JP2008016381A - Electrode for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means capable of contributing to improvement of output characteristics of a battery by retaining an active material of small particle diameter in a conductive material and by improving conductivity of an active material layer in an electrode for the battery which can be used under high output conditions. <P>SOLUTION: This is the electrode 1 for battery having a current collector 2, and the active material layer 3 containing the active material 4 and an electroconductive material formed on the surface of the current collector. The problems are solved by the electrode for battery in which electroconductive material has an electroconductive structure 5 containing the electroconductive material and having micropores. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery electrode. In particular, the present invention relates to an improvement for improving the output characteristics of a lithium ion secondary battery.

  In recent years, hybrid vehicles, electric vehicles, and fuel cell vehicles have been manufactured and sold from the viewpoints of environment and fuel efficiency, 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 a lithium ion secondary battery, particularly a lithium ion secondary battery using carbon powder as a conductive aid for the positive electrode active material, a sufficient capacity can be drawn out particularly at a high current density (for example, 10 mA / cm ² or more). One of the causes is that the internal resistance of the battery is not sufficiently reduced. As a countermeasure against this problem, a method of using an electrode containing fine metal powder as a conductive assistant (see, for example, Patent Document 1) or a method of controlling a conductive assistant (see, for example, Patent Document 2) is considered. It has been.
Japanese Patent Laid-Open No. 11-238527 JP 2004-207034 A

  However, the countermeasure considered in the lithium ion secondary battery according to the prior art is that the particle diameter of the positive electrode active material is sufficiently larger than the particle diameter of the conductive auxiliary agent (for example, active material 20 μm, conductive auxiliary agent 1 μm). It was assumed that the conductive auxiliary agent was dispersed in the gaps to form a good conductive network.

  In recent years, attempts have been made to reduce the particle diameter of the active material (for example, less than 1 μm) in order to increase the specific surface area of the active material. There was a problem that it was difficult to form. When an active material having a particle diameter of less than 1 μm is used, it is conceivable to reduce the particle size of the conductive auxiliary agent in proportion, but the conductive auxiliary agent uses carbon particles, and the particle size can be reduced. Since there is a limit (about 0.1 μm), the conductive network is not sufficiently formed, resulting in the generation of active material particles with insufficient electronic conduction, and the overall output is increased despite the increased surface area. The reason is that it does not come out.

  Accordingly, an object of the present invention is to provide means for forming a conductive network that can reliably supply electrons to minute active material particles in a battery electrode of a lithium ion secondary battery used under high current density conditions. To do.

  The present inventors have conducted intensive research to solve the above problems. At that time, in the active material layer of the electrode, an attempt was made to use not only the particulate conductive additive but also various shapes of conductive materials as the conductive material. As a result, it has been found that by using a conductive porous sheet as a conductive material, a conductive network capable of reliably supplying electrons to minute active material particles is formed, and the present invention has been completed.

  That is, the present invention provides a battery electrode having a current collector and an active material layer including an active material and a conductive material formed on a surface of the current collector, wherein the conductive material is a conductive material. A battery electrode characterized by being a structure having fine pores.

  In the active material layer of the battery electrode of the present invention, a conductive structure having fine holes is used as a conductive material. As a result, the active material particles are filled in the micropores of the conductive structure, and a conductive network that can reliably supply electrons to the minute active material particles can be formed, reducing the resistance during large current discharge. can do. Therefore, the electrode of the present invention can contribute to the improvement of the output characteristics of the battery.

  Hereinafter, embodiments of the present invention will be described. 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.

(First embodiment)
(Constitution)
The present invention provides a battery electrode having a current collector and an active material layer including an active material and a conductive material formed on a surface of the current collector, the conductive material comprising a conductive material. It is an electrode for batteries characterized by being an electroconductive structure which contains and has a fine hole.

  Hereinafter, the structure of the battery electrode of the present invention will be described with reference to the drawings. In the present invention, the drawings are exaggerated for convenience of explanation, and the technical scope of the present invention is not limited to the forms shown in the drawings. Also, embodiments other than the drawings may be employed.

  FIG. 1 is a schematic cross-sectional view showing one embodiment of a battery electrode of the present invention. The battery electrode 1 having the form shown in FIG. 1 is an electrode in which an active material layer 3 is formed on one surface of a current collector 2. As will be described later, the composition of the battery electrode is mainly an electrode active material, a conductive structure, and a binder.

  As shown in FIG. 1, the battery electrode 1 (hereinafter also simply referred to as “electrode”) 1 of the present invention includes an active material layer 3 in which an active material 4 and a binder (not shown) are connected to a conductive structure 5. It is characterized in that it fills the existing micropores.

  In the embodiment shown in FIG. 1, when the diameter of the active material is reduced due to the presence of the conductive structure 5 having fine pores, a conductive aid having a relatively large particle diameter as in the prior art was used. Compared to the case, a better conductive network can be formed.

  The battery electrode of the present invention can be employed in, for example, a bipolar lithium ion secondary battery (hereinafter also simply referred to as “bipolar battery”). Of course, it may be adopted for other batteries.

  Hereinafter, the configuration of the battery electrode of the present invention will be described by taking as an example a case where it is employed in a lithium ion secondary battery. The battery electrode of the present invention is characterized in that a conductive structure filled with an active material exists in the active material layer. There is no particular limitation on the selection of the current collector, active material, binder, supporting salt (lithium salt), ion-conducting polymer, and other compounds added as necessary. Depending on the intended use, it may be selected by appropriately referring to conventionally known knowledge. In addition, the battery electrode of the present invention can be applied to both the positive electrode and the negative electrode. However, when applied to the positive electrode particularly in consideration of the reaction surface, the negative electrode often uses a highly conductive material as an active material. Compared to the above, a more remarkable effect can be obtained. When applied to the positive electrode, a compound known to act as a current collector and positive electrode active material for the positive electrode may be employed as the current collector and active material.

[Current collector]
The current collector 2 is made of a conductive material such as an aluminum foil, a nickel foil, a copper foil, or a stainless steel (SUS) foil. The general thickness of the current collector is 1 to 30 μm. However, a current collector having a thickness outside this range may be used.

  The size of the current collector is determined according to the intended use of the battery. If a large electrode used for a large battery is manufactured, a current collector having a large area is used. If a small electrode is produced, a current collector with a small area is used.

[Active material layer]
An active material layer 3 is formed on the current collector 2. The active material layer 3 is a layer including an active material and a conductive material that play a central role in the charge / discharge reaction. When the electrode of the present invention is used as a positive electrode, the active material layer contains a positive electrode active material. On the other hand, when the electrode of the present invention is used as a negative electrode, the active material layer contains a negative electrode active material.

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

  As the negative electrode active material, the above lithium transition metal-composite oxide or carbon is preferable. Examples of carbon include graphite-based carbon materials such as natural graphite, artificial graphite, and expanded graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. In some cases, two or more negative electrode active materials may be used in combination.

  The average particle size of the active material is not particularly limited. However, the smaller the average particle diameter, the more easily the electron conduction path is divided. Therefore, the smaller the average particle diameter of the active material, the more the effects of the present invention can be exhibited. From such a viewpoint, the average particle diameter of the active material is preferably 20 μm or less, more preferably 10 μm or less, and particularly preferably 3 μm or less. However, forms outside these ranges can also be employed. In the present application, an average value measured by a laser diffraction scattering method is adopted as the average particle diameter of the active material.

  In the electrode of the present invention, the conductive material is a conductive structure including a conductive material and having fine holes.

  As the conductive material used for the conductive structure, a material mainly composed of a polymer material, a material mainly composed of a metal material, a material mainly composed of a carbon material, or the like can be used.

  When a material mainly composed of a polymer material is used as the conductive material, the polymer material includes polypyrrole, polyaniline, polythiophene, a network, a fiber, a foam, or these using a conductive polymer derived therefrom. Structures such as an assembly of When a material mainly composed of a polymer material is used, there is an advantage that it is lightweight and hardly reacts with an electrolyte or a salt. The polymer material is preferably contained in an amount of 30% by mass or more, more preferably 60% by mass or more based on the conductive material.

  In the case of using a material mainly composed of a metal material, examples of the metal material include structures such as foams and nanowhisker aggregates using various metals such as aluminum, gold, and silver. When a material mainly composed of a metal material is used, there is an advantage that high conductivity can be secured. The metal material is preferably contained in an amount of 40% by mass or more, more preferably 70% by mass or more based on the conductive material.

  When using a material mainly composed of a carbon material, as the carbon material, acetylene black, graphite, activated carbon, carbon nanotubes, or a network using a so-called heterocarbon in which some of these carbon atoms are substituted with other atoms, Various fine structures such as a fibrous shape and a fine flat plate shape are exemplified. When a material mainly composed of a carbon material is used, it is lighter than a metal and can have higher conductivity than a polymer. The carbon material is preferably contained in an amount of 30% by mass or more, more preferably 60% by mass or more based on the conductive material. In addition, the material which brings about conductivity is not limited to those listed here, and can be used.

  The conductive structure may be composed entirely of a conductive material, or may be composed of an inner base material and a surface conductive material. As the internal substrate, for example, a polymer material such as polypropylene can be used. For example, a composite structure in which a metal material such as aluminum providing conductivity is arranged on the surface by a method such as vapor deposition can be used, and a lightweight conductive material can be produced. These configurations are appropriately selected depending on the type of conductive material to be used, the type of surrounding material, the size of the battery, the manufacturing / use environment, and the like.

  These conductive structures can be formed in a sheet shape on the current collector, but can themselves serve as a current collector. Preferably, the conductive structure is formed on the current collector in the form of a sheet having a thickness of 5 to 200 μm, more preferably 10 to 50 μm.

  The conductive structure has fine pores that can be filled with active material particles. The average effective pore size of the fine pores can be determined according to the particle size of the active material, but is preferably 0.1 to 50 μm, more preferably 0.5 to 20 μm, and still more preferably 1 to 10 μm. Here, the “average effective pore diameter” means an average diameter when a sphere is assumed in a space in the three-dimensional network structure, and an average diameter in a structure in which fibers are bundled. The distance between the typical fibers is shown. In the present application, the average effective pore diameter of the conductive structure is measured by the following method. The structure is embedded in a resin, polished and observed with a microscope or the like, and the area of substantially spherical pores is measured by image analysis. Here, the number of pores to be measured is preferably as high as possible. However, in general, measurement may be performed for 300 or more pores. Since the pore area obtained here is a cross section in a plane passing through a part of the pore and is not the maximum value, the following three-dimensional correction is performed. The pore diameter distribution is obtained from the observed pore area, and the pore diameter occupying 50% of the total pore volume in the cumulative pore volume distribution is defined as the average pore diameter.

  The ratio A / B between the average effective pore diameter A of the conductive structure and the average particle diameter B of the active material is preferably 0.5 or more and 20 or less. Since both A and B are average values, even if A / B is a numerical value less than 1, the particles can be held in the conductive structure by forcibly pushing them in. However, if it is less than 0.5, even if the conductive structure is somewhat deformed, the active material particles are not easily held in the conductive structure, and if it exceeds 20, the active material is held in the space in the conductive structure. Makes it difficult to get enough contact. In addition, when A / B is less than 1, a preferable value varies depending on the type of material forming the conductive structure. That is, 0.9 or more, more preferably 0.95 or more is preferable for carbon materials or metal materials that are relatively difficult to deform, and 0.8 or more is more preferable for polymer materials that are easily deformed by applying pressure, for example. Is preferably 0.9 or more. A / B is more preferably 20 or less, and still more preferably 10 or less.

  The porosity of the conductive structure (ratio of the space in the total volume) is preferably 0.5 to 0.99, more preferably 0.7 to 0.95. When the porosity of the conductive structure is 0.99 or less, a conductive network in the active material layer can be formed. When the porosity of the conductive structure is 0.5 or more, a sufficient amount of active material can be supported, and high output characteristics can be obtained.

  The active material layer 3 may contain other materials if necessary. For example, a binder, a supporting salt (lithium salt), an ion conductive polymer, and the like can be included. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

  Examples of the binder include polyvinylidene fluoride (PVdF) and a synthetic rubber binder. By using the binder, the active material carried in the conductive structure can be fixed and stably held.

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

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers. Here, the polymer may be the same as or different from the ion conductive polymer used in the electrolyte layer of the battery in which the electrode of the present invention is employed, but is preferably the same.

  The polymerization initiator is added to act on the crosslinkable group of the ion conductive polymer to advance the crosslinking reaction. Depending on the external factor for acting as an initiator, it is classified into a photopolymerization initiator, a thermal polymerization initiator and the like. Examples of the polymerization initiator include azobisisobutyronitrile (AIBN), which is a thermal polymerization initiator, and benzyl dimethyl ketal (BDK), which is a photopolymerization initiator.

  The compounding ratio of the components contained in the active material layer 3 is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. Preferably, the compounding ratio of the binder is 5 to 20% by mass with respect to the amount of the active material.

(Production method)
The method for producing the battery electrode of the present invention is not particularly limited, and the electrode of the present invention can be produced by appropriately referring to conventionally known knowledge in the field of battery electrode production. Hereinafter, as shown in FIG. 1, a method for manufacturing an electrode 1 having a structure having fine holes made of a conductive material as a conductive material will be briefly described.

  The electrode 1 can be produced, for example, by preparing an active material slurry containing an active material, impregnating the active material slurry into a conductive structure, and coating the surface of the current collector. Hereinafter, such a manufacturing method will be described in detail in the order of steps.

  In this step, a desired positive electrode active material and other components (for example, a binder, a supporting salt (lithium salt), an ion conductive polymer, a polymerization initiator, etc.) are mixed in a solvent, if necessary. An active material slurry is prepared. The specific form of each component blended in the active material slurry is as described in the column of the configuration of the electrode of the present invention, and thus detailed description thereof is omitted here. In addition, it is natural that a positive electrode active material should be added to the slurry to produce the positive electrode, and a negative electrode active material should be added to the slurry to produce the negative electrode.

  The kind of solvent and the mixing means are not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. As an example of the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylformamide and the like can be used. When adopting polyvinylidene fluoride (PVdF) as a binder, NMP is preferably used as a solvent.

  Subsequently, a current collector 2 for forming the active material layer 3 is prepared. The specific form of the current collector prepared in this step is the same as that described in the column of the configuration of the electrode of the present invention, and a detailed description thereof will be omitted here.

  Subsequently, a conductive structure 5 for filling the active material 4 is prepared. Since the specific form of the conductive structure prepared in this step is as described in the column of the configuration of the electrode of the present invention, detailed description is omitted here. The method for preparing the sheet-like conductive structure is not particularly limited, and can be prepared by appropriately referring to conventionally known knowledge.

  Subsequently, by impregnating the conductive structure with the active material slurry prepared above, the active material can be retained in the conductive structure. The impregnation method is not particularly limited, but a method of mechanically pushing in addition to simple mixing may be employed. Examples of the mechanical pushing method include making the active material easily enter the space of the conductive structure by applying vibration, and pressing the active material into the space of the conductive structure by applying pressure with a press or the like. There is a way. Alternatively, a method may be used in which the conductive structure is expanded by changing the temperature so that the active material easily enters the space of the conductive structure. When pushing in applying pressure, Preferably it pressurizes at 0.2-20 Mpa using a roll press etc.

  The filling rate of the micropores of the conductive structure can be estimated using a method such as measuring the weight before and after filling. A higher filling factor can be obtained by mechanically pushing the active material. The higher the filling rate of the active material, the better. However, it is substantially preferably 50% by mass or more, more preferably 70% by mass or more.

  The conductive structure impregnated with the active material is applied to the surface of the current collector 2 prepared above to form a coating film. Thereafter, a drying process is performed. Thereby, the solvent in a coating film is removed and the coating film which should become an active material layer is formed. The thickness of the coating film to be formed is not particularly limited, but is usually about 5 to 200 μm.

  The application means for applying the conductive structure impregnated with the active material is not particularly limited. Commonly used means such as adhesion or pressure bonding can be employed. For example, it can be bonded using a battery binder or the like as an adhesive.

(Second Embodiment)
In 2nd Embodiment, a battery is comprised using the battery electrode of said 1st Embodiment.

  That is, the second embodiment of the present invention is a lithium ion secondary battery having at least one single battery layer in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order, and at least one of the positive electrode and the negative electrode Is a battery which is an electrode of the present invention. The electrode of the present invention can be applied to any of a positive electrode, a negative electrode, and a bipolar electrode. A battery including the electrode of the present invention as at least one electrode belongs to the technical scope of the present invention. However, preferably, all of the electrodes constituting the battery are the electrodes of the present invention. By adopting such a configuration, the durability of the battery can be effectively improved.

  The battery of the present invention may be a bipolar lithium ion secondary battery (hereinafter also referred to as “bipolar battery”). FIG. 2 is a cross-sectional view showing a battery of the present invention which is a bipolar battery. Hereinafter, the bipolar battery shown in FIG. 2 will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  The bipolar battery 10 of this embodiment shown in FIG. 2 has a structure in which a substantially rectangular battery element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior.

  As shown in FIG. 2, the battery element 21 of the bipolar battery 10 of this embodiment includes a plurality of bipolar electrodes in which a positive electrode active material layer 13 and a negative electrode active material layer 15 are formed on each surface of a current collector 11. Have one. Each bipolar electrode is laminated via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar electrode and electrolyte layer are arranged such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. 17 are stacked.

  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 battery 10 has a configuration in which the single battery layers 19 are stacked. In addition, an insulating layer 31 for insulating adjacent current collectors 11 is provided on the outer periphery of the unit cell layer 19. The current collector (outermost layer current collector) (11a, 11b) located in the outermost layer of the battery element 21 has a positive electrode active material layer 13 (positive electrode side outermost layer current collector 11a) or a negative electrode only on one side. One of the active material layers 15 (negative electrode side outermost layer current collector 11b) is formed.

  Further, in the bipolar battery 10 shown in FIG. 2, the positive electrode side outermost layer current collector 11a is extended to form a positive electrode tab 25, which is led out from a laminate sheet 29 which is an exterior. On the other hand, the negative electrode side outermost layer current collector 11 b is extended to form a negative electrode tab 27, which is similarly derived from the laminate sheet 29.

  Hereinafter, members constituting the bipolar battery 10 of the present embodiment will be briefly described. However, since the components constituting the electrode are as described above, the description thereof is omitted here. Further, the technical scope of the present invention is not limited to the following forms, and conventionally known forms can be similarly adopted.

[Electrolyte layer]
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

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

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

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  In the case where the electrolyte layer 17 is composed of a liquid electrolyte or a gel electrolyte, a separator may be used for the electrolyte layer 17. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer 17 is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

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

[Insulation layer]
In the bipolar battery 10, an insulating layer 31 is usually provided around each unit cell layer 19. This insulating layer 31 is provided for the purpose of preventing the adjacent current collectors 11 in the battery from contacting each other and the occurrence of a short circuit due to a slight unevenness at the end of the unit cell layer 19 in the battery element 21. It is done. The installation of such an insulating layer 31 ensures long-term reliability and safety, and can provide a high-quality bipolar battery 10.

  The insulating layer 31 only needs to have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance under battery operating temperature, etc. Urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Of these, urethane resins and epoxy resins are preferred from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming properties), economy, and the like.

[tab]
In the bipolar battery 10, a tab (positive electrode tab 25 and negative electrode tab 27) electrically connected to the outermost current collector (11a, 11b) is used for taking out current to the outside of the battery. Take out to the outside. Specifically, the positive electrode tab 25 electrically connected to the positive electrode outermost layer current collector 11a and the negative electrode tab 27 electrically connected to the negative electrode outermost layer current collector 11b are formed on the laminate sheet 29. Take out to the outside.

  The material of the tabs (the positive electrode tab 25 and the negative electrode tab 27) is not particularly limited, and a known material conventionally used as a tab for a bipolar battery can be used. Examples thereof include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. Note that the same material may be used for the positive electrode tab 25 and the negative electrode tab 27, or different materials may be used. As in the present embodiment, the outermost layer current collectors (11a, 11b) may be extended to form tabs (25, 27), or a separately prepared tab may be connected to the outermost layer current collector. Good.

[Exterior]
In the bipolar battery 10, the battery element 21 is preferably housed in an exterior such as a laminate sheet 29 in order to prevent external impact and environmental degradation during use. The exterior is not particularly limited, and a conventionally known exterior can be used. A polymer-metal composite laminate sheet or the like excellent in thermal conductivity can be preferably used in that heat can be efficiently transferred from a heat source of an automobile and the inside of the battery can be rapidly heated to the battery operating temperature.

  According to the bipolar battery 10 of the present embodiment, a bipolar electrode in which the electrode of the present invention is formed on both surfaces of the current collector 11 is employed. For this reason, the bipolar battery of this embodiment is excellent in output characteristics.

  Here, the operational effects of the present invention as described above can be particularly remarkably exhibited in a secondary battery used under high output conditions. Therefore, the secondary battery of the present invention is preferably used under high output conditions. Specifically, the secondary battery of the present invention is used under conditions that require an output of preferably 20 C or higher, more preferably 50 C or higher, and even more preferably 100 C or higher.

(Third embodiment)
In the third embodiment, a plurality of the bipolar batteries of the second embodiment are connected in parallel and / or in series to constitute an assembled battery.

  FIG. 3 is a perspective view showing the assembled battery of the present embodiment.

  As shown in FIG. 3, the assembled battery 40 is configured by connecting a plurality of the bipolar batteries of the second embodiment. Specifically, each bipolar battery 10 is connected by connecting the positive electrode tab 25 and the negative electrode tab 27 of each bipolar battery 10 using a bus bar. On one side surface of the assembled battery 40, electrode terminals (42, 43) are provided as electrodes of the entire assembled battery 40.

  The connection method when connecting the plurality of bipolar batteries 10 constituting the assembled battery 40 is not particularly limited, and a conventionally known method can be appropriately employed. For example, a technique using welding such as ultrasonic welding or spot welding, or a technique of fixing using rivets, caulking, or the like can be employed. According to such a connection method, the long-term reliability of the assembled battery 40 can be improved.

  According to the assembled battery 40 of the present embodiment, each bipolar battery 10 constituting the assembled battery 40 is excellent in output characteristics, and therefore, an assembled battery excellent in output characteristics can be provided.

  The connection of the bipolar batteries 10 constituting the assembled battery 40 may be all connected in parallel, all may be connected in series, or a combination of series connection and parallel connection may be used. Also good.

(Fourth embodiment)
In the fourth embodiment, the bipolar battery 10 of the second embodiment or the assembled battery 40 of the third embodiment is mounted as a motor driving power source to constitute a transportation system. As a transportation system using the bipolar battery 10 or the assembled battery 40 as a power source for a motor, for example, a complete electric vehicle not using gasoline, a hybrid vehicle such as a series hybrid vehicle or a parallel hybrid vehicle, and a fuel cell vehicle, a wheel motor is used. Vehicles such as automobiles driven by

  For reference, FIG. 4 shows a schematic diagram of an automobile 50 on which the assembled battery 40 is mounted. The assembled battery 40 mounted on the automobile 50 has the characteristics as described above. For this reason, the automobile 50 equipped with the assembled battery 40 has excellent output characteristics and can provide sufficient output even after being used for a long period of time.

  As described above, some preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications, omissions, and additions can be made by those skilled in the art. . For example, in the above description, a bipolar lithium ion secondary battery (bipolar battery) has been described as an example. However, the technical scope of the battery of the present invention is not limited to a bipolar battery. A non-type lithium ion secondary battery may be used. For reference, FIG. 5 is a cross-sectional view showing an outline of a lithium ion secondary battery 60 that is not bipolar. In the lithium ion secondary battery 60 shown in FIG. 5, the negative electrode active material layer 15 is slightly smaller than the positive electrode active material layer 13, but is not limited to such a form. A negative electrode active material layer 15 that is the same as or slightly larger than the positive electrode active material layer 13 may also be used.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited to only the forms shown in the following examples.

<Example 1>
<Preparation of positive electrode>
As a positive electrode active material, spinel type lithium manganate (LiMn ₂ O ₄ ) having an average particle size of 10 μm was pulverized by wet pulverization until the average particle size became 0.2 μm. This spinel type lithium manganate (80 parts by mass) and polyvinylidene fluoride (PVdF) (10 parts by mass) as a binder are mixed and then dispersed in N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent. Thus, a positive electrode active material slurry was prepared.

  On the other hand, an aluminum foil (thickness: 20 μm) was prepared as a positive electrode current collector. The positive electrode active material slurry prepared above was impregnated into a polypyrrole porous membrane (average effective pore diameter of 0.5 μm), which is a conductive structure, and then superimposed on one surface of the prepared current collector and pressurized at 5 MPa. By drying, a positive electrode having an active material layer with a thickness of 30 μm was formed.

<Production of negative electrode>
Graphite (average particle size: 0.5 μm) (90 parts by mass) as a negative electrode active material and polyvinylidene fluoride (PVdF) (10 parts by mass) as a binder are mixed, and then N-methyl as a slurry viscosity adjusting solvent. A negative electrode active material slurry was prepared by dispersing in 2-pyrrolidone (NMP).

  On the other hand, a copper foil (thickness: 20 μm) was prepared as a current collector for the negative electrode. The negative electrode active material slurry prepared above was applied to one surface of the prepared current collector, pressurized at 5 MPa, and dried to form a negative electrode having an active material layer with a thickness of 25 μm.

<Example 2>
A test cell was produced in the same manner as in Example 1 except that carbon fibers (average effective pore diameter of 0.5 μm) were used as the conductive structure. The thickness of the positive electrode active material layer was 30 μm.

<Example 3>
Except that an aggregate (average effective pore diameter of 1 μm) in which carbon nanofibers are fixed with an epoxy resin, which is a thermosetting resin, was used as the conductive structure, the test was performed in the same manner as in Example 1 above. A cell was produced. The thickness of the positive electrode active material layer was 30 μm.

<Example 4>
Example 1 except that an alumina whisker aggregate (average effective pore size 0.5 μm) was used as the conductive structure, impregnated with the positive electrode active material slurry, and press-molded at 5 MPa on a flat surface. A test cell was produced in the same manner as described above. The thickness of the positive electrode active material layer was 30 μm.

<Example 5>
A test cell was produced in the same manner as in Example 4 except that 20 parts by mass of polyvinylidene fluoride (PVdF) was used as the binder. The thickness of the positive electrode active material layer was 30 μm.

<Comparative Example 1>
As the positive electrode active material, spinel type lithium manganate (LiMn ₂ O ₄ ) having an average particle size of 10 μm was pulverized by wet pulverization until the average particle size became 0.2 μm. Mixing this spinel type lithium manganate (80 parts by mass), acetylene black (average particle size 0.4 μm) (10 parts by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) (10 parts by mass) as a binder Then, it is dispersed in N-methyl-2-pyrrolidone (NMP) which is a slurry viscosity adjusting solvent to prepare a positive electrode active material slurry, and the positive electrode active material slurry is applied to one surface of a current collector and dried. Each electrode was produced in the same manner as in Example 1 except that the positive electrode was produced. The thickness of the positive electrode active material layer was 30 μm.

<Comparative example 2>
A test cell was produced in the same manner as in Comparative Example 1 except that 70 parts by mass of spinel type lithium manganate and 20 parts by mass of polyvinylidene fluoride (PVdF) were used as a binder. The thickness of the positive electrode active material layer was 30 μm.

<Production of test cell>
In order to use as a positive electrode and a negative electrode of a test cell, the positive electrode and the negative electrode prepared in each of the above examples and comparative examples were punched into 68 mm square and 70 mm square using punches, respectively.

Furthermore, a polypropylene microporous film (thickness: 25 μm) was prepared as a separator. Further, as an electrolytic solution was prepared that the LiPF ₆ is equal volume mixture of lithium salt of ethylene carbonate (EC) and diethyl carbonate (DEC) was dissolved in a concentration of 1M.

  The negative electrode, separator, and positive electrode obtained above were laminated in this order, and the electrolyte was injected into the separator. Next, a current extraction terminal (aluminum terminal for the positive electrode and a nickel terminal for the negative electrode) is connected to the negative electrode and the positive electrode, respectively, and the battery element is placed in an aluminum laminate film so that the current extraction terminal is exposed to the outside. The opening of the laminate film was sealed under reduced pressure to produce a test cell.

<Evaluation of battery characteristics of test cell>
Test cells were prepared for each of the above Examples and Comparative Examples, and initial charging and degassing were performed. Each test cell was charged with a constant current (CC) to 2.7 V, and then charged with a constant voltage (CV) for a total of 15 hours. Next, the laminate was opened and degassed at room temperature. Degassing was performed by placing the battery on a flat plate in a container and placing a weight on the upper surface to decompress the inside of the container.

  Thereafter, the produced test cell was discharged for 5 seconds from full charge with a 50 CA current value calculated from the active material theoretical capacity, and a resistance value was calculated from the potential and current value after 5 seconds, and used as an output index. . Table 1 below shows the specific output of the test cell produced in each example when the comparative example is 1.

  From the comparison between each example and the comparative example, in the active material layer of the electrode, by using a conductive structure having fine pores as the conductive material, even when the particle size of the active material is small, good conductivity of the active material layer is obtained. It can be seen that the output of the battery can be improved. In particular, in Example 4, since the conductive structure is made of aluminum having very high conductivity, it is considered that the output is greatly improved and the surface of the fine active material particles is effectively used. Furthermore, from the comparison between Example 5 and Comparative Example 1, the electrode of the present invention has an active material holding function in the porous structure itself, so that the amount of the binder can be reduced as compared with the conventional electrode. I understand.

  As described above, the electrode of the present invention enables the formation of a good conductive network between a conductive material and an active material, which has conventionally been difficult when an active material having a small particle diameter is used, and as a result, the output of the battery It can contribute effectively to the improvement of characteristics.

It is a schematic sectional drawing which shows one Embodiment (1st Embodiment) of the battery electrode of this invention. It is sectional drawing which shows preferable one Embodiment of the bipolar battery of 2nd Embodiment. It is a perspective view which shows the assembled battery of 3rd Embodiment. It is the schematic of the motor vehicle of 4th Embodiment carrying the assembled battery of 3rd Embodiment. It is sectional drawing which shows the outline | summary of the lithium ion secondary battery which is not a bipolar type.

Explanation of symbols

1 electrode,
2 current collector,
3 active material layer,
4 active materials,
5 conductive structure,
10 Bipolar battery,
11 Current collector,
11a, 11b outermost layer current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 battery elements,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet,
31 insulating layer,
33 positive electrode current collector,
35 negative electrode current collector,
40 battery packs,
42, 43 electrode terminals,
50 cars,
60 Lithium ion secondary battery that is not bipolar.

Claims (11)

A battery electrode comprising: a current collector; and an active material layer including an active material and a conductive material formed on a surface of the current collector,
The electrode for a battery, wherein the conductive material is a conductive structure including a conductive material and having fine holes.   The battery electrode according to claim 1, wherein the entire conductive structure is made of a conductive material.   The battery electrode according to claim 1, wherein the conductive structure includes an inner base material and a surface conductive material.   The battery electrode according to claim 1, wherein the conductive material is a material mainly composed of a polymer material.   The battery electrode according to claim 1, wherein the conductive material is a material mainly composed of a metal material.   The battery electrode according to any one of claims 1 to 3, wherein the conductive material is a material mainly composed of a carbon material.   The battery electrode according to any one of claims 1 to 6, wherein a ratio between an average effective pore size of the conductive structure and an average particle size of the active material is 0.5 or more and 20 or less.   The manufacturing method of the battery electrode of any one of Claims 1-7 including pushing the particle | grains of an active material into the micropore of the said electroconductive structure mechanically. A lithium ion secondary battery having at least one single cell layer in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order,
The lithium ion secondary battery whose at least one of the said positive electrode or the said negative electrode is the electrode for batteries of any one of Claims 1-7.   An assembled battery using the lithium ion secondary battery according to claim 9.   A vehicle equipped with the lithium ion secondary battery according to claim 10 or the assembled battery according to claim 10.

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