JP5704189B2 - Battery electrode - Google Patents

Description

  The present invention relates to a battery electrode. In particular, the present invention relates to an improvement for preventing separation of an active material from a binder due to charge / discharge, thermal shock, and the like.

  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 the electrolyte layer and accommodated in a battery case (for example, refer patent document 1).

JP 2003-7345 A

  Conventionally, when an electrode of a lithium ion secondary battery is manufactured, an active material layer is formed by preparing an active material slurry containing an active material or a binder and applying the slurry to the surface of a current collector. Is common.

  When charging and discharging a battery including an electrode manufactured by such a method, the binder retains the active material in the active material layer. Therefore, when the particle size of the active material is not so small, a small amount of binder is used. Thus, the active material can be stably held, and the charge / discharge reaction can proceed uniformly.

  However, in response to the demand for higher performance of batteries, in recent years, attempts have been made to reduce the active material diameter (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 maintain the capacity. This is because, when the particle size of the active material is small, the fine particles of the active material fall off from the binder, and the dropped fine particles move to the counter electrode due to migration or convection, causing an increase in resistance or a short circuit.

  In the active material layer of the electrode, the active material is fixed by the binder, but even if the active material is fixed in the initial state, the electrode structure is gradually peeled off and dropped out while being repeatedly charged and discharged. At this time, if it is merely electrically insulated in the electrode, there is no major problem with a slight decrease in capacity, but if it is a charged particle, the inside of the battery is caused by an electric field. Will move. At this time, when the positive electrode active material moves to the negative electrode side, it is reduced on the negative electrode surface and consumes lithium in the system, resulting in a decrease in capacity and an adverse effect of reducing the activity of the electrode surface by the reduction product. In addition, when the negative electrode active material moves to the positive electrode side, the negative electrode active material generally has conductivity, and thus when there is a certain amount of dropout, a short circuit may occur.

  Accordingly, an object of the present invention is to provide means for strengthening the electrode structure by holding an active material having a small particle size on the surface layer of the active material layer of the electrode in a battery electrode that can be used under high output conditions. And

  The present inventors have conducted intensive research to solve the above problems. At that time, an attempt was made to strengthen the electrode structure by holding an active material using an adhesive material together with a binder. As a result, it has been found that the above-mentioned problems can be solved by using an adhesive material on the entire surface of the active material layer, and the present invention has been completed.

  That is, the present invention is a battery electrode having a current collector and an active material layer including an active material formed on a surface of the current collector, wherein the active material layer includes an adhesive material. The battery electrode.

  According to the battery electrode of the present invention, the active material powder can be held in the active material layer. Therefore, the electrode of the present invention can contribute to improvement of battery durability.

It is a schematic sectional drawing which shows one Embodiment (1st Embodiment) of the battery electrode of this invention. It is a schematic sectional drawing which shows other 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.

  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 is a battery electrode having a current collector and an active material layer including an active material formed on a surface of the current collector, wherein the active material layer includes an adhesive material, It is a battery electrode.

  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.

  1 and 2 are schematic cross-sectional views showing embodiments of the battery electrode of the present invention. The battery electrode 1 in the form shown in FIGS. 1 and 2 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 additive (in particular, a positive electrode), and a binder.

  A battery electrode (hereinafter also simply referred to as “electrode”) 1 of the present invention is characterized in that an active material layer 3 includes an adhesive material 5 as shown in FIGS. 1 and 2.

  The pressure-sensitive adhesive material of the present invention is characterized in that particles are collected in the active material layer 3. In the form shown in FIG. 1, the adhesive material 5 is included on the outermost surface of the active material layer 3. In order to prevent and collect the particles of the active material 4 in the active material layer 3, it is only necessary that at least the outermost surface portion contains an adhesive material. FIG. 2 is a schematic cross-sectional view showing another embodiment of the battery electrode of the present invention. In the embodiment shown in FIG. 2, the adhesive material 5 is included so as to be distributed throughout the active material layer 3, thereby preventing the particles of the active material 4 from peeling and dropping from the entire active material layer 3.

  In the electrode of the present invention, the active material may be held using only an adhesive material, or the adhesive material may be used in combination with a binder. In order to make the electrode a stronger structure, it is preferable to use a binder having a strong initial binding force and an adhesive material capable of collecting the separated and dropped particles. When the adhesive material is used in combination with a binder, the particles of the active material can be held with a small amount of binder as compared with the case where only the binder is used.

  According to the electrode of the present invention, when a nano-size active material having a large specific surface area is conventionally used in the active material layer, the binder cannot sufficiently fix the active material by covering the surface of the active material. As a result, the problem that the active material falls off is solved.

  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 a battery electrode having a current collector and an active material layer containing an active material formed on a surface of the current collector, wherein the active material layer includes an adhesive material. This is an electrode for a battery. 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. The battery electrode of the present invention can be applied to both the positive electrode and the negative electrode. For example, when applied to the positive electrode, the current collector and the active material are used as the current collector and the positive electrode active material for the positive electrode. A compound known to act may be employed.

[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 containing an active material formed on the surface of the current collector that plays 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 shape of the active material is not particularly limited, and may be particulate, plate-like, fibrous, or indefinite, but is preferably particulate. When the particulate active material is used, the active material layer easily falls off, and the effect of the present invention that prevents the active material from falling off is significantly exhibited by including an adhesive material.

  When using a particulate active material, the average particle diameter of the active material is not particularly limited. However, the smaller the average particle diameter, the easier it is to drop out of the active material layer. 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 10 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less. However, forms outside these ranges can also be employed. In the present application, the average particle diameter of the active material is a value measured by a laser diffraction scattering method.

  The active material layer 3 may contain other materials if necessary. For example, a binder, a conductive additive, 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.

  The pressure-sensitive adhesive material is a kind of adhesive material, and is a material that does not use water, solvent, heat, or the like, and adheres by applying a slight pressure at room temperature for a short time. As the adhesive material, it is preferable to use a material that swells in the electrolyte and has ion permeability. For example, as the adhesive material, a polymer having a polyethylene oxide structure or a silicone-based adhesive material can be used. In particular, the silicone-based adhesive material has high chemical stability, sufficient stability against charge / discharge, and high adhesiveness. For example, the polymer having a polyethylene oxide structure includes polyalkylene oxide having a molecular weight of 50,000 to 10,000,000. In particular, polyethylene oxide having a molecular weight of 100,000 to 5,000,000, a boric acid ester compound of polyethylene oxide, and the like are preferable. Examples of the silicone-based pressure-sensitive adhesive material include methyl-based and phenyl-based materials, and include polydimethylsiloxane having a molecular weight of 50,000 to 5,000,000. In addition, the value of the weight average molecular weight measured by the liquid chromatography method shall be employ | adopted for the said molecular weight.

  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 powder such as graphite and various carbon fibers such as vapor grown carbon fiber (VGCF).

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 , and LiCF ₃ SO ₃ .

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers. This 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.

(Production method)
The electrode of the present invention is prepared by, for example, preparing an active material slurry by adding an active material and an adhesive material to an organic solvent, applying the active material slurry to the surface of a current collector, and forming a coating film. Can be manufactured. According to such a method, an electrode as shown in FIG. 2 can be produced. 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 conductive auxiliary agent, a supporting salt (lithium salt), an ion conductive polymer, a polymerization initiator, etc.) and a binder as necessary. Mix in a solvent to prepare an active material slurry. 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. Since the specific form of the current collector prepared in this step is as described in the section of the electrode configuration of the present invention, detailed description thereof is omitted here.

  Subsequently, the active material slurry prepared above 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. Although the thickness of the coating film to be formed is not particularly limited, it is usually about 10 to 100 μm.

  The application means for applying the active material slurry is not particularly limited. For example, a commonly used means such as a coater can be adopted.

  Then, the manufacturing method of the electrode of the form shown in FIG. 1 is demonstrated. The electrode shown in FIG. 1 can be manufactured by applying an active material slurry not containing an adhesive material to a current collector, applying the adhesive material, and finally pressing the entire coating film.

  Therefore, the active material slurry preparation step is the same as described above except that the active material slurry does not contain an adhesive material, and thus the description thereof is omitted here.

  In the above-described manufacturing method of the electrode of FIG. 2, the active material slurry prepared by mixing the adhesive material is uniformly applied to the current collector. On the other hand, when the electrode of FIG. 1 is manufactured, an active material slurry not containing an adhesive material is applied to a current collector by a general coater to form a uniform coating film, and then the adhesive material is further added. It can be prepared by dissolving in a solvent and applying with a coater, or applying to a substrate sheet without dissolving in the solvent, pressing against the electrode, peeling off the substrate sheet and transferring.

  The type of solvent and the mixing means for dissolving the adhesive material are not particularly limited, and conventionally known knowledge can be appropriately referred to. The solvent may be the same as or different from the solvent used for preparing the active material slurry. As a solvent for dissolving the adhesive material, for example, acetonitrile or the like can be used when a polymer having a polyethylene oxide structure is used as the adhesive material, and toluene or the like can be used when a silicone adhesive material is used.

  Although the thickness of the film | membrane of the adhesive material formed is not restrict | limited in particular, Usually, it is about 0.1-30 micrometers. At this time, the adhesive material may be applied after the coating film formed by applying the active material slurry not containing the adhesive material is dried.

  According to the method described above, the electrodes as shown in FIGS. 1 and 2 can be formed.

(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 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, and at least one of the positive electrode and the negative electrode is the present invention. It is a battery which is an electrode. 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. 3 is a cross-sectional view showing a battery of the present invention which is a bipolar battery. Hereinafter, although the bipolar battery shown in FIG. 3 will be described in detail as an example, the technical scope of the present invention is not limited to such a form.

  The bipolar battery 10 of this embodiment shown in FIG. 3 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. 3, 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 laminated. 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. 3, 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. 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 tab (positive electrode tab 25 and negative electrode tab 27) electrically connected to the outermost layer current collector (11a, 11b) is used for taking out the current outside the battery. Take out to the outside. Specifically, the positive electrode tab 25 electrically connected to the positive electrode outermost layer current collector 11 a and the negative electrode tab 27 electrically connected to the negative electrode outermost layer current collector 11 b 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. 4 is a perspective view showing the assembled battery of the present embodiment.

  As shown in FIG. 4, 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, a transportation system is provided in which 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. As a transportation system using the bipolar battery 10 or the assembled battery 40 as a motor power source, for example, a complete electric vehicle that does not use 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. In addition to cars driven by, trains, motorcycles, ships, aircraft and the like.

  For reference, FIG. 5 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. 6 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. 6, 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. The weight average molecular weight of the adhesive material was measured by the following method.

  As the apparatus, a gel permeation chromatography method, which is a kind of liquid chromatography, was used. A porous styrene divinylbenzene copolymer column was used, and measurement was performed through a mixture of acetonitrile and a sample of 10 mg as a solvent.

< Reference Example 1>
<Preparation of positive electrode>
Lithium cobaltate (LiCo ₂ O ₄ ) (average particle size: 10 μm) (85 parts by mass) as a positive electrode active material, acetylene black (5 parts by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder (5 parts by mass) was mixed, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent was added to prepare a positive electrode active material slurry.

  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 applied to one surface of the prepared current collector by a doctor blade method to form a coating film. Subsequently, this coating film was pressed to produce a positive electrode having an active material layer having a thickness of 20 μm.

<Production of negative electrode>
Hard carbon (average particle size: 9 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. An appropriate amount of 2-pyrrolidone (NMP) was added to prepare a negative electrode active material slurry.

  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 by the doctor blade method to form a coating film. Next, this coating film was pressed to produce a negative electrode having an active material layer having a thickness of 30 μm.

  Furthermore, for the positive electrode and the negative electrode, an adhesive material in which 15 g of polyethylene oxide having a weight average molecular weight of about 3,000,000 was dissolved in 85 g of acetonitrile was cast on an electrode and vacuum-dried. Polyethylene oxide was included on the surface of the material layer.

< Reference Example 2>
Each electrode was produced in the same manner as in Reference Example 1 except that 15 g of polydimethylenesiloxane having a weight average molecular weight of about 500,000 was used as the adhesive material instead of polyethylene oxide.

< Reference Example 3>
The polyethylene oxide of Reference Example 1 was applied to the base material sheet without being dissolved in the solvent, pressed against the positive electrode and the negative electrode, and the base material sheet was peeled off to transfer the polyethylene oxide to the surface layer of the active material layer. Except for the above, each electrode was produced in the same manner as in Reference Example 1 above.

<Example 4>
Each electrode was produced in the same manner as in Reference Example 1 except that the average particle diameter of the positive electrode active material was 0.8 μm and the average particle diameter of the negative electrode active material was 0.8 μm.

<Comparative Example 1>
Each electrode was produced by the same method as in Reference Example 1 except that the cell was produced without including polyethylene oxide.

<Comparative Example 2>
Each electrode was produced by the same method as in Example 4 except that the cell was produced without including polyethylene oxide.

<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 , Comparative Examples , and Reference Example were punched into 68 mm square and 70 mm square using punches, respectively.

Furthermore, a separator (thickness: 20 μm) prepared by punching an aramid nonwoven fabric having an average diameter of 3 μm into a 75 mm square was prepared. 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 test cell was produced by sealing in a vacuum.

<Evaluation of battery characteristics of test cell>
For each of the above examples , comparative examples , and reference examples , 10 identical test cells were prepared, and each test cell was charged to 4.2 V at 7.5 mA and then to 2.5 V. After discharging, a hole was once formed in the exterior and vacuum sealing was performed. Thereafter, charging / discharging was performed from 2.5 V to 4.2 V at 15 mA, and the capacity retention rate and short-circuit rate after 100 cycles were measured.

  The results obtained for each of the above measured values are shown in Table 1 below as average values of 10 test cells.

From the comparison between each example, the comparative example , and the reference example , by including an adhesive material in the active material layer of the electrode, the capacity after repeated charge and discharge can be maintained, and the short circuit rate can be suppressed to a low value. This effect is presumed to be because the active material was stably maintained in the active material layer mainly by using the adhesive material. Furthermore, from the comparison between Example 4 and Comparative Example 2 , the effect of the present invention is remarkable when the average particle size of the active material is 1 μm or less. When the average particle size of the active material is small, the surface area becomes relatively large, and thus it is considered that the active material cannot be sufficiently fixed with a small amount of binder.

  As described above, the electrode of the present invention retains the electrode active material in the active material layer, which has been difficult to fix stably with a binder alone, particularly when the average particle size is 1 μm or less. It is possible to effectively contribute to maintaining the capacity of the battery and reducing short circuits.

1 electrode,
2 current collector,
3 active material layer,
4 active materials,
5 Adhesive materials,
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 (4)

A battery electrode having a current collector and an active material layer including an active material formed on a surface of the current collector, wherein the active material layer includes an adhesive material;
The adhesive material consists only of a polymer having a polyethylene oxide structure,
The active material has an average particle size of 1 μm or less,
The battery electrode, wherein the adhesive material is contained at least on the outermost surface of the active material layer.   The battery electrode according to claim 1, wherein the active material layer further includes a binder, and the binder is polyvinylidene fluoride (PVdF) or a synthetic rubber binder.   The battery electrode according to claim 1, wherein the battery electrode is a positive electrode.   The battery according to any one of claims 1 to 3, wherein the battery has 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. Battery that is an electrode.