Electrode manufacturing method

Abstract

To increase the upper limit value of a coating weight of an active material layer.SOLUTION: An electric field is formed between a substrate and a screen by applying a first voltage to the substrate and applying a second voltage to the screen. Coating powder is introduced into the electric field through the screen. An electrode is manufactured by causing the coating powder to adhere to the substrate. The first voltage has a polarity opposite to a polarity of the second voltage. When the coating powder passes through the screen, the coating powder comes into contact with the screen to apply a charge to the coating powder. The coating powder flies in the electric field by an electrostatic force to reach the substrate. An angle between a flight direction of the coating powder and a vertically downward direction is 90 degrees to 270 degrees.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open No. 2018-192380 (Patent Document 1) discloses an electrostatic powder coating device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-192380 Summary of the Invention [Problem to be solved by the invention]

[0004] It has been proposed to manufacture electrodes using electrostatic coating technology. For example, an electric field is formed. One end of the electric field is the workpiece (substrate). Powder paint is sprayed into the electric field. The powder paint contains active material particles. Electrostatic force acts on the powder paint. The electrostatic force causes the powder paint to fly toward the substrate. The electrostatic force also causes the powder paint to adhere to the substrate. The powder paint adheres to the substrate, forming an active material layer.

[0005] For example, it is possible to adjust the angle between the direction of flight of the powder paint in the electric field and the vertical downward direction to 90 to 270 degrees. This is expected to produce a filtering effect. The "filtering effect" refers to the action of removing metallic foreign matter from the powder paint.

[0006] Powder paint may contain metallic foreign matter. For example, metallic foreign matter may be mixed in during the production of active material particles. Metallic foreign matter may adversely affect battery performance. Thrust and gravity act on the powder paint during flight. For example, if the flight direction is vertically upward, the thrust and gravity may act in different directions. Typically, metallic foreign matter is a coarse particle. Metallic foreign matter may have a larger mass than active material particles. Furthermore, metallic foreign matter is a conductor and therefore is considered to be less likely to become charged. Therefore, gravity acting on the metallic foreign matter may be greater than the thrust of flight (electrostatic force, wind pressure, etc.). Due to the increased effect of gravity, the metallic foreign matter may not fly, or may fall even if it does fly. This is expected to remove the metallic foreign matter from the powder paint.

[0007] However, in exchange for this filtering effect, the coating weight (amount of coating per unit area) of the active material layer is limited. Powder coating adheres to the substrate due to electrostatic force. In other words, the adhesive force of the powder coating is proportional to the electrostatic force. The greater the coating weight (the thicker the active material layer), the greater the distance between the surface of the active material layer and the substrate (electrode). The electrostatic force is inversely proportional to the square of the distance. Therefore, the thicker the active material layer, the weaker the electrostatic force (adhesion force) acting on the surface of the active material layer. For example, when the powder coating is flying vertically upward, gravity can act in a direction that pulls the powder coating away from the substrate. When the active material layer reaches a certain thickness, gravity exceeds the adhesive force. When gravity exceeds the adhesive force, new powder coating cannot adhere. In other words, the coating weight of the active material layer reaches its upper limit.

[0008] An object of the present disclosure is to increase the upper limit of the basis weight of the active material layer. [Means for solving the problem]

[0009] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0010] 1. The method for producing an electrode includes the following steps (a) to (c): (a) A first voltage is applied to the substrate and a second voltage is applied to the screen, thereby forming an electric field between the substrate and the screen. (b) The powder coating is introduced into the electric field through a screen. (c) An electrode is produced by depositing the powder coating on a substrate. The first voltage has an opposite polarity to the second voltage. When the powder paint passes through the screen, it comes into contact with the screen, imparting an electric charge to the powder paint. In the electric field, the powder paint flies due to electrostatic force, and reaches the substrate. The angle between the flight direction of the powder paint and the vertical downward direction is 90 to 270 degrees.

[0011] The filtering effect is expected to be achieved by ensuring that the angle between the powder paint's flight direction and the vertical downward direction is 90 to 270 degrees.

[0012] Conventionally, the substrate, which is one end of the electric field, is set to ground (0 V). In other words, no voltage is applied to the substrate. In this case, the electrostatic force (adhesion force) acting on the powder paint adhered to the substrate is equal to the image force. As the powder paint accumulates on the substrate, the active material layer becomes thicker. The thicker the active material layer, the smaller the image force acting on the surface of the active material layer. When the image force and gravity are balanced on the surface of the active material layer, the basis weight of the active material layer reaches its upper limit.

[0013] In the present disclosure, a first voltage is applied to the substrate. The first voltage applied to the substrate has a polarity opposite to that of a second voltage applied to the screen. The powder paint is charged by the screen. Thus, the substrate has a charge of the opposite polarity to that of the powder paint. When the substrate has a charge of the opposite polarity to that of the powder paint, an electrostatic force exceeding the image force can be generated. Therefore, it is expected that the upper limit of the basis weight of the active material layer will be increased.

[0014] Furthermore, the increased adhesive strength is expected to increase the frequency with which the powder coating adheres to the substrate, and the increased frequency of adhesion is expected to increase the adhesion rate.

[0015] 2. The powder paint may fly, for example, vertically upward.

[0016] This is because it is expected to enhance the filtering effect. The angle between the vertically upward and vertically downward directions is 180 degrees.

[0017] 3. The first voltage may be, for example, positive polarity.

[0018] That is, the second electrode may be, for example, negative.

[0019] 4. The powder coating may include, for example, composite particles. The composite particles include active material particles and a coating. The coating covers at least a portion of the surface of the active material particles. The coating includes a binder.

[0020] Conventionally, an active material layer is formed by applying a liquid paint. The liquid paint is called a slurry, a paste, or the like. The liquid paint is prepared by dispersing active material particles, a binder, and the like in a dispersion medium. When the liquid paint dries, the binder may migrate toward the surface of the coating film as the dispersion medium (liquid) evaporates. This phenomenon is also called "binder migration." Binder migration can cause variations in the composition (binder distribution) of the active material layer. Binder migration can cause problems such as increased resistance and decreased peel strength.

[0021] In the composite particles of the present disclosure, the active material particles and the binder are bonded together in advance. The powder coating used in electrostatic coating technology may not require a dispersion medium. In other words, there are fewer factors that can move the binder during the active material layer formation process. Therefore, it is expected that the binder will be distributed uniformly in the active material layer.

[0022] 5. The binder may include, for example, a fluororesin.

[0023] Fluorine resin is on the most negative side of the triboelectric series, and it is expected that the charging of the powder paint will be promoted by including fluororesin in the binder.

[0024] 6. The relationship of the following formula (1) may be satisfied. Ed <f(pd) (1) In the above formula (1), "E" indicates the field strength of the electric field. "d" indicates the distance between the substrate and the screen. "p" denotes the gas pressure in the electric field. "f(pd)" indicates the spark voltage calculated from the product of the gas pressure and the distance and the Paschen curve.

[0025] By satisfying the above formula (1), it is expected that spark discharge will be reduced during the production of the electrode.

[0026] 7. Electrodes may be produced in batches.

[0027] Electrode manufacturing methods are broadly divided into continuous and batch methods. In the manufacturing method "1." above, a first voltage is applied to the substrate. For example, when an electrode is manufactured by a continuous method (roll-to-roll method), the substrate may be several thousand meters long. Since the first voltage is applied to most of the manufacturing equipment, the manufacturing equipment may become complex and expensive. Furthermore, in the manufacturing method "1." above, electrodes with a large basis weight can be manufactured. When an electrode with a large basis weight (a thick electrode) is wound onto a roll, problems such as cracking of the active material layer may occur.

[0028] The manufacturing method described in "1." above is suitable for batchwise manufacturing of large-area, sheet-form electrodes. Large-area, sheet-form electrodes can be used, for example, in large-area stacked batteries. The use of a batchwise manufacturing method is also expected to enable the downsizing of manufacturing facilities.

[0029] 8. The electrode includes a substrate and an active material layer. The substrate includes a first region and a second region. The first region is covered with the active material layer. The second region is exposed from the active material layer. The second region is adjacent to the first region. The active material layer has a side end surface. The side end surface is in contact with the boundary between the first region and the second region. The angle formed between the side end surface and the substrate is 45 to 90 degrees. The active material layer includes composite particles. The composite particles include active material particles and a coating. The coating covers at least a portion of the surface of the active material particles. The coating includes a binder. The relationship of the following formula (2) is satisfied. 0.90≦α / β≦1.10 (2) In the above formula (2), "α" indicates the mass concentration of a specific element derived from the binder in the upper portion. "β" indicates the mass concentration of a particular element in the lower part. The active material layer is divided into two equal parts in the thickness direction, and the upper and lower parts are separated. The lower part is located between the upper part and the substrate.

[0030] In the present disclosure, an electrode including the configuration of "8." above can be manufactured.

[0031] For example, when an active material layer is formed by applying a liquid coating, dripping may occur. That is, the edge of the liquid coating may drip outward from the coating film (active material layer before drying). As a result, the side end surface of the active material layer becomes inclined. The angle (inclination angle) between the side end surface of the active material layer and the substrate is less than 45 degrees.

[0032] In the present disclosure, powder coating is used. In the present disclosure, there are few factors that cause the side end surfaces of the active material layer to be inclined. Therefore, an inclination angle of 45 to 90 degrees can be realized. The closer the inclination angle is to 90 degrees, the more the dead space between the positive and negative electrodes in the battery can be reduced. Reducing the dead space is expected to improve the energy density of the battery.

[0033] In the present disclosure, the binder can be uniformly distributed. The binder distribution can be evaluated by the migration index. "α / β" in the above formula (2) represents the migration index. It is believed that the closer the migration index is to 1, the more uniformly the binder is distributed. For example, if binder migration occurs when a liquid paint dries, the binder will be unevenly distributed at the top of the active material layer. In this case, the migration index can take a value of, for example, 2 to 3. In the present disclosure, composite particles in which active material particles and a binder are previously bonded can be used. Furthermore, factors that cause the binder to migrate (such as evaporation of the dispersion medium) are few. Therefore, a migration index of 0.9 to 1.1 can be achieved.

[0034] 9. The active material layer is, for example, 20 mg / cm 2 The fiber may have a weight per unit area of ​​at least 10 ...

[0035] In the present disclosure, the upper limit of the basis weight is large. Therefore, for example, 20 mg / cm 2 The above basis weight can be realized.

[0036] 10. The active material layer may have a thickness of, for example, 100 to 1000 μm.

[0037] In the present disclosure, the upper limit of the thickness is large, so that a thickness of, for example, 100 to 1000 μm can be realized.

[0038] 11. The active material layer may have a rectangular planar shape, and in plan view, the length of one side of the active material layer may be, for example, 500 mm or more.

[0039] In the present disclosure, large area, single-layer electrodes can be manufactured.

[0040] 12. In the active material layer, the density of metallic foreign particles is 1 particle / m 2 It may be the following:

[0041] In the present disclosure, metallic foreign matter can be reduced by the filtering effect during electrode manufacturing.

[0042] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 is a schematic flowchart of a method for producing an electrode according to this embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing a method for manufacturing an electrode in this embodiment. [Figure 3] FIG. 3 is a conceptual diagram showing a method for manufacturing an electrode according to the reference embodiment. [Figure 4] FIG. 4 is a conceptual diagram of a composite particle in this embodiment. [Figure 5] FIG. 5 is a schematic plan view showing the electrodes in this embodiment. [Figure 6] FIG. 6 is a schematic partial cross-sectional view showing an electrode in this embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing an electrode manufacturing apparatus in this example. [Figure 8] FIG. 8 is a graph showing the relationship between coating time and coating weight. [Figure 9] FIG. 9 is an SEM image showing the results of the second experimental example. [Figure 10] FIG. 10 shows the concept of how to measure the migration index. [Figure 11] Figure 11 is an example of a Paschen curve. [Figure 12] FIG. 12 is a conceptual diagram showing the angle formed between the flight direction of the powder paint and the vertical downward direction. DETAILED DESCRIPTION OF THE INVENTION

[0044] <Definitions of terms, etc.> The terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even closed-ended terms do not exclude additional elements that are normally incidental impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0045] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0046] Elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only a single particle but also an aggregate of particles (powder, powder, particle group).

[0047] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0048] For example, unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be set as a new upper 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 described elsewhere in this specification, in a table, a figure, or the like.

[0049] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed with significant figures. Measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0050] When a compound is expressed by a stoichiometric formula (e.g., "LiCoO2"), the stoichiometric formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobalt oxide is expressed as "LiCoO2," unless otherwise specified, the lithium cobalt oxide is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2" and may contain Li, Co, and O in any composition ratio. Furthermore, doping or substitution with trace elements may be permitted.

[0051] Geometric terms (e.g., "parallel," "perpendicular," and the like) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms used in this specification may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each drawing may not match the actual dimensional relationships. To facilitate understanding of the disclosed technology, the dimensional relationships (length, width, thickness, and the like) in each drawing may be changed. Furthermore, some configurations may be omitted.

[0052] "Planar view" refers to viewing an object from a line of sight parallel to the thickness direction of the object.

[0053] Figure 12 is a conceptual diagram showing the angle between the flight direction of the powder paint and the vertical downward direction. The "angle (Θ)" is defined as the positive direction in the counterclockwise direction from the vertical downward direction (vd) toward the flight direction (fd). When the angle (Θ) is 90 degrees or 270 degrees, the flight direction (fd) is horizontal. When the angle (Θ) is 180 degrees, the flight direction (fd) is vertically upward. For example, "90 to 270 degrees" may also be written as "90 to 270°".

[0054] "D50" is defined as the particle size at which the cumulative frequency of the smaller particle size reaches 50% in a volume-based particle size distribution. "D99" is defined as the particle size at which the cumulative frequency of the smaller particle size reaches 99% in a volume-based particle size distribution. D50 and D99 can be measured using a laser diffraction particle size distribution analyzer.

[0055] Metallic foreign matter (particles) have a "minor diameter" and a "major diameter." The major diameter indicates the distance between the two most distant points on the contour line of a particle image. The minor diameter indicates the diameter perpendicular to the line segment that forms the major diameter at its midpoint. The minor diameter may be equal to the major diameter.

[0056] The "density of metallic foreign matter" can be measured by the following procedure. (1) An electrode is prepared. An active material layer is recovered from the electrode. The active material layer is dispersed in a dispersion medium to prepare a particle dispersion. The dispersion medium is selected depending on the type of binder. For example, N-methyl-2-pyrrolidone (NMP) or the like may be used. (2) A bar magnet is immersed in the particle dispersion to capture magnetic materials in the particle dispersion. Metallic foreign matter contaminated in powder paints is usually magnetic. (3) The bar magnet is pulled out of the particle dispersion, and the magnetic material attached to the bar magnet is collected. For example, the magnetic material may be collected using adhesive tape. (4) For example, the composition of the magnetic material is identified by XRF (X-ray Fluorescence) or the like. Based on the composition of the magnetic material, it is determined whether the magnetic material is a metallic foreign object or not. The number of metallic foreign objects is counted. (5) The density (pieces / m) is calculated by dividing the number of metallic particles by the area of ​​the active material layer. 2 ) is obtained.

[0057] The "melting point" refers to the peak-top temperature of the melting peak (endothermic peak) in a DSC (Differential Scanning Calorimetry) curve. The DSC curve can be measured in accordance with JIS K 7121. The "near the melting point" can refer to, for example, a range of ±20°C of the melting point.

[0058] "Electrode" is a general term for a positive electrode and a negative electrode. The electrode may be a positive electrode or a negative electrode. The electrode may be for, for example, a lithium ion battery. The lithium ion battery may be, for example, a liquid-based battery or an all-solid-state battery. However, the electrode may be applied to any electrochemical device. In this embodiment, an application example to a lithium ion battery will be described as an example.

[0059] "Positive voltage" refers to a voltage having a positive polarity (+). "Positive charge" refers to a charge having a positive polarity. "Negative voltage" refers to a voltage having a negative polarity (-). "Negative charge" refers to a charge having a negative polarity. Positive polarity and negative polarity are opposite polarities to each other.

[0060] The "inclination angle of the side end face" refers to the acute angle between the side end face and the substrate (see "θ" in FIG. 6). The inclination angle (θ) is measured in a cross-sectional image of the electrode 10. The cross-sectional image is captured in a portion of the substrate 11 extending outward from the side end face 12b. The cross-sectional image may be captured using, for example, an optical microscope (OM) or a scanning electron microscope (SEM). For example, an appropriate observation device is selected depending on the thickness of the active material layer 12, etc. The side end face 12b may be curved. In the cross-sectional image, a line segment connecting the leading end of the side end face 12b to the trailing end of the side end face 12b is drawn. The leading end is the point of contact between the side end face 12b and the substrate 11. The trailing end is the boundary between the side end face 12b and the main surface 12a of the active material layer 12. The angle (θ) formed by the line segment and the main surface of the substrate 11 is measured. The "principal surface" refers to the surface having the largest area among the outer surfaces of an object (typically a hexahedron).

[0061] The "migration index" is measured using the following procedure: A sample is cut from an electrode. The cut surface is parallel to the thickness direction of the active material layer. A cross-sectional sample is prepared by cross-sectional processing of the cut surface of the active material layer. For example, cross-sectional processing may be performed using an ion milling device. The cross-sectional sample is analyzed using an EPMA (Electron Probe Micro Analyzer). Figure 10 illustrates a conceptual diagram of a method for measuring the migration index. In the cross-sectional sample, the active material layer 12 is divided into two equal parts in the thickness direction, thereby dividing the active material layer 12 into an upper part 1 and a lower part 2. The lower part 2 is located between the upper part 1 and the substrate 11. A specific element is selected depending on the type of binder. The specific element is an element that can serve as a binder marker. For example, if the binder contains polyvinylidene fluoride (PVdF), fluorine may be used as the specific element. If the binder does not contain an appropriate element, the cross-sectional sample may be subjected to a known dyeing process to impart the specific element to the binder. The EPMA measures the mass concentration (α) of a specific element in the upper portion 1 and the mass concentration (β) of a specific element in the lower portion 2. The migration index (α / β) is calculated by dividing α by β.

[0062] A "Paschen curve" represents the relationship between the product (p×d) of gas pressure (p) and inter-electrode distance (d), and the spark voltage. The product (p×d) is also written as "pd." FIG. 11 is an example of a Paschen curve. The graph in FIG. 11 is a logarithmic graph. The Paschen curve may have a minimum value. FIG. 11 shows the Paschen curve for air as an example. The Paschen curve may vary depending on the type of gas. A known Paschen curve is available for any gas type.

[0063] "Aerosol" refers to a dispersion system in which at least one of a solid and a liquid is dispersed in a gas. An aerosol may also be called, for example, a mist, a cloud powder, etc. The appearance of an aerosol may be described, for example, as cloud-like, plume-like, etc.

[0064] <Electrode manufacturing method> Fig. 1 is a schematic flowchart of a method for producing an electrode according to this embodiment. Hereinafter, "a method for producing an electrode according to this embodiment" may be abbreviated as "the present production method." The present production method includes "(a) formation of an electric field," "(b) charging," and "(c) coating." The present production method may further include, for example, "(d) fixing," etc.

[0065] (a) Formation of an electric field 2 is a conceptual diagram showing a method for manufacturing an electrode in this embodiment. The manufacturing method includes applying a first voltage (V1) to the substrate 11 and a second voltage (V2) to the screen to form an electric field.

[0066] The substrate 11 is conductive. The substrate 11 may be, for example, in the form of a sheet. The substrate 11 may be, for example, a current collector. The substrate 11 may include, for example, a metal foil. The substrate 11 may be referred to, for example, as a "current collector foil." The substrate 11 may include, for example, at least one selected from the group consisting of aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), titanium (Ti), and iron (Fe). The substrate 11 may include, for example, an Al foil, an Al alloy foil, a Cu foil, or the like. The substrate 11 may have a thickness of, for example, 5 to 50 μm.

[0067] The screen 122 is porous. The screen 122 may have through holes. The screen 122 is conductive. For example, a screen used in electrostatic screen printing may be used. The screen 122 may be, for example, a metal mesh or the like. The screen 122 may be, for example, a stainless steel mesh or the like. For example, the mesh size of the screen 122 may be adjusted so that the powder paint passes through the screen 122 and the frequency of contact between the powder paint and the screen 122 is appropriate. The mesh size of the screen 122 may be, for example, 30 to 300 μm or 50 to 200 μm.

[0068] The substrate 11 and the screen 122 are connected to a DC power supply 133. A first high-voltage power supply 131 is connected to the substrate 11. The first high-voltage power supply 131 applies a first voltage (V1) to the substrate 11. A second high-voltage power supply 132 is connected to the screen 122. The second high-voltage power supply 132 applies a second voltage (V2) to the screen 122.

[0069] The first voltage (V1) has a polarity opposite to that of the second voltage (V2). This is expected to increase the upper limit of the basis weight. For example, the first voltage (V1) may be a positive voltage and the second voltage (V2) may be a negative voltage. For example, the first voltage (V1) may be a negative voltage and the second voltage (V2) may be a positive voltage.

[0070] The electric field strength (E) is calculated by dividing the difference (V1-V2) between the first voltage and the second voltage by the distance (d) between the substrate 11 and the screen 122. The electric field strength (E) may be less than the spark voltage, for example. The spark voltage is calculated from the product of the gas pressure (p) and the distance (d) and the Paschen curve. That is, the relationship of the above formula (1) may be satisfied. The gas in the electric field may be, for example, air or an inert gas such as nitrogen or argon. The gas pressure (p) may be, for example, atmospheric pressure. The gas pressure (p) may be, for example, 0.01 to 1 MPa.

[0071] The electric field strength (E) may be, for example, 500 V / mm or less. The electric field strength may be, for example, 100 to 500 V / mm. The first voltage (V1) may be, for example, +500 to +1500 V. The second voltage (V2) may be, for example, -3500 to -2500 V. The distance (d) may be, for example, 1 to 20 mm, or 5 to 10 mm.

[0072] The flight direction of the powder paint is adjusted by the positional relationship between the substrate 11 and the screen 122. The direction from the screen 122 toward the substrate 11 is the flight direction of the powder paint. The angle between the flight direction and the vertical downward direction is 90 to 270 degrees. For example, when the flight direction is resolved into a vertical component (Z-axis direction in FIG. 2) and a horizontal component (X-axis direction in FIG. 2), the flight direction may include a vertical upward component. By including a vertical upward component in the flight direction, an enhanced filtering effect is expected. The flight direction may be, for example, horizontal. The flight direction may be, for example, vertical upward. The angle between the flight direction and the vertical downward direction may be, for example, 120 to 240 degrees, or 150 to 210 degrees.

[0073] (b) Charged The method includes introducing powder paint into the electric field through a screen 122. The powder paint is described below. For example, the powder paint (particles 5) may be transported to the screen by a gas flow. The gas may be, for example, air or an inert gas. For example, the powder paint and the gas may be mixed to form an aerosol. The aerosol may be introduced into the electric field.

[0074] When the powder paint (particles 5) passes through the screen 122, the powder paint comes into contact with the screen 122. This causes an electric charge to be injected into the powder paint. The polarity of the electric charge is the same as the polarity of the second voltage (V2). For example, when the second voltage (V2) is a negative voltage, a negative electric charge is injected into the powder paint.

[0075] The particles 5 that have passed through the screen 122 are introduced into an electric field. An electrostatic force acts on the particles 5 introduced into the electric field. The particles 5 fly due to the electrostatic force. The flight of the particles 5 may be assisted by, for example, wind pressure in addition to the electrostatic force. For example, a gas flow by a blower may be used in combination.

[0076] 《(c)Painting》 This manufacturing method includes manufacturing an electrode 10 by applying a powder coating to a substrate 11. The particles 5 fly in an electric field, and reach the substrate 11. The particles 5 adhere to the substrate 11. The particles 5 are deposited on the substrate, and an active material layer 12 is formed.

[0077] An electrostatic force (F) acts on the particles 5 attached to the substrate 11. The electrostatic force (F) is expressed by the following formula (3).

[0078] F=k×q1q2 / r 2 (3) "F" indicates electrostatic force. "k" indicates the proportionality constant. "q1" indicates the amount of electricity imparted to the powder paint. “q2” indicates the amount of electricity imparted to the substrate 11. "r" indicates the distance between the substrate 11 and the powder paint.

[0079] When the first voltage is not applied to the substrate 11 and the substrate 11 is at ground (0 V), the relationship "q1 = q2" is satisfied in the above formula (3). When the relationship "q1 = q2" is satisfied, the electrostatic force is equal to the image force.

[0080] Gravity (mg) also acts on the particles 5 attached to the substrate 11. "m" represents the mass of the particles 5, and "g" represents the gravitational acceleration. Gravity (mg) acts in a direction that pulls the particles 5 away from the substrate 11.

[0081] In this manufacturing method, a first voltage (V1) is applied to the substrate 11. This increases the amount of electricity in the substrate 11. When the first voltage (V1) is applied to the substrate 11, the amount of electricity in the substrate 11 is expressed by "α×q1" (α>1). Therefore, the particle 5 is charged by "F=k×αq1q2 / r 2 " electrostatic force acts. This is expected to improve the adhesion of the powder paint. The improved adhesion is expected to increase the upper limit of the coating weight. It is also expected that the frequency with which the powder paint adheres to the substrate 11 will increase. The increased frequency of adhesion is expected to increase the adhesion speed.

[0082] FIG. 3 is a conceptual diagram showing a method for manufacturing an electrode in a reference embodiment. In FIG. 3, a high-voltage power supply is not connected to the substrate 11. That is, a first voltage (V1) is not applied to the substrate 11. The substrate 11 is grounded (GND=0V). A second voltage (V2) is applied to the screen 122. In the reference embodiment, the electrostatic force acting on the particle 5 is equal to the image force. That is, the electrostatic force acting on the particle 5 is expressed by the formula: F=k×q1q2 / r 2 The electrostatic force in the reference embodiment is 1 / α of the electrostatic force in the present manufacturing method. In other words, the electrostatic force in the reference embodiment is smaller than the electrostatic force in the present manufacturing method. Therefore, in the reference embodiment, the upper limit of the basis weight may be smaller than in the present manufacturing method. In the reference embodiment, the deposition rate may be lower than in the present manufacturing method.

[0083] (d) Establishment The present manufacturing method may include applying at least one of pressure and heat to the active material layer 12 to fix the active material layer 12 to the substrate 11. Fixing the active material layer 12 is expected to improve the peel strength of the active material layer 12.

[0084] Pressure and heat may be applied separately. Pressure and heat may be applied substantially simultaneously. For example, the active material layer 12 may be compressed using a heat roll, a heat plate, or the like. The heating temperature of the active material layer 12 may be, for example, a temperature near the melting point of the binder. The heating temperature may be, for example, 80 to 200°C. The pressure may be adjusted depending on, for example, the target thickness, target density, etc. of the active material layer 12. For example, a pressure of 50 to 200 MPa may be applied to the active material layer 12.

[0085] In this manner, the electrode 10 can be manufactured. The electrode 10 may be manufactured, for example, in a continuous manner. The electrode 10 may be manufactured, for example, in a batch manner.

[0086] 《Powder paint》 The liquid paint has a different composition from the active material layer 12. This is because the liquid paint contains a dispersion medium (liquid). On the other hand, the powder paint may have the same composition as the active material layer 12. The powder paint contains active material particles. In addition to the active material particles, the powder paint may further contain, for example, a binder, a conductive material, a solid electrolyte, etc.

[0087] The active material particles may have a D50 of, for example, 1 to 30 μm, a D50 of 1 to 20 μm, or a D50 of 1 to 10 μm.The active material particles may have a D99 of, for example, 30 to 50 μm.

[0088] The active material particles cause an electrode reaction. The active material particles may contain any component. The active material particles may contain, for example, a positive electrode active material. The active material particles may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, the "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 may be, for example, 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.

[0089] The active material particles may include, for example, a negative electrode active material such as graphite, soft carbon, hard carbon, silicon, silicon oxide, a silicon-based alloy, tin, tin oxide, a tin-based alloy, and Li4Ti5O 12 It may contain at least one selected from the group consisting of:

[0090] The binder may be in powder form. The binder binds the solid materials together in the active material layer 12. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the active material particles. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of PVdF, polytetrafluoroethylene (PTFE), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyimide (PI), polyamideimide (PAI), and polyacrylic acid (PAA).

[0091] The binder may contain, for example, a fluororesin. The fluororesin may contain, for example, at least one selected from the group consisting of PVdF, PVdF-HFP, and PTFE. When the binder contains a fluororesin, the charging of the powder coating material can be promoted. This is because the fluororesin is located on the most negative side of the triboelectric series.

[0092] The conductive material may be in powder form. The conductive material may form an electron conduction path in the active material layer 12. The amount of conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material particles. The conductive material may contain any component. The conductive material may include, for example, conductive carbon particles, conductive carbon fibers, etc. The conductive material may include, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fiber, carbon nanotubes, and graphene flakes. The carbon black may include, for example, at least one selected from the group consisting of acetylene black, furnace black, channel black, and thermal black.

[0093] The solid electrolyte may be in powder form. The solid electrolyte may form an ion conduction path in the active material layer 12. The amount of the solid electrolyte may be, for example, 10 to 100 parts by volume per 100 parts by volume of the active material particles. The solid electrolyte may contain any component. For example, the solid electrolyte may contain at least one selected from the group consisting of Li2S-P2S5, LiI-Li2S-P2S5, LiBr-Li2S-P2S5, and LiI-LiBr-Li2S-P2S5.

[0094] FIG. 4 is a conceptual diagram of a composite particle in this embodiment. The powder coating may contain composite particles 6. The composite particles 6 may be formed by combining active material particles 7 with other materials. The composite particles 6 contain active material particles 7 and a coating 8. The active material particles 7 are the cores of the composite particles 6. The coating 8 is the shell of the composite particles 6. The coating 8 covers at least a portion of the surface of the active material particles 7. The coating 8 contains a binder. The coating 8 may further contain a conductive material, a solid electrolyte, etc.

[0095] The composite particles 6 can be formed by any method. For example, the composite particles 6 may be formed by mixing the active material particles 7 with other materials under conditions in which a strong shear force is applied. Any particle-composite device can be used in this production method. After the composite particles 6 are formed, the composite particles 6 may be subjected to a heat treatment, for example, at a temperature near the melting point of the binder. The heat treatment softens, melts, and re-solidifies the binder. As a result, the coating 8 is expected to be firmly fixed to the surface of the active material particles 7. If the fixing strength is low, the coating 8 may peel off from the surface of the active material particles 7, for example, when the composite particles 6 fly.

[0096] <Electrode> 5 is a schematic plan view showing an electrode in this embodiment. Electrode 10 includes a substrate 11 and an active material layer 12. Active material layer 12 is disposed on a portion of the main surface of substrate 11. Active material layer 12 may be formed on only one surface of substrate 11, or on both the front and back surfaces.

[0097] The active material layer 12 may have any planar shape. For example, the active material layer 12 may have a rectangular planar shape. The active material layer 12 may have a large area. In a planar view, the length of one side of the active material layer 12 may be, for example, 500 mm or more, 1000 mm or more, or 1500 mm or more. In a planar view, the length of one side of the active material layer 12 may be, for example, 3000 mm or less.

[0098] The active material layer 12 can have a large basis weight. For example, the active material layer 12 has a basis weight of 20 mg / cm. 2 It may have a basis weight of 40 mg / cm or more. 2 It may have a basis weight of 60 mg / cm or more. 2 The active material layer 12 may have a weight per unit area of ​​120 mg / cm or more, for example. 2 It may have a basis weight of 100 mg / cm or less. 2 The following basis weights may be used.

[0099] FIG. 6 is a schematic partial cross-sectional view showing an electrode according to this embodiment. The substrate 11 includes a first region 11a and a second region 11b. FIG. 6 shows the vicinity of the boundary between the first region 11a and the second region 11b. The first region 11a is covered by the active material layer 12. The second region 11b is adjacent to the first region 11a. The second region 11b is exposed from the active material layer 12. The second region 11b extends outward beyond the active material layer 12. The second region 11b may be referred to as, for example, an "uncoated portion" or "uncoated portion." A current collecting member may be bonded to the second region 11b. The current collecting member may be bonded by, for example, ultrasonic bonding, spot welding, laser welding, or the like. The current collecting member may include, for example, a current collecting plate, a lead tab, an electrode terminal, or the like.

[0100] The active material layer 12 includes a main surface 12a and a side end surface 12b. The side end surface 12b is connected to the main surface 12a. The side end surface 12b is in contact with the boundary between the first region 11a and the second region 11b. The angle (θ) formed between the side end surface 12b and the main surface of the substrate 11 is 45 to 90 degrees. The closer the angle (θ) is to 90 degrees, the more improved the energy density is expected. The angle (θ) may be, for example, 60 to 90 degrees, 70 to 90 degrees, or 80 to 90 degrees.

[0101] The active material layer 12 may have a thickness of, for example, 100 to 1000 μm, or 200 to 500 μm.

[0102] The active material layer 12 contains composite particles 6. The active material layer 12 is formed by an aggregate of composite particles 6, which allows for a uniform distribution of the binder. The active material layer 12 has a migration index of 0.9 to 1.10. That is, the relationship of the above formula (2) is satisfied. The active material layer 12 may have a migration index of, for example, 0.92 or more, or may have a migration index of 0.94 or more. The active material layer 12 may have a migration index of, for example, 1.08 or less, or may have a migration index of 1.06 or less.

[0103] The density of the metallic foreign particles in the active material layer 12 may be low. The density of the metallic foreign particles may be, for example, 1 particle / m 2 May be less than 0.5 pieces / m 2 or less. The density of the metallic foreign matter may be zero. The metallic foreign matter may be, for example, a magnetic material. The metallic foreign matter may contain, for example, a component derived from stainless steel (SUS), iron (Fe), iron oxide, etc. The metallic foreign matter may be a coarse particle. The minor axis of the metallic foreign matter may be, for example, larger than the D99 of the active material particles. The minor axis of the metallic foreign matter may be, for example, 2 to 10 times, 2 to 5 times, or 2 to 3 times the D99 of the active material particles. [Example]

[0104] <First Experimental Example> In the first experimental example, the polarity of the first voltage was investigated.

[0105] 《First manufacturing example》 The following materials were prepared: Active material particles: Li(NiCoMn)O2 Conductive material: acetylene black Binder: PVdF

[0106] A mixing device called the "Multi-Purpose Mixer" manufactured by Nippon Coke Engineering Co., Ltd. was prepared. The device includes a spherical tank (mixing vessel). The spherical tank's convection-promoting effect generates strong shear forces, allowing solid materials to be compounded.

[0107] Active material particles, conductive material, and binder were placed in a spherical tank. The material mixing ratio was "active material particles / conductive material / binder = 90 / 5 / 5 (mass ratio)." The rotation speed of the stirring blade was set to 10,000 rpm. The materials were mixed for 10 minutes. This resulted in the formation of composite particles. The composite particles contained active material particles and a coating. The coating covered the surface of the active material particles. The coating contained the binder and conductive material.

[0108] A metal tray was prepared. A composite particle aggregate (powder) was thinly spread on the tray. The tray was stored in an oven, whereby the composite particles were heat-treated. The oven temperature was set to 160°C. The storage time was 30 minutes. It is believed that the heat treatment caused the coating to adhere to the surface of the active material particles. Thus, a powder coating containing composite particles was prepared.

[0109] 7 is a schematic cross-sectional view showing an electrode manufacturing apparatus in this example. The electrode manufacturing apparatus 100 includes an introduction section 110, a development section 120, and an electric field forming section .

[0110] The introduction section 110 includes an agitating blade 111, a perforated plate 112, and a fan 113. The perforated plate 112 is an alumina perforated plate (opening size 10 μm, plane size 75 mm×75 mm).

[0111] The developing unit 120 includes a developing electrode 121 and a screen 122. The screen 122 is a SUS mesh (openings: 100 μm). The gap between the developing electrode 121 and the screen 122 is 8 mm.

[0112] The electric field forming unit 130 includes a first high-voltage power supply 131, a second high-voltage power supply 132, and a DC power supply 133. The first high-voltage power supply 131 applies a positive voltage to the developing electrode 121. The second high-voltage power supply 132 applies a negative voltage to the screen 122.

[0113] A substrate 11 was placed on the surface of the developing electrode 121. The substrate 11 was an Al foil (thickness: 12 μm). The substrate 11 had the same potential as the developing electrode 121. A powder coating material was supplied onto a perforated plate 112. A fan 113 supplied a gas flow to the powder coating material, causing the powder coating material to be stirred up. The gas type was air. The gas flow rate was 25 L / min. An agitating blade 111 mixed the powder coating material with the gas, forming an aerosol 9. The agitating blade 111 rotated at 120 rpm. The aerosol 9 passed through a screen 122. The charged aerosol 9 was introduced into an electric field. When the aerosol 9 came into contact with the surface of the substrate 11, the powder coating material adhered to the substrate 11. This resulted in the formation of an active material layer 12. The planar size of the active material layer 12 was 60 mm × 200 mm.

[0114] After the active material layer 12 was formed, the electrode 10 was sandwiched between two heat plates (flat plates). The temperature of the heat plates was 160°C. A load of 15 tf was applied to the active material layer 12 by the heat plates. This fixed the active material layer 12 to the substrate 11. In this way, the electrode 10 was produced.

[0115] 《Second manufacturing example》 As shown in Table 1 below, an attempt was made to manufacture an electrode 10 in the same manner as in the first manufacturing example, except that the first voltage (V1) and the second voltage (V2) were changed.

[0116] 《Third manufacturing example》 As shown in Table 1 below, an attempt was made to manufacture an electrode 10 in the same manner as in the first manufacturing example, except that the first voltage (V1) and the second voltage (V2) were changed.

[0117] [Table 1]

[0118] FIG. 8 is a graph showing the relationship between coating time and coating weight. In all of the first to third production examples, the electric field strength was 500 V / mm. However, in the second production example, the powder paint did not adhere to the substrate. In the second production example, the first voltage (V1) has the same polarity as the second voltage (V2). A negative charge is injected into the powder paint at the screen. The substrate also has a negative charge. It is believed that electrostatic repulsion causes the powder paint to move away from the substrate.

[0119] In the first and third production examples, active material layers without defects were formed. The coating weight increases with increasing coating time and eventually saturates, reaching an upper limit. The upper limit of the coating weight in the third production example was higher than in the first production example. In Figure 8, the steeper the slope of the curve, the higher the deposition rate. The third production example showed a higher deposition rate than the first production example. The coating weight after 50 seconds also indicates the deposition rate (see Table 1 above).

[0120] In the first manufacturing example, the first voltage (V1) is 0 V (GND). In the third manufacturing example, the first voltage (V1) has the opposite polarity to the second voltage (V2). It is believed that the negatively charged powder paint is attracted to the positively charged substrate, thereby promoting adhesion of the powder paint.

[0121] <Second Experimental Example> In the second experiment, the filtering effect was investigated.

[0122] SUS particles were prepared as metallic foreign matter. The SUS particles had a minor axis of 45 to 90 μm. 10% by mass of SUS particles were mixed into the powder coating (composite particles) prepared in the first experimental example. The SUS particles had a minor axis larger than the D99 of the active material particles.

[0123] Electrode production was attempted under the same conditions as in the third manufacturing example in the first experimental example, except that a powder coating containing metallic foreign matter was used. A predetermined amount of powder sample was collected at each stage: the initial powder coating (before flight), the aerosol (during flight), and the active material layer (after deposition). The powder samples were observed by SEM.

[0124] Figure 9 is an SEM image showing the results of the second experimental example. The presence of metallic impurities (SUS particles) can be confirmed in the initial powder coating. On the other hand, no metallic impurities can be confirmed in the aerosol or active material layer. It is believed that the metallic impurities were removed by the filtering action of this manufacturing method.

[0125] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0126] 1 upper part, 2 lower part, 5 particle, 6 composite particle, 7 active material particle, 8 coating, 9 aerosol, 10 electrode, 11 substrate, 11a first region, 11b second region, 12 active material layer, 12a main surface, 12b side end surface, 100 electrode manufacturing apparatus, 110 introduction section, 111 stirring blade, 112 perforated plate, 113 fan, 120 development section, 121 development electrode, 122 screen, 130 electric field forming section, 131 first high-voltage power supply, 132 second high-voltage power supply, 133 DC power supply.

Claims

1. (a) applying a first voltage to a substrate and a second voltage to a screen to form an electric field between the substrate and the screen; (b) introducing powder coating material through the screen into the electric field; and (c) producing an electrode by depositing the powder coating on the substrate; Including, the first voltage has an opposite polarity to the second voltage; When the powder coating material passes through the screen, the powder coating material comes into contact with the screen, thereby imparting an electric charge to the powder coating material; In the electric field, the powder paint flies due to electrostatic force, and the powder paint reaches the substrate; the angle between the flight direction of the powder paint and the vertical downward direction is 90 to 270 degrees; In the step (c), the powder coating material is deposited on the substrate to form an active material layer; The active material layer thickens vertically downward, The active material layer has a thickness of 20 mg / cm 2 It is formed to have the above weight per unit area and a thickness of 100 to 1000 μm. Electrode manufacturing method.

2. The flying direction of the powder paint is vertically upward. A method for manufacturing the electrode according to claim 1.

3. the first voltage is positive; The method for manufacturing the electrode according to claim 1 or 2.

4. The powder coating comprises composite particles, the composite particles include active material particles and a coating, the coating covers at least a portion of the surface of the active material particles, The coating includes a binder. The method for manufacturing the electrode according to any one of claims 1 to 3.

5. The binder contains a fluororesin. The method for manufacturing the electrode according to claim 4 .

6. The following formula (1): Ed<f(pd) (1) The relationship is fulfilled, In the above formula (1), E denotes the field strength of the electric field, d represents the distance between the substrate and the screen; p denotes the gas pressure in the electric field, f(pd) represents the spark voltage calculated from the product of the gas pressure and the distance and the Paschen curve. The method for manufacturing the electrode according to any one of claims 1 to 5.

7. The electrode is produced in a batch process. The method for manufacturing the electrode according to any one of claims 1 to 6.

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