Battery slurry manufacturing method

Abstract

A battery slurry manufacturing method comprising: a step for obtaining a kneaded material by kneading, with a kneader, a mixture containing particles having a D50 particle diameter of 0.1-100 μm and a dispersion medium; and a step for obtaining a slurry by performing bead mill treatment on a kneaded liquid containing the kneaded material, wherein the proportion of the particles in the mixture is 28 vol% or less, and the filling percentage of beads in the bead mill treatment is 60 vol% or less.

Description

Method for producing battery slurry

[0001] The present disclosure relates to a method for producing a battery slurry.

[0002] Electrodes used in batteries such as lithium ion batteries are produced, for example, by applying a slurry containing an active material to a current collector and drying it.

[0003] For example, Japanese Patent Application Laid-Open No. 2014-182892 describes a method for producing a slurry for an electrode of a lithium secondary battery, which is characterized by dispersing a solvent containing fibrous carbon using a media-type disperser to obtain a slurry, and kneading the slurry with an electrode active material to obtain a slurry to be applied to a current collector.

[0004] Furthermore, as a technique for producing a slurry, Japanese Patent Application Laid-Open No. 2006-156204 describes a method for producing a conductor paste for printing, which includes the steps of kneading a conductor powder, a binder, and a first solvent, adding a dispersant and / or a second solvent to the mixture obtained by the kneading step to reduce the viscosity and obtain a conductor paste, dispersing the conductor paste using a non-open type first dispersing device, and dispersing the conductor paste dispersed using the first dispersing device using a non-open type second dispersing device different from the first dispersing device. Japanese Patent Application Laid-Open No. 2006-156202 describes a method for producing a dielectric paste for printing, which includes the steps of kneading a dielectric powder, a binder, and a first solvent, adding a dispersant and / or a second solvent to the mixture obtained by the kneading step to reduce the viscosity and obtain a dielectric paste, dispersing the dielectric paste using a non-open type first dispersing device, and dispersing the dielectric paste dispersed using the first dispersing device using a non-open type second dispersing device different from the first dispersing device.

[0005] The active material used in electrodes is particulate, and conventionally, kneading, dispersion, and other processes have been performed to break down coarse particles (specifically, aggregates of primary particles). However, as the breakdown of coarse particles progresses, fine particles smaller than the target particle size may be generated. As the amount of fine particles increases, electrical resistance tends to increase and a solid electrolyte interphase interface (SEI) film tends to be more easily formed. Therefore, there is a need to suppress the generation of fine particles when breaking down coarse particles.

[0006] Therefore, the problem to be solved by one embodiment of the present disclosure has been made in consideration of the above circumstances, and is to provide a method for producing a battery slurry that is capable of obtaining a slurry in which the secondary particle size is controlled and in which particles having a particle size smaller than the target secondary particle size are reduced.

[0007] The present disclosure includes the following aspects. <1> A method for producing a battery slurry, comprising: kneading a mixture containing particles having a D50 particle size of 0.1 μm to 100 μm and a dispersion medium using a kneader to obtain a kneaded mixture; and performing a bead mill treatment on a kneading solution containing the kneaded mixture to obtain a slurry, wherein the proportion of particles in the mixture is 28% by volume or less, and the bead filling rate in the bead mill treatment is 60% by volume or less. <2> The method for producing a battery slurry according to <1>, wherein the particles are inorganic particles. <3> The method for producing a battery slurry according to <1> or <2>, wherein the particles have a primary particle size of 0.1 μm to 10 μm. <4> The method for producing a battery slurry according to any one of <1> to <3>, wherein the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture is 0.1 to 0.5. <5> The method for producing a battery slurry according to any one of <1> to <4>, wherein a shear rate applied to the mixture is 50 / s to 1500 / s. <6> The method for producing a battery slurry according to any one of <1> to <5>, wherein the viscosity of the kneaded product is 1000 Pa s or less. <7> The method for producing a battery slurry according to any one of <1> to <6>, wherein the mixture further contains a carbon material and a polymer.

[0008] According to one embodiment of the present disclosure, there is provided a method for producing a slurry for a battery, which is capable of obtaining a slurry in which the secondary particle size is controlled and in which particles having a size smaller than the target secondary particle size are reduced.

[0009] The method for producing a battery slurry according to the present disclosure will be described in detail below.

[0010] In this specification, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0011] As used herein, the amount of each component in a composition refers to the total amount of the components in the composition unless otherwise specified, when the composition contains multiple substances corresponding to each component. In this specification, a combination of two or more preferred aspects is a more preferred aspect. As used herein, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0012] [Method for Producing Battery Slurry] The method for producing a battery slurry according to the present disclosure (hereinafter also referred to as "method for producing a slurry") includes a step of kneading a mixture containing particles having a D50 particle size of 0.1 μm to 100 μm and a dispersion medium using a kneader to obtain a kneaded mixture (hereinafter also referred to as "kneading step"), and a step of performing a bead mill treatment on a kneading liquid containing the kneaded mixture to obtain a slurry (hereinafter also referred to as "dispersion step"), wherein the proportion of particles in the mixture is 28% by volume or less, and the bead filling rate in the bead mill treatment is 60% by volume or less.

[0013] The slurry produced by the method for producing a slurry of the present disclosure is used in batteries, and in particular in battery electrodes.

[0014] The type of battery in which the slurry is used is not particularly limited, and examples thereof include lithium ion batteries, nickel-metal hydride batteries, and fuel cells.

[0015] According to the method for producing a slurry of the present disclosure, it is possible to obtain a slurry in which the secondary particle size is controlled and the amount of particles smaller than the target secondary particle size is reduced. The reason for this is not clear, but is presumed to be as follows.

[0016] In the method for producing a slurry according to the present disclosure, particles contained in the mixture having a D50 particle size of 0.1 μm to 100 μm exist as secondary particles formed by aggregation of primary particles. When the mixture is kneaded, by setting the particle ratio in the mixture to 28% by volume or less, shear forces are less likely to act on the aggregated secondary particles, and fine particles are less likely to peel off from the surfaces of the aggregated secondary particles. Therefore, it is believed that, while particle crushing proceeds during the kneading process, the generation of fine particles is suppressed. Furthermore, when a kneading liquid containing the kneaded product obtained in the kneading process is subjected to a bead mill treatment, by setting the bead filling rate to 60% by volume or less, particle crushing proceeds due to collisions between the beads. Meanwhile, it is believed that shear forces are less likely to act between the beads, and the generation of fine particles is suppressed. Therefore, it is believed that, by controlling the particle ratio in the mixture and the bead filling rate, it is possible to control the secondary particle size and obtain a slurry in which particles smaller than the desired secondary particle size are reduced.

[0017] On the other hand, JP 2014-182892 A does not describe the proportion of particles in the kneaded product. Furthermore, in JP 2014-182892 A, a bead mill treatment is not performed after the kneaded product is obtained. In JP 2006-156204 A and JP 2006-156202 A, the solid content concentration of the mixture in the kneading step is 85 to 95 wt %, which is an extremely high concentration.

[0018] Each step of the method for producing the slurry will be described below.

[0019] <Kneading Step> The kneading step is a step in which a mixture containing particles having a D50 particle size of 0.1 μm to 100 μm (hereinafter also referred to as "specific particles") and a dispersion medium is kneaded using a kneader to obtain a kneaded mixture. In the kneading step, the mixture before kneading is referred to as the "mixture", and the mixture after kneading is referred to as the "kneaded mixture".

[0020] The specific particles contained in the mixture have a D50 particle size of 0.5 μm to 50 μm, preferably 1 μm to 10 μm. In the method for producing a slurry according to the present disclosure, by using particles having a D50 particle size of 0.1 μm to 100 μm, it is possible to produce a slurry in which the secondary particle size is controlled and the amount of fine particles is reduced, regardless of the particle material.

[0021] The D50 particle size refers to the particle size of particles when the number of particles in the measured particle population is a cumulative 50% by volume.

[0022] In the present disclosure, the D50 particle size is measured using a laser diffraction / scattering particle size distribution analyzer, such as the MT-3200II manufactured by Microtrac.

[0023] The specific particles preferably have a primary particle diameter of 0.1 μm to 10 μm, more preferably 0.5 μm to 5 μm. If the primary particle diameter is 0.1 μm or more, the specific particles are less likely to re-aggregate once disintegrated, making it easier to control the secondary particle diameter. On the other hand, if the primary particle diameter is 10 μm or less, the specific particles are less likely to settle, making it easier to homogenize the mixture and kneaded product.

[0024] In the present disclosure, the primary particle size of a specific particle is measured using a laser diffraction / scattering particle size distribution measuring device.

[0025] The specific particles contained in the mixture may be organic particles, inorganic particles, or composite particles of an inorganic substance and an organic substance.

[0026] The specific particles are preferably inorganic particles because the particle size can be easily controlled.

[0027] Examples of inorganic particles include particles of metals (alkali metals, alkaline earth metals, transition metals, or alloys of these metals); particles of metalloids (silicon, etc.); particles of metal or metalloid compounds (oxides, hydroxides, nitrides, etc.); and particles of pigments including carbon black, etc.

[0028] Examples of inorganic particles include particles of minerals such as mica, and inorganic pigment particles.

[0029] The organic particles are not particularly limited as long as they are particles of solid organic matter, including resin particles, graphite, and organic pigment particles.

[0030] Examples of composite particles of an inorganic substance and an organic substance include composite particles in which inorganic particles are dispersed in a matrix of an organic substance, composite particles in which organic particles are coated with an inorganic substance, and composite particles in which inorganic particles are coated with an organic substance.

[0031] The specific particles may be surface-treated for the purpose of imparting dispersibility, etc. The specific particles may be surface-treated to become the above-mentioned composite particles.

[0032] In addition, from the viewpoint of obtaining a slurry for a battery, the specific particles are preferably an electrode active material.

[0033] The electrode active material may be a negative electrode active material or a positive electrode active material, and examples of the negative electrode active material and the positive electrode active material include negative electrode active materials and positive electrode active materials in known lithium ion secondary batteries.

[0034] Specific examples of the negative electrode active material include carbon-based materials such as graphite, metal oxide materials such as silicon oxide, titanium oxide, vanadium oxide, and lithium titanium composite oxide, and metal nitride materials such as lithium nitride, lithium cobalt composite nitride, and lithium nickel composite nitride.

[0035] Specific examples of the positive electrode active material include lithium transition metal composite oxides containing lithium and transition metal elements. Examples of the lithium transition metal composite oxides include lithium nickel composite oxides (e.g., LiNiO ２ ), and lithium nickel cobalt manganese composite oxide (e.g., LiNi１／３ Co １／３ Mn １／３ O ２ ) are listed.

[0036] The dispersion medium contained in the mixture is not particularly limited, but is preferably water from the viewpoint of dispersion stability.

[0037] The content of the specific particles is preferably 70% by mass to 99% by mass, and more preferably 85% by mass to 95% by mass, based on the total amount of the mixture, and the content of water is preferably 30% by mass to 70% by mass, and more preferably 40% by mass to 60% by mass, based on the total amount of the mixture.

[0038] The mixture may contain components other than the specific particles and the dispersion medium.

[0039] From the viewpoint of improving battery characteristics, the mixture preferably further contains a carbon material and a polymer.

[0040] Examples of carbon materials include carbon black (e.g., acetylene black, ketjen black, furnace black, channel black, lamp black, thermal black, etc.), activated carbon, graphite, and carbon fiber. These carbon materials function as a conductive additive.

[0041] Examples of the polymer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and styrene-butadiene rubber (SBR). These polymers function as binders to bind the specific particles to the current collector when a slurry containing the specific particles is applied to the current collector.

[0042] Examples of the polymer include carboxyl methyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl methyl cellulose (HPMC). These polymers function as thickeners to adjust the viscosity of the slurry.

[0043] Examples of polymers include polyvinylpyrrolidone and polyvinyl alcohol, which function as dispersants to disperse specific particles in a mixture.

[0044] The content of the carbon material is preferably 0.5% by mass to 5% by mass relative to the total amount of the mixture, and the content of the polymer is preferably 0.5% by mass to 5% by mass relative to the total amount of the mixture.

[0045] The kneader used when kneading the mixture may be of a continuous type or a batch type, but from the viewpoint of controlling the secondary particle size, a batch type is preferred.

[0046] The batch mixer is preferably a blade mixer. The direction of the rotation axis of the blade may be vertical or horizontal. Examples of the mixer include a spiral mixer, a planetary mixer, and a kneader.

[0047] When the mixture is kneaded, the shear rate applied to the mixture is preferably 50 / s to 1500 / s, and more preferably 100 / s to 1000 / s, from the viewpoint of suppressing the generation of fine particles.

[0048] The time for kneading the mixture is, for example, 10 to 180 minutes.

[0049] When the mixture is kneaded, the ratio of the specific particles in the mixture is 28% by volume or less. By having the ratio of the specific particles be 28% by volume or less, shear force is less likely to act on the specific particles, and fine particles are less likely to peel off from the surfaces of the specific particles. Therefore, in the kneading step, the disintegration of the specific particles proceeds, but the generation of fine particles is suppressed.

[0050] Although there is no particular lower limit for the proportion of the specific particles in the mixture, it is preferably 20% by volume from the viewpoint of efficiently proceeding with the crushing of the specific particles.

[0051] The viscosity of the kneaded product obtained by the kneading step (viscosity at a shear rate of 1 / s) is preferably 1000 Pa s or less. The lower limit of the viscosity of the kneaded product is not particularly limited, but is preferably 1 Pa s for kneading.

[0052] In the present disclosure, viscosity is measured at 25° C. using a viscometer. Examples of the viscometer include MCR72 manufactured by Anton Paar.

[0053] The viscosity of the kneaded product can be adjusted by the content of the dispersion medium, the content of the specific particles, or the content of the thickener in the mixture.

[0054] The D50 particle size of the kneaded product obtained by the kneading step is preferably 0.1 μm to 100 μm, and more preferably 0.5 μm to 50 μm.

[0055] <Dispersion Step> The dispersion step is a step in which a kneading liquid containing a kneaded material is subjected to a bead mill treatment to obtain a slurry.

[0056] As described above, the mixture after kneading is referred to as a "kneaded product." The kneaded product to be used in the bead mill treatment is referred to as a "kneaded liquid."

[0057] The kneaded material obtained in the kneading step may be used as it is in the dispersing step. That is, the kneaded material and the kneading liquid may be the same. Alternatively, water may be further added to the kneaded material to form the kneading liquid.

[0058] The proportion of the specific particles in the kneading liquid is preferably 28% by volume or less. Although the lower limit of the proportion of the specific particles in the kneading liquid is not particularly limited, it is preferably 20% by volume from the viewpoint of efficiently proceeding with the crushing of the specific particles.

[0059] The bead mill treatment can be carried out using a commonly known bead mill disperser.

[0060] Examples of materials for the beads used in bead mill treatment include inorganic compounds such as zirconia, yttria-stabilized zirconia, alumina, steatite, silicon carbide, silicon nitride, silica, sand, agate, steel balls, stainless steel, glass, low-alkali glass, and non-alkali glass, and polymers such as polystyrene, polymethyl methacrylate, polytetrafluoroethylene, polyamide, polyethylene, polypropylene, polyether ether ketone (PEEK), and polyimide. Among these, zirconia is preferred as the material for the beads from the viewpoint of wear resistance.

[0061] The bead diameter is not particularly limited, but from the viewpoint of controlling the D50 after dispersion, it is preferably 0.5 mm to 5 mm, and more preferably 1 mm to 3 mm.

[0062] The bead filling rate is 60% by volume or less.

[0063] When the bead filling rate is 60% by volume or less, the crushing of specific particles proceeds due to collisions between the beads, but shear forces are less likely to act between the beads, suppressing the generation of fine particles.

[0064] Although there is no particular restriction on the lower limit of the bead filling rate, it is preferably 30% by volume from the viewpoint of efficiently proceeding with the crushing of specific particles.

[0065] The bead packing ratio refers to the ratio of the volume of the closest packed beads, including the voids between the beads, to the volume of the space in which the bead mill treatment of the bead mill disperser is carried out.

[0066] The bead mill disperser may be of a continuous type or a batch type, but is preferably of a batch type from the viewpoint of controlling the secondary particle diameter.

[0067] The shape of the stirring mechanism of the bead mill disperser is not particularly limited, and examples thereof include a disk type, a pin type, and an annular gap type.

[0068] The direction of the rotation axis of the stirring mechanism may be vertical or horizontal.

[0069] The rotation speed of the bead mill disperser is, for example, 1 m / s to 20 m / s.

[0070] The processing time for the bead mill treatment is, for example, 1 to 20 minutes.

[0071] The bead mill dispersing device may or may not be equipped with a bead separation mechanism. If the device does not have a bead separation mechanism, the slurry can be obtained by filtering the beads.

[0072] The D50 particle size of the slurry obtained by the dispersion treatment is preferably 1 μm to 10 μm.

[0073] From the viewpoint of dispersion control, the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture is preferably 0.1 to 0.5.

[0074] <Other Steps> The method for producing a slurry according to the present disclosure may include steps other than the kneading step and the dispersing step. For example, the method for producing a slurry according to the present disclosure may include a step of preparing a mixture to be used in the kneading step (hereinafter also referred to as a "mixture preparation step") before the kneading step is performed.

[0075] In the mixture preparation step, the components contained in the mixture may be mixed together, or only some of the components contained in the mixture may be mixed and the remaining components may be added later to prepare the mixture.

[0076] When the specific particles are electrode active materials, the specific particles and the conductive additive may be mixed first in order to coat the electrode active material with the conductive additive. In this case, it is preferable to perform dry mixing without adding a dispersion medium. It is also preferable to prepare the mixture by adding a dispersion medium after the dry mixing. Depending on the amount of dispersion medium added, the proportion of particles in the mixture can be adjusted to 28% by volume or less.

[0077] Hereinafter, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples as long as it does not depart from the gist of the disclosure.

[0078] [Mixture Preparation Step] The following components were mixed to obtain a mixture: spinel-type lithium titanate...24.6% by volume; carbon black...4% by volume; carboxymethyl cellulose...2% by volume; carbon nanotube dispersion (2% by mass)...69.4% by volume.

[0079] [Kneading step] The prepared mixture was kneaded using a planetary mixer (product name "Hivismix 2P-1", manufactured by Primix Corporation) for the time shown in Table 1. The rotation speed of the planetary mixer was adjusted so that the shear rate applied to the mixture would be the value shown in Table 1. The proportion of specific particles in the mixture used in the kneading step is shown in Table 1.

[0080] [Dispersion step] After the kneading step, in Example 1, Examples 4 to 8, Comparative Example 1, and Comparative Example 2, water and styrene-butadiene rubber were added so that the ratio of the specific particles in the kneading liquid was the value shown in Table 1. A bead mill disperser (product name "LMZ015", manufactured by Ashizawa Finetech Co., Ltd.) was used to carry out a dispersion treatment under the following conditions to obtain a slurry: Peripheral speed: 10 m / s Bead material: zirconia Bead diameter: 0.5 mm Bead filling rate: Value shown in Table 1 Dispersion time: Value shown in Table 1

[0081] <D50 Particle Diameter, Proportion of Fine Particles> The particle size distribution was obtained for each of the mixture obtained in the mixture preparation step, the kneaded product obtained in the kneading step, and the slurry obtained in the dispersion step using a laser diffraction / scattering particle size distribution analyzer (product name "MT-3200II", manufactured by Microtrac). The D50 particle size was determined from the particle size distribution. Furthermore, the proportion of particles with a particle size of 1 μm or less ("Proportion of fine particles" in Table 1) was calculated from the particle size distribution. The measurement conditions were as follows. The measurement results are shown in Table 1. Measurement mode: Reflection method Solvent refractive index: 1.333 (water) Transmittance: Approximately 0.9 Ultrasonic irradiation: 30 W, 60 seconds Method: The measurement sample was diluted approximately 10 times and placed in a circulation bath until the transmittance reached approximately 0.9. After the transmittance reached approximately 0.9, ultrasonic irradiation was performed and measurement was performed.

[0082] <Viscosity> The viscosity of the kneaded material at a shear rate of 1 / s was measured using a viscometer (product name "MCR72", manufactured by Anton Paar). The measurement results are shown in Table 1.

[0083] In Table 1, "D50 ratio" means the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture.

[0084]

[0085] As shown in Table 1, in Examples 1 to 8, the proportion of particles in the mixture was 28% by volume or less, and the bead filling rate in the bead mill treatment was 60% by volume or less, so that it was possible to obtain a slurry with controlled secondary particle size and reduced fine particles. On the other hand, in Comparative Example 1, the proportion of particles in the mixture was more than 28% by volume, indicating a high proportion of fine particles. In Comparative Example 2, the bead filling rate in the bead mill treatment was more than 60% by volume, indicating a high proportion of fine particles.

[0086] In Example 1, the shear rate applied to the mixture was 50 / s or higher, and compared to Example 6, all materials were more easily mixed uniformly during the kneading process. In Example 1, the shear rate applied to the mixture was 1500 / s or lower, and it was found that the proportion of fine particles in the slurry was further reduced compared to Example 7. In Example 1, the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture was 0.1 or higher, and compared to Example 8, it was possible to suppress the deterioration of battery performance associated with the increase in fine particles. In Example 1, the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture was 0.5 or lower, and compared to Example 6, it was possible to suppress the deterioration of battery performance associated with the increase in coarse particles.

[0087] The disclosure of Japanese Patent Application No. 2023-163977, filed on September 26, 2023, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing a slurry for batteries, comprising: kneading a mixture containing particles having a D50 particle size of 0.1 μm to 100 μm and a dispersion medium using a kneading machine to obtain a kneaded mixture; and performing a bead mill process on a kneading liquid containing the kneaded mixture to obtain a slurry, wherein the proportion of the particles in the mixture is 28 volume % or less, and the bead filling rate in the bead mill process is 60 volume % or less.

2. The method for producing a battery slurry according to claim 1, wherein the particles are inorganic particles.

3. The method for producing a battery slurry according to claim 1 or 2, wherein the particles have a primary particle diameter of 0.1 μm to 10 μm.

4. The method for producing a slurry for a battery according to claim 1 or 2, wherein the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture is 0.1 to 0.

5.

5. The method for producing a battery slurry according to claim 1 or 2, wherein a shear rate applied to the mixture is 50 / s to 1500 / s.

6. The method for producing a battery slurry according to claim 1 or 2, wherein the viscosity of the kneaded mixture is 1000 Pa·s or less.

7. The method for producing a battery slurry according to claim 1 or 2, wherein the mixture further contains a carbon material and a polymer.

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