Method for manufacturing positive electrode active material mixture and method for manufacturing battery

Abstract

To provide a method for manufacturing a positive electrode active material mixture that suppresses a decrease in peel strength in a positive electrode and improves electrical conductivity, and a method for manufacturing a battery which includes the method.SOLUTION: A method for manufacturing a positive electrode active material mixture includes the steps of kneading positive electrode active material secondary particles formed by agglomerating a plurality of positive electrode active material particles with a first binder resin solution containing a first binder resin and a solvent and having a viscosity of 3500 mPa s to 8000 mPa s at 20°C to prepare a first slurry, and adding a second binder resin solution containing a second binder resin having a proportion of amorphous parts of 20 mass% to 50 mass% and a solvent to the first slurry and kneading the mixture to prepare a second slurry.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a positive electrode active material mixture and a method for manufacturing a battery.

Background Art

[0002] Lithium ion secondary batteries are widely used in electric vehicles, small electronic devices (smartphones, personal computers), and energy facilities.

[0003] In order to improve the performance of such lithium ion secondary batteries, many studies have been made. For example, as a positive electrode for a lithium ion secondary battery, a positive electrode has been disclosed in which the ratio of a binder and a conductive material covering the surface of the positive electrode active material in the positive electrode does not fall below a certain ratio (Patent Document 1).

[0004] By using a structurally stable positive electrode active material, the above positive electrode provides a lithium ion secondary battery with good cycle characteristics.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a positive electrode, by increasing the specific surface area of the positive electrode active material particles used, the reaction area increases and the internal resistance decreases, so that further high output of the battery can be expected. However, as positive electrode active material particles having a large specific surface area, secondary particles in which small primary particles having a small particle size are aggregated can be considered, and these secondary particles have many uneven portions on the surface. Therefore, the binder resin often enters the uneven portions on the surface of the positive electrode active material particles, and in the positive electrode, a decrease in peel strength and a decrease in conductivity due to insufficient conductive paths may occur.

[0007] The problem to be solved by one embodiment of the present disclosure is to provide a method for manufacturing a positive electrode active material binder that suppresses a decrease in peel strength and improves conductivity in a positive electrode, and a method for manufacturing a battery including the above method.

Means for Solving the Problem

[0008] The means for solving the above problems include the following aspects. <1> A method for manufacturing a positive electrode active material binder, comprising kneading a positive electrode active material secondary particle in which a plurality of positive electrode active material particles are aggregated, a first binder resin, and a first binder resin solution containing a solvent and having a viscosity at 20°C of 3500 mPa·s to 8000 mPa·s to prepare a first slurry; and adding and kneading a second binder resin solution containing a second binder resin having a proportion of amorphous part of 20% by mass to 50% by mass and a solvent to the first slurry to prepare a second slurry. A method for manufacturing a positive electrode active material binder, including the above steps. <2> The method for manufacturing a positive electrode active material binder according to <1>, satisfying at least one of the following condition A and condition B. Condition A: The second binder resin solution contains a conductive agent. Condition B: After the step of preparing the first slurry and before the step of preparing the second slurry, the method has a step of adding and kneading a conductive agent dispersion liquid containing a conductive agent and a solvent to the first slurry. <3> The method for manufacturing a positive electrode active material binder according to <1> or <2>, wherein the viscosity of the second binder resin solution at 20°C is 300 mPa·s to 1500 mPa·s. <4> The method for manufacturing a positive electrode active material binder according to any one of <1> to <3>, wherein the positive electrode active material secondary particle has a BET specific surface area of 1.70 m 2 / g to 2.00 m 2 / g. <5> The method for manufacturing a positive electrode active material binder according to any one of <2> to <4>, wherein the conductive agent is carbon nanotube (CNT). <6> The method for manufacturing a positive electrode active material binder according to any one of <1> to <5>, wherein the first binder resin is modified polyvinylidene fluoride (modified PVDF). <7> The method for producing a positive electrode active material mixture according to any one of <1> to <6>, wherein the second binder resin is poly(vinylidene fluoride-co-hexafluoropropylene). <8> A method for manufacturing a battery, including the method for manufacturing a positive electrode active material mixture according to any one of <1> to <7>.

Advantages of the Invention

[0009] According to one embodiment of the present disclosure, there is provided a method for manufacturing a positive electrode active material mixture that suppresses a decrease in peel strength in a positive electrode and improves conductivity, and a method for manufacturing a battery including the above method.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described. The description is illustrative of the embodiments and does not limit the scope of the present disclosure.

[0012] In this specification, a numerical range indicated using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0013] In this specification, the term "step" includes not only an independent step but also the step when it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0014] In this specification, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Also, the size of the members in each drawing is conceptual, and the relative size relationship between the members is not limited thereto.

[0015] In this specification, each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, in the case where there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0016] <Method for producing a positive electrode active material mixture> The method for producing a positive electrode active material mixture of the present disclosure is positive electrode active material secondary particles in which a plurality of positive electrode active material particles are aggregated, a first binder resin solution containing a first binder resin and a solvent and having a viscosity of 3500 mPa·s to 8000 mPa·s at 20°C, are kneaded to prepare a first slurry (hereinafter also referred to as "first slurry preparation step"), a second binder resin solution containing a second binder resin having a proportion of amorphous part of 20% by mass to 50% by mass and a solvent is added to the first slurry and kneaded to prepare a second slurry (hereinafter also referred to as "second slurry preparation step"), is included. By including the above steps, a positive electrode active material mixture capable of suppressing a decrease in peel strength and improving conductivity in the positive electrode can be obtained.

[0017] (First slurry preparation step) In the first slurry preparation step, a first binder resin solution containing secondary positive electrode active material particles in which a plurality of primary positive electrode active material particles are aggregated, a first binder resin, and a solvent, and having a viscosity of 3500 mPa·s to 8000 mPa·s at 20°C is kneaded to prepare a first slurry.

[0018] -Secondary positive electrode active material particles- The secondary positive electrode active material particles are secondary particles in which a plurality of primary positive electrode active material particles (primary particles) are aggregated. Examples of the positive electrode active material particles include particles made of a lithium composite oxide. Examples of the lithium composite oxide include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganate (NCM), lithium iron phosphate (LiFePO4), and the like.

[0019] The shape of the secondary positive electrode active material particles is not particularly limited, and may be a spherical shape (e.g., a true spherical shape, an elliptical spherical shape, etc.), a fibrous shape, or the like. Further, the secondary positive electrode active material particles may have a hollow structure or a solid structure.

[0020] Here, the secondary positive electrode active material particles having a hollow structure will be described. Examples of the secondary positive electrode active material particles having a hollow structure include secondary particles in the forms shown in FIGS. 3(A) to 3(D). Each of the positive electrode active material particles 10 shown in FIGS. 3(A) to 3(D) takes the form of a secondary particle 60 having a shell portion in which the positive electrode active material particles 10 are gathered together and a hollow portion formed inside the shell portion. As shown in FIGS. 3(A) to 3(D), the positive electrode active material particles 10 can mainly form four types of secondary particles 60 depending on the direction in which the positive electrode active material particles 10 gather together and the number of particles that gather together. The positive electrode active material particles 10 shown in FIG. 3(A) are oriented to form secondary particles 60 such that the region of contact with each other is minimized, that is, the specific surface area is increased, and the unevenness on the surface of the shell portion is suppressed to be small. The positive electrode active material particles 10 shown in Fig. 3(B) are oriented to form secondary particles 60 such that the area of contact between them is minimized, i.e., the specific surface area is increased, and the unevenness on the surface of the shell part is increased. The positive electrode active material particles 10 shown in Fig. 3(C) are oriented to form secondary particles 60 such that they overlap and contact each other, i.e., the specific surface area is small, and the unevenness on the surface of the shell part is suppressed to be small. The positive electrode active material particles 10 shown in Fig. 3(D) are oriented to form secondary particles 60 such that they overlap and contact each other, i.e., the specific surface area is small, and the unevenness on the surface of the shell part is increased.

[0021] The form of the positive electrode active material secondary particles with a hollow structure preferably takes the forms shown in Fig. 3(A) and Fig. 3(B), and more preferably takes the form of Fig. 3(A).

[0022] The BET specific surface area of the positive electrode active material secondary particles is preferably 1.70 m 2 / g to 2.00 m 2 / g. When the BET specific surface area of the positive electrode active material secondary particles is 1.00 m 2 / g or more, the positive electrode active material secondary particles have a high specific surface area, so the reaction area increases, the internal resistance decreases, and the battery is likely to have a high output. On the other hand, when the BET specific surface area of the positive electrode active material secondary particles is 2.00 m 2 / g or less, it is easy to suppress the manufacturing cost of the positive electrode. The BET specific surface area of the positive electrode active material secondary particles is more preferably 1.72 m 2 / g to 1.98 m 2 / g, and even more preferably 1.74 m 2 / g to 1.96 m 2 / g.

[0023] The BET specific surface area of the positive electrode active material secondary particles can be obtained, for example, by analyzing the adsorption / desorption isotherm obtained by the adsorption / desorption measurement of nitrogen gas (temperature: -196°C) using the BET (Brenauer-Emmet-Teller) multi-point method, and the measurement can be carried out using a known measuring device (for example, a high-precision automatic gas / vapor adsorption amount measuring device "BELSORP MAX" manufactured by BEL Japan, Inc.).

[0024] In addition, the particle size of the positive electrode active material secondary particles (when the positive electrode active material secondary particles have a hollow structure, it is the outer diameter) may be 0.1 μm to 30 μm, and may further be 10 μm to 20 μm. The particle size of the positive electrode active material secondary particles can be obtained as follows. A cross-section cut along the thickness direction of the layer formed of the positive electrode active material composite material (positive electrode active material composite material layer) is observed with a scanning electron microscope (SEM), and image analysis is performed on any 10 positive electrode active material secondary particles. Then, the straight-line distance that becomes the longest when connecting one end to the other end in the longitudinal direction of the outer peripheral surface of the positive electrode active material secondary particles is defined as the particle size of the positive electrode active material secondary particles.

[0025] -First Binder Resin Solution- The first binder resin solution contains a first binder resin and a solvent (hereinafter also referred to as "first solvent"), and has a viscosity at 20°C of 3500 mPa·s to 8000 mPa·s.

[0026] Examples of the first binder resin include polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride (modified PVDF), polytetrafluoroethylene (PTFE), etc. Among them, from the viewpoint of setting the binder resin solution within a desired high viscosity range, coating the positive electrode active material secondary particles, and suppressing the penetration of the binder resin and the conductive agent into the uneven portions on the surface of the positive electrode active material secondary particles, modified polyvinylidene fluoride (modified PVDF) is preferable.

[0027] Examples of the solvent (first solvent) include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), etc. Among them, N-methylpyrrolidone (NMP) is preferable as the first solvent.

[0028] As described above, the viscosity of the first binder resin solution at 20°C is 3500 mPa·s to 8000 mPa·s, preferably 4000 mPa·s to 7600 mPa·s, more preferably 4500 mPa·s to 7300 mPa·s, and even more preferably 5000 mPa·s to 7000 mPa·s. When the viscosity of the first binder resin solution at 20°C is 3500 mPa·s or more, most of the surface of the secondary particles of the positive electrode active material will be covered by the first binder resin, so that the penetration of the binder resin and the conductive agent into the uneven portions on the surface can be suppressed, and the decrease in the peeling strength of the positive electrode can be suppressed and the conductivity can be improved. On the other hand, when the viscosity of the first binder resin solution at 20°C is 8000 mPa·s or less, the first binder resin solution does not become too highly viscous and can be well coated on the surface of the secondary particles of the positive electrode active material. Note that the viscosity of the first binder resin solution at 20°C can be adjusted, for example, by selecting the type of resin used as the first binder resin.

[0029] The viscosity of the first binder resin solution can be determined as follows. The viscosities of the first binder resin solution and the second binder resin solution at 20°C can be measured, for example, in accordance with JIS K7117 (1999), and the viscosity measured at a measurement temperature of 20°C using a B-type viscometer can be adopted.

[0030] The kneading method is not particularly limited and may be performed by a known method. For example, kneading can be performed using a planetary mixer, a sand mill, a ball mill, a planetary mill, a roll mill, an extruder, etc. When kneading, kneading with a formulation of 0.5% by mass to 1.0% by mass, for example, 0.7% by mass of the first binder resin solution with respect to the total weight of the positive electrode active material particles can preferably cover the entire surface of the secondary particles of the positive electrode active material without leaving an excess of the first binder resin.

[0031] (Second slurry preparation step) In the second slurry preparation step, a second binder resin solution containing a second binder resin having an amorphous portion ratio of 20% by mass to 50% by mass and a solvent is added to the first slurry and kneaded to prepare a second slurry.

[0032] -Second binder resin solution- The second binder resin solution contains a second binder resin having an amorphous portion ratio of 20% by mass to 50% by mass and a solvent (hereinafter also referred to as "second solvent"). As described above, the second binder resin has an amorphous portion ratio of 20% by mass to 50% by mass. Since the amorphous portion ratio of the second binder resin is 20% by mass or more, the second binder resin is excellent in electrolyte swelling property, and the diffusion resistance of ions (for example, lithium ions) in the positive electrode decreases, so the conductivity is improved. On the other hand, since the amorphous portion ratio of the second binder resin is 50% by mass or less, excessive swelling of the binder resin by the electrolyte can be suppressed, and inhibition of ion movement and deterioration of the electrode can be prevented.

[0033] The ratio of the amorphous portion in the second binder resin can be measured by the following method. Solid of binder resin 19 By measuring F-NMR and obtaining the area ratio of the resulting spectrum, the amorphous portion ratio can be calculated.

[0034] Examples of the second binder resin include poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorofluoroethylene), and the like. Among them, poly(vinylidene fluoride-co-hexafluoropropylene) is preferable from the viewpoint that the amorphous portion ratio is easily set to 20% by mass to 50% by mass.

[0035] Examples of the solvent (second solvent) include N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and the like. Note that it is preferable to use the same solvent for the second solvent as the first solvent used in the first binder resin solution. Specifically, it is preferable to use N-methylpyrrolidone (NMP) similar to the first solvent.

[0036] The kneading of the first slurry and the second slurry can be performed by a known method in the same manner as when the first slurry was kneaded during its preparation.

[0037] The viscosity of the second binder resin solution at 20 °C is preferably 300 mPa·s to 1500 mPa·s, more preferably 500 mPa·s to 1000 mPa·s, and even more preferably 500 mPa·s to 600 mPa·s. When the viscosity of the second binder resin solution is 1500 mPa·s or less, the viscosity of the entire positive electrode active material mixture can be reduced, and the formability of the positive electrode active material mixture layer in the battery can be improved. On the other hand, when the viscosity of the second binder resin solution is 300 mPa·s or more, the second binder resin can be well coated on the first slurry.

[0038] In addition, from the viewpoint of obtaining the effects of the present disclosure, it is preferable that the method for producing the positive electrode active material mixture of the present disclosure satisfies at least one of the following conditions A and B. Condition A: The second binder resin solution contains a conductive agent. Condition B: After the step of preparing the first slurry and before the step of preparing the second slurry, the method has a step of adding a conductive agent dispersion liquid containing a conductive agent and a solvent to the first slurry and kneading them.

[0039] In the above Condition A, the second binder resin solution contains a conductive agent.

[0040] - Conductive agent - Examples of the conductive agent include carbon materials such as acetylene black, ketjen black, vapor-grown carbon fiber (VGCF (registered trademark)), and carbon nanotube (CNT). In terms of being more likely to obtain the effects of the present disclosure, carbon nanotube (CNT) is preferable as the conductive agent. The content of the conductive agent may be, for example, 0.5% by mass to 1.0% by mass based on the total weight of the second binder resin solution.

[0041] In the condition B, after the step of preparing the first slurry and before the step of preparing the second slurry, there is a step of adding a conductive agent dispersion liquid containing a conductive agent and a solvent to the first slurry and kneading them.

[0042] -Conductive Agent Dispersion Liquid- The conductive agent dispersion liquid contains the conductive agent and the solvent. The conductive agent dispersion liquid may further contain a binder resin, and it is particularly preferable to contain the same resin as the first binder resin.

[0043] The method for adding and kneading the conductive agent dispersion liquid to the first slurry is not particularly limited and may be the same as the method described above.

[0044] When the method for producing the positive electrode active material mixture of the present disclosure particularly satisfies the above condition B, it is easy to suppress a decrease in the peel strength and improve the conductivity in the positive electrode.

[0045] According to the above description, a positive electrode active material mixture that suppresses a decrease in the peel strength and improves the conductivity in the positive electrode can be obtained.

[0046] FIG. 1 is a schematic cross-sectional view showing an example of the structure of a positive electrode active material mixture according to a method for manufacturing a positive electrode active material mixture of the present disclosure (a solvent is not shown). As shown in FIG. 1, the positive electrode active material mixture 100 includes positive electrode active material secondary particles in which a plurality of positive electrode active material particles (primary particles) 10 are aggregated, a first binder resin 20, and a second binder resin 30. As shown in FIG. 1, the surface of the positive electrode active material secondary particles in which a plurality of positive electrode active material particles (primary particles) 10 are aggregated is covered with the first binder resin 20, that is, the unevenness on the surface of the positive electrode active material secondary particles is filled with the first binder resin 20. Therefore, the entry of the second binder resin 30 and the conductive agent 40 into the uneven portions on the surface is suppressed. Note that the second binder resin 30 in which the ratio of the amorphous portion is within a specific range is excellent in electrolyte swelling property, that is, has a high performance of retaining the electrolyte. Since this second binder resin 30 is present well on the surface of the positive electrode active material secondary particles without entering the uneven portions of the positive electrode active material secondary particles, the electrolyte retention property on the surface of the positive electrode active material secondary particles can be enhanced. As a result, a decrease in the peel strength of the positive electrode can be suppressed and the conductivity can be improved. In addition, when the positive electrode active material mixture contains a conductive agent, as described above, the entry of the conductive agent 40 into the uneven portions on the surface of the positive electrode active material secondary particles is also suppressed. Since the conductive agent 40 is present well on the surface without entering the uneven portions of the positive electrode active material secondary particles, the conductivity can be improved also from this viewpoint.

[0047] On the other hand, FIG. 2 is a schematic cross-sectional view showing an example of the structure of another positive electrode active material mixture other than the positive electrode active material mixture according to the method for manufacturing a positive electrode active material mixture of the present disclosure (a solvent is not shown). As shown in FIG. 2, the positive electrode active material mixture 200 includes positive electrode active material secondary particles in which a plurality of positive electrode active material particles (primary particles) 10 are aggregated and an arbitrary binder resin 50. As shown in FIG. 2, the surface of the positive electrode active material secondary particles in which a plurality of positive electrode active material particles (primary particles) 10 are aggregated is not covered with the first binder resin 20. Therefore, the entry of the binder resin 50 and the conductive agent 40 into the uneven portions on the surface is likely to occur.

[0048] The above-described positive electrode active material mixture can be applied and dried on the surface of a current collector to manufacture a positive electrode.

[0049] -Current collector- Examples of the current collector include those made of Cu, Al, Fe, Co, Ni, Cr, Ni-plated steel, stainless steel, etc.

[0050] The thickness of the current collector may be 5 μm to 30 μm.

[0051] Coating can be performed by known methods such as knife coating and gravure coating.

[0052] The coating weight (g / cm 2 ) is not particularly limited as long as the effects of the present disclosure are not impaired. For example, it may be 1 g / cm 2 ~10 g / cm 2 . Also, the coating may be performed so that the electrode density of the positive electrode is 1.00 g / cm 3 ~3.00 g / cm 3 .

[0053] Drying may be appropriately selected from natural drying, vacuum drying, and heat drying. For example, when the solvent contained in the positive electrode active material mixture is NMP, it may be heat drying at 80°C to 135°C.

[0054] After drying, the positive electrode active material mixture may be pressed, if necessary, by roll pressing, cold isostatic pressing (CIP), etc. to be adjusted to a predetermined thickness or electrode density (g / cm 3 ). Also, after pressing, it may be further cut by a slitter and adjusted to a predetermined size.

[0055] <Method for manufacturing a battery> The method for manufacturing a battery of the present disclosure includes the method for manufacturing the positive electrode active material mixture.

[0056] In addition to the method for manufacturing the positive electrode active material mixture, the method for manufacturing a battery of the present disclosure may further include a step of manufacturing a negative electrode (hereinafter also referred to as "negative electrode manufacturing step"), a step of laminating the positive electrode and the negative electrode (hereinafter also referred to as "laminating step"), etc.

[0057] - Anode manufacturing process - In the anode manufacturing process, an anode active material mixture is prepared to manufacture an anode. The anode active material mixture contains anode active material particles, a binder resin, and a solvent. Examples of the anode active material include carbon - based anode active materials such as natural graphite, artificial graphite, and graphite, Li - based anode active materials such as lithium titanate (e.g., Li4Ti5O 12 ) etc., and Si - based anode active materials such as elemental Si. Examples of the binder resin and the solvent are the same as those exemplified for the cathode active material mixture. The anode active material mixture can be prepared by kneading the anode active material particles, the binder resin, and the solvent. The kneading can be carried out in the same manner as the method described above for the preparation of the cathode active material mixture. The anode can be manufactured by applying and drying the anode active material mixture on the surface of the current collector. The coating and drying can be carried out in the same manner as the method described above for the cathode active material mixture.

[0058] - Lamination process - In the lamination process, the cathode and the anode are laminated via a separator. Examples of the separator include resin sheets such as polyethylene (PE) and polypropylene (PP). The lamination can be carried out using a known lamination apparatus.

[0059] The method for manufacturing the battery of the present disclosure may further include a terminal welding process, a sealing process, an electrolyte injection process, etc. in addition to the anode manufacturing process and the lamination process.

Example

[0060] Hereinafter, the embodiments of the present disclosure will be described in more detail with reference to examples, but the embodiments of the present disclosure are not limited to the following examples.

[0061] <Example 1> For lithium nickel cobalt manganese oxide (manufactured by Sumitomo Metal Mining Co., Ltd.) as a positive electrode active material having a hollow structure secondary particle, a first binder resin solution containing modified PVDF (Solef 5130 manufactured by Solvay, molecular weight 1 million to 1.2 million) and NMP (manufactured by Mitsubishi Chemical Corporation) with a viscosity at 20 °C of 5000 mPa·s was added and kneaded with a ball mill to prepare a first slurry (positive electrode active material: modified PVDF = 97.5:0.7 (mass ratio)). Next, to the obtained first slurry, a conductive agent dispersion liquid containing carbon nanotubes (CNT) (multi-walled carbon nanotubes manufactured by sigma Aldrich), modified PVDF (Solef 5130 manufactured by Solvay, molecular weight 1 million to 1.2 million), and NMP (CNT: modified PVDF = 0.8:0.3 (mass ratio)) was added and kneaded with a disper. Next, to the first slurry containing this conductive agent, a second binder resin solution containing poly(vinylidene fluoride-co-hexafluoropropylene) (Solef 21216 manufactured by Solvay, molecular weight 570,000 to 600,000) with a non-crystallinity ratio of 38% by mass and NMP was added and kneaded. The second binder resin solution was added at a ratio of 50% by mass based on the total amount of the positive electrode active material binder to obtain a positive electrode active material binder (second slurry).

[0062] <Example 2> A first slurry (including with conductive agent) and a positive electrode active material binder (second slurry) were prepared in the same manner as in Example 1, except that a first binder resin solution with a viscosity at 20 °C of 7000 mPa·s was used.

[0063] <Comparative Example 1> A first slurry (including with conductive agent) and a positive electrode active material binder (second slurry) were prepared in the same manner as in Example 1, except that a first binder resin solution with a viscosity at 20 °C of 3000 mPa·s was used.

[0064] <Comparative Example 2> A positive electrode active material binder (second slurry) was prepared in the same manner as in Example 2, except that the positive electrode active material, the first binder resin solution, and the conductive agent dispersion liquid were simultaneously added and kneaded.

[0065] <Comparative Example 3> Except for not using the second binder resin solution, a first slurry (including those containing a conductive agent) and a positive electrode active material mixture (second slurry) were prepared in the same manner as in Example 1.

[0066] <Comparative Example 4> Except for using a second binder resin solution containing poly(vinylidene fluoride-co-hexafluoropropylene) with a non-crystallinity ratio of 10% by mass, a first slurry (including those containing a conductive agent) and a positive electrode active material mixture (second slurry) were prepared in the same manner as in Example 1.

[0067] <Measurement and Evaluation> The first slurry containing a conductive agent obtained in the examples and comparative examples was applied and dried on an aluminum foil (thickness 12 μm) to prepare positive electrode plates, respectively. For each prepared positive electrode plate, the PVDF coating rate (%), peel strength (N / m), and ACIR ratio (%) were determined as follows. Also, for the positive electrode active material mixture (second slurry), a positive electrode plate was prepared in the same manner, and the DCIR ratio (%) of each positive electrode plate was determined as follows. The basis weight during the preparation of the positive electrode plate was 5.56 g / cm 2 , and the electrode density was 2.56 g / cm 3 in all cases.

[0068] -Coating Rate (%) by the First Binder Resin- Using FE-EPMA (field emission type electron beam microanalyzer, "JXA-8530F" manufactured by JEOL Ltd.), the cross-section of the positive electrode plate coated with the first slurry containing a conductive agent was analyzed to obtain the concentration distribution of the F element. Then, using image analysis software ("Image J"), the ratio of the positive electrode active material secondary particle portion and the ratio of the F element portion were calculated, respectively. The value obtained by dividing the ratio of the F element portion by the ratio of the positive electrode active material particle portion was calculated as the coating rate (%) by the first binder resin. The results are shown in Table 1.

[0069] -Peel Strength (N / m)- Evaluation was carried out in accordance with JIS Z0237:2009 by a 90-degree peel test method using a tensile testing machine. Specifically, a double-sided tape of a predetermined size was attached onto a steel plate, and the positive electrode active material mixture layer of a positive electrode plate cut out to a width of 10 mm × a length of 80 mm was adhered to the surface on the side opposite to the steel plate side of the double-sided tape, and peeled while pulling in the 90° direction at a speed of 40 mm / min. The average value of the stress at this time was taken as the peel strength (N / m). The results are shown in Table 1.

[0070] -ACIR ratio (%)- The positive electrode plate was clamped with a gold-plated terminal, and the ACIR (mΩ) at that time was measured with an ACIR measuring instrument (Resistance Meter RM3545 manufactured by Hioki E.E. Corporation). Next, based on the ACIR (mΩ) of the positive electrode plate of Example 3, the ACIR ratio (%) was calculated. The results are shown in Table 1.

[0071] -DCIR ratio (%)- The DCIR (mΩ) at 25°C, SOC (State Of Charge) 50%, 0.3C, and 1.3C was measured with a DCIR measuring instrument (High Performance Charge and Discharge System 580 manufactured by Scribner Associates). Next, based on the DCIR (mΩ) of the positive electrode plate of Comparative Example 2, the DCIR ratio (%) was calculated. The results are shown in Table 1.

[0072]

Table 1

[0073] As shown in Table 1, in the positive electrode containing positive electrode active material particles with a large coating rate by the first binder resin, the peel strength in the positive electrode has not decreased and the conductivity has also improved. Further, when the first slurry is further coated with a second binder resin in which the proportion of the amorphous part is 20% by mass to 50% by mass, the conductivity is further improved.

Explanation of Signs

[0074] 100, 200 Positive electrode active material mixture 10 Positive electrode active material particles (primary particles) 20 First binder resin 30 Second binder resin 40 Conductive agent 50 Binder resin 60 Positive electrode active material particles (secondary particles)

Claims

1. A method for manufacturing a positive electrode active material mixture, comprising: positive electrode active material secondary particles in which a plurality of positive electrode active material particles are aggregated; a first binder resin solution containing a first binder resin and a solvent, having a viscosity at 20°C of 3500 mPa·s to 8000 mPa·s; kneading them to prepare a first slurry; adding to the first slurry a second binder resin solution containing a second binder resin having a proportion of amorphous part of 20% by mass to 50% by mass and a solvent, and kneading to prepare a second slurry; A method for manufacturing a positive electrode active material mixture, comprising the above.

2. The method for manufacturing a positive electrode active material mixture according to Claim 1, satisfying at least one of the following Condition A and Condition B. Condition A: The second binder resin solution contains a conductive agent. Condition B: After the step of preparing the first slurry and before the step of preparing the second slurry, the method has a step of adding a conductive agent dispersion liquid containing a conductive agent and a solvent to the first slurry and kneading.

3. The method for manufacturing a positive electrode active material mixture according to Claim 1, wherein the viscosity of the second binder resin solution at 20°C is 300 mPa·s to 1500 mPa·s.

4. The BET specific surface area of the positive electrode active material secondary particles is 1.70 m ２ / g to 2.00 m ２ / g, and the method for producing the positive electrode active material mixture according to claim 1.

5. The method for manufacturing a positive electrode active material mixture according to Claim 2, wherein the conductive agent is carbon nanotube (CNT).

6. The method for manufacturing a positive electrode active material mixture according to Claim 1, wherein the first binder resin is modified polyvinylidene fluoride (modified PVDF).

7. The method for manufacturing a positive electrode active material mixture according to Claim 1, wherein the second binder resin is poly(vinylidene fluoride - co - hexafluoropropylene).

8. A method for manufacturing a battery, comprising the method for manufacturing a positive electrode active material mixture according to any one of Claims 1 to 7.

Images