Electrode manufacturing method

Abstract

The present invention provides a method for manufacturing electrodes that can increase battery capacity and suppress capacity degradation compared to conventional methods. [Solution] The electrode manufacturing method comprises a mixing step of mixing a main active material and a silicon-based active material, which constitute an electrode used in a non-aqueous electrolyte secondary battery, with dry powder; a dilution step of adding a liquid agent to the mixture mixed in the mixing step to produce a slurry; and a forming step of forming the slurry produced in the dilution step into an electrode, wherein the main active material is graphite, hard carbon, soft carbon, Li4Ti5O 12 At least one of Sn, SnO, SnS, and Ge is used as the silicon-based active material, and at least one of Si, SiO, and SiC is used as the silicon-based active material. The materials are mixed using a high-speed shear impact mixer having a first blade for mixing the materials overall and a second blade for applying a shear force to the materials.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrode used in a secondary battery.

Background Art

[0002] Conventionally, when manufacturing an electrode used in a secondary battery, a technique using graphite and a silicon-based material as active materials has been adopted (for example, refer to Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to increase the capacity of a battery, silicon having a high capacitance may be added during the manufacture of an electrode. In a battery manufactured using such an electrode, since the silicon-based material has a larger volume change (expansion and contraction) associated with charge and discharge than graphite, the capacity deterioration becomes large when charge and discharge are repeated, and an increase in capacity and suppression of capacity deterioration have been demanded.

[0005] The present invention has been made in view of the above circumstances, and the problem to be solved by the present invention is to provide a method for manufacturing an electrode that can increase the battery capacity and suppress capacity deterioration as compared with the prior art.

Means for Solving the Problems

[0006] Hereinafter, means for solving the above problems will be described.

[0007] The electrode manufacturing method according to the present invention comprises a mixing step of mixing a material containing a main active material and a silicon-based active material, which constitute an electrode used in a non-aqueous electrolyte secondary battery, with dry powder; a dilution step of adding a liquid agent to the mixture mixed in the mixing step to produce a slurry; and a forming step of forming the slurry produced in the dilution step onto the electrode, wherein the main active material is graphite, hard carbon, soft carbon, Li4Ti5O 12 At least one of Sn, SnO, SnS, and Ge is used, and at least one of Si, SiO, and SiC is used as the silicon-based active material. The material is composed of a main active material having a particle size distribution of 5 μm or more and 50 μm or less, and a silicon-based active material having a particle size distribution of 5 nm or more and 1000 nm or less, such that the main active material is 10 times or more and 30 times or less in weight than the silicon-based active material. In the mixing step, the materials are mixed together. Mixing arm Then, a shear force is applied to the aforementioned material. Chopper wings and, mixer The materials are mixed using [a specific method / tool]. [Effects of the Invention]

[0008] According to the electrode manufacturing method of the present invention, it is possible to increase the battery capacity and suppress capacity degradation compared to conventional methods. [Brief explanation of the drawing]

[0009] [Figure 1] A flowchart illustrating the manufacturing method of electrodes. [Figure 2] (a) and (b) are schematic cross-sectional views showing a high-speed shear impact mixer. [Figure 3] A schematic cross-sectional view showing a twin-axis planetary agitator mixer. [Figure 4] This figure compares the initial Coulomb efficiency of the present electrode and a reference electrode. [Figure 5] This figure compares the capacity and capacity retention rate of the electrode in this invention with that of a reference electrode. [Modes for carrying out the invention]

[0010] [Method for manufacturing electrodes] First, an electrode manufacturing method according to one embodiment of the present invention will be described using Figure 1. The electrode according to this embodiment can be used as a negative electrode. The electrode manufacturing method according to this embodiment is used when constructing an electrode for a non-aqueous electrolyte secondary battery. As shown in Figure 1, the electrode manufacturing method comprises 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.

[0011] In this embodiment, the mixing step (S01) is a step of mixing a material containing a main active material, a silicon-based active material, a conductive material, and a thickener as dry powder. The mixing step (S01) is a step of mixing the main active material and the silicon-based active material as dry powder, but as in this embodiment, dry powder materials such as conductive materials and thickeners can also be mixed simultaneously in the mixing step (S01) as appropriate. In this step, a high-speed shear impact mixer 10 is used as shown in Figures 2(a) and (b). The high-speed shear impact mixer 10 has a mixing arm which is a first blade 11 that mixes the material overall, and a chopper blade which is a second blade 12 that applies a shear force to the material.

[0012] As shown in Figures 2(a) and (b), the high-speed shear impact mixer 10 in this embodiment is configured such that three first blades 11 and three second blades 12 rotate inside a mixing container 10a, which has a material input port 10b formed at the top. As shown in Figure 2(a), the first blades 11 rotate inside the mixing container 10a by the driving force of a motor (not shown) transmitted via a first shaft 11a. Similarly, the second blades 12 rotate inside the mixing container 10a by the driving force of a motor (not shown) transmitted via a second shaft 12a.

[0013] In the high-speed shear impact mixer 10 in the present embodiment, as shown by the arrow R1 in FIG. 2(b), the first blade 11 is configured to rotate in the first rotation direction. On the other hand, as shown by the arrow R2 in FIG. 2(b), the second blade 12 is configured to rotate in the direction opposite to the first rotation direction. In the high-speed shear impact mixer 10 configured as described above, the material is mixed as a whole by the first blade 11, and a shearing force is applied to the material by the second blade 12.

[0014] The high-speed shear impact mixer 10 configured as described above mixes the material as a whole by the first blade 11 while applying a shearing force to the material by the second blade 12. In the high-speed shear impact mixer 10, the speed of the tip of the second blade 12 is set to be 5 m / s or more and 40 m / s or less per second.

[0015] Next, in the kneading step (S02), a solvent is added to the mixture mixed in the mixing step (S01) and kneaded. Then, in the dilution step (S03), a liquid agent and a binder are 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 on the electrode.

[0016] In the above-mentioned kneading step (S02) and dilution step (S03), as shown in FIG. 3, a two-shaft planetary stirring mixer 20 can be used. In these steps, it is also possible to adopt a configuration in which another mixer such as a self-rotating and revolving mixer different from the two-shaft planetary stirring mixer 20 is used.

[0017] As shown in FIG. 3, the two-shaft planetary stirring mixer 20 in the present embodiment is configured such that a first stirring part 23a and a second stirring part 23b, which are bent rods, rotate inside a mixing container 20a. As shown in FIG. 3, the first stirring part 23a and the second stirring part 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 part 23a and the second stirring part 23b are each configured to revolve while rotating on their own axes.

[0018] As described above, according to the method for manufacturing an electrode according to this embodiment, in the mixing step (S01), dry powder mixing is performed using the high-speed shear impact mixer 10 having the second blades 12 that can apply a strong shearing force. Thus, a material composed of a plurality of powders with a fine particle size of several tens of nm to several tens of μm can be uniformly dispersed. Further, by applying strong shear to the powder, a silicon-based active material with a relatively fine particle size is adhered to the surface of the main active material to be coated and compounded, thereby increasing the battery capacity and suppressing capacity deterioration.

[0019] As described above, in the method for manufacturing an electrode according to this embodiment, in the high-speed shear impact mixer 10, the silicon-based active material can be coated and compounded on the surface of the main active material using the second blades 12. Therefore, an electrode in which the main active material and the silicon-based active material are compounded can be manufactured. For this reason, according to this embodiment, it is also possible to adopt a configuration in which the kneading step (S02) is omitted and the dilution step (S03) is performed after the mixing step (S01). However, since performing the kneading step does not affect the dispersibility, when using a powder that is difficult to be compatible with the solvent, it is preferable to perform the kneading step in order to make the solvent and the powder compatible with each other.

[0020] Further, in the method for manufacturing an electrode according to this embodiment, a thickener is also mixed together during dry powder mixing, and the thickener that easily forms lumps is dispersed in a solvent and a powder that is easily compatible with the solvent. Thereby, the aggregation of the thickener disappears, and the contact area between the thickener and the solvent increases, so that the dissolution of the thickener is accelerated.

[0021] Incidentally, when kneading the silicon-based active material particles with a fine particle size and aggregated as in the conventional case together with a solvent using the biaxial planetary stirrer 20, it is necessary to apply a share (kneading force in kneading actions such as compression, shear, and stretching) to the raw materials by performing a kneading step with powder and a small amount of solvent to break up the aggregation and perform dispersion. In this case, since the share in kneading acts only in a part where the blades and the container approach each other, it is difficult to make the main active material and the silicon-based active material in a compounded state.

[0022] Furthermore, as the processing equipment becomes larger, the blades and container get closer to the amount of powder put into the container, reducing the share ratio that can be applied (the amount of powder increases with the cube of the container diameter, while the length of the blades is only twice the container diameter, thus reducing the share ratio). In addition, as the container becomes larger, the gap between the blades and the container needs to be widened to prevent contact between the blades and the container, which further reduces the share that can be applied. Therefore, as the equipment becomes larger, the compounding of the main active material and silicon-based active material becomes even more difficult.

[0023] Furthermore, since the thickening agent begins to dissolve from the part that comes into contact with the liquid, if the thickening agent is agglomerated, a highly viscous film forms at the point of contact with the liquid, preventing the liquid from penetrating the inside, resulting in a condition known as "clumping," which hinders dissolution. As the highly viscous film on the surface of the clumps gradually thins and dissolves, it takes a long time for the entire thickening agent to dissolve.

[0024] [Component materials for electrodes and slurries] The active material is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. In other words, any inorganic material that can undergo oxidation-reduction through charging and discharging is acceptable. For example, for the negative electrode, the main active material could be graphite, hard carbon, soft carbon, or Li4Ti5O 12 Sn, SnO, SnS, Ge, etc. can be used. The main active material may be one of these materials used alone, or two or more may be used in combination. Of these, graphite is preferred as the main active material because the silicon-based active material is easily supported in the mixing process in which the dry powder is mixed as described above.

[0025] Furthermore, because graphite has high electronic conductivity, it has the effect of providing conductivity to the supported silicon-based active material. Graphite can be broadly classified into artificial graphite and natural graphite, but both can be used favorably, and both can be used in combination. The higher the degree of graphitization, the higher the Coulomb efficiency and the higher the capacity, so graphite with a degree of graphitization of 80% or higher is preferable. The degree of graphitization can be calculated from the peak corresponding to the 002 plane of the XRD pattern obtained with an X-ray diffractometer compliant with JIS0131-1996.

[0026] The active material may be spherical, granular, elliptical, fibrous, or plate-shaped, but it is preferably spherical because it exhibits minimal viscosity changes during storage and facilitates densification of the mixed material layer by pressing after application. The main active material is preferably a powder with a particle size of 5 μm to 50 μm.

[0027] For increasing capacity, silicon-based active materials such as Si, SiO, and SiC can be used. The silicon-based active material preferably has a particle size of 1 / 1000 or more and 1 / 50 or less of the particle size of the main active material. That is, the particle size of the silicon-based active material is preferably between 5 nm and 1000 nm. In this embodiment, the particle size is the volume-based diameter and can be measured by laser diffraction scattering.

[0028] The conductive material is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. In other words, any carbon powder with electronic conductivity will suffice. Examples include acetylene black, furnace black, graphite, hollow carbon, carbon fiber, carbon nanotubes, and graphene.

[0029] The thickener is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. In other words, any resin that can increase the viscosity of the slurry is acceptable. Examples include carboxymethylcellulose, hydroxypropylcellulose, and xanthan gum.

[0030] The binder is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. In other words, any resin that can bind the active material, conductive material, and current collector is acceptable. Examples include styrene-butadiene rubber, polyacrylic, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, and polyamide-imide. In this disclosure, the binder can be used as a solid such as a powder, but it is preferable to use it in the form of a solution or emulsion because it provides excellent homogeneity of the slurry.

[0031] The current collector is not particularly limited as long as it is made of a material used in non-aqueous electrolyte secondary batteries. In other words, any metal that is electrically conductive and does not react during charging and discharging is acceptable. Examples include copper, aluminum, nickel, iron, titanium, and carbon. There are no particular restrictions on the shape of the current collector, but for example, foil, plate, fibrous, mesh, and porous materials can be used.

[0032] The electrode according to this embodiment is manufactured by vaporizing and removing the liquid agent contained in the slurry. For example, by applying a slurry consisting of an active material, a conductive material, a thickener, a binder, and a liquid agent onto a current collector and heating it at 50°C or higher, the liquid agent in the slurry can be vaporized and removed. This makes it possible to obtain an electrode with a structure in which a composite material consisting of an active material, a conductive material, a thickener, and a binder is provided on the current collector.

[0033] Here, "slurry" refers to a fluid in which active material, conductive material, thickener, and binder are dispersed or dissolved in a liquid. In other words, "liquid" refers to a fluid that has the property of dispersing or dissolving solids such as active material, conductive material, thickener, and binder, and that can be vaporized and removed by heating.

[0034] Examples of liquids used in the dilution process and solvents used in the solid mixing process include water, N-methyl-2-pyrrolidone, alcohols, and ketones. The liquid used in the dilution process and the solvent used in the solid mixing process may be the same liquid or different liquids.

[0035] [Nonaqueous 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 rechargeable battery that uses an electrolyte that does not contain water as a component. Examples include lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, and calcium-ion batteries.

[0036] In particular, when graphite is used as the main active material, lithium-ion batteries or potassium-ion batteries are preferred because they provide capacitance based on intercalation reactions, resulting in a higher energy density. Furthermore, lithium-ion batteries are preferred from the viewpoint of electromotive force and cycle stability.

[0037] A non-aqueous electrolyte secondary battery consists of at least three components: a positive electrode, a negative electrode, and an electrolyte. If the electrolyte is fluid, a separator is also required between the positive and negative electrodes.

[0038] The electrolyte is not particularly limited as long as it is a material used in non-aqueous electrolyte secondary batteries. In other words, it only needs to have ionic conductivity. Examples include electrolyte solutions, gel electrolytes, ionic liquids, and solid electrolytes.

[0039] The separator is not particularly limited as long as it is made of a material used in non-aqueous electrolyte secondary batteries. In other words, it can be any film made of a material that does not conduct electricity and has countless through-holes.

[0040] [Evaluation Test] The applicant conducted evaluation tests using negative electrodes manufactured by the electrode manufacturing method according to the present embodiment (hereinafter referred to as "electrode (1)" and "electrode (2)") and negative electrodes manufactured by the electrode manufacturing method according to the prior art (hereinafter referred to as "comparative electrode"). The method and results of the evaluation tests are described below. For electrodes (1), (2), and the comparative electrode, negative electrodes were manufactured with three different ratios of graphite, the main active material, and Si in the silicon-based active material: graphite:Si = 96.5:3.5 parts by weight, graphite:Si = 95:5 parts by weight, and graphite:Si = 92:8 parts by weight. Hereafter, unless otherwise specified, graphite refers to artificial graphite.

[0041] In manufacturing electrodes (1) and (2) of the present invention, graphite, the main active material for manufacturing electrodes for non-aqueous electrolyte secondary batteries, and Si, a silicon-based active material, were mixed in a high-speed shear impact mixer 10 (mixing step S01). In this test, graphite with an average particle size of 20 μm was used as the main active material, Si with an average particle size of 50 nm was used as the silicon-based active material, acetylene black was used as the conductive material, and carboxymethylcellulose was used as the thickener. In the high-speed shear impact mixer 10, mixing was performed for 5 minutes at a rotation speed of 56 rpm by the mixing arm, which is the first blade 11 that mixes the whole, and at a rotation speed of 4470 rpm (electrode (1)) or 8950 rpm (electrode (2)) by the chopper blade, which is the second blade 12 that applies a strong shear force.

[0042] Subsequently, the powder mixed in the high-speed shear impact mixer 10, along with acetylene black (a conductive material) and styrene-butadiene rubber (a binder), were put into a rotary-type mixer. Water (a liquid agent) was added, and the rotary-type mixer was operated at 2000 rpm for 5 minutes to produce a slurry (dilution step S03). Furthermore, a negative electrode was formed using the slurry produced by the above method (forming step S04).

[0043] In manufacturing the reference electrode, similar to the electrode of the present invention, materials containing graphite as the active material, a conductive material, a thickener, and a binder were placed in a rotary-type mixer, water as the liquid agent was added, and the rotary-type mixer was operated at 2000 rpm for 5 minutes to form the negative electrode using the slurry.

[0044] Furthermore, electrodes (1) and (2) and the reference electrode were manufactured using coin cells, each utilizing a current collector, counter electrode, separator, and electrolyte. A 10 μm thick copper foil was used for the current collector, a 500 μm thick lithium metal for the counter electrode, a 16 mm diameter glass filter (GA-100) or a PP / PE / PP microporous membrane (25 μm thick) for the separator, 1 M LiPF6 / EC:DEC (=50:50 vol%) for the electrolyte, and an R2032 type coin cell for the battery case. The electrode heat treatment conditions were vacuum, 120°C, and 12 hours.

[0045] Batteries manufactured using each electrode type were evaluated through cycle testing. In the cycle testing, the ambient temperature was 30°C, the cutoff voltage was 0.001V-1.0V, and the current value was 0.1C-rate.

[0046] As shown in Figure 4, the initial Coulomb efficiencies of the manufactured batteries were 72.1-80.6% for the reference electrode, while the electrode (1) of the present invention achieved 82.5-92.2% and the electrode (2) of the present invention achieved 83.4-89.7%, demonstrating significantly higher efficiencies.

[0047] In a battery with a ratio of graphite:Si = 96.5:3.5, which is the ratio of the main active material, graphite, to the silicon-based active material Si, the cycle test results after 10 cycles showed that the capacity of the reference electrode was 385.5 mAh / g, while the electrode (1) of the present invention was 440.0 mAh / g and the electrode (2) was 413.7 mAh / g, representing increases of 114.1% and 107.3% of the reference electrode, respectively.

[0048] Furthermore, when comparing the capacities at 280 cycles, as shown in Figure 5, the reference electrode was 223.8 mAh / g, while electrode (1) of the present invention was 296.0 mAh / g and electrode (2) was 291.6 mAh / g, representing increases of 132.3% and 130.3% of the reference electrode, respectively. Thus, the negative electrode manufactured using the electrode manufacturing method according to the present invention was able to increase the battery capacity compared to the conventional reference electrode.

[0049] Furthermore, as shown in Figure 5, the capacity retention rate at 280 cycles compared to 10 cycles was 58.1% for the reference electrode, while electrode (1) of the present invention maintained 67.3% and electrode (2) maintained 70.5%, demonstrating that capacity degradation was suppressed compared to the reference electrode. Thus, the negative electrode manufactured using the electrode manufacturing method of the present invention was able to suppress capacity degradation compared to the conventional reference electrode. [Explanation of Symbols]

[0050] 10. High-speed shear impact mixer 10a Mixing container 10b Inlet 11 First feather 11a First shaft 12 Second wing 12a Second axis 20. Twin-axis planetary agitator mixer 20a Mixing container 21 Rotating shaft 22 Planetary gear mechanism 23a First stirring section 23b Second stirring section S01 Mixing process S02 Hardening process S03 Dilution process S04 Forming process R1 First rotation direction R2 Second rotation direction

Claims

1. A mixing step in which the main active material and the silicon-based active material, which constitute the electrodes used in a non-aqueous electrolyte secondary battery, are mixed as dry powders, A dilution step is performed in which a liquid agent is added to the mixture mixed in the above mixing step to produce a slurry. The process includes a forming step of forming the slurry produced in the dilution step onto the electrode, The main active material is graphite, hard carbon, soft carbon, Li ４ Ti ５ O １２ At least one of the following is used: Sn, SnO, SnS, Ge. As the silicon-based active material, at least one of Si, SiO, and SiC is used. A method for manufacturing electrodes, comprising mixing the materials using a high-speed shear impact mixer having a first blade for mixing the materials overall and a second blade for applying a shear force to the materials.

2. The particle size of the main active material is 5 μm or more and 50 μm or less. The method for manufacturing an electrode according to claim 1, wherein the particle size of the silicon-based active material is 1 / 1000 or more and 1 / 50 or less of the particle size of the main active material.

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

4. The method for manufacturing an electrode according to claim 1, wherein in the mixing step, the speed of the blade tip of the second blade is set to be 5 m / s or more and 40 m / s or less.

5. The process includes a kneading step in which, after the mixing step and before the dilution step, a solvent is added to the mixture mixed in the mixing step and kneaded. A method for manufacturing an electrode according to any one of claims 1 to 4, wherein in the dilution step, the liquid agent is added to the mixture kneaded in the solid kneading step to produce the slurry.

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