JP5315595B2 - Battery electrode and manufacturing method thereof - Google Patents

Description

  The present invention relates to a battery electrode and a method for producing the same. In particular, the present invention relates to an improvement for improving the output characteristics of a battery.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, a lithium ion secondary battery having the highest theoretical energy among all the batteries is attracting attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

  The lithium ion secondary battery used as a motor drive power source for automobiles as described above has extremely high output characteristics as compared with consumer lithium ion secondary batteries used in mobile phones, laptop computers, etc. The current situation is that research and development is underway to meet such demands.

Here, as a technique for improving the output characteristics of a lithium ion secondary battery in consideration of mounting in an automobile, for example, a positive electrode active material for a lithium secondary battery containing a Li—Mn—Ni composite oxide, A positive electrode for a lithium secondary battery, wherein an average diameter of primary particles of Li—Mn—Ni composite oxide is 2.0 μm or less and a BET specific surface area is 0.4 m ² / g or more. An active material is disclosed (see Patent Document 1).
JP 2003-68299 A

  According to the technique described in Patent Document 1, a lithium ion secondary battery having excellent discharge capacity characteristics and cycle durability can be provided. This is because, when the average diameter and specific surface area of the Li—Mn—Ni composite oxide, which is the positive electrode active material, are controlled to the above values, the surface area of the positive electrode active material that can come into contact with the electrolytic solution increases. This is probably because the reaction can proceed sufficiently.

  Thus, it is preferable to reduce the particle size of the active material contained in the active material layer of the electrode from the viewpoint of increasing the output of the battery. However, in order to efficiently build a conductive network that contributes to higher output, an excessive amount of conductive auxiliary agent or binder is required, which increases the volume of the electrode and decreases the capacity per volume. was there.

  Therefore, the present invention provides a means capable of improving output characteristics in a lithium ion secondary battery while minimizing a decrease in capacity per volume due to an increase in the use amount of a conductive additive or a binder. Objective.

  As a result of accumulating intensive studies in view of the above problems, the present inventors can reduce the volume of the electrode by using a high molecular weight polymer material as the binder in the active material layer, and the output per electrode volume. It has been found that can be increased.

That is, the present invention provides an active material layer including a current collector and a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ disposed on the surface of the current collector. A battery electrode and a method for manufacturing the same.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for batteries which can improve an output characteristic, and its manufacturing method can be provided, suppressing the fall of the capacity | capacitance per volume accompanying the increase in the usage-amount of a conductive support agent or a binder.

  Embodiments of the present invention will be described below.

(First embodiment)
(Constitution)
The first of the present invention is a current collector and an active material including a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ disposed on the surface of the current collector. A battery electrode and a method for manufacturing the same.

  First, 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 cross-sectional view showing one embodiment of a unit cell using the battery electrode of the present invention. As shown in FIG. 1, the cell 1 includes a positive electrode in which a positive electrode active material layer 13 is formed on a current collector 11, and a negative electrode in which a negative electrode active material layer 15 is formed on another current collector 11. Are stacked with the electrolyte layer 17 interposed therebetween.

The present invention is characterized in that the active material layer includes a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ . According to such a form, without adding an excessive amount of binder, the binder can hold the active material having a small particle diameter and, if necessary, the conductive assistant. As a result, the volume of the electrode can be reduced, and the capacity per volume of the battery can be increased.

Hereinafter, an embodiment of a battery configuration using the battery electrode of the present invention will be described with reference to FIG. The electrode of this embodiment includes a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ in the active material layers of both the positive electrode and the negative electrode. What is the technical scope of the present invention? It is not restricted only to such a form, The form in which any one of a positive electrode or a negative electrode contains the binder mentioned above can also be included. There are no particular restrictions on the selection of the current collector, active material, type of conductive additive, supporting salt (lithium salt), electrolyte, and other compounds added as necessary. Depending on the intended use, it may be selected by appropriately referring to conventionally known knowledge. Hereinafter, members constituting the battery electrode of the present invention will be described in detail.

[Current collector]
The current collector 11 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 (13, 15) is formed on the current collector 11. The active material layers (13, 15) are layers containing an active material that plays a central role in the charge / discharge reaction. In the present invention, either one or both of the positive electrode active material layer 13 and the negative electrode active material layer 15 includes a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ . 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.

  Examples of the positive electrode active material include lithium-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-iron composite oxide, lithium-nickel-cobalt composite oxide, and lithium-manganese-cobalt. Examples include composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-manganese-cobalt composite oxides, lithium-metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination.

  Examples of the negative electrode active material include carbon materials such as graphite and amorphous carbon, lithium-transition metal compounds, metal materials, and lithium alloys such as lithium aluminum alloys, lithium tin alloys, and lithium silicon alloys. . In some cases, two or more negative electrode active materials may be used in combination.

  In the unit cell of the lithium ion secondary battery of the present embodiment, the average particle diameter of the positive electrode active material contained in the positive electrode active material layer 13 is not particularly limited, but is preferably 10 μm or less from the viewpoint of high output. The average particle size is more preferably 5 μm or less, further preferably 3 μm or less, and most preferably 1 μm or less. In addition, from the viewpoint of obtaining the effects of the present invention, the lower limit value of the average particle diameter of the positive electrode active material is not particularly limited, but from the viewpoint of high output of the unit cell, high dispersibility of the positive electrode active material, and aggregation prevention. The average particle size of the positive electrode active material is preferably 0.01 μm or more, more preferably 0.1 μm or more.

  On the other hand, in the unit cell of the lithium ion secondary battery of the present embodiment, the average particle size of the negative electrode active material contained in the negative electrode active material layer 15 is not particularly limited, but is preferably 10 μm or less from the viewpoint of high output. . The average particle size is more preferably 5 μm or less, further preferably 3 μm or less, and most preferably 1 μm or less. From the viewpoint of obtaining the effects of the present invention, the lower limit value of the average particle diameter of the negative electrode active material is not particularly limited, but from the viewpoint of high output of the unit cell, high dispersibility of the negative electrode active material, and aggregation prevention. The average particle size of the negative electrode active material is preferably 0.01 μm or more, more preferably 0.1 μm or more. Here, in this application, D50 value measured by the laser diffraction method shall be adopted as a value of a particle size of an active material.

The active material layers (13, 15) include a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ . Specific examples of the binder include polyethylene, polypropylene, polyethylene terephthalate, polyacrylonitrile, aromatic polyamide, cellulose, carboxymethyl cellulose, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene rubber, isoprene rubber, butadiene. High thermoplasticity of rubber, ethylene-propylene rubber, ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer, its hydrogenated product, styrene-isoprene-styrene block copolymer, its hydrogenated product, etc. Molecule, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-butylene glycol, polyvinyl alcohol, polyvinyl propinal, polyvinyl butyler , Hydroxyl group-containing compounds such as polyacrylamide, polyethylene glycol, polypropylene glycol, polybutylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetra Fluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyfluorinated Fluorine resin such as vinyl (PVF), vinylidene fluoride-hexafluoropropylene-based fluoro rubber (VDF-HFP-based fluoro rubber), vinylidene fluoride-he Safluoropropylene-tetrafluoroethylene fluorine rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoro Ethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene Examples thereof include polymer materials such as vinylidene fluoride type fluororubber such as fluororubber (VDF-CTFE type fluororubber). These binders may be used alone or in combination of two or more. In particular, from the viewpoint of chemical resistance to the electrolytic solution and resistance to potential in the battery, cellulose, carboxymethyl cellulose, polyacrylonitrile, polyvinyl chloride, styrene-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, PVdF Fluorine rubber is more preferable, and PVdF is most preferable.

  Although there is no restriction | limiting in particular about the shape of the said binder, A fibrous form, a lump form, or a particulate form is used preferably.

The binder has a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ . If the viscosity average molecular weight is less than 1.0 × 10 ⁵ , an excessive amount of binder may be required and the volume of the electrode may increase, and if it exceeds 1.0 × 10 ⁸ , in the active material slurry preparation step described later. The binder is not preferable because it becomes difficult to dissolve in the solvent of the active material slurry and the distribution of the binder in the active material layer formed in the subsequent process may become non-uniform. In addition, in this application, the value obtained by the measuring method of the Example mentioned later shall be employ | adopted for the said viscosity average molecular weight.

  For example, when the binder is fibrous, the average fiber diameter measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is preferably smaller than the average particle diameter of the active material. When the binder is in the form of a lump or particles, it is preferable that the average particle diameter measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is smaller than the average particle diameter of the active material. The reason for this is considered to be that the binder enters a shape between the particles of the active material, and the distribution of the binder in the active material layer tends to be more uniform.

  The active material layers (13, 15) may contain other materials if necessary. For example, a conductive aid, 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.

  A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive aid include carbon black such as acetylene black, carbon powder such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark).

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

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers. 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 layers (13, 15) is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery.

  The thickness of the active material layers (13, 15) is not particularly limited, and conventionally known knowledge about the lithium ion secondary battery can be appropriately referred to. As an example, the thickness of the active material layers (13, 15) is preferably about 10 to 100 μm, and more preferably 20 to 50 μm. When the active material layers (13, 15) are about 10 μm or more, the battery capacity can be sufficiently secured. On the other hand, when the active material layers (13, 15) are about 100 μm or less, it is possible to suppress the occurrence of the problem of an increase in internal resistance due to the difficulty in diffusing lithium ions in the electrode deep part (current collector side).

(Production method)
Then, the manufacturing method of the battery electrode of this invention is demonstrated.

  First, a method for manufacturing the battery electrode 1 having the configuration shown in FIG. 1 will be described.

  In the electrode of the present invention, for example, an active material and a predetermined binder are added to a solvent to prepare an active material slurry (active material slurry preparation step), and this active material slurry is applied to the surface of the current collector. And it can manufacture by forming a coating film by drying (coating film formation process), and pressing the laminated body produced through the said coating film formation process in the lamination direction (pressing process). When an ion conductive polymer is added to the active material slurry and a polymerization initiator is further added for the purpose of crosslinking the ion conductive polymer, it is simultaneously with drying in the coating film forming process, or before or after the drying. A polymerization treatment may be performed (polymerization step).

  Hereinafter, although such a manufacturing method is demonstrated in detail in order of a process, it is not restrict | limited only to the following form.

[Active material slurry preparation process]
In this step, a desired active material, a predetermined binder, and other components (for example, a conductive assistant, an ion conductive polymer, a supporting salt (lithium salt), a polymerization initiator, etc.) in a solvent To prepare an active material slurry. Since 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, detailed description is omitted here.

  The type of the solvent is not particularly limited, and conventionally known knowledge about electrode production can be referred to as appropriate. 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.

  The mixing method is not particularly limited, but (1) A method in which a dry mixture of the active material and the binder is put into a solvent and kneaded and dispersed; (2) The binder is dissolved in the active material. (3) A method in which the active material and the first binder are previously dry-mixed, and are added to a solution in which the second binder is dissolved, and kneaded and dispersed; 4) A method in which the active material is charged into a wet pulverizer filled with a solution in which the binder is dissolved, and the active material is pulverized and dispersed. In the coating film to be formed, the distribution of the active material and the binder tends to be uniform, which is preferable.

  When the active material layer contains a conductive additive, the active material slurry contains a conductive agent. As a mixing method at that time, (5) dry mixing the active material, the binder, and the conductive aid in advance. (6) A mixture obtained by previously dry-mixing the active material and the conductive additive is put into a solution in which the binder is dissolved, and kneaded and dispersed. (7) A method in which the active material and the conductive additive are separately added to a solution in which the binder is dissolved and dispersed; (8) the active material, the first binder, and the conductive material A method in which a mixture obtained by dry-mixing an auxiliary agent in advance is put into a solution in which a second binder is dissolved, and kneaded and dispersed; (9) The active material and the conductive auxiliary agent are dissolved in the binder. Have In a coating film obtained in the coating film forming step described below, the active material is charged into a wet pulverizing apparatus filled with a liquid, and a method of pulverizing and dispersing the active material and the conductive auxiliary agent; It is preferable because the distribution of the conductive assistant and the binder tends to be uniform.

  The dry mixing apparatus used in the above-described methods (1), (3), (5), (6), and (8) is not particularly limited, but a mechanofusion (registered trademark; manufactured by Hosokawa Micron Corporation) system, etc. Use of the fine particle composite device is preferable because the active material and the binder are combined and the distribution of the active material and the binder in the active material layer tends to be uniform.

Further, the first binder and the second binder used in the methods (3) and (8) described above are the same in either or both of the type of polymer material used and the viscosity average molecular weight. Or different. Further, each of the first binder and the second binder may be a mixture of two or more polymer materials. In a preferred form in the above methods (3) and (8), the viscosity average molecular weight of the first binder is preferably 1.0 × 10 ^{5 to} 5.0 × 10 ⁶ . The viscosity average molecular weight is preferably 5.0 × 10 ^{6 to} 1.0 × 10 ⁸ .

[Coating film forming process]
Subsequently, a current collector is prepared, and the active material slurry prepared above is applied to the surface of the current collector and dried. Thereby, the coating film which consists of an active material slurry is formed on the surface of an electrical power collector. This coating film becomes an active material layer through a pressing step described later.

  The specific form of the current collector to be prepared is as described in the column of the configuration of the electrode of the present invention, and thus detailed description thereof is omitted here.

  The application means for applying the active material slurry is not particularly limited, but generally used means such as a self-propelled coater may be employed.

  A coating film is formed according to the desired arrangement | positioning form of the electrical power collector and active material layer in the electrode manufactured. For example, when the manufactured electrode is a bipolar electrode, a coating film containing a positive electrode active material is formed on one surface of the current collector, and a coating film containing a negative electrode active material is formed on the other surface. On the other hand, when an electrode that is not a bipolar type is manufactured, a coating film containing either a positive electrode active material or a negative electrode active material is formed on both surfaces of one current collector.

  Thereafter, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed.

  The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the application amount of the active material slurry and the volatilization rate of the solvent of the slurry.

  When a coating film contains a polymerization initiator, the ion conductive polymer in a coating film is bridge | crosslinked by a crosslinkable group by performing a superposition | polymerization process further.

  The polymerization treatment in the polymerization step is not particularly limited, and conventionally known knowledge may be referred to as appropriate. For example, when the coating film contains a thermal polymerization initiator (AIBN or the like), the coating film is subjected to heat treatment. Moreover, when a coating film contains a photoinitiator (BDK etc.), light, such as an ultraviolet light, is irradiated. In addition, the heat processing for thermal polymerization may be performed simultaneously with said drying process, and may be performed before or after the said drying process.

[Pressing process]
Then, the laminated body produced through the said coating-film formation process is pressed to the lamination direction. Thereby, the battery electrode of the present invention is completed. At this time, the porosity of the active material layer can be controlled by adjusting the pressing conditions.

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

(Second Embodiment)
In 2nd Embodiment, a lithium ion secondary battery is comprised using said battery electrode of 1st Embodiment. That is, a second aspect of the present invention is a lithium ion secondary battery including at least one single cell 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 or the negative electrode is a main battery layer. It is a lithium ion secondary battery which is the battery electrode of the invention. The electrode of the present invention can be applied to any of a positive electrode, a negative electrode, and a bipolar electrode. A lithium ion secondary 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 lithium ion secondary battery are the electrodes of the present invention. By adopting such a configuration, the output characteristics of the lithium ion secondary 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 lithium ion secondary battery according to an embodiment 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 bipolar electrode (a positive electrode active material layer 13 and a negative electrode active material layer 15 formed on each surface of a current collector 11 ( (Not shown). Each bipolar electrode is stacked 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 outermost layer current collector 11 a is extended to form a positive electrode tab 25, which is led out from a laminate sheet 29 that 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 single battery layer 19. The insulating layer 31 is provided for the purpose of preventing the adjacent current collectors 11 in the battery from contacting each other and short-circuiting due to a slight unevenness at the end of the battery 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, the tabs (the positive electrode tab 25 and the negative electrode tab 27) electrically connected to the outermost current collector (11 a, 11 b) are taken out of the exterior for the purpose of taking out the current outside the battery. . Specifically, a positive electrode tab 25 electrically connected to the positive electrode outermost layer current collector 11a and a negative electrode tab 27 electrically connected to the negative electrode outermost layer current collector 11b are provided outside the exterior. It is taken out.

  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.

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

  A connection method in particular when connecting the some bipolar battery 10 which comprises the assembled battery 40 is not restrict | limited, A conventionally well-known method can be employ | adopted suitably. 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 this embodiment, since each bipolar battery 10 constituting the assembled battery 40 is excellent in output characteristics, an assembled battery excellent in output characteristics can be provided.

  The bipolar batteries 10 constituting the assembled battery 40 may be connected in parallel to each other, or may be connected in series, or a combination of series connection and parallel connection. May be.

(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 vehicle. As a vehicle using the bipolar battery 10 or the assembled battery 40 as a motor power source, 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. A car 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 is excellent in output characteristics.

  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-described second embodiment, 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. For example, it may be a lithium ion secondary battery that is not a bipolar type. For reference, FIG. 5 is a cross-sectional view showing an outline of a lithium ion secondary battery 60 that is not a bipolar type.

  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 only to the following examples.

<Example 1>
<Preparation of positive electrode>
Lithium manganese composite oxide (average particle size: 1 μm) (86% by mass) as a positive electrode active material, carbon black (7% by mass) as a conductive additive, and a viscosity average molecular weight of 3.0 × 10 ⁶ as a binder Polyvinylidene fluoride (PVdF) (4.9% by mass) and PVdF (2.1% by mass) having a viscosity average molecular weight of 7.0 × 10 ⁷ were prepared.

  The viscosity average molecular weight was measured under the following conditions.

First, lithium manganese composite oxide, carbon black, and PVdF having a viscosity average molecular weight of 3.0 × 10 ⁶ are charged into a Mechano-Fusion (registered trademark; manufactured by Hosokawa Micron Corporation) system and loaded with 5 kW load power for 10 minutes. The composite was composed of three components of lithium manganese composite oxide, carbon black, and PVdF.

Next, after adding anhydrous NMP having a purity of 99.9% to the dispersing mixer, PVdF having a viscosity average molecular weight of 7.0 × 10 ⁷ was introduced and sufficiently dissolved in NMP.

  The composite obtained above was added little by little to this PVdF solution, and after being well adapted to NMP, NMP was further added to adjust the viscosity to obtain a positive electrode active material slurry.

  The obtained positive electrode active material slurry was applied on an aluminum foil (thickness: 20 μm) as a positive electrode current collector by a doctor blade method and dried on a hot stirrer to form a positive electrode active material layer. Next, the laminate was pressed using a roll press so that the thickness of the formed positive electrode active material layer was 40 μm.

  As a result of visual observation, the dispersibility of the solid component of the obtained positive electrode active material layer and the adhesion between the positive electrode active material layer and the current collector were good.

  An output terminal was connected to the current collector to produce a test positive electrode.

<Production of negative electrode>
N− which is a slurry viscosity adjusting solvent with respect to a solid content of hard carbon (average particle size: 10 μm) (90% by mass) as a negative electrode active material and polyvinylidene fluoride (PVdF) (10% by mass) as a binder. An appropriate amount of methyl-2-pyrrolidone (NMP) was added to prepare a negative electrode active material slurry.

  The negative electrode active material slurry prepared above was applied onto a copper foil (thickness: 15 μm) as a negative electrode current collector by a doctor blade method and dried to obtain a laminate. Next, the obtained laminate was pressed using a roll press, and an output terminal was connected to the current collector to produce a test negative electrode.

<Preparation of electrolyte>
Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed at a volume ratio of 2: 2: 6 to obtain a plasticizer (organic solvent) of the electrolytic solution. Then, the plasticizer, the addition of LiPF ₆ as lithium salt to a concentration of 1M, to prepare an electrolytic solution.

<Production of evaluation battery>
Using the positive electrode and the negative electrode produced above, a polyethylene microporous membrane (thickness: 25 μm) as a lithium ion battery separator was sandwiched. Next, the obtained sandwiched body was inserted into an aluminum laminate pack which is a three-side sealed exterior material. Thereafter, the electrolytic solution prepared above was injected into the aluminum laminate pack, and the pack was vacuum-sealed so that the output terminals were exposed from the pack, thereby completing a laminate battery.

<Example 2>
A zirconia bead having a particle diameter of 0.5 mm was filled in a processing container of a wet pulverization processing apparatus (manufactured by Ashizawa Finetech Co., Ltd., Labostar) at a volume ratio of 70%. Water, which is a solvent, is added thereto, and thereafter, styrene-butadiene rubber particles (viscosity average molecular weight: 1.0 × 10 ⁶ ) (5.0 mass%) as a binder and carboxymethyl cellulose (viscosity average molecular weight: 1. 0 × 10 ⁵ ) (5.0 mass%) were sequentially added to obtain a binder slurry.

  Into this slurry, hard carbon (average particle size: 10 μm) (90% by mass) as a negative electrode active material was added, and wet pulverization was performed for 2 hours under the condition of a rotational speed of 13 m / sec. When the obtained slurry was diluted with water and then dispersed using ultrasonic waves, and the particle size distribution was measured, the average particle size of the hard carbon was 1.0 μm.

  The obtained slurry was applied on a copper foil (thickness: 15 μm) as a negative electrode current collector by a doctor blade method and dried on a hot stirrer to obtain a laminate. Next, the obtained laminate was pressed using a press machine, an output terminal was connected to the current collector, and a negative electrode for testing was produced.

  An evaluation battery was produced in the same manner as in Example 1 except that the negative electrode was produced as described above.

<Example 3>
A battery for evaluation was produced in the same manner as in Example 1 except that the lithium manganese composite oxide having an average particle diameter of 3 μm was used. In addition, when the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer and the adhesion between the positive electrode active material layer and the current collector were good.

<Example 4>
A battery for evaluation was produced in the same manner as in Example 1 except that a lithium manganese composite oxide having an average particle size of 5 μm was used. In addition, when the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer and the adhesion between the positive electrode active material layer and the current collector were good.

<Example 5>
A battery for evaluation was produced in the same manner as in Example 1 except that the lithium manganese composite oxide having an average particle size of 10 μm was used. In addition, when the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer and the adhesion between the positive electrode active material layer and the current collector were good.

<Comparative Example 1>
Using a lithium manganese composite oxide having an average particle diameter of 1 μm, instead of PVdF having a viscosity average molecular weight of 7.0 × 10 ⁷ and PVdF having a viscosity average molecular weight of 3.0 × 10 ⁶ , a viscosity average molecular weight A positive electrode was produced in the same manner as in Example 1 except that PVdF having a thickness of 3.0 × 10 ⁴ was used. When the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer was good, but the adhesion between the positive electrode active material layer and the current collector was extremely poor, and an evaluation battery could not be produced. .

<Comparative example 2>
A positive electrode was produced in the same manner as in Comparative Example 1 except that a lithium manganese composite oxide having an average particle size of 3 μm was used. When the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer was good, but the adhesion between the positive electrode active material layer and the current collector was extremely poor, and an evaluation battery could not be produced. .

<Comparative Example 3>
A battery for evaluation was produced in the same manner as in Comparative Example 1 except that a lithium manganese composite oxide having an average particle diameter of 5 μm was used. When the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer was good, but the adhesion between the positive electrode active material layer and the current collector was poor, and a battery for evaluation could barely be produced. It was in a state.

<Comparative example 4>
A battery for evaluation was produced in the same manner as in Comparative Example 1 except that a lithium manganese composite oxide having an average particle size of 10 μm was used. In addition, when the obtained positive electrode was visually observed, the dispersibility of the solid component of the positive electrode active material layer and the adhesion between the positive electrode active material layer and the current collector were good.

(Measurement of adhesion of positive electrode)
A peel test of the positive electrode produced in each of the above Examples and Comparative Examples was performed, and the adhesion between the positive electrode active material layer and the current collector was measured. The results are shown in Table 1 below.

  Specifically, an adhesive tape was applied to the surface of the positive electrode, one end of the tape was pulled at a rate of 10 cm / min with a tensile tester, and a 90-degree peel test was performed.

(Evaluation of battery resistance)
A charge / discharge test was performed using the batteries prepared in the above Examples and Comparative Examples 3 to 4. Specifically, initial charge was performed at a constant current of 0.2 C, discharge was performed at a constant current of 0.5 C, and a charge / discharge test of 10 cycles was performed at a constant current of 1 C. Thereafter, the battery resistance at 1C was evaluated. The relative value of the battery resistance of each battery when the comparative example 3 was set to 100 was calculated. The results are shown in Table 2 below.

  As is clear from Table 2 above, the comparative example of the electrode including the binder having a low molecular weight has low adhesion, and in Comparative Examples 1 and 2 where the particle size of the active material is small, before performing the peel test, Phenomena such as exfoliation of the active material layer and brittle part of the active material layer were observed. On the other hand, all the electrodes of the present invention including a binder having a high molecular weight as an example showed high adhesion.

  The battery resistance was lower than that of the comparative example in all examples. In particular, in Examples 1 to 3 in which the particle size of the active material was 3 μm or less, the effect of reducing battery resistance was greater.

As described above, the battery electrode of the present invention including an active material layer containing a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ is an adhesion between the active material layer and the current collector. By using the electrode, the battery having low battery resistance can be provided.

  The battery electrode of the present invention is suitably used in a lithium ion secondary battery used as a power source for driving a motor of an automobile or the like.

It is 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 cell,
10 Bipolar battery,
11 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 terminal,
27 negative terminal,
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 (10)

A current collector,
An active material layer including an active material having an average particle diameter of 1 to 3 μm and a binder having a viscosity average molecular weight of 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ disposed on the surface of the current collector;
A battery electrode comprising:   The active material is one or two selected from the group consisting of lithium-manganese composite oxide, lithium-nickel composite oxide, lithium-cobalt composite oxide, lithium-iron composite oxide, graphite, and amorphous carbon The battery electrode according to claim 1, wherein the battery electrode includes at least one kind of material.   One or two selected from the group consisting of cellulose, carboxymethylcellulose, polyacrylonitrile, polyvinyl chloride, styrene-butadiene rubber, butadiene rubber, ethylene-propylene-diene copolymer, polyvinylidene fluoride, and fluororubber. The battery electrode according to claim 1, wherein the battery electrode is a polymer material of a kind or more.   The battery electrode according to any one of claims 1 to 3, wherein the binder has a fibrous shape, a lump shape, or a particulate shape.   The battery electrode according to claim 1, wherein an average fiber diameter or an average particle diameter of the binder is smaller than an average particle diameter of the active material.   The battery electrode according to any one of claims 1 to 5, wherein the active material layer further includes a conductive auxiliary agent, and the conductive auxiliary agent is a carbon material. A lithium ion secondary battery including 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 a battery electrode of any one of Claims 1-6. A step of preparing an active material slurry by mixing an active material, a first binder and a second binder, and a solvent;
Applying the active material slurry to the surface of the current collector and drying;
Have
The viscosity average molecular weight of the first binder and the second binder is 1.0 × 10 ^{5 to} 1.0 × 10 ⁸ ;
The method for producing a battery electrode, wherein the viscosity average molecular weight of the first binder is smaller than the viscosity average molecular weight of the second binder, and the average particle diameter of the active material is 1 to 3 μm .   The step of preparing the active material slurry is characterized in that a dry mixture of the active material and the first binder is put into a solution in which the second binder is dissolved, and is kneaded and dispersed. The method for producing a battery electrode according to claim 8.   In the step of preparing the active material slurry, the active material, the first binder, and the conductive additive are mixed in advance into a solution in which the second binder is dissolved, and kneaded and dispersed. The method for producing a battery electrode according to claim 8, wherein:

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