secondary battery.

  The present invention provides 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, the positive electrode active material layer, and the negative electrode active material layer An electrolyte layer in which an electrolyte is held in a separator, interposed between a plurality of the bipolar electrodes stacked so as to face each other, and the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer A bipolar secondary battery including a sealing member disposed on a current collector of the bipolar battery so as to surround the unit cells stacked in this order, and at least constituting the bipolar electrode A plurality of hole portions are provided in a portion of the current collector where the seal member is to be disposed, and the seal member is disposed so as to fill the hole portion. This is a bipolar secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the sealing performance by a sealing member can improve in the bipolar secondary battery, suppressing the fall of the volume energy density of a battery to the minimum. As a result, a highly reliable bipolar battery can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, for easy understanding, each component may be exaggerated in the drawings.

(First embodiment: bipolar secondary battery)
FIG. 1 is a cross-sectional view showing the structure of the bipolar secondary battery of the present embodiment.

  In the bipolar secondary battery 10 of the present embodiment, a positive electrode active material layer 12 and a negative electrode active material layer 13 are respectively formed at the center of both surfaces of a current collector 11 other than both ends. A separator 14 is interposed between the material layer 12 and the negative electrode active material layer 13, and the positive electrode active material layer 12, the separator 14, and the negative electrode active material layer 13 are laminated in this order to form a unit cell 15. The bipolar secondary battery 10 of this embodiment has a structure in which a plurality of the unit cells 15 are stacked. An electrode in which the positive electrode active material layer 12 is formed on one surface of the current collector 11 and the negative electrode active material layer 13 is formed on the other surface is referred to as a bipolar electrode 16. Further, current collectors (referred to as terminal current collectors 17) present at both ends are connected to the electrodes of the entire bipolar secondary battery 10 of the present embodiment.

  Further, separators 14 and bipolar electrodes 16 are alternately stacked, and a sealing member 18 is disposed on the current collector 11 so as to surround the unit cell 15 to form a battery element 20.

  The battery element 20 is connected to electrode tabs 30a and 30b for drawing out current. The electrode tab 30a (positive electrode tab) is connected to the positive electrode side of the battery element 20, and the electrode tab 30b (negative electrode tab) is connected to the negative electrode side. The battery element 20 is sealed with an exterior 40.

  The exterior 40 is formed by two laminate sheets 41. The laminate sheet 41 has a three-layer structure in which both surfaces of an aluminum layer are covered with a resin layer. At least one of the laminate sheets 41 is processed into a medium-high shape in order to provide a space that encloses the battery element 20. The edge of the laminate sheet 41 is bonded by heat fusion or the like. Thereby, the battery element 20 is sealed inside the exterior 40.

  Hereinafter, the characteristic configuration of the bipolar battery 10 of the present embodiment will be described in detail with reference to the drawings.

  FIG. 2 is a cross-sectional view showing the structure of the battery element 20 of the bipolar secondary battery 10 of the present embodiment. 3 is a cross-sectional view (plan view) along the line III-III shown in FIG. In the form shown in FIG. 2, the current collector 11 in which only one of the positive electrode active material layer 12 or the negative electrode active material layer 13 is formed in the outermost layer on each of the positive electrode side and the negative electrode side; The terminal current collector 17 is electrically connected by a terminal current collector connection sheet. However, it is not limited only to such a form, The collector 11 located in each outermost layer of a positive electrode side and a negative electrode side may be used as a terminal collector as it is.

  As shown in FIG. 2, the bipolar secondary battery 10 according to the present embodiment includes a plurality of hole portions 11 ′ (in the region where the seal member 18 is to be disposed in the current collector 11 constituting the bipolar electrode 16. 3 is provided, and the sealing member 18 is characterized in that it is disposed so as to fill the hole 11 ′. In addition, the material which comprises a sealing member is mentioned later.

  The conventional seal member is disposed between the current collectors 11 constituting the bipolar electrode 16 and exhibits a seal function only by adhesion between the current collector and the seal member. On the other hand, in the bipolar battery 10 of the present embodiment, the current collector 11 constituting the bipolar electrode 16 is provided with a hole portion 11 ′, and the hole member 11 ′ is filled with the seal member 18. Are arranged to be. For this reason, not only the conventional adhesion between the current collector and the seal member but also the adhesion between the seal members via the air holes 11 'can contribute to the performance of the sealing function. As a result, the sealing performance by the sealing member is improved, and the occurrence of problems such as peeling of the sealing member at high temperatures and the accompanying liquid leakage and moisture intrusion is suppressed, and a highly reliable bipolar battery can be provided.

  There is no restriction | limiting in particular about the shape and size of void | hole part 11 ', What is necessary is just to determine suitably considering desired sealing performance, the simplicity of manufacture, etc. As an example of the shape of the hole portion 11 ′, there are an elliptical shape, a square shape, a rectangular shape, a triangular shape, and the like in addition to the circular shape shown in FIG. 3. However, it will be appreciated that other shapes may be employed.

  In the form shown in FIGS. 1 to 3, the ratio of the area of the hole portion to the total area (the total of the current collector—the adhesion area of the seal member and the area of the hole portion) where the seal member is disposed Although not limited, it is preferably about 5 to 15%. If the area ratio of the hole part is too large, there is a concern of liquid junction through the hole part, so the ratio of the area of the hole part is set in consideration of the balance between the increase in adhesive strength and the possibility of liquid junction. Should be decided. However, it is needless to say that a form outside these ranges may be adopted. Here, consider a case where the ratio is 10%. The adhesive strength between the seal members is about four times at least as compared with the adhesive strength between the current collector and the seal member. Then, the adhesive strength due to the arrangement of the seal member is 0.9 × 1 + 0.1 × 4 = 1.3, assuming that the adhesive strength in the case of only adhesion between the current collector and the seal member is 1, and at least 1 Expected to be more than 3 times.

  In the bipolar secondary battery of the present embodiment, the hole 11 ′ is provided in the current collector 11 where the seal member is to be disposed. In particular, as shown in FIG. The body 17 is preferably provided with a hole 11 ′ and filled with a seal member 18. According to such a form, the sealing member 18 is filled in the relatively thick terminal current collector, thereby suppressing the swelling of the battery element accompanying the progress of the charge / discharge cycle. Preferably, the terminal current collector and all other current collectors are provided with the hole 11 ′ and filled with the seal member 18.

  Further, in the bipolar secondary battery of the present embodiment, the separator 14 has a shape overlapping with the seal member 18 when viewed from the stacking direction of the unit cells 15. In such a form, as shown in FIG. 4, the separator 14 constituting the electrolyte layer is also provided with a hole portion 14 ′ similarly to the current collector 11, and the seal member 18 is provided in the hole portion 14 ′. Is preferably filled. According to such a configuration, the vibration resistance of the battery is improved, and a more reliable bipolar battery can be provided.

  Furthermore, in the bipolar secondary battery according to the present embodiment, as shown in FIG. 1, the terminal current collector 17 positioned in the outermost layer of the battery element 20 of the bipolar secondary battery 10 is stacked with the single battery 15. The electrode tabs 30a and 30b are separately connected so as to have a shape overlapping the seal member 18 when viewed from the direction. In such a configuration, it is preferable that the electrode tabs 30a and 30b are also provided with a hole portion and the hole portion is filled with a seal member, as described for the separator 14. Such a configuration can also improve the vibration resistance of the battery and provide a more reliable bipolar battery.

  In a more preferred form, the arrangement form of the air holes 11 'provided in the current collector 11 (in some cases, the separator 14 and the electrode tabs 30a and 30b) is also controlled. Specifically, the hole 11 ′ provided in the current collector 11 will be described as an example. In a preferred embodiment, as shown in FIG. 5, a plurality of holes 11 ′ provided in the current collector 11 are used. However, it arrange | positions so that there may be no site | part which does not exist seeing from the direction perpendicular | vertical to the end surface of the cell 15. FIG. According to such a form, even if the adhesion between the current collector and the sealing member is peeled off, the liquid from the inside of the battery element to the outside of the battery is maintained if the adhesion between the sealing members is secured. Even if leakage or water intrusion from the outside of the battery into the battery element occurs through the interface between the current collector and the seal member, it cannot pass through the interface at the shortest distance. It will pass around the adhesion site. As a result, the occurrence of the above problems can be further suppressed, which can contribute to an improvement in battery reliability. In addition, although arrangement | positioning form of void | hole part 11 'in the bipolar battery 10 of the form shown in FIG. 5 is shown in FIG. 6, it is not limited only to such a form, It is the same also with the form shown in FIGS. The following effects can be obtained. Of course, other arrangements may be adopted.

  Hereinafter, the bipolar secondary battery of the present invention will be described for each component, but the technical scope of the present invention is not limited to the following modes.

[Current collector]
The current collector that can be used in the present invention is not particularly limited, and conventionally known current collectors can be used. For example, aluminum foil, stainless steel (SUS) foil, nickel-aluminum clad material, copper-aluminum clad material, or a plating material of a combination of these metals can be cited. In order to obtain an electric body, stainless steel foil is preferable, and among them, SUS316L having a Mo component is preferable.

  Further, a current collector in which a metal surface is coated with aluminum may be used. In some cases, a current collector in which two or more metal foils are bonded together may be used.

  Furthermore, as a current collector that can be used in the present invention, a current collector formed by forming a film into a desired shape by a thin film manufacturing technique such as spray coating can be used. For example, it is formed by heating a current collector metal paste containing a metal powder such as aluminum, copper, titanium, nickel, stainless steel, and alloys thereof as a main component and containing a binder (resin) and a solvent. . These metal powders may be used singly or as a mixture of two or more, and moreover, metal powders of different types are laminated in multiple layers taking advantage of the manufacturing characteristics. May be.

  The binder is not particularly limited. For example, a conventionally known resin binder material such as an epoxy resin can be used, and a conductive polymer material may be used. The conductive polymer here is a filler-dispersed conductive polymer composed of a polymer material and a conductive filler for adding conductivity. The polymer material itself has conductivity. Includes both polymers. It is preferable to use a current collector using a conductive polymer material because the current can be reduced and the current collector can withstand both positive and negative electrode potentials.

  Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers.

[Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material. In addition to this, a conductive aid for increasing the electron conductivity, a lithium salt for increasing the ionic conductivity, a binder, an electrolyte (for example, a polymer gel electrolyte), and the like may be included.

Among these, the positive electrode active material is not particularly limited, and those usable for a solution type lithium ion secondary battery can be appropriately used. Preferably, it is a composite oxide of a transition metal and lithium (lithium-transition metal composite oxide) because a battery having excellent capacity and output characteristics can be formed. 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 Examples thereof include Fe-based composite oxides. In addition, transition metal and lithium phosphate compounds and sulfate compounds such as LiFePO ₄ ; transition metal oxides and sulfides such as V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , and MoO ₃ ; PbO ₂ , AgO, NiOOH or the like can also be used.

  The particle size of the positive electrode active material is smaller than the particle size generally used for solution (electrolyte) type lithium ion secondary batteries that are not bipolar type in order to reduce the electrode resistance of the bipolar type secondary battery. Should be used. Specifically, the average particle diameter of the positive electrode active material fine particles is 0.1 to 10 μm, preferably 0.1 to 5 μm.

  Examples of the conductive aid for increasing the electron conductivity include acetylene black, carbon black, and graphite. However, it is not necessarily limited to these.

The lithium salt to increase the ionic conductivity, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10 inorganic acid anion salts such as, LiCF ₃ SO ₃ , organic acid anion salts such as Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, or a mixture thereof. However, it is not necessarily limited to these.

  As the binder, polyvinylidene fluoride (PVDF) or the like can be used. However, it is not necessarily limited to these.

  In the positive electrode, the amount of electrolyte such as positive electrode active material, conductive additive, binder, polymer gel electrolyte (polymer matrix, electrolyte, etc.), etc. depends on the intended use of the battery (emphasis on output, energy, etc.), ion conductivity Should be taken into consideration. For example, if the amount of the polymer gel electrolyte in the positive electrode is too small, the ion conduction resistance and the ion diffusion resistance in the positive electrode are increased, and the battery performance is deteriorated. On the other hand, if the amount of the polymer gel electrolyte in the positive electrode is too large, the energy density of the battery is lowered. Therefore, in consideration of these factors, the polymer gel electrolysis mass suitable for the purpose is determined.

  The thickness of the positive electrode is not particularly limited, and should be determined in consideration of the intended use of the battery (emphasis on output, emphasis on energy, etc.) and ion conductivity, as described for the blending amount. A typical positive electrode layer has a thickness of about 10 to 500 μm.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material active material. In addition to this, a conductive additive for increasing the electron conductivity, a lithium salt for increasing the ionic conductivity, a binder, an electrolyte (for example, a polymer gel electrolyte), and the like may be included.

  Except for the type of the negative electrode active material, the contents are basically the same as those described in the section “Positive electrode active material layer”, and thus the description thereof is omitted here.

  The negative electrode active material is not particularly limited, and a material usable for a bipolar secondary battery can be appropriately used. Specifically, carbon, metal oxide, lithium-metal composite oxide, and the like can be used, and carbon or lithium-transition metal composite oxide is preferable. This is because a battery excellent in capacity and output characteristics (for example, the battery voltage can be increased) can be configured by using these. As the lithium-transition metal composite oxide, for example, a lithium-titanium composite oxide can be used. Moreover, as carbon, graphite, graphite, acetylene black, carbon black etc. can be used, for example. As the metal oxide, for example, a transition metal oxide such as titanium oxide can be used.

[Electrolyte layer]
In the bipolar secondary battery of this embodiment, the electrolyte layer has a configuration in which an electrolyte is held by a separator. The electrolyte may be either a liquid electrolyte or a polymer gel electrolyte as long as it exhibits ionic conductivity.

  Among these, it is preferable to use a polymer gel electrolyte. By using a gel electrolyte as the electrolyte, it is possible to prevent leakage as compared with a liquid electrolyte, and a highly reliable bipolar secondary battery can be configured. The polymer gel electrolyte is not particularly limited, and those used in conventional polymer gel electrolyte layers can be appropriately used. Here, the polymer gel electrolyte means an electrolyte solution held in a polymer matrix. Specifically, a polymer having ion conductivity (all solid polymer electrolyte) containing an electrolyte solution usually used in a lithium ion secondary battery, or a polymer skeleton having no lithium ion conductivity. Also included are those holding the same electrolyte.

  The polymer matrix of the polymer gel electrolyte is not particularly limited, and conventionally known ones can be used. Preferably, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), PAN, polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), poly (methyl methacrylate) (PMMA) And their copolymers are desirable, and preferred solvents are ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. .

Among these, examples of the polymer having ion conductivity include known solid polymer electrolytes such as PEO, PPO, and polyalkylene oxide polymers such as copolymers thereof. A polyalkylene oxide polymer such as PEO and PPO can dissolve lithium salts such as LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) ₂ well. Moreover, excellent mechanical strength is exhibited by forming a crosslinked structure.

  Examples of the polymer having no lithium ion conductivity include PVDF, polyvinyl chloride (PVC), PAN, and PMMA. However, it is not necessarily limited to these. Note that PAN, PMMA, and the like are in a class that has almost no ionic conductivity, and thus can be a polymer having the ionic conductivity. Here, the polymer used for the polymer gel electrolyte is exemplified as a polymer having no lithium ion conductivity.

  The electrolyte solution contained in the polymer gel electrolyte is not particularly limited, and conventionally known electrolyte solutions can be used. What is necessary is just normally used with a lithium ion battery, and what contains lithium salt (supporting salt) and solvents, such as an organic solvent and an ionic liquid, etc. can be used.

Specifically, as the lithium salt as a supporting salt, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, Li 2 B 10 Cl 10, LiTFSI, LiFSI, LiBETI, such as LiBOB Examples include inorganic acid anion salts, organic acid anion salts such as LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, and Li (C ₂ F ₅ SO ₂ ) ₂ N. These are used alone or in combination. Can be used. Among these lithium salts, it is more preferable to include any one of LiBF ₄ , LiTFSI, LiFSI, LiBETI, and LiBOB as a supporting salt in order to add high heat resistance.

  The organic solvent is not particularly limited, but cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC); chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate (DEC); Ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-dibutoxyethane; lactones such as γ-butyrolactone; nitriles such as acetonitrile; methyl propionate, etc. Esters using amides such as dimethylformamide; those using an organic solvent (plasticizer) such as an aprotic solvent in which at least one selected from methyl acetate and methyl formate is mixed. Can be used.

  The ionic liquid is not particularly limited. Examples of the cation constituting the ionic liquid include amidinium cations such as imidazolinium cation, imidazolium cation, tetrahydropyrimidinium cation, and dihydropyrimidinium cation. Guanidinium cations having an imidazolinium skeleton, guanidinium cations having an imidazolium skeleton, guanidinium cations having a tetrahydropyrimidinium skeleton, guanidinium cations having a dihydropyrimidinium skeleton, etc. Examples thereof include a nium cation and a tertiary ammonium cation such as methyldilauryl ammonium. The cation may be used alone or in combination of two or more.

  Examples of the anion constituting the ionic liquid include organic acid and inorganic acid anions.

  Examples of the organic acid include carboxylic acid, sulfate ester, higher alkyl ether sulfate ester, sulfonic acid, sulfonate ester, and phosphate ester.

  Examples of inorganic acids include super strong acids (for example, borofluoric acid, tetrafluoroboric acid, perchloric acid, hexafluorophosphoric acid, hexafluoroantimonic acid, and hexafluoroarsenic acid). Examples thereof include phosphoric acid and boric acid. The anion may be used alone or in combination of two or more of the organic acids and inorganic acids.

  The proportion of the electrolytic solution in the polymer gel electrolyte in the present embodiment may be determined according to the purpose of use and is not particularly limited. From the viewpoint of ionic conductivity and the like, it can be suitably used in the range of several mass% to 98 mass%.

  These electrolytes may be held in a separator, or a polymer gel electrolyte may be impregnated in an electrode.

  The thickness of the electrolyte layer is not particularly limited as long as the desired electrolyte performance can be effectively expressed. However, in order to obtain a compact bipolar secondary battery, it is preferable to make it as thin as possible within a range in which the function as the electrolyte layer can be secured. Generally, it is about 10-100 micrometers.

  The electrolyte can be included in the positive electrode active material layer and / or the negative electrode active material layer in addition to the electrolyte layer constituting the battery. Different electrolytes may be used depending on the electrolyte layer, the positive electrode, and the negative electrode constituting the battery, or the same electrolyte may be used. Further, different electrolytes may be used depending on each unit cell layer (each constituent member thereof).

[Separator]
Examples of the constituent material of the separator include resin materials such as polyolefin such as polyethylene and polypropylene, polyamide, and polyimide. A separator can be produced by molding these resin materials into a microporous film having a porosity of about 10 to 80%.

  In particular, when the separator is in the form of a microporous membrane, the pores are opened only in the direction perpendicular to the surface direction of the membrane, there is no leakage in the surface direction (lateral direction) from the sealing member, and sealing can be performed easily. This is preferable because the discharge capacity is maintained even when stored at a higher temperature.

  The diameter of the micropores in the microporous membrane is preferably 1 μm or less (usually a pore diameter of about several tens of nm). When the average pore diameter of the microporous membrane is within the above range, the “shutdown phenomenon” in which the microporous membrane melts and closes due to heat generated by overcharging occurs rapidly, and the positive electrode of the battery (electrode) ( Li ions cannot pass from the (+) to the negative electrode (-) side, and no more can be charged. As a result, in addition to improving the heat resistance (safety) of the battery, it is possible to prevent gas from being generated and the heat fusion part (seal member) of the battery exterior material from opening. Here, the average diameter of the micropores of the separator is calculated as an average diameter obtained by observing the separator with a scanning electron microscope or the like and statistically processing the photograph with an image analyzer or the like.

  The porosity of the microporous membrane is preferably 20 to 50%. The reason why the porosity of the microporous membrane separator is within the above range prevents the output from being reduced due to the resistance of the electrolyte (electrolyte) and prevents the liquid junction due to the fine particles penetrating through the pores (micropores) of the separator. Therefore, there is an effect of ensuring both output and reliability. Here, the porosity of the microporous membrane separator is a value obtained as a volume ratio from the density of the raw material resin and the density of the microporous membrane separator of the final product.

  The thickness of the microporous membrane cannot be uniquely defined because it varies depending on the intended use. In applications such as secondary batteries for driving motors such as electric vehicles (EV), fuel cell vehicles, and hybrid vehicles thereof, the thickness is preferably 1 to 60 μm in a single layer or multiple layers from the viewpoint of battery thinning. Since the thickness of the microporous membrane is in such a range, it is preferable to prevent the liquid junction caused by the fine particles biting into the separator and to narrow the gap between the electrodes for high output. There is an effect of ensuring mechanical strength and high output performance. In addition, when a plurality of batteries are connected, the electrode area increases, so that it is preferable to use a thick separator in the above range in order to increase the reliability of the battery.

[Seal material]
The sealing member is disposed on the current collector so as to surround the unit cell, and has a function of blocking contact between the unit cell and the outside. Thereby, the liquid junction which may arise when using a liquid or a gel-like electrolyte can be prevented. In addition, the reaction between air or moisture contained in the air and the active material can be suppressed. Furthermore, in this embodiment, it fills with the void | hole part provided in the electrical power collector (the separator and current collection tab depending on the case), and can improve the sealing performance between the adjacent single cells.

  Although there is no restriction | limiting in particular about the material which comprises a sealing member, It is preferable to use resin bonded by heating. By using the sealing resin that can be heated and bonded as a constituent material of the sealing member, in particular, a liquid junction (short circuit) due to leakage of the electrolytic solution can be prevented by heating and bonding with the current collector. This is advantageous in that a liquid junction can be prevented even if the pressurization at the time of thermal bonding is insufficient even if the bonding by thermal bonding is sufficiently performed.

  The “resin that is bonded by heating” used as the constituent material of the seal member of the present invention is an excellent seal (prevents seepage of electrolyte) under any use environment of the bipolar secondary battery as the seal member. ) There is no particular limitation as long as the effect can be exhibited, and a material that meets the required conditions depending on the application can be appropriately selected. That is, the constituent material of the sealing member may be a thermosetting resin that cures with a chemical reaction when heated, or a thermoplastic resin that melts when heated and is solidified again when returned to room temperature. Good.

  Especially, as a material which comprises the sealing member used for this invention, it is preferable to use polyolefin resin and a thermosetting resin. Examples of the polyolefin resin include polypropylene and polyethylene. Thermosetting resins are advantageous in that they are easy to handle and can simplify the manufacturing process because the state before curing is liquid. The thermosetting resin is not particularly limited as long as it can exhibit an excellent sealing effect, but is preferably one selected from the group consisting of epoxy resins, phenol resins, polyimides, silicone resins, and polyurethanes. The above resins are used. These resins are more preferable because they have chemical stability to the electrolyte and improve the reliability of the seal. Among these, polypropylene, polyethylene, and epoxy resin can be particularly preferably used.

  The seal member of the present invention may contain a resin other than the above-described materials. Examples of such a resin include rubber resins such as silicone-based, fluorine-based, and nitrile-based materials that are bonded by pressing.

  The sealing member of the present invention is bonded by heating, but a pressurizing operation may be applied to improve the sealing performance.

[Electrode tab]
The electrode tab is attached to a current collector constituting the outermost layer electrode for taking out current as required. When used, it has a function as a terminal and is preferably as thin as possible from the viewpoint of thinning. However, since the laminated positive electrode, negative electrode, electrolyte layer, and current collector are all weak in mechanical strength, they are supported by being sandwiched from both sides, and moreover, the sealing member can be more securely bonded. It is desirable to have strength. Furthermore, it can be said that the thickness of the electrode tab is usually preferably about 0.1 to 2 mm from the viewpoint of suppressing the internal resistance at the electrode tab.

  As the material of the electrode tab, a material used in a normal bipolar secondary battery can be used. For example, aluminum, copper, titanium, nickel, stainless steel, alloys thereof, and the like can be used.

  The material of the electrode tab (positive electrode tab) on the positive electrode side for current extraction and the electrode tab (negative electrode tab) for the negative electrode may be the same or different. Further, the electrode tabs on the positive electrode side and the negative electrode side may be formed by laminating different materials.

  The positive electrode and the negative electrode tab are preferably configured to cover all of the positive electrode and the negative electrode terminal electrode. With such a configuration, it becomes possible to receive the current of the bipolar secondary battery on the surface, and the output of the battery is improved.

  The bipolar secondary battery of the present invention is manufactured by appropriately using a conventionally known method by combining the above elements and a conventionally known exterior material.

(Second embodiment: assembled battery)
In the second embodiment, an assembled battery is configured by connecting a plurality of the bipolar secondary batteries of the first embodiment in parallel and / or in series.

  FIG. 10 is a plan view of a bipolar secondary battery, FIG. 11 is a trihedral view showing the bipolar secondary battery housed in the case, and FIG. 12 is a trihedral view showing the assembled battery.

  As shown in FIG. 10, when the bipolar secondary battery 10 is viewed from the planar direction, the positive electrode tab 30a and the negative electrode tab 30b are drawn out on both sides. For example, as shown in FIG. 11, four such bipolar secondary batteries 10 are stacked and stored in the case 50. In FIG. 11, the positive electrode tabs 30 a and the negative electrode tabs 30 b are arranged on the same side and are connected to each other by a positive electrode terminal 51 and a negative electrode terminal 52.

  The battery case 50 in which the bipolar secondary battery 10 is stored is laminated and integrated by a connecting plate 61 and a fixing screw 62, and an assembled battery 60 as shown in FIG. 12 is formed. In the assembled battery 60, the positive terminals 51 and the negative terminals 52 of each battery case 50 are connected to each other by plate-like bus bars 63 and 64. Thus, an assembled battery 60 in which a plurality of bipolar secondary batteries are connected in parallel is formed.

  In this assembled battery 60, ultrasonic welding, thermal welding, laser welding, rivets, caulking, electron beam, or the like can be used as a connection method when connecting a plurality of bipolar secondary batteries 10. By adopting such a connection method, the assembled battery 60 with long-term reliability can be manufactured.

  According to this embodiment, long-term reliability as an assembled battery can be improved by using the bipolar secondary battery 10 according to the first embodiment described above to form an assembled battery.

  In addition, by using a case for connecting a small number of bipolar secondary batteries 10 as described above, it is possible to configure assembled batteries with various designs without manufacturing many assembled battery types. Can be reduced.

Note that the connection of the bipolar secondary battery 10 as the assembled battery is not limited to the parallel connection as described above. A plurality of them may be connected in series, and a series connection and a parallel connection may be combined.
(Third embodiment: vehicle)
In the third embodiment, the bipolar secondary battery 10 of the first embodiment or the assembled battery 60 of the second embodiment is mounted as a motor driving power source to constitute a vehicle. As a vehicle using the bipolar secondary battery 10 or the assembled battery 60 as a motor driving power source, there is an automobile whose wheels are driven by a motor, such as an electric automobile and a hybrid automobile.

  For reference, FIG. 13 shows a schematic diagram of an automobile 70 on which the assembled battery 60 is mounted. The assembled battery 60 mounted on the automobile 70 has the characteristics described above. For this reason, the automobile on which the assembled battery 60 is mounted has high durability and can provide a sufficient output even after being used for a long period of time.

  The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples.

<Example 1: Preparation of a liquid electrolyte bipolar secondary battery>
1. Formation of Bipolar Electrode A. Formation of Positive Electrode Active Material Layer First, LiMn ₂ O ₄ [85% by mass] as a positive electrode active material, acetylene black [5% by mass] as a conductive additive, PVDF [10% by mass] as a binder, and a slurry viscosity adjusting solvent A material composed of N-methyl-2-pyrrolidone (NMP) was mixed at the above ratio until the viscosity became optimum for the coating process to prepare a positive electrode active material slurry. The NMP is volatilized and removed when the electrode is dried. Therefore, an appropriate amount was added so as to obtain an appropriate slurry viscosity, not an electrode constituent material. Moreover, the said ratio shows the ratio converted with the component except a slurry viscosity adjustment solvent.

  The positive electrode slurry was applied to one side of a SUS foil (thickness 20 μm) as a current collector, and was placed in a vacuum oven and dried to form a positive electrode active material layer having a thickness of 30 μm.

B. Negative electrode active material layer First, a viscosity composed of hard carbon [90% by mass] as a negative electrode active material, PVDF [10% by mass] as a binder, and NMP as a slurry viscosity adjusting solvent at the above ratio is the optimum viscosity for the coating process. The negative electrode slurry was prepared by mixing until The NMP is volatilized and removed when the electrode is dried. Therefore, an appropriate amount was added so as to obtain an appropriate slurry viscosity, not an electrode constituent material. Moreover, the said ratio shows the ratio converted with the component except a slurry viscosity adjustment solvent.

  The negative electrode slurry was applied to the opposite surface of the SUS foil on which the positive electrode was formed, placed in a vacuum oven, and dried to form a negative electrode having a thickness of 30 μm.

  A bipolar electrode was formed by forming a positive electrode and a negative electrode on both surfaces of a SUS foil as a current collector.

  These bipolar electrodes were cut to 170 × 120 (mm), and both the positive electrode and the negative electrode were peeled off by 20 mm from the outer peripheral portion to expose the SUS surface as a current collector (see FIG. 14).

3. Formation of Seal Member Precursor A seal precursor (one-component uncured epoxy resin) was applied to the outer periphery of the electrode as shown in FIG. At this time, an uncoated portion having a width of about 10 mm was provided on the outer peripheral portion of the seal member precursor so that the electrode holding mechanism described later can hold the electrode.

  Next, a 180 × 130 (mm) separator (made of polyethylene) was installed so as to cover all of the SUS foil as the positive electrode current collector. Thereafter, a seal precursor was applied to the outer peripheral portion of the electrode as shown in FIG. 16 using a dispenser from above the separator to a portion where the electrode was not applied (the same portion as the portion where the seal precursor was applied).

4). Setting to the electrode holding mechanism With the bipolar electrode created above with the negative electrode face up, the electrodes do not contact each other and are not displaced in the direction perpendicular to the electrode surface direction. Six sheets were set in a chuckable bipolar electrode holding mechanism (see FIG. 17). No seal member and separator were installed on the bottom electrode, and no electrolyte was applied to the positive electrode surface. Further, no electrolyte was applied to the negative electrode surface of the uppermost electrode.

5. Preparation and Introduction of Electrolytic Solution As an electrolytic solution, a solution was prepared by dissolving LiPF ₆ that is a lithium salt and a small amount of a surfactant in an equal volume mixed solution of propylene carbonate (PC) and ethylene carbonate (EC). The lithium salt concentration in the solution (electrolytic solution) was adjusted to 1M.

  The prepared solution (electrolyte) was dropped 1 mL at a time using a micropipette on the negative electrode active material layer of the six bipolar electrodes set in the electrode holding mechanism prepared above, and the negative electrode of each electrode The active material layer was soaked.

6). Introduction into a vacuum chamber The electrode holding mechanism was introduced into a vacuum chamber having a lamination part and a pressurizing / heating press part, and the inside of the vacuum chamber was evacuated by a vacuum pump (see FIG. 18).

7). Stacking of electrodes The bipolar secondary battery in which the bipolar electrode is stacked on the electrode pedestal while keeping the electrode holding mechanism down (see FIG. 19), and five single cells are stacked in a vacuum. A structure was produced.

8). Pressing the bipolar secondary battery The above-mentioned bipolar secondary battery structure is moved together with the electrode cradle to the press site in a vacuum, and hot-pressed for 1 hour at a surface pressure of 1 kg / cm ² and 80 ° C. with a hot press. Thus, the uncured seal member was cured. By this step, the seal member can be pressed to a predetermined thickness and further cured (see FIG. 20).

9. Removal from the vacuum chamber After the inside of the vacuum chamber was leaked and returned to atmospheric pressure, the bipolar secondary battery structure was taken out to complete a liquid electrolyte type bipolar secondary battery.

<Example 2: Production of gel electrolyte bipolar secondary battery>
As an electrolyte retained in the separator, instead of the electrolyte prepared in Example 1 above, 90% by mass of LiPF ₆ and 10% by mass of PVDF-HFP copolymer (host polymer) in an equal volume mixture of PC and EC. In addition, dimethyl carbonate (DMC) was added as a viscosity adjusting solvent until the viscosity became optimum for the coating step to prepare a pregel electrolyte. The lithium salt concentration in the total amount of the pregel electrolyte excluding DMC was adjusted to 1M.

  The pregel electrolyte prepared above is applied to both the positive electrode active material layer and the negative electrode active material layer of the bipolar electrode so that the gel electrolyte is infiltrated into the active material layer, and finally DMC is volatilized to form the bipolar electrode. Produced.

  Except for the above, a gel electrolyte bipolar secondary battery was fabricated in the same manner as in Example 1 above.

It is sectional drawing which shows the structure of the bipolar secondary battery of 1st Embodiment. It is an expanded sectional view which shows the structure of the battery element of the bipolar secondary battery of 1st Embodiment. It is sectional drawing along the III-III line | wire shown in FIG. It is an expanded sectional view which shows the structure of the battery element of the modification of the bipolar secondary battery of 1st Embodiment. It is a top view for demonstrating the arrangement | positioning form of the void | hole part in the bipolar secondary battery of 1st Embodiment. It is an enlarged plan view which shows the void | hole part in the bipolar secondary battery of 1st Embodiment. It is an enlarged plan view which shows the modification of the void | hole part in the bipolar secondary battery of 1st Embodiment. It is an enlarged plan view which shows the modification of the void | hole part in the bipolar secondary battery of 1st Embodiment. It is an enlarged plan view which shows the modification of the void | hole part in the bipolar secondary battery of 1st Embodiment. It is a top view of a bipolar secondary battery. It is a three-plane figure which shows the bipolar secondary battery stored in the case. It is a three-plane figure which shows an assembled battery. The schematic of the motor vehicle carrying an assembled battery is shown. It is a cross-sectional schematic diagram which shows one Embodiment of the bipolar electrode used for this invention. FIG. 15 is a schematic cross-sectional view showing the bipolar electrode of FIG. 14 in which an electrolyte layer and a seal member precursor are formed. It is the cross-sectional schematic which shows what installed the separator in the bipolar electrode of FIG. FIG. 17 is a schematic cross-sectional view showing that the bipolar electrode created in FIG. 16 is set in a bipolar electrode holding mechanism. It is a figure which shows the process which introduce | transduces an electrode holding mechanism into the vacuum chamber which has a lamination | stacking site | part, pressurization, and a heating press site | part, and evacuates the inside of a vacuum chamber with a vacuum pump. It is the cross-sectional schematic which shows having laminated | stacked the said bipolar electrode on the electrode base so that it might not shift | deviate, moving down an electrode holding mechanism. It is a figure which shows the process of moving a bipolar secondary battery structure to a press site | part with the electrode base in a vacuum, and hot-pressing with a hot press machine.

Explanation of symbols

10 Bipolar secondary battery,
11 Current collector,
11 'hole part,
12 positive electrode active material layer,
13 negative electrode active material layer,
14 separator,
14 'hole part,
15 cells,
16 Bipolar electrode,
17 terminal current collector,
18 sealing member,
19 Terminal current collector connection sheet,
20 battery elements,
30a positive electrode tab,
30b negative electrode tab,
40 exterior,
41 Laminate sheet,
50 battery case,
51 positive terminal,
52 negative terminal,
60 battery packs,
61 connecting plate,
62 fixing screws,
63, 64 bus bar,
70 cars.

Claims (6)

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;
An electrolyte layer in which an electrolyte is held in a separator, interposed between a plurality of the bipolar electrodes laminated so that the positive electrode active material layer and the negative electrode active material layer face each other;
The positive electrode active material layer, the electrolyte layer, and the negative active way material layer surrounding the unit cells are laminated in this order, the seal member disposed on a current collector of the bipolar electrodes,
A bipolar secondary battery comprising:
A plurality of hole portions are provided in a portion of the current collector constituting the bipolar electrode where the seal member is to be disposed, and the seal member is filled in the hole portion. Be arranged,
The bipolar secondary battery according to claim 1, wherein a ratio of the hole portion to a total area where the seal member is disposed is 5 to 15%.   The bipolar secondary battery according to claim 1, wherein the current collector filled with the seal member is a terminal current collector.   At least a part of the separator has a shape overlapping with the seal member when viewed from the stacking direction of the unit cells, and a plurality of hole portions are provided in the overlapping part of the separator, The bipolar secondary battery according to claim 1, wherein the bipolar secondary battery is disposed so as to be filled in the hole portion.   When an electrode tab is additionally connected to the terminal current collector located on the outermost layer of the battery element of the bipolar secondary battery, at least a part of the electrode tab is the seal as viewed from the stacking direction of the unit cells. 2. A shape overlapping with a member, wherein a plurality of hole portions are provided in the overlapping portion of the electrode tab, and the sealing member is disposed so as to fill the hole portion. The bipolar secondary battery according to any one of to 3.   The plurality of holes provided in the current collector, the separator, or the electrode tab are arranged so that there is no portion that does not exist when viewed from a direction perpendicular to the end face of the unit cell. 5. The bipolar secondary battery according to any one of 4 above.   The bipolar secondary battery according to any one of claims 1 to 5, wherein a material constituting the sealing member is polypropylene, polyethylene, or an epoxy resin.

Images