JP2007042385A - Electrode for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means of securing both electron conduction and lithium ion conduction for an electrode for a battery usable under high output conditions. <P>SOLUTION: In the electrode for a battery provided with a current collector, and an active material layer containing active material formed on the surface of the collector, a low-density area with comparatively low density and a high-density area with comparatively high density are made to exist in the active material layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  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 manufacturing an electrode of a lithium ion secondary battery, an active material slurry containing an active material or a binder is prepared, and this is applied to the surface of a current collector, thereby providing an active material having a uniform composition. It is common to form layers.

  When charging / discharging a battery equipped with an electrode manufactured by such a method, when charging / discharging at a not so high output, even in an active material layer having a uniform composition, the charge / discharge reaction proceeds uniformly. sell.

  However, in response to the demand for higher performance of the battery, when the battery is charged and discharged at a higher output, in the active material layer having a uniform composition, the conduction of electrons from the current collector to the active material, There is a possibility that the conduction of lithium ions present in the electrolyte layer or the active material layer to the active material is not compatible. That is, in an active material layer having a uniform composition, if the density of the active material layer is relatively small, the active materials in the active material layer cannot be sufficiently in contact with each other. . In order to solve this problem, it is common to add a conductive additive.

  According to the addition of the conductive assistant, electronic conduction in the active material layer is ensured. However, there is a problem that lithium ion conduction is inhibited by the addition of the conductive aid. In addition, from the viewpoint of improving the output density of the battery, there are cases where the electrode on which the active material layer is produced is pressed. However, if the density of the active material layer is uniformly increased by such a pressing process, lithium is similarly applied. There is a possibility that a problem that the ion conduction path is not sufficiently secured may occur.

  As described above, in the active material layer of the battery electrode, ensuring the electron conduction and ensuring the lithium ion conduction are in a trade-off relationship, and this problem can be solved only by uniformly controlling the density of the entire active material layer. The current situation is difficult. Note that the problems described above are significant in bipolar batteries that are being developed with higher output in mind.

  Therefore, an object of the present invention is to provide means for sufficiently ensuring both electronic conduction and lithium ion conduction in a battery electrode that can be used under high output conditions.

  The present inventors have conducted intensive research to solve the above problems. At that time, various attempts were made to control the density of the active material layer of the electrode. As a result, it has been found that by coexisting a relatively low density region and a relatively high density region in the active material layer of the electrode, it is possible to solve the above-mentioned problem in the trade-off relationship. The invention has been completed.

  That is, the present invention provides a battery electrode having a current collector and an active material layer containing an active material formed on the surface of the current collector, and the active material layer has a relatively low density. The battery electrode is characterized in that a low density region and a high density region having a relatively high density exist.

  In the active material layer of the battery electrode of the present invention, a low density region and a high density region coexist. Thereby, both electronic conduction and lithium ion conduction in the active material layer can be sufficiently ensured. Therefore, the electrode of the present invention can contribute to the improvement of the output characteristics of the battery.

  Hereinafter, embodiments of the present invention will be described. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following embodiments.

(First embodiment)
(Constitution)
The present invention is a battery electrode having a current collector and an active material layer containing an active material formed on the surface of the current collector, wherein the active material layer has a relatively low density and a low density. The battery electrode is characterized in that a density region and a high-density region having a relatively high density exist.

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

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

  As shown in FIG. 1, a battery electrode (hereinafter also simply referred to as “electrode”) 1 of the present invention includes an active material 4, a conductive additive (not shown), and a binder (not shown) in the active material layer 3. ) Or the like, and a low density region (hereinafter also referred to as “LD region”) having a relatively low density, and a high density region (hereinafter referred to as “HD region”) in which the above components are clogged. It has a feature in that it exists.

  In the form shown in FIG. 1, the thickness of the LD region is larger than the thickness of the HD region. In the form shown in FIG. 1, LD regions and HD regions exist alternately. As shown in FIG. 1, the form in which the LD region and the HD region exist alternately is not particularly limited, and examples thereof include the forms shown in FIGS. 2 and 3. 2 and 3 are plan views of the electrode of the present invention as viewed from the electrolyte layer side (the side opposite to the current collector). In the form shown in FIG. 2, square HD regions exist at a predetermined interval. In the form shown in FIG. 3, circular HD areas are also present at predetermined intervals. In other words, in a preferred embodiment of the present invention, at least one of the LD region and the HD region exists regularly and periodically. Note that “exist regularly and periodically” means that the LD region or the HD region is arranged according to a certain rule, and the rule is arranged repeatedly. At this time, the specific period is not particularly limited, but from the viewpoint of obtaining the effect of the present invention sufficiently, the period in which the LD region and / or the HD region exists is preferably 1 mm or less, and more preferably Is 300 μm or less, more preferably 100 μm or less.

  FIG. 4 is a schematic sectional view showing another embodiment of the electrode of the present invention. The battery electrode of the form shown in FIG. 4 is also shown in FIG. 1 in that the active material layer 3 is formed on one surface of the current collector 2 and the LD region and the HD region exist alternately. It is the same as the electrode of the form.

  However, the electrode of the form shown in FIG. 4 differs from the electrode of the form shown in FIG. 1 in that the LD region and the HD region have substantially the same thickness. In the electrode of the form shown in FIG. 4, the form in which the LD region and the HD region are alternately present is not particularly limited, but the form shown in FIGS. 2 and 3 described above for the electrode of the form shown in FIG. Can be exemplified.

  In the electrode of the present invention, the LD region and the HD region may be scattered as shown in FIGS. 2 and 3, but may be present in a linear shape or a net shape. Even in such a form, the interval between adjacent LD regions and between adjacent HD regions is preferably 1 mm or less, more preferably 300 μm or less, and even more preferably 100 μm or less.

According to the electrode of the present invention, the presence of the LD region and the HD region in the active material layer makes it possible to achieve both electron conduction and lithium ion conduction in the active material layer that have been in a trade-off relationship. Although this mechanism is not completely clear, the following mechanism is presumed. That is, according to the electrode of the present invention, the electrons (e ⁻ ) move favorably in the HD region where components such as the active material 4 and the conductive auxiliary agent are concentrated, as indicated by solid lines in FIGS. To do. In other words, the HD region can function as an electron conduction path. Further, as shown by broken lines in FIGS. 1 and 4, lithium ions (Li ⁺ ) preferably move in the LD region where each component is not concentrated. In other words, the LD region can function as a lithium ion conduction path. As described above, in the electrode of the present invention, the electron conduction path and the lithium ion conduction path are separated from each other, so that it is possible to achieve both conduction of electrons and lithium ions, which has been a problem in the past. Even if the electrode of the present invention contributes to the solution of such a problem by other mechanisms, the technical scope of the present invention is not affected at all.

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

  Hereinafter, the configuration of the battery electrode of the present invention will be described by taking as an example a case where it is employed in a lithium ion secondary battery. The battery electrode of the present invention is characterized in that an LD region and an HD region exist in the active material layer. There is no particular limitation on the selection of the current collector, active material, binder, supporting salt (lithium salt), ion-conducting polymer, and other compounds added as necessary. Depending on the intended use, it may be selected by appropriately referring to conventionally known knowledge. 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 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 average particle diameter of the active material is not particularly limited. However, the smaller the average particle diameter, the more easily the electron conduction path is divided. Therefore, the smaller the average particle diameter of the active material, the more the effects of the present invention can be exhibited. From such a viewpoint, the average particle diameter of the active material is preferably 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.

  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 , LiCF ₃ SO _{3 and the} like.

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

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

  The compounding ratio of the components contained in the active material layer 3 is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

The active material layer 3 has an LD region and an HD region, and it is essential that the density of the HD region is larger than the density of the LD region, but the specific value of each density is not particularly limited. However, as an example, the density of the LD region is preferably about 1 to ³ g / cm ³ , and more preferably 1.5 to 2.5 g / cm ³ . If the density of the LD region is too small, the cycle performance may be significantly reduced due to a decrease in the binding force. On the other hand, if the density of the LD region is too large, the density is almost the same as that of the HD region, and the lithium ion permeability may be reduced. However, forms outside these ranges can also be employed.

On the other hand, the density of the HD region is preferably about 1.5 to 3.5 g / cm ³ , more preferably 2 to ³ g / cm ³ . If the density of the HD region is too small, the density is almost the same as that of the LD region, and there is a possibility that the electron conductivity is lowered. On the other hand, if the density of the HD region is too large, the electrolytic solution cannot completely enter, and an active material that cannot participate in the reaction may be generated. However, forms outside these ranges can also be employed. Here, the density of the HD region is preferably larger than the density of the LD region by 0.5 g / cm ³ or more.

  Note that the “density” of the LD region and HD region in the present application adopts a value calculated from an actual weight of the active material and a measured value of its thickness.

  As shown in FIG. 1, when the LD region and the HD region have different thicknesses, the specific thickness values are not particularly limited. However, as an example, when the thickness of the HD region is smaller than the LD region as shown in FIG. 1, the thickness of the HD region is preferably about 1 to 100 μm, more preferably 5 to 50 μm. If the thickness of the HD region is too small, the capacity may decrease or the density may increase. On the other hand, if the thickness of the HD region is too large, there is a possibility that the difference from the LD region is eliminated or the density is decreased. In such a form, the thickness of the LD region is preferably about 5 to 200 μm, more preferably 10 to 100 μm. If the thickness of the LD region is too small, there is a possibility that the difference from the HD region is eliminated or the density is increased. On the other hand, if the thickness of the LD region is too large, the active material tends to fall off the electrode, and cycle deterioration may occur.

(Production method)
The method for producing the battery electrode of the present invention is not particularly limited, and the electrode of the present invention can be produced by appropriately referring to conventionally known knowledge in the field of battery electrode production. Hereinafter, an electrode (1) having active material layers having different thicknesses in the LD region and the HD region as shown in FIG. 1, and an active region having substantially the same thickness in the LD region and the HD region as shown in FIG. The manufacturing method will be briefly described separately for the electrode (2) having a material layer.

  The electrode (1) is, for example, a mold having an active material, forming an active material slurry, applying the active material slurry to the surface of the current collector to form a coating film, and further having a desired groove It can be produced by patterning the coating film using 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 additive, a supporting salt (lithium salt), an ion conductive polymer, a polymerization initiator, etc.) are added in a solvent. Mix 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. The specific form of the current collector prepared in this step is the same as that described in the column of the configuration of the electrode of the present invention, and a detailed description thereof will be omitted here.

  Subsequently, 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.

  Thereafter, a mold is prepared. This mold is used for the purpose of forming a desired pattern on the surface of the coating film obtained above. Specifically, a mold having a shape desired to be patterned on the surface of the coating film is prepared on the surface of a metal mold substrate. For example, when it is desired to form an electrode having the form shown in FIGS. 2 and 3, a mold having a projecting portion in which a portion corresponding to the HD region in FIGS. 2 and 3 protrudes may be prepared. The specific form of the convex portion of the mold is not particularly limited, and can be appropriately set according to the shape of the electrode desired to be manufactured. However, as described above, since the HD regions are preferably adjacent to each other with an interval of 1 mm or less, the convex portions are also preferably adjacent to each other with an interval of 1 mm or less. Further, the height of the convex portion (corresponding to the depth of the HD region with respect to the surface of the LD region) is not particularly limited, but is usually about 1 to 200 μm, preferably 5 to 100 μm. Further, as described above, the convex portion may be formed in a linear shape or a net shape.

  Subsequently, the laminate in which the coating film is formed on the surface of the current collector and the mold prepared above are overlapped and pressed so that the coating film and the convex side of the mold face each other. Thus, the surface of the coating film can be patterned according to the pattern of the mold. That is, a concave portion is formed along the convex portion of the mold, and this concave portion becomes the HD region.

  At this time, the pressing means is not particularly limited, and conventionally known means can be appropriately employed. If an example of a press means is given, a calendar roll, a flat plate press, etc. will be mentioned.

  As mentioned above, although the preferable form which produces an electrode (1) using a metal mold | die was demonstrated in detail, the electrode (1) can be manufactured also with another manufacturing method. For example, the electrode (1) may be formed by forming a large number of recesses (that is, HD regions) on the surface of the coating film with a thin rod having no sharp tip.

  Then, the manufacturing method of the electrode (2) of the form shown in FIG. 4 is demonstrated. When the active material slurry is applied to the current collector, the electrode (2) is thinly applied to a portion corresponding to the LD region (that is, a thin coating film is formed), and is dark in a portion corresponding to the HD region. It can be manufactured by applying (ie, forming a thick coating) and finally pressing the entire coating.

  Therefore, since the active material slurry preparation step is the same as described above, the description thereof is omitted here.

  In the manufacturing method of the electrode (1) described above, the prepared active material slurry is uniformly applied to the current collector. On the other hand, when manufacturing the electrode (2), the amount of slurry applied varies depending on the location. Therefore, when applying the active material slurry during the production of the electrode (2), it is effective to form a uniform coating film with a general coater and then apply it further using a spray or ink jet method. According to spray atomization, the density of the slurry can be generated by a simple method. In addition, when an ink jet method is used, it is possible to generate fine shading with high accuracy. At this time, the second application by spraying or an ink jet method is preferably performed after drying the coating film formed by the first application.

  According to the method described above, a coating film as shown in FIG. 1 is formed at first glance. In this manufacturing method, a flat plate press treatment is performed on the entire coating film. Thereby, an electrode as shown in FIG. 4 can be formed.

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

  That is, a third aspect 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 an electrode of the present invention. There is a battery. 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. 5 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. 5 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 the present embodiment shown in FIG. 5 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. 5, the battery element 21 of the bipolar battery 10 of the present embodiment includes a positive electrode active material layer 13 in which an LD region and an HD region exist, and a negative electrode active material layer in which an LD region and an HD region also exist. 15 has a plurality of bipolar electrodes formed on each surface of the current collector 11. In FIG. 5, although the LD region and the HD region exist in the active material layer of the electrode as described above, each active material layer is illustrated as a single layer. Each bipolar electrode is laminated via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar electrode and electrolyte layer are arranged such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. 17 are stacked.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar battery 10 has a configuration in which the single battery layers 19 are stacked. In addition, an insulating layer 31 for insulating adjacent current collectors 11 is provided on the outer periphery of the unit cell layer 19. The current collector (outermost layer current collector) (11a, 11b) located in the outermost layer of the battery element 21 has a positive electrode active material layer 13 (positive electrode side outermost layer current collector 11a) or a negative electrode only on one side. One of the active material layers 15 (negative electrode side outermost layer current collector 11b) is formed.

  Furthermore, in the bipolar battery 10 shown in FIG. 5, 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 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 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. 6 is a perspective view showing the assembled battery of the present embodiment.

  As shown in FIG. 6, the assembled battery 40 is configured by connecting a plurality of the bipolar batteries of the second embodiment. Specifically, each bipolar battery 10 is connected by connecting the positive electrode tab 25 and the negative electrode tab 27 of each bipolar battery 10 using a bus bar. On one side surface of the assembled battery 40, electrode terminals (42, 43) are provided as electrodes of the entire assembled battery 40.

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

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

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

(Fourth embodiment)
In the fourth embodiment, the bipolar battery 10 of the second embodiment or the assembled battery 40 of the third embodiment is mounted as a motor driving power source to constitute a transportation system. As a transportation system using the bipolar battery 10 or the assembled battery 40 as a 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. 7 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. 8 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. 8, the negative electrode active material layer 15 is slightly smaller than the positive electrode active material layer 13, but is not limited to such a form. A negative electrode active material layer 15 that is the same as or slightly larger than the positive electrode active material layer 13 may also be used.

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

<Example 1>
<Preparation of positive electrode>
Spinel-type lithium manganate (LiMn ₂ O ₄ ) (average particle size: 1 μm) (85 parts by mass) as a positive electrode active material, acetylene black (10 parts by mass) as a conductive auxiliary agent, and polyvinylidene fluoride as a binder ( PVdF) (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. The coating film was then dried.

<Production of negative electrode>
Graphite (average particle size: 1 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-2 as a slurry viscosity adjusting solvent. -An appropriate amount of 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. The coating film was then dried.

  Further, a mold was prepared in which strip-like grooves each having a width of 50 μm and a depth of 50 μm were formed on the surface of a nickel foil (thickness: 200 μm) every 50 μm.

  Along with the prepared mold, each electrode precursor formed with the active material layer coating film prepared above is subjected to a roll press to form a fine groove structure on the active material layer coating film of each electrode. Then, each electrode was completed. When the thickness of the obtained electrode was measured from an electron micrograph, the thickness of the groove (high density region) was 17 μm, and the thickness of the portion where the groove did not exist (low density region) was 28 μm.

<Example 2>
The same as in Example 1 above, except that a metal foil having a width of 25 μm and a depth of 25 μm is formed every 25 μm on the surface of a nickel foil (thickness: 200 μm) is used. A test cell was produced by the method. As in Example 1, when the thickness of the obtained electrode was measured, the thickness of the groove (high density region) was 17 μm, and the thickness of the portion where the groove was not present (low density region) was 28 μm. Met.

<Example 3>
As in Example 1 above, a coating film of the active material layer was formed on the current collector of each electrode and dried.

  Subsequently, the active material slurry used to form the coating film was sprayed on the surface of the coating film of each of the obtained active material layers, and droplets of the active material slurry were adhered. The size of the adhered droplets and the interval between the droplets were measured from electron micrographs, which were about 70 μm and about 90 μm, respectively.

  The coating film to which the droplets adhered was pressed by a roll press machine to complete each electrode having an active material layer having a substantially uniform thickness (21 μm).

<Comparative Example 1>
Each electrode was produced by the same method as in Example 1 except that it was applied to a roll press without using a mold. It was 20 micrometers when the thickness of each obtained electrode was measured from the electron micrograph.

<Comparative example 2>
Each electrode was produced in the same manner as in Example 1 above, except that it was applied again to the roll press machine after using the roll press machine without using the mold. It was 17 micrometers when the thickness of each obtained electrode was measured from the electron micrograph.

<Comparative Example 3>
Each electrode was produced by the same method as in Example 1 except that the obtained coating film was used as an active material layer as it was without applying a roll press. It was 28 micrometers when the thickness of each obtained electrode was measured from the electron micrograph.

<Production of test cell>
For use as a positive electrode and a negative electrode of a test cell, the positive electrode and the negative electrode prepared in each of the above Examples and Comparative Examples were punched into 68 mm square and 70 mm square using punches, respectively.

Furthermore, a polypropylene microporous film (thickness: 15 μm) was prepared as a separator. Further, as an electrolytic solution was prepared that the LiPF ₆ is equal volume mixture of lithium salt of ethylene carbonate (EC) and diethyl carbonate (DEC) was dissolved in a concentration of 1M.

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

<Evaluation of battery characteristics of test cell>
For each of the above examples and comparative examples, 10 identical test cells were prepared, and each test cell was charged and discharged 10 times at a constant current of 30 mA, and the discharge capacity at that time Was measured. Further, AC impedance at a frequency of 1 kHz was measured as an index of the internal resistance of the test cell.

  Then, the discharge capacity when it was kept at a constant potential (4.2 V) and then discharged at a constant current of 300 mA was 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 and the comparative example, in the active material layer of the electrode, by coexisting the low density region and the high density region, the internal resistance value in the electrode can be suppressed to a low value (that is, the electron conduction is sufficient). Secured). This electron conduction is presumed to be mainly carried by the high-density region. In addition, according to the electrode of the present invention, the capacity under high output conditions can also be maintained at a high value (that is, lithium ion conduction is sufficiently ensured). This lithium ion conduction is presumed to be mainly carried by the low density region.

  Thus, the electrode of the present invention can make it possible to ensure both electron conduction and lithium ion conduction, which have been in a trade-off relationship. As a result, it can contribute effectively to the improvement of the output characteristics of the battery.

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

Explanation of symbols

1 electrode,
2 current collector,
3 active material layer,
4 active materials,
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,
HD high density (HD) area,
LD Low density (LD) region.

Claims (14)

A battery electrode having a current collector and an active material layer containing an active material formed on a surface of the current collector,
The battery electrode, wherein the active material layer includes a low density region having a relatively low density and a high density region having a relatively high density.   The battery electrode according to claim 1, wherein a thickness of the low density region is larger than a thickness of the high density region.   The battery electrode according to claim 1, wherein the low density region and the high density region have substantially the same thickness.   The battery electrode according to any one of claims 1 to 3, wherein the low-density region and / or the high-density region are scattered in the thickness direction of the electrode.   The battery electrode according to any one of claims 1 to 3, wherein the low density region and / or the high density region are present in a linear shape when viewed from the thickness direction of the electrode.   The battery electrode according to any one of claims 1 to 3, wherein the low density region and / or the high density region are present in a net shape when viewed from the thickness direction of the electrode.   The battery electrode according to claim 1, wherein the low density region and the high density region exist regularly and periodically.   The battery electrode according to any one of claims 1 to 7, wherein the low density region and / or the high density region are regularly and periodically present at a cycle of 1 mm or less.   The battery electrode according to claim 1, wherein the active material has an average particle size of 10 μm or less. 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,
The battery whose at least one of the said positive electrode or the said negative electrode is a battery electrode of any one of Claims 1-9.   The battery according to claim 10, which is a nonaqueous electrolyte battery.   The battery according to claim 10 or 11, which is a bipolar lithium ion secondary battery.   The assembled battery using the battery of any one of Claims 10-12.   A transportation vehicle equipped with the battery according to any one of claims 10 to 12, or the assembled battery according to claim 13.

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