JP2017182989A - Positive electrode mixture slurry, positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a novel and improved positive electrode mixture slurry which makes possible to suppress the occurrence of migration and therefore, to enhance the characteristics of a nonaqueous electrolyte secondary battery; a positive electrode for a nonaqueous electrolyte secondary battery; and a nonaqueous electrolyte secondary battery.SOLUTION: To solve the above problem, a positive electrode mixture slurry is provided according to an aspect of the present invention. The positive electrode mixture slurry comprises: a solvent; a composite positive electrode active material including a positive electrode active material and a first binder covering the surface of the positive electrode active material and insoluble in the solvent; a fibrous carbon material of 40 nm or less in average fiber diameter and 500 or more in average aspect ratio; and a second binder soluble in the solvent. In the positive electrode mixture slurry, the percentage of a mass of the first binder is 0.2-1.5 mass% to a total mass of the composite positive electrode active material; the percentage of a mass of the fibrous carbon material is 0.01-0.5 mass% to a total mass of all of solid contents; and the percentage of a mass of the second binder is 0.1-0.5 mass% to the total mass of all the solid contents; and b/a is 5.0 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode mixture slurry, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

  In recent years, with the miniaturization of information processing apparatuses such as mobile phones and notebook personal computers (note PCs), there has been a demand for higher energy density of nonaqueous electrolyte secondary batteries used as power sources for these information processing apparatuses. As a technique for increasing the energy density of the nonaqueous electrolyte secondary battery, it has been proposed to increase the thickness of the positive electrode active material layer.

  Here, the positive electrode active material layer is generally manufactured by the following steps. That is, the coating layer is formed on the current collector by coating the positive electrode mixture slurry on the positive electrode current collector. Here, the positive electrode mixture slurry includes at least a positive electrode active material, a binder, and a solvent. Next, the solvent is removed from the coating layer by drying the coating layer. Through the above steps, a positive electrode active material layer is formed on the positive electrode current collector. The positive electrode current collector and the positive electrode active material layer constitute the positive electrode of the nonaqueous electrolyte secondary battery. Here, in order to increase the thickness of the positive electrode active material layer, it is necessary to increase the thickness of the coating layer described above.

Patent No. 5382120 Japanese Patent No. 5733314

  However, when the coating layer is thickened, there is a problem that a phenomenon that the binder moves to the surface of the coating layer when the coating layer is dried, that is, so-called migration is likely to occur. And when many binders move to the surface of the coating layer, the binder is unevenly distributed on the surface of the positive electrode active material layer. When the binder is unevenly distributed on the surface of the positive electrode active material layer, the flexibility of the positive electrode active material layer may be reduced. When the flexibility of the positive electrode active material layer is lowered, problems such as breakage of the positive electrode current collector may occur during the production of the winding element. Here, the winding element is an element in which a positive electrode, a negative electrode, and a separator are wound. Furthermore, since the amount of the binder at the interface between the positive electrode current collector and the positive electrode active material layer is reduced, there is a possibility that the adhesiveness thereof is also reduced. Further, the ion permeability on the surface of the positive electrode active material layer may be reduced, and the high rate discharge characteristics and the capacity retention rate may be reduced. When binder migration occurs, all of these phenomena may occur, but only one of them may occur.

  As a method for solving the above problem, it is conceivable to reduce the amount of binder in the positive electrode mixture slurry. However, simply reducing the amount of binder in the positive electrode mixture slurry not only results in insufficient binding force between the positive electrode active materials and between the positive electrode active material and the positive electrode current collector, but also decreases the viscosity of the positive electrode mixture slurry. End up. When the viscosity of the positive electrode mixture slurry is lowered, there is a problem that the positive electrode active material is likely to settle in the coating layer. And when many positive electrode active materials settle, the positive electrode active material density of the surface of a positive electrode active material layer will fall. Even when the density of the positive electrode active material on the surface of the positive electrode active material layer is lowered, there is a possibility that the high rate discharge characteristics and the capacity retention rate are lowered. Therefore, simply reducing the amount of the binder in the positive electrode mixture slurry cannot solve the migration problem.

  By the way, Patent Documents 1 and 2 disclose techniques relating to a binder of a positive electrode active material layer. In the technique disclosed in Patent Document 1, polyvinylidene fluoride (PVdF) or a copolymer containing vinylidene fluoride is used as a binder for the positive electrode active material layer. Furthermore, the positive electrode active material layer contains fluorine rubber particles. In the technique disclosed in Patent Document 2, a binder containing tetrafluoroethylene (TFE) and propylene (P) as monomers is used. However, none of the techniques can solve the migration problem.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress the occurrence of migration and thus improve the characteristics of the nonaqueous electrolyte secondary battery. An object of the present invention is to provide a novel and improved positive electrode mixture slurry, a positive electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery.

In order to solve the above problems, according to an aspect of the present invention, a composite positive electrode active material comprising a solvent, a positive electrode active material, and a first binder that covers the surface of the positive electrode active material and is insoluble in the solvent; A fibrous carbon material having an average fiber diameter of 40 nm or less and an average aspect ratio of 500 or more, and a second binder soluble in a solvent, the first binder having a total mass of the composite positive electrode active material The mass% is 0.2 to 1.5 mass%, and the mass% of the fibrous carbon material with respect to the total mass of the total solid content is 0.01 to 0.5 mass%. 2% by mass of the binder is 0.1 to 0.5% by mass, the specific surface area of the positive electrode active material is a (m ² / g), and the mass% of the first binder with respect to the total mass of the composite positive electrode active material. Is b (mass%), b / a is 5.0 or less. The positive electrode mixture slurry is provided.

  As described above, the mass% of the second binder is 0.1 to 0.5 mass% with respect to the total mass of the total solid content of the positive electrode mixture slurry. Therefore, most of all the binders in the positive electrode mixture slurry become the first binder. That is, in this aspect, the first binder is mainly used, and the second binder functions as the second binder (specifically, the function as a viscosity stabilizer of the positive electrode mixture slurry, and the positive electrode active). It is used only to the minimum necessary to develop the function of binding the material layer to the positive electrode current collector. The first binder is insoluble in the solvent and is compounded on the surface of the positive electrode active material.

  Therefore, the first binder is difficult to migrate when the coating layer is dried. The second binder may migrate when the coating layer is dried, but the content of the second binder itself is very low. Furthermore, the positive electrode mixture slurry includes a fibrous carbon material that functions as a viscosity stabilizer and a second binder. Therefore, the positive electrode active material is unlikely to settle in the coating layer. That is, the positive electrode active material can be more uniformly distributed in the positive electrode active material layer. Therefore, according to this aspect, it is possible to increase the thickness of the positive electrode active material layer while suppressing the occurrence of migration. Furthermore, the positive electrode active material can be more uniformly distributed in the positive electrode active material layer. Furthermore, since the flexibility of the positive electrode active material layer can be ensured, breakage of the positive electrode current collector during winding can be suppressed. Therefore, according to this aspect, it is possible to improve the characteristics of the nonaqueous electrolyte secondary battery, specifically, the high rate discharge characteristics and the capacity retention rate.

  Further, the first binder may be a copolymer containing tetrafluoroethylene (TFE).

  According to this aspect, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

  The first binder is a tetrafluoroethylene-propylene copolymer (P (TFE / P)) and a vinylidene fluoride-tetrafluoroethylene copolymer (P) containing a tetrafluoroethylene component in a proportion of 50 mol% or more. (VdF / TFE)) may be selected from any one or more selected from the group consisting of.

  According to this aspect, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

  The second binder is composed of polyvinylidene fluoride (PVdF), modified polyvinylidene fluoride, modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and a ratio of tetrafluoroethylene component of less than 50 mol%. Vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)) and a modified vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE) containing a tetrafluoroethylene component in a proportion of less than 50 mol%. )), Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (P (VdF / HFP / TFE)), modified vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, hydrogenated acrylonitrile butadiene copolymer Combined (hydrogenated N R), acrylate-vinylidene fluoride copolymer (P (Acrylate / VdF)), acrylate-vinylidene fluoride-hexafluoropropylene copolymer (P (Acrylate / VdF / HFP)), acrylate-vinylidene fluoride-tetra Selected from the group consisting of a fluoroethylene copolymer (P (Acrylate / VdF / TFE)) and an acrylate-vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (P (Acrylate / VdF / HFP / TFE)) copolymer Any one or more of these may be used.

  According to this aspect, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

  In addition, the second binder is a modified fluorine containing polyvinylidene fluoride (PVdF), a modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and a tetrafluoroethylene component in a proportion of less than 50 mol%. It may be composed of any one or more selected from the group consisting of vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)).

  According to this aspect, even if the amount of the second binder is small, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

  The positive electrode active material may be a lithium-containing transition metal oxide.

  According to this aspect, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

  The solvent may be N-methylpyrrolidone (NMP).

  According to this aspect, it is possible to further improve the characteristics of the nonaqueous electrolyte secondary battery.

According to another aspect of the present invention, a positive electrode active material, a first binder insoluble in the solvent of the positive electrode mixture slurry, a fibrous carbon material having an average fiber diameter of 40 nm or less and an average aspect ratio of 500 or more, And a second binder insoluble in the solvent of the positive electrode mixture slurry, and the mass% of the first binder with respect to the total mass of the positive electrode active material and the first binder is 0.2 to 1.5 mass%. The mass% of the fibrous carbon material with respect to the total mass of the total solid content is 0.01 to 0.5 mass%, and the mass% of the second binder with respect to the total mass of the total solid content is 0.1 to 0.5. When the specific surface area of the positive electrode active material is a (m ² / g), and the mass% of the first binder with respect to the total mass of the positive electrode active material and the first binder is b (mass%), b / A is 5.0 or less, for non-aqueous electrolyte secondary battery Poles are provided.

  In the positive electrode of this aspect, the occurrence of migration is suppressed. Furthermore, the positive electrode active material is more uniformly distributed in the positive electrode. Furthermore, the flexibility of the positive electrode is ensured. Therefore, the characteristics of the nonaqueous electrolyte secondary battery using this positive electrode are further improved.

  According to another aspect of the present invention, there is provided a nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery according to this aspect has excellent characteristics.

  As described above, according to the present invention, it is possible to suppress the occurrence of migration and thus improve the characteristics of the nonaqueous electrolyte secondary battery.

It is a plane sectional view showing a schematic structure of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. It is a scanning electron microscope (SEM) photograph which shows an example of a composite positive electrode active material. It is a scanning electron microscope (SEM) photograph which shows an example of the positive electrode active material not covered with the 1st binder.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Structure of positive electrode mixture slurry>
First, the configuration of the positive electrode mixture slurry according to the present embodiment will be described. The positive electrode mixture slurry is used for producing a positive electrode active material layer of a nonaqueous electrolyte secondary battery. The positive electrode mixture slurry includes a solvent, a composite positive electrode active material, a fibrous carbon material, and a second binder.

(1-1. Solvent)
The solvent should just be a solvent used for the conventional positive mix slurry, for example, N-methylpyrrolidone.

(1-2. Composite cathode active material)
The composite positive electrode active material includes a positive electrode active material and a first binder that covers the surface of the positive electrode active material. The positive electrode active material is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions. For example, lithium-containing transition metal oxide, nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide Etc. Examples of the lithium-containing transition metal oxide include lithium cobalt oxide (LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobaltaluminate (hereinafter sometimes referred to as “NCA”), nickel cobalt manganate. Examples thereof include lithium (hereinafter sometimes referred to as “NCM”), lithium manganate, lithium iron phosphate, and the like. These positive electrode active materials may be used independently and 2 or more types may be used together.

  Of the examples listed above, the positive electrode active material is preferably a lithium-containing transition metal oxide, and particularly preferably a lithium salt of a transition metal oxide having a layered rock salt structure.

  Moreover, in order to suppress a side reaction with the electrolyte solution at the time of a high voltage, the positive electrode active material may be obtained by subjecting each of the above materials to a surface treatment. The average agglomerated particle size of the positive electrode active material is desirably 10 to 30 μm from the viewpoint of safety and filling properties of the positive electrode active material. The average agglomerated particle size of the positive electrode active material is a 50% volume integrated value (D50 value) of the distribution of diameters when the secondary particles in which the primary particles of the positive electrode active material are agglomerated are considered as spheres. laser) It can be measured by diffraction / scattering method.

  The first binder is a binder that binds the positive electrode active material layer to the positive electrode current collector. Furthermore, the first binder is insoluble in the solvent. That is, in this embodiment, the surface of the positive electrode active material is covered with the first binder that is insoluble in the solvent. Here, in the present embodiment, it is determined whether or not the first binder is dissolved in the solvent based on the solubility in the solvent. Specifically, when the first binder is added to the solvent and the solubility at this time is less than 1% by mass, it is determined that the first binder is insoluble in the solvent. Here, the solubility is defined as the concentration of the first binder, that is, mass% with respect to the total mass of the solution of the first binder dissolved in the solvent. For example, when a tetrafluoroethylene-propylene copolymer is used as the first binder and NMP is used as the solvent, the solubility is 0% by mass. Moreover, the mass% of the first binder with respect to the total mass of the composite positive electrode active material is 0.2 to 1.5 mass%. When the mass% of the first binder is less than 0.2 mass%, the first binder is too small to sufficiently secure the adhesion between the positive electrode current collector and the positive electrode active material layer. On the other hand, when the mass% of the first binder exceeds 1.5 mass%, the first binder is too much, and the high rate discharge characteristics and the capacity maintenance rate of the nonaqueous electrolyte secondary battery are reduced.

Furthermore, when the specific surface area of the positive electrode active material is a (m ² / g) and the mass% of the first binder with respect to the total mass of the composite positive electrode active material is b (mass%), b / a is 5.0. It becomes as follows. As shown in the examples described later, when b / a is 5.0 or less, the characteristics of the nonaqueous electrolyte secondary battery are improved. When b / a exceeds 5.0, since the mass of the first binder with respect to the positive electrode active material is too large, the high rate discharge characteristics and capacity retention rate of the nonaqueous electrolyte secondary battery may be lowered. In addition, even if there is too little 1st binder with respect to a specific surface area, since the characteristic of a nonaqueous electrolyte secondary battery may fall similarly, it is preferable that b / a is 0.8 or more. b / a is more preferably 0.9 to 4.1. Here, the specific surface area of the positive electrode active material is a so-called BET specific surface area and can be measured by a gas adsorption method or the like.

  Specifically, the first binder is preferably a copolymer containing tetrafluoroethylene (TFE). The first binder is a tetrafluoroethylene-propylene copolymer (P (TFE / P)) and a vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF) containing a tetrafluoroethylene component in a proportion of 50 mol% or more. / TFE)) is more preferably selected from one or more selected from the group consisting of: In this case, the flexibility, oxidation resistance, and electrochemical stability of the first binder are improved. That is, since the flexibility of the positive electrode active material layer is improved, the positive electrode current collector is hardly broken when the positive electrode is wound. Furthermore, the high rate discharge characteristics and capacity retention rate of the nonaqueous electrolyte secondary battery are improved.

  It can be confirmed by SEM or the like that the first binder covers the surface of the positive electrode active material (that is, is composited on the surface). FIG. 2 shows an SEM photograph of the composite positive electrode active material, and FIG. 3 shows an SEM photograph of the non-composited positive electrode active material.

  The composite positive electrode active material can be produced, for example, by a wet method using a rolling fluid coating apparatus. Specifically, first, an aqueous dispersion of a first binder (so-called emulsion) is sprayed on the positive electrode active material. Thereby, an aqueous dispersion adheres to the surface of a positive electrode active material. Next, the positive electrode active material with the aqueous dispersion adhered to the surface is dried. The composite positive electrode active material is produced through the above steps. The mass of the first binder compounded into the positive electrode active material by subtracting the mass of the positive electrode active material before compounding (that is, before spraying the aqueous dispersion) from the mass of the composite cathode active material after drying. Can be requested.

  In addition, the first binder is produced, for example, by emulsion polymerization of a monomer constituting the first binder. The result of the emulsion polymerization is an aqueous dispersion of the first binder. Therefore, this aqueous dispersion may be used as it is for producing a composite positive electrode active material. The first binder may be produced by suspension polymerization of a monomer constituting the first binder.

(1-3. Fibrous carbon material)
The fibrous carbon material functions as a conductive additive in the positive electrode active material layer. Therefore, the fibrous carbon material has conductivity. Furthermore, the fibrous carbon material also functions as a viscosity stabilizer for the positive electrode mixture slurry. That is, the fibrous carbon material can make the composite positive electrode active material difficult to settle in the coating layer by increasing the viscosity of the coating layer to some extent. In other words, the fibrous carbon material can distribute the composite positive electrode active material more uniformly in the coating layer. Here, the average fiber diameter of the fibrous carbon material is 40 nm or less, and the average aspect ratio (fiber length / fiber diameter) is 500 or more. When the size of the fibrous carbon material satisfies these conditions, the fibrous carbon material can sufficiently exhibit the above-described functions. The fiber diameter, fiber length, and aspect ratio of the fibrous carbon material can be measured by observing the fibrous carbon with an SEM or the like. These average values are arithmetic average values of the fiber diameter, fiber length, and aspect ratio of a plurality of fibrous carbons, for example. In addition, it is preferable that an average fiber diameter is 1.4 nm or more, and it is more preferable that it is 2-10 nm. The average fiber diameter is preferably as small as possible within the above range. The average aspect ratio is preferably 100,000 or less. Specific examples of the fibrous carbon material include carbon nanotubes and carbon nanofibers. The average fiber length is not particularly limited, but is preferably 1 μm or more.

  Furthermore, the mass% of the fibrous carbon material with respect to the total mass of the total solid content of the positive electrode mixture slurry is 0.01 to 0.5 mass%. When the mass% of the fibrous carbon material is less than 0.01 mass%, the fibrous carbon material cannot sufficiently exhibit the functions as a conductive additive and a viscosity stabilizer. On the other hand, if the mass% of the fibrous carbon material exceeds 0.5 mass%, the high-rate discharge characteristics and capacity maintenance rate of the non-aqueous electrolyte secondary battery will be reduced because it will hinder the smooth movement of ions. descend. In addition, there is a possibility that sufficient adhesion between the positive electrode active material layer and the positive electrode current collector cannot be ensured. Here, when the positive electrode mixture slurry is composed of a solvent, a composite positive electrode active material, a fibrous carbon material, and a second binder, the total solid content of the positive electrode mixture slurry is a composite positive electrode active material, a fibrous material. It becomes a carbon material and a second binder.

  In addition, the positive electrode mixture slurry may contain a conductive additive other than the fibrous carbon material. Other conductive aids are, for example, carbon black such as Ketjen black and acetylene black, natural graphite, artificial graphite, graphene, etc., but may be used to increase the conductivity of the positive electrode. There is no particular limitation. The mass% of the other conductive auxiliary agent with respect to the total mass of the total solid content of the positive electrode mixture slurry is not particularly limited as long as it does not impair the effect of the present embodiment, but for example, 0 mass% or more and 1.5 mass% or less. It may be. Other conductive aids can function alone as viscosity stabilizers, but in order for other conductive aids to function sufficiently as viscosity stabilizers, more other conductive aids can be combined with the positive electrode. It is necessary to put it in the agent slurry. For this reason, even if the viscosity of the positive electrode mixture slurry is stabilized, other functions (for example, adhesion between the positive electrode active material layer and the positive electrode current collector, etc.) deteriorate. Therefore, a fibrous carbon material is necessary even when other conductive aids are used.

(1-4. Second binder)
The second binder is a binder that is soluble in a solvent. The second binder binds the positive electrode active material layer to the positive electrode current collector. Furthermore, the second binder also functions as a viscosity stabilizer for the positive electrode mixture slurry, similarly to the fibrous carbon material. The mass% of the second binder with respect to the total mass of the total solid content of the positive electrode mixture slurry is 0.1 to 0.5 mass%. When the mass% of the second binder is less than 0.1 mass%, the second binder cannot sufficiently bind the positive electrode active material layer to the positive electrode current collector. Furthermore, the second binder does not function sufficiently as a viscosity stabilizer. On the other hand, when the mass% of the second binder exceeds 0.5 mass%, the influence of the migration of the second binder becomes large. That is, the flexibility of the positive electrode active material layer may be reduced due to the migration of the second binder. Furthermore, the adhesion between the positive electrode current collector and the positive electrode active material layer may be reduced. Furthermore, there is a possibility that the high rate discharge characteristics and the capacity maintenance rate of the nonaqueous electrolyte secondary battery are lowered.

Specifically, the second binder contains 50 mol% of polyvinylidene fluoride (PVdF), modified polyvinylidene fluoride, modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and tetrafluoroethylene component. Vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)) containing less than 50%, and a modified vinylidene fluoride-tetrafluoroethylene copolymer containing less than 50 mol% of tetrafluoroethylene component (P ( VdF / TFE)), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (P (VdF / HFP / TFE)), modified vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, hydrogenated acrylonitrile Butadiene copolymer (H NBR), acrylate-vinylidene fluoride copolymer (P (Acrylate / VdF)), acrylate-vinylidene fluoride-hexafluoropropylene copolymer (P (Acrylate / VdF / HFP)), acrylate-vinylidene fluoride-tetra Selected from the group consisting of a fluoroethylene copolymer (P (Acrylate / VdF / TFE)) and an acrylate-vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (P (Acrylate / VdF / HFP / TFE)) copolymer It is preferable that it is comprised by any 1 type or more.

  Moreover, from the viewpoint that a large binding property can be expressed with a small amount, the second binder is made of polyvinylidene fluoride (PVdF), modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and tetra More preferably, it is composed of at least one selected from the group consisting of a modified vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)) containing a fluoroethylene component in a proportion of less than 50 mol%.

  As described above, the mass% of the second binder is 0.1 to 0.5 mass% with respect to the total mass of the total solid content of the positive electrode mixture slurry. Therefore, most of all the binders in the positive electrode mixture slurry become the first binder. That is, in the present embodiment, the first binder is mainly used, and the second binder is used only as much as necessary for the second binder to exhibit the above-described functions. The first binder is insoluble in the solvent and is compounded on the surface of the positive electrode active material. Therefore, the first binder is difficult to migrate when the coating layer is dried. The second binder may migrate when the coating layer is dried, but the content of the second binder itself is very low. The mass% of the second binder is preferably 0.2 to 0.4 mass%.

  Furthermore, the positive electrode mixture slurry includes a fibrous carbon material that functions as a viscosity stabilizer and a second binder. Therefore, the positive electrode active material is unlikely to settle in the coating layer. That is, the positive electrode active material can be more uniformly distributed in the positive electrode active material layer. Therefore, according to this embodiment, it is possible to increase the thickness of the positive electrode active material layer while suppressing the occurrence of migration. Furthermore, the positive electrode active material can be more uniformly distributed in the positive electrode active material layer. Furthermore, since the flexibility of the positive electrode active material layer can be ensured, breakage of the positive electrode current collector during winding can be suppressed. Therefore, according to this embodiment, it is possible to improve the characteristics of the nonaqueous electrolyte secondary battery, specifically, the high rate discharge characteristics and the capacity retention rate.

<2. Method for producing positive electrode active material layer>
Next, the manufacturing method of the positive electrode active material layer using a positive mix slurry is demonstrated. Although the manufacturing method of the positive electrode active material layer itself is not particularly limited, for example, the following method may be used. First, a positive electrode mixture slurry having the above-described composition is prepared. Next, the positive electrode mixture slurry is applied onto the positive electrode current collector. Thereby, a coating layer is formed. Next, the coating layer is rapidly dried. Rapid drying is performed using, for example, a hot air furnace. The time for rapid drying is not particularly limited, but may be 90 to 120 seconds, for example. The hot air temperature of the drying furnace may be 70 to 130 degrees, and the air volume may be 0.5 to 5 m / second. However, from the viewpoint of suppressing migration as much as possible, it is preferable to slow down the evaporation rate of the solvent as much as possible. For this reason, it is desirable that the hot air temperature and the air volume be as low as possible within a range where 99% by volume or more of the solvent can be evaporated within the rapid drying time. Next, the coated layer after rapid drying is rolled and vacuum dried. Thereby, the positive electrode active material layer is formed on the positive electrode current collector.

  The coating method is not particularly limited. For example, a doctor blade method, a slot die method, a knife coater method, a gravure coater method, or the like is used. Also good.

<3. Configuration of non-aqueous electrolyte secondary battery>
Next, a configuration example of a non-aqueous electrolyte secondary battery using the positive electrode active material layer described above will be described with reference to FIG. FIG. 1 shows a plan sectional view of the winding element 1a and an enlarged view in which a region A of the winding element 1a is enlarged. The nonaqueous electrolyte secondary battery 1 includes a winding element 1a, a nonaqueous electrolyte solution, and an exterior material 40. Therefore, the nonaqueous electrolyte secondary battery 1 is a so-called wound type secondary battery. The winding element 1 a is obtained by winding an electrode laminate in which a positive electrode 10, a separator 20, a negative electrode 30, and a separator 20 are laminated in this order in the longitudinal direction and compressing in an arrow B direction. Of course, the stacking order of each component is not limited to this. Of course, the present embodiment may be applied to a non-aqueous electrolyte secondary battery other than a wound secondary battery.

(3-1. Positive electrode)
The positive electrode 10 has a strip shape and includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode current collector 11 is not particularly limited, and is made of, for example, aluminum (Al), stainless steel, nickel plated steel, or the like. The positive electrode current collector 11 is preferably made of aluminum (Al) or stainless steel from the viewpoint of electrochemical stability. A positive electrode terminal is connected to the positive electrode current collector 11.

  As described above, the positive electrode active material layer 12 is produced using the positive electrode mixture slurry according to the present embodiment. Therefore, the positive electrode active material layer 12 includes a positive electrode active material, a first binder, a fibrous carbon material, and a second binder. The first binder covers the surface of the positive electrode active material, but a part of the first binder may be detached from the positive electrode active material. However, b / a remains unchanged and is 5.0 or less. b is the mass% of the first binder with respect to the total mass of the positive electrode active material and the first binder.

  The thickness of the positive electrode active material layer 12 is not particularly limited, and can be at least as thick as a conventional nonaqueous electrolyte secondary battery. Furthermore, in this embodiment, even if the positive electrode active material layer 12 is thickened, the occurrence of migration can be suppressed and the positive electrode active material can be more uniformly distributed in the positive electrode active material layer. Therefore, the positive electrode active material layer 12 can be made thicker than before.

  About the separator 20, the negative electrode 30, electrolyte solution, and an exterior material, what can be used with a general nonaqueous electrolyte secondary battery can be used arbitrarily. These will be briefly described as follows.

(3-2. Separator)
The separator 20 is not particularly limited, and any separator can be used as long as it is used as a separator for a general nonaqueous electrolyte secondary battery. As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. The separator may be coated with an inorganic material such as Al ₂ O ₃ , Mg (OH) ₂ , SiO ₂ . Examples of the material constituting the separator include, for example, polyolefin resins represented by polyethylene, polypropylene, and the like, polyethylene terephthalate, and polybutylene terephthalate. Polyester resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinylether (perfluorovinylether) Polymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone (Hexafluoroacetone) copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetra Fluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetra It can be used Ruoroechiren copolymer. The porosity of the separator is not particularly limited, and the porosity of the separator of the nonaqueous electrolyte secondary battery can be arbitrarily applied.

(3-3. Negative electrode)
The negative electrode 30 has a strip shape and includes a negative electrode current collector 31 and a negative electrode active material layer 32. The negative electrode current collector 31 is made of, for example, copper (Cu), nickel (Ni), or the like. Here, the negative electrode active material layer 32 may be any material as long as it is used as the negative electrode active material layer of the nonaqueous electrolyte secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a negative electrode binder. Examples of the negative electrode active material include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), silicon (Si), tin (Sn), or oxides thereof. A mixture of fine particles of graphite and a graphite active material, fine particles of silicon or tin, alloys based on silicon or tin, and titanium oxide (TiO _x ) compounds such as Li ₄ Ti ₅ O ₁₂ can be used. . Note that the oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, for example, metallic lithium can be used as the negative electrode active material.

Examples of the binder for the negative electrode include polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, SBR butadiene, and acrylonitrile rubber. butadiene rubber, fluoroelastomer, poly (vinyl acetate), polymethyl methacrylate, polyethylene (polyethylene), nitrocellulose (nitro)
cellulose), carboxymethylcellulose (carboxymethyl)
cellulose) sodium salt and the like. The negative electrode binder is not particularly limited as long as it can bind the negative electrode active material and the conductive additive onto the negative electrode current collector 31. Further, the content of the negative electrode binder is not particularly limited and may be any content as long as it is applied to the negative electrode active material layer of the nonaqueous electrolyte secondary battery.

(3-4. Electrolytic solution)
As the electrolytic solution, the same non-aqueous electrolytic solution conventionally used for lithium secondary batteries can be used without any particular limitation. Here, the electrolytic solution has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate and the like. ); Cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate linear carbonates such as hyl carbonate, chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1, 3-dioxane (1,3-dioxane), 1,4-dioxane (1,4-dioxane), 1,2-dimethoxyethane (1,2-dioxyethane), 1,4-dibutoxyethane (1,4- ethers such as dibutoxyether and methyldiglyme; acetonitrile, benzonitrile nitriles such as trile; dioxolane or a derivative thereof; ethylene sulfide, sulfolane, sultone, or a derivative thereof alone, or a mixture of two or more thereof However, the present invention is not limited to these.

Examples of the electrolyte salt include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO _4. , Inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K), such as KSCN, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NC _{lO 4, (n-C 4} H 9) 4 NI, (C 2 H 5) 4 N-maleate, (C 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-phtalate, stearyl acid Organic ion salts such as lithium (lithium stearyl sulfate), lithium octyl sulfonate (lithium octyl sulfate), lithium dodecylbenzene sulfonate (lithium dodecylbenzene sulfate), and the like can be used. These ionic compounds can be used alone or in admixture of two or more. Further, the concentration of the electrolyte salt may be the same as that of the nonaqueous electrolytic solution used in the conventional lithium secondary battery, and is not particularly limited. In the present invention, an electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.5 to 2.0 mol / L can be used. The exterior material 40 is, for example, an aluminum laminate, but may be a metal exterior material.

<4. Manufacturing method of non-aqueous electrolyte non-aqueous electrolyte secondary battery>
Next, the manufacturing method of a nonaqueous electrolyte nonaqueous electrolyte secondary battery is demonstrated.
(4-1. Manufacturing method of positive electrode)
The manufacturing method of the positive electrode 10 is as described above.

(4-2. Manufacturing Method of Negative Electrode)
The negative electrode 30 is produced by the following method, for example. That is, a negative electrode mixture slurry is formed by dispersing the material of the negative electrode active material layer in a solvent (for example, water), and this negative electrode mixture slurry is applied onto the current collector. Thereby, a coating layer is formed. Next, the coating layer is dried. Next, the dried coating layer is rolled together with the negative electrode current collector 31. Thereby, the negative electrode 30 is produced.

(4-3. Winding element and battery manufacturing method)
Next, the positive electrode 10, the separator 20, the negative electrode 30, and the separator 20 are laminated in this order to produce an electrode laminate. Next, the electrode laminate is wound. Thereby, the winding element 1a is produced. Next, the flat winding element 1a is produced by crushing the winding element 1a in the direction of arrow B, for example. Next, the non-aqueous electrolyte secondary battery 1 is manufactured by inserting the flat winding element 1a into the exterior body (for example, a laminate film) 40 together with the non-aqueous electrolyte and sealing the exterior body. Note that, when sealing the exterior body, the terminals that are electrically connected to the current collectors are projected outside the exterior body.

<1. Example 1>
Next, examples of the present invention will be described. In Example 1, a non-aqueous electrolyte secondary battery according to Example 1 was produced by the following steps.

(1-1. Preparation of composite cathode active material)
As an aqueous dispersion of the first binder, an aqueous dispersion of a tetrafluoroethylene-propylene copolymer was prepared. In addition, lithium cobalt oxide having a specific surface area of 0.22 (m ² / g) was prepared as a positive electrode active material. The specific surface area of lithium cobaltate was measured by a high-speed specific surface area / pore distribution measuring device (NOVA manufactured by Quantachrome). And the composite positive electrode active material was produced by spraying an aqueous dispersion with a solid content of 3.3% by mass onto lithium cobaltate using a rolling fluidized coating apparatus (MP-mini manufactured by Powrex) and then drying. . Subsequently, the mass of the tetrafluoroethylene-propylene copolymer complexed with lithium cobaltate was calculated by subtracting the mass of lithium cobaltate before complexing from the mass of the composite cathode active material. And based on this mass, the mass% of the tetrafluoroethylene-propylene copolymer with respect to the total mass of a composite positive electrode active material was computed. As a result, the mass% of the tetrafluoroethylene-propylene copolymer was 0.2% by mass. Therefore, b / a was 0.91.

Next, a carbon nanotube dispersion liquid having an average fiber diameter of 10 nm, an average fiber length after dispersion treatment of 5 μm, and an average aspect ratio of 500 was prepared as a fibrous carbon material. Further, as another conductive auxiliary, carbon black having a DBP oil absorption of 210 (ml / 100 g) and a specific surface area of 180 m ² / g was prepared. Further, modified polyvinylidene fluoride was prepared as the second binder. Here, the modified polyvinylidene fluoride had a mass average molecular weight of 1,000,000 and a carboxyl group modification amount of 1.0 mol% or less.

  Next, the composite positive electrode active material, the fibrous carbon material dispersion, and the second binder were charged into NMP to prepare a positive electrode mixture slurry. Here, the mass% of the fibrous carbon material with respect to the total mass of the total solid content of the positive electrode mixture slurry is 0.1 mass%, the mass% of the other conductive auxiliary is 0.6 mass%, and the mass of the second binder. % Was 0.4 mass%. The composition of the positive electrode mixture slurry is shown in Table 1. In addition, the numerical value with the underline shows that it is a value outside the numerical range shown in the embodiment. In addition, the notation “−” indicates that the material with the notation is not used.

  Here, the solubility of the tetrafluoroethylene-propylene copolymer in NMP was confirmed by the following steps. That is, 5 mass% (mass% with respect to the mass of NMP) of tetrafluoroethylene-propylene copolymer was added to NMP, and the mixture was stirred with a mix rotor for 24 hours in a normal temperature environment. Next, the tetrafluoroethylene-propylene copolymer was separated from the solvent, and the mass loss of the tetrafluoroethylene-propylene copolymer was measured. And solubility was measured based on the measured value. As a result, the solubility was 0% by mass.

  Next, this positive electrode mixture slurry was applied to both sides of an aluminum foil current collector having a thickness of 12 μm, and rapidly dried for 100 seconds under drying conditions of a hot air temperature of 80 ° C. and an air volume of 2 m / sec. A layer was made. Then, it rolled so that the density of solid content of a coating layer might be set to 4.1 g / cc. Subsequently, the positive electrode was produced by vacuum-drying the coating layer after rolling. Next, an aluminum lead wire was welded to the positive electrode end.

(1-2. Production of negative electrode)
A negative electrode mixture slurry was prepared by dissolving and dispersing graphite, styrene butadiene rubber (SBR), and sodium salt of carboxymethyl cellulose in an aqueous solvent at a mass ratio of solid content of 98: 1: 1. Subsequently, this negative electrode mixture slurry was applied to both surfaces of a 6 μm thick copper foil current collector (negative electrode current collector 31) and then dried. The coating layer after drying was rolled and vacuum dried to prepare a negative electrode. Thereafter, a nickel lead wire was welded to the end of the negative electrode.

(1-3. Production of winding element)
A positive electrode, a separator (ND314 manufactured by Asahi Kasei E-Materials Co., Ltd.), a negative electrode, and a separator were laminated in this order, and this laminate was wound in the longitudinal direction using a core having a diameter of 3 cm. After fixing the end with tape, the winding core is removed, the cylindrical electrode winding element is sandwiched between two 3 cm thick metal plates, and held for 3 seconds. Obtained.

(1-4. Production of non-aqueous electrolyte secondary battery)
The electrode winding element was sealed under reduced pressure with an electrolyte so that two lead wires were exposed to a laminate film composed of three layers of polypropylene / aluminum / nylon, thereby producing a battery. The electrolyte used was a solution in which 10% by volume of FEC (fluoroethylene carbonate) and 1.3M LiPF ₆ were dissolved in a solvent in which ethylene carbonate / ethyl methyl carbonate was mixed at a ratio of 3 to 7 (volume ratio). . The battery was sandwiched between two 3 cm thick metal plates heated to 90 ° C. and held for 5 minutes. A non-aqueous electrolyte secondary battery was produced through the above steps.

(1-5. Stability evaluation of positive electrode mixture slurry)
Before producing the positive electrode, the stability of the positive electrode mixture slurry was evaluated as follows. That is, the positive electrode mixture slurry was allowed to stand for 1 day. Thereafter, the positive electrode mixture slurry was observed, and the presence or absence of sedimentation of the composite positive electrode active material was confirmed. When the composite positive electrode active material settled and the positive electrode mixture slurry was separated into the composite positive electrode active material and other materials, the stability was evaluated as “x”. When the stability is “x”, it is presumed that the viscosity stabilizing action of at least one of the fibrous carbon material and the second binder was weak. In addition, when such separation could not be confirmed (that is, when the composite positive electrode active material was not precipitated), the stability was evaluated as “◯”. In Example 1, the evaluation of stability was “◯”. The evaluation results are summarized in Table 2. In addition, “-” in Table 2 indicates that evaluation is not performed.

(1-6. Evaluation of Adhesiveness of Coating Layer)
Before rolling the coating layer, the adhesion of the coating layer was evaluated as follows. That is, the 180 degreeC peeling test of the coating layer was done. A universal testing machine (AGS-X manufactured by Shimadzu Corporation) was used as a test apparatus. And if peel strength was 5 mN / mm or more, adhesiveness was evaluated as "(circle)", and if less than 5 mN / mm, adhesiveness was evaluated as "x". When the evaluation of adhesion is “x”, it is estimated that the migration of the second binder is remarkable. In Example 1, the evaluation of adhesion was “◯”. The evaluation results are summarized in Table 2.

(1-7. Evaluation of flexibility of positive electrode)
Before producing the wound element, the flexibility of the positive electrode was evaluated as follows. That is, the flexibility (that is, flexibility) of the positive electrode was evaluated by bending the produced positive electrode by 180 °. When the flexibility of the positive electrode is low, the positive electrode current collector is broken after being bent by 180 °. When the positive electrode current collector is broken, the characteristics of the nonaqueous electrolyte secondary battery are remarkably deteriorated. Therefore, in this test, the presence or absence of breakage (including pinholes) of the positive electrode current collector was visually confirmed after bending 180 °. When the fracture could not be confirmed, the flexibility was evaluated as “◯”, and when the fracture was confirmed, the flexibility was evaluated as “x”. In Example 1, the evaluation of flexibility was “◯”. The evaluation results are summarized in Table 2.

(1-8. Activation treatment)
The following activation treatment was performed before evaluating the characteristics of the nonaqueous electrolyte secondary battery. That is, the nonaqueous electrolyte secondary battery was charged at a constant current and a constant voltage under a room temperature environment with a battery voltage of 4.40 V, a current of 0.2 C, and a final current of 0.05 C. Subsequently, the non-aqueous electrolyte secondary battery was discharged at a constant current of 0.2 C until the battery voltage reached 2.75V. Thereby, the nonaqueous electrolyte secondary battery was fully activated. Thereafter, each non-aqueous electrolyte secondary battery was subjected to the following evaluations.

(1-9. Evaluation of high rate discharge characteristics)
The high rate discharge characteristics of the nonaqueous electrolyte secondary battery were evaluated as follows. That is, the nonaqueous electrolyte secondary battery was charged at a constant current and a constant voltage at a battery voltage of 4.40 V, a current of 0.5 C, and a termination current of 0.05 C in a room temperature environment. Next, the nonaqueous electrolyte secondary battery was discharged at a constant current of 1.5 C until the battery voltage reached 3.0V. The discharge capacity obtained as a result was measured. Furthermore, the relative capacity ratio (%) was calculated based on the measured discharge capacity and the discharge capacity of Comparative Example 1 measured by the same method. The relative capacity ratio means the discharge capacity when the discharge capacity of Comparative Example 1 is 100. And when the relative capacity ratio was 115 or more, it was evaluated that the high rate discharge characteristics were at a satisfactory level. When the relative capacity ratio is less than 115, it is estimated that the migration of the second binder is remarkable. The evaluation results are summarized in Table 2.

(1-10. Evaluation of capacity maintenance rate)
The following charge / discharge cycles were performed 200 times at room temperature, and the discharge capacity at the 200th relative to the discharge capacity at the 1st cycle was calculated as the capacity retention rate.
Charging: Battery voltage 4.40V, current 0.7C, end current 0.05C, constant current constant voltage charge Discharge: current 1C, end voltage 3.0V, constant current discharge Capacity maintenance rate is 80% or more The rate was evaluated as a good level. When the capacity retention rate is less than 80%, it is estimated that the migration of the second binder is remarkable or the first binder is excessive. The evaluation results are summarized in Table 2.

<2. Example 2>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<3. Example 3>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<4. Example 4>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<5. Example 5>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<6. Example 6>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, the type of the fibrous carbon material, the mass% of the fibrous carbon material, and the mass% of the second binder were changed. . The fibrous carbon material had an average fiber diameter of 40 nm, an average fiber length of 20 μm, and an average aspect ratio of 500. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<7. Example 7>
The same treatment as in Example 6 was performed except that the type and mass% of the fibrous carbon material were changed. The fibrous carbon material had an average fiber diameter of 10 nm, an average fiber length of 100 μm, and an average aspect ratio of 10,000. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<8. Example 8>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, the type of the fibrous carbon material, the mass% of the fibrous carbon material, and the mass% of the second binder were changed. . The fibrous carbon material had an average fiber diameter of 2 nm, an average fiber length of 1 μm, and an average aspect ratio of 500. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<9. Example 9>
The same treatment as in Example 1 was performed, except that the type of the positive electrode active material, the mass% of the first binder, b / a, and the mass% of the second binder were changed. The specific surface area of the positive electrode active material was 0.6 (m ² / g). The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<10. Example 10>
The same treatment as in Example 9 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<11. Example 11>
The same processing as in Example 1 was performed except that the type of the first binder, the mass% of the first binder, b / a, and the mass% of the second binder were changed. In Example 11, a vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)) was used as the first binder. The vinylidene fluoride-tetrafluoroethylene copolymer contains a tetrafluoroethylene component in a proportion of 50 mol%. The solubility of this binder was 0% by mass. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<12. Comparative Example 1>
Same as Example 1, except that the positive electrode active material was not combined with the first binder, the fibrous carbon material was not used, and the other conductive assistants and the second binder mass% were changed. Was processed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<13. Comparative Example 2>
The same treatment as in Comparative Example 1 was performed except that the mass% of the second binder was changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<14. Comparative Example 3>
The same treatment as in Example 1 was performed except that the positive electrode active material was not combined with the first binder and the mass% of the second binder was changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<15. Comparative Example 4>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, the type of the fibrous carbon material, the mass% of the fibrous carbon material, and the mass% of the second binder were changed. It was. The average fiber diameter of the fibrous carbon material was 50 nm, the average fiber length was 25 μm, and the average aspect ratio was 500. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<16. Comparative Example 5>
The same treatment as in Comparative Example 4 was performed except that the mass% of the second binder was changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<17. Comparative Example 6>
The same treatment as in Example 1 was performed except that the positive electrode active material was not combined with the first binder and the type and mass% of the second binder were changed. Here, in Comparative Example 6, a mixture of the modified polyvinylidene fluoride and hydrogenated acrylonitrile butadiene rubber used in Example 1 was used as the second binder. The mixing ratio was 2: 1 by mass. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<18. Comparative Example 7>
The same treatment as in Example 1 was performed, except that the mass% of the first binder, b / a, the type of the fibrous carbon material, and the mass% of the second binder were changed. The fibrous carbon material had an average fiber diameter of 10 nm, an average fiber length of 3 μm, and an average aspect ratio of 300. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.
<19. Comparative Example 8>
The same treatment as in Example 1 was performed except that the mass% of the first binder, b / a, and the mass% of the second binder were changed. The composition of the positive electrode mixture slurry is shown in Table 1. The evaluation results are shown in Table 2.

<21. Discussion>
In Examples 1 to 11, all evaluations were good. Note that the characteristics of the nonaqueous electrolyte secondary batteries of Examples 5, 6, and 9 were slightly lower than those of Examples 1 to 4, 7, 8, 10, and 11. Regarding Example 5, it is estimated that b / a was larger than 4.1. Regarding Example 6, it is presumed that the average fiber diameter deviated from the preferred range of 2 to 10 nm. Regarding Example 9, it is estimated that the mass% of the second binder deviated from the preferred range of 0.2 to 0.4 mass%. On the other hand, other Examples 1-4, 7, 8, 10, and 11 not only satisfy the requirements of this embodiment, but b / a is in a preferred range of 0.9 to 4.1, and the average fiber diameter is also The preferred range was 2 to 10 nm, and the mass% of the second binder was also the preferred range of 0.2 to 0.4 mass%. Therefore, it is estimated that the characteristics of the other Examples 1 to 4, 7, 8, 10, and 11 were good in this respect as well.

  On the other hand, in Comparative Examples 1 and 2, the positive electrode active material was not combined with the first binder. Furthermore, no fibrous carbon material was used. For this reason, in order to stabilize a positive mix slurry, it was necessary to use many other conductive support agents and 2nd binders. Therefore, in Comparative Example 1, the stability of the positive electrode mixture slurry was “◯”, but the evaluation of adhesion and flexibility was both “x”. In Comparative Example 1, the evaluation of flexibility was “x”, but in order to obtain a reference value for evaluation of high rate discharge characteristics, the thickness of the aluminum foil current collector was set to 15 μm, and the secondary battery Was made. In other words, the aluminum foil current collector was made thick so as not to break. Also in Comparative Example 2, the stability of the positive electrode mixture slurry was “◯”, but the evaluation of adhesion was “x”. Since other evaluations are estimated to have the same results as in Comparative Example 1, the evaluation of flexibility and the evaluation of the nonaqueous electrolyte secondary battery were not performed.

  In Comparative Example 3, a fibrous carbon material was used, but the positive electrode active material was not combined with the first binder. For this reason, it was necessary to use many second binders in order to stabilize the positive electrode mixture slurry. Therefore, in Comparative Example 3, the stability of the positive electrode mixture slurry was “◯”, but the evaluation of adhesion and flexibility was “x”. Based on these results, the evaluation of the non-aqueous electrolyte secondary battery could not be expected. Therefore, the evaluation of the non-aqueous electrolyte secondary battery was not performed.

  In Comparative Example 4, since the size of the fibrous carbon material did not satisfy the conditions of this embodiment, the positive electrode mixture slurry was not stable. For this reason, no other evaluation was performed. In Comparative Example 5, the same fibrous carbon material as in Comparative Example 4 was used, but the amount of the second binder used was increased in order to stabilize the positive electrode mixture slurry. As a result, the positive electrode mixture slurry was stabilized and the adhesion was “◯”. However, the evaluation of flexibility was “x”. From this, it is estimated that the migration of the second binder has occurred remarkably. In Comparative Example 5, since the evaluation of flexibility was bad, the evaluation of the nonaqueous electrolyte secondary battery could not be expected. For this reason, the non-aqueous electrolyte secondary battery was not evaluated.

  In Comparative Example 6, a fibrous carbon material was used, but the positive electrode active material was not combined with the first binder. For this reason, it was necessary to use many second binders in order to stabilize the positive electrode mixture slurry. However, in Comparative Example 6, a softer binder was used as the second binder. For this reason, the evaluation of flexibility was “◯”, but the adhesion was “x”. In Comparative Example 6, evaluation of the nonaqueous electrolyte secondary battery was performed, but sufficient characteristics were not obtained. In Comparative Example 7, since the size of the fibrous carbon material did not satisfy the conditions of this embodiment, the positive electrode mixture slurry was not stable. For this reason, no other evaluation was performed. In Comparative Example 8, b / a exceeded 5.0. Therefore, in Comparative Example 8, since the mass of the first binder with respect to the positive electrode active material is too large, the high rate discharge characteristics and the capacity retention rate of the nonaqueous electrolyte secondary battery were lowered. Therefore, in Examples 1 to 11 that satisfy the feature configuration of the present embodiment, good results were obtained, but in Comparative Examples 1 to 8 that do not satisfy any one or more of the feature configurations of the present embodiment, good results were obtained. No result was obtained.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 1a Winding element 10 Positive electrode 11 Positive electrode collector 12 Positive electrode active material layer 20 Separator 30 Negative electrode 31 Negative electrode collector 32 Negative electrode active material layer

Claims (9)

A solvent,
A composite positive electrode active material comprising: a positive electrode active material; and a first binder that covers a surface of the positive electrode active material and is insoluble in the solvent;
A fibrous carbon material having an average fiber diameter of 40 nm or less and an average aspect ratio of 500 or more;
A second binder soluble in the solvent,
The mass% of the first binder with respect to the total mass of the composite cathode active material is 0.2 to 1.5 mass%,
The mass% of the fibrous carbon material with respect to the total mass of the total solid content is 0.01 to 0.5 mass%,
The mass% of the second binder with respect to the total mass of the total solid content is 0.1 to 0.5 mass%,
When the specific surface area of the positive electrode active material is a (m ² / g) and the mass% of the first binder with respect to the total mass of the composite positive electrode active material is b (mass%), b / a is 5. A positive electrode mixture slurry characterized by being 0 or less.   The positive electrode mixture slurry according to claim 1, wherein the first binder is a copolymer containing tetrafluoroethylene (TFE).   The first binder includes a tetrafluoroethylene-propylene copolymer (P (TFE / P)) and a vinylidene fluoride-tetrafluoroethylene copolymer (P (T) containing a tetrafluoroethylene component in a proportion of 50 mol% or more. The positive electrode mixture slurry according to claim 2, wherein the positive electrode mixture slurry is composed of at least one selected from the group consisting of VdF / TFE)).   The second binder comprises polyvinylidene fluoride (PVdF), modified polyvinylidene fluoride, modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and a tetrafluoroethylene component in a proportion of less than 50 mol%. Containing vinylidene fluoride-tetrafluoroethylene copolymer (P (VdF / TFE)), modified vinylidene fluoride-tetrafluoroethylene copolymer containing tetrafluoroethylene component in a proportion of less than 50 mol% (P (VdF / TFE)) ), Vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (P (VdF / HFP / TFE)), modified vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, hydrogenated acrylonitrile butadiene copolymer (Hydrogenated NB ), Acrylate-vinylidene fluoride copolymer (P (Acrylate / VdF)), acrylate-vinylidene fluoride-hexafluoropropylene copolymer (P (Acrylate / VdF / HFP)), acrylate-vinylidene fluoride-tetrafluoro Selected from the group consisting of ethylene copolymer (P (Acrylate / VdF / TFE)) and acrylate-vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene (P (Acrylate / VdF / HFP / TFE)) copolymer. The positive electrode mixture slurry according to any one of claims 1 to 3, wherein the positive electrode mixture slurry is composed of any one or more of the following.   The second binder is a modified fluoride containing a polyvinylidene fluoride (PVdF), a modified vinylidene fluoride-hexafluoropropylene copolymer (P (VdF / HFP)), and a tetrafluoroethylene component in a proportion of less than 50 mol%. The positive electrode mixture slurry according to claim 4, comprising at least one selected from the group consisting of vinylidene-tetrafluoroethylene copolymer (P (VdF / TFE)).   The positive electrode mixture slurry according to claim 1, wherein the positive electrode active material is a lithium-containing transition metal oxide.   The positive electrode mixture slurry according to claim 1, wherein the solvent is N-methylpyrrolidone (NMP). A positive electrode active material;
A first binder insoluble in the solvent of the positive electrode mixture slurry;
A fibrous carbon material having an average fiber diameter of 40 nm or less and an average aspect ratio of 500 or more;
A second binder insoluble in the solvent of the positive electrode mixture slurry,
The mass% of the first binder with respect to the total mass of the positive electrode active material and the first binder is 0.2 to 1.5 mass%,
The mass% of the fibrous carbon material with respect to the total mass of the total solid content is 0.01 to 0.5 mass%,
The mass% of the second binder with respect to the total mass of the total solid content is 0.1 to 0.5 mass%,
When the specific surface area of the positive electrode active material is a (m ² / g) and the mass% of the first binder with respect to the total mass of the positive electrode active material and the first binder is b (mass%), b / a Is a positive electrode for a non-aqueous electrolyte secondary battery.   A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to claim 8.