Insulating paint, and secondary batteries

Abstract

To provide an insulating coating that can increase the productivity of electrodes by suppressing defects caused by mixing the electrode slurry and the insulating coating. [Solution] The present invention provides an insulating coating for forming an insulating film on the electrodes of a secondary battery, comprising an insulating filler, a binder resin, and a solvent, wherein the insulating filler is dispersed in the solvent, the binder resin is dissolved in the solvent, and the insulating filler includes an organic filler.

Description

[Technical Field]

[0001] This disclosure relates to insulating paints and secondary batteries. [Background technology]

[0002] In secondary batteries, from the perspective of improving quality and safety, it is necessary to prevent short circuits caused by contact between electrodes and other components during manufacturing or use. For this reason, an insulating coating containing an insulating filler is usually provided at the contact point between the current collector and the electrode composite layer in the electrode. For example, Patent Documents 1 and 2 disclose an insulating paint containing alumina particles as an insulating filler, and a secondary battery equipped with an insulating coating using the same. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-074359 [Patent Document 2] Japanese Patent Publication No. 2007-103356 [Overview of the project] [Problems that the invention aims to solve]

[0004] Applying the electrode slurry, which forms the electrode composite layer, and the insulating paint, which forms the insulating film, simultaneously onto the current collector can increase electrode production productivity. However, simultaneous application of the electrode slurry and insulating paint can lead to mixing of the two, resulting in a non-uniform boundary between the electrode composite layer and the insulating film. Electrodes with such defects exhibit reduced electrical conductivity, raising concerns about decreased productivity when producing electrodes by simultaneously applying the electrode slurry and insulating paint.

[0005] The present disclosure aims to provide an insulating paint for forming an insulating film on an electrode of a secondary battery to solve such problems, the insulating paint being capable of suppressing the occurrence of defects due to the mixing of an electrode slurry and the insulating paint. Further, the present disclosure aims to provide a secondary battery using such an insulating paint. **Means for Solving the Problem**

[0006] The present disclosure provides an insulating paint described in the following [1] to

[10] , and a secondary battery described in

[11] to

[16] . [1] An insulating paint for forming an insulating film on an electrode of a secondary battery, comprising an insulating filler, a binder resin, and a solvent, wherein the insulating filler is dispersed in the solvent, the binder resin is dissolved in the solvent, and the insulating filler contains an organic filler. [2] The insulating paint according to [1], wherein the apparent specific gravity of the insulating filler is 1.0 or more and 1.8 or less. [3] The insulating paint according to [1] or [2], wherein the insulating filler consists of an organic filler. [4] The insulating paint according to any one of [1] to [3], wherein the organic filler is a resin having a crosslinked structure. [5] The insulating paint according to any one of [1] to [4], wherein the organic filler is a resin having a thermogravimetric reduction amount of 2.0% or less at 200 °C based on the mass at 100 °C. [6] The insulating paint according to any one of [1] to [5], wherein the organic filler is a resin having a thermal decomposition temperature of 280 °C or more and 400 °C or less. [7] The insulating paint according to any one of [1] to [6], wherein the average aspect ratio of the organic filler is 1.0 or more and 1.2 or less. [8] The insulating paint according to any one of [1] to [7], wherein the average primary particle diameter of the organic filler is 0.05 μm or more and 8.0 μm or less. [9] The insulating paint according to any one of [1] to [8], wherein the number ratio of coarse fillers having a primary particle diameter of 20 μm or more in the organic filler is 1000 ppm or less.

[10] The insulating paint according to any one of [1] to [9], wherein the organic filler comprises at least one selected from the group consisting of an acrylic resin having a cross-linked structure, an acrylic-styrene resin having a cross-linked structure, a benzoguanamine-formaldehyde condensation resin having a cross-linked structure, a melamine-formaldehyde condensation resin having a cross-linked structure, and a benzoguanamine / melamine-formaldehyde condensation resin having a cross-linked structure.

[11] A secondary battery comprising a positive electrode having a positive electrode current collector and a positive electrode composite material layer covering a portion of at least one of the main surfaces of the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode composite material layer covering a portion of at least one of the main surfaces of the negative electrode current collector, wherein the battery has an insulating coating covering at least one selected from the contact portion between the surface of the positive electrode composite material layer and the positive electrode current collector, and the insulating coating comprises an insulating filler and a binder resin, and the insulating filler comprises an organic filler.

[12] The apparent specific gravity of the insulating filler is 1.0 or more and 1.8 or less, as described in

[11] .

[13] The secondary battery according to

[11] or

[12] , wherein the insulating filler is an organic filler.

[14] The organic filler is a resin having a cross-linked structure, as described in any one of

[11] to

[13] .

[15] The organic filler is a resin whose thermal weight loss at 200°C is 2.0% or less, based on the mass at 100°C, as described in any one of

[11] to

[14] .

[16] The organic filler is a resin with a thermal decomposition temperature of 280°C or higher and 400°C or lower, as described in any one of

[11] to

[15] . [Effects of the Invention]

[0007] According to this disclosure, an insulating coating for forming an insulating film on the electrodes of a secondary battery can be provided that can suppress defects caused by mixing the electrode slurry with the insulating coating. Furthermore, according to this disclosure, a secondary battery using such an insulating coating can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] (a) is a plan view showing an example of an electrode. (b) is a cross-sectional view of (a) taken along the Ib-Ib line. [Figure 2] This is a perspective view showing an example of a coating apparatus. [Figure 3] This is a cross-sectional view showing an example of a coated body in which an electrode slurry and insulating paint have been applied to an electrode current collector. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure are described below. However, this disclosure is not limited to the embodiments described below. The upper or lower limits of the numerical ranges expressed in this disclosure may be replaced with any of the values ​​shown in the examples. In addition, the upper and lower limits described individually may be combined in any way. In this disclosure, the term "(meth)acrylic acid" means acrylic acid and methacrylic acid.

[0010] <Insulating coating> An insulating coating according to one embodiment comprises an insulating filler, a binder resin, and a solvent, and is an insulating coating for forming an insulating film on the electrodes of a secondary battery, characterized in that the insulating filler is dispersed in the solvent, the binder resin is dissolved in the solvent, and the insulating filler includes an organic filler.

[0011] Such insulating coatings contain an organic filler with a low apparent specific gravity, making the insulating filler easily dispersed within the coating. Therefore, when the insulating coating and electrode slurry are simultaneously applied to a current collector, the insulating coating overlapping the edges of the electrode slurry can be prevented from mixing with the electrode slurry due to the precipitation of the insulating filler. This prevents defects from occurring at the boundary between the electrode composite layer and the insulating coating formed after the electrode slurry and insulating coating have dried. In this disclosure, "electrode" refers to both the positive electrode and the negative electrode.

[0012] A defect refers to a blurred area at the boundary between the electrode composite layer on the current collector and the insulating coating, as seen in an image taken from above. The number of defects can be determined by image analysis of the above image to detect the black electrode composite layer and the white insulating coating, and then detecting the areas where the black and white colors are blurred at the boundary between the electrode composite layer and the insulating coating. Image analysis can be performed using known methods. The number of defects may be 3 or less, 2 or less, 1 or less, or 0. A defect is counted as 1 regardless of its size, as long as it is a continuous blur.

[0013] An organic filler is a filler composed of an organic compound, and may also be a filler composed of a resin. Its shape is not particularly limited and may be particulate, fibrous, or lumpy. Examples of resins that constitute particulate organic fillers include acrylic resins, acrylic-styrene resins, benzoguanamine-formaldehyde condensation resins, melamine-formaldehyde condensation resins, and benzoguanamine / melamine-formaldehyde condensation resins. Examples of resins that constitute fibrous organic fillers include aromatic aramid resins. From the viewpoint of suppressing the occurrence of streaks and pinholes on the insulating coating to improve appearance and further increase the productivity of electrodes, the organic filler may be particulate, spherical, or especially perfectly spherical. The insulating filler may contain only one type of such organic filler, or it may contain two or more types.

[0014] Note that "streaks" refer to lines with a length of 1 mm or more visible on the insulating coating in an image taken from above. "Pinholes" refer to dots with a length and width of 1 mm or more visible on the insulating coating in an image taken from above. Streaks and pinholes share the common characteristic of having a dimension of 1 mm or more in at least one direction, and the different names are merely for convenience, depending on the aspect ratio (therefore, there is essentially no need to distinguish between streaks and pinholes). The total number of streaks and pinholes may be 10 or less, 5 or less, 1 or less, or 0. The total number of streaks and pinholes on the insulating coating can be determined by detecting lines with a length of 1 mm or more, and dots with a length and width of 1 mm or more, through image analysis in an image taken from above.

[0015] The apparent specific gravity of the organic filler may be between 1.0 and 1.8, 1.0 and 1.7, 1.0 and 1.6, 1.0 and 1.5, 1.0 and 1.4, 1.0 and 1.3, 1.0 and 1.2, or 1.0 and 1.1. Having the apparent specific gravity of the organic filler within the above range allows the insulating filler to disperse easily in the insulating paint, further suppressing defects caused by the mixing of the insulating paint with the electrode slurry. The apparent specific gravity of the organic filler can be determined by the constant volume expansion method, for example, using a dry automatic densimeter (Shimadzu Corporation, AccuPic II 1340) as described in the examples.

[0016] The insulating filler may also contain an inorganic filler. Examples of inorganic fillers include alumina particles and silica particles. The insulating filler may contain only one type of inorganic filler, or it may contain two or more types.

[0017] The content of insulating filler in insulating paint may be 15% by mass or more and 70% by mass or 20% by mass or more and 60% by mass. By having an insulating filler content within the above range, the insulating properties of the insulating paint can be improved.

[0018] Examples of binder resins include fluororesins, acrylonitrile copolymers, methacrylic acid ester copolymers, methacrylic acid copolymers, vinylpyrrolidone-acrylic acid (salt) copolymers, styrene copolymers, rubber compounds, carboxymethylcellulose, hydroxypropylcellulose and its modified products, polyimide resins, and amide copolymers.

[0019] Examples of fluororesins include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene. Examples of acrylonitrile copolymers include polyacrylonitrile. Examples of methacrylic acid ester copolymers include polymethyl methacrylate. Examples of methacrylic acid copolymers include polyacrylic acid. Examples of vinylpyrrolidone-acrylic acid (salt) copolymers include polyvinylpyrrolidone. Examples of styrene copolymers include styrene-(meth)acrylic acid ester copolymers. Examples of rubber compounds include styrene-butadiene rubber. Examples of amide copolymers include polyacrylamide and poly-N-vinylacetamide.

[0020] The binder resin content in the insulating paint may be 15% by mass or more and 70% by mass or 20% by mass or more and 60% by mass. By having the binder resin content in the insulating paint within the above range, the adhesion of the insulating film to the electrode can be improved.

[0021] Examples of solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water. From the viewpoint of solubility of the binder resin, NMP is preferred as the solvent.

[0022] The apparent specific gravity of the insulating filler may be 1.0 to 1.8, 1.0 to 1.7, 1.0 to 1.6, 1.0 to 1.5, 1.0 to 1.4, 1.0 to 1.3, 1.0 to 1.2, or 1.0 to 1.1.

[0023] As mentioned above, apparent specific gravity is the specific gravity determined by the constant volume expansion method. If the insulating filler consists of only one type of organic filler, theoretically, the apparent specific gravity will match the true specific gravity of the organic filler. If the insulating filler contains two or more types of fillers (for example, two or more types of organic fillers, or an organic filler plus an inorganic filler), the apparent specific gravity of the insulating filler can be adjusted by changing the mixing ratio of the two or more fillers with different true specific gravities, and theoretically, it will match the sum of the products of the true specific gravity and the abundance ratio (volume %) of each filler contained in the insulating filler. Whether the insulating filler contains only one type of organic filler or two or more types of fillers, the apparent specific gravity of the insulating filler can be determined by the constant volume expansion method. For example, all insulating fillers can be placed together in the sample chamber of a dry automatic densimeter (Shimadzu Corporation, AccuPic II 1340) and their specific gravity measured.

[0024] The content of organic filler in the insulating filler may be 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more. Furthermore, it is preferable that the insulating filler consists of an organic filler. Since an insulating filler consisting of an organic filler has an even lower apparent specific gravity, the insulating filler disperses more easily in the insulating paint, and defects caused by the mixing of the insulating paint with the electrode slurry can be further suppressed.

[0025] The organic filler may be a resin having a cross-linked structure. The use of a resin with a cross-linked structure as the organic filler strengthens the insulating film on the electrode and improves the heat resistance of the electrode and the secondary battery.

[0026] The organic filler may contain at least one selected from the group consisting of acrylic resins having a cross-linked structure, acrylic-styrene resins having a cross-linked structure, benzoguanamine-formaldehyde condensation resins having a cross-linked structure, melamine-formaldehyde condensation resins having a cross-linked structure, and benzoguanamine / melamine-formaldehyde condensation resins having a cross-linked structure. The use of the above-mentioned resins as the organic filler strengthens the insulating film on the electrodes and improves the heat resistance of both the insulating film and the secondary battery.

[0027] The presence of a cross-linked structure in a resin can be determined by heating the resin in a solvent such as toluene, recovering the solid content by filtration, and calculating the recovery rate. Specifically, this can be confirmed, for example, by following the procedure below.

[0028] First, 1.0 g of resin as the sample and 0.03 g of boiling chips are accurately weighed and placed into a 200 mL round-bottom flask. Then, 100 mL of toluene is poured in, a condenser is attached to the round-bottom flask, and the flask is immersed in an oil bath maintained at 130°C and refluxed for 24 hours.

[0029] After reflux, the contents (solvent) in the round-bottom flask are filtered using a TOP Buchner funnel type filter 3G (glass particle pore diameter 20-30 μm, volume 30 mL) equipped with ADVANTEC glass fiber filters "GB-140 (φ37 mm)" and "GA-200 (φ37 mm)" and weighed to collect the solids in the Buchner funnel type filter 3G. The solids collected in the Buchner funnel type filter 3G are then dried in a vacuum oven at 130°C for 1 hour, followed by drying at a gauge pressure of 0.06 MPa for 2 hours to remove toluene, and finally cooled to room temperature. This recovers the solids as a powder.

[0030] The weight (g) of the solid content of the recovered powder can be determined by subtracting the weights of the Buchner funnel filter 3G, glass fiber filter, and boiling chips from the total weight of the Buchner funnel filter 3G, glass fiber filter, boiling chips, and solid content after recovery. From the determined weight of the powder's solid content and the weight (g) of the resin sample before heating, the recovery rate of the solid content can be calculated using the following formula (1). Recovery rate (mass %) = {solid content weight (g) / sample weight (g)} × 100 (1)

[0031] If the recovery rate is 90% by mass or higher, the melting of the resin due to heating is suppressed, and the resin has sufficient heat resistance, so it can be said that the resin has a cross-linked structure. From the viewpoint of further improving the heat resistance of the resin, the recovery rate of the resin may be 95% by mass or higher, or even 99% by mass or higher.

[0032] Examples of acrylic resins having a cross-linked structure include "Epostor MV1002", "Epostor MV1004", "Epostor MV1006", "Epostor MV1010", "Epostor MX050W", "Epostor MX100W", "Epostor MX200W", and "Epostor MX300W" manufactured by Nippon Shokubai Co., Ltd. Examples of acrylic-styrene resins having a cross-linked structure include "Epostor MA2003" manufactured by Nippon Shokubai Co., Ltd. Examples of benzoguanamine-formaldehyde condensation resins having a cross-linked structure include "Epostor MS", "Epostor M05", and "Epostor L15" manufactured by Nippon Shokubai Co., Ltd. Examples of melamine-formaldehyde condensation resins having a cross-linked structure include "Epostor SS", "Epostor S", "Epostor FS", "Epostor S6", and "Epostor S12" manufactured by Nippon Shokubai Co., Ltd. Examples of benzoguanamine / melamine-formaldehyde condensation resins having a cross-linked structure include "Eposter M30" manufactured by Nippon Shokubai Co., Ltd.

[0033] The organic filler may be a resin with a thermal weight loss of 2.0% or less, 1.8% or less, or 1.7% or less at 200°C, based on the mass at 100°C. Resins with a thermal weight loss within the above range have small mass changes even at high temperatures and have sufficiently high heat resistance. Therefore, the heat resistance of the insulating coating on the electrode can be further improved. The above thermal weight loss may be 0.1% or more. The thermal weight loss can be determined by thermogravimetric analysis, where the resin is heated at 10°C / min, the masses of the resin at 100°C and 200°C are measured, and the ratio of the difference between the mass of the resin at 100°C and the mass of the resin at 200°C is calculated based on the mass of the resin at 100°C. The masses of the resin at 100°C and 200°C can be determined, for example, using a thermal analyzer (Shimadzu Corporation, DTG-50M) by the method described in the examples.

[0034] The organic filler may be a resin with a thermal decomposition temperature of 280°C to 400°C, 300°C to 380°C, or 310°C to 370°C. Resins with thermal decomposition temperatures within the above ranges have sufficiently high heat resistance. Therefore, by using the above-mentioned resins as the organic filler, the heat resistance of the insulating coating on the electrode can be further improved. The thermal decomposition temperature can be determined, for example, using a thermal analyzer (Shimadzu Corporation, DTG-50M) by the method described in the examples.

[0035] The average aspect ratio of the organic filler may be 1.0 or more and 1.2 or 1.0 or more and 1.1 or less. Having the average aspect ratio of the organic filler within the above range suppresses defects at the boundary between the electrode composite layer and the insulating coating, while also suppressing the occurrence of streaks and pinholes on the insulating coating. The organic filler may also be a perfectly spherical resin. The average aspect ratio can be determined, for example, using a scanning electron microscope by the method described in the examples.

[0036] The average primary particle diameter of the organic filler may be between 0.05 μm and 8.0 μm, between 0.07 μm and 6.5 μm, or between 0.09 μm and 4.5 μm. In this disclosure, the average primary particle diameter is volume-based. By having the average primary particle diameter of the organic filler within the above range, the organic filler can be sufficiently dispersed in the insulating coating, further suppressing defects at the boundary between the electrode composite layer and the insulating film. The average primary particle diameter can be determined, for example, using a precision particle size distribution analyzer (Beckman Coulter, Coulter Multisizer III) that uses the Coulter principle, by the method described in the examples. In the case of an organic filler whose average primary particle diameter is smaller than the detection limit of the Coulter principle (e.g., 0.8 μm), the particle diameter of 100 spherical particles can be calculated using a scanning electron microscope, and the average value can be obtained as the average primary particle diameter.

[0037] In organic fillers, the number proportion of coarse fillers with a primary particle diameter of 20 μm or more may be 1000 ppm or less, 600 ppm or less, 300 ppm or less, or 150 ppm or less. By keeping the number proportion of coarse fillers within the above range, the number of large coarse particles is reduced, allowing the organic filler to be sufficiently dispersed in the insulating coating, further suppressing defects at the boundary between the electrode composite layer and the insulating film. In addition, it is possible to suppress the formation of irregularities on the surface of the insulating film that may affect visual inspection. From the viewpoint of ease of obtaining organic fillers, the number proportion of coarse fillers with a primary particle diameter of 20 μm or more may be 0.1 ppm or more, 0.5 ppm or more, 1.0 ppm or more, or 5.0 ppm or more. The number percentage of coarse fillers with a primary particle diameter of 20 μm or more can be determined, for example, by measuring the primary particle diameter of 30,000 particles using a precision particle size distribution analyzer based on the Coulter principle (Beckman Coulter, Coulter Multisizer III), and then calculating the number percentage of particles with a particle diameter of 20 μm or more.

[0038] In insulating coatings, the volume ratio of insulating filler to binder resin may be 2.0 to 6.0, or 3.0 to 5.0. The mass ratio of insulating filler to binder resin may be 0.5 to 10, or 1 to 5. By keeping the volume and / or mass ratio of binder resin to insulating filler within the above range, the coating properties of the insulating coating are improved, and both the insulating properties and adhesion of the insulating film on the electrode can be achieved. Insulating coatings may be prepared by mixing insulating filler, binder resin, and solvent. Alternatively, the binder resin and insulating filler may be pre-mixed and then diluted with a solvent to a viscosity suitable for coating to prepare the insulating coating.

[0039] The solid content in the insulating coating may be 15% by mass or more and 70% by mass or 20% by mass or more and 60% by mass. Having the solid content within the above range improves the coating properties of the insulating coating, allowing for both insulation and adhesion of the insulating film on the electrode.

[0040] Insulating paints may contain other components besides binder resins and insulating fillers. These other components may include polymers such as (meth)acrylic polymers, nitrile polymers, diene polymers, and other non-fluorinated polymers; fluorinated polymers such as polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as styrene-maleic acid copolymers and polymeric dispersants such as polyvinylpyrrolidone; thickeners such as carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), and alkali-soluble (meth)acrylic acid-(meth)acrylic acid ester copolymers; and preservatives.

[0041] <Secondary battery> A secondary battery according to one embodiment comprises a positive electrode having a positive electrode current collector and a positive electrode composite material layer covering a portion of at least one of the main surfaces of the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode composite material layer covering a portion of at least one of the main surfaces of the negative electrode current collector, wherein the battery has an insulating coating covering at least one selected from the contact portion between the surface of the positive electrode composite material layer and the positive electrode current collector, and the contact portion between the surface of the negative electrode composite material layer and the negative electrode current collector, and the insulating coating comprises an insulating filler and a binder resin, wherein the insulating filler comprises an organic filler.

[0042] Figure 1(a) is a plan view showing an example of an electrode. Figure 1(b) is a cross-sectional view obtained by cutting Figure 1(a) along the line Ib-Ib. The electrode 50 has an electrode current collector 10, an electrode composite layer 30 formed on one main surface of the electrode current collector 10, and an insulating coating 20 that covers the contact portion K between the surface of the electrode composite layer 30 and the electrode current collector 10. In Figure 1(b), the electrode current collector 10 has a rectangular shape extending in the left-right direction. The electrode composite layer 30 is formed on the main surface such that one side (right side) of the electrode current collector 10 protrudes. Therefore, the electrode current collector 10 has a non-protruding portion 11 on the main surface where the electrode composite layer 30 is formed, and a protruding portion 12 on the main surface where the electrode composite layer 30 is not formed. The contact portion K is the three boundary portions of the non-protruding portion 11, the protruding portion 12, and the electrode composite layer 30. In Figure 1(b), the electrode composite layer 30 and the insulating coating 20 are formed on one main surface of the electrode current collector 10, but the electrode composite layer 30 and the insulating coating 20 may be formed on both main surfaces of the electrode current collector 10.

[0043] The size of the protruding portion 12 can be set as appropriate as needed. The protruding portion 12 has an exposed portion 121 on which the electrode current collector 10 does not have an insulating coating 20, and a covered portion 122 on which the electrode current collector 10 has an insulating coating 20. The exposed portion 121 is a connection portion with a conductive member (not shown). On the other hand, the covered portion 122 is not connected to a conductive member. Therefore, if the covered portion 122 were not covered with the insulating coating 20, it could cause a short circuit.

[0044] The insulating coating 20 covers the contact portion K between the surface of the electrode composite layer 30 and the electrode current collector 10. This allows the insulating coating 20 to cover the covering portion 122 at the protruding portion 12, thereby preventing short circuits of the electrodes. The insulating coating 20 includes an insulating filler and a binder resin. The insulating filler includes an organic filler. The insulating coating 20 is formed by the insulating paint described above. Therefore, the description of the insulating paint described above applies to the insulating filler, binder resin, and organic filler. Since the insulating coating 20 is formed by the insulating paint described above, defects at the boundary between the insulating coating 20 and the electrode composite layer 30 can be suppressed, and the productivity of the electrodes 50 can be increased. This can increase the productivity of secondary batteries.

[0045] The apparent specific gravity of the insulating filler may be between 1.0 and 1.8, 1.0 and 1.7, 1.0 and 1.6, 1.0 and 1.5, 1.0 and 1.4, 1.0 and 1.3, 1.0 and 1.2, or 1.0 and 1.1. Having the apparent specific gravity of the insulating filler within the above range allows the insulating filler to disperse easily in the insulating paint, further suppressing defects caused by the mixing of the insulating paint with the electrode slurry.

[0046] The insulating filler may consist of an organic filler. Since an insulating filler made of an organic filler has an even lower apparent specific gravity, the insulating filler disperses more easily in the insulating paint, and defects caused by the mixing of the insulating paint with the electrode slurry can be further suppressed.

[0047] The organic filler may be a resin having a cross-linked structure. The use of a resin with a cross-linked structure for the organic filler strengthens the insulating film 20 on the electrode 50, improves the heat resistance of the electrode 50, and suppresses the degradation of the secondary battery.

[0048] The organic filler may be a resin whose thermal weight loss at 200°C, based on its mass at 100°C, is 2.0% or less, 1.8% or less, or 1.7% or less. Resins with a thermal weight loss within the above range exhibit small mass changes even at high temperatures and have sufficiently high heat resistance. Therefore, the heat resistance of the insulating coating on the electrode 50 can be further improved, and the degradation of the secondary battery can be suppressed. The above thermal weight loss may also be 0.1% or more.

[0049] The organic filler may be a resin with a thermal decomposition temperature of 280°C to 400°C, 300°C to 380°C, or 310°C to 370°C. Resins with thermal decomposition temperatures within the above ranges have sufficiently high heat resistance. Therefore, the heat resistance of the insulating coating on the electrode 50 can be further improved, and the degradation of the secondary battery can be suppressed.

[0050] The electrode 50 may be a positive electrode or a negative electrode. When the electrode 50 is a positive electrode, the electrode current collector 10 may be a positive electrode current collector, and the electrode composite layer 30 may be a positive electrode composite layer. On the other hand, when the electrode 50 is a negative electrode, the electrode current collector 10 may be a negative electrode current collector, and the electrode composite layer 30 may be a negative electrode composite layer. The positive electrode and negative electrode in this disclosure will be described below.

[0051] (positive electrode) The positive electrode of the secondary battery according to this embodiment may be one in which a positive electrode composite layer is formed on a positive electrode current collector. Examples of positive electrode current collectors include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum, with aluminum being preferred.

[0052] The positive electrode composite layer may contain a positive electrode active material represented by the following formula (1). M 1 v Ni x Co y Mn z O (2+w) ...(1)

[0053] In formula (1), M 1represents an alkali metal atom, which may be, for example, Li or Na, and may be Li.

[0054] In formula (1), v, x, y, z, and w are real numbers representing the number of moles, where 0.2 ≦ v ≦ 1.2, 0.3 ≦ x ≦ 0.9, 0 < y ≦ 0.3, 0 < z ≦ 0.4, x + y + z = 1, and -0.2 ≦ w ≦ 0.2.

[0055] In formula (1), v is preferably 0.5 or more and 1.2 or less, more preferably 0.8 or more and 1.1 or less, and still more preferably 1.

[0056] In formula (1), w is preferably -0.1 or more and 0.1 or less, and more preferably 0.

[0057] Examples of the positive electrode active material represented by formula (1) include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, or LiNi 0.7 Co 0.2 Mn 0.1 O2 is preferred, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, or LiNi 0.5 Co 0.3 Mn 0.2 O2 is more preferred. These positive electrode active materials may be used alone or in combination of two or more. <۰۰۰۰۲۷۵> Of course, the positive electrode active material is not limited to the positive electrode active material represented by formula (1), but may also be LiFePO4, LiMn2O4, LiCoO2, LiCoNiAlO2, etc.

[0059] The apparent specific gravity of the positive electrode active material may be between 3.0 and 6.0, between 3.5 and 5.5, or between 4.0 and 5.0. Having the apparent specific gravity of the positive electrode active material within the above range increases the difference in specific gravity between it and the insulating paint, further suppressing mixing between the insulating paint and the positive electrode slurry.

[0060] The content of the positive electrode active material in the positive electrode composite layer may be 75% by mass or more and 99% by mass or 85% by mass or more and 95% by mass or less, from the viewpoint of improving the output characteristics and electrical characteristics of the secondary battery.

[0061] The positive electrode composite layer may further contain a conductive additive. Examples of conductive additives include carbon black such as Ketjenblack and acetylene black, carbon fiber, and graphite, with acetylene black and graphite being preferred. These conductive additives may be used individually or in combination of two or more.

[0062] The content of the conductive additive in the positive electrode composite layer may be 0.5% by mass or more and 20% by mass or 1% by mass or more and 10% by mass or less, from the viewpoint of improving the output characteristics and electrical characteristics of the secondary battery.

[0063] The positive electrode composite layer may further contain a binder. Examples of binders include fluororesins such as polyvinylidene fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamide-imide; polyolefin resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; and cellulose resins such as carboxymethylcellulose, with polyvinylidene fluoride being preferred. These binders may be used individually or in combination of two or more. The binder content in the positive electrode composite layer may be 0.5% by mass or more and 10% by mass or less, or 1% by mass or more and 5% by mass or less.

[0064] The positive electrode composite layer may further contain other components as needed. These other components may include, for example, polymers such as non-fluorinated polymers like (meth)acrylic polymers, nitrile polymers, and diene polymers, and fluorinated polymers such as polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as polymeric dispersants like styrene-maleic acid copolymers and polyvinylpyrrolidone; thickeners such as carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), and alkali-soluble (meth)acrylic acid-(meth)acrylic acid ester copolymers; and preservatives. The content of other components in the positive electrode composite layer may be 0% by mass or more and 15% by mass or less, or 0% by mass or more and 10% by mass or less.

[0065] The positive electrode active material, conductive additive, and binder may be dispersed or dissolved in a solvent to form a positive electrode slurry. Examples of solvents include NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water, with NMP being preferred. The solid content of the positive electrode slurry may be 20% to 60% by mass, 25% to 55% by mass, or 30% to 50% by mass, from the viewpoint of improving the coating properties of the positive electrode slurry and the electrical characteristics of the secondary battery.

[0066] (Negative electrode) In this embodiment, the negative electrode of the secondary battery may be one in which a negative electrode composite layer is formed on a negative electrode current collector. The negative electrode current collector may be the same as that of the positive electrode current collector, and is preferably made of copper.

[0067] The negative electrode composite layer may contain, as a negative electrode active material, graphite such as artificial graphite or natural graphite, carbon materials such as mesophase calcined bodies made from coal or petroleum pitch, non-graphitizable carbon, Si-based negative electrode materials such as Si, Si alloys, or SiO, Sn-based negative electrode materials such as Sn alloys, lithium alloys such as lithium titanate, lithium metal, or lithium-aluminum alloy, and it is preferable that it contains graphite. The content of the negative electrode active material in the negative electrode composite layer may be 80% by mass or more and 99% by mass or less, or 90% by mass or more and 98% by mass or less.

[0068] The apparent specific gravity of the negative electrode active material may be between 0.4 and 7.5, between 1.2 and 5.5, or between 2.0 and 3.6. Having the apparent specific gravity of the negative electrode active material within the above range increases the difference in specific gravity between it and the insulating paint, further suppressing mixing between the insulating paint and the negative electrode slurry.

[0069] The negative electrode composite layer may further contain a conductive additive. The conductive additive may be the same as that used in the positive electrode composite layer described above, or it may be carbon fiber. The content of the conductive additive in the negative electrode composite layer may be 0.1% by mass or more and 10% by mass or less, or 1% by mass or more and 5% by mass or less.

[0070] The negative electrode composite layer may further contain a binder. The binder may be the same as that used in the positive electrode composite layer described above, and is preferably styrene-butadiene rubber and carboxymethylcellulose. The binder content in the negative electrode composite layer may be 0.1% by mass or more and 10% by mass or less, or 1% by mass or more and 5% by mass or less.

[0071] The negative electrode composite layer may contain other components as needed. These other components may be the same as those in the positive electrode composite layer. The content of these other components in the negative electrode composite layer may be the same as that of these other components in the positive electrode composite layer.

[0072] The negative electrode active material, conductive additive, and binder may be dispersed or dissolved in a solvent to form a negative electrode slurry. The solvent may be the same as that used for the positive electrode slurry, and water is preferred. The solid content of the negative electrode slurry may be 20% to 60% by mass, 25% to 55% by mass, or 30% to 50% by mass, from the viewpoint of improving the coating properties of the negative electrode slurry and the electrical characteristics of the secondary battery.

[0073] (Method of manufacturing electrodes) A method for manufacturing an electrode may include, for example, a coating step of simultaneously coating an electrode slurry and an insulating paint onto at least one main surface of an electrode current collector using a coating apparatus; a drying step of drying the electrode slurry and the insulating paint to form an electrode composite layer and an insulating film covering the contact portion between the surface of the electrode composite layer and the electrode current collector; and a cutting step of cutting the electrode composite layer and the electrode current collector along the coating direction of the electrode slurry and the insulating paint. The coating apparatus is not particularly limited, and conventionally known apparatuses can be used. The electrode slurry may be a positive electrode slurry or a negative electrode slurry.

[0074] Figure 2 is a perspective view showing an example of a coating apparatus. The coating apparatus 80 is a slot-die type coating apparatus capable of applying two types of fluids. The coating apparatus 80 has a first discharge port 82 for applying electrode slurry and second discharge ports 84 and 86 for applying insulating paint. The first discharge port 82 is located between the second discharge ports 84 and 86. The first discharge port 82 and the second discharge ports 84 and 86 are separated by a partition wall 88. The partition wall 88 is provided to prevent the electrode slurry and insulating paint from mixing inside the coating apparatus 80.

[0075] In the coating process, for example, the coating apparatus 80 is fixed, and the electrode current collector 10 is moved while the electrode slurry 32 is discharged from the first discharge port 82 and the insulating paint 22 is discharged from the second discharge ports 84 and 86, thereby simultaneously coating at least one main surface of the electrode current collector 10 with the electrode slurry 32 and the insulating paint 22. By coating in this manner, a coated body 60 is obtained in which the electrode slurry 32 is coated on the electrode current collector 10 and the insulating paint 22 is coated on the upper part of the end C of the electrode slurry 32, as shown in the cross-sectional view in Figure 3. Alternatively, the electrode current collector 10 may be fixed, and the electrode slurry 32 and insulating paint 22 may be simultaneously coated while the coating apparatus 80 is moved.

[0076] The coating speed may be 2 m / min to 20 m / min, 4 m / min to 15 m / min, or 6 m / min to 10 m / min. By having the coating speed within the above range, the productivity of the electrode 50 can be further improved.

[0077] The dry basis weight (mass per unit area after drying) of electrode slurry 32 is 80 g / m². 2 More than 300g / m 2 Below 150g / m 2 More than 250g / m 2 The following, or 180g / m² 2 More than 230g / m 2 The following may also be the case. Furthermore, the dry weight of the insulating paint 22 is 5 g / m². 2 More than 30g / m 2 Below 10g / m 2 More than 25g / m 2 The following, or 15g / m² 2 More than 20g / m 2 The following is also possible. By coating the electrode slurry and insulating paint so that their dry weights fall within the above range, an electrode 50 with a sufficiently formed insulating film 20 can be obtained.

[0078] The insulating paint 22 in the coated body 60 contains an organic filler as an insulating filler. Here, since the organic filler has a low apparent specific gravity, it can be sufficiently dispersed in the insulating paint 22. Therefore, in the insulating paint 22 applied to the upper part of the end C, it is possible to suppress the precipitation of the insulating filler and the mixing of the insulating paint 22 and the electrode slurry 32.

[0079] In the drying process, the electrode slurry and insulating paint applied in the coating process are dried to remove the solvent, forming an insulating film 20 that covers the electrode composite layer 30 and the contact area K between the surface of the electrode composite layer 30 and the electrode current collector 10. The drying process may also be carried out by passing the coated body 60 through a dryer. Drying in the drying process may be done by hot air drying. The drying temperature may be 60°C or more and 250°C or less, or 100°C or more and 200°C or less. The drying time may be 1 minute or more and 15 hours or less, or 30 minutes or more and 2 hours or less. After drying, pressure pressing may be performed. Pressure pressing can be carried out, for example, by a roll press.

[0080] In the cutting process, the electrode mixture layer 30 and the electrode current collector 10 are cut along the coating direction of the electrode slurry and insulating paint. Thus, two electrodes 50 are obtained by cutting. In the cutting process, the electrode mixture layer 30 and the electrode current collector 10 may also be cut into two equal parts. The cutting method may be a known method.

[0081] In this way, an electrode 50 having an insulating coating 20 covering the contact portion K as shown in Figure 1 can be obtained. The electrode 50 obtained by this manufacturing method is less prone to defects at the boundary between the electrode composite layer 30 and the insulating coating 20, and the productivity of the electrode 50 can be increased.

[0082] The secondary battery according to this embodiment may include an electrolyte and a separator. The electrolyte is not particularly limited as long as it can move ions between the positive electrode and the negative electrode, and conventionally known electrolytes can be used. The separator is arranged to separate the positive electrode and the negative electrode. The type of separator is not particularly limited, and conventionally known separators can be used. The secondary battery according to this embodiment may be housed in a battery casing material from a protective standpoint. The material of the battery casing material is not particularly limited, and conventionally known casing materials can be used. The shape of the secondary battery according to this embodiment is not particularly limited, and can be a known shape, such as cylindrical, prismatic, laminated, coin-type, or large. [Examples]

[0083] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the examples. Furthermore, various physical properties of the insulating filler were measured and evaluated as follows.

[0084] [Apparent specific gravity of insulating filler] The apparent specific gravity of the insulating filler was measured using a dry automatic densimeter (Shimadzu Corporation, AccuPic II 1340) with helium gas as the gas phase, by constant volume expansion method. The volume of the sample cell was 3.5 cm³. 3 The measurement temperature was set to 25°C.

[0085] [Average aspect ratio of insulating filler] Using a scanning electron microscope, insulating fillers were observed, and 20 arbitrary particles were selected. The major and minor axes of each particle were measured, the major axis / minor axis ratio was calculated, and the average value of these ratios was used as the average aspect ratio.

[0086] [Thermal decomposition temperature and thermogravimetric loss of insulating fillers] The thermal decomposition temperature and thermogravimetric loss of the insulating filler were measured using a thermal analyzer (Shimadzu Corporation, DTG-50M). Using a precision balance, 15 mg of the sample was weighed into an aluminum cup. This aluminum cup was placed in the designated position on the thermal analyzer, and the air flow was adjusted to a specified rate (20 mL / min). After the air flow rate stabilized, the temperature was increased to 500°C at a rate of 10°C / min. The intersection of the extension of the baseline (horizontal line) of the obtained TG curve and the tangent to the mass loss portion (downward-sloping shaded area) was defined as the thermal decomposition temperature (°C) of the insulating filler. Furthermore, the decrease in mass at 200°C, relative to the mass at 100°C, was defined as the thermogravimetric loss (%).

[0087] [Average primary particle size of insulating filler] The average primary particle diameter of the insulating filler was measured on a volume basis using a precision particle size distribution analyzer (Beckman Coulter, Coulter Multisizer III) based on the Coulter principle. Since the Coulter Multisizer III has a particle diameter detection limit of 0.8 μm, if the average primary particle diameter of the insulating filler was smaller than 0.8 μm, the insulating filler was observed with a scanning electron microscope to calculate the average primary particle diameter. Specifically, the particle diameters of 100 arbitrary spherical particles were calculated using a scanning electron microscope, and the average value was used as the average primary particle diameter.

[0088] [Percentage of coarse fillers] The number proportion of coarse fillers was measured using a precision particle size distribution analyzer (Beckman Coulter: Coulter Multisizer III) based on the Coulter principle. The primary particle size was measured for 30,000 insulating fillers, and the number proportion of coarse fillers with a primary particle size of 20 μm or larger was calculated.

[0089] [Preparation of insulating paint] (Example 1) Epostor MV1002 (manufactured by Nippon Shokubai Co., Ltd., a spherical acrylic crosslinked resin), an organic filler, was used as the insulating filler. Acryset ARL468 (manufactured by Nippon Shokubai Co., Ltd., a styrene-(meth)acrylic acid ester copolymer) was used as the binder resin. NMP was used as the solvent. The insulating filler and binder were kneaded to a volume ratio of 4:1, and diluted with NMP to a viscosity suitable for coating, to prepare an insulating coating with a final solid content (insulating filler and binder resin) of 32.5% by mass. Various physical properties of the insulating filler are shown in Tables 1 and 2.

[0090] (Example 2) An insulating coating was prepared using the same procedure as in Example 1, except that Epostor MV1006 (manufactured by Nippon Shokubai Co., Ltd., a spherical acrylic crosslinked resin), an organic filler, was used as the insulating filler. The various physical properties of the insulating filler are shown in Tables 1 and 2.

[0091] (Example 3) An insulating coating was prepared using the same procedure as in Example 1, except that an organic filler, Epostor MS (manufactured by Nippon Shokubai Co., Ltd., a spherical benzoguanamine-formaldehyde condensation resin), was used as the insulating filler. The various physical properties of the insulating filler are shown in Tables 1 and 2.

[0092] (Example 4) An insulating coating was prepared using the same procedure as in Example 1, except that Epostor M05 (manufactured by Nippon Shokubai Co., Ltd., a spherical benzoguanamine-formaldehyde condensation resin), an organic filler, was used as the insulating filler. The various physical properties of the insulating filler are shown in Tables 1 and 2.

[0093] (Example 5) An insulating coating was prepared using the same procedure as in Example 1, except that an organic filler, Epostor SS (manufactured by Nippon Shokubai Co., Ltd., a spherical melamine-formaldehyde condensation resin), was used as the insulating filler. The various physical properties of the insulating filler are shown in Tables 1 and 2.

[0094] (Example 6) An insulating coating was prepared using the same procedure as in Example 1, except that Epostor S12 (manufactured by Nippon Shokubai Co., Ltd., a spherical melamine-formaldehyde condensation resin), an organic filler, was used as the insulating filler. The various physical properties of the insulating filler are shown in Tables 1 and 2.

[0095] (Example 7) Epostor MV1002, an organic filler, was used as the insulating filler. KF Polymer 9305 (manufactured by Kureha Corporation, polyvinylidene fluoride (PVdF) resin, solids content 5%) was used as the binder resin. NMP was used as the solvent. The insulating filler and binder were kneaded to a volume ratio of 4:1, and diluted with NMP to a viscosity suitable for coating, preparing an insulating coating with a final solids content (insulating filler and binder resin) of 24.0% by mass.

[0096] (Example 8) Epostor MV1002, an organic filler, was used as the insulating filler. Polyvinylpyrrolidone K-90 (manufactured by Nippon Shokubai Co., Ltd.) was used as the binder resin. NMP was used as the solvent. The insulating filler and binder were kneaded to a volume ratio of 4:1, and diluted with NMP to a viscosity suitable for coating, to prepare an insulating coating with a final solid content (insulating filler and binder resin) of 38.1% by mass.

[0097] (Example 9) Epostor MV1002, an organic filler, was used as the insulating filler. Acryset EF-022 (manufactured by Nippon Shokubai Co., Ltd., styrene-(meth)acrylic acid ester copolymer) was used as the binder resin. NMP was used as the solvent. The insulating filler and binder were kneaded to a volume ratio of 4:1, and diluted with NMP to a viscosity suitable for coating, to prepare an insulating coating with a final solid content (insulating filler and binder resin) of 53.9% by mass.

[0098] (Example 10) An insulating coating was prepared using the same procedure as in Example 9, except that an organic filler, Epostor MS, was used as the insulating filler.

[0099] (Example 11) A commercially available aromatic aramid fiber (pulp form), an organic filler, was used as the insulating filler. KF Polymer 9305 (manufactured by Kureha Corporation, polyvinylidene fluoride (PVdF) resin, solids content 5%) was used as the binder resin. The insulating filler and binder resin were kneaded to a volume ratio of 4:1, diluted with NMP to a viscosity suitable for coating, and an insulating coating with a final solids content (insulating filler and binder resin) of 24.0% by mass was prepared. Various physical properties of the insulating filler are shown in Tables 1 and 2. In Tables 1 and 2, physical properties that were not measured are indicated with "-".

[0100] (Example 12) An insulating coating was prepared in the same manner as in Example 1, except that aromatic aramid fibers used in Example 11 were used as the insulating filler.

[0101] (Example 13) An insulating coating was prepared in the same manner as in Example 8, except that aromatic aramid fibers used in Example 11 were used as the insulating filler.

[0102] (Comparative Example 1) Commercially available alumina (in bulk form), an inorganic filler, was used as the insulating filler. KF Polymer 9305 (manufactured by Kureha Corporation, polyvinylidene fluoride (PVdF) resin, solids content 5%) was used as the binder resin. The insulating filler and binder resin were kneaded to a volume ratio of 4:1, diluted with NMP to a viscosity suitable for coating, and an insulating paint with a final solids content (insulating filler and binder resin) of 24.0% by mass was prepared. Various physical properties of the insulating filler are shown in Tables 1 and 2. In Tables 1 and 2, physical properties that were not measured are indicated with "-".

[0103] (Comparative Example 2) An insulating coating was prepared in the same manner as in Example 1, except that commercially available alumina (in block form), which was used in Comparative Example 1, was used as the insulating filler.

[0104] (Comparative Example 3) An insulating coating was prepared in the same manner as in Example 8, except that commercially available alumina (in block form), which was used in Comparative Example 1, was used as the insulating filler.

[0105] [Preparation of positive electrode slurry] Commercially available NMC523 positive electrode active material (manufactured by Beijing Dangsheng, LiNi 0.5 Co 0.3 Mn 0.2 O2, acetylene black (manufactured by Denka Co., Ltd.), graphite (manufactured by Timcal, product number: KS-6), and PVDF (manufactured by Kureha Corporation, KF Polymer 1100) were weighed in a mass ratio of 100:3:3:3, and mixed in a planetary mixer with NMP as the solvent to prepare a cathode slurry with a solid content of 47.0%.

[0106] [Fabrication of the positive electrode] Using a slot-die coating apparatus capable of coating two types of fluids, the central 180 mm width of the slot die's coating width (200 mm) was set as the discharge area for the positive electrode slurry (first discharge port), and the 10 mm widths at each end were set as the discharge areas for the insulating paint (second discharge port). The positive electrode slurry and the insulating paint of each example and comparative example were simultaneously coated onto the positive electrode current collector. The positive electrode current collector used was aluminum foil (15 μm thick, 240 mm wide). The coating conditions were: coating speed of 8 m / min, gap between the slot die and the positive electrode current collector of 200 μm, and dry basis weight (mass per unit area after drying) of the positive electrode slurry of 214 g / m². 2 ±4.3g, dry weight of insulating paint is 19g / m 2 The sample was adjusted to be ±0.6g. The insulating paint and positive electrode slurry were simultaneously coated to a thickness of 100m, and after coating, the sample was passed through a drying oven set to a drying temperature of 130°C. In this way, a positive electrode was obtained having an insulating coating that covers the contact area between the surface of the positive electrode composite layer and the positive electrode current collector.

[0107] The number of defects in the obtained positive electrode, as well as the total number of streaks and pinholes, were evaluated. Image analysis of a 100m positive electrode taken from above detected the black electrode composite layer and the white insulating film. Furthermore, areas where the black and white colors bled at the boundary between the electrode composite layer and the insulating film were detected as defects, and the number of defects was calculated. Additionally, lines or points with a dimension of 1mm or more in at least one direction were detected as streaks and pinholes on the insulating film, and the total number of streaks and pinholes was calculated. The results are shown in Table 2.

[0108] [Table 1]

[0109] [Table 2]

[0110] As is clear from Tables 1 and 2, using organic fillers as insulating fillers resulted in fewer defects compared to using inorganic fillers. Therefore, it was shown that using insulating paints containing organic fillers can suppress the occurrence of defects that reduce the electrical conductivity of electrodes, even when the electrode slurry and insulating paint are applied simultaneously. [Explanation of Symbols]

[0111] 10... Electrode current collector, 11... Non-protruding part, 12... Protruding part, 20... Insulating coating, 30... Electrode composite layer, 50... Electrode, K... Contact part, 60... Coating body, 22... Insulating paint, 32... Electrode slurry, C... End part, 80... Coating device, 82... First discharge port, 84, 86... Second discharge port, 88... Partition wall, 121... Exposed part, 122... Covered part.

Claims

1. It comprises an insulating filler, a binder resin, and a solvent. An insulating coating for forming an insulating film on the electrodes of a secondary battery, The insulating filler is dispersed in the solvent, The binder resin is dissolved in the solvent, An insulating paint characterized in that the insulating filler includes an organic filler.

2. The insulating paint according to claim 1, wherein the apparent specific gravity of the insulating filler is 1.0 or more and 1.8 or less.

3. The insulating paint according to claim 1 or 2, wherein the insulating filler is an organic filler.

4. The insulating paint according to claim 1 or 2, wherein the organic filler is a resin having a cross-linked structure.

5. The insulating paint according to claim 1 or 2, wherein the organic filler is a resin whose thermal weight loss at 200°C, based on its mass at 100°C, is 2.0% or less.

6. The insulating paint according to claim 1 or 2, wherein the organic filler is a resin having a thermal decomposition temperature of 280°C or higher and 400°C or lower.

7. The insulating paint according to claim 1 or 2, wherein the average aspect ratio of the organic filler is 1.0 or more and 1.2 or less.

8. The insulating paint according to claim 1 or 2, wherein the average primary particle size of the organic filler is 0.05 μm or more and 8.0 μm or less.

9. The insulating paint according to claim 1 or 2, wherein the organic filler has a primary particle size of 20 μm or more, and the number ratio of coarse fillers is 1000 ppm or less.

10. The insulating paint according to claim 1 or 2, wherein the organic filler comprises at least one selected from the group consisting of a cross-linked acrylic resin, a cross-linked acrylic-styrene resin, a cross-linked benzoguanamine-formaldehyde condensation resin, a cross-linked melamine-formaldehyde condensation resin, and a cross-linked benzoguanamine / melamine-formaldehyde condensation resin.

11. A positive electrode comprising a positive electrode current collector and a positive electrode composite material layer covering a portion of at least one main surface of the positive electrode current collector, A secondary battery comprising a negative electrode having a negative electrode current collector and a negative electrode composite material layer covering a portion of at least one main surface of the negative electrode current collector, The coating has an insulating film that covers at least one of the contact portion between the surface of the positive electrode composite layer and the positive electrode current collector, and the contact portion between the surface of the negative electrode composite layer and the negative electrode current collector. The insulating coating comprises an insulating filler and a binder resin. A secondary battery characterized in that the insulating filler includes an organic filler.

12. The secondary battery according to claim 11, wherein the apparent specific gravity of the insulating filler is 1.0 or more and 1.8 or less.

13. The secondary battery according to claim 11 or 12, wherein the insulating filler is an organic filler.

14. The secondary battery according to claim 11 or 12, wherein the organic filler is a resin having a cross-linked structure.

15. The secondary battery according to claim 11 or 12, wherein the organic filler is a resin having a thermal weight loss of 2.0% or less at 200°C based on its mass at 100°C.

16. The secondary battery according to claim 11 or 12, wherein the organic filler is a resin having a thermal decomposition temperature of 280°C or higher and 400°C or lower.

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