JP5523678B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a secondary battery and a non-aqueous electrolyte secondary battery using the same.

  In recent years, secondary batteries for automobiles have been required to have higher output characteristics, and in particular, the power density can be significantly improved by controlling the electrode structure by setting the particle diameter of the active material to 5 μm or less. Has been confirmed (see Patent Document 1).

Such a technique is considered to be strongly demanded in applications such as automobiles and electric tools that require high output.
Japanese Patent Laid-Open No. 2002-151055

  However, it is not sufficient to use an active material with a small particle diameter for reducing the resistance of the electrode to increase the output, and it is necessary to form an appropriate conductive path that draws out the characteristics exhibited by the active material with a small particle diameter. is necessary.

  However, reducing the particle size of the active material for higher output and increasing the amount of conductive agent as necessary inevitably increases the amount of binder in the electrode, which may cause a problem of increased resistance. .

  In response to the above problem, when the amount of the binder is reduced, the binding force between the current collector and the electrode layer becomes extremely weak. As a result, the electrode layer is peeled off, and the resistance is increased due to the peeling and the durability is increased. There is a risk of deteriorating the performance.

  The present invention has been made in view of such problems of the prior art, and its object is to achieve a high output effect when small particles are used as a constituent material (active material) of a positive electrode for a secondary battery. Is to provide a positive electrode for a secondary battery having high durability while maintaining low resistance, and a non-aqueous electrolyte secondary battery using the same, by suppressing peeling of the electrode layer in order to extract the maximum possible .

  According to the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery that has both low resistance and high output characteristics and high durability.

  Embodiments of the present invention will be described below.

(First embodiment)
(Positive electrode configuration)
In a first embodiment of the present invention, in a positive electrode for a secondary battery comprising a current collector and an electrode layer containing an active material, a conductive agent, and a binder, the current collector has a surface roughness R _zjis of 5 μm. The secondary battery positive electrode has a peel strength between the electrode layer and the current collector of 0.1 N / mm or more.

  The positive electrode for a secondary battery according to the present invention includes a current collector, an active material, a conductive agent, and a binder as electrode constituent materials. In the present specification, the term “active material” simply means a positive electrode active material.

[Current collector on the positive electrode side]
The current collector used for the positive electrode for the secondary battery of the present invention has a surface roughness R _zjis of 5 μm or less and a peel strength between the current collector and the electrode layer of 0.1 N / mm or more. Features. The surface roughness R _zjis is preferably 1 to 5 μm, and more preferably 2 to 4 μm.

When the surface roughness R _zjis of the current collector exceeds 5 μm, the volume change accompanying the expansion / contraction of the active material during charge / discharge locally generates large stress repeatedly on the metal foil as the current collector. Leads to. Uneven stress on the current collector foil becomes a factor for promoting deterioration, and for example, pitting corrosion of the current collector foil is likely to occur, which may adversely affect the durability of the battery. In applications where durability is particularly required, for example, batteries for automobiles, it is necessary to have a current collector with less surface roughness and sufficient adhesive strength to ensure durability. On the other hand, when the surface roughness of the current collector is extremely small, the anchor effect of the active material is weak, and the bond between the current collector and the electrode layer becomes more dependent on the chemical bond via the binder. In such a case, the peel strength at the interface between the electrode layer and the current collector is 0.1 N / mm or more, preferably 0.1 to 0.5 N / mm, more preferably 0.15 to 0.3 N / mm. By strengthening the bonding state at the interface, it becomes possible to maintain an electronic connection between the electrode layer and the current collector, exhibit low resistance and high output characteristics, Such a state can be maintained for a long time. In addition, in this specification, the surface roughness and peeling strength of a collector are the values measured by the method described in the below-mentioned Example.

  Although it does not restrict | limit especially as a manufacturing method of the electrical power collector of this invention, For example, the rolled foil manufacturing method etc. are mentioned.

  Moreover, as a constituent material of the current collector, a metal foil such as aluminum (Al) foil, nickel (Ni), iron (Fe), titanium (Ti), stainless steel, copper (Cu), and the above metal foil are physically used. It is preferable to use a material that has been (mechanically) and / or chemically surface-treated. From the viewpoint of being used for the positive electrode, more preferably, an Al foil and a physical (mechanical) and / or chemically surface-treated Al foil are used. By using Al foil, there is an effect that excellent corrosion resistance is exhibited in an application in which anodic polarization is performed at a high potential in an organic electrolyte. Examples of the physical (mechanical) treatment include, but are not limited to, punching and a method of processing with a mold roll and a receiving roll to give unevenness. The chemical treatment is not limited to the following, and examples thereof include plating treatment, adhesive application, alloying, and rust prevention treatment. The thickness of the current collector is preferably 5 to 20 μm, and more preferably 10 to 15 μm. When a current collector satisfying such conditions is used, a stronger bond is formed between the current collector and the electrode layer due to the anchor effect (mechanical bond), physical interaction, and a binder is used. A stronger chemical bond formation (chemical interaction) is obtained. Therefore, it is possible to prepare a positive electrode capable of obtaining a good binding state even with a small particle active material.

[Active material on the positive electrode side]
The active material of the present invention preferably has an average particle size of 5 μm or less, more preferably 0.1 to 5 μm, and particularly preferably 1 to 3 μm. By using an active material having an average particle diameter in such a range, the capacity density of the battery can be increased, and a high output electrode can be produced. In the present specification, the median diameter obtained by using the laser diffraction scattering method can be used as the particle size value of the active material.

  The positive electrode active material is not limited to the following, but is one or more selected from the group consisting of lithium manganate, lithium nickelate, lithium cobaltate, lithium manganese nickel cobaltate and olivine-type iron phosphate Is preferred. When these are used, the average particle diameter can be easily adjusted to the above range, and the surface state of the current collector can be made more uniform.

[Conductive agent on the positive electrode side]
The conductive agent used in the positive electrode for secondary battery of the present invention preferably contains one or more carbon materials selected from the group consisting of graphite, amorphous carbon and fibrous carbon. Thereby, even in the above-described active material having a small particle diameter, the conductivity in the electrode can be ensured, and the resistance of the electrode can be reduced and the output can be increased.

  The graphite is not limited to the following, but the amorphous carbon such as flakes and fibers is not limited to the following, for example, carbon black, more specifically, Examples include acetylene black, ketjen black, and furnace black, which may be naturally derived or artificial. The fibrous carbon preferably has a diameter of 10 to 150 nm, and more preferably 20 to 100 nm. Moreover, it is preferable that it is 1-150 micrometers in length, and it is more preferable that it is 10-100 micrometers. When the fibrous carbon is in such a range, there is an effect that conductivity is imparted. Although not limited to the following, for example, carbon nanofibers, carbon nanotubes and the like can be mentioned.

[Binder on the positive electrode side]
It is preferable that the binder used for the positive electrode for secondary batteries of the present invention contains a fluororesin as a main component. In such a case, there is an excellent effect that chemical resistance (electrolytic solution resistance) can be maintained well. The term “main component” as used herein means a component having the highest blending ratio among the components of the binder. The fluororesin is preferably contained in the binder in an amount of 20% by mass or more, more preferably 50% by mass or more, and particularly preferably 80% by mass or more.

  Further, the fluororesin is not limited to the following, but for example, vinylidene fluoride resin, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / Perfluoroalkyl vinyl ether copolymer (PFA), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride, ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene Copolymer (ECTFE), copolymers comprising at least one of these as a main component, and vinylidene fluoride fluoride rubber, propylene / tetrafluoroethylene fluorine rubber, and tetrafluoroethylene / perful Such as fluorine rubber, such as Russia alkyl vinyl ether type fluorine-containing rubber. Among these, a vinylidene fluoride resin is preferable, and a vinylidene fluoride resin containing a functional group having polarity is more preferable. By using a vinylidene fluoride resin as a binder, there is an advantage that uniform dispersion is possible even if the active material is finely divided, and that a slurry can be easily prepared during production. Although it does not limit to the following as said functional group, For example, polar groups, such as a known carboxyl group, an epoxy group, and a hydroxyl group, can be used. The fluororesin containing such a polar group is a modified product of the fluororesin, and can further improve the binding property as compared with an “unmodified product” having no such polar group. As a modification method for the modified product, as for the modification method of vinylidene fluoride resin, copolymerization with other monomers, vinylidene fluoride resin homopolymer or modification in a solvent that dissolves or swells the copolymer. Although it is not limited to a specific method such as a method of reacting with an agent (JP-A-6-93025) and a method of modifying by grafting by irradiating radiation (JP-A-2005-047275), it is particularly by copolymerization Is preferred. Among the denaturing conditions, the denaturing agent, denaturing temperature and denaturing time are as follows. The denaturing agent is not limited to the following, and examples thereof include monoesters of unsaturated dibasic acids. Preferably, it is a C5-C8 thing among the monoester of the said unsaturated dibasic acid. Specific examples include maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, citraconic acid monoethyl ester, and the like. More preferred is maleic acid monomethyl ester or citraconic acid monomethyl ester. The denaturation temperature is more preferably 10 to 50 ° C. The modification time is preferably 10 to 100 hours.

  In the case of a modified product, the weight average molecular weight of the binder is preferably 350,000 to 1,000,000, and more preferably 450,000 to 700,000. On the other hand, in the case of an unmodified product, it is preferably 500,000 to 1,000,000, and more preferably 500,000 to 700,000. When it exists in this range, while desired high peel strength is obtained, the viscosity adjustment of an electrode slurry is comparatively easy, and application | coating of an electrode can be performed easily. The molecular weight of the present invention is measured by GPC (Gel Permeation Chromatography).

  The amount of the binder is preferably 10 parts by mass or less, more preferably 3 to 10 parts by mass, and particularly preferably 4 to 8 parts by mass with respect to 100 parts by mass of the active material. . On the other hand, the amount of the binder is preferably 90 parts by mass or less, more preferably 40 to 90 parts by mass, and particularly preferably 50 to 80 parts by mass with respect to 100 parts by mass of the conductive agent. preferable. As described above, the binder of the present invention can be obtained in a significantly smaller amount compared with the conventional one, and without obtaining an increase in electrode resistance due to an increase in the amount of the binder, to obtain desired peel strength and output characteristics. In addition, the capacity density can be kept high.

  Thus, the important elements of the binder are the type, amount added and molecular weight. In general, the modified product has better binding properties than the unmodified product. As the amount of addition increases, the capacity density of the battery decreases, but the binding property improves. As for the molecular weight, generally, the larger the molecular weight, the better the binding property.

[Others]
In addition, the electrode layer may include a supporting salt (lithium salt), an ion conductive polymer, and the like, if necessary. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

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

  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 above components contained in the electrode layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries and the like.

  The thickness of the electrode layer is not particularly limited, and conventionally known knowledge about lithium ion secondary batteries and the like can be appropriately referred to. For example, the thickness of the electrode layer is preferably about 10 to 100 μm, and more preferably 20 to 50 μm. When the thickness of the electrode layer is about 10 μm or more, the battery capacity can be sufficiently secured. On the other hand, if the thickness of the electrode layer is about 100 μm or less, the problem of an increase in internal resistance due to the difficulty of diffusing lithium ions or the like into the electrode deep part (current collector side) can be suppressed. The negative electrode and the electrolyte layer will be described in detail in the following third embodiment.

  Moreover, in the volume occupied by the positive electrode for the secondary battery, the porosity representing the ratio of the volume other than the solid content to the volume of the solid content of the electrode layer is preferably 33.0% or more, and 33.0 to 50 More preferably, it is 0.0%. If the porosity is 33.0% or more, a high output performance can be obtained because it is possible to hold an electrolytic mass sufficient to secure a desired battery capacity and to improve lithium diffusibility. It is done. On the other hand, if the porosity is 50.0% or less, the positive electrode material is arranged so as to realize both high energy density and high output of the battery by further controlling the film thickness while securing the conductive network. be able to.

(Second Embodiment)
The second embodiment of the present invention is obtained by preparing the current collector of the first embodiment and mixing the electrode layer material including the active material, conductive agent and binder of the first embodiment. For preparing a positive electrode active material slurry by dispersing the mixture in a slurry viscosity adjusting solvent, and applying and drying the positive electrode active material slurry on one surface of the current collector. It is a manufacturing method of a positive electrode. As described in the first embodiment, the peel strength between the current collector and the electrode layer containing the active material, the conductive agent, and the binder is 0.1 N / mm or more. And In addition, among the constituent elements of the positive electrode for the secondary battery, the current collector, the active material, the conductive agent, and the binder are the same as those in the first embodiment, and thus description thereof is omitted here.

  Although the said slurry viscosity adjustment solvent is not restrict | limited to the following, For example, NMP etc. are mentioned. The slurry is converted into ink from the solvent and the solid content using a homogenizer or a kneader. Application is performed by a hot plate method or a hot air drying method. Among the application (coating film) conditions, the application temperature is preferably 100 to 150 ° C, and more preferably 120 to 140 ° C. The coating time is preferably 3 to 30 minutes, and more preferably 5 to 15 minutes.

(Third embodiment)
(Battery structure)
The third embodiment of the present invention is a non-aqueous electrolyte secondary battery configured by the positive electrode for secondary battery of the first embodiment or the positive electrode for secondary battery obtained by the manufacturing method of the second embodiment. It is. The configuration of the positive electrode according to the present invention (the first embodiment) can be applied to both a stacked battery and a bipolar battery. Hereinafter, the negative electrode and the two battery structures will be described.

[Configuration of negative electrode]
A conventionally well-known structure can be employ | adopted for the structure of the negative electrode used for the nonaqueous electrolyte secondary battery of this invention.

  The current collector is made of a conductive material. Although it does not specifically limit, For example, aluminum foil, nickel foil, copper foil, etc. are mentioned. 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 negative electrode active material is not particularly limited, and examples thereof include carbon such as graphite and amorphous carbon, metal materials, and lithium alloys such as lithium aluminum alloy, lithium tin alloy, and lithium silicon alloy. From the viewpoint of being able to construct a battery having excellent capacity and output characteristics, carbon is preferred. In some cases, two or more negative electrode active materials may be used in combination. The average particle size is not particularly limited. The content of the negative electrode active material is not particularly limited, but is preferably 70 to 95 parts by mass, more preferably 80 to 90 parts by mass, with the total mass of each of the positive electrode material and the negative electrode material being 100 parts by mass. . Within such a range, the high energy density and high output of the battery can be balanced, which is preferable.

  Further, if necessary, a conductive agent, a binder, a supporting salt (lithium salt), an ion conductive polymer, and the like can be included. When an ion conductive polymer is included, a polymerization initiator for polymerizing the polymer may be included.

  Examples of the conductive agent include, but are not limited to, carbon black such as acetylene black, carbon powder such as graphite, and various carbon fibers such as vapor grown carbon fiber (VGCF). Can be mentioned. Although the content of the conductive agent is not particularly limited, the total mass of each of the positive electrode material and the negative electrode material is 100% by mass, preferably 1-20% by mass, and preferably 5-10% by mass. More preferred. Within this range, it is preferable because both the high energy density and high output of the battery can be achieved.

  Examples of binders include, but are not limited to, thermoplastic resins such as polyvinylidene fluoride (PVDF), polyvinyl acetate, polyimide and urea resins, and thermosetting resins such as epoxy resins and polyurethane resins. And rubber materials such as butyl rubber and styrene rubber.

  The supporting salt (lithium salt), the ion conductive polymer, and the polymerization initiator are the same as those in the first embodiment, and description thereof is omitted here. The blending ratio of these components is not particularly limited, and can be adjusted by appropriately referring to known knowledge about secondary batteries such as lithium ion secondary batteries.

  The thickness of the electrode layer is the same as in the first embodiment, and the description thereof is omitted here.

<Bipolar battery>
The battery of the present invention may be a bipolar non-aqueous electrolyte secondary battery (hereinafter also referred to as “bipolar battery”).

  A positive electrode having a positive electrode material electrically coupled to one surface of the current collector, a negative electrode having a negative electrode material electrically coupled to the other surface of the current collector, and disposed between the positive electrode and the negative electrode The non-aqueous electrolyte secondary battery is formed by alternately laminating electrolyte layers. The positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to the first embodiment. By employing a bipolar battery, there is an advantage that a higher power density and a higher voltage can be obtained as compared with a stacked battery.

  FIG. 1 is a cross-sectional view showing a bipolar battery of the present invention. Hereinafter, the bipolar battery shown in FIG. 1 will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  The bipolar battery 10 of this embodiment shown in FIG. 1 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. 1, the battery element 21 of the bipolar battery 10 of the present embodiment includes a bipolar electrode 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 a plurality. Each bipolar electrode is laminated via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar type is formed 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. An electrode and an electrolyte layer 17 are laminated.

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

  Further, in the bipolar battery 10 shown in FIG. 1, the positive electrode side outermost layer current collector 11a is extended to form a positive electrode tab (terminal) 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 (terminal) 27, which is similarly derived from the laminate sheet 29.

  Hereinafter, the member which comprises the bipolar battery 10 of this embodiment is demonstrated. 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]
The electrolyte constituting the electrolyte layer 17 is not particularly limited, but a liquid electrolyte or a polymer electrolyte can be used.

  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), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). 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 polymer electrolyte containing an electrolytic solution (gel electrolyte) and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, a polymer of polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), hexafluoropyrene (HFP), Examples thereof include PAN, PMMA, and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved. Moreover, as an example of a plasticizer, it is possible to use the electrolyte solution normally used for nonaqueous electrolyte secondary batteries, such as a lithium ion battery.

  In the case where the electrolyte layer 17 is composed of a liquid electrolyte or a gel polymer 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 gel polymer electrolyte or intrinsic polymer electrolyte can express 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.

  In the present invention, the electrolyte layer is preferably made of a gel polymer electrolyte. By using a gel polymer electrolyte as the electrolyte, the fluidity of the electrolyte is lost, the bipolar battery can be easily manufactured, and the sealing performance can be improved. Examples of the host polymer and the plasticizer of the gel polymer electrolyte are as described above.

  More preferably, the electrolyte layer is made of an all-solid electrolyte. By using an all-solid electrolyte as the electrolyte, the fluidity of the electrolyte is lost, the electrolyte does not flow out to the current collector, and the ion conductivity between the layers can be more reliably cut off.

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

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

[tab]
In the bipolar battery 10, a laminate sheet 29 in which the tabs (the positive electrode tab 25 and the negative electrode tab 27) electrically connected to the outermost layer current collector (11 a, 11 b) are the exterior for the purpose of taking out current outside the battery. It is taken out 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 case]
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. Further, as described above, by using the positive electrode for a secondary battery of the present invention, a secondary battery having high output and excellent durability can be obtained. In particular, an aluminum laminate exterior body having a high degree of freedom in shape. When is used, the durability can be further improved. This is because the laminate cell has a structure that cannot hold the contact between the electrode and the foil due to structural pressure applied like a metal cylindrical or square cell. This is because it is considered to be more important.

  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.

<Stacked battery>
The battery of the present invention may be a laminated nonaqueous electrolyte secondary battery (hereinafter also referred to as “laminated battery”).

  A positive electrode having a positive electrode material electrically coupled to both surfaces of one current collector; a negative electrode having a negative electrode material electrically coupled to both surfaces of another current collector; It is a non-aqueous electrolyte secondary battery in which electrolyte layers disposed between negative electrodes are alternately stacked. The positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to the first embodiment. For reference, FIG. 2 is a cross-sectional view showing an outline of a stacked nonaqueous electrolyte secondary battery 60.

(Fourth embodiment)
(Battery)
A plurality of the secondary batteries of the third embodiment are connected in parallel and / or in series to constitute an assembled battery.

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

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

  A connection method in particular when connecting the some bipolar battery 10 which comprises the assembled battery 40 is not restrict | limited, A conventionally well-known method can be employ | adopted suitably. For example, a technique using welding such as ultrasonic welding or spot welding, or a technique of fixing using rivets, caulking, or the like can be employed. According to such a connection method, the long-term reliability of the assembled battery 40 can be improved.

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

  The bipolar batteries 10 constituting the assembled battery 40 may be connected in parallel to each other, or may be connected in series, or a combination of series connection and parallel connection. May be. As a result, the capacity and voltage can be freely adjusted.

(Fifth embodiment)
(vehicle)
In the fifth embodiment, the bipolar battery 10 of the third embodiment or the assembled battery 40 of the fourth embodiment is mounted as a motor driving power source to constitute a vehicle. As a vehicle using the bipolar battery 10 or the assembled battery 40 as a motor power source, for example, a complete electric vehicle 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. As well as other vehicles (for example, trains). As a result, it is possible to manufacture a vehicle having a longer life and higher reliability than conventional ones.

  For reference, FIG. 4 shows a schematic diagram of an automobile 50 on which the assembled battery 40 is mounted. The assembled battery 40 mounted on the automobile 50 has the characteristics as described above. For this reason, the automobile 50 equipped with the assembled battery 40 is excellent in output characteristics, and has a long life and high reliability.

  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. .

  Hereinafter, the effect of the positive electrode for a secondary battery according to the present invention will be described using the following examples and comparative examples, but the technical scope of the present invention is not limited to these examples.

[Example 1]
<Preparation of positive electrode>
As the active material, lithium manganate having an average particle diameter D50 of 1 μm was used. Further, acetylene black was used as a conductive agent, and a carboxylic acid-modified product of polyvinylidene fluoride having a weight average molecular weight of 500,000 was used as a binder. The binder was used so that the content of the binder was 7 parts by mass with respect to 100 parts by mass of the active material and 60 parts by mass with respect to 100 parts by mass of the conductive agent. These were mixed and then dispersed in NMP which is a slurry viscosity adjusting solvent to prepare a positive electrode active material slurry.

On the other hand, an aluminum (Al) foil having a surface roughness R _zjis of 2.81 μm and a thickness of 20 μm was prepared as a current collector, and the slurry was applied to one surface of the current collector, followed by pressing after drying. Thus, a positive electrode was produced.

  In addition, among the above, the measuring method of the average particle diameter of an active material and the surface roughness of an electrical power collector is as follows.

(Particle size measurement)
・ Method: Laser diffraction scattering method 50% cumulative particle measurement (D50)
・ Device: X-100 manufactured by Microtrack
(Measurement of surface roughness of current collector)
Method: Laser microscope roughness measurement (JIS B 0601-1994)
Test piece preparation: The electrode was cut to a width of 10 mm and impregnated with an NMP solution (2 days). The electrode layer that floated was peeled off by sonication for 3 minutes in the impregnated container. The remaining current collector was attached to a slide glass to obtain a measurement sample.
Apparatus: Laser microscope (manufactured by Olympus LEXT-OLS3000)
Measurement data: Calculation of 10-point average roughness (R _zjis ), optical microscope image observation.

(Measurement of porosity)
A mercury intrusion method was used as a method for measuring the porosity, and Autopore IV9510 type (manufactured by Shimadzu Corporation) was used as the measuring device. In addition, the measurement conditions are for a range of pore diameters of Φ10 μm to 3 nm, and the volume of mercury that has entered the sample (positive electrode) is defined as the volume corresponding to the volume of the voids in the electrode layer, and the solid content relative to the solid content volume of the electrode layer The volume ratio other than was defined as the porosity.

<Production of negative electrode>
Non-graphitizable carbon as a negative electrode active material, acetylene black as a conductive auxiliary agent, and PVDF as a binder were mixed, and then dispersed in NMP, a slurry viscosity adjusting solvent, to prepare a negative electrode active material slurry. The binder was tested so that the content of the binder was 12 parts by mass with respect to 100 parts by mass of the negative electrode active material and 200 parts by mass with respect to 100 parts by mass of the conductive agent.

  Further, a copper (Cu) foil having a thickness of 10 μm was prepared as a current collector, and the above slurry was applied to one surface of the current collector, dried and pressed to prepare a negative electrode.

<Production of evaluation cell>
The positive electrode and the negative electrode produced as described above were cut into a size of 10 cm in length and 10 cm in width, and laminated so as to face each other through a polyethylene (PE) separator having a thickness of 20 μm to produce an evaluation battery element. In addition, nickel (Ni) and aluminum (Al) tab leads were connected to each electrode by ultrasonic welding. Next, the battery element for evaluation was placed in a laminate outer pair, 1 cc of electrolyte was injected, and then vacuum-sealed to prepare an evaluation cell. The electrolytic solution is obtained by dissolving 1M LiPF ₆ in a solvent of PC: EC = 1: 1.

[Example 2]
As the active material, lithium manganate having an average particle size D50 of 3 μm was used, and as the current collector, an aluminum (Al) foil having a surface roughness R _zjis of 3.65 μm and a thickness of 20 μm was used. About the others, the positive electrode, the negative electrode, and the cell for evaluation were produced by the same method and conditions as Example 1.

[Comparative Example 1]
As the active material, lithium manganate having an average particle diameter D50 of 1 μm was used. Further, acetylene black was used as the conductive agent, and an unmodified polyvinylidene fluoride product having a weight average molecular weight of 350,000 was used as the binder. The binder was used so that the content of the binder was 13 parts by mass with respect to 100 parts by mass of the active material and 100 parts by mass with respect to 100 parts by mass of the conductive agent. These were mixed and then dispersed in NMP which is a slurry viscosity adjusting solvent to prepare a positive electrode active material slurry.

On the other hand, an aluminum (Al) foil having a surface roughness R _zjis of 2.81 μm and a thickness of 20 μm was prepared as a current collector, and the slurry was applied to one surface of the current collector, followed by pressing after drying. Thus, a positive electrode was produced.

  The constituent elements other than the positive electrode are the same as in the example.

[Comparative Example 2]
As the active material, lithium manganate having an average particle size D50 of 3 μm was used, and as the current collector, an aluminum (Al) foil having a surface roughness R _zjis of 3.65 μm and a thickness of 20 μm was used. About the others, the positive electrode, the negative electrode, and the cell for evaluation were produced by the method and conditions similar to the comparative example 1.

[Comparative Example 3]
Lithium manganate having an average particle diameter D50 of 6 μm was used as the active material, and an aluminum (Al) foil having a surface roughness R _zjis of 6.02 μm and a thickness of 20 μm was used as the current collector. Further, a carboxylic acid-modified product of polyvinylidene fluoride having a weight average molecular weight of 500,000 was used as a binder. The binder was used so that the content of the binder was 7 parts by mass with respect to 100 parts by mass of the active material and 60 parts by mass with respect to 100 parts by mass of the conductive agent. These were mixed and then dispersed in NMP which is a slurry viscosity adjusting solvent to prepare a positive electrode active material slurry. About the others, the positive electrode, the negative electrode, and the cell for evaluation were produced by the method and conditions similar to the comparative example 1.

<Evaluation>
(Measurement of peel strength)
Means: Measurement using a T-type test piece.
Test piece preparation: The electrode was cut to a width of 10 mm and processed into a T-type test piece state that could be peeled off with a double-sided tape.
-Equipment: Material testing machine 5867 manufactured by Instron
Measurement conditions: Test speed: 200 / min, test temperature is room temperature (23 ° C.)
Intensity data: 10 mm before and after the obtained data was deleted, and the range of 60 mm was targeted (average value of N = 3).

  Table 1 shows the measurement results of the above tests.

  In Table 1, the exfoliation site means whether exfoliation occurred in the electrode layer (hereinafter referred to as “in-layer”) or occurred at the interface between the current collector and the electrode layer (hereinafter referred to as “interface”). ). If delamination occurs in the "layer" instead of the "interface", it means that the binding property at the "interface" is strong. In such a case, the increase in resistance is suppressed over a long period of time, and high input / output is achieved. The durability required for applications that require the development of characteristics can be satisfied. From Table 1, it can be seen that the binding property at the “interface” in the positive electrodes of Examples 1 and 2 is strong. This can be explained quantitatively by the peel strength. The peel strength of Examples 1 and 2 is 0.1 N / mm or more, while the peel strength of Comparative Examples 1 and 2 is 0.1 N / mm. It turns out that it is less than mm. Moreover, about the porosity, in Examples 1 and 2, it exists in the preferable range of 33.0% or more, On the other hand, Comparative Examples 1-3 was out of the said range. Therefore, the electrode obtained by the present invention can maintain a sufficient electrolytic mass to ensure a desired battery capacity and can improve lithium diffusibility, as compared with the conventional electrode. Further, when the thickness of the electrode layer is further reduced, the resistivity can be further reduced. At the same time, it was clarified that both high energy density and high power of the battery can be realized.

(Measurement of IV resistance value)
Using the evaluation cell described above, the measurement was started from the state of SOC 50% after the first charge / discharge. Initial measurement conditions were a room temperature of 25 ° C., an average value of current values 1, 2, and 3C, and a discharge time of 10 seconds (evaluation apparatus: HJ100ISM8 manufactured by Hokuto Denko). In addition, the same measurement was performed at the beginning of the test and at 1 month and 8 months after the start of the test. The storage temperature for 1 month and 8 months was 55 ° C., and the measurement temperature was 25 ° C.

  The measurement results are shown in Table 1. The relative values using the results of Comparative Example 1 as reference values are also shown along with the actual measurement values. In Table 1, “IV resistance” (initial) and “relative value with respect to Comparative Example 1” (after 1 month and after 8 months) are obtained when the IV resistance value of the cell in Comparative Example 1 is 100. The relative ratio (%) or value of IV resistance in each Example and Comparative Example is shown. The lower the “IV resistance” and the “relative value with respect to Comparative Example 1” (hereinafter also simply referred to as “relative value”), the more the electrical resistance is reduced. From Table 1, it was found that “IV resistance” and “relative value” in Examples were always significantly lower than those in Comparative Examples. In addition, with time, the difference between the “IV resistance” and the “relative value” between the example and the comparative example widened, and it became clear that the superiority of the example over the comparative example became clearer.

(Rate increase rate)
About each cell, the change rate of IV resistance value after storing at 55 degreeC for 1 month and 8 months was measured, respectively. The measurement results are shown in Table 1, and the rate of increase / decrease with the initial value as the reference value is shown. That is, the “resistance increase rate from the initial value” indicates the increase rate (unit:%) of the IV resistance value after 1 month and 8 months with respect to the IV resistance value of the cell at the initial measurement stage. The lower the “resistance increase rate from the initial value”, the better the durability of the battery.

From Table 1, when the surface roughness R _zjis is 5 μm or less and the peel strength is 0.1 N / mm or more (Examples 1 and 2), the peeled portion is always in the electrode layer, and “ It was found that the “resistance increase rate from the initial value” was always significantly lower than that of the comparative example. In addition, over time, the difference between the “IV resistance” and the “resistance increase rate from the initial value” increases between the example and the comparative example, and the superiority of the example over the comparative example becomes clearer. I made it. That is, in the positive electrode having a surface roughness R _zjis of 5 μm or less and a peel strength of 0.1 N / mm or more, since the binding property between the current collector and the electrode layer is high, the electrical resistance is reduced, As a result, it was clarified that high input / output characteristics and high durability can be realized. On the other hand, when the surface roughness R _zjis exceeds 5 μm (Comparative Example 3) or the peel strength is less than 0.1 N / mm (Comparative Examples 1 and 2), the electrical resistance (IV resistance) and “initial” It was clarified that the “resistance increase rate from the value” was higher than that of the example. Comparative Example 3 shows an example in which the characteristics are worse than those of the Examples even when the initial peel strength is 0.1 N / mm or more. The results of Comparative Example 3 indicate that in a current collector with a surface roughness of R _zjis exceeding 5 μm, the bonding state may not be maintained unless the bonding force by the binder species is sufficient. When the result of Comparative Example 3 is seen, due to the fact that the behavior of expansion / contraction of the active material accompanying charge / discharge cannot be suppressed by the binder, an electrolyte solution or the like enters a portion having a large surface roughness, thereby collecting current. Desorption of particles from the body is promoted, and a phenomenon in which the peel strength cannot be maintained occurs. Therefore, it was found that the resistance value increased in Comparative Example 3. On the other hand, when the surface roughness is large and the peel strength is weak, the structure cannot be maintained from the initial stage as in the case of the comparative example 3, so that the resistance value is estimated to be large. In addition, regarding Comparative Examples 1 and 2, the resistance value is higher than the value of the Example due to the interface peeling. However, when the comparative examples 1 and 2 are compared, when the peel strength is doubled, the “resistance increase rate from the initial value” is suppressed to about ½, and the tendency between the strength and the resistance increase rate is It was confirmed that the tendency was similar to the above-described examples and Comparative Example 3.

  In addition, by setting the average particle diameter of the active material to 5 μm or less, the specific surface area can be increased, and the output characteristics can be improved (Examples 1 and 2). When the binder of the present invention, particularly a modified fluororesin having a higher molecular weight, is used in comparison with Examples and Comparative Examples, the binding property between the current collector and the electrode layer is further reduced in a smaller amount than in the past. It has also been clarified that the electrical resistance can be further reduced while being able to be increased.

  The above results show that the use of the positive electrode for a secondary battery obtained by the present invention further reduces the resistance, the durability of the battery, and the high durability as compared with the case of using a conventional positive electrode for a secondary battery. It shows that it is achieved at the same time.

  Next, the effect of the positive electrode for secondary batteries by the amount of the binder of the present invention was examined.

[Example 3]
The content of lithium manganate (active material), acetylene black (conductive agent), and carboxylic acid-modified product (binder) of polyvinylidene fluoride having a weight average molecular weight of 500,000 is 5 parts by mass with respect to 100 parts by mass of the active material. And it is the same as that of Example 1 except having tried the said binder so that it might become 40 mass parts with respect to 100 mass parts of said electrically conductive agents. Components other than the positive electrode are the same as those in the first embodiment.

[Example 4]
The content of lithium manganate (active material), acetylene black (conductive agent), and carboxylic acid-modified product (binder) of polyvinylidene fluoride having a weight average molecular weight of 500,000 is 10 parts by mass with respect to 100 parts by mass of the active material. And it is the same as that of Example 1 except having tried the said binder so that it might become 80 mass parts with respect to 100 mass parts of said electrically conductive agents. Components other than the positive electrode are the same as those in the first embodiment.

<Evaluation>
The same as in the first embodiment. The measurement results are shown in Table 2.

When the surface roughness R _zjis is 5 μm or less and the peel strength is 0.1 N / mm or more, by adjusting the surface roughness R _zjis and the peel strength, a high bond between the current collector and the electrode layer is obtained. It was clarified that the IV resistance and the rate of increase in resistance can be adjusted to a desired relationship while maintaining the wearability. More specifically, the binding agent of the present invention can obtain a desired binding force with a small amount of addition so that the resistance does not increase. The resistance increase rate can be decreased while maintaining the IV resistance lower (Examples 3 and 4).

  As described above, according to the positive electrode for a secondary battery of the present invention, it is possible to increase the binding property between the current collector and the electrode layer, to reduce the electrical resistance, and to further reduce the activity of a smaller average particle diameter. By using the substance and a smaller amount of the binder, a secondary battery having both higher binding properties and capacity density than before can be obtained.

It is sectional drawing which shows the bipolar battery in one Embodiment of this invention. It is sectional drawing which shows the laminated battery in one Embodiment of this invention. It is a perspective view which shows the assembled battery obtained by connecting two or more bipolar type batteries in one Embodiment of this invention. It is the schematic of the motor vehicle carrying the assembled battery in one Embodiment of this invention.

Explanation of symbols

10 Bipolar battery,
11 Current collector,
11a Positive electrode side outermost layer current collector,
11b The negative electrode side 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 (terminal),
27 Negative electrode tab (terminal),
29 Laminate sheet,
31 insulating layer,
33 positive electrode current collector,
35 negative electrode current collector,
40 battery packs,
42, 43 electrode terminals,
50 cars,
60 Stacked battery.

Claims (9)

A current collector,
In the positive electrode for a nonaqueous electrolyte secondary battery comprising an active material, a conductive agent, and an electrode layer containing a binder,
In the volume occupied by the positive electrode for the nonaqueous electrolyte secondary battery, the porosity representing the volume ratio other than the solid content to the volume of the solid content of the electrode layer is 33.0% or more,
The current collector has a surface roughness R _zjis of 5 μm or less,
A positive electrode for a non-aqueous electrolyte secondary battery, wherein a peel strength between the electrode layer and the current collector is 0.1 N / mm or more. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the active material is lithium manganate. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2 , wherein the active material has an average particle size of 5 µm or less. The amount of the binder, the not more than 10 parts by weight with respect to the active material to 100 parts by mass is 90 parts by mass or less with respect to the conductive liquid 100 parts by weight, any one of claims 1 to 3 A positive electrode for a non-aqueous electrolyte secondary battery according to 1. The electrode layer does not contain a polyvalent organic acid, a non-aqueous electrolyte secondary battery positive electrode according to any one of claims 1-4. The positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the binder contains a fluorine-based resin as a main component. The non-aqueous electrolyte secondary solution according to claim 1, wherein the conductive agent contains one or more carbon materials selected from the group consisting of graphite, amorphous carbon, and fibrous carbon. Battery positive electrode. The positive electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the current collector is an aluminum foil or an aluminum foil obtained by physical treatment or chemical treatment. Nonaqueous electrolyte composed of a positive electrode for a secondary battery, a nonaqueous electrolyte secondary battery according to any one of claims 1-8.

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