JP5371032B2 - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode for secondary battery which has high durability while maintaining low resistance, and to provide a nonaqueous electrolyte secondary battery using the same. <P>SOLUTION: In the positive electrode for secondary battery including a positive electrode active material, a conductive agent and a binder, and the nonaqueous electrolyte secondary battery using the same, the quantity of the binder is 10 pts.mass or less relative to 100 pts.mass of the positive electrode active material, and the electrode has a porosity of 30-50%, and a pore diameter of 0.09-0.30 &mu;m. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a positive electrode for a secondary battery and a non-aqueous electrolyte secondary battery using the same. More specifically, the present invention relates to a positive electrode for a secondary battery that can exhibit both high output characteristics and durability, which are difficult to realize with a conventional 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 are being developed rapidly. Up to now, as a method for increasing the output of the secondary battery, a spinel structure manganese oxide having a BET specific surface area of 3 m ² / g or more is used for the positive electrode, or an electrode having a specific surface area of 4 m ² / g or more. It has been proposed to use it.

  It has also been proposed that a high-power battery having improved cycle characteristics and output characteristics can be obtained by not only increasing the specific surface area of the active material but also extremely reducing the particle size of the electrode constituent material.

  In many cases, the lower limit of the particle size of the electrode constituent material employed in such a technique, particularly the average particle size of the positive electrode active material, was 5 μm or more. The reason for this is not only the problem in terms of process such as dispersibility, but also the content of solids other than the active material such as the binder increases as the active material becomes smaller, and the amount of active material per unit mass In other words, the main reason is that the capacity density decreases.

  However, in applications such as automobiles and power tools, it is necessary to apply high output even if the capacity density is somewhat sacrificed. For example, Patent Document 1 confirms that the power density is significantly improved by controlling the electrode structure by reducing the particle diameter of the active material of the electrode constituent material to 5 μm or less.

Furthermore, when the particle size of the active material that is an electrode constituent material is extremely small, the specific surface area is increased, so that a large amount of conductive agent is required to form a conductive path that connects the particles and to fully bring out the effect. It has been confirmed.
Japanese Patent Laid-Open No. 2002-151055

  However, it is not enough to use an active material with a small particle size to reduce the resistance of the electrode to increase the output, and the formation of an appropriate conductive path that draws out the characteristics exhibited by the use of an active material with a small particle size. is necessary.

  Even with the same amount of conductive agent, the conductive paths formed may differ depending on the electrode density. When the density of the electrode decreases, the distance between the constituent materials such as the active material and conductive agent, which are electrode components, becomes vacant, and the conductive path is broken to increase the number of short ones, which causes the resistance to increase gradually as the usage period increases. sell. On the other hand, if the electrode density is too high, the resistance increases because the solid content constituting the electrode is inhibited from being diffused due to the reduction of the voids. Thus, the electrode density is one of the factors that affect the resistance of the electrode. In order to increase the output, not only the amount of the conductive agent but also the optimization of the electrode density is required.

  There are other factors that affect resistance. For example, binders used in secondary batteries play an important role in maintaining the electrode structure by binding active materials or between active materials and current collectors, but most of them are insulating materials. Therefore, there is a point that the resistance per electrode volume increases as the amount of the binder increases. Increasing the particle size of the active material for higher output as described above and increasing the amount of conductive agent as necessary inevitably increases the amount of binder in the electrode, increasing the overall resistance of the electrode. Can cause problems.

  On the other hand, when an electrode is produced with a very small amount of binder, the electrode structure has a very low holding capacity, and the electrode layer easily peels off due to the impregnation of the electrolyte or expansion / contraction of the active material accompanying charge / discharge. . When the electrode layer is peeled off, the flow of electrons is cut, and the electrical resistance is likely to increase. Such an electrode may cause a problem that it does not satisfy the durability required in battery applications that need to suppress increase in resistance and develop high input / output characteristics over a long period of time, for example, automotive battery applications.

  The present invention has been made in view of the above problems, and its purpose is to achieve a high durability in which the rate of increase in resistance is suppressed while maximizing the effect of increasing the output by reducing the particle size of the active material. Another object is to provide a positive electrode for a secondary battery and a non-aqueous electrolyte secondary battery using the same. A further object is to provide a secondary battery for an automobile having a function of maintaining a high output.

  As a result of intensive studies to solve the above problems, the present inventors have improved the binding properties and electrode density in the electrode layer when using small particles as the active material of the positive electrode for secondary batteries. As a result, the present invention has been completed.

  That is, the positive electrode for secondary batteries of the present invention includes a positive electrode active material, a conductive agent, and a binder. And the positive electrode for secondary batteries of the present invention, the amount of the binder is 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, the porosity of the electrode is 30% or more and 50% or less, The pore diameter is 0.09 μm or more and 0.30 μm or less.

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

  Embodiments of the present invention will be described below.

(Positive electrode configuration)
One typical embodiment of the present invention relates to a positive electrode for a secondary battery including a positive electrode active material, a conductive agent, and a binder. And the positive electrode for secondary batteries of the present invention, the amount of the binder is 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, the porosity of the electrode is 30% or more and 50% or less, The pore diameter is 0.09 μm or more and 0.30 μm or less. 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.

  FIG. 1 is a schematic diagram illustrating a positive electrode for a secondary battery according to the present invention. The electrode layer 2 includes a positive electrode active material 3, a conductive agent 4, a binder 5, and voids 6. The electrode layer 2 is formed on the current collector 1.

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

[Porosity]
The positive electrode for a secondary battery of the present invention is characterized in that the porosity of the electrode is 30% to 50%, preferably 30% to 45%. In the present invention, “porosity” means the ratio of the total volume of voids (pores) existing inside the electrode layer to the volume of the electrode layer. The method for calculating the porosity is not particularly limited. For example, the porosity can be calculated from the electrode density of the electrode layer and the true density of the constituent material constituting the electrode layer using the following formula. Here, the “electrode density” refers to the density in consideration of the pores in the electrode layer. Among the electrodes composed of the electrode layer and the current collector, the average filling degree of the solid content of the electrode layer, that is, in the electrode layer The average density of solid content. The “true density” refers to a theoretical density that does not take into account pores of solids constituting the electrode layer.

  The electrode density can be calculated, for example, by measuring the mass and thickness of the electrode and the current collector and using the following relational expression from the measured mass and thickness values.

  When the compounding ratio of the positive electrode active material, the conductive agent, and the binder is x: y: z, the true density of the solid content composed of the positive electrode active material, the conductive agent, and the binder can be obtained by the following formula. it can.

  Alternatively, the volume of voids (pores) existing inside the electrode layer may be measured by measuring the pore distribution by a mercury intrusion method, and the porosity may be obtained as a ratio to the volume of the electrode layer. The mercury intrusion method is a method of theoretically calculating how much pressure is applied and how much mercury enters the hole. By detecting the change in the surface of the mercury liquid surface (that is, the amount of mercury penetrating into the pores) while continuously increasing the applied pressure, the size and volume of the pores on the sample surface can be measured.

  The apparatus used for the measurement is not particularly limited, but a precision balance having a measuring ability of about 0.01 mg and a film thickness meter having a measuring ability of about several μm, more preferably about 0.1 μm are preferably used. preferable.

  Charging / discharging of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries is performed by the lithium ions of the active material entering and exiting the electrolyte filling the voids in the electrode layer, and at the same time, electrons move through the conductive agent. The For this reason, it is considered that the resistance of the electrode is greatly influenced by the mobility of lithium ions inside the void filled with the electrolyte and at the interface of the active material and the mobility of electrons at the interface between the active material and the conductive agent. In general, since the movement speed of ions is slower than the movement speed of electrons, in the charge / discharge of a lithium ion secondary battery, control of lithium ion diffusivity is important for reducing resistance. For this reason, by increasing the specific surface area of the active material and securing a void region sufficient for the diffusion of lithium ions, the transport of lithium ions can be improved, and the resistance of the entire electrode can be suppressed. On the other hand, even if a sufficient diffusion region of lithium ions is secured, if the electron conduction path is weak, the original performance of the active material cannot be sufficiently obtained, which causes the resistance of the electrode to increase.

  In the present invention, by adopting the porosity in the above range, it is possible to secure a sufficiently large void region in which lithium ions diffuse and to reduce inhibition of lithium ion diffusion due to solid content. Can be suppressed. If the porosity exceeds 50%, the energy density is lowered, the conductive path is weakened, and the resistance gradually increases with an increase in the period of use, which is not preferable. Moreover, when the porosity is less than 30%, the diffusion of lithium ions due to the filling of the solid content is inhibited, and the resistance is increased, which is not preferable.

[Pore diameter]
The positive electrode of the secondary battery of the present invention is characterized in that the pore diameter is 0.09 μm or more and 0.30 μm or less, preferably 0.1 μm or more and 0.25 μm or less. In the present invention, the “pore diameter” means an average value of pore diameters of voids (pores) existing in the electrode structure. The method for measuring the pore diameter is not particularly limited, and can be determined, for example, by measuring the pore distribution by mercury porosimetry.

  In the electrode layer, it is considered that the voids other than the solid content in which the active material or the like is bound by the binder are pores, and lithium ions diffuse through these pores filled with the electrolyte. . Since the diffusion of lithium ions is responsible for the charge / discharge reaction, it is possible to suppress the resistance of the entire electrode by ensuring a pore size having an appropriate size for the diffusion of lithium ions.

  In the present invention, it is preferable to use an electrode having a pore diameter in the above-mentioned range because the electrolyte is satisfactorily impregnated in the void portion, the lithium ion diffusion is improved, and the resistance of the electrode can be suppressed. When the pore diameter exceeds 0.30 μm, the conductive path is weakened, which may increase resistance. In addition, when the pore diameter is less than 0.09 μm, the void region in which lithium ions diffuse is narrow, so that inhibition of lithium ion diffusion is likely to occur.

  As described above, the secondary battery positive electrode of the present invention can control the porosity and pore diameter, thereby ensuring a strong conductive path and reducing the inhibition of lithium ion diffusion and enabling the resistance increase rate to be suppressed. To do.

[Positive electrode active material]
The positive electrode active material used for the positive electrode for secondary batteries of the present invention preferably has an average particle size of 0.1 to 10 μm, more preferably 0.5 to 7 μm, and more preferably 1 to 5 μm. It is particularly preferable to use those. By using an active material having an average particle diameter in such a range, the reaction resistance of the electrode can be reduced and the capacity density of the battery can be increased, and a high output electrode can be produced. In addition, in this invention, D50 value (median diameter) obtained using the laser diffraction scattering method shall be employ | adopted for an average particle diameter.

  The positive electrode active material is not limited to the following, but is at least one 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.

[Binder on the positive electrode side]
In the positive electrode for a secondary battery of the present invention, the amount of the binder 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 described above. It is especially preferable that it is -8 mass parts. The amount of the binder is preferably 90 parts by mass or less, more 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. Particularly preferred. 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 resistance of the entire electrode may increase. By setting the amount of the binder within the above range, the amount of the binder that can fluctuate with a change in the particle size is always suppressed to a small amount, filling the voids in the electrode with the binder and the active material and the conductive agent, etc. It becomes possible to suppress the coating of the solid content.

  The binder of the present invention preferably 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 content of the fluororesin is not particularly limited as long as it does not impair the object of the present invention, but it is preferably contained in the binder at 20% by mass or more, more preferably 50% by mass or more, It is particularly preferable that the content is 80% by mass or more.

  Examples of the fluororesin include, but are not limited to, 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 Polymers (ECTFE), copolymers based on at least one of these, vinylidene fluoride fluoropolymers, propylene / tetrafluoroethylene fluororubbers, and tetrafluoroethylene / perful Such as fluorine rubber, such as Russia alkyl vinyl ether type fluorine-containing rubber.

  Among them, preferred is a vinylidene fluoride resin, and more preferred is a vinylidene fluoride resin containing a functional group having polarity. 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. Further, the binder is preferably fibrous from the viewpoint of preventing the coating of the active material and the conductive agent.

  The functional group contained in the vinylidene fluoride resin is not limited to the following, and for example, known polar groups such as a carboxyl group, an epoxy group, and a hydroxyl group can be used. Such a fluororesin containing a polar group is a modified product of a fluororesin (hereinafter also referred to as a “modified fluororesin”), and is further bonded to an “unmodified product” that does not have such a polar group. Wearability can be improved. In the present specification, the above-mentioned “modification treatment” means introducing a functional group having polarity with respect to the polymer.

  Further, as the binder, the above-mentioned unmodified fluororesin or modified fluororesin may be used alone or both may be contained.

  As a method of the modification treatment, the modification method of the vinylidene fluoride resin is not limited to a specific method. For example, (a) a method of copolymerizing a vinylidene fluoride monomer and a monomer having a functional group; (b) a method of reacting with a modifier in a solvent that dissolves or swells the vinylidene fluoride resin; (C) There is a method of modifying treatment by irradiating with radiation and performing grafting treatment. Among these, (a) a method by copolymerizing a vinylidene fluoride monomer and a monomer having a functional group is preferable. 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 (the method described in JP-A-6-172451 (hereinafter also referred to as “Document 1”))
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, or fluoroalkyl vinyl ether. . 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. it can. Among these, aqueous suspension polymerization or emulsion polymerization is preferable from the viewpoint of ease of post-treatment and the like, 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 adopted with reference to the conditions described in Document 1.

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 (hereinafter also referred to as “Document 2”))
In this modification treatment method, a vinylidene fluoride resin and a modifier are reacted to modify the vinylidene fluoride resin. Here, the modifier is preferably at least one selected from the group consisting of a silane coupling agent having a group capable of reacting with a vinylidene fluoride resin and a hydrolyzable group and a titanate coupling agent. Can be used.

  Examples of the vinylidene fluoride resin used in this modification treatment include vinylidene fluoride homopolymers obtained by suspension polymerization, emulsion polymerization, solution polymerization, etc., or vinylidene fluoride and vinylidene fluoride having unsaturated double bonds. Examples thereof include a copolymer with a polymerizable monomer. 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. Among these, 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 preferable. 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 having an ability to potentially react with a vinylidene fluoride resin, such as an isocyanate group that reacts with moisture in the system or the atmosphere to generate an amino group, In the method of this modification | denaturation process, the same effect is brought about.

Examples of the hydrolyzable group, a methoxy group, an alkoxy group such as ethoxy group, a formyloxy group, an acetoxy group, an acyloxy group such as a propionyloxy _{group, -ON = C (CH 3)} 2 group, -ON = C (CH ₃ ) C ₂ H ₅ group oximo group and the like can be mentioned. More preferred is an alkoxy group.

  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.

  As the amount of the coupling agent, it is preferable that the mass of silicon in the silane coupling agent or titanium in the titanate coupling agent is 100 to 8000 ppm relative to the mass of the vinylidene fluoride resin. In addition, when using together a silane coupling agent and a titanate coupling agent, it is preferable to make the total amount of the silicon and titanium in both coupling agents into the said range. 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, the reaction conditions such as the reaction temperature can be appropriately adopted with reference to the reaction conditions described in Document 2.

(C) Method of modifying treatment by irradiating with radiation and performing graft treatment (method described in JP-A-2005-47275 (hereinafter also referred to as “Document 3”))
This modification treatment method is performed through the following steps (1) to (4).

  (1) Melt-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 preferably contains 2 to 20 carbon atoms. 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).

  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, or maleic anhydride Etc.

  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 Document 3.

  Among the modification treatment methods (a) to (c) described above, in particular, (a) a modification treatment method by copolymerization of a vinylidene fluoride monomer and another monomer having a polar group. Is preferred.

  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 the weight average molecular weight is 350,000 or more, it is possible to ensure a sufficient peel strength for maintaining the electrode structure. On the other hand, if the weight average molecular weight is 1,000,000 or less, it is relatively easy to adjust the viscosity of the electrode slurry, and the electrode can be easily applied. The molecular weight of the present invention is measured by GPC (Gel Permeation Chromatography).

  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.

  The binding agent of the present invention can improve the retention and output characteristics of the electrode structure without increasing the resistance of the electrode due to an increase in the amount of the binding agent in a significantly smaller amount compared to the conventional one, The capacity density can be kept high.

[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 such a carbon material, the conductivity in the electrode can be ensured even when an active material having a small particle diameter as described above is used, the resistance of the positive electrode is reduced, and the output of the secondary battery is increased. Is possible.

  Examples of the graphite include flakes and fibers, but are not limited thereto. Further, the amorphous carbon is not limited to the following, for example, carbon black, more specifically, acetylene black, ketjen black, furnace black, etc., these may be naturally derived, It may be 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. Specific examples include, but are not limited to, carbon nanofibers and carbon nanotubes.

[Current collector on the positive electrode side]
As the current collector used for the positive electrode for secondary battery of the present invention, various known materials used for non-aqueous electrolyte secondary batteries can be used. Specifically, metal foil such as aluminum foil, nickel foil, iron foil, titanium foil, stainless steel foil, or copper foil, or those obtained by subjecting the metal foil to physical surface treatment or chemical surface treatment are preferable. Can be 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.

  The thickness of the current collector is preferably 5 to 20 μm, and more preferably 10 to 15 μm.

  By using the current collector as described above, formation of a stronger mechanical bond between the current collector and the electrode layer due to the anchor effect, physical interaction between the current collector and the electrode layer, or a binder Formation of a stronger chemical bond between the current collector and the electrode layer when used can be obtained. 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.
[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 of the positive electrode for the secondary battery of the present invention is not particularly limited, and is adjusted by appropriately referring to known knowledge about secondary batteries such as lithium ion secondary batteries. sell.

  The thickness of the electrode layer on the positive electrode side is also not particularly limited, and conventionally known knowledge about secondary batteries such as lithium ion secondary batteries can be appropriately referred to. As an example, the thickness of the positive electrode layer is preferably about 10 to 100 μm, 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 obtained by a method including the following steps (1) to (3).

(1) A step of preparing a positive electrode active material slurry containing the above positive electrode active material, a conductive agent and a binder. (2) A step of applying the positive electrode active material slurry to a current collector and drying it. (3) Obtained drying The step of adjusting the porosity by pressing an object As described above, the amount of the binder is 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, and the porosity of the electrode is 30% or more 50% or less, and the pore diameter is 0.09 μm or more and 0.30 μm or less.

  The positive electrode for a secondary battery of the present invention can be produced by a conventionally known method. Specific examples thereof include a production method including the following steps (1) to (3).

(1) A step of preparing a positive electrode active material slurry by dispersing a mixture of the positive electrode active material, the conductive agent and the binder in a slurry viscosity adjusting solvent. (2) The positive electrode active material slurry on the surface of the current collector. (3) The step of adjusting the porosity by pressing the obtained dried product Among the components of the positive electrode for the secondary battery, the active material, the conductive agent and the binder are described above. Since it is the same as that described, the description 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. The application means for applying the slurry to the current collector is not particularly limited, and generally used means such as a self-propelled coater, a doctor blade method, and a spray method may be employed.

  Thereafter, the coating film formed on the surface of the current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the slurry and the volatilization rate of the slurry viscosity adjusting solvent.

  The positive electrode for a secondary battery of the present invention is characterized in that the porosity of the electrode is 30% or more and 50% or less, and the pore diameter is 0.09 μm or more and 0.30 μm or less. This porosity can be adjusted to the desired range as described above by adjusting the load and gap in the pressing stage after the positive electrode active material slurry is applied to the current collector and dried. Here, the gap refers to a gap between the electrode and the press roll.

  In addition, the positive electrode for a secondary battery of the present invention is characterized in that the pore diameter is 0.09 μm or more and 0.30 μm or less. The pore diameter can be adjusted to the desired range as described above by adjusting the particle diameter and shape of the active material, the porosity in the electrode layer, and the type and amount of the conductive auxiliary agent and binder. A person skilled in the art can confirm whether or not the desired pore diameter has been obtained by using a mercury intrusion method or the like. Therefore, by adjusting the particle diameter of the active material and the porosity in the electrode layer, a desired pore diameter can be obtained. The pore size can be controlled.

  The positive electrode for a secondary battery of the present invention can be used for a non-aqueous electrolyte secondary battery. 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.

(Battery structure)
The non-aqueous electrolyte secondary battery of the present invention is constituted by the above-described positive electrode for a secondary battery. According to the nonaqueous electrolyte secondary battery of the present embodiment, since the positive electrode for a secondary battery constituting the nonaqueous electrolyte secondary battery is excellent in output characteristics, a nonaqueous electrolyte secondary battery excellent in output characteristics is provided. Can be provided.

(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.

  Although it does not specifically limit as a negative electrode active material, For example, lithium alloys, such as carbon, metal materials, and lithium aluminum alloy, lithium tin alloy, and lithium silicon alloy, such as graphite, amorphous carbon difficulty, and non-graphitizable carbon Is mentioned. 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 active materials may be used in combination.

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

  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. Content of the said electrically conductive agent is not specifically limited, The well-known knowledge about secondary batteries, such as a lithium secondary battery, can be referred suitably.

  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 in the above embodiment, and the 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 current collector on the negative electrode side 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 negative electrode current collector is 1 to 30 μm. However, a current collector having a thickness outside this range may be used.

  Regarding the thickness of the electrode layer on the negative electrode side, conventionally known knowledge can be referred to as appropriate.

(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 active material layer electrically coupled to both surfaces of one current collector, a negative electrode having a negative electrode active material layer electrically coupled to both surfaces of another current collector, the positive electrode, and the It is a non-aqueous electrolyte secondary battery in which electrolyte layers disposed between negative electrodes are alternately stacked. The positive electrode is a positive electrode for a non-aqueous electrolyte secondary battery according to the above embodiment.

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

  The stacked battery 10 of this embodiment shown in FIG. 2 has a structure in which a substantially rectangular battery element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 22 that is an exterior.

  As shown in FIG. 2, the battery element 17 of the stacked battery 10 of the present embodiment includes a plurality of single battery layers 16. The unit cell layer 16 includes an electrolyte layer 13, a positive electrode active material layer 12 formed on one surface of the electrolyte layer 13, and a negative electrode active material layer 15 formed on the other surface of the electrolyte layer 13. The A positive electrode current collector 11 is disposed between the positive electrode active material layers 12, and a negative electrode current collector 14 is disposed between the negative electrode active material layers 15. That is, the battery element 17 includes a plurality of single battery layers 16 and a plurality of current collectors (the positive electrode current collector 11 and the negative electrode current collector 14).

  The positive electrode current collector 11 and the negative electrode current collector 14 are electrically connected to the positive electrode tab 18 and the negative electrode tab 19, respectively. The battery element 17 is sealed with a laminate sheet 22 as an exterior so that the positive electrode tab 18 and the negative electrode tab 19 are led out to the outside.

  In the stacked battery 10 shown in FIG. 2, the positive electrode active material layer 12 is slightly larger than the negative electrode active material layer 15, but is not limited to such a form. A positive electrode active material layer 13 that is the same as or slightly smaller than the negative electrode active material layer 15 may also be used.

  Hereinafter, members constituting the stacked battery 10 of the present embodiment will be briefly described. However, since the components constituting the electrode are as described above, the description thereof is omitted here. Further, the technical scope of the present invention is not limited to the following forms, and conventionally known forms can be similarly adopted.

[Electrolyte layer]
The electrolyte layer 13 is a layer containing an electrolyte. The electrolyte (specifically, lithium salt) contained in the electrolyte layer 13 has a function as a carrier of lithium ions that moves between the positive and negative electrodes during charge and discharge. The electrolyte 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 a supporting salt (lithium salt), it is added to an active material layer of an electrode such as Li (C ₂ F ₅ SO ₂ ) ₂ N, LiBETI, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _3. Compounds that can be used can be employed as well.

  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. Examples thereof include polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), hexafluoropyrene (HFP) polymer, PAN, PMMA, and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved. Moreover, as 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 13 is composed of a liquid electrolyte or a gel polymer electrolyte, a separator may be used for the electrolyte layer 13. 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 13 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.

[tab]
In the laminated battery 10, the tab (positive electrode tab 18 and negative electrode tab 19) electrically connected to the outermost positive electrode current collector (11a) is used for taking out current outside the battery. Take out to the outside. Specifically, the positive electrode tab 18 electrically connected to the positive electrode current collector 11 and the negative electrode tab 19 electrically connected to the negative electrode current collector 14 are taken out of the exterior.

  The material which comprises a tab (the positive electrode tab 18 and the negative electrode tab 19) is not restrict | limited in particular, The well-known material conventionally used as a tab for laminated batteries can be used. Examples of the constituent material of the tab include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. Note that the positive electrode tab 18 and the negative electrode tab 19 may be made of the same material or different materials. Further, as in the present embodiment, separately prepared tabs (18, 19) may be connected to the current collector (11, 14), or the current collector may be extended to form a tab.

[Exterior]
In the laminated battery 10, the battery element 17 is preferably housed in an exterior such as a laminate sheet 22 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. Is preferably used. In the present invention, “aluminum laminate” refers to a laminate containing aluminum. Use of an aluminum laminate outer package makes it possible to further improve the durability of the nonaqueous electrolyte secondary battery of the present invention. The reason for this is that the laminate cell has a structure that cannot hold the contact between the electrode and the foil because structural pressure is applied like a metal cylindrical or square cell. This is because is considered to be more important. Specific examples of the aluminum laminate include, for example, a laminate film having a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order, but are not limited thereto.

  According to the laminated battery 10 shown in FIG. 2, since the positive electrode for secondary batteries of the present invention is employed, a nonaqueous electrolyte secondary battery having excellent output characteristics can be provided.

  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 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.

(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 active material electrically coupled to one surface of the current collector, a negative electrode having a negative electrode active material electrically coupled to the other surface of the current collector, and the positive electrode and the negative electrode It is a non-aqueous electrolyte secondary battery in which the arranged electrolyte layers are alternately stacked. The positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery of the present invention described above. By adopting 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.

  For reference, FIG. 3 is a cross-sectional view showing an outline of a bipolar nonaqueous electrolyte secondary battery 30.

(Battery)
A plurality of the secondary batteries of the present invention may be connected in parallel and / or in series to form an assembled battery.

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

  As shown in FIG. 3, the assembled battery 300 is configured by connecting a plurality of the stacked batteries 10 described in the above embodiment. Each stacked battery 10 is connected by connecting the positive electrode tab 18 and the negative electrode tab 19 of each stacked battery 10 using a bus bar. On one side surface of the assembled battery 300, electrode terminals (320 and 330) are provided as electrodes of the entire assembled battery 300.

  The connection method when connecting the plurality of stacked batteries 10 constituting the assembled battery 300 is not particularly limited, and a conventionally known method can be appropriately employed. For example, a technique using welding such as ultrasonic welding or spot welding, or a technique of fixing using rivets, caulking, or the like can be employed. According to such a connection method, the long-term reliability of the assembled battery 300 can be improved.

  According to the assembled battery 300 of the present invention, since the individual stacked batteries 10 constituting the assembled battery 300 are excellent in output characteristics, an assembled battery excellent in output characteristics can be provided.

  The connection of the stacked batteries 10 constituting the assembled battery 300 may be all connected in parallel, all may be connected in series, and a combination of series connection and parallel connection is also possible. May be. As a result, the capacity and voltage can be freely adjusted.

(vehicle)
The battery of the present invention can be mounted on a vehicle using the above-described stacked battery 10 or the assembled battery 300 as a motor driving power source. Examples of the vehicle using the stacked battery 10 or the assembled battery 300 as a motor power source include an automobile whose wheels are driven by a motor, and other vehicles (for example, a train). Examples of the automobile include a complete electric car that does not use gasoline, a hybrid automobile such as a series hybrid automobile and a parallel hybrid automobile, and a fuel cell automobile. 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 equipped with an assembled battery. The assembled battery 300 mounted on the automobile 400 has the characteristics as described above. For this reason, the automobile 400 equipped with the assembled battery 300 is excellent in output characteristics, and has a long life and high reliability.

  The preferred embodiments of the present invention have been described above, but 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. The average particle diameter and electrode density of the active material were measured by the methods described below.

(Measurement of average particle size)
Method: The cumulative 50% particle diameter (D50) was measured by the laser diffraction scattering method.

Device: Nikkiso Co., Ltd. Microtrack X-100
(Measurement of electrode density)
Method: The electrode was cut into a disk having a diameter of 16 mm, and the mass and thickness of the cut electrode and current collector were measured. The electrode density was calculated from the measured mass and thickness values using the relational expression (2). A precision balance (measuring ability of about 0.01 mg) was used for measuring the mass, and a constant-pressure film thickness meter (measuring ability of several μm) was used for measuring the thickness. This data was collected three times, and the average value was taken as the electrode density.

[Example 1]
(Preparation of positive electrode)
As the positive electrode active material, lithium manganate having an average particle diameter D50 of 2.0 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 in an amount of 7.1 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.

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 prepare a positive electrode having a thickness of 61 μm. The electrode density after pressing was 2.10 g / cm ³ and the porosity was 42.9%.

(Preparation 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 binder was used in an amount of 12 parts by mass with respect to 100 parts by mass of the active material and 200 parts by mass with respect to 100 parts by mass of the conductive agent.

  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 produced 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 to produce an evaluation battery element. The nickel tab lead was connected to the negative electrode, and the aluminum tab lead was connected to the positive electrode 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]
The same as in Example 1 except that the thickness after pressing was changed to 59 μm, the electrode density was set to 2.57 g / cm ³ , and the porosity was set to 34.7% by changing the pressing conditions at the time of producing the positive electrode. An evaluation cell was produced.

[Example 3]
Lithium manganate having an average particle diameter D50 of 1.5 μm was used as the positive electrode active material, and a polyvinylidene fluoride carboxylic acid modified product having a weight average molecular weight of 350,000 was used as the positive electrode binder. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was set to 33.5% by changing the pressing conditions when producing the 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.

[Example 4]
Lithium manganate having an average particle diameter D50 of 1.5 μm was used as the positive electrode active material, and an unmodified polyvinylidene fluoride having a weight average molecular weight of 500,000 was used as the positive electrode binder. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was set to 33.5% by changing the pressing conditions when producing the 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.

[Example 5]
As the positive electrode binder, an unmodified polyvinylidene fluoride product having a weight average molecular weight of 700,000 was used. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was set to 33.5% by changing the pressing conditions when producing the positive electrode. An evaluation cell was produced in the same manner as in Example 4 except that the positive electrode was produced as described above.

[Example 6]
A polyvinylidene fluoride unmodified product having a weight average molecular weight of 1,000,000 was used as a binder for the positive electrode. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was changed to 31.9% by changing the pressing conditions at the time of producing the positive electrode. An evaluation cell was produced in the same manner as in Example 4 except that the positive electrode was produced as described above.

[Example 7]
A polyvinylidene fluoride-modified carboxylic acid modified product having a weight average molecular weight of 500,000 was used as a binder for the positive electrode. The amount of the binder was 4.65 parts by mass with respect to 100 parts by mass of the active material and 40 parts by mass with respect to 100 parts by mass of the conductive agent. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was set to 31.5% by changing the pressing conditions when producing the positive electrode. An evaluation cell was produced in the same manner as in Example 4 except that the positive electrode was produced as described above.

[Example 8]
As the positive electrode active material, lithium manganate having an average particle diameter D50 of 7.0 μm was used. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was set to 30.3% by changing the pressing conditions when producing the 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.

[Example 9]
As the positive electrode active material, lithium manganate having an average particle diameter D50 of 10.0 μm was used. The electrode density after pressing was changed to 2.60 g / cm ³ and the porosity was changed to 31.9% by changing the pressing conditions at the time of producing the 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 1]
As the positive electrode active material, lithium manganate having an average particle diameter D50 of 2.0 μm was used. 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 12.5 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. The electrode density after pressing was 2.58 g / cm ³ , and the porosity was 31.8%. 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 produced in the same manner as in Comparative Example 1 except that the electrode density after pressing was 2.07 g / cm ³ and the porosity was 39.3% during the production of the positive electrode.

[Comparative Example 3]
An evaluation cell was produced in the same manner as in Comparative Example 1 except that the electrode density after pressing was 2.87 g / cm ³ and the porosity was 25.0% when the positive electrode was produced.

[Comparative Example 4]
An evaluation cell was produced in the same manner as in Example 1 except that the electrode density after pressing was 1.50 g / cm ³ and the porosity was 56.2% when the positive electrode was produced.

(Evaluation)
(Measurement of porosity and pore diameter)
With respect to the positive electrode produced above, the pore distribution and the volume of pores existing in the electrode layer (volume of voids) were measured in the range of φ10 to 0.003 μm by mercury porosimetry (Evaluation apparatus: Autopore, manufactured by Shimadzu Corporation). IV 9510 type, measurement pore size range: about φ420 μm to 3 nm). And the ratio of the volume of the space | gap with respect to the volume of the whole electrode layer was computed as a porosity. The measurement results are shown in Table 1. In addition, the pore diameter in a table | surface represents the diameter (median diameter) of a pore. For reference, a pore distribution diagram obtained by pore distribution measurement for the positive electrode prepared in Example 1 is shown in FIG.

(Measurement of IV resistance)
Using the evaluation cell described above, 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 3 C, and a discharge time of 10 seconds (evaluation apparatus: HJ-1001SM8, manufactured by Hokuto Denko Corporation).

  The evaluation results of IV resistance for each evaluation cell are shown in Table 1 below. It shows that electrical resistance is reduced, so that IV resistance is low.

(Measurement of rate characteristics)
For the evaluation cell produced above, the ratio of the discharge capacity at the discharge rate 20C and the discharge capacity at the discharge rate 1C (discharge capacity at 20C / 1 discharge capacity at 1C) was determined as a rate characteristic. The results are shown in Table 1.

(Rate increase rate)
The IV resistance value after each of the evaluation cells prepared above and subjected to a series of tests was stored at 55 ° C. for 3 months was measured. And the increase rate (resistance increase rate) of the resistance value with respect to the initial IV resistance value was calculated | required. A lower resistance increase rate means that the durability of the battery is improved. The evaluation results of the IV resistance value and the resistance increase rate after storage for 3 months for each evaluation cell are shown in Table 1 below.

  From Table 1, when the positive electrode of Examples 1 to 9 in which the amount of the binder, the porosity, and the pore diameter are in the desired ranges of the present invention are used, at least one of these is a comparative example that deviates from the desired range of the present invention. It was found that the electrical resistance in the electrode and the rate of increase in resistance were suppressed as compared with the case where 1-4 positive electrodes were used.

  When the positive electrodes of Comparative Examples 1 to 3 in which the amount of the binder exceeded 10 parts by mass with respect to 100 parts by mass of the positive electrode active material, the electric resistance and the resistance increase rate in the electrode were increased. In Comparative Examples 1 to 3, it was considered that the resistance increased due to the covering of the active material or the like with the binder and the filling of the voids.

  When the positive electrode of Comparative Example 3 having a porosity of less than 30% and a pore diameter exceeding 0.30 μm was used, the electrical resistance in the electrode and the rate of increase in resistance were large. In Comparative Example 3, it is considered that the diffusion of lithium ions was inhibited and the resistance of the electrode was increased.

  Further, in the positive electrode having a porosity exceeding 50%, it is considered that the resistance is increased because the conductive path is weak. When the positive electrode of Comparative Example 4 having a porosity exceeding 50% was used, the IV resistance and the resistance increase rate were very large values. In the positive electrode having a porosity of more than 50%, the resistance is considered to be increased because the conductive path is weak.

  On the other hand, the positive electrodes of Examples 1 to 9 show that a strong conductive path is ensured, inhibition of lithium ion diffusion can be suppressed, and resistance in the electrode is reduced.

  Further, the comparison between Examples 1 to 9 and Comparative Examples 1 to 4 shows that the rate characteristics can be generally improved by using the secondary battery positive electrode of the present invention.

  From the above, when the porosity is 30 to 50%, the pore diameter is 0.09 to 0.30 μm, and the amount of the binder is 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, It was found that the IV resistance and the rate of increase in resistance can be adjusted to a desired relationship while maintaining high binding properties.

  As described above, according to the positive electrode for a secondary battery of the present invention, the binding property in the electrode layer can be improved and the electric resistance can be reduced. Furthermore, by using an active material with a smaller average particle size and a smaller amount of a binder, and ensuring voids that allow good diffusion of lithium ions, higher binding properties, capacity density and durability than before are achieved. 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 the laminated battery by one Embodiment of this invention. It is sectional drawing which shows the bipolar battery by one Embodiment of this invention. It is a perspective view showing an assembled battery obtained by connecting a plurality of stacked batteries according to an embodiment of the present invention. It is the schematic of the motor vehicle carrying the assembled battery by one Embodiment of this invention. It is a hole diameter distribution map about the positive electrode of Example 1 obtained by the pore distribution measurement by the mercury intrusion method.

Explanation of symbols

1 current collector,
2 electrode layers,
3 positive electrode active material,
4 Conductive agent,
5 binders,
6 gaps,
10 stacked battery,
11 positive electrode current collector,
11a Outermost layer positive electrode current collector,
12, 32 positive electrode active material layer,
13, 35 electrolyte layer,
14 negative electrode current collector,
15, 33 negative electrode active material layer,
16, 36 cell layer,
17, 37 battery element,
18, 38 Positive electrode tab (terminal),
19, 39 Negative electrode tab (terminal),
20, 40 Positive terminal lead,
21, 41 Negative terminal lead,
22, 42 Laminate sheet,
30 Bipolar battery,
31 current collector,
31a The outermost layer current collector on the positive electrode side,
31b The outermost layer current collector on the negative electrode side,
34 Bipolar electrode,
34a, 34b The electrode located in the outermost layer,
43 Insulating layer,
300 battery packs,
320, 330 electrode terminal,
400 cars.

Claims (8)

A positive electrode for a secondary battery comprising a positive electrode active material, a conductive agent, and a binder,
The amount of the binder is 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material,
The porosity of the electrode is 30% or more and 50% or less,
A positive electrode for a secondary battery having a pore diameter of 0.09 μm or more and 0.30 μm or less. The positive electrode for a secondary battery according to claim 1, wherein the conductive agent does not include a fibrous conductive agent. Containing fluoroplastics that the binder is denatured treated as the main component, a positive electrode for a secondary battery according to claim 1 or 2. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein the binder is a fluororesin having a weight average molecular weight of 350,000 to 1,000,000. The positive active material is lithium manganese oxide, lithium nickel oxide, lithium cobalt oxide is at least one selected from the group consisting of lithium manganese nickel cobalt oxide, and olivine-type iron phosphate, claim 1 any one of the 4 The positive electrode for secondary batteries as described in the paragraph. The conductive agent contains at least one carbon material selected from graphite, and amorphous carbon hydride Ranaru group, a positive electrode for a secondary battery according to any one of claims 1-5. A step of preparing a positive electrode active material slurry containing a positive electrode active material, a conductive agent and a binder, a step of applying and drying the positive electrode active material slurry on a current collector, and an electrode by pressing the obtained dried product The positive electrode for secondary batteries as described in any one of Claims 1-6 which can be obtained by the method including the step of adjusting a density. Rechargeable battery composed of a positive electrode, a nonaqueous electrolyte secondary battery according to any one of claims 1-7.

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