WO2025069787A1 - Battery slurry manufacturing method - Google Patents

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

Manufacturing method of battery slurry

This disclosure relates to a method for producing a slurry for batteries.

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 then drying it.

For example, JP 2014-182892 A describes a method for producing an electrode slurry for 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.

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 first non-open type dispersing device, and dispersing the conductor paste dispersed using the first dispersing device using a second non-open type 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 first non-open type dispersing device, and dispersing the dielectric paste dispersed using the first dispersing device using a second non-open type dispersing device different from the first dispersing device.

The active material used in electrodes is particulate, and in the past, processes such as kneading and dispersion were carried out to break down coarse particles (specifically, agglomerates of primary particles). However, as the break down of coarse particles progressed, fine particles with a particle size smaller than the target particle size were sometimes generated. As the amount of fine particles increased, electrical resistance tended to increase, and a solid electrolyte interphase interface (SEI) film tended to be more easily formed. For this reason, there is a demand to suppress the generation of fine particles when breaking down coarse particles.

The problem that one embodiment of the present disclosure aims to solve 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 smaller than the desired secondary particle size are reduced.

The present disclosure includes the following aspects.
＜1＞
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 product;
The method includes a step of subjecting the kneaded liquid containing the kneaded material to a bead mill treatment to obtain a slurry,
The proportion of particles in the mixture is 28% by volume or less;
A method for producing a slurry for a battery, wherein the bead packing rate in a bead mill treatment is 60 volume % or less.
＜2＞
The method for producing a slurry for a battery according to <1>, wherein the particles are inorganic particles.
＜3＞
The method for producing a slurry for a battery according to <1> or <2>, wherein the particles have a primary particle diameter of 0.1 μm to 10 μm.
＜4＞
<3> The method for producing a slurry for a battery according to any one of <1> to <3>, wherein a ratio of a D50 particle size of the slurry to a D50 particle size of the mixture is 0.1 to 0.5.
＜5＞
<4> The method for producing a slurry for a battery 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 slurry for a battery according to any one of <1> to <5>, wherein the kneaded mixture has a viscosity of 1000 Pa·s or less.
＜７＞
The method for producing a slurry for a battery according to any one of <1> to <6>, wherein the mixture further contains a carbon material and a polymer.

According to one embodiment of the present disclosure, a method for producing a slurry for batteries is provided that can obtain a slurry in which the secondary particle size is controlled and particles smaller than the desired secondary particle size are reduced.

The manufacturing method for the battery slurry disclosed herein is described in detail below.

In this specification, the 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 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 a certain numerical range. In addition, 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.

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

[Method for producing battery slurry]
The manufacturing method of the battery slurry of the present disclosure (hereinafter, also simply referred to as the "slurry manufacturing method")
The method 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 the "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 the "dispersion step"), in which the ratio of particles in the mixture is 28 vol. % or less, and the filling rate of beads in the bead mill treatment is 60 vol. % or less.

The slurry produced by the slurry production method disclosed herein is used in batteries, and in particular in battery electrodes.

The type of battery in which the slurry is used is not particularly limited, but examples include lithium ion batteries, nickel-metal hydride batteries, fuel cells, etc.

The method for producing a slurry disclosed herein allows for the production of a slurry in which the secondary particle size is controlled and in which the amount of particles smaller than the desired secondary particle size is reduced. The reason for this is unclear, but is presumed to be as follows.

In the method for producing a slurry according to the present disclosure, the particles contained in the mixture and having a D50 particle size of 0.1 μm to 100 μm are present as secondary particles formed by agglomeration of primary particles. When the mixture is kneaded, by making the ratio of particles in the mixture 28% by volume or less, shear force is unlikely to act on the agglomerated secondary particles, and fine particles are unlikely to peel off from the surfaces of the agglomerated secondary particles. Therefore, it is believed that, although the disintegration of particles proceeds in the kneading step, the generation of fine particles is suppressed.
In addition, when the bead mill treatment is performed on the kneaded liquid containing the kneaded product obtained in the kneading step, by setting the bead filling rate to 60 volume % or less, the particles are crushed by collision between the beads, while the shear force is unlikely to act between the beads, which is thought to suppress the generation of fine particles.
Therefore, it is believed that by controlling the particle ratio in the mixture and the bead filling rate, the secondary particle size can be controlled and a slurry can be obtained in which the amount of particles smaller than the desired secondary particle size is reduced.

On the other hand, JP 2014-182892 A does not disclose the ratio of particles in the kneaded material. Furthermore, in JP 2014-182892 A, a bead mill treatment is not performed after the kneaded material is obtained.
In JP-A Nos. 2006-156204 and 2006-156202, the solid content of the mixture in the kneading step is 85 to 95% by weight, which is an extremely high concentration.

The steps in the slurry manufacturing process are explained below.

<Kneading process>
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 product.
In the kneading step, the mixture before kneading is referred to as a "mixture", and the mixture after kneading is referred to as a "kneaded product".

The specific particles contained in the mixture have a D50 particle size of 0.5 μm to 50 μm, and 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.

D50 particle size refers to the particle size when the number of particles in the population of particles being measured is 50% by volume.

In this disclosure, the D50 particle size is measured using a laser diffraction/scattering type particle size distribution measuring device. For example, the MT-3200II manufactured by Microtrac is used as the laser diffraction/scattering type particle size distribution measuring device.

The specific particles preferably have a primary particle size of 0.1 μm to 10 μm, and more preferably 0.5 μm to 5 μm.
When the primary particle size is 0.1 μm or more, the specific particles once disintegrated are less likely to re-aggregate, and the secondary particle size is easier to control. On the other hand, when the primary particle size is 10 μm or less, the specific particles are less likely to settle, and the mixture and kneaded product are easier to homogenize.

In this disclosure, the primary particle size of a specific particle is measured using a laser diffraction/scattering type particle size distribution measuring device.

The specific particles contained in the mixture may be organic particles, inorganic particles, or composite particles of inorganic and organic substances.

The specific particles are preferably inorganic particles, since it is easier to control the particle size.

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.

Examples of inorganic particles include particles of minerals such as mica, inorganic pigment particles, etc.

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.

Examples of composite particles of inorganic and organic substances include composite particles in which inorganic particles are dispersed in a matrix of organic substances, composite particles in which organic particles are coated with inorganic substances, and composite particles in which inorganic particles are coated with organic substances.

The specific particles may be subjected to a surface treatment for the purpose of imparting dispersibility, etc.
The composite particles may be formed by subjecting the particles to a surface treatment.

In addition, from the viewpoint of obtaining a battery slurry, it is preferable that the specific particles are electrode active materials.

Examples of the electrode active material include a negative electrode active material and a positive electrode active material.
Examples of the negative electrode active material and positive electrode active material include negative electrode active materials and positive electrode active materials in known lithium ion secondary batteries.

Specific examples of negative electrode active materials 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.

Specific examples of the positive electrode active material include lithium transition metal composite oxides containing lithium and transition metal elements, such as lithium nickel composite oxides (e.g., _LiNiO2 ) and lithium nickel cobalt manganese composite oxides (e.g., LiNi1 _{/3Co1 / 3Mn1/ 3O2} ).

The dispersion medium contained in the mixture is not particularly limited, but from the viewpoint of dispersion stability, water is preferable.

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.
The water content 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.

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

From the viewpoint of improving the battery characteristics, it is preferable that the mixture further contains a carbon material and a polymer.

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 conductive additives.

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

Other examples of polymers include carboxymethylcellulose (CMC), methylcellulose (MC), and hydroxypropylmethylcellulose (HPMC). These polymers function as thickeners to adjust the viscosity of the slurry.

Furthermore, examples of polymers include polyvinylpyrrolidone and polyvinyl alcohol. These polymers function as dispersants that disperse specific particles in the mixture.

The content of the carbon material is preferably 0.5% by mass to 5% by mass based on the total amount of the mixture.
The content of the polymer is preferably 0.5% by mass to 5% by mass based on the total amount of the mixture.

The kneader used to knead the mixture may be of the continuous type or the batch type, but from the viewpoint of controlling the secondary particle size, it is preferable to use the batch type.

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

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.

The mixture is kneaded for, for example, 10 to 180 minutes.

When the mixture is kneaded, the ratio of the specific particles in the mixture is 28 volume % or less.
By setting the ratio of the specific particles to 28% by volume or less, shear force is unlikely to act on the specific particles, and fine particles are unlikely 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.

The lower limit of the proportion of the specific particles in the mixture is not particularly limited, but from the viewpoint of efficiently proceeding with the disintegration of the specific particles, it is preferably 20% by volume.

The viscosity of the kneaded product obtained by the kneading process (viscosity at a shear rate of 1/s) is preferably 1000 Pa·s or less. There is no particular lower limit to the viscosity of the kneaded product, but for kneading purposes, it is preferably 1 Pa·s.

In this disclosure, viscosity is measured at 25°C using a viscometer such as the MCR72 manufactured by Anton Paar.

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

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

<Dispersion process>
The dispersion step is a step in which a kneading liquid containing the kneaded material is subjected to a bead mill treatment to obtain a slurry.

As mentioned above, the mixture after kneading is called the "kneaded product." The kneaded product used in the bead mill process is called the "kneaded liquid."

The kneaded product obtained in the kneading step may be used as it is in the dispersion step, that is, the kneaded product and the kneading liquid may be the same.
Moreover, water may be further added to the kneaded material to prepare a kneading liquid.

The ratio of the specific particles in the kneading liquid is preferably 28% by volume or less.
The lower limit of the ratio of the specific particles in the kneading liquid is not particularly limited, but from the viewpoint of efficiently proceeding with the disintegration of the specific particles, it is preferably 20% by volume.

Bead mill processing can be carried out using a commonly known bead mill disperser.

Examples of materials for the beads used in the 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, from the viewpoint of wear resistance, the material of the beads is preferably zirconia.

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.

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

When the bead filling rate is 60% by volume or less, the collisions between the beads will cause the crushing of certain particles, but shear forces between the beads will be less likely to act, suppressing the generation of fine particles.

The lower limit of the bead filling rate is not particularly limited, but from the viewpoint of efficiently disintegrating specific particles, it is preferable that the filling rate is 30% by volume.

The bead packing rate refers to the ratio of the volume of closely packed beads, including the voids between the beads, to the volume of the space in which the bead milling process of the bead mill disperser takes place.

The bead mill disperser may be of the continuous type or the batch type, but from the viewpoint of controlling the secondary particle size, the batch type is preferable.

The shape of the stirring mechanism of the bead mill disperser is not particularly limited, and examples include disk type, pin type, and annular gap type.

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

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

The processing time for bead mill processing is, for example, 1 to 20 minutes.

The bead mill dispersion device may or may not have a bead separation mechanism. If it does not have a bead separation mechanism, the slurry can be obtained by filtering the beads.

The D50 particle size of the slurry obtained by the dispersion process is preferably 1 μm to 10 μm.

In addition, from the viewpoint of dispersion control, it is preferable that the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture is 0.1 to 0.5.

<Other processes>
The method for producing a slurry according to the present disclosure may include other steps in addition to the kneading step and the dispersing step.
The method for producing a slurry according to the present disclosure may include, for example, a step of preparing a mixture to be used in the kneading step (hereinafter also referred to as a "mixture preparation step") before carrying out the kneading step.

In the mixture preparation process, 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.

When the specific particles are electrode active materials, the specific particles and the conductive assistant may be mixed first in order to coat the electrode active material with the conductive assistant. 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. The proportion of particles in the mixture can be adjusted to 28 volume % or less by adjusting the amount of dispersion medium added.

The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to the following examples as long as they do not deviate from the gist of the disclosure.

[Mixture preparation process]
The following ingredients 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

[Kneading process]
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 was the value shown in Table 1.
The proportion of specific particles in the mixture used in the kneading step is shown in Table 1.

[Dispersion process]
After the kneading step, in Examples 1, 4 to 8, Comparative Examples 1 and 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.
Dispersion treatment was carried out under the following conditions using a bead mill disperser (product name "LMZ015", manufactured by Ashizawa Finetech Co., Ltd.) to obtain a slurry.
Circumferential speed: 10 m/s
Bead material: Zirconia Bead diameter: 0.5mm
Bead packing ratio: Value shown in Table 1 Dispersion time: Value shown in Table 1

<D50 particle size, proportion of fine particles>
The particle size distribution of 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 was obtained using a laser diffraction/scattering type particle size distribution measurement device (product name "MT-3200II", manufactured by Microtrac Corporation).
The D50 particle size was determined from the particle size distribution.
Furthermore, the proportion of particles having 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 are as follows. The measurement results are shown in Table 1.
Measurement mode: Reflection method Solvent refractive index: 1.333 (water)
Transmittance: approx. 0.9
Ultrasonic irradiation: 30 W, 60 seconds. Method: The measurement sample was diluted about 10 times and placed in a circulation bath until the transmittance reached about 0.9. After the transmittance reached about 0.9, ultrasonic irradiation was performed and measurement was performed.

<Viscosity>
The viscosity of the kneaded product 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.

In Table 1, "D50 ratio" refers to the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture.

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 a slurry with a controlled secondary particle size and reduced fine particles was obtained.
On the other hand, in Comparative Example 1, the proportion of particles in the mixture was more than 28 volume %, indicating that the proportion of fine particles was high.
In Comparative Example 2, the bead filling rate in the bead mill treatment was more than 60 volume %, indicating that the proportion of fine particles was high.

In Example 1, the shear rate applied to the mixture is 50/s or more, and compared to Example 6, all the materials are more likely to be mixed uniformly in the kneading step.
In Example 1, the shear rate applied to the mixture was 1500/s or less, 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 is 0.1 or more, and compared to Example 8, the deterioration of battery performance due to an increase in fine particles can be suppressed.
In Example 1, the ratio of the D50 particle size of the slurry to the D50 particle size of the mixture is 0.5 or less, and compared to Example 6, the deterioration of battery performance due to an increase in coarse particles can be suppressed.

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 (7)

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 product;
A step of subjecting the kneaded liquid containing the kneaded material to a bead mill treatment to obtain a slurry,
The proportion of the particles in the mixture is 28% by volume or less;
The method for producing a slurry for a battery, wherein a filling rate of beads in the bead mill treatment is 60 volume % or less. The method for producing a battery slurry according to claim 1, wherein the particles are inorganic particles. 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. The method for producing a battery slurry 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. The method for producing a battery slurry according to claim 1 or 2, wherein the shear rate applied to the mixture is 50/s to 1500/s. The method for producing a battery slurry according to claim 1 or 2, wherein the viscosity of the kneaded material is 1000 Pa·s or less. The method for producing a battery slurry according to claim 1 or 2, wherein the mixture further contains a carbon material and a polymer.