Method for manufacturing electrode

Abstract

This method for manufacturing an electrode comprises: a mixing step (S01) for mixing, with dry powder, a material that constitutes an electrode used in a nonaqueous electrolyte secondary battery and that contains an active material, a conductive material, and a thickener; a dilution step (S03) for producing a slurry by adding a liquid agent to the mixture mixed in the mixing step; and a formation step (S04) for forming the slurry produced in the dilution step into an electrode. In the mixing step, the material is mixed using a high-speed shear impact mixer 10 having a first blade 11 for mixing the material as a whole and a second blade 12 for applying a shear force to the material.

Description

Electrode manufacturing method

[0001] The present invention relates to a method for producing an electrode used in a non-aqueous electrolyte secondary battery.

[0002] Conventionally, in order to manufacture electrodes for use in non-aqueous electrolyte secondary batteries, a technique has been adopted in which a liquid agent is added to materials containing an active material, a conductive material, etc. to manufacture a slurry (see, for example, Patent Document 1).

[0003] JP 2016-103391 A

[0004] When producing the above-mentioned slurry, a two-shaft planetary agitation mixer is sometimes used. When adding a liquid agent to a material to produce a slurry using a two-shaft planetary agitation mixer, a long processing time is required, so there was a demand for improved productivity.

[0005] The present invention has been made in view of the above circumstances, and the problem that the present invention aims to solve is to provide a method for manufacturing an electrode that can shorten the manufacturing time of a slurry without deteriorating battery performance compared to conventional methods.

[0006] Below, we will explain means for solving the above problems.

[0007] The method for producing an electrode according to the present invention comprises a mixing step of mixing materials containing an active material, a conductive material, and a thickener, which constitute an electrode for use in a non-aqueous electrolyte secondary battery, in the form of dry powder; a dilution step of adding a liquid agent to the mixture mixed in the mixing step to produce a slurry; and a formation step of forming the slurry produced in the dilution step into the electrode, wherein in the mixing step, the materials are mixed using a high-speed shear impact mixer having a first blade that mixes the materials overall and a second blade that applies a shear force to the materials.

[0008] In addition, it is preferable that a binder be added to the mixture in the dilution step.

[0009] In the electrode manufacturing method, it is preferable that in the mixing step, the speed of the tip of the second blade is set to 5 m / sec or more and 40 m / sec or less.

[0010] Furthermore, in the method for manufacturing an electrode, it is preferable to provide a kneading step, after the mixing step and before the dilution step, in which a solvent is added to the mixture mixed in the mixing step and kneaded, and in the dilution step, the liquid agent is added to the mixture kneaded in the kneading step to produce the slurry.

[0011] In the electrode manufacturing method, it is preferable to use a two-shaft planetary agitation mixer in the kneading step and the dilution step.

[0012] According to the method for producing an electrode of the present invention, the time required for producing a slurry can be shortened without deteriorating the battery performance compared to the conventional method.

[0013] Fig. 1 is a flow diagram showing a method for manufacturing an electrode. Fig. 2 is a schematic cross-sectional view showing a high-speed shear impact mixer. Fig. 3 is a schematic cross-sectional view showing a high-speed shear impact mixer. Fig. 4 is a schematic cross-sectional view showing a two-shaft planetary agitation mixer. Fig. 5 is a diagram showing the results of an electrode evaluation test.

[0014] [Electrode Manufacturing Method] First, a method for manufacturing an electrode according to one embodiment of the present invention will be described with reference to Fig. 1. The electrode manufacturing method according to this embodiment is used when constructing an electrode for a non-aqueous electrolyte secondary battery. As shown in Fig. 1, the electrode manufacturing method includes a mixing step (S01), a kneading step (S02), a dilution step (S03), and a forming step (S04). Each step will be described in order below.

[0015] In this embodiment, the mixing step (S01) involves mixing materials containing an active material, a conductive material, and a thickener in dry powder form. As shown in Figures 2A and 2B, a high-speed shear impact mixer 10 is used in this step. The high-speed shear impact mixer 10 has a mixing arm, which is a first blade 11 that thoroughly mixes the materials, and a chopper blade, which is a second blade 12 that applies a shear force to the materials.

[0016] 2A and 2B, the high-speed shear impact mixer 10 of this embodiment is configured so that three first blades 11 and six second blades 12 rotate inside a mixing vessel 10a having a material inlet 10b formed at the top. As shown in Fig. 2A, the first blades 11 rotate inside the mixing vessel 10a by the driving force of a motor (not shown) transmitted through a first shaft 11a. Similarly, the second blades 12 rotate inside the mixing vessel 10a by the driving force of a motor (not shown) transmitted through a second shaft 12a.

[0017] In the high-speed shear impact mixer 10 of this embodiment, the first blade 11 is configured to rotate in a first rotation direction, as shown by arrow R1 in Fig. 2B. On the other hand, the second blade 12 is configured to rotate in a direction opposite to the first rotation direction, as shown by arrow R2 in Fig. 2B. In the high-speed shear impact mixer 10 configured in this manner, the first blade 11 thoroughly mixes the materials, and the second blade 12 applies a shear force to the materials.

[0018] The high-speed shear impact mixer 10 configured as described above applies shear force to the materials with the second blades 12 while thoroughly mixing the materials with the first blades 11. In the high-speed shear impact mixer 10, the speed of the blade tip of the second blades 12 is set to 5 m / s or more and 40 m / s or less.

[0019] Next, in the kneading step (S02), a solvent is added to the mixture mixed in the mixing step (S01) and kneaded. After that, in the dilution step (S03), a liquid agent is added to the kneaded product kneaded in the kneading step (S02) to produce a slurry. Next, in the forming step (S04), the slurry produced in the dilution step (S03) is formed into an electrode.

[0020] In the above-mentioned kneading step (S02) and dilution step (S03), a two-shaft planetary agitation mixer 20 is used, as shown in Fig. 3. Note that it is also possible to use other mixers in these steps.

[0021] As shown in Fig. 3, the two-shaft planetary stirring mixer 20 in this embodiment is configured so that a first stirring unit 23a and a second stirring unit 23b, which are bent rods, rotate inside a mixing container 20a. As shown in Fig. 3, the first stirring unit 23a and the second stirring unit 23b are connected to a rotating shaft 21 via a planetary gear mechanism 22. When a driving force from a motor (not shown) is transmitted to the rotating shaft 21, the first stirring unit 23a and the second stirring unit 23b revolve while rotating on their own axes.

[0022] As described above, in the electrode manufacturing method according to this embodiment, in the mixing step (S01), dry powder mixing is performed using a high-speed shear impact mixer 10 having second blades 12 capable of applying strong shear force, which makes it possible to disperse a material made up of multiple powders with fine particle sizes ranging from several μm to several tens of μm. By dispersing multiple powders in this way, even if the materials re-agglomerate after dispersion, the impact on battery performance can be suppressed.

[0023] As described above, in the electrode manufacturing method according to this embodiment, since the material consisting of multiple powders can be dispersed using the second blade 12 in the high-speed shear impact mixer 10, there is no need to disperse the agglomerated powder, and a slurry with little agglomeration can be produced in a short time by blending the powder with the solvent. For this reason, according to this embodiment, it is also possible to omit the kneading step (S02) and perform the dilution step (S03) after the mixing step (S01). However, since performing the kneading step does not affect dispersibility, when using a powder that is not easily blended with the solvent, it is preferable to perform the kneading step to make the powder more easily blended with the solvent.

[0024] In addition, in the electrode manufacturing method according to this embodiment, a thickener is mixed with the dry powder during mixing, dispersing the thickener, which tends to form lumps, into a powder that is more compatible with the solvent. This prevents the thickener from aggregating and increases the contact area between the thickener and the solvent, accelerating dissolution of the thickener. As a result, the time required for the dilution process can be shortened without affecting battery performance.

[0025] In the case of conventional mixing of agglomerated particles with a solvent in a two-shaft planetary agitation mixer 20, it is necessary to add powder and a small amount of solvent and perform a kneading process to break down the agglomerates and disperse them by applying shear (a mixing force in a kneading action such as compression, shear, or stretching) to the raw material. In this case, the shear during mixing only acts in the area where the blades and the container come close to each other, so a long processing time is required.

[0026] Furthermore, as the processing equipment becomes larger, the blades and container get closer to each other relative to the amount of powder put into the container, reducing the rate at which shear can be applied (the amount of powder increases as the cube of the container diameter, while the length of the blades is only multiplied by the container diameter, reducing the rate at which shear can be applied). Furthermore, as the container becomes larger, the gap between the blades and the container must be widened to prevent them from coming into contact, reducing the amount of shear that can be applied. Therefore, as the equipment becomes larger, the slurry production time becomes even longer, reducing productivity.

[0027] In addition, since the thickener begins to dissolve from the part that comes into contact with the liquid, if the thickener aggregates, a high-viscosity film forms where the liquid comes into contact, preventing the liquid from penetrating into the interior, creating a state known as "lumps," making it difficult to dissolve. Since the high-viscosity film on the surface of the lumps gradually thins, it takes a long time for the entire thickener to dissolve.

[0028] [Constituent Materials of Electrode and Slurry] The electrode according to this embodiment is composed of at least an active material, a conductive material, a thickener, a binder, and a current collector.

[0029] The active material is not particularly limited as long as it is a material that can be used in non-aqueous electrolyte secondary batteries. That is, it is sufficient if it is an inorganic material that can undergo oxidation-reduction by charging and discharging. For example, in the case of a positive electrode, LiCoO ２ , LiNiO ２ , Li(Ni-Co-Mn)O ２ , LiMn ２ O ４ , LiFePO ４ , LiMnPO ４ For the negative electrode, graphite, hard carbon, soft carbon, Li ４ Ti５ O １２ , Sn, SnO, SnS, Ge, Si, SiO, etc., may be used alone or in combination of two or more. The shape of the active material may be spherical, granular, elliptical, fibrous, or plate-like, but spherical is preferred because the viscosity change during storage of the slurry is small and the composite layer after application is easy to densify by pressing. The particle diameter of the active material is preferably a powder of 0.01 μm or more and 100 μm or less.

[0030] The conductive material is not particularly limited as long as it is a material that can be used in non-aqueous electrolyte secondary batteries. That is, it may be a carbon powder having electronic conductivity. Examples include acetylene black, furnace black, graphite, hollow carbon, carbon fiber, carbon nanotubes, and graphene.

[0031] The thickener is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. That is, it may be a resin that can increase the viscosity of the slurry. Examples of the thickener include carboxymethyl cellulose, hydroxypropyl cellulose, and xanthan gum.

[0032] The binder is not particularly limited as long as it is a material used in nonaqueous electrolyte secondary batteries. That is, it may be a resin capable of binding the active material, conductive material, and current collector together. Examples include styrene-butadiene rubber, polyacrylic, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, and polyamide-imide. In the present disclosure, the binder may be used as a solid such as a powder, but is preferably used in the form of a solution or emulsion because of the excellent homogeneity of the slurry.

[0033] The current collector is not particularly limited as long as it is made of a material that can be used in non-aqueous electrolyte secondary batteries. That is, it may be made of a metal that is electronically conductive and does not react during charging and discharging. Examples of the current collector include copper, aluminum, nickel, iron, titanium, and carbon. There are no particular restrictions on the shape of the current collector, and it may be, for example, a foil, plate, fiber, mesh, or porous material.

[0034] The electrode according to this embodiment is manufactured by vaporizing and removing the liquid agent contained in the slurry. For example, a slurry composed of an active material, a conductive material, a thickener, a binder, and the liquid agent is applied to a current collector and heated to 50° C. or higher, whereby the liquid agent in the slurry can be vaporized and removed. This makes it possible to obtain an electrode having a structure in which a composite composed of an active material, a conductive material, a thickener, and a binder is provided on a current collector.

[0035] Here, the term "slurry" refers to a fluid in which an active material, a conductive material, a thickener, and a binder are dispersed or dissolved in a liquid. That is, the liquid agent refers to a fluid that has the property of dispersing or dissolving solid materials such as the active material, the conductive material, the thickener, and the binder, and that can be vaporized and removed by heating.

[0036] Examples of the liquid used in the dilution step and the solvent used in the kneading step include water, N-methyl-2-pyrrolidone, alcohols, ketones, etc. The liquid used in the dilution step and the solvent used in the kneading step may be the same liquid or different liquids.

[0037] [Non-aqueous electrolyte secondary battery] The electrode according to this embodiment can be used as an electrode for a non-aqueous electrolyte secondary battery. Here, a non-aqueous electrolyte secondary battery refers to a chargeable and dischargeable battery that uses an electrolyte that does not contain water. Examples of non-aqueous electrolyte secondary batteries include lithium ion batteries, sodium ion batteries, potassium ion batteries, magnesium ion batteries, and calcium ion batteries.

[0038] A non-aqueous electrolyte secondary battery is composed of at least three components: a positive electrode, a negative electrode, and an electrolyte. If the electrolyte has fluidity, a separator is also required between the positive electrode and the negative electrode.

[0039] The electrolyte is not particularly limited as long as it is a material used in nonaqueous electrolyte secondary batteries. That is, it is sufficient if it has ion conductivity. Examples include electrolytic solutions, gel electrolytic solutions, ionic liquids, and solid electrolytes.

[0040] The separator is not particularly limited as long as it is made of a material that can be used in non-aqueous electrolyte secondary batteries, that is, it may be a film made of a material that is not electronically conductive and that has numerous through-holes.

[0041] The electrode according to this embodiment can be used as a positive electrode and / or a negative electrode.

[0042] [Evaluation Test] The applicant of the present application conducted an evaluation test using an electrode manufactured by the electrode manufacturing method according to the present embodiment (hereinafter referred to as the "electrode of the present application") and an electrode manufactured by a conventional electrode manufacturing method (hereinafter referred to as the "comparative electrode"). The method and results of the evaluation test are described below.

[0043] To manufacture the electrode of the present invention, materials including an active material, a conductive material, and a thickener for manufacturing an electrode for a nonaqueous electrolyte secondary battery were mixed in a high-speed shear impact mixer 10 (mixing step S01). In this test, graphite was used as the active material, acetylene black as the conductive material, and carboxymethyl cellulose as the thickener. Furthermore, in the high-speed shear impact mixer 10, mixing was performed for 5 minutes at a rotation speed of 27 rpm by the mixing arm (first blade 11) that mixes the entire mixture, and a rotation speed of 2200 rpm by the chopper blade (second blade 12) that applies a strong shear force.

[0044] The powder mixed in the high-speed shear impact mixer 10 and the styrene-butadiene rubber binder were then loaded into the biaxial planetary mixer 20, and 150 g of water was added. The biaxial planetary mixer 20 was then operated at 100 rpm for 5 minutes to produce a slurry (dilution step S03). The slurry produced by the above method was then used to form a negative electrode (the present electrode) (formation step S04). As described above, the time required to produce the slurry used for the present electrode was 10 minutes in total, consisting of 5 minutes in the high-speed shear impact mixer 10 and 5 minutes in the biaxial planetary mixer 20.

[0045] When producing the comparative electrode, materials including an active material, a conductive material, a thickener, and a binder were charged into the biaxial planetary mixer 20, as in the case of the electrode of the present invention, and 80 g of water as a liquid was added. The biaxial planetary mixer 20 was then operated at 100 rpm for 100 minutes. The remaining 70 g of water was then charged into the biaxial planetary mixer 20, and the biaxial planetary mixer 20 was operated at 100 rpm for 30 minutes to produce a slurry. As described above, the time required to produce the slurry used for the comparative electrode was 130 minutes using the biaxial planetary mixer 20.

[0046] Coin cells were also fabricated using the present electrode or comparative electrode, current collector, counter electrode, separator, and electrolyte. The current collector was a 10 μm thick copper foil, the counter electrode was a 500 μm thick lithium metal, the separator was a 16 mm diameter glass filter (GA-100), and the separator was a PP / PE / PP microporous membrane (25 μm thick). The electrolyte was 1M LiPF ６ The battery was an R2032 coin cell, and the heat treatment conditions were vacuum, 120°C, and 12 hours.

[0047] The batteries manufactured using each electrode were evaluated by a cycle test, in which the ambient temperature was 30°C, the cutoff voltage was 0.001V-1.0V, and the current value was 0.1C-rate.

[0048] As a result of a cycle test (100 cycles), both the present electrode and the comparative electrode exhibited the same battery performance, with a discharge capacity of 100% (see Figure 4). That is, when the performance of the batteries was evaluated using the electrodes manufactured by both manufacturing methods, no difference in battery performance was observed. Thus, it was confirmed that the present electrode significantly shortens the manufacturing time without deteriorating battery performance compared to the comparative electrode manufactured by the commonly used standard manufacturing method.

[0049] The electrode manufacturing method according to the present invention is useful because it makes it possible to shorten the slurry manufacturing time without deteriorating battery performance compared to conventional methods.

[0050] REFERENCE SIGNS LIST 10 High-speed shear impact mixer 10a Mixing vessel 10b Feeding port 11 First blade 11a First shaft 12 Second blade 12a Second shaft 20 Two-shaft planetary stirring mixer 20a Mixing vessel 21 Rotating shaft 22 Planetary gear mechanism 23a First stirring section 23b Second stirring section S01 Mixing process S02 Thick kneading process S03 Dilution process S04 Forming process R1 First rotation direction R2 Second rotation direction

Claims

1. A method for manufacturing an electrode, comprising: a mixing step of mixing materials containing an active material, a conductive material, and a thickener, which constitute an electrode for use in a non-aqueous electrolyte secondary battery, in the form of dry powder; a dilution step of adding a liquid agent to the mixture mixed in the mixing step to produce a slurry; and a formation step of forming the slurry produced in the dilution step into the electrode, wherein in the mixing step, the materials are mixed using a high-speed shear impact mixer having a first blade that mixes the materials overall and a second blade that applies a shear force to the materials.

2. The method for producing an electrode according to claim 1, wherein a binder is added to the mixture in the dilution step.

3. The method for manufacturing an electrode according to claim 2, wherein in the mixing step, the speed of the tip of the second blade is set to 5 m / sec or more and 40 m / sec or less.

4. A method for manufacturing an electrode as described in any one of claims 1 to 3, further comprising, after the mixing step and before the dilution step, a kneading step of adding a solvent to the mixture mixed in the mixing step and kneading the mixture, and in the dilution step, adding the liquid agent to the mixture kneaded in the kneading step to produce the slurry.

5. The method for producing an electrode according to claim 4, wherein a two-shaft planetary agitation mixer is used in the kneading step and the dilution step.

Images