Electrode for secondary battery, and method for manufacturing electrode for secondary battery

Abstract

To provide a secondary battery electrode capable of increasing the degree of orientation of active material particles without depending on the magnetism of the active material particles to reduce the internal resistance of a battery, and a method for manufacturing the secondary battery electrode.SOLUTION: An electrode for a secondary battery includes a current collector foil 10, and a mixture layer 20 formed on the surface of the current collector foil 10, and the mixture layer 20 includes a composite material 30 in which a film 32 exhibiting magnetism is formed on at least one surface along the long axis direction of flat active material particles 31, and the composite material 30 is oriented such that the long axis direction is substantially perpendicular to the surface of the current collector foil 10.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Secondary batteries are widely used as so-called portable power sources such as personal computers and mobile terminals, and as power sources for vehicle driving. Among secondary batteries, in particular, lithium-ion secondary batteries, which are lightweight and have a high energy density, are suitably used as high-output power sources for driving vehicles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles. A lithium-ion secondary battery is a secondary battery that can be charged and discharged by the movement of lithium ions in an electrolyte between an anode (anode plate) and a cathode (cathode plate) that occlude and release lithium ions.

[0003] An electrode used in a secondary battery such as a lithium-ion secondary battery includes a conductive current collector foil (current collector) and a composite material layer containing electrode materials such as an active material and a conductive material held on the current collector foil. In such a secondary battery, in order to improve battery characteristics, the electrode resistance is reduced by increasing the degree of orientation of the electrode materials in the composite material layer.

[0004] Patent Document 1 discloses the following non-aqueous battery and a method for manufacturing the same. The non-aqueous battery and the method for manufacturing the same described in Patent Document 1 include at least a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode includes a current collector, an intermediate layer, and an active material layer. The intermediate layer is interposed between the current collector and the active material layer. The intermediate layer includes graphite particles and insulating particles. In the cross-section in the thickness direction of the intermediate layer, the graphite particles have a major axis diameter that is 1 time or more the thickness of the intermediate layer. In the X-ray diffraction measurement of the intermediate layer by the Out-of-Plane method, the ratio of the intensity of the diffraction line of the graphite crystal to the intensity of the 002 diffraction line of the graphite crystal is 0.0011 or more.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technology described in Patent Document 1, the graphite particles contained in the intermediate layer are oriented by a magnetic field. On the other hand, for example, in the positive electrode of a lithium-ion secondary battery, a lithium composite oxide having a high capacity and excellent thermal stability is preferably used as the active material particles. However, since such active material particles are less likely to be oriented by a magnetic field, there has been a problem that the degree of orientation cannot be increased in the technology described in Patent Document 1.

[0007] The present invention has been made to solve such problems, and an object thereof is to provide a secondary battery electrode capable of increasing the degree of orientation regardless of the magnetism of the active material particles and reducing the internal resistance of the battery, and a method for manufacturing the secondary battery electrode.

Means for Solving the Problems

[0008] The secondary battery electrode according to one embodiment has a current collector foil and a composite layer formed on the surface of the current collector foil. The composite layer includes a composite material having a film formed thereon that exhibits magnetism on at least one surface along the major axis direction of the flat active material particles, and the composite material is oriented such that the major axis direction is substantially perpendicular to the surface of the current collector foil.

[0009] In addition, a method for manufacturing an electrode for a secondary battery according to an embodiment includes a composite material forming step of forming a composite material having a film that exhibits magnetism with respect to a magnetic field applied from the outside on at least one surface along the major axis direction of flat active material particles, a coating step of coating a paste for forming a composite material layer containing at least the composite material and a solvent on the surface of a current collector foil, and a magnetic field application step of applying a magnetic field substantially perpendicular to the surface of the current collector foil to the composite material layer-containing coating film formed by the paste for forming a composite material layer applied to the surface of the current collector foil before the coating film for forming a composite material layer dries, thereby orienting the composite material contained in the coating film for forming a composite material layer, and a composite material layer forming step of drying the coating film for forming a composite material layer in which the composite material is oriented to form a composite material layer on the surface of the current collector foil.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an electrode for a secondary battery that can increase the degree of orientation regardless of the magnetism of active material particles and reduce the internal resistance of the battery, and a method for manufacturing an electrode for a secondary battery.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0012] Embodiment 1 Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are simplified as appropriate.

[0013] In this embodiment, the "minor axis diameter" is the average of the longest diameters in the minor axis direction of the active material particles 31 and the composite material 30, respectively. The "major axis diameter" in this embodiment is the average of the longest diameters in the major axis direction of the active material particles 31 and the composite material 30, respectively. Also, each of the minor axis direction and the major axis direction coincides between the active material particles 31 and the composite material 30.

[0014] Hereinafter, as one of the preferred embodiments of the electrode for a secondary battery according to this embodiment, it will be specifically described by embodying it in the electrode of a lithium-ion secondary battery. A lithium-ion secondary battery is a secondary battery in which lithium ions, which are charge carriers, are conducted in an electrolytic solution between a positive electrode (positive electrode plate) and a negative electrode (negative electrode plate) during an electrochemical reaction, thereby realizing charge and discharge. Such a lithium-ion secondary battery is suitably used, for example, as a driving power source for vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHEV).

[0015] Referring to FIG. 1, the outline of the electrode for a secondary battery (electrode plate 1) according to this embodiment will be described. FIG. 1 is a cross-sectional view showing the electrode for a secondary battery according to Embodiment 1. The cross-sectional view shown in FIG. 1 shows a part of the cross-section of the electrode plate 1 orthogonal to the surface of the current collector foil 10.

[0016] As shown in FIG. 1, the electrode plate 1 has a current collector foil 10 and a composite layer 20 formed on the current collector foil 10. The current collector foil 10 is formed in a plate shape or a foil shape and is composed of a metal with good conductivity. When it is a positive electrode, the metal constituting the current collector foil 10 includes, for example, aluminum, aluminum alloy, etc. When it is a negative electrode, the metal constituting the current collector foil 10 includes, for example, copper, copper alloy, etc. The current collector foil 10 has a thickness of, for example, 5 μm to 50 μm.

[0017] The composite material layer 20 is formed on at least one surface of the current collector foil 10, excluding the edge portion along one edge in the width direction. Further, the electrode plate 1 has an exposed portion where the composite material layer 20 is not formed and the current collector foil 10 is exposed at the edge portion of the current collector foil 10. The exposed portion is electrically connected to an external terminal. The composite material layer 20 contains at least a composite material 30 mainly composed of active material particles 31 and is held by the current collector foil 10. The composite material layer 20 may contain a conductive material, a binder, and other additives (such as a thickening agent and a dispersant) as necessary.

[0018] The density of the composite material layer 20 is not particularly limited. For example, in the case of a positive electrode, it is preferably 1.0 g / cm 3 ~3.8 g / cm 3 and more preferably 1.5 g / cm 3 ~3.0 g / cm 3 and particularly preferably 1.8 g / cm to 2.7 g / cm 3 The thickness of the composite material layer 20 is not particularly limited either. For example, it is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm.

[0019] Each of the composite materials 30 included in the composite material layer 20 is oriented such that the major axis direction is substantially perpendicular to the surface of the current collector foil 10. That is, the degree of orientation, which is the average value of the angle formed by the surface of the current collector foil 10 and the major axis direction of the composite material 30 (active material particles 31), is 45° to 90°, and particularly preferably 90°.

[0020] In the electrode plate 1 when a lithium-ion secondary battery is configured, the electrolyte penetrates into the voids in the composite material layer 20. Therefore, when the composite materials 30 are oriented in one direction in the composite material layer 20, the movement path of lithium ions in the composite material layer 20 becomes linear, so that the conductivity of the ions in the electrolyte increases and the resistance is reduced. It is considered that the movement path of lithium ions in the composite material layer 20 is the shortest when the composite materials 30 are oriented at 90°.

[0021] As the conductive material, for example, carbon black such as acetylene black (AB), activated carbon, graphite, carbon materials such as carbon nanotubes, etc. can be used. When using carbon nanotubes, for example, the proportion of the conductive material in the entire composite layer 20 is preferably 0.1% by mass to 5% by mass, more preferably 0.3% by mass to 3% by mass, and particularly preferably 0.5% by mass to 1.5% by mass.

[0022] As the binder, for example, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), styrene-butadiene rubber (SBR), butyl rubber (BR), etc. can be used. The proportion of the binder in the entire composite layer 20 is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, and particularly preferably 0.1% by mass to 2% by mass.

[0023] Subsequently, with reference to FIG. 2, the details of the composite material 30 will be described. FIG. 2 is a diagram showing the composite material included in the electrode for a secondary battery shown in FIG. 1. As shown in FIG. 2, the composite material 30 has active material particles 31 and a coating 32. The active material particles 31 are materials capable of occluding and releasing lithium ions. Further, the active material particles 31 may be materials oriented by a magnetic field or may be materials not oriented by a magnetic field.

[0024] In the case of the positive electrode plate 1, as the active material particles 31, for example, various lithium composite oxides, etc. can be used. Examples of the lithium composite oxide having a layered rock salt type crystal structure include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium nickel manganese cobalt oxide (LiNi x Mn y Co z O2, x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1), etc. Examples of the lithium composite oxide having a spinel type crystal structure include lithium manganate (LiMn2O4), lithium nickel manganate (LiNi x Mn yExamples include O4, x + y = 2, 0 ≤ x ≤ 0.5). Examples of the lithium composite oxide having an olivine-type crystal structure include lithium iron phosphate (LiFePO4).

[0025] A preferred example of the active material particles 31 is a lithium composite oxide having a layered rock salt-type crystal structure containing at least one transition metal element of nickel, cobalt, and manganese in addition to lithium. Further, the lithium composite oxide may contain other metal elements.

[0026] In the case of the electrode plate 1 of the negative electrode, examples of the active material particles 31 include silicon oxide (SiO), tin oxide (SnO), and lithium titanate (Li4Ti5O 12 ).

[0027] Further, the active material particles 31 are formed in a flat shape having a predetermined aspect ratio. The aspect ratio is the ratio of the major axis diameter to the minor axis diameter of the active material particles 31 (major axis diameter / minor axis diameter). The active material particles 31 preferably have an aspect ratio of 1.5 or more. When the aspect ratio is less than 1.5, the degree of orientation of the composite material 30 tends to decrease. From the viewpoint of increasing the degree of orientation of the composite material 30, the larger the aspect ratio of the active material particles 31, the more preferable.

[0028] The active material particles 31 may be primary particles or secondary particles formed by aggregation of a plurality of primary particles. Observation of the shape of the active material particles 31 can be performed based on an image obtained by SEM (Scanning Electron Microscope) observation.

[0029] When the active material particles 31 are secondary particles, for example, the average particle diameter per particle of the active material particles 31 is preferably 1 μm to 20 μm, more preferably 2 μm to 15 μm, and particularly preferably 3 μm to 10 μm. The average particle diameter of the active material particles 31 can be measured by SEM or particle size distribution measurement.

[0030] The coating 32 is formed on at least one surface along the major axis direction of the active material particles 31. FIG. 2 illustrates two types of composite materials 30. Among the two types of composite materials 30 shown in FIG. 2, the composite material 30 shown on the upper side of FIG. 2 has a coating 32 on one side along the major axis direction of the active material particles 31. The composite material 30 shown on the lower side of FIG. 2 has coatings 32 on both sides along the major axis direction of the active material particles 31. The coating 32 is formed of a carbon material, a metal, or an alloy thereof that exhibits magnetism. Further, from the viewpoint of improving the conductivity of the electrode plate 1, it is preferable that the coating 32 itself has conductivity.

[0031] The composite material 30 is configured such that the volume ratio of the coating 32 to the volume of the active material particles 31 is 5% by volume to 20% by volume. When the volume ratio of the coating 32 to the volume of the active material particles 31 is less than 5% by volume, the sensitivity of the composite material 30 to the magnetic field becomes insufficient and the degree of orientation tends to decrease. When the volume ratio of the coating 32 to the volume of the active material particles 31 is greater than 20% by volume, the ratio of the coating 32 in the entire composite material layer 20 increases, and the capacity tends to decrease. The coating 32 is preferably formed as a uniform film, but may be a film formed non-uniformly within a range that does not affect the magnetic field orientation during the formation of the composite material layer 20.

[0032] Next, with reference to FIG. 3, a method for manufacturing an electrode for a secondary battery according to the present embodiment will be described. FIG. 3 is a flowchart showing a method for manufacturing an electrode for a secondary battery according to Embodiment 1. The method for manufacturing an electrode for a secondary battery according to the present embodiment is applicable to both the positive and negative electrode plates 1.

[0033] Here, for example, for the positive electrode of a lithium-ion secondary battery, a lithium composite oxide having a high capacity and excellent thermal stability is preferably used as the active material particles 31. The active material particles 31 formed of the lithium composite oxide typically have a form of secondary particles in which a plurality of primary particles, each of which is a single crystal, are randomly oriented, and have a property of being difficult to be oriented by a magnetic field. Therefore, when such polycrystalline active material particles 31 are used alone, it is difficult to control the orientation of the active material particles 31.

[0034] In contrast, in the method for manufacturing an electrode for a secondary battery according to the present embodiment, the active material particles 31 can be magnetically oriented regardless of the magnetism of the active material particles 31. Therefore, the method for manufacturing an electrode for a secondary battery according to the present embodiment is suitably used for the electrode plate 1 including the active material particles 31 with poor orientation.

[0035] As shown in FIG. 3, the method for manufacturing an electrode for a secondary battery according to the present embodiment includes the following steps S1 to S4. In the composite material forming step of step S1, a composite material 30 is formed in which a film 32 that exhibits magnetism with respect to a magnetic field applied from the outside is formed on at least one surface along the major axis direction of the flat active material particles 31. In the coating step of step S2, a paste for forming a composite material layer containing at least the composite material 30 and a solvent is coated on the surface of the current collector foil 10.

[0036] In the magnetic field orientation step of step S3, before the coating film 21 for forming a composite material layer formed by the paste for forming a composite material layer coated on the surface of the current collector foil 10 dries, a magnetic field substantially perpendicular to the surface of the current collector foil 10 is applied to the coating film 21 for forming a composite material layer to orient the composite material 30 contained in the coating film 21 for forming a composite material layer. In the composite material layer forming step of step S4, the coating film 21 for forming a composite material layer in which the composite material 30 is oriented is dried to form a composite material layer 20 on the surface of the current collector foil 10.

[0037] Each of the above steps will be described in more detail with reference to FIGS. 4 to 8. FIG. 4 is a first diagram for explaining the composite material forming step. FIG. 5 is a second diagram for explaining the composite material forming step. FIG. 6 is a third diagram for explaining the composite material forming step. FIG. 7 is a diagram for explaining the coating step. FIG. 8 is a diagram for explaining the magnetic field orientation step. Note that the cross-sectional views shown in FIGS. 4 to 8 show a part of the cross section in the direction perpendicular to the surface of each of the current collector foil 10 or the substrate 40. Further, the active material particles 31 shown in FIGS. 4 to 6 are shown in an elliptical shape by simplifying secondary particles, and this ellipse corresponds to one particle of the active material particles 31.

[0038] First, the composite material forming process includes the first to fourth steps. First, as shown in S1-1 of FIG. 4, in the first step, a paste for forming a composite material containing active material particles 31 and a solvent is applied to the surface of a flat substrate 40. As the solvent, the same solvent as that used in the coating process described later may be used, or different types of solvents may be used.

[0039] The paste for forming a composite material is prepared by adding a solvent to the active material particles 31 and kneading them using a kneader such as a planetary mixer. Also, the paste for forming a composite material is applied to the surface of the substrate 40 using a coating method such as a die coater, a slit coater, a comma coater, a gravure coater, or a blade coater.

[0040] FIG. 4 shows a method using a die coater. The die coater has a die head 50 that discharges a slurry toward the opposing substrate 40 through a predetermined gap G and coats the slurry on the surface of the substrate 40. When using a die coater, the paste for forming a composite material is discharged from the die head 50 and applied to the surface of the substrate 40 with a gap G corresponding to the average particle size per particle of the active material particles 31 provided between the substrate 40 and the die head 50. Thereby, a coating film 60 for forming a composite material having a film thickness corresponding to the average particle size per particle of the active material particles 31 is formed on the surface of the substrate 40. The viscosity of the paste for forming a composite material is appropriately set within a range that can form the coating film 60 for forming a composite material having the above thickness and does not impair the coatability.

[0041] Next, as shown in S1-2 of FIG. 4, in the second step, the coating film 60 for forming a composite material formed in the first step is dried to remove the solvent contained in the coating film 60 for forming a composite material. As the drying method, drying by natural means, hot air, low humidity air, vacuum, infrared rays, far infrared rays, electron beams, etc. can be used alone or in combination. When the solvent is removed from the coating film 60 for forming a composite material, a plurality of randomly oriented active material particles 31 can be obtained on the surface of the substrate 40.

[0042] Next, as shown in S1-3 of FIG. 5, in the third step, by pressing the active material particles 31 disposed on the surface of the substrate 40 using a pressing method such as a roll press or a flat press, the active material particles 31 are oriented in a certain direction. FIG. 5 shows an example in which the active material particles 31 are pressed against the surface of the substrate 40 in a direction substantially perpendicular by the roll 70 of the roll press machine.

[0043] In this way, as shown in S1-4 of FIG. 5, the active material particles 31 can be oriented so that the active material particles 31 do not overlap each other on the surface of the substrate 40 and the major axis direction is substantially parallel to the surface of the substrate 40.

[0044] Next, as shown in S1-5 of FIG. 6, in the fourth step, a film 32 is formed on the active material particles 31 oriented in a certain direction in the third step. The film 32 can be formed, for example, by a chemical vapor deposition (CVD) method, a physical vapor deposition (PVD) method, an ionized vapor deposition method, or the like.

[0045] Since the active material particles 31 are oriented so that the major axis direction is substantially parallel to the surface of the substrate 40, one surface along the major axis direction is exposed upward. Therefore, the film 32 can be formed on at least one surface along the major axis direction of the active material particles 31 using various vapor deposition methods.

[0046] Then, as shown in S1-6 of FIG. 6, the composite material 30 having the film 32 formed on at least one surface along the major axis direction of the active material particles 31 is recovered from the substrate 40. In this way, the composite material 30 can be formed.

[0047] Also, by repeating the steps of the above first to fourth steps again, the film 32 may be formed on a plurality of surfaces. When the film 32 is formed on a plurality of surfaces of the active material particles 31, for example, the composite material 30 shown on the lower side of FIG. 2 can be formed. By forming the film 32 on a plurality of surfaces of the active material particles 31, the rotational force applied to the composite material 30 during magnetic field orientation is applied to the composite material 30 at a plurality of locations, and since the rotational force increases, the orientation of the composite material 30 becomes higher.

[0048] Subsequently, as shown in FIG. 7, in the coating step, first, a solvent is added to the powder containing the composite material 30 and, if necessary, a conductive material, a binder, and other additives, and kneaded using a kneader such as a planetary mixer to prepare a paste for forming a composite layer.

[0049] The solvent is appropriately selected according to the binder to be used. As the solvent, for example, non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK), dimethylformamide (DMF), toluene, etc., mixed solvents combining non-aqueous solvents, water, and aqueous solvents such as water-based mixed solvents can be used.

[0050] The viscosity of the paste for forming the composite layer is preferably 3 Pa·s or less, and more preferably 1 Pa·s or less. From the viewpoint of increasing the degree of orientation of the composite material 30, the lower the viscosity of the paste for forming the composite layer, the more preferable. The lower limit of the viscosity of the paste for forming the composite layer is appropriately set within a range that does not impair the coatability.

[0051] Next, by coating the prepared paste for forming the composite layer on the surface of the current collector foil 10, a coating film 21 for forming the composite layer is formed on the surface of the current collector foil 10. The paste for forming the composite layer can be coated using various coating methods exemplified in the composite material forming step.

[0052] Subsequently, as shown in FIG. 8, in the magnetic field orientation step, the magnetic field generator is disposed near the current collector foil 10 such that the direction of the magnetic field lines is substantially perpendicular to the surface of the current collector foil 10. Then, a magnetic field in which magnetic field lines are generated in a direction substantially perpendicular to the surface of the current collector foil 10 is applied to the coating film 21 for forming the composite material layer. The magnetic field generator is not particularly limited as long as it can generate a required magnetic field. For example, a permanent magnet, an electromagnet, or the like can be used.

[0053] In the magnetic field orientation step, the magnetic flux density of the magnetic field applied to the coating film 21 for forming the composite material layer is preferably 350 mT or more, more preferably 500 mT or more. The higher the magnetic flux density of the magnetic field, the higher the degree of orientation of the composite material 30 can be increased. Further, the time for applying the magnetic field to the coating film 21 for forming the composite material layer is, for example, about 1 second to 120 seconds. The composite material 30 contained in the coating film 21 for forming the composite material layer to which the magnetic field is applied is oriented such that the major axis direction thereof is substantially perpendicular to the surface of the current collector foil 10.

[0054] Subsequently, in the composite material layer forming step, the coating film 21 for forming the composite material layer containing the composite material 30 oriented as described above is dried to remove the solvent contained in the coating film 21 for forming the composite material layer. The coating film 21 for forming the composite material layer can be dried using various drying methods exemplified in the composite material forming step. Further, the dried product is pressed as necessary. Thereby, the composite material layer 20 can be formed on the surface of the current collector foil 10.

[0055] By the above steps, the electrode plate 1 shown in FIG. 1 can be manufactured. According to the method for manufacturing the electrode for a secondary battery according to the present embodiment, since the coating film 32 exhibits magnetism, the degree of orientation of the active material particles 31 can be increased using a magnetic field regardless of the magnetism of the active material particles 31 themselves.

[0056] Hereinafter, examples and comparative examples will be described. Note that the examples do not limit the present invention. First, an evaluation battery cell was constructed according to the following procedure.

[0057] (Example) [Fabrication of Electrode Plate 1] The positive electrode plate was manufactured according to the flow shown in FIG. 3. The active material particles 31 are made of lithium nickel 1 / 3 cobalt 1 / 3 manganese 1 / 3 lithium nickel manganese cobalt oxide secondary particles (NMC particles) having an average composition represented by O2 were used. The NMC particles have a substantially elliptical shape, with a major axis diameter (average): 5 μm, a minor axis diameter (average): 3 μm, and a volume: 188.5 μm 3 .

[0058] In the composite material forming step, using a dicoter, a paste for forming a composite material obtained by kneading NMC particles and NMP was applied to the surface of the substrate 40 to form a coating film 60 for forming a composite material. The application amount of the paste for forming a composite material was adjusted so that the film thickness of the coating film 60 for forming a composite material was 6 μm. Then, the coating film 60 for forming a composite material was dried with hot air to obtain a plurality of NMC particles randomly oriented on the surface of the substrate 40. Thereafter, roll pressing was performed on the NMC particles arranged on the surface of the substrate 40 to orient them in a certain direction so that the active material particles 31 did not overlap each other.

[0059] Then, the substrate 40 together with the active material particles 31 was put into a plasma CVD apparatus. A gas containing hydrocarbon was decomposed using the plasma CVD apparatus, and carbon was deposited on one side along the major axis direction of the active material particles 31 to form a film 32 made of a carbon material having a graphite structure (layered structure), thereby forming a composite material 30. At this time, the film formation amount was adjusted so that the ratio of the volume of the film 32 to the volume of the active material particles 31 was 10% by volume, and a film 32 having a film thickness of 0.4 μm was formed.

[0060] In the coating step, the composite material 30, AB as a conductive material, and PVdF as a binder were mixed at a predetermined mixing ratio, and NMP was added as a solvent and kneaded to prepare a paste for forming a composite layer (viscosity 1.2 Pa·s). The prepared paste for forming a composite layer was applied to both sides of an aluminum foil (thickness 15 μm) which is the current collector foil 10. The paste for forming a composite layer has a basis weight of 10 mg / cm 2The coating amount was adjusted so as to achieve this. As a result, a coating film 21 for forming a composite material layer was formed on the surface of the aluminum foil.

[0061] In the magnetic field orientation step, a pair of permanent magnets was arranged so as to sandwich the aluminum foil having the coating film 21 for forming a composite material layer formed on its surface from above and below, and a magnetic field was applied to the coating film 21 for forming a composite material layer. The magnetic flux density of the magnetic field was 500 mT, and the application time of the magnetic field was 2.0 seconds. The direction of the magnetic field lines when applying the magnetic field was substantially perpendicular to the surface of the aluminum foil. As a result, the composite material 30 was oriented so that the major axis direction was substantially perpendicular to the surface of the aluminum foil.

[0062] After the coating film 21 for forming a composite material layer containing the composite material 30 thus magnetically oriented was dried with hot air at 110°C, it was cut into a predetermined size and pressed to manufacture a positive electrode plate. The composite material layer 20 after pressing had a density of 2.7 g / cm 3 and a thickness of 45 μm.

[0063] [Adjustment of Electrolyte] An electrolyte was prepared by dissolving supporting salt LiPF6 at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed so that the volume ratio was 1:1:1.

[0064] [Construction of Evaluation Battery Cell] The composite material layer 20 sides of the manufactured positive electrode plates were opposed to each other, and an electrode body with a separator having a three-layer structure (PE / PP / PE) in which a polyethylene (PE) layer and a polypropylene (PP) layer were laminated was housed inside an aluminum laminate exterior material, and an electrolyte was added and sealed to construct a laminated type evaluation battery cell (positive electrode opposed cell).

[0065] (Comparative Example) A positive electrode plate was manufactured in the same manner as in the example except that the magnetic field orientation step was omitted in the manufacturing process of the positive electrode plate, and then an evaluation battery cell of the comparative example was constructed in the same manner as in the example using this positive electrode plate.

[0066] [Evaluation] Next, the battery performance of each evaluation battery cell of the examples and comparative examples was evaluated. When evaluating the battery performance, for each evaluation battery cell, after performing a conditioning process at 3.0 V to 4.2 V, it was adjusted to 50% SOC (State Of Charge) under an environment of 25 °C, and then the resistance value (Ω) was measured by the alternating current impedance method. The measurement conditions were an input voltage of 100 mV and a frequency range of 0.1 Hz to 100,000 Hz.

[0067] From the Nyquist plot of the impedance obtained by the measurement, the diameter of the semicircle was read, and the resistance value of each evaluation battery cell was derived. As a result, when the resistance value of the evaluation battery cell of the comparative example was taken as 100%, the relative value of the resistance value of the evaluation battery cell of the example was 96.2%.

[0068] Also, using the value of the ionic resistance R ion obtained by the alternating current impedance method, the average value of the tortuosity in each evaluation battery cell was calculated. The ionic resistance R ion is the resistance related to the movement of lithium ions inside the electrode. The tortuosity is a value indicating the degree of bending of the movement path of lithium ions in the composite layer and can be calculated by the following formula (1). τ = {R ion (κεS) / L} ··· Formula (1)

[0069] Here, τ is the tortuosity, R ion is the ionic resistance ( / Ω·cm 2 ), L is the thickness (μm) of the composite layer, κ is the conductivity (S / m) of the electrolyte, ε is the porosity (%) of the composite layer, and S is the area (μm 2 ) of the reaction interface. The closer the tortuosity is to 1, the more linear the movement path is. Therefore, inside the electrode, the conductivity of ions in the electrolyte increases and the resistance is reduced.

[0070] The tortuosity of the evaluation battery cell of the example was 2.0, and the tortuosity of the evaluation battery cell of the comparative example was 2.8. As can be seen from this result, in the evaluation battery cell of the example, since the tortuosity was lower than that of the evaluation battery cell of the comparative example, it was confirmed that the conductivity of the ions in the electrolyte improved and the electrical resistance decreased inside the electrode.

[0071] As described above, the presence of the composite material 30 with a high degree of orientation in the composite material layer 20 makes the movement path of lithium ions in the composite material layer 20 linear (the tortuosity approaches 1), and the movement distance of lithium ions from the main surface of the composite material layer 20 to the current collector foil 10 can be shortened.

[0072] As described above, in the secondary battery electrode according to the present embodiment, the composite material layer 20 formed on the surface of the current collector foil 10 includes the composite material 30 on which the film 32 showing magnetism is formed on at least one surface along the major axis direction of the flat active material particles 31. The composite material 30 is oriented so that the major axis direction is substantially perpendicular to the surface of the current collector foil 10.

[0073] With such a configuration, the degree of orientation of the active material particles 31 can be increased using a magnetic field regardless of the magnetism of the active material particles 31. In addition, since the flat active material particles 31 are vertically oriented with respect to the surface of the current collector foil 10, the movement distance of lithium ions in the composite material layer 20 is shortened, so that the conductivity of the ions in the electrolyte can be improved inside the electrode. As a result, a lithium ion secondary battery with reduced internal resistance can be obtained.

[0074] Furthermore, the ratio of the volume of the film 32 to the volume of the active material particles 31 is preferably 5% by volume to 20% by volume. With such a configuration, since the composite material 30 having sufficient sensitivity to the magnetic field can be formed, the degree of orientation of the composite material 30 containing the active material particles 31 can be further increased.

[0075] Furthermore, the active material particles 31 preferably have an aspect ratio of 1.5 or more. With such a configuration, the degree of orientation of the composite material 30 containing the active material particles 31 can be further increased.

[0076] Furthermore, the coating film 32 preferably has conductivity. With such a configuration, since the coating film 32 having conductivity is formed on the surface of the active material particles 31, the conductivity of the electrode plate 1 is improved. As a result, the output performance of the battery is improved.

[0077] Furthermore, the active material particles 31 are preferably secondary particles formed by aggregation of a plurality of primary particles of a lithium composite oxide containing at least one of nickel, cobalt, and manganese. With such a configuration, even the active material particles 31 of polycrystals with poor orientation can have their degree of orientation increased using a magnetic field.

[0078] Therefore, according to the electrode for a secondary battery according to the present embodiment, the degree of orientation can be increased regardless of the magnetism of the active material particles 31, and the internal resistance of the battery can be reduced.

[0079] And according to the method for manufacturing an electrode for a secondary battery according to the present embodiment, an electrode for a secondary battery having the above-described effects can be manufactured.

Explanation of reference numerals

[0080] 1 Electrode plate 10 Current collector foil 20 Composite material layer 21 Coating film for forming composite material layer 30 Composite material 31 Active material particles 32 Coating film 40 Substrate 50 Die head 60 Coating film for forming composite material 70 Roll G Gap

Claims

1. A current collector foil, and a composite layer formed on the surface of the current collector foil, and has the composite layer includes a composite material having a film formed thereon that exhibits magnetism on at least one surface along the major axis direction of the flat active material particles, the composite material is an electrode for a secondary battery that is oriented such that the major axis direction is substantially perpendicular to the surface of the current collector foil.

2. The electrode for a secondary battery according to claim 1, wherein the ratio of the volume of the film to the volume of the active material particles is 5% by volume to 20% by volume.

3. The electrode for a secondary battery according to claim 1 or 2, wherein the active material particles have an aspect ratio of 1.5 or more.

4. The electrode for a secondary battery according to any one of claims 1 to 3, wherein the film has conductivity.

5. The electrode for a secondary battery according to any one of claims 1 to 4, wherein the active material particles are secondary particles formed by aggregation of a plurality of primary particles of a lithium composite oxide containing at least one of nickel, cobalt, and manganese.

6. A composite material forming step of forming a composite material having a film formed thereon that exhibits magnetism with respect to a magnetic field applied from the outside on at least one surface along the major axis direction of the flat active material particles, a coating step of coating a paste for forming a composite layer containing at least the composite material and a solvent on the surface of the current collector foil, a magnetic field orientation step of orienting the composite material contained in the coating film for forming a composite layer by applying a magnetic field substantially perpendicular to the surface of the current collector foil to the coating film for forming a composite layer before the coating film for forming a composite layer formed by the paste for forming a composite layer coated on the surface of the current collector foil dries, a composite layer forming step of drying the coating film for forming a composite layer in which the composite material is oriented to form a composite layer on the surface of the current collector foil, and a method for manufacturing an electrode for a secondary battery having the same.

7. The method for manufacturing an electrode for a secondary battery according to claim 6, wherein the ratio of the volume of the film to the volume of the active material particles is 5% by volume to 20% by volume.

8. The method for manufacturing an electrode for a secondary battery according to claim 6 or 7, wherein the active material particles have an aspect ratio of 1.5 or more.

9. The method for manufacturing an electrode for a secondary battery according to any one of claims 6 to 8, wherein the film has conductivity.

10. The method for manufacturing an electrode for a secondary battery according to any one of claims 6 to 9, wherein the active material particles are secondary particles formed by aggregation of a plurality of primary particles of a lithium composite oxide containing at least one of nickel, cobalt, and manganese.

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