Negative electrode and method for manufacturing same

Abstract

The invention relates to a negative electrode and a manufacturing method thereof. A method for producing a negative electrode, the method comprising: a step for producing granulated particles containing a Si-based active material, a conductive material, and a first binder containing an imide skeleton; a step for producing a negative electrode mixture containing the granulated body particles, graphite particles, and a second binder that does not contain an imide skeleton; and a step for coating and drying the negative electrode mixture on a current collector, the weight ratio of the first binder contained in the granulated particles being 5-15%, and the average diameter of the granulated particles being 50 [mu] m or less.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode and a method for manufacturing the same. Background Art

[0002] Regarding the negative electrode disclosed in Japanese Patent Application Laid-Open No. 2016-225079, various techniques have been proposed. Summary of the invention

[0003] For active materials that expand and shrink, such as Si, it is necessary to use a high-strength adhesive such as a polyimide adhesive. However, polyimide adhesives have low conductivity and easily increase resistance, so they cannot be added too much to electrodes using Si-based active materials. In previous technologies, the capacity degradation caused by the expansion and contraction of Si-based active materials could not be fully suppressed.

[0004] The present disclosure has been made in view of the above-mentioned actual situation, and its main purpose is to provide a negative electrode and a method for manufacturing the negative electrode that can improve the initial discharge capacity and capacity retention rate of a lithium ion secondary battery.

[0005] That is, the present disclosure includes the following aspects.

[0006] <1> A method for manufacturing a negative electrode, comprising: a step of preparing granulated particles, wherein the granulated particles contain a Si-based active material, a conductive material, and a first binder containing an imide skeleton; a step of preparing a negative electrode composite, wherein the negative electrode composite contains the granulated particles, graphite particles, and a second binder not containing an imide skeleton; and a step of applying the negative electrode composite to a current collector and drying it, wherein the weight ratio of the first binder contained in the granulated particles is greater than 5% and less than 15%, and the average diameter of the granulated particles is less than 50 μm.

[0007] <2> The method for producing a negative electrode according to <1>, wherein the first binder is at least one of polyimide and polyamideimide.

[0008] <3> The method for producing a negative electrode according to <1> or <2>, wherein the second binder is at least one selected from the group consisting of carboxymethyl cellulose, styrene butadiene rubber, and polyacrylic acid.

[0009] <4> The method for producing a negative electrode according to any one of <1> to <3>, wherein the Si-based active material is at least one selected from a Si single substance, a Si oxide, and a Si alloy.

[0010] <5> The negative electrode is a negative electrode comprising a current collector and a negative electrode composite material arranged on the current collector, wherein the negative electrode composite material has granulated particles, graphite particles, and a second adhesive that does not contain an imide skeleton, the granulated particles contain a Si-based active material, a conductive material, and a first adhesive containing an imide skeleton, the weight ratio of the first adhesive contained in the granulated particles is greater than 5% and less than 15%, and the average diameter of the granulated particles is less than 50 μm.

[0011] The negative electrode and the manufacturing method thereof disclosed in the present invention can improve the initial discharge capacity and the capacity retention rate of the lithium ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0013] Figure 1 This is a schematic cross-sectional view showing an example of the granulated particles of the present disclosure.

[0014] Figure 2 It is a schematic cross-sectional view showing an example of the negative electrode of the present disclosure. DETAILED DESCRIPTION

[0015] The following is a description of the embodiments of the present disclosure. It should be noted that matters other than those specifically mentioned in this specification and matters required for the implementation of the present disclosure (such as the general structure and manufacturing process of the negative electrode that are not the characteristics of the present disclosure) can be grasped as design matters for those skilled in the art based on the prior art in this field. The present disclosure can be implemented based on the contents disclosed in this specification and the technical common sense in this field.

[0016] In the present disclosure, unless otherwise specified, the average particle size of particles is the value of the median diameter (D50) measured by laser diffraction / scattering particle size distribution measurement on a volume basis. In addition, in the present disclosure, the so-called median diameter (D50) refers to the diameter (volume average diameter) at which the cumulative volume of particles becomes half (50%) of the total volume when the particles are arranged in order from the smallest particle size.

[0017] The present disclosure provides a method for manufacturing a negative electrode, which includes: a process for preparing granulated particles, wherein the granulated particles contain a Si-based active material, a conductive material, and a first adhesive containing an imide skeleton; a process for preparing a negative electrode composite, wherein the negative electrode composite contains the granulated particles, graphite particles, and a second adhesive not containing an imide skeleton; and a process for coating the negative electrode composite on a current collector and drying it, wherein the weight ratio of the first adhesive contained in the granulated particles is greater than 5% and less than 15%, and the average diameter of the granulated particles is less than 50 μm.

[0018] In order to suppress capacity degradation due to expansion and contraction of the Si-based active material, it is necessary to use a high-strength binder that suppresses the expansion of the distance between particles and a conductive material that assists in maintaining the electron path between the particles.

[0019] It also depends on the method and type of use of the Si-based active material. Generally, in the case of an electrode using a Si-based active material alone (not compounded with graphite particles), a weight ratio of Si-based active material: high-strength binder: conductive material in the composite material is generally around 80:15:5 in the research field.

[0020] Typical examples of high-strength binders that can be used in negative electrodes of lithium-ion secondary batteries include polyimide and polyacrylic acid, each of which has the following characteristics.

[0021] It is reported that polyimide has high elasticity and high ductility, and is most suitable for Si-based active materials. In addition, since a part of the skeleton reacts with Li, it has ion permeability, and even if it is mixed in the composite material at a high ratio (more than 5%), the electrode resistance will not increase significantly. On the other hand, as the disadvantages of polyimide, the high price of the material can be listed; it is difficult to dissolve in water, and the paste easily becomes NMP-based; it is in the state of polyamic acid in the state of binder solution, and a heating treatment of about 250°C or more is required for polyimidization; because it reacts with Li, it becomes the main reason for the increase in the irreversible capacity of the negative electrode.

[0022] Polyacrylic acid is inferior to polyimide in ductility, but has high elasticity comparable to that of polyimide. In addition, the polymer can be easily dissolved in an aqueous solution, so there is no need for heat treatment for curing. However, due to the lack of ion permeability, the electrode resistance is easily increased, so the input into the composite material is mostly within 3% (due to molecular weight, the characteristics vary slightly).

[0023] Based on the above premise, in the present disclosure, when the high-strength binder is used in a hybrid electrode composed of a Si-based active material and graphite particles, the high-strength binder is configured to exist only around the necessary Si-based active material.

[0024] The present disclosure adopts the following structure: first, polyimide which can be used in a relatively large amount is used to prepare granules in which the Si-based active material and the conductive material are firmly fixed, and then the granules and graphite particles are fixed with a small amount of polyacrylic acid.

[0025] The advantages of this method are: the granulation manufacturing process using polyimide and the electrode coating process are separated, so there is no need to sinter the electrode itself, which is beneficial for mass production; polyimide and conductive materials are only present around the Si-based active material, so from the perspective of the electrode as a whole, the usage is suppressed to a minimum; further, another adhesive is used to combine the granules with the particles firmly fixed with graphite and the collector, so it is easy to achieve high strength with less adhesive as a whole.

[0026] In the present disclosure, the charge and discharge efficiency can be improved by allowing a specific amount of polyimide or a conductive material required for improving durability to exist only around the active material.

[0027] By making the polyimide and conductive material required to improve the durability of Si only exist around the Si-based active material, the irreversible capacity is suppressed to a minimum. In addition, polyacrylic acid is a stronger binder, but its ion permeability is lower than that of polyimide, and the amount added cannot be increased. The polyimide in the granules is used to assist the deficiency of the binder, so that the charge and discharge efficiency can be improved. In addition, with respect to polyimide, in order to imidize the polyamic acid, a heating treatment of more than 250°C is generally required, but the present disclosure can only heat-treat the granules, so there is no need for countermeasures such as oxidation of the collector caused by heating and decomposition of polyacrylic acid, etc.

[0028] The negative electrode production method disclosed in the present invention includes a granulated particle production step, a negative electrode composite material production step, and a drying step.

[0029] [Granulated particle production process]

[0030] The granulated particle production step is a step of producing granulated particles containing a Si-based active material, a conductive material, and a first binder containing an imide skeleton.

[0031] The granulated particles can be prepared by preparing a granulated particle paste containing a Si-based active material, a conductive material, a first binder containing an imide skeleton, and a solvent such as N-methylpyrrolidone (NMP), and performing a spray granulation treatment using the granulated particle paste.

[0032] The weight ratio of the first binder contained in the granulated particles is 5% or more and 15% or less.

[0033] The average diameter of the granulated particles may be 50 μm or less, may be 47 μm or less, and may be 14 μm or more.

[0034] The average diameter of the granulated particles was calculated by observing 20 granulated particles using a SEM, with the longest line connecting two points on the periphery being the diameter of the granulated particles.

[0035] The first binder may be at least any one of polyimide and polyamideimide.

[0036] The Si-based active material may be at least one selected from a Si single substance, a Si oxide, a Si—C complex, and a Si alloy.

[0037] As the conductive material, known conductive materials can be used, for example, carbon materials and metal particles can be listed. As the carbon material, for example, acetylene black (AB), furnace black, VGCF, carbon nanotubes (CNT) and carbon nanofibers can be listed. Among them, from the viewpoint of electronic conductivity, it can be at least one selected from VGCF, carbon nanotubes, and carbon nanofibers. As metal particles, particles of Ni, Cu, Fe and SUS can be listed.

[0038] The content of the conductive material in the granulated particles is not particularly limited, and the weight ratio of the conductive material contained in the granulated particles may be 1% or more and 5% or less.

[0039] [Negative electrode composite material production process]

[0040] The negative electrode composite material (negative electrode mixed material) preparation step is a step of preparing a negative electrode composite material including the granulated particles, graphite particles, and a second binder not containing an imide skeleton.

[0041] The graphite particles may be selected from at least one of natural graphite particles and artificial graphite particles.

[0042] The second binder may be selected from at least one of carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and polyacrylic acid.

[0043] The weight ratio of the granulated particles contained in the negative electrode composite material may be 6% or more and 21.6% or less.

[0044] The weight ratio of the graphite particles contained in the negative electrode composite material may be greater than or equal to 76.7% and less than or equal to 92.2%.

[0045] The weight ratio of the second binder contained in the negative electrode material may be greater than or equal to 0.2% and less than or equal to 1.6%.

[0046] The negative electrode composite material contains the above-mentioned conductive material as necessary.

[0047] [Drying process]

[0048] The drying step is a step of applying the negative electrode material to a current collector and drying the negative electrode material.

[0049] The material of the current collector may be a material that is not alloyed with Li, for example, SUS, copper, and nickel can be listed. As the form of the current collector, for example, foil and plate can be listed. There is no particular limitation on the top view shape of the current collector, for example, a circular shape, an elliptical shape, a rectangular shape, and any polygonal shape can be listed. In addition, the thickness of the current collector varies depending on the shape, for example, it can be in the range of 1 μm to 50 μm, and can be in the range of 5 μm to 20 μm.

[0050] As for the method of applying the negative electrode composite material to the collector and drying it, for example, the negative electrode composite material is put into a solvent and stirred to prepare a slurry for the negative electrode layer, and the slurry for the negative electrode layer is applied to one side of a support such as a collector and dried to obtain a negative electrode layer.

[0051] Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone.

[0052] There is no particular limitation on the method of coating the negative electrode layer slurry on one side of a support such as a current collector, and examples thereof include doctor blade method, metal mask printing method, electrostatic coating method, dip coating method, spraying method, roller coating method, gravure coating method, and screen printing method.

[0053] As the support, any self-supporting support can be appropriately selected and used without particular limitation, and for example, metal foil of Cu, Al, or the like can be used.

[0054] The negative electrode disclosed in the present invention is a negative electrode comprising a current collector and a negative electrode composite material arranged on the current collector, wherein the negative electrode composite material has granulated particles, graphite particles, and a second adhesive that does not contain an imide skeleton, the granulated particles contain a Si-based active material, a conductive material, and a first adhesive that contains an imide skeleton, the weight ratio of the first adhesive contained in the granulated particles is greater than 5% and less than 15%, and the average diameter of the granulated particles is less than 50 μm.

[0055] The negative electrode includes a current collector and a negative electrode composite material disposed on the current collector.

[0056] The current collector and the negative electrode composite material are as described above.

[0057] Figure 1 This is a schematic cross-sectional view showing an example of the granulated particles of the present disclosure.

[0058] like Figure 1 As shown, the granulated particles include a Si-based active material 10, a conductive material 20, and a first binder 30 including an imide skeleton.

[0059] Figure 2 It is a schematic cross-sectional view showing an example of the negative electrode of the present disclosure.

[0060] like Figure 2 As shown, the negative electrode includes a negative electrode current collector 70 and a negative electrode composite material disposed on the negative electrode current collector 70 , wherein the negative electrode composite material includes granulated particles 40 , graphite particles 50 , and a second binder 60 that does not contain an imide skeleton.

[0061] The negative electrode disclosed herein can be used in a lithium ion secondary battery.

[0062] A lithium ion secondary battery includes a positive electrode, a negative electrode of the present disclosure, and an electrolyte layer between the positive electrode and the negative electrode.

[0063] The lithium-ion secondary battery includes an outer casing that houses a positive electrode, a negative electrode, an electrolyte layer, and the like as necessary.

[0064] The material of the outer casing is not particularly limited as long as it is stable to the electrolyte, and examples thereof include resins such as polypropylene, polyethylene, and acrylic resins.

[0065] Examples of the shape of the lithium ion secondary battery include a coin shape, a stacked shape, a cylindrical shape, and a square shape.

[0066] The lithium ion secondary battery can be a liquid lithium ion secondary battery using an electrolyte as an electrolyte, or a solid lithium ion secondary battery using a solid electrolyte as an electrolyte. As the purpose of the lithium ion secondary battery, for example, the power supply of vehicles such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), electric vehicles (BEV), gasoline vehicles, and diesel vehicles can be listed. Among them, it can be used as a driving power supply for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) or electric vehicles (BEV). In addition, the lithium ion secondary battery can be used as a power supply for mobile bodies (such as railways, ships, and aircraft) other than vehicles, and can also be used as a power supply for electrical products such as information processing devices.

[0067] (Example 1)

[0068] [Positive electrode production]

[0069] The positive electrode active material (average particle size: 10 μm, LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), conductive material (granular acetylene black) and binder (PVdF) were kneaded with NMP in a ratio of 93:4:3 to prepare positive electrode paste. NMP was used to adjust the solid content of the paste to 65%. The prepared positive electrode paste was coated on a 15μm thick aluminum foil using a doctor blade coater and dried in a drying oven at 120°C for 10 minutes to obtain a coated body. The single-sided unit area mass after drying was adjusted to 22mg / cm 2Next, the coated body was pressed using a roll press. The positive electrode composite material density of the pressed positive electrode was 2.9 g / cc.

[0070] [Production of negative electrode granulated particles]

[0071] As the negative electrode active material, silicon monoxide particles with an average particle size of 6 μm were used, as the binder (first binder), polyamic acid (U varnish A manufactured by UBE) was used, and as the conductive material, Ketjen black was used. They were mixed so as to become 85:10:5, and NMP was added for kneading to prepare a paste in a manner that the solid content became 52%. Next, using the paste, a spray granulation treatment was performed using a mini spray dryer B290 manufactured by Buchi. The drying temperature after spraying was set to 200°C. The obtained granulated particles were placed in an atmosphere furnace and calcined at 400°C for 30 minutes in an argon atmosphere. The average diameter of the treated granulated particles was observed using SEM. Since the granulated particles are irregular in shape, the longest line among the straight lines connecting the two points on the periphery is set as the diameter of the granulated particles, and 20 granulated particles are observed to calculate the average diameter. In this result, the average diameter of the granulated particles is 28 μm.

[0072] [Production of negative electrode]

[0073] 16 g of spherical natural graphite with an average particle size of 17 μm, 4.5 g of the above-mentioned granulated particles, 3 g of a polyacrylic acid solution (SW-100 manufactured by Sumitomo Seika Chemicals Co., Ltd.) as a binder (second adhesive), and 15 g of ion exchange water were mixed and kneaded for 20 minutes using a planetary mixer to prepare a coating paste. Next, the paste was applied on a copper foil with a thickness of 15 μm using a blade coater and dried at 120°C for 10 minutes. The negative electrode was pressed using a roller press. It should be noted that the coating gap of the blade coater was adjusted to achieve the desired mass per unit area. The mass per unit area of ​​the obtained negative electrode was 6.3 mg / cm 2 .

[0074] [Manufacturing of coin-type batteries]

[0075] The positive electrode and negative electrode were punched into a 16 mm diameter disc, placed opposite each other via a 19 mm diameter disc separator (polyethylene porous body with a porosity of 55% and a thickness of 20 μm), and placed in a coin-shaped battery can. An electrolyte (EC: FEC: EMC: DMC = 0.2: 0.1: 0.3: 0.4 (volume ratio), LiPF 6 1 [mol / kg]) 100 μl, the coin can was sealed by caulking to prepare a coin-type battery.

[0076] [Evaluation of battery characteristics]

[0077] The charge and discharge test was carried out according to the following procedure.

[0078] Initial charge and discharge

[0079] Charging: 4.2V, CCCV, 0.1mA cut-off, current value: 1mA

[0080] Discharge: 2.5V, CCCV, 0.1mA cut-off, current value: 1mA

[0081] ·Capacity calculation

[0082] The initial discharge capacity [mAh] was used.

[0083] ·Determination of DC resistance

[0084] Calculated from the voltage drop at the start of the initial discharge.

[0085] Cycle test (100 cycles)

[0086] Charging: 4.2V, CCCV, 0.5mA cut-off, current value: 5mA

[0087] Discharge: CC, 2.5V cut-off, current value: 0.5mA

[0088] Table 1 shows the composition of the granulated particles, Table 2 shows the composition of the negative electrode composite material, and Table 3 shows the charge and discharge test results.

[0089] (Example 2, Comparative Example 6)

[0090] Except having changed the ratio of the polyimide in the granulated particles as shown in Table 1, the same method as in Example 1 was carried out.

[0091] (Example 3, Example 4, Comparative Example 7)

[0092] The same method as in Example 1 was carried out except that the average diameter of the granulated particles was changed as shown in Table 1 by adjusting the solid content of the spray paste during granulation.

[0093] (Example 5)

[0094] The same method as in Example 1 was carried out except that the silicon-based active material used in the granulated particles was changed to silicon particles having an average particle size of 0.7 μm.

[0095] (Example 6)

[0096] The silicon particles used in Example 5, polyamic acid (U Varnish A manufactured by UBE) solution, and polyvinylidene fluoride (#7300) were mixed in a weight ratio of 1:15:3 and fired at 1200°C for 1 hour in an atmosphere furnace under an Ar atmosphere. The fired solid was crushed with a ball mill and classified (balled) with a sieve to obtain a Si-C composite with an average particle size of 3 μm. The same method as in Example 1 was used except that the Si-C composite was used as the active material of the granulated particles.

[0097] (Example 7)

[0098] The same method as in Example 1 was carried out except that a polyamide-imide solution (Biomac HR-11MM manufactured by Toyobo Co., Ltd.) was used instead of polyamide-imide as the first binder used in the granulated particles.

[0099] (Example 8)

[0100] The same method as in Example 1 was carried out except that the conductive material used in the granulated particles was changed to CNT (TUBALL manufactured by OCSIAL CORPORATION) and the CNT was added to the negative electrode composite material in the composition shown in Table 2.

[0101] (Example 9)

[0102] The same method as in Example 1 was carried out except that the second binder used in the negative electrode composite was changed to CMC and SBR to have the composition shown in Table 2.

[0103] (Example 10)

[0104] The same method as in Example 1 was used except that the graphite particles used for the negative electrode composite material were changed to artificial graphite having an average particle size of 10 μm.

[0105] (Comparative Examples 1 to 5)

[0106] The same method as in Example 1 was carried out except that the granulated particles were not used and the SiO used in the granulated particles of Example 1 was directly mixed with the negative electrode composite material to have the composition shown in Table 2.

[0107]

Table 1

[0108]

[0109]

Table 2

[0110]

[0111]

Table 3

[0112] test Initial discharge capacity[mAh] Capacity maintenance rate [%] Example 1 8.00 93 Example 2 8.02 88 Example 3 8.10 93 Example 4 8.05 93 Example 5 8.41 89 Example 6 8.30 91 Example 7 8.05 92 Example 8 8.01 95 Example 9 8.00 90 Example 10 8.07 93 Comparative Example 1 7.90 45 Comparative Example 2 6.44 88 Comparative Example 3 8.42 37 Comparative Example 4 3.14 2 Comparative Example 5 7.66 22 Comparative Example 6 8.01 34 Comparative Example 7 7.95 Short circuit stops at 25th cycle

[0113] [Inspection of the results]

[0114] From the comparison among Example 1, Example 2, and Comparative Example 6, it is understood that when the ratio of the first binder in the granules is too low, the cycle characteristics deteriorate.

[0115] From the comparison among Example 1, Example 3, Example 4 and Comparative Example 7, it can be seen that if the size of the granules is larger than 50 μm, short-circuiting behavior occurs during the cycle.

[0116] In Comparative Example 7, the electrode after short circuit was observed and uneven lithium deposition was found. Therefore, it is considered that if the granules are too large, the in-plane variation of the lithium acceptance capacity in the negative electrode mixture becomes excessively large, and uneven charge and discharge reactions occur.

[0117] In Examples 6 to 10, a part of the material was changed, but also in such cases, the effect of the present disclosure was confirmed.

[0118] From the comparison between Example 1 and Comparative Examples 1 and 2, it can be seen that when the granules are not used and the mixture is simply mixed as in Comparative Examples 1 and 2, the cycle characteristics are deteriorated in Comparative Example 1 where the polyimide content is extremely low. If the polyimide ratio is increased to be approximately the same as the polyimide ratio in the granules of Example 1 as in Comparative Example 2, the amount of polyimide in the entire negative electrode composite is excessive, and the initial capacity is reduced due to the generation of its irreversible capacity. In addition, if the capacity is reduced to that of Comparative Example 2, the energy density of the battery is reduced compared to the case where a graphite single substance electrode without mixing SiO is used.

[0119] Regarding Comparative Examples 3 and 4, similarly to Comparative Example 1, no granules were used, and the binder in the negative electrode composite was polyacrylic acid. It can be seen that when there is less binder as in Comparative Example 3, the cycle characteristics deteriorate. If the binder increases, the battery resistance becomes extremely high, and the initial capacity and cycle characteristics are greatly deteriorated.

[0120] In Comparative Example 5, similarly to Comparative Example 1, no granules were used and the binder was changed to CMC and SBR which are commonly used in graphite negative electrodes. However, similarly to Comparative Examples 1 and 3, the cycle characteristics were significantly deteriorated.

[0121] Comparison between Example 1 and Comparative Examples 1 to 5 shows that the use of granules can improve both the initial discharge capacity and the capacity retention rate.

Claims

1. A method for manufacturing a negative electrode, comprising: A step of preparing granulated particles, wherein the granulated particles include a Si-based active material, a conductive material, and a first binder including an imide skeleton; a step of preparing a negative electrode composite material, wherein the negative electrode composite material comprises the granulated particles, graphite particles, and a second binder not containing an imide skeleton; and The negative electrode material is applied to the current collector and dried. The weight ratio of the first binder contained in the granulated particles is 5% or more and 15% or less, and the average diameter of the granulated particles is 50 μm or less.

2. The method for manufacturing a negative electrode according to claim 1, wherein: The first binder is at least one of polyimide and polyamideimide.

3. The method for manufacturing a negative electrode according to claim 1, wherein: The second binder is at least one selected from carboxymethyl cellulose, styrene butadiene rubber and polyacrylic acid.

4. The method for manufacturing a negative electrode according to claim 1, wherein: The Si-based active material is at least one selected from Si single substance, Si oxide and Si alloy.

5. A negative electrode comprising a current collector and a negative electrode composite material disposed on the current collector, wherein the negative electrode composite material comprises granulated particles, graphite particles, and a second binder not containing an imide skeleton, wherein the granulated particles comprise a Si-based active material, a conductive material, and a first binder containing an imide skeleton, The weight ratio of the first binder contained in the granulated particles is 5% or more and 15% or less, and the average diameter of the granulated particles is 50 μm or less.

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