Method for preparing electrode active material slurry

Abstract

An object of the present disclosure is to improve the dispersibility of a raw material mixture by thermal convection generated during kneading of the raw material mixture, thereby improving the quality of an electrode active material slurry.SOLUTION: The method of the present disclosure for producing an electrode active material slurry is a method for producing an electrode active material slurry, comprising kneading a raw material mixture in a kneading device, wherein the kneading device has a heating part that heats a lowermost part of the raw material mixture and a cooling part that cools an uppermost part of the raw material mixture, and during kneading, a temperature of the heating part is higher than a temperature of the cooling part by 5 °C or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing an electrode active material slurry. [Background technology]

[0002] In recent years, the range of uses of lithium-ion secondary batteries has expanded to various applications, such as being installed in hybrid vehicles, etc. This has led to an increasing need for improved performance of lithium-ion secondary batteries, and the importance of technologies related to improving the performance of lithium-ion secondary batteries has increased.

[0003] In the manufacturing process of a lithium ion secondary battery, an electrode active material slurry (or paste) for an anode and an electrode active material slurry (or paste) for a cathode are generally used to form an anode active material layer and a cathode active material layer, respectively. Since the quality of each slurry is directly related to the performance of the lithium ion secondary battery, quality control of the slurry in the manufacturing process of the lithium ion secondary battery is a very important factor.

[0004] For example, Patent Document 1 discloses a paste manufacturing method including a powder mixing step in which raw powders for the paste are mixed to produce a powder mixture, a first dispersion medium addition step in which a dispersion medium is added to the powder mixture to produce raw materials, a hardening step in which the raw materials are kneaded to promote dispersion of the powder mixture in the raw materials, and a second dispersion medium generation step in which a dispersion medium is further added to the raw materials that have undergone the hardening step, the method comprising: determining correlations between the amount of dispersion medium added in the first dispersion medium addition step and the viscosity, particle size, and peel strength of the paste when the hardening time of the hardening step is constant; and determining an optimal amount of dispersion medium to be added in the first dispersion medium addition step based on the correlations. The method described in Patent Document 1 is said to control the manufacturing conditions in the hardening step, enable paste quality control, enable the supply of paste of consistent quality, and contribute to consistent quality of lithium secondary batteries.

[0005] Patent Document 2 discloses a method for producing a slurry for battery electrodes by introducing at least an electrode active material and various constituent materials such as a binder into an agitation tank of an agitation device to produce a slurry for battery electrodes, the agitation device comprising: a bottom-side blade that rotates closest to the bottom wall of the agitation tank and acts to push the material introduced into the agitation tank toward the inner wall; a dispersion blade that is provided above the bottom-side blade and rotates a resistance member formed in a vertical direction around a rotation center to improve the dispersibility of the material introduced; and a vortex flow generating blade that is provided above the dispersion blade and generates a vortex flow in the central region of the agitation tank. The method described in Patent Document 2 is said to enable the production of a slurry suitable for battery electrodes with good coatability and dispersibility in a short period of time.

[0006] Patent Document 3 discloses a kneading method for producing a battery electrode slurry by forcing, transporting, and kneading materials for producing a battery electrode slurry including a binder, the method comprising: a first step of supplying a plurality of materials for producing the battery electrode slurry, kneading the supplied plurality of materials, and continuously discharging the supplied materials; a second step of transporting the materials discharged in the first step; a third step of measuring the temperature of at least one of the materials being kneaded in the first step and the materials being transported in the second step; and a fourth step of controlling, based on the measurement result in the third step, the temperature of at least one of the materials being supplied for kneading in the first step, the materials being kneaded in the first step, and the materials being transported in the second step to be lower than the curing temperature of the binder. The method described in Patent Document 3 is said to be able to maintain stable quality of the battery electrode slurry.

[0007] Patent Document 4 discloses a method for producing an electrode slurry containing a solvent, active material particles, and a resin dissolved in the solvent, the method comprising: a stirring step of stirring the active material particles and the resin to form a dispersed slurry; and a fluidized and stored step of causing the stirred dispersed slurry to flow to a storage section and storing it in the storage section, the stirring step and the fluidized and stored step being performed while maintaining the temperature of the dispersed slurry and the temperature of members in contact with the dispersed slurry at any location where the dispersed slurry will be present higher than the dew point temperature of the atmosphere in contact with the dispersed slurry at that location. The method described in Patent Document 4 is said to be able to prevent deterioration of properties due to moisture contamination during the process from kneading to storage.

[0008] Patent Document 5 discloses an apparatus for measuring the viscosity of electrode slurry, comprising: a slurry chamber for containing electrode slurry obtained by mixing electrode powder and a solvent; a slurry inlet for introducing the electrode slurry into the slurry chamber; a slurry outlet for discharging the electrode slurry from the slurry chamber; a vibration viscometer disposed in the slurry chamber; and a slurry flow generator for providing a constant slurry flow to the vibration viscometer. The apparatus described in Patent Document 5 is said to be capable of measuring the viscosity of electrode slurry for quality control in continuous production in situ. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent Publication No. 2010-257653 [Patent Document 2] Patent Publication No. 2013-093140 [Patent Document 3] Patent Publication No. 2017-188397 [Patent Document 4] Patent Publication No. 2010-182485 [Patent Document 5] Patent Publication No. 2018-060703 Summary of the Invention [Problem to be solved by the invention]

[0010] In the production of electrode active material slurries, mechanical mixing is generally used, and a raw material mixture is mixed using a mixing device. In this case, when mixing the electrode active material slurry, the raw material mixture may not be sufficiently dispersed, resulting in aggregation. If aggregation of the raw material mixture occurs, the homogeneity and quality of the electrode active material slurry will be reduced.

[0011] Therefore, an object of the present disclosure is to improve the dispersibility of the raw material mixture by using thermal convection that occurs during kneading of the raw material mixture, thereby improving the quality of the electrode active material slurry. [Means for solving the problem]

[0012] The present disclosure achieves the above object by the following means.

[0013] (Aspect 1) A method for producing an electrode active material slurry, comprising kneading a raw material mixture in a kneading device, the kneading device has a heating section that heats the lowest part of the raw material mixture and a cooling section that cools the highest part of the raw material mixture; and During kneading, the temperature of the heating zone is 5°C or more higher than the temperature of the cooling zone. A method for producing an electrode active material slurry. (Aspect 2) 2. The method of claim 1, wherein the temperature of the bottom of the raw mixture is at least 5° C. higher than the temperature of the top of the raw mixture during kneading. (Aspect 3) 3. The method of claim 1, wherein the raw material mixture has a viscosity of 90,000 mPa·s or more. (Aspect 4) Producing an electrode active material slurry by the method according to any one of aspects 1 to 3; and applying and drying the electrode active material slurry to form an electrode active material layer; A method for manufacturing a secondary battery, comprising: [Effects of the Invention]

[0014] According to the method of the present disclosure, the thermal convection that occurs during kneading of the raw material mixture can improve the dispersibility of the raw material mixture, and the resulting improvement in the quality of the electrode active material slurry can be achieved. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of a kneading device that can be used in the method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Method for producing electrode active material slurry> The disclosed method for producing an electrode active material slurry comprises: A method for producing an electrode active material slurry, comprising kneading a raw material mixture in a kneading device, the kneading device has a heating section that heats the lowest part of the raw material mixture and a cooling section that cools the highest part of the raw material mixture; and During kneading, the temperature of the heating section is higher than the temperature of the cooling section by 5° C. or more.

[0017] According to the method of the present disclosure for producing an electrode active material slurry, it is possible to improve the dispersibility of the raw material mixture and, as a result, improve the quality of the electrode active material slurry.

[0018] In conventional manufacturing methods, the raw material mixture is kneaded in a kneading device. However, in this case, the materials are not sufficiently dispersed, and aggregation of the raw material mixture occurs. Such aggregation of the raw material mixture reduces the homogeneity and quality of the electrode active material slurry.

[0019] In contrast, according to the method of the present disclosure, the kneading apparatus has a heating section that heats the bottom of the raw material mixture and a cooling section that cools the top of the raw material mixture, and the raw material mixture is kneaded in a state in which the temperature of the heating section of the kneading apparatus is at least 5°C higher than the temperature of the cooling section of the kneading apparatus. This allows thermal convection, particularly Bénard convection, to occur in the raw material mixture during kneading. This thermal convection can improve the dispersibility of the raw material mixture and, therefore, the quality of the electrode active material slurry can be improved.

[0020] Specifically, during kneading, the temperature of the heating zone may be higher than the temperature of the cooling zone by at least 5° C., at least 10° C., at least 20° C., at least 30° C., at least 40° C., at least 50° C., or at least 60° C. Furthermore, this temperature difference may be 100° C. or less, 90° C. or less, 80° C. or less, or 70° C. or less.

[0021] The temperature of the heating zone may be 60°C or higher, 65°C or higher, or 70°C or higher, and may be 90°C or lower, 85°C or lower, or 80°C or lower. The temperature of the cooling zone may be 0°C or higher, 5°C or higher, or 10°C or higher, and may be 30°C or lower, 25°C or lower, or 20°C or lower. In particular, when the temperatures of the heating zone and the cooling zone are both 5°C or higher and 80°C or lower, extreme deterioration of the slurry can be suppressed.

[0022] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present disclosure.

[0023] The method for producing an electrode active material slurry in the present disclosure includes kneading a raw material mixture in a kneading device.

[0024] In the method of the present disclosure, kneading can be performed using a kneading device such as a mixer, a ball mill, a sand mill, a bead mill, a disperser, an ultrasonic disperser, a homogenizer, a homomixer, a planetary mixer, a planetary stirring and degassing device, etc. The mixing speed in the kneading device can be freely set within a range of speeds at which each component of the electrode active material slurry can be sufficiently dispersed or dissolved.

[0025] The kneading device has a heating section for heating the lowermost part of the raw material mixture and a cooling section for cooling the uppermost part of the raw material mixture.

[0026] Specifically, the heating unit may be an electric heater, a heat exchanger having a heating fluid flow path, or the like. The cooling unit may be a heat exchanger having a cooling fluid flow path, or the like. The heating unit and the cooling unit may be in direct contact with the bottom and top of the raw material mixture, respectively, or may be in contact with the bottom and top of the raw material mixture via a heat-conductive medium such as metal, or may be disposed with a gap between them.

[0027] For example, as shown in FIG. 1, the kneading device 10 used in the method of the present disclosure includes a kneading container 2 in which the raw material mixture 20 is accommodated, a stirrer 4, a heating section 6 that heats the bottom 20b of the raw material mixture 20, and a cooling section 8 that cools the top 20a of the raw material mixture 20.

[0028] (Electrode active material slurry) The electrode active material slurry is produced by kneading a raw material mixture in a kneading device. The raw material mixture may contain an electrode active material powder and a dispersion medium.

[0029] The viscosity of the raw material mixture is -1The viscosity of the raw material mixture may be 80,000 mPa·s or more, 90,000 mPa·s or more, or 100,000 mPa·s or more, or 150,000 mPa·s or less, 140,000 mPa·s or less, or 130,000 mPa·s or less. In particular, a raw material mixture having a viscosity of 90,000 mPa·s or more is preferred for generating Benard convection within the raw material mixture and improving the homogeneity of the resulting electrode active material slurry. In other words, the electrode active material slurry produced by the method of the present disclosure has a relatively high viscosity and may therefore be in a state generally referred to as a paste.

[0030] The viscosity of the raw material mixture is measured, for example, using a viscosity measuring instrument at a measurement temperature of 25°C and a shear rate of 0.1 s -1 The viscosity can be measured under the conditions shown above. A Kinexus series rotational rheometer (NETZSCH) or the like can be used as a viscosity measuring device. When the viscosity of the raw material mixture changes during kneading, the raw material mixture can have the above viscosity for at least a portion of the period during kneading.

[0031] The electrode active material powder may be a positive electrode active material powder or a negative electrode active material powder. The raw material mixture may further contain a conductive additive, a binder, etc. When producing a positive electrode active material slurry as an electrode active material slurry, the raw material mixture may contain, in addition to a dispersion medium, a positive electrode active material powder, a binder, and, if necessary, a conductive additive. When producing a negative electrode active material slurry as an electrode active material slurry, the raw material mixture may contain, in addition to a dispersion medium, a negative electrode active material powder, a binder, and, if necessary, a conductive additive. The active material powder may be 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more of the raw material mixture, and may be 96 parts by mass or less, 98 parts by mass or less, or 100 parts by mass or less.

[0032] (Cathode active material) The material of the positive electrode active material is not particularly limited. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), lithium manganese oxide (LiMnO), and nickel-cobalt-manganese lithium oxide (NCM:LiCO1 / 3 Ni 1 / 3 Mn 1 / 3 O2), lithium nickel-cobalt-aluminate (LiNi 0.8 (CoAl) 0.2 O2), Li 1+x Mn 2-x-y M y The material may be, but is not limited to, a heteroelement-substituted Li-Mn spinel having a composition represented by O4 (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni, and Zn).

[0033] The shape of the positive electrode active material is not particularly limited. The positive electrode active material may be in the form of primary particles or secondary particles formed by agglomeration of a plurality of primary particles. The average particle diameter D of the positive electrode active material 50 The average particle size D may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. 50 is the particle size (median size) at 50% cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering method.

[0034] (Negative electrode active material) The material of the negative electrode active material is not particularly limited, and may be metallic lithium or a material capable of absorbing and releasing metal ions such as lithium ions. Examples of materials capable of absorbing and releasing metal ions such as lithium ions include alloy-based negative electrode active materials, carbon materials, and lithium titanate (Li4Ti5O 12 ) and the like can be mentioned, but are not limited to these.

[0035] The alloy-based negative electrode active material is not particularly limited, and examples thereof include Si alloy-based negative electrode active materials and Sn alloy-based negative electrode active materials. Si alloy-based negative electrode active materials include silicon, silicon oxide, silicon carbide, silicon nitride, and solid solutions thereof. Si alloy-based negative electrode active materials can also include metal elements other than silicon, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. Sn alloy-based negative electrode active materials can also include tin, tin oxide, tin nitride, and solid solutions thereof. Sn alloy-based negative electrode active materials can also include metal elements other than tin, such as Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Ti, and Si.

[0036] The carbon material is not particularly limited, and examples thereof include hard carbon, soft carbon, graphite, and the like.

[0037] The shape of the negative electrode active material is not particularly limited. The negative electrode active material may be in the form of primary particles or secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter D of the negative electrode active material 50 The average particle size D may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. 50 is the particle size (median size) at 50% cumulative value in the volume-based particle size distribution determined by laser diffraction / scattering method.

[0038] (Conductive additive) The conductive additive may be a carbon powder such as acetylene black, furnace black, or carbon black. A mixture of these may also be used. The amount of the conductive additive may be 0.001 parts by mass or more, 0.003 parts by mass or more, or 0.005 parts by mass or more, or 0.3 parts by mass or less, 0.2 parts by mass or less, or 0.1 parts by mass or less, of the raw material mixture.

[0039] (binder) Examples of binders that can be used include organic solvent-based (non-aqueous) binders such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), which are dissolved in an organic solvent. Examples of aqueous binders include water-dispersible styrene butadiene rubber (SBR), ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, and aqueous polymers such as carboxymethyl cellulose (CMC), which is not only used in combination with SBR but has also recently attracted attention as a binder, and alginic acid compounds. Mixtures of these binders can also be used. The binder may be present in an amount of 0.01 parts by mass or more, 0.05 parts by mass or more, or 0.1 parts by mass or more of the raw material mixture, and may be present in an amount of 9 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less.

[0040] The binder can be dissolved or dispersed in a solvent. Examples of the solvent include N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, toluene, and water, and a mixture of these can also be used. These can be selected appropriately depending on the type and properties of the thickener and active material used.

[0041] (dispersion medium) Specific examples of the dispersion medium that can be used include N-methyl-2-pyrrolidone (hereinafter sometimes abbreviated as "NMP"), dimethylformamide, dimethylacetamide, methanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, tetrahydrofuran, and water. These dispersion media may be used alone or in combination of two or more. From the viewpoints of versatility, ease of removal, and the like, NMP or water is preferred as the dispersion medium. The amount of the dispersion medium may be 0.01 parts by mass or more, 0.05 parts by mass or more, or 0.1 parts by mass or more of the raw material mixture, or may be 9 parts by mass or less, 7 parts by mass or less, or 5 parts by mass or less.

[0042] <Secondary battery manufacturing method> The disclosed method for manufacturing a secondary battery includes: Producing an electrode active material slurry by the method of the present disclosure; and applying and drying the electrode active material slurry to form an electrode active material layer; Includes:

[0043] The electrode active material slurry can be applied to a current collector and then dried, or can be applied to a transfer substrate, dried, and then transferred to a current collector.

[0044] The present disclosure will be described in more detail with reference to the following examples, but the scope of the present disclosure is not limited to these examples. [Example]

[0045] Hereinafter, an electrode active material slurry was produced according to the production method according to the embodiment.

[0046] Comparative Example 1 A raw material mixture containing the following materials was prepared: Active material: Artificial graphite (D 50 =20μm), 95 parts by mass Dispersion medium: carboxymethyl cellulose (CMC), 1 part by mass Conductive additive: carbon nanotubes (CNT), 0.1 parts by mass Binder: styrene butadiene rubber (SBR), 3.9 parts by mass

[0047] A planetary mixer was used as the kneading device. The kneading device had a cooling section at the top of the kneading device and a heating section at the bottom of the kneading device. The raw material mixture was supplied to the kneading device and kneaded under the following conditions to obtain an electrode active material slurry of Comparative Example 1. The temperature of the top of the raw material mixture was substantially the same as the temperature of the cooling section at the top of the kneading device, and the temperature of the bottom of the raw material mixture was substantially the same as the temperature of the heating section at the bottom of the kneading device.

[0048] Temperature of the upper cooling section of the kneading device (top of the raw material mixture): 25°C Temperature of the heating section at the bottom of the kneading device (bottom of the raw material mixture): 25°C Temperature difference: 0℃

[0049] Comparative Example 2 and Examples 1 to 6 The electrode active material slurries of Comparative Example 2 and Examples 1 to 6 were obtained in the same manner as Comparative Example 1, except that the temperature of the upper cooling section of the kneading device (the top of the raw material mixture) and the temperature of the lower heating section of the kneading device (the bottom of the raw material mixture) were changed as shown in Table 1 below.

[0050] <Evaluation> The viscosity of the electrode active material slurries of Comparative Examples 1 and 2 and Examples 1 to 6 was measured using a rheometer. -1 The viscosity was 120,000 mPa·s. The electrode active material slurries of Comparative Examples 1 and 2 and Examples 1 to 6 were evaluated for the presence or absence of aggregation using a grind gauge (particle size gauge). Specifically, each electrode active material slurry was squeegeeed on the grind gauge, and electrode active material slurries that showed no streaks up to 200 μm were determined to have no aggregation, and electrode active material slurries that showed streaks up to 200 μm or more were determined to have aggregation. The evaluation results are shown in Table 1 below.

[0051] [Table 1]

[0052] From Table 1, it can be seen that aggregation was observed in the electrode active material slurries of Comparative Examples 1 and 2, in which the difference in temperature between the cooling section (top of the raw material mixture) and the heating section (bottom of the raw material mixture) was less than 5°C, whereas aggregation was not observed in the electrode active material slurries of Examples 1 to 6, in which the difference in temperature between the cooling section (top of the raw material mixture) and the heating section (bottom of the raw material mixture) was 5°C or more. [Explanation of symbols]

[0053] 2. Mixing vessel 4 Stirring bar 6 Heating section 8 Cooling section 10 Kneading equipment 20 Raw material mixture 20a Top of raw material mixture 20b Bottom of raw material mixture

Claims

1. A method for producing an electrode active material slurry, comprising kneading a raw material mixture in a kneading device, the kneading device has a heating section that heats the lowest part of the raw material mixture and a cooling section that cools the highest part of the raw material mixture; and During kneading, the temperature of the heating section is higher than the temperature of the cooling section by 5°C or more. A method for producing an electrode active material slurry.

2. 2. The method of claim 1, wherein the temperature of the bottom of the raw material mixture is at least 5°C higher than the temperature of the top of the raw material mixture during kneading.

3. 2. The method of claim 1, wherein the viscosity of the raw mixture is 90,000 mPa·s or more.

4. Producing an electrode active material slurry by the method of claim 1; and applying and drying the electrode active material slurry to form an electrode active material layer; A method for manufacturing a secondary battery, comprising:

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