JP5371024B2 - Positive electrode for secondary battery and non-aqueous electrolyte secondary battery using the same - 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, and more specifically, can exhibit high output characteristics and durability that have been difficult to realize with conventional secondary batteries. 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. To date, spinel structure manganese oxide having a BET specific surface area of 3 m ² / g or more has been used for the positive electrode, The use of an electrode having a surface area of 4 m ² / g or more has been proposed.

  On the other hand, Patent Document 1 provides a high-power battery having improved cycle characteristics and output characteristics by not only increasing the specific surface area of the active material but also extremely reducing the particle size of the electrode constituent material. It is disclosed.

In many cases, the particle size of the electrode constituent material employed in such a technique, particularly the positive electrode active material, has a lower limit average particle size of 5 μm or more. The reason for this is not only the problem of the process such as dispersibility, but also the content of other solids such as the binder used as one component of the electrode as the active material becomes smaller, and the active material per unit mass The main background is considered to be a decrease in quantity, that is, capacity density.
JP 2003-151547 A

  The reduction in the particle size of the active material and the accompanying increase in the amount of the conductive agent for the purpose of increasing the output as described above require an increase in the amount of the binder in the electrode. In addition, the reduction in the particle size of the active material reduces the anchor effect of the particles themselves on the current collector foil. For this reason, the bond between the active material and the current collector becomes more dependent on the chemical bond by the binder, and the required amount of the binder increases. Even if the reaction resistance and electronic resistance are reduced by reducing the particle size of the active material and adjusting the amount of conductive agent, the increase in the amount of binder increases the reaction resistance and diffusion resistance, increasing the total resistance value. Will do.

  On the other hand, when an electrode is produced with a very small amount of the binder, the binding force between the current collector and the electrode layer is very weak, and the current collection due to the impregnation of the electrolyte solution or expansion / contraction of the active material due to charge / discharge, etc. Peeling between the body and the electrode layer occurs easily. The peeling of the electrode layer from the current collector cuts the flow of electrons, and the electric resistance tends to increase. The use of such an electrode does not satisfy the durability required in battery applications that need to suppress an increase in resistance over a long period of time and exhibit high input / output characteristics, for example, automotive battery applications. This can cause problems.

  The present invention has been made in view of such problems of the prior art, and its purpose is to maximize the effect of high output when particles having a small particle diameter are used as the active material of the positive electrode for secondary batteries. An object of the present invention is to provide a positive electrode for a secondary battery that suppresses peeling of an electrode layer in order to make a limit and maintains high resistance while maintaining low resistance, and a nonaqueous electrolyte secondary battery using the same.

  As a result of intensive studies to solve the above problems, the present inventors have improved the binding property in the electrode layer by using a specific binder as a constituent material of the positive electrode for the secondary battery. The present inventors have found that the above problems can be solved and have completed the present invention.

That is, the present invention provides a positive electrode for a secondary battery comprising a current collector and an electrode layer containing a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material has a tap density of 2.0 g / cm ³ or less, the amount of the binder is 90 parts by mass or less with respect to 100 parts by mass of the conductive agent, and the peel strength between the current collector and the electrode layer is 0.1 N / mm or more This is a positive electrode for a secondary battery.

  According to the present invention, a non-aqueous electrolyte secondary battery having both high output characteristics and high durability can be obtained.

  Embodiments of the present invention will be described below.

(Positive electrode configuration)
The present invention is a positive electrode for a secondary battery comprising a current collector and an electrode layer containing a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material has a tap density of 2.0 g / cm ^3. The amount of the binder is 90 parts by mass or less with respect to 100 parts by mass of the conductive agent, and the peel strength between the current collector and the electrode layer is 0.1 N / mm or more. , A positive electrode for a secondary battery.

  FIG. 1 is a schematic diagram illustrating a positive electrode for a secondary battery according to the present invention. An electrode layer 2 is formed on the current collector 1. The electrode layer 2 includes a positive electrode active material 3, a conductive agent 4, and a binder 5.

The positive electrode for a secondary battery of the present invention has a tap density of the positive electrode active material of 2.0 g / cm ³ or less, an amount of the binder of 90 parts by mass or less with respect to 100 parts by mass of the conductive agent, The peel strength between the body and the electrode layer is 0.1 N / mm or more. According to such a form, the resistance in an electrode is reduced, it has a high output characteristic, and the positive electrode for secondary batteries which has the outstanding durability can be obtained.

  As described above, the positive electrode for a secondary battery of the present invention includes a current collector, a positive electrode active material, a conductive agent, and a binder as an electrode constituent material. Hereinafter, this constituent material will be described in detail.

[Current collector on the positive electrode side]
Uneven stress on the current collector becomes a factor for promoting deterioration, and for example, pitting corrosion of the current collector is likely to occur, which may adversely affect the durability of the battery. In applications where durability is particularly required, such as automobile batteries, it is necessary to have sufficient adhesive strength between the current collector and the electrode layer to ensure durability. The peel strength at the interface between the electrode layer of the positive electrode for a secondary battery of the present invention and the current collector is 0.1 N / mm or more, preferably 0.1 to 0.5 N / mm, more preferably 0.15 to 0.00. 3 N / mm. If the peel strength is within the above range, the bonding state at the interface is strengthened, and the electronic connection between the electrode layer and the current collector can be maintained, and the low resistance characteristics of the secondary battery In addition, high output characteristics are exhibited, and such a state can be maintained for a long time. In the present invention, as the peel strength, a value measured by the method described in Examples described later is adopted.

  Examples of the material constituting the current collector include metal foil such as aluminum foil, nickel foil, iron foil, titanium foil, stainless steel foil, or copper foil, or physical surface treatment or chemical surface treatment of the metal foil. Those subjected to are preferably mentioned. From the viewpoint of use in the positive electrode, an aluminum foil or an aluminum foil subjected to physical surface treatment or chemical surface treatment is more preferable. By using an aluminum foil, a positive electrode having excellent corrosion resistance can be obtained. Examples of the physical surface treatment include, for example, punching or a method of processing with a mold roll and a receiving roll in order to give unevenness. Examples of the chemical surface treatment include plating treatment, adhesive application, alloying, or rust prevention treatment. In addition, although it does not specifically limit, when using a modified polymer, what forms the surface state which is easy to chemically bond among these is preferable.

  The thickness of the current collector is preferably 5 to 20 μm, and more preferably 8 to 15 μm.

  By using the current collector as described above, in the positive electrode for a secondary battery of the present invention, formation of a stronger mechanical bond between the current collector and the electrode layer by the anchor effect, It is possible to obtain physical interaction or formation of a stronger chemical bond between the current collector and the electrode layer when using a binder. Therefore, even if it is a positive electrode active material with a small particle diameter, the positive electrode which shows a favorable binding state can be manufactured.

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

[Positive electrode active material]
The positive electrode active material used for the positive electrode for a secondary battery of the present invention includes at least one selected from the group consisting of lithium manganate, lithium nickelate, lithium cobaltate, lithium manganese nickel cobaltate and olivine type iron phosphate. It is preferable that these may be used in combination. When these are used, the average particle diameter of the positive electrode active material can be easily adjusted, and the surface of the current collector can be made more uniform.

In the present invention, the tap density of the positive electrode active material is 2.0 g / cm ³ or less.

  When the tap density is too small, the positive electrode active material becomes bulky, and the distance between the particles of the positive electrode active material tends to be difficult to shorten. For this reason, it is difficult to maintain the conductive network and electrode structure in the electrode, which may adversely affect the durability of the battery. In applications that require durability, such as automobile batteries, it is necessary that the tap density is small to some extent and that the electrode has sufficient strength within the electrode to fix a bulky active material. On the other hand, an increase in the internal strength of the electrode by simply increasing the amount of the binder leads to an increase in electrode resistance and a decrease in energy density. For this reason, by devising the kind of binder and increasing the peel strength between the current collector and the electrode layer, the electronic connection in the electrode layer is maintained for a long time, and the secondary battery It is possible to reduce resistance and maintain high output characteristics for a long time.

In view of the above, the tap density is preferably from 1.0 to 2.0 g / cm ^3, further preferably 1.4~1.8g / cm ^3. When the tap density exceeds 2.0 g / cm ³ , the filling property becomes too high and the voids in the electrode become extremely small and small. Since Li ions move through the electrode gap through the electrolytic solution, the reduction of the gap leads to a situation where Li ions are difficult to move, that is, diffuse. As a result, it is considered that the diffusion resistance increases and the output decreases. In the present invention, as the tap density, a value measured by a method described in Examples described later is adopted.

The average particle diameter of the positive electrode active material is preferably 10 μm or less, more preferably 1 to 10 μm, and particularly preferably 2 to 8 μm. By using a positive electrode active material having an average particle diameter in such a range, the capacity density of the battery can be increased, and a high-power secondary battery can be produced. Furthermore, by using a positive electrode active material having an average particle diameter in such a range, the gaps in the electrodes are more uniformly present throughout the electrodes, and the gaps are adjacent to each other, and Li ions move. It is thought that it can form an environment that is easy to do. In the present invention, the average particle diameter shall be adopted D ₅₀ values obtained using a laser diffraction scattering method (median diameter).

The specific surface area of the positive electrode active material is preferably 1 to ³ m ² / g. By using a positive electrode active material having a specific surface area in such a range, the reaction resistance can be reduced while suppressing a decrease in energy density. In the present invention, the specific surface area is a value measured by the BET method.

[Conductive agent on the positive electrode side]
The conductive agent used in the positive electrode for secondary battery of the present invention is preferably at least one carbon material selected from the group consisting of graphite, amorphous carbon, and fibrous carbon. By using the carbon material as described above, it is possible to ensure the conductivity in the electrode even when the active material having a small particle diameter as described above is used, reducing the resistance of the positive electrode and increasing the output of the secondary battery. Can be realized.

Examples of the graphite include flaky graphite and fibrous graphite. Examples of the amorphous carbon include, for example, carbon black, more specifically acetylene black, ketjen black, furnace black and the like, 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 diameter and length of the fibrous carbon are within such a range, there is an effect that conductivity is imparted. Examples of the fibrous carbon include carbon nanofibers and carbon nanotubes. Moreover, in scaly graphite, D ₅₀ is preferably 6 μm or less, and more preferably 3 μm or less. Preferably 3μm or less in _{D 50} is carbon black, more preferably not more than 1 [mu] m.

[Binder on the positive electrode side]
Examples of the binder used in the positive electrode for the secondary battery of the present invention include a fluoropolymer, a modified fluoropolymer, a thermoplastic resin such as polyvinyl acetate, polyimide, and a urea resin, an epoxy resin, a polyurethane resin, and the like. Preferred examples include thermosetting resins, rubber materials such as butyl rubber and styrene rubber. These may be used alone or in combination of two or more. Among these, it is preferable to include one or both of a fluorine-based polymer and a modified fluorine-based polymer, and it is more preferable to include a modified fluorine-based polymer. The chemical resistance (electrolytic solution resistance) of the positive electrode for a secondary battery of the present invention is improved by including one or both of the fluorine-based polymer and the modified fluorine-based polymer in the binder. An excellent effect can be obtained. In the present specification, the above-mentioned “modification treatment” means introducing a functional group having polarity with respect to the polymer.

  The amount of either or both of the fluoropolymer and the modified fluoropolymer in the binder is preferably 30% by mass or more, more preferably 50% by mass or more, and 100 More preferably, it is at least mass%.

  Examples of the fluoropolymer include, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride resin, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / Perfluoroalkyl vinyl ether copolymer (PFA), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride, ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), or Fluorine resins such as copolymers obtained by copolymerizing at least two types of monomers selected from the group consisting of monomers as raw materials for these polymers or copolymers; or vinylidene fluoride fluororubber, tetra Fluoro Styrene - propylene fluorine rubber or tetrafluoroethylene, - fluoro rubber, such perfluoroalkylvinylether type fluorine rubber. These may be used alone or in combination of two or more.

  As an example of the modified fluoropolymer, a polymer having a polar functional group introduced into the fluororesin described above, that is, a fluorofunctional resin modified or a functional group having polarity introduced into the fluororubber is introduced. Examples thereof include polymers, that is, modified fluororubber. These may be used alone or in combination of two or more.

  Among these, a vinylidene fluoride resin or a modified vinylidene fluoride resin is preferable, and a modified vinylidene fluoride resin is more preferable. By using one or both of vinylidene fluoride resin and modified vinylidene fluoride resin as a binder, uniform dispersion is possible even when the active material is finely divided, and slurry is produced during electrode production. Can be adjusted easily. Examples of the functional group introduced into the vinylidene fluoride resin by the modification treatment include a polar group such as a carboxyl group, an epoxy group, or a hydroxy group. Such a vinylidene fluoride-based resin containing a polar group, that is, a modified vinylidene fluoride-based resin, can further improve the binding property with an active material compared to a vinylidene fluoride-based resin having no polar group. it can. Examples of the method for modifying the vinylidene fluoride resin include: (a) a method of copolymerizing a vinylidene fluoride monomer and a monomer having a functional group described in JP-A-6-172451. (B) a method of reacting a vinylidene fluoride resin described in JP-A-6-93025 with a modifying agent in a solvent that dissolves or swells; (c) irradiation with radiation described in JP-A-2005-047275; And a modification method by grafting. Hereinafter, the modification treatment methods (a) to (c) will be described in detail.

(A) Copolymerization of a vinylidene fluoride monomer and a monomer having a polar group (method described in JP-A-6-172452)
The vinylidene fluoride used in the method of the modification treatment may be vinylidene fluoride alone or a mixture of vinylidene fluoride and other monomers. Examples of the other monomers include fluorine monomers copolymerizable with vinylidene fluoride or hydrocarbon monomers such as ethylene and propylene. Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, and fluoroalkylvinyl ether. it can. The amount of these other monomers copolymerizable with vinylidene fluoride is determined by considering the balance between solvent solubility and solvent resistance of the resulting copolymer and the amount of vinylidene fluoride and other monomers. It is preferably less than 20% by mass of the total amount.

  As a monomer to be copolymerized with the above-described monomer having vinylidene fluoride as a main component (hereinafter also referred to as “vinylidene fluoride monomer”), an unsaturated dibasic acid having 5 to 8 carbon atoms is used. The monoester is preferred. Specific examples include maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester. More preferred is maleic acid monomethyl ester or citraconic acid monomethyl ester.

  For copolymerization of vinylidene fluoride monomer and unsaturated dibasic acid monoester (hereinafter also referred to as “polar monomer”), methods such as suspension polymerization, emulsion polymerization, and solution polymerization are employed. However, aqueous suspension polymerization or emulsion polymerization is preferable from the viewpoint of ease of post-treatment, and aqueous suspension polymerization is more preferable.

  The type and amount of suspending agent used in the aqueous suspension polymerization, the type and amount of polymerization initiator, the type and amount of chain transfer agent, the amount of monomer charged, the polymerization temperature, the polymerization time, etc. The polymerization conditions can be appropriately employed with reference to the conditions described in JP-A-6-172452.

The charged amount of the polar monomer (that is, monoester of unsaturated dibasic acid) to be copolymerized with the vinylidene fluoride monomer is preferably 0.1 to 100 parts by mass of the vinylidene fluoride monomer. 3 parts by mass, more preferably 0.3-2 parts by mass. If it is less than 0.1 parts by mass, the effect of introducing polar groups such as adhesion of the obtained copolymer to a substrate such as metal may be poor. On the other hand, when the amount exceeds 3 parts by mass, the chemical resistance of the resulting copolymer tends to decrease. For the same reason, the obtained vinylidene fluoride copolymer preferably contains 1 × 10 ^{−5 to} 5 × 10 ⁻⁴ mol / g of carbonyl group.

(B) A method of reacting a vinylidene fluoride resin with a modifier in a solvent that dissolves or swells (a method described in JP-A-6-93025)
In this modification treatment method, at least selected from the group consisting of a vinylidene fluoride resin, a silane coupling agent having a group capable of reacting with the vinylidene fluoride resin and a hydrolyzable group, and a titanate coupling agent. One type is reacted to modify the vinylidene fluoride resin.

  As the vinylidene fluoride resin used in the method of the modification treatment, a vinylidene fluoride homopolymer obtained by suspension polymerization, emulsion polymerization, solution polymerization, or the like, or vinylidene fluoride and a fluoride having an unsaturated double bond are used. Examples thereof include a copolymer of vinylidene and a monomer copolymerizable with vinylidene. Monomers that can be copolymerized with vinylidene fluoride include fluorine monomers such as vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, ethylene, methyl methacrylate, acrylic Non-fluorinated monomers such as acids can be mentioned. From the viewpoint of solvent solubility and chemical resistance, a vinylidene fluoride homopolymer or a copolymer of vinylidene fluoride and a fluorine-based monomer is preferred. In the case of a copolymer, it is preferable to carry out copolymerization in an amount that is 80 mol% or more of the copolymer from which vinylidene fluoride is obtained. Although it does not specifically limit as a polymerization form, Suspension polymerization is preferable at the point from which high purity resin is obtained.

  The silane coupling agent or titanate coupling agent used in this modification treatment method needs to have a group capable of reacting with the vinylidene fluoride resin and a hydrolyzable group.

  Examples of the group (reactive group) that can react with the vinylidene fluoride resin include an amino group, a mercapto group, a ureido group, or a group containing these groups. Examples of the group containing an amino group, mercapto group, or ureido group include, for example, β-aminoethyl group, γ-aminopropyl group, N-β-aminoethyl-γ-aminopropyl group, N-phenyl-γ- Examples include aminopropyl group, γ-mercaptopropyl group, and γ-ureidopropyl group. In addition, a precursor group of the reactive group that has the ability to react with a potentially vinylidene fluoride resin, such as an isocyanate group, which reacts with moisture in the system or in the atmosphere to generate an amino group. However, the same effect can be obtained in the present modification treatment method.

Examples of the hydrolyzable groups include methoxy groups, alkoxy groups such as ethoxy group, a formyloxy group, acetoxy group, an acyloxy group such as a propionyloxy _{group, -ON = C (CH 3)} 2 group, -ON An oximo group of ═C (CH ₃ ) C ₂ H ₅ group and the like are mentioned, and an alkoxy group is more preferable.

  Preferable specific examples of the silane coupling agent and titanate coupling agent used in the method of the modification treatment include N-β (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl). -Γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, or N-phenyl-γ-amino Isocyanates such as aminosilanes such as propyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptosilane such as γ-mercaptopropylmethyldimethoxysilane, and γ-isocyanatopropyltrimethoxysilane Toshiran or isopropyl tri, (N-aminoethyl - aminoethyl) such as amino titanate such as titanates. These may be used alone or in combination of two or more. More preferred is γ-aminopropyltriethoxysilane or γ-mercaptopropyltriethoxysilane.

  This modification treatment method is performed by adding and mixing at least one of the above coupling agents to a solution obtained by dissolving or swelling the vinylidene fluoride resin in a solvent. At this time, the vinylidene fluoride resin and the coupling agent react, and the coupling agent additionally binds to the vinylidene fluoride resin.

  Examples of the solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethyl sulfoxide. Examples of the solvent for swelling the vinylidene fluoride resin include 2-butanone, acetone, cyclohexanone, ethyl acetate, and tetrahydrofuran. These solvents are used alone or in combination of two or more. be able to.

  The amount of the coupling agent is the mass of silicon in the silane coupling agent or titanium in the titanate coupling agent (in the case where a silane coupling agent and a titanate coupling agent are used together, the total of silicon and titanium). Is preferably 100 to 8000 ppm based on the mass of the vinylidene fluoride resin. If it is less than 100 ppm, when the modified polymer is used as a binder or an adhesive, the adhesive force to the substrate or filler may be insufficient. If it exceeds 8000 ppm, the adhesive strength with the substrate or the like may hardly increase as compared to the increase in the amount added, or rather may decrease.

  In addition, reaction conditions such as reaction temperature can be appropriately employed with reference to the reaction conditions described in JP-A-6-93025.

(C) Method of modifying treatment by irradiating with radiation and performing graft treatment (method described in JP-A-2005-47275)
This modification treatment method is performed through the following steps (1) to (4).

(1) Melt and mix vinylidene fluoride resin and unsaturated monomer,
(2) The mixture obtained in (1) is formed into a film, sheet, granule or powder,
(3) The product obtained in the step (2) is irradiated with photons (γ) or electrons (β) at a dose of 1 to 15 Mrad in the absence of air,
(4) If necessary, the product obtained in (3) is further treated to remove all or part of the unsaturated monomer not grafted to the vinylidene fluoride resin.

  The vinylidene fluoride resin used in the method for the modification treatment is the same as that in the method for the modification treatment (b) described above, and the description thereof is omitted here.

  Specific examples of the unsaturated monomer include carboxylic acids and derivatives thereof, acid chlorides, isocyanates, oxazolines, epoxides, amines, and hydroxides. The carboxylic acid contains 2 to 20 carbon atoms, and specific examples include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. Examples of these carboxylic acid derivatives include, for example, unsaturated carboxylic acid anhydrides, ester derivatives, amide derivatives, imide derivatives, and metal salts (such as alkali metal salts). Also included is undecylenic acid.

  Among these, preferred unsaturated monomers are unsaturated dicarboxylic acids having 4 to 10 carbon atoms and derivatives thereof, or anhydrides thereof. Specific examples include, for example, maleic acid, fumaric acid, itaconic acid, citraconic acid, allyl succinic acid, 4-cyclohexyl-1,2-dicarboxylic acid, 4-methyl-4-cyclohexyl-1,2-dicarboxylic acid, bicyclo [2,2,1] hept-5-ene-2,3-dicarboxylic acid, x-methylbicyclo [2,2,1] hept-5-ene-2,3-dicarboxylic acid, maleic anhydride, Itaconic acid, citraconic acid, allyl succinic acid, 4-cyclohexyne-1,2-dicarboxylic acid, 4-methylene-4-cyclohexyne-1,2-dicarboxylic acid, bicyclo [2,2,1] hept-5 -Ene-2,3-dicarboxylic acid or x-methylbicyclo [2,2,1] hept-5-ene-2,2-dicarboxylic acid.

  Other examples of unsaturated monomers include, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, diethyl maleate, monomethyl fumarate, Dimethyl fumarate, monomethyl isoconate, diethyl isoconate, acrylamide, methacrylamide, monoamide of maleic acid, diamide of maleic acid, N-monoethylamide of maleic acid, N, N-diethylamide of maleic acid, N- of maleic acid Monobutylamide, maleic acid N, N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid N-monoethylamide, fumaric acid N, N-diethyla N-monobutylamide of fumaric acid, N, N-dibutylamide of fumaric acid, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, or potassium methacrylate Can be mentioned. Among these, maleic anhydride is more preferable.

  The implementation conditions of the above steps (1) to (4) can be appropriately adopted with reference to the implementation conditions described in JP-A-2005-47275.

  Among the modification methods (a) to (c) as described above, in particular, (a) a modification method by copolymerization of a vinylidene fluoride monomer and another monomer having a polar group is provided. preferable. The reason is that the above-mentioned vinylidene fluoride copolymer has excellent chemical resistance and good adhesion to a substrate such as a metal, and copolymerization with other monomers having a polar group is: This is because it can be formed even by water polymerization, so that it is easy to handle.

  The weight average molecular weight of the fluoropolymer is preferably 350,000 or more, more preferably 350,000 to 1,000,000, and further preferably 450,000 to 700,000 when it is modified. On the other hand, when not modified, it is preferably 500,000 to 1,000,000, and more preferably 500,000 to 700,000. If the weight average molecular weight is within this range, the peel strength between the current collector and the electrode layer can be increased, the viscosity adjustment of the positive electrode active material slurry becomes relatively easy, and the application of the positive electrode active material slurry can be performed. It can be done easily. In the present invention, the weight average molecular weight is a value measured by a GPC (Gel Permeation Chromatography) method using polystyrene as a standard substance.

  The amount of the binder in the positive electrode for a secondary battery of the present invention is 90 parts by mass or less, preferably 40 to 90 parts by mass, and 50 to 80 parts by mass with respect to 100 parts by mass of the conductive agent. It is more preferable that

  Further, the amount of the binder in the positive electrode for secondary battery of the present invention is preferably 10 parts by mass or less, more preferably 3 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. It is preferably 4 to 8 parts by mass. When the amount of the binder exceeds 90 parts by mass with respect to 100 parts by mass of the conductive agent, or when the amount of the binder exceeds 10 parts by mass with respect to 100 parts by mass of the positive electrode active material, the surface of the active material There is a possibility that the ratio of covering the conductive agent and the binder increases and the reaction resistance increases, and the binder reduces the contact between the conductive agent and the active material, thereby reducing the conductivity.

  As described above, the binder of the present invention can be obtained in a significantly smaller amount compared to the conventional one, and without obtaining an increase in the resistance of the electrode due to an increase in the amount of the binder, to obtain a desired peel strength and output characteristics. In addition, the capacity density can be kept high.

[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 below.

  The positive electrode for a secondary battery of the present invention can be produced by a conventionally known method. Specific examples thereof include, for example, a step of preparing the current collector, a step of mixing an electrode layer material including the positive electrode active material, the conductive agent, and the binder, and a slurry obtained by mixing the obtained mixture. Examples of the method include a step of preparing a positive electrode active material slurry by dispersing in a viscosity adjusting solvent, and a step of applying and drying the positive electrode active material slurry on one surface of the current collector. The current collector, the active material, the conductive agent, and the binder, which are the constituent elements of the positive electrode for the secondary battery, are the same as described above, and thus the description thereof is omitted here.

  The slurry viscosity adjusting solvent is not particularly limited, and examples thereof include NMP. 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. The coating temperature is preferably 100 to 150 ° C, more preferably 120 to 140 ° C. The coating time is preferably 3 to 30 minutes, and more preferably 5 to 15 minutes.

  The present invention is also a non-aqueous electrolyte secondary battery configured using the above-described positive electrode for a secondary battery or the positive electrode for a secondary battery obtained by the above-described manufacturing method. The configuration of the positive electrode according to the present invention can be applied to both a stacked battery and a bipolar battery. Below, the structure of the negative electrode used for the nonaqueous electrolyte secondary battery of this invention and the nonaqueous electrolyte secondary battery of this invention is demonstrated.

(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 on the negative electrode side is made of a conductive material. Although the said material is not specifically limited, For example, an aluminum foil, nickel foil, or copper foil etc. are mentioned as a specific example. The thickness of the current collector is preferably 1 to 30 μm. However, a current collector having a thickness outside this range may be used.

  The negative electrode active material used is not particularly limited. For example, carbon materials such as graphite, non-graphitizable carbon, or amorphous carbon, metal materials, and lithium alloys such as lithium aluminum alloy, lithium tin alloy, and lithium silicon alloy are used. A specific example is given. Among these, carbon is preferable from the viewpoint that a battery excellent in capacity and output characteristics can be configured. In some cases, two or more negative electrode active materials may be used in combination.

  The average particle diameter of the negative electrode active material and the content of the negative electrode active material are not particularly limited, and known knowledge about secondary batteries such as lithium ion secondary batteries can be referred to as appropriate.

  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 carbon black such as acetylene black, carbon powder such as graphite, or various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark). The content of the conductive agent is not particularly limited, and conventionally known knowledge about secondary batteries such as lithium ion secondary batteries can be referred to as appropriate.

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

  Specific examples of the supporting salt (lithium salt), the ion conductive polymer, and the polymerization initiator are the same as in the case of the positive electrode, and a description thereof is omitted here. The blending ratio of these components is not particularly limited, and conventionally known knowledge about secondary batteries such as lithium ion secondary batteries can be referred to as appropriate.

  Conventionally known knowledge can be appropriately referred to for the thickness of the electrode layer in the negative electrode.

(Non-aqueous electrolyte secondary battery)
The battery using the positive electrode of the present invention can be a non-aqueous electrolyte secondary battery having a conventionally known form such as a stacked type or a bipolar type.

  FIG. 2 is a cross-sectional view showing a bipolar battery as an example of a non-aqueous electrolyte secondary battery using the positive electrode of the present invention. Hereinafter, the bipolar battery shown in FIG. 2 will be described in detail, but the technical scope of the present invention is not limited to such a form.

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

  As shown in FIG. 2, the battery element 21 of the bipolar battery 10 of this embodiment includes a bipolar electrode 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. 2, 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.

  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 gel polymer electrolyte host polymer and plasticizer 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, or the like can be used. Of these, urethane resins or 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. 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 is used. If it is, durability can be further improved. The reason for this is that the laminate cell does not have a structure capable of maintaining contact between the electrode and the foil by structural pressure, such as a metal cylindrical cell or square cell. This is because the adhesive force is considered to be more important.

  According to the bipolar battery 10 shown in FIG. 2, 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.

  The effects of the present invention as described above can be particularly noticeable 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 preferably 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.

<Battery assembly>
In the present embodiment, a plurality of the non-aqueous electrolyte secondary batteries 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.

<Vehicle>
In the present embodiment, the bipolar battery 10 or the assembled battery 40 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 power source for a motor, 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, or a wheel of a fuel cell vehicle or the like by a motor. Examples include a driving automobile or other vehicle (eg, a train). 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. . 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 secondary battery may be used. For reference, FIG. 5 is a cross-sectional view showing an outline of a multilayer nonaqueous electrolyte secondary battery 60.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, the technical scope of this invention is not limited to these Examples. The average particle diameter of the active material and the tap density of the active material were measured by the methods described in Table 1 below.

[Example 1]
<Preparation of positive electrode>
As a cathode active material, the average particle diameter _{D 50} using lithium manganate 1.4 [mu] m. 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 in an amount of 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.

  As the current collector, an aluminum foil having a thickness of 20 μm was prepared, the slurry prepared above was applied to one surface of the current collector, dried and pressed to produce a positive electrode.

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

  Furthermore, a copper foil having a thickness of 10 μm was prepared as a current collector on the negative electrode side, 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 prepared 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 separator having a thickness of 20 μm, thereby preparing an evaluation battery element. Each electrode was connected with a nickel tab lead and an aluminum tab lead by ultrasonic welding. Next, the battery element for evaluation was placed inside a pair of laminate sheaths, and 1 ml of electrolyte solution was injected and vacuum sealed to prepare an evaluation cell. Incidentally, the electrolyte, the _{1MLiPF 6 PC: EC = 1:} 1 were used as dissolved in a solvent (volume ratio).

[Example 2]
Except that the average particle size D ₅₀ as the positive electrode active material a lithium manganate 3.3μm was prepared cell for evaluation in the same manner as in Example 1.

[Example 3]
An evaluation cell was prepared in the same manner as in Example 1 except that a carboxylic acid-modified product of polyvinylidene fluoride having a weight average molecular weight of 500,000 was used in an amount of 40 parts by mass with respect to 100 parts by mass of acetylene black. Produced.

[Example 4]
An evaluation cell was prepared in the same manner as in Example 1 except that a carboxylic acid-modified product of polyvinylidene fluoride having a weight average molecular weight of 350,000 was used as the positive electrode binder.

[Comparative Example 1]
As a cathode active material, the average particle diameter _{D 50} using lithium manganate 1.4 [mu] m. In addition, 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 in an amount of 100 parts by mass with respect to 100 parts by mass of the conductive agent and 13 parts by mass with respect to 100 parts by mass of the active material. 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 foil having a thickness of 20 μm was prepared as a current collector, the slurry was applied to one surface of the current collector, dried and pressed to produce a positive electrode.

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

[Comparative Example 2]
An evaluation cell was prepared in the same manner as in Comparative Example 1 except that an unmodified polyvinylidene fluoride having a weight average molecular weight of 350,000 was used in an amount of 60 parts by mass with respect to 100 parts by mass of acetylene black. .

[Comparative Example 3]
Except that the average particle size D ₅₀ as the positive electrode active material using lithium manganate 1.3μm was prepared cell for evaluation in the same manner as in Comparative Example 1.

[Comparative Example 4]
The average particle size D ₅₀ as the positive electrode active material except for using lithium manganate of 8.8 .mu.m, to prepare a cell for evaluation in the same manner as in Comparative Example 2.

<Evaluation>
(Measurement of peel strength)
The peel strength between the positive electrode current collectors and electrode layers prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was measured under the conditions shown in Table 2 below.

(Measurement of IV resistance)
Using the evaluation cells prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the measurement was started from the state of SOC 50% after the first charge / discharge. The measurement conditions were a measurement temperature of 25 ° C., a current value of 1.23 C, and a discharge time of 10 seconds (evaluation apparatus: HJ-1001SM8, manufactured by Hokuto Denko Corporation).

(Rate increase rate)
About the evaluation cell produced in Examples 1-4 and Comparative Examples 1-4, the change rate of IV resistance value after preserve | saving for 30 days at 45 degreeC was measured, respectively.

  Table 3 shows the results of physical property evaluation using the evaluation cells obtained in Examples 1 to 4 and Comparative Examples 1 to 4.

(Specific surface area measurement)
Measurement method: Nitrogen adsorption BET single-point method Measurement apparatus: HORIBA, Ltd., continuous flow surface area meter SA9601 was used.

  In Table 3, “peeling part” refers to whether peeling occurred in the current collector film (hereinafter also referred to as “inside the film”) or the interface between the current collector and the electrode layer (hereinafter also referred to as “interface”). ). If delamination occurs "in the film" instead of "interface", it means that the binding at the "interface" is strong. In such a case, an increase in resistance at the electrode is suppressed over a long period of time. Therefore, the durability required for applications requiring high input / output characteristics can be satisfied.

  Moreover, the result of IV resistance and a resistance increase rate was represented by the ratio which used the result of the comparative example 1 as the reference value. A low IV resistance leads to a reduction in electrical resistance in the electrode.

From Table 3, the tap density of the positive electrode active material is 2.0 g / cm ³ or less, the amount of the positive electrode active material is 90 parts by mass or less with respect to 100 parts by mass of the conductive agent, and the current collector and electrode layer When the positive electrodes of Examples 1 to 4 having a peel strength between them of 0.1 N / mm or more were used, it was found that the peeled portion was always in the film, and the IV resistance and the rate of increase in resistance were lower values. It was. That is, the tap density of the positive electrode active material is 2.0 g / cm ³ or less, the amount of the positive electrode active material is 90 parts by mass or less with respect to 100 parts by mass of the conductive agent, and between the current collector and the electrode layer It was found that the positive electrode for a secondary battery of the present invention having a peel strength of 0.1 N / mm or more has a high binding property between the current collector and the electrode layer, thereby reducing the electrical resistance in the electrode. Further, it was found that when the positive electrode of the present invention is used, a secondary battery having excellent input / output characteristics and excellent durability can be obtained. On the other hand, when the positive electrode of Comparative Examples 1 to 4 in which the tap density of the positive electrode active material, the amount of the positive electrode active material, or the peel strength between the current collector and the electrode layer is outside the scope of the present invention, It was found that the electrical resistance (IV resistance) was higher than that of the example. Moreover, when the positive electrode of Comparative Examples 1-3 was used, it turned out that resistance increase rate becomes high compared with the case where the positive electrode of an Example is used.

  As described above, according to the positive electrode for secondary battery of the present invention, the binding property between the current collector and the electrode layer can be increased, and the electrical resistance in the electrode can be reduced. In addition, by using the positive electrode for a secondary battery of the present invention using a positive electrode active material having a smaller average particle diameter and a smaller amount of the binder than the conventional one, binding properties and capacity density higher than the conventional ones can be obtained. Can be obtained.

It is a schematic diagram which shows the positive electrode for secondary batteries by one Embodiment of this invention. It is sectional drawing which shows a bipolar battery as an example of the nonaqueous electrolyte secondary battery using the positive electrode of this invention. It is a perspective view which shows the assembled battery obtained by connecting two or more bipolar batteries using the positive electrode of this invention. It is the schematic which shows the motor vehicle carrying an assembled battery. It is sectional drawing which shows the laminated battery which is an example of the nonaqueous electrolyte secondary battery using the positive electrode of this invention.

Explanation of symbols

1 current collector,
2 electrode layers,
3 positive electrode active material,
4 Conductive agent,
5 binders,
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 (8)

A current collector,
An electrode layer containing a positive electrode active material, a conductive agent, and a binder;
A positive electrode for a secondary battery comprising:
The positive electrode active material has a tap density of 2.0 g / cm ³ or less, the positive electrode active material has an average particle size of 1.4 to 3.3 μm, and the amount of the binder is 100 parts by mass of the conductive agent. And a peel strength between the current collector and the electrode layer is 0.1 N / mm or more.   The positive electrode for a secondary battery according to claim 1, wherein the binder contains a modified fluoropolymer.   The positive electrode for a secondary battery according to claim 2, wherein the modified fluoropolymer has a weight average molecular weight of 350,000 or more. The positive electrode for secondary batteries of any one of Claims 1-3 whose specific surface area of the said positive electrode active material is 1-3 m < ² > / g. The positive electrode active material, lithium manganate, lithium nickelate, lithium cobaltate, comprises at least one member selected from the group consisting of manganese-nickel lithium cobaltate and olivine-type iron phosphate, any one of the claims 1-4 The positive electrode for secondary batteries as described in the paragraph. The said electrically conductive agent is a positive electrode for secondary batteries of any one of Claims 1-5 containing the at least 1 sort (s) of carbon material selected from the group which consists of graphite, an amorphous carbon, and fibrous carbon. The positive electrode for a secondary battery according to any one of claims 1 to 6 , wherein the current collector is an aluminum foil, or an aluminum foil subjected to a physical surface treatment or a chemical surface treatment. A non-aqueous electrolyte secondary battery including at least one single cell layer in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order,
A non-aqueous electrolyte secondary battery, wherein the positive electrode is the positive electrode for a secondary battery according to any one of claims 1 to 7 .

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