Electrode manufacturing method and electrode manufacturing device

Abstract

The present disclosure provides an electrode manufacturing method and an electrode manufacturing device. A slurry is prepared by mixing active material particles, a binder and a dispersion medium. A first coating is formed by applying the slurry to the surface of a substrate. A second coating is formed by drying the first coating. A recess is formed on the surface of the second coating by pressing a convex mold on the surface of the second coating. An active material layer is formed by drying the second coating after the recess is formed. In the second coating, a solid phase, a liquid phase and a gas phase form a pendulum state or a cable state.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an electrode and an apparatus for manufacturing an electrode. Background Art

[0002] Japanese Patent Application Laid-Open No. 2015-138619 discloses spraying a solvent onto the surface of the negative electrode active material mixture layer before pressing a mold having a concavo-convex pattern onto the negative electrode active material mixture layer. Summary of the invention

[0003] It has been proposed to form recessed portions on the surface of an active material layer. The recessed portions are expected to function as, for example, a permeation path for an electrolyte solution, a discharge path for a gas, and the like.

[0004] The active material layer can be formed by applying a slurry. That is, the slurry is prepared by mixing active material particles, a binder and a dispersion medium. The slurry is applied on the surface of the substrate to form a coating. The active material layer is formed by drying the coating.

[0005] The concave portion can be formed by molding. That is, the concave portion is formed by pressing a convex mold onto the surface of the dried active material layer. In the dried active material layer, there is a tendency for the fluidity of the solid material (active material particles, etc.) to be low. Therefore, at the bottom of the concave portion, the density will increase locally by compressing the solid material. By generating a density deviation in the active material layer, it is conceivable that, for example, the electrode reaction becomes uneven.

[0006] For example, by spraying liquid (dispersion medium) on the surface of the dried active material layer, fluidity can be imparted to the solid material on the surface layer of the active material layer. As a result, it is expected to reduce the density deviation caused by the molding process. However, there is still room for improvement in demolding. That is, adhesion will be generated due to the wetting of the solid material. The solid material may adhere to the convex mold, thereby failing to form the desired concave portion. In addition, it is believed that the re-sprayed liquid will not penetrate into the deep layer of the active material layer. In the deep layer of the active material layer, it is still possible that the density deviation cannot be eliminated due to the low fluidity of the solid material.

[0007] An object of the present disclosure is to provide a method for manufacturing an electrode with a recessed portion.

[0008] The following is an explanation of the technical structure and effects of the present disclosure. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[0009] 1. A method for manufacturing an electrode, comprising the following (a) to (e).

[0010] (a) A slurry is prepared by mixing active material particles, a binder and a dispersion medium.

[0011] (b) The slurry is applied to the surface of the substrate to form a first coating film.

[0012] (c) The first coating film is dried to form a second coating film.

[0013] (d) A convex mold is pressed against the surface of the second coating film to form a concave portion on the surface.

[0014] (e) After forming the recessed portions, the second coating film is dried to form an active material layer.

[0015] In the second coating film, the solid phase, the liquid phase, and the gas phase form a pendulum state or a cord state.

[0016] By drying the slurry (coating film) applied on the substrate, the liquid phase (dispersion medium) decreases and a gas phase (bubbles, voids) is generated. Finally, the coating film is in a dry state (solid phase and gas phase).

[0017] Figure 1 This is a conceptual diagram showing the drying process of a coating film.

[0018] The coating reaches the "dry state" after passing through the "slurry state", "capillary state", "funicular state" and "pendular state". The classification of dry states is described in detail in "Particle Size Enlargement" by CECAPES (Elsevier Scientific Publishing Company, 1980). In each state, the relationship between the solid phase (active material particles), liquid phase (dispersion medium) and gas phase (gas) is different.

[0019] The "slurry state" consists of a solid phase (active material particles 1) and a liquid phase (dispersion medium 2). The gas phase (gas 3) does not substantially exist. The solid phase (active material particles 1) is suspended in the liquid phase (dispersion medium 2). The solid phase is dispersed in the liquid phase and is not continuous.

[0020] "Capillary state" means a state where the liquid phase is reduced from the slurry state. The capillary state is composed of a solid phase, a liquid phase, and a gas phase (gas 3). The solid phase is covered by the liquid phase. The liquid phase is continuous around the solid phase. The gas phase is in contact with the liquid phase. The gas phase is not in contact with the solid phase.

[0021] The "cord state" is a state in which the liquid phase is further reduced from the capillary state. The cord state is composed of a solid phase, a liquid phase, and a gas phase. The liquid phase is continuous around the solid phase. A part of the solid phase is in contact with the gas phase.

[0022] The "pendulum state" is a state in which the liquid phase is further reduced from the cord state. The pendulum state is composed of a solid phase, a liquid phase, and a gas phase. The liquid phase is discontinuous. The liquid phase cross-links the solid phases. The gas phase contacts both the solid phase and the liquid phase.

[0023] The "dry state" consists of a solid phase and a gas phase. The liquid phase does not actually exist.

[0024] According to the new insights disclosed herein, the coating film is in a pendulum state or a cable state, so that it can have both demoulding properties and fluidity during molding. That is, the coating film in a pendulum state or a cable state is difficult to adhere to the punch and has a tendency to be difficult to produce density deviation. It is believed that this is because the coating film in a pendulum state or a cable state has low adhesion and can flow as a whole.

[0025] On the other hand, for example, when the coating film is in a capillary state, the coating film tends to be easily attached to the punch. For example, when the coating film is in a dry state, the density deviation tends to increase.

[0026] 2. The slurry may have a solid content of, for example, 50 to 65% by mass. The second coating film may have a solid content of, for example, 70 to 99% by mass.

[0027] When the solid content is 50 to 65%, the slurry state tends to be easily formed. When the solid content is 70 to 99%, the pendulum state or the cord state tends to be easily formed.

[0028] 3. The active material particles may include, for example, a positive electrode active material. The slurry may have, for example, a solid content of 55 to 65% by mass. The second coating may have, for example, a solid content of 80 to 99% by mass.

[0029] When the active material particles are positive electrode active material particles, they tend to be in a slurry state when the solid content is 55 to 65%, and tend to be in a pendulum state or a cord state when the solid content is 80 to 99%.

[0030] 4. The active material particles may contain, for example, a negative electrode active material. The slurry may have, for example, a solid content of 50 to 60% by mass. The second coating may have, for example, a solid content of 70 to 99% by mass.

[0031] When the active material particles are negative electrode active material particles, they tend to be in a slurry state when the solid content is 50 to 60%, and tend to be in a pendulum state or a cord state when the solid content is 70 to 99%.

[0032] 5. When viewed from above, the second coating film may have a long side direction and a short side direction. In the short side direction, a liquid dripping portion may be formed at the end of the second coating film. The convex mold may be pressed against the second coating film in such a manner that at least a portion of the liquid dripping portion does not contact the convex mold.

[0033] For example, it is also possible to prepare a pendulum state or a rope state coating from the beginning without passing through the slurry state. The coating can be, for example, a wet powder (wet powder or wet granules). Granules are also called granules. Granules can be formed by granulating a powder.

[0034] The slurry can have high fluidity. In the coating film formed by the slurry, a liquid drop portion is formed at the end thereof. In the liquid drop portion, the coating film is inclined to the outside.

[0035] Wet powder has lower fluidity than slurry. In the coating formed by wet powder, there is a tendency that the end is difficult to be inclined. If the coating without an inclined portion at the end is subjected to embossing, a concave portion will be formed until near the front end of the coating. By forming a concave portion until near the front end, the coating may peel off or collapse at the end.

[0036] In the liquid dripping part, the thickness of the coating film gradually decreases as it moves toward the outside. Therefore, the embossing process can be performed in a manner that the convex mold contacts the coating film in the center of the coating film and the convex mold does not contact the coating film at the end of the coating film (liquid dripping part). By not forming a concave part at the end of the coating film (liquid dripping part), it is expected that the detachment and collapse of the coating film at the end of the coating film can be reduced.

[0037] 6. The method for manufacturing an electrode may further include, for example, the following (f).

[0038] (f) Compressing the active material layer.

[0039] The dried coating film (active material layer) with recessed portions may be further subjected to compression processing.

[0040] 7. An electrode manufacturing device, comprising a conveying device, a coating device, a first drying device, a molding device and a second drying device. The conveying device is configured to convey the substrate in the order of the coating device, the first drying device, the molding device and the second drying device. The coating device is configured to form a first coating film by coating a slurry on the surface of the substrate. The slurry contains active material particles, a binder and a dispersion medium. The first drying device is configured to form a second coating film by drying the first coating film. The molding device is configured to form a recessed portion on the surface of the second coating film by pressing a convex mold on the surface of the second coating film. The second drying device is configured to form an active material layer by drying the second coating film.

[0041] The molding process is performed in the molding device. By arranging the first drying device before the molding device, the coating film can be adjusted to a pendulum state or a cord state before the molding process. That is, the electrode manufacturing method of the above-mentioned "1." can be implemented.

[0042] 8. The second coating film may be formed to have a long side direction and a short side direction when viewed from above. The electrode manufacturing apparatus may be configured such that the coating device forms the first coating film and the first drying device dries the first coating film in such a manner that a liquid dripping portion is formed at an end of the second coating film in the short side direction.

[0043] By forming the liquid dripping portion, it is expected that peeling, chipping, and the like of the coating film at the edge of the coating film can be reduced.

[0044] 9. The molding device may include, for example, an embossing roller. A convex mold may be formed on the surface of the embossing roller. The molding device may be configured to press the embossing roller against the second coating film so that at least a portion of the liquid dripping portion does not contact the convex mold.

[0045] According to the electrode manufacturing device of the above-mentioned "9.", the electrode manufacturing method of the above-mentioned "5." can be implemented.

[0046] 10. The electrode manufacturing apparatus may further include a compressing device. The transporting device may be configured to transport the substrate having passed through the second drying device to the compressing device. The compressing device may be configured to compress the active material layer.

[0047] According to the electrode manufacturing device of the above-mentioned "10.", the electrode manufacturing method of the above-mentioned "6." can be implemented.

[0048] The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a conceptual diagram showing the drying process of a coating film.

[0050] Figure 2 This is a schematic flowchart of the method for manufacturing an electrode in this embodiment.

[0051] Figure 3 It is a schematic diagram showing electrodes in this embodiment.

[0052] Figure 4 It is a first schematic cross-sectional view showing an electrode in this embodiment.

[0053] Figure 5 It is a top view showing the electrode in this embodiment.

[0054] Figure 6It is a second schematic cross-sectional view showing the electrode in this embodiment.

[0055] Figure 7 It is a conceptual diagram showing an electrode manufacturing apparatus in this embodiment.

[0056] Figure 8 These are cross-sectional images and top surface images of electrodes in the first to third test examples.

[0057] Fig. 9 This is a graph showing the relationship between the solid content and the drying time in the first test example.

[0058] Fig.10 This is a graph showing the relationship between the solid content and the drying time in the second test example. DETAILED DESCRIPTION

[0059] <Definitions of Terms, etc.>

[0060] Hereinafter, an embodiment of the present disclosure (may be referred to as “the present embodiment” for short) and an example of the present disclosure (may be referred to as “the present example” for short) will be described. However, the embodiment and the example do not limit the technical scope of the present disclosure.

[0061] In this specification, the descriptions such as "having", "including", "having" etc. are open-ended. Open-ended means that in addition to the essential elements, additional elements may or may not be included. The description such as "consisting of..." is closed-ended. However, even if it is closed-ended, it does not exclude the usual impurities or additional elements that are irrelevant to the technology disclosed herein. The description such as "consisting of..." is semi-closed. In the semi-closed form, it is allowed to add elements that do not substantially affect the basic and novel characteristics of the technology disclosed herein.

[0062] In the method described in this specification, with respect to multiple steps, tasks, operations, etc., unless otherwise specified, the execution order is not limited to the order of description. For example, multiple steps can be performed simultaneously. For example, multiple steps can also be performed sequentially.

[0063] In this specification, elements expressed in the singular also include the plural form unless otherwise specified. For example, "particle" does not only mean "one particle" but also can mean "an aggregate of particles (powder, powder, particle group)".

[0064] In this specification, the expressions “may” and “may” are used in the sense of “possibility” rather than the obligatory meaning of “must”.

[0065] In this specification, a numerical range such as "70 to 99%" includes both the upper limit and the lower limit unless otherwise specified. That is, "70 to 99%" means a numerical range of "70% or more and 99% or less". In addition, a numerical value arbitrarily selected from the numerical range may be used as a new upper limit or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value recorded in other parts, tables, figures, etc. in this specification.

[0066] In this specification, all numerical values ​​are modified by the term "about". The term "about" can represent, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​are approximate values ​​that can vary depending on the utilization of the disclosed technology. All numerical values ​​are expressed with significant figures. The measured value can be an average value of multiple measurements. The number of measurements can be more than 3 times, more than 5 times, or more than 10 times. The measured value can be rounded based on the number of significant figures. The measured value may include errors such as those associated with the detection limit of the measuring device.

[0067] The geometric terms in this specification (such as "parallel", "perpendicular", "orthogonal", etc.) should not be understood in a strict sense. For example, "parallel" may slightly deviate from "parallel" in a strict sense. The geometric terms in this specification may include, for example, tolerances, errors, etc. in design, operation, and manufacturing. The dimensional relationships in the figures are sometimes inconsistent with the actual dimensional relationships. In order to facilitate the understanding of the disclosed technology, the dimensional relationships (length, width, thickness, etc.) in the figures may sometimes be changed. In addition, a part of the structure may sometimes be omitted.

[0068] The term "planar view" in this specification means observing an object (eg, an electrode) in a line of sight parallel to the thickness direction of the object. The term "cross-sectional view" in this specification means observing an object in a line of sight perpendicular to the thickness direction of the object.

[0069] In this specification, when a compound is represented by a stoichiometric composition formula such as "LiCoO2", the stoichiometric composition formula is only a representative example. The composition ratio may also be non-stoichiometric. For example, when lithium cobalt oxide is represented as "LiCoO2", unless otherwise specified, lithium cobalt oxide is not limited to the composition ratio of "Li / Co / O=1 / 1 / 2", and may contain Li, Co and O in any composition ratio. In addition, doping and substitution of trace elements may also be allowed.

[0070] The "solid content" in this specification refers to the mass fraction (percentage) of the components other than the liquid in a solid-liquid mixture. The solid content may also be referred to as "NV (Nonvolatile content)". In slurries and coatings, the dispersion medium is a liquid. When a binder is dissolved in the dispersion medium, the binder (solute) is regarded as the component other than the liquid.

[0071] In this specification, "D50" is defined as the particle size at which the cumulative frequency of the smaller particle size in the volume-based particle size distribution reaches 50%. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring apparatus.

[0072] <Electrode Manufacturing Method>

[0073] Figure 2 This is a schematic flowchart of the method for manufacturing an electrode in this embodiment.

[0074] Hereinafter, “the method for manufacturing an electrode in the present embodiment” may be simply referred to as “the present manufacturing method”.

[0075] The present manufacturing method includes "(a) slurry preparation", "(b) coating", "(c) first drying", "(d) molding", and "(e) second drying". The present manufacturing method may also include "(f) compression" and the like. Each step may be performed in the atmosphere, for example, in dry air.

[0076] In this manufacturing method, a lithium-ion battery can be manufactured. However, a lithium-ion battery is only an example. In this manufacturing method, any battery can be manufactured. In this manufacturing method, both a positive electrode and a negative electrode can be manufactured. In this manufacturing method, at least one of the positive electrode and the negative electrode can be manufactured.

[0077] 《(a) Preparation of slurry》

[0078] The present manufacturing method comprises preparing a slurry by mixing active material particles, a binder and a dispersion medium. The slurry is a liquid coating. In the present manufacturing method, the slurry can be prepared by any stirring device. For example, a planetary mixer, a "high-speed mixer series (made by Earthtechnica)" or the like can be used.

[0079] Active material particles, a binder and a dispersion medium are added to a stirring tank of a stirring device. For example, any additional component (conductive material, etc.) may be added. The slurry may be prepared by mixing the materials under predetermined conditions.

[0080] 〈Active material particles〉

[0081] The active material particles are the dispersed phase of the slurry. The active material particles can have any shape. For example, the active material particles can be spherical, blocky, flake, columnar, etc. The active material particles can have any size. For example, the active material particles can have a D50 of 1 to 30 μm, or a D50 of 5 to 20 μm.

[0082] The active material particles contain a positive electrode active material or a negative electrode active material. When the active material particles contain a positive electrode active material, a positive electrode can be manufactured. When the active material particles contain a negative electrode active material, a negative electrode can be manufactured.

[0083] The positive electrode active material can absorb and release lithium ions at a higher potential than the negative electrode active material. The positive electrode active material can contain any component. For example, the positive electrode active material can contain at least one selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2 and LiFePO4. For example, the "(NiCoMn)" in "Li(NiCoMn)O2" means that the total of the composition ratio in the brackets is 1. As long as the total is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 can contain Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2、Li(Ni 0.5 Co 0.2 Mn 0.3 )O2、Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, etc.

[0084] The negative electrode active material can absorb and release lithium ions at a lower potential than the positive electrode active material. The negative electrode active material can contain any component. For example, the negative electrode active material can contain a material selected from graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, and Li4Ti5O 12 At least one of .

[0085] 〈Adhesives〉

[0086] The binder can bind solid materials to each other. The binder can be soluble in the dispersion medium or insoluble in the dispersion medium. The amount of the binder can be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the active material particles. The binder can contain any component. The binder can, for example, contain at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide (PI), polyamide-imide (PAI) and polyacrylic acid (PAA).

[0087] 〈Conductive Materials〉

[0088] A conductive material may be mixed in the slurry. The conductive material is capable of forming an electron conduction path in the active material layer. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the active material particles. The conductive material may contain any component. The conductive material may, for example, contain at least one selected from carbon black, vapor-grown carbon fibers, carbon nanotubes, and graphene sheets. Carbon black may, for example, contain at least one selected from acetylene black, furnace black, channel black, and thermal black.

[0089] 〈Dispersion Medium〉

[0090] The dispersion medium is a liquid. The dispersion medium may be a solvent for the binder. The dispersion medium may be selected, for example, according to the type of active material particles, the type of binder, etc. The dispersion medium may include, for example, water, N-methyl-2-pyrrolidone (NMP), etc.

[0091] The amount of the dispersion medium is adjusted according to the solid content of the slurry. The slurry may have a solid content of, for example, 50 to 65%. When the active material particles contain positive electrode active materials, the slurry may have a solid content of, for example, 55 to 65%. When the active material particles contain negative electrode active materials, the slurry may have a solid content of, for example, 50 to 60%. Within these solid content ranges, it is difficult for the active material particles to aggregate and settle, and the slurry state tends to be easily maintained.

[0092] 《(b) Coating》

[0093] The present production method includes forming a first coating film by coating the slurry on the surface of the substrate. In the present production method, the slurry can be coated by any coating device. For example, a die coater, a roll coater, etc. can be used.

[0094] The slurry has high fluidity. Therefore, a liquid drop portion can be formed on the first coating film. The liquid drop portion can be formed at the end of the short side direction when viewed from above. The short side direction is orthogonal to the long side direction. The long side direction can be the same direction as the conveying direction of the workpiece in the coating device.

[0095] 〈Base Material〉

[0096] The substrate is a support for the active material layer. The substrate may be, for example, in sheet form. The substrate may also be, for example, in strip form. The substrate may have electrical conductivity. The substrate may function as a current collector. The substrate may include, for example, a metal foil, etc. The substrate may include, for example, at least one selected from aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, nickel (Ni) foil, Ni alloy foil, titanium (Ti) foil, and Ti alloy foil. When the electrode is a positive electrode, the substrate may include, for example, Al foil, etc. When the electrode is a negative electrode, the substrate may include, for example, Cu foil, etc. The substrate may have, for example, a thickness of 5 to 50 μm, or a thickness of 5 to 20 μm.

[0097] 《(c) 1st Drying》

[0098] The present production method includes forming a second coating film by drying the first coating film. The first drying may be referred to as "pre-drying", for example. In the first drying, any drying device may be used. For example, a hot air drying device, an infrared drying device, etc. may be used.

[0099] In the present production method, the drying conditions are adjusted so that the solid phase, the liquid phase, and the gas phase form a pendulum state or a rope state in the second coating film. The drying conditions may include, for example, the drying temperature, the drying time, etc. The drying state of the second coating film is confirmed by the following method.

[0100] <How to check the dryness>

[0101] When viewed from above, the second coating film has a long side direction and a short side direction. The long side direction may be the same direction as the conveying direction of the workpiece in the drying device. The short side direction may be referred to as the "width direction". The second coating film is divided into five equal parts in the short side direction, thereby being divided into five regions. For example, by a cutter, a sample (the second coating film) is cut from the vicinity of the center of each region together with the substrate. That is, five samples are prepared.

[0102] Prepare Cryo-SEM (Cryo Scanning Electron Microscopy).

[0103] In the atmosphere, the sample is rapidly frozen by liquid nitrogen. The time from the first drying to the rapid freezing is preferably within 10 minutes. After freezing, the sample is introduced into the Cryo chamber. In the Cryo chamber, the sample is subjected to cross-section processing. After the cross-section processing, the sample is introduced into a cooling stage. The sample is observed by SEM on the cooling stage. The observation magnification can be 1000 to 5000 times.

[0104] In the SEM image, "active material particles whose surface is partially covered by the dispersion medium" are considered to be in a pendulum state or a string state. In other words, active material particles other than the following (i) and (ii) are considered to be in a pendulum state or a string state.

[0105] (i) “Active material particles whose entire surface is covered by the dispersion medium”

[0106] (ii) “Active material particles whose entire surface is covered with a gas phase (voids)”

[0107] In the SEM image of each sample, the state of more than 20 active material particles is confirmed. That is, the state of more than 100 active material particles in total is confirmed. It is believed that the more the number of confirmed particles is, the higher the reliability of the measurement result is. When more than 50% of the active material particles are in a pendulum state or a rope state by number fraction, it is considered that in the second coating film, the solid phase, liquid phase and gas phase form a pendulum state or a rope state.

[0108] For example, 70% or more of the active material particles may be in a pendulum state or a rope state. For example, 80% or more of the active material particles may be in a pendulum state or a rope state.

[0109] 〈Solid content〉

[0110] The solid content of the second coating film may also be confirmed. For example, a sample (second coating film) may be cut out together with the substrate. The area of ​​the sample may be, for example, 10 to 50 cm 2 The mass of the sample in the wet state and the mass of the sample in the dry state are measured. The mass of the dispersion medium is calculated from the difference between the mass in the wet state and the mass in the dry state. The solid content is then calculated from the mass of the dispersion medium.

[0111] The second coating film may have a solid content of, for example, 70 to 99%. At a solid content of 70 to 99%, a pendulum state or a cord state tends to be easily formed.

[0112] When the active material particles contain positive electrode active material, the second coating film may have a solid content of 80 to 99%, for example. When the active material particles contain positive electrode active material, at a solid content of 80 to 99%, there is a tendency to easily form a pendulum state or a rope state. When the active material particles contain positive electrode active material, the second coating film may have a solid content of 81 to 97%, for example.

[0113] When the active material particles include negative electrode active materials, the second coating film may have a solid content of, for example, 70 to 99%. When the active material particles include negative electrode active materials, at a solid content of 70 to 99%, there is a tendency to easily form a pendulum state or a rope state. When the active material particles include negative electrode active materials, the second coating film may have a solid content of, for example, 72 to 96%.

[0114] 《(d) Molding process》

[0115] This production method includes forming recessed portions on the surface of the second coating film by pressing a convex mold against the surface of the second coating film.

[0116] In the molding process, for example, an embossing roller or the like can be used. In this manufacturing method, the second coating film (processing object) is in a pendulum state or a cable state. As a result, the demoulding property of the second coating film is good. That is, the second coating film (material) is difficult to adhere to the punch. In addition, since the contact portion with the punch and its surroundings can flow as a whole, the generation of density deviation can be reduced. In addition, compared with the dry state, it also has the advantage of being able to be molded with a small load.

[0117] In this manufacturing method, more than one concave portion is formed. A plurality of concave portions may also be formed. By forming a plurality of concave portions, a concave-convex structure can be formed on the surface of the second coating film. Each concave portion may be, for example, a straight line, a curved line, a wavy line, or a dot. The planar pattern of the concave portion may be, for example, a linear shape (e.g., a shape of a plurality of parallel lines) or a lattice shape.

[0118] (e) Second drying

[0119] The present production method includes forming the active material layer by drying the second coating film after forming the recessed portions.

[0120] The second drying step may be referred to as "main drying". In the second drying step, the second coating film is dried to a dry state (see Figure 1 ). Thus, an active material layer (a coating film in a dried state) is formed. Any drying device can be used in the second drying. For example, a hot air drying device, an infrared drying device, etc. can be used.

[0121] (f) Compression

[0122] The manufacturing method may include compressing the active material layer. By compressing, the thickness and density of the active material layer can be adjusted. For example, the active material layer can be compressed using a roller pressing device.

[0123] The electrode (rolled material) can be manufactured in the above manner. The rolled material can be cut into a predetermined shape according to the specifications of the battery.

[0124] <Electrode>

[0125] Figure 3 It is a schematic diagram showing electrodes in this embodiment.

[0126] The electrode 100 includes a substrate 110 and an active material layer 120. The details of the substrate 110 are as described above. The active material layer 120 is formed on the surface of the substrate 110. The active material layer 120 may be formed only on one side of the substrate 110. The active material layer 120 may also be formed on both the front and back sides of the substrate 110. The active material layer 120 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 200 μm.

[0127] The active material layer 120 includes active material particles and a binder. The active material layer 120 may also include, for example, a conductive material, etc. The details of each material are as described above. A recess 121 (groove) is formed on the surface of the active material layer 120. One recess 121 may be formed, or a plurality of recesses 121 (groove groups) may be formed.

[0128] Figure 4 It is a first schematic cross-sectional view showing an electrode in this embodiment.

[0129] The cross-sectional shape of the recess 121 is arbitrary. When viewed in cross section, the bottom of the recess 121 may be, for example, flat, curved, or inclined. When viewed in cross section, the recess 121 may be, for example, V-shaped or U-shaped.

[0130] The pitch 121p of the recesses 121 indicates the distance between the deepest parts of adjacent recesses 121. When the bottom of the recess 121 is flat, the center of the bottom is regarded as the deepest part. The pitch 121p may be, for example, 0.1 to 10 mm, 0.5 to 5 mm, or 1 to 3 mm.

[0131] The depth 121d of the concave portion 121 indicates the depth from the surface of the active material layer 120 (the top of the convex portion 122) to the deepest part of the concave portion 121. The depth 121d may be, for example, 10 to 150 μm, or 50 to 100 μm. The ratio of the depth 121d of the concave portion 121 to the thickness 120t of the active material layer 120 may be, for example, 0.1 to 0.9, 0.2 to 0.8, or 0.3 to 0.7.

[0132] The convex portion 122 is formed between the concave portion 121 and the concave portion 121. In the present embodiment, it is expected that the density deviation (density difference) between the concave portion 121 and the convex portion 122 is small. The ratio of the density of the active material particles in the convex portion 122 to the density of the active material particles in the concave portion 121 can be, for example, 0.7 to 1.0, 0.8 to 1.0, or 0.9 to 1.0. For example, in the cross-sectional SEM image of the active material layer 120, the ratio of the area of ​​the active material particles contained in the concave portion 121 to the area of ​​the concave portion 121 can be regarded as the density of the concave portion 121. For example, the ratio of the area of ​​the active material particles contained in the convex portion 122 to the area of ​​the convex portion 122 can be regarded as the density of the convex portion 122.

[0133] Figure 5 It is a top view showing the electrode in this embodiment.

[0134] When viewed from above (XY plane), the active material layer 120 has a long side direction (Y axis direction) and a short side direction (X axis direction). The long side direction may be referred to as the "length direction". The short side direction may be referred to as the "width direction". The concave portion 121 and the convex portion 122 extend along the short side direction. However, the concave portion 121 and the convex portion 122 may also extend along the long side direction, for example.

[0135] In the short side direction (X-axis direction), the active material layer 120 includes a central portion 123 and an end portion 124. The end portion 124 is connected to the central portion 123. The end portion 124 can be formed on both sides of the central portion 123, or only on one side. The width of the end portion 124 (on one side) can be, for example, 0.001 to 10 mm, 0.01 to 5 mm, or 0.1 to 3 mm. The central portion 123 can have any width. The ratio of the width of the end portion 124 (on one side) to the width of the central portion 123 can be, for example, 0.001 to 0.05.

[0136] Figure 6 It is a second schematic cross-sectional view showing the electrode in this embodiment.

[0137] The end portion 124 may include, for example, a liquid dripping portion 125. The liquid dripping portion 125 may be referred to as an "inclined portion". In the liquid dripping portion 125, the active material layer 120 is inclined. That is, in the liquid dripping portion 125, the thickness of the active material layer 120 gradually decreases toward the outside. The inclination angle 125θ of the liquid dripping portion 125 may be, for example, 1 to 60 degrees, or 1 to 30 degrees. The width 125w of the liquid dripping portion 125 may be, for example, 0.1 to 3 mm, or 0.5 to 2 mm.

[0138] For example, since the convex mold does not reach the liquid dripping portion 125, the concave portion 121 may not be formed in at least a portion of the liquid dripping portion 125. As a result, for example, it is expected that the peeling and collapse of the active material layer 120 at the end 124 can be reduced. In the short side direction, the distance between the front end of the liquid dripping portion 125 and the front end of the concave portion 121 can be, for example, 0.1 to 3 mm, or 0.5 to 2 mm.

[0139] <Electrode manufacturing equipment>

[0140] Figure 7 It is a conceptual diagram showing an electrode manufacturing apparatus in this embodiment.

[0141] The present manufacturing method can be implemented in the electrode manufacturing device 200. In the electrode manufacturing device 200, the electrode can be manufactured by a roll-to-roll method. The electrode manufacturing device 200 includes a conveying device 210, a coating device 220, a first drying device 230, a molding device 240, and a second drying device 250. The electrode manufacturing device 200 may further include a compression device 260, etc.

[0142] The electrode manufacturing device 200 may further include a mixing device (not shown) and the like. The mixing device may, for example, prepare slurry. The electrode manufacturing device 200 may further include a cutting device (not shown) and the like. The cutting device may, for example, cut the compressed electrode into a predetermined shape. The electrode manufacturing device 200 may further include a control device (not shown) and the like. The control device may, for example, control the operation and cooperation of each device.

[0143] 《Conveying device》

[0144] The conveying device 210 conveys the substrate 110. The conveying device 210 may include, for example, a delivery roller 211 and a take-up roller 212. For example, the delivery roller 211 delivers the substrate 110. The take-up roller 212 takes up the substrate 110 (electrode 100). The substrate 110 may pass through each device in the order of the coating device 220, the first drying device 230, the molding device 240, the second drying device 250, and the compression device 260.

[0145] 《Coating device》

[0146] The coating device 220 applies the slurry to the surface of the substrate 110. Thus, a first coating film can be formed. The coating device 220 can apply the slurry by any method. The coating device 220 can include, for example, a die coater, a roller coater, etc. The first coating film can be formed in a manner that the second coating film has a liquid dripping portion. For example, the inclination and width of the liquid dripping portion can be adjusted according to the unit area weight, viscosity, etc. of the slurry.

[0147] 《1st drying device》

[0148] The first drying device 230 forms a second coating film by drying the first coating film. The first drying device 230 can dry the first coating film in such a way that the second coating film has a liquid dripping portion. For example, the inclination and width of the liquid dripping portion can be adjusted by drying conditions (drying temperature, drying time, etc.). The first drying device 230 can dry the first coating film by any method. The first drying device 230 can include, for example, a hot air drying device, an infrared drying device, etc. The drying conditions are adjusted so that in the second coating film, the solid phase, the liquid phase, and the gas phase form a pendulum state or a rope state.

[0149] Molding device

[0150] The molding device 240 forms a recess on the surface of the second coating film by pressing a convex mold onto the surface of the second coating film. The molding device 240 may include, for example, an embossing roller 241. One or more convex molds are formed on the surface of the embossing roller 241. The recess may be formed according to the pattern of the convex mold. The surface of the embossing roller 241 may be formed with a ceramic layer, for example. The ceramic layer may be formed with a convex mold. By making the contact portion with the active material layer a ceramic layer, for example, the mixing of metallic foreign matter into the active material layer can be reduced. The ceramic layer may include, for example, aluminum oxide, titanium dioxide, etc. For example, a convex mold may be formed on the ceramic layer by laser engraving. For example, the depth of the recess may be adjusted by the height of the convex mold, etc. The convex mold may have a height of, for example, 50 to 200 μm. The core of the embossing roller 241 may be formed of, for example, a stainless steel material, etc.

[0151] 《Second drying device》

[0152] The second drying device 250 forms an active material layer by drying the second coating film. The second drying device 250 can use any method to dry the second coating film. The second drying device 250 can include, for example, a hot air drying device, an infrared drying device, etc. The drying conditions are adjusted so that the active material layer is in a dry state.

[0153] Compression Device

[0154] The compression device 260 compresses the active material layer. The compression device 260 can compress the active material layer using any method. The compression device 260 can include, for example, a roller press device.

[0155] Example

[0156] Hereinafter, this embodiment will be described.

[0157] <First Test Example>

[0158] In the first test example, a positive electrode was manufactured.

[0159] 《(a) Preparation of slurry》

[0160] Prepare the following materials.

[0161] Active material particles: Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2

[0162] Conductive material: Acetylene black

[0163] Adhesive: PVDF

[0164] Dispersion medium: NMP

[0165] A planetary mixer was prepared as a stirring device. 90 parts by mass of active material particles, 2 parts by mass of a binder, and 8 parts by mass of a conductive material were placed in a stirring tank of the stirring device. Furthermore, a dispersion medium was placed in the stirring tank in such a manner that the solid content of the slurry became 62.5%. The materials were mixed in the stirring tank to prepare a slurry.

[0166] 《(b) Coating》

[0167] An Al foil was prepared as a substrate, and a die coater was prepared as a coating device. The slurry was applied on the surface of the substrate to form a first coating film.

[0168] 《(c) 1st Drying》

[0169] The second coating film was formed by drying the first coating film (initial solid content: 62.5%). The solid content of the second coating film was 80%. The drying state of the second coating film was confirmed by the above method. In the second coating film, the solid phase, liquid phase and gas phase formed a pendulum state or a rope state. The target thickness of the second coating film was 150μm.

[0170] 《(d) Molding process》

[0171] The embossing roller forms recesses on the surface of the second coating film. The height of the convex mold is 100 μm. The recesses are formed in a line shape. That is, when viewed from above, a concave-convex structure is formed by a plurality of parallel lines. Each recess extends along the short side direction (width direction) of the second coating film. The spacing between the recesses is 1 mm. The line pressure is 40 N / cm.

[0172] (e) Second drying

[0173] After the recessed portions are formed, the second coating film is dried to form an active material layer.

[0174] (f) Compression

[0175] The active material layer was compressed by a roll press at a linear pressure of 4 t / cm. An electrode (positive electrode) was manufactured in the above manner.

[0176] <Test Example 2>

[0177] In the second test example, a negative electrode was manufactured.

[0178] 《(a) Preparation of slurry》

[0179] Prepare the following materials.

[0180] Active material particles: graphite

[0181] Adhesive: CMC, SBR

[0182] Dispersion medium: water

[0183] A planetary mixer was prepared as a stirring device. 98 parts by mass of active material particles and 2 parts by mass of a binder (1 part by mass of CMC and 1 part by mass of SBR) were placed in a stirring tank of the stirring device. Furthermore, a dispersion medium was placed in the stirring tank in such a manner that the solid content of the slurry became 60%. The materials were mixed in the stirring tank to prepare a slurry.

[0184] 《(b) Coating》

[0185] A Cu foil was prepared as a substrate, and a die coater was prepared as a coating device. The slurry was applied to the surface of the substrate to form a first coating film.

[0186] 《(c) 1st Drying》

[0187] The second coating film was formed by drying the first coating film (initial solid content: 60%). The solid content of the second coating film was 72%. The drying state of the second coating film was confirmed by the above method. In the second coating film, the solid phase, liquid phase and gas phase formed a pendulum state or a rope state.

[0188] 《(d) Molding process》

[0189] The embossing roller forms recesses on the surface of the second coating film. The recesses are formed in a linear shape. Each recess extends along the short side direction (width direction) of the second coating film. The spacing between the recesses is 1 mm. The linear pressure is 40 N / cm.

[0190] (e) Second drying

[0191] After the recessed portions are formed, the second coating film is dried to form an active material layer.

[0192] (f) Compression

[0193] The active material layer was compressed by a roll press at a linear pressure of 1 t / cm. An electrode (negative electrode) was manufactured in the above manner.

[0194] 《Test Example 3》

[0195] A positive electrode was manufactured in the third test example. In the third test example, a coating film was formed using a wet powder instead of a slurry. The materials used were the same as those in the first test example.

[0196] As a stirring device, a high-speed stirrer (manufactured by Earth Technica) was prepared. 90 parts by mass of active material particles, 2 parts by mass of binder and 8 parts by mass of conductive material were put into the stirring tank of the stirring device. The solid materials were mixed in the stirring tank for 15 seconds. The rotation speed of the mixing blade was 4500 rpm. After mixing, liquid (NMP) was added in such a way that the solid content became 90%. After adding the liquid, the materials were mixed in the stirring tank for 30 seconds. The rotation speed of the mixing blade was 300 rpm. The materials were micronized by mixing the materials for another 2 seconds. The rotation speed of the mixing blade was 4500 rpm.

[0197] A roller coater was prepared as a coating device. In the gap between the rollers, the wet powder was compacted to form a sheet-like molded body. The molded body was transferred to the surface of the substrate to form a coating film. The shape of the end of the coating film was adjusted by a scraper-like scraping tool. Thereafter, molding, drying, and compression were performed in the same manner as in the first test example to manufacture an electrode (positive electrode).

[0198] <Results>

[0199] Figure 8 These are cross-sectional images and top surface images of electrodes in the first to third test examples.

[0200] In the first and second test examples, the active material layer was formed by applying the slurry. As shown in the cross-sectional image, a liquid dripping portion (inclined portion) was formed at the end in the short side direction (X-axis direction). The liquid dripping portion was formed in a range of about 1 mm.

[0201] In the third test example, the active material layer was formed by wetting the powder. Furthermore, the coating was scraped off at the end in the short side direction (X-axis direction). As shown in the cross-sectional image, in the third test example, the liquid dripping part was almost not visible. In the third test example, the deviation between the upper surface and the lower surface of the active material layer was about 20 μm.

[0202] As shown in the upper surface image, in the first and second test examples, the concave portion did not extend to the front end in the short side direction (X-axis direction). This is believed to be because in the first and second test examples, a liquid drop portion was formed at the end in the short side direction. At the end in the short side direction, no peeling or collapse of the active material layer (coating) was observed.

[0203] As shown in the upper surface image, in the third test example, the concave portion extends to the vicinity of the front end in the short side direction. This is considered to be because no liquid dripping portion is formed. In the third test example, peeling and collapse of the active material layer occurred at the end in the short side direction.

[0204] Fig. 9 This is a graph showing the relationship between the solid content and the drying time in the first test example.

[0205] Fig. 9 The horizontal axis represents the drying time in "(c) first drying". Fig. 9 The vertical axis represents the solid content after "(c) 1st drying". In the first test example (positive electrode), the formation of a pendulum state or a rope state was confirmed at a solid content of 80 to 99%. At a solid content of 80 to 99%, a recess of the target shape was formed. The depth of the recess was 60 to 80 μm. At a solid content of less than 80%, the material adhered to the punch, making it difficult to form a recess of the target shape.

[0206] Fig.10 This is a graph showing the relationship between the solid content and the drying time in the second test example.

[0207] Fig.10 The horizontal axis represents the drying time in "(c) first drying". Fig.10 The vertical axis represents the solid content after "(c) 1st drying". In the second test example (negative electrode), the formation of a pendulum state or a rope state was confirmed at a solid content of 70 to 99%. At a solid content of 70 to 99%, a recess of the target shape was formed. The depth of the recess was 70 to 80 μm. At a solid content of less than 70%, the material adhered to the punch, making it difficult to form a recess of the target shape.

[0208] <Note>

[0209] The present embodiment and the present example also disclose the following “electrode”.

[0210] An electrode comprises a substrate and an active material layer.

[0211] The active material layer is formed on the surface of the substrate,

[0212] The active material layer includes active material particles and a binder.

[0213] Concave portions and convex portions are formed on the surface of the active material layer,

[0214] The ratio of the density of the active material particles in the protrusions to the density of the active material particles in the recesses is 0.7 to 1.0,

[0215] When viewed from above, the active material layer has a long side direction and a short side direction.

[0216] An inclined portion (liquid dripping portion) is formed at an end portion of the active material layer in the short-side direction.

[0217] An electrode, wherein the concave portion extends along the short side direction.

[0218] The recessed portion does not extend to the front end of the inclined portion (liquid dripping portion).

[0219] The present embodiment and the present example are illustrative in all respects. The present embodiment and the present example are not restrictive. The technical scope of the present disclosure includes all changes within the meaning and scope equivalent to the description of the scope of the claims. For example, it is predetermined from the outset that any technical configurations can be extracted from the present embodiment and the present example and combined arbitrarily.

Claims

1. A method for manufacturing an electrode, comprising: (a) preparing a slurry having a solid content of 50 to 65% by mass by mixing active material particles, a binder and a dispersion medium; (b) forming a first coating film by applying the slurry to a surface of a substrate; (c) forming a second coating film having a solid content of 70 to 99% by mass fraction by drying the first coating film, wherein the second coating film has a long side direction and a short side direction when viewed from above, and a liquid dripping portion is formed at an end of the second coating film in the short side direction, the liquid dripping portion is inclined in a manner that the thickness gradually decreases toward the outside, the inclination angle of the liquid dripping portion is 1 to 60 degrees, and the width of the liquid dripping portion is 0.1 to 3 mm; (d) forming a concave portion on the surface of the second coating film by pressing the convex mold against the surface of the second coating film in a manner such that at least a portion of the liquid dripping portion does not contact the convex mold, wherein a distance between the front end of the liquid dripping portion and the front end of the concave portion in the short side direction is 0.1 to 3 mm; and (e) forming an active material layer by drying the second coating film after forming the recessed portions, In the second coating film, the solid phase, liquid phase and gas phase form a pendulum state or a cable state. In the cable state, the liquid phase is continuous around the solid phase and a portion of the solid phase is in contact with the gas phase. In the pendulum state, the liquid phase is discontinuous, the liquid phase cross-links the solid phases with each other, and the gas phase contacts both the solid phase and the liquid phase.

2. The method for producing an electrode according to claim 1, The active material particles include a positive electrode active material, The slurry has a solid content of 55 to 65% by mass. The second coating film has a solid content of 80 to 99% by mass.

3. The method for manufacturing an electrode according to claim 1, The active material particles include a negative electrode active material, The slurry has a solid content of 50 to 60% by mass. The second coating film has a solid content of 70 to 99% by mass.

4. The method for producing an electrode according to claim 1 or 2, The method further includes (f) compressing the active material layer.

5. An electrode manufacturing device, comprising a conveying device, a coating device, a first drying device, a forming device, a second drying device and an embossing roller, The conveying device is configured to convey the substrate in the order of the coating device, the first drying device, the molding device, and the second drying device. The coating device is configured to form a first coating film by coating a slurry having a solid content of 50 to 65% by mass on the surface of the substrate. The slurry contains active material particles, a binder and a dispersion medium. The first drying device is configured to form a second coating film having a solid content of 70 to 99% by mass fraction by drying the first coating film. The molding device is configured to form a recessed portion on the surface by pressing a convex mold against the surface of the second coating film. The second drying device is configured to form an active material layer by drying the second coating film. The second coating film is formed to have a long side direction and a short side direction when viewed from above. The electrode manufacturing device is configured such that the coating device forms the first coating film and the first drying device dries the first coating film in such a manner that a liquid dripping portion is formed at the end of the second coating film in the short side direction, the liquid dripping portion is inclined in such a manner that the thickness gradually decreases toward the outside, the inclination angle of the liquid dripping portion is 1 to 60 degrees, and the width of the liquid dripping portion is 0.1 to 3 mm, The convex mold is formed on the surface of the embossing roller, The molding device is configured to press the embossing roller against the surface of the second coating film in a manner that at least a portion of the liquid dripping portion does not contact the convex mold, thereby forming a concave portion on the surface of the second coating film, and a distance between the front end of the liquid dripping portion and the front end of the concave portion in the short side direction is 0.1 to 3 mm, The molding device is constructed so that the solid phase, liquid phase and gas phase in the second coating film form a pendulum state or a cable state. In the cable state, the liquid phase is continuous around the solid phase and a part of the solid phase is in contact with the gas phase. In the pendulum state, the liquid phase is discontinuous, the liquid phase cross-links the solid phases with each other, and the gas phase contacts both the solid phase and the liquid phase.

6. The electrode manufacturing device according to claim 5, Also includes a compression device, The conveying device is configured to convey the substrate having passed through the second drying device to the compressing device. The compression device is configured to compress the active material layer.

Images