Method for manufacturing negative electrode

Abstract

Provided is a method for producing a negative electrode with which it is possible to improve the degree of graphite orientation in a negative electrode mixture. A method for producing a negative electrode, the method comprising: a step for supplying a negative electrode mixture containing graphite to a metal foil, which is a current collector; and a step for applying a magnetic field to the negative electrode mixture supplied to the metal foil, the step for supplying the negative electrode mixture being a step for supplying the negative electrode mixture to the metal foil conveyed along the outer peripheral surface of a magnetic roller, which is a support roller. The step of applying the magnetic field includes: a first magnetic field application step in which the magnetic roller applies a magnetic field to the negative electrode mixture; and a second magnetic field application step for further applying a magnetic field to the negative electrode mixture after the metal foil to which the negative electrode mixture has been supplied passes through the magnetic roller.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing the negative electrode. Background Technology

[0002] Japanese Patent Application Publication No. 2024-073970 discloses a method for manufacturing a lithium-ion secondary battery, which includes: a step of supplying a negative electrode mixture containing graphite to a metal foil serving as a current collector, and a step of applying a magnetic field to the negative electrode mixture. As one embodiment, it discloses an embodiment in which a back roller supporting the metal foil is used as a magnetic field roller.

[0003] Japanese Patent Publication No. 6-105644 discloses a magnetic roller with multiple magnetic pole pieces arranged circumferentially. Summary of the Invention

[0004] As disclosed in Japanese Patent Application Publication No. 2024-073970, when the graphite in the negative electrode mixture is oriented solely by a magnetic roller, although the degree of orientation is improved due to the orientation in the high shear rate region (low viscosity), the orientation time is insufficient, making it difficult to obtain a negative electrode with a high degree of orientation.

[0005] This disclosure was made in view of the above circumstances, and its main objective is to provide a method for manufacturing a negative electrode that can improve the orientation degree of graphite in the negative electrode mixture.

[0006] That is, this disclosure includes the following methods.

[0007] <1>

[0008] A method for manufacturing a negative electrode, comprising:

[0009] The process of supplying a negative electrode mixture containing graphite to a metal foil serving as a current collector; and

[0010] The process of applying a magnetic field to the negative electrode mixture supplied to the metal foil.

[0011] The process of supplying the negative electrode mixture is the process of supplying the negative electrode mixture to the metal foil that is being conveyed along the outer peripheral surface of the magnetic roller, which serves as a support roller.

[0012] The process of applying the magnetic field includes: a first magnetic field application process in which the magnetic roller applies a magnetic field to the negative electrode mixture; and a second magnetic field application process in which the metal foil, to which the negative electrode mixture has been supplied, further applies a magnetic field to the negative electrode mixture after it passes through the magnetic roller.

[0013] <2>

[0014] According to the negative electrode manufacturing method described in <1>, in the first magnetic field application step, the wrap angle of the magnetic roller relative to the metal foil to which the negative electrode mixture is supplied is 90 degrees or more and 350 degrees or less.

[0015] <3>

[0016] According to the negative electrode manufacturing method described in <1>, in the first magnetic field application step, the wrap angle of the magnetic roller relative to the metal foil to which the negative electrode mixture is supplied is 180 degrees or more and 350 degrees or less.

[0017] According to this disclosure, the orientation degree of graphite in the negative electrode mixture can be improved. Attached Figure Description

[0018] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein like reference numerals denote like elements.

[0019] Figure 1 This is a diagram illustrating an example of the structure of a negative electrode manufacturing device.

[0020] Figure 2 This is another example of the structure of a negative electrode manufacturing device.

[0021] Figure 3 This is another example of the structure of a negative electrode manufacturing device.

[0022] Figure 4 This is a diagram showing a specific example of a magnetic roller.

[0023] Figure 5 This is a coordinate graph illustrating an example of the relationship between the shear rate and viscosity of a negative electrode compound.

[0024] Figure 6 This is a coordinate graph showing the relationship between the orientation degree of negative electrode samples 1 to 7 and the time of magnetic field application. Detailed Implementation

[0025] Conventionally, to improve the orientation degree of graphite in the negative electrode mixture through magnetic field orientation, operations such as reducing the viscosity of the negative electrode mixture, slowing down the conveying speed of the metal foil (which serves as a current collector) to extend the orientation time, or increasing the size of the magnet used for magnetic field orientation are performed. In the manufacturing method of this disclosure, a magnetic roller is used as the support roller for supporting the metal foil. A first magnetic field application step is performed, in which a magnetic field is applied to the negative electrode mixture immediately after it has been coated onto the metal foil using the magnetic roller. Subsequently, a second magnetic field application step is performed, further applying a magnetic field to the negative electrode mixture on the metal foil after it has passed through the magnetic roller. In the manufacturing method of this disclosure, after the graphite in the negative electrode mixture is oriented through the first magnetic field application step, the orientation degree can be further improved through the second magnetic field application step. Therefore, compared with conventional methods, the orientation degree of graphite in the negative electrode mixture can be improved. Furthermore, in the first magnetic field application step, by applying a magnetic field to the negative electrode mixture in a low-viscosity state in the high-shear-rate region, the orientation degree of graphite in the negative electrode mixture can be improved in a shorter time compared to applying a magnetic field to the negative electrode mixture in a high-viscosity state. Therefore, in the manufacturing method disclosed herein, the magnetic field application time (orientation time) for achieving sufficient orientation of graphite in the negative electrode mixture can be shortened.

[0026] Furthermore, in the manufacturing method disclosed herein, the orientation degree of graphite in the negative electrode mixture can be sufficiently improved through the first magnetic field application step and the second magnetic field application step, thus eliminating the need to reduce the viscosity of the negative electrode mixture. Therefore, it is possible to increase the thickness of the negative electrode mixture, for example, by setting the dried area weight of the negative electrode mixture to 25 mg / cm². 2 Above (e.g., 25–100 mg / cm³) 2 In addition, by not reducing the viscosity of the negative electrode compound, edge collapse at the coating end can be suppressed.

[0027] Furthermore, in the manufacturing method of this disclosure, in the first magnetic field application step, the support roller is a magnet for applying the magnetic field, so it is not necessary to place a large magnet for applying the magnetic field. In addition, by performing the first and second magnetic field application steps, even if the magnetic field application unit used in the second magnetic field application step is miniaturized, the graphite in the negative electrode mixture can achieve sufficient orientation. Therefore, in the manufacturing method of this disclosure, miniaturization of the device and cost reduction can be achieved.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings, but the present disclosure is not limited to the embodiments described herein. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. Sometimes, the same reference numerals are used to label components or parts that perform the same function, and repeated descriptions are omitted or simplified.

[0029] Furthermore, matters necessary for the implementation of this disclosure, other than those specifically mentioned in this specification (e.g., the general configuration and manufacturing process of a negative electrode manufacturing apparatus that are not features of this disclosure), can be grasped by those skilled in the art based on existing technology. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the art.

[0030] Figure 1 This describes the structure of a negative electrode manufacturing apparatus used in one embodiment of this disclosure.

[0031] Figure 1 The negative electrode manufacturing apparatus 100 shown includes a metal foil supply unit 10, a first magnetic field application unit 20, a second magnetic field application unit 30, and a drying unit 40.

[0032] In the metal foil supply section 10, a metal foil 1 (e.g., copper foil) that serves as a current collector is wound around the core 11 and supplied to the travel path 12. The travel path 12 may also include a guide 13 for guiding the metal foil 1 along a predetermined path.

[0033] The first magnetic field application step 20 includes: a process of supplying a negative electrode mixture 2 containing graphite to a metal foil 1; and a first magnetic field application step in which a magnetic roller 21, which serves as a support roller for supporting the metal foil 1, applies a magnetic field to the negative electrode mixture 2 supplied to the metal foil 1.

[0034] Negative electrode agent 2 is a paste-like mixture containing graphite as the negative electrode active material. The viscosity of negative electrode agent 2 can be, for example, at a shear rate of 0.01 s⁻¹. -1 The value measured under the given conditions was 1.0 × 10⁻⁶. 5 mPa·s~5.0×10 5 Around mPa·s, or, alternatively, at a shear rate of 100 s. -1 The value measured under the given conditions was 1.0 × 10⁻⁶. 3 mPa·s~5.0×10 3 Approximately mPa·s.

[0035] The graphite contained in the negative electrode compound 2 can be any material oriented by a magnetic field. Graphite, for example, has a layered structure in which multiple layers of hexagonal plate-like crystals are stacked. Specifically, carbon-based materials such as natural graphite, artificial graphite, or their amorphous carbon are used.

[0036] The negative electrode compound 2 may also contain adhesives (binders) such as styrene-butadiene rubber (SBR), conductive additives such as vapor-grown carbon fiber (VGCF) or carbon nanotubes (CNT), thickeners or solvents such as carboxymethyl cellulose (CMC).

[0037] The first magnetic field application unit 20 includes a magnetic roller 21 serving as a support roller for the metal foil 1, and a mold 22 for spraying the negative electrode mixture 2. The magnetic roller 21 is arranged along a travel path 12 and serves as both a roller supporting the metal foil 1 and a magnet for applying a magnetic field to the negative electrode mixture 2 on the metal foil 1. The mold 22 is positioned opposite the magnetic roller 21 and sprays and supplies the negative electrode mixture 2 onto the metal foil 1, which is being conveyed along the outer peripheral surface of the magnetic roller 21. In the first magnetic field application unit 20, while the negative electrode mixture 2 is being supplied onto the metal foil 1, the magnetic roller 21 supporting the metal foil 1 applies a magnetic field to the negative electrode mixture 2 on the metal foil 1. Therefore, it is possible to apply a magnetic field to the negative electrode mixture 2 on the metal foil 1 in high shear rate regions during coating (e.g., shear rate of 100 s). -1 The above area can also be 100s. -1 ~600s -1 Applying a magnetic field to the negative electrode mixture 2 in the region of negative electrode mixture 2 results in a short time increase in the orientation of graphite in the negative electrode mixture 2.

[0038] In the first magnetic field application step, by increasing the wrap angle of the magnetic roller 21 relative to the metal foil 1 to which the negative electrode mixture 2 has been supplied, the time for applying the magnetic field to the negative electrode mixture 2 on the metal foil 1 (i.e., the orientation time) can be increased without reducing the conveying speed of the metal foil 1. Here, the wrap angle of the magnetic roller 21 relative to the metal foil 1 to which the negative electrode mixture 2 has been supplied refers to the angle between the starting point of contact between the metal foil 1 and the magnetic roller 21 and the ending point of contact where the metal foil 1 begins to leave the magnetic roller 21 while the negative electrode mixture 2 is held on its surface, with the center point of the cross-section of the magnetic roller 21 as a reference. The starting point of the wrap angle can be the position of the nozzle of the mold 22. The wrap angle can be an indicator of the size of the magnetic field application area or the orientation time in the first magnetic field application step. The wrap angle can be, for example, 90 degrees or more, 120 degrees or more, 180 degrees or more, 200 degrees or more, or 270 degrees or more. On the other hand, from the viewpoint of ease of manufacturing, it can be 350 degrees or less, 300 degrees or less, 270 degrees or less, or 200 degrees or less. For example, by increasing the wrap angle from 90 degrees to 270 degrees, the orientation time in the first magnetic field application step can be increased by three times. Furthermore, in the manufacturing method of this disclosure, as described above, it is not necessary to reduce the viscosity of the negative electrode agent 2, thus allowing for an increase in the wrap angle.

[0039] Figure 2 and Figure 3 Indicates and Figure 1 The example shown is a negative electrode manufacturing apparatus 100 with an increased wrap angle compared to the aforementioned negative electrode manufacturing apparatus. Figure 1 , Figure 2 and Figure 3 In this context, the aforementioned wrap angle is denoted as α.

[0040] As magnetic roller 21, for example Figure 4As shown in the magnetic roller 21A, a magnetic roller with multiple magnetic pole portions 23 arranged in a manner in which S poles and N poles are alternately arranged along the circumference and opposite each other can be used. Furthermore, Figure 4 The arrows shown indicate the direction of the magnetic flux.

[0041] Alternatively, a magnetic roller having a magnetic pole portion 23 and a non-magnetic material portion 24 can also be used. For example, a magnetic roller having a magnetic pole portion 23 and a non-magnetic material portion 24... Figure 4 As shown in the magnetic roller 21B, examples can be found in magnetic rollers where multiple magnetic pole portions 23 are arranged in a manner where S and N poles are alternately arranged circumferentially with the S and N poles facing each other, and where a portion of the magnetic pole portions 23 are replaced with non-magnetic material portions 24. By using such a magnetic roller with a portion made of non-magnetic material, the orientation of the graphite in the negative electrode mixture 2 can be patterned along the conveying direction of the metal foil 1. Furthermore, after patterning is performed in the first magnetic field application step, even if the second magnetic field application step is performed, patterning can be formed by varying the magnetic field application time. For example, patterning can be performed at the center or end of the negative electrode to accommodate uneven reaction of the negative electrode, and any pattern can be achieved.

[0042] In a magnetic roller having a magnetic pole portion 23 and a non-magnetic material portion 24, from the viewpoint of fully ensuring the magnetic field application area in the first magnetic field application process and from the viewpoint of achieving the desired pattern orientation, the area ratio (magnetic pole portion: non-magnetic material portion) of the magnetic pole portion 23 to the non-magnetic material portion 24 in the cross section orthogonal to the roller axis can be set, for example, to 95:5 to 80:20.

[0043] In the second magnetic field application section 30, a second magnetic field application process is performed, where a magnetic field is further applied to the negative electrode mixture 2 after the metal foil 1, which has been supplied with the negative electrode mixture 2, passes through the magnetic roller 21. This second magnetic field application process can occur in a relatively low shear rate region (e.g., a shear rate of 0.01 s) after a predetermined time has elapsed since coating. -1 The following area, or it could be 0.01s. -1 ~0.05s -1 The process of applying a magnetic field to the negative electrode mixture 2 in the region to orient the graphite in the negative electrode mixture 2.

[0044] The magnetic field applying unit in the second magnetic field applying section 30 is not particularly limited. In the manufacturing method of this disclosure, since orientation is performed based on the first magnetic field applying step described above, even if the magnetic field applying unit in the second magnetic field applying section 30 is miniaturized, sufficient orientation of the graphite in the negative electrode mixture can be achieved. For example, the magnetic field applying unit in the second magnetic field applying section 30... Figure 1As shown, a pair of magnets 31 may be arranged opposite each other, clamping a metal foil 1 traveling along the travel path 12. In this case, the pair of magnets 31 arranged opposite each other, clamping the metal foil 1, are respectively arranged such that one side faces the metal foil 1 as the S pole and the other side as the N pole. The magnets 31 may be made of permanent magnets, or they may be made of electromagnets that generate magnetic force through electrical action.

[0045] The manufacturing method disclosed herein, as a step of applying a magnetic field to the negative electrode mixture 2 supplied to the metal foil 1, includes at least the first magnetic field application step and the second magnetic field application step described above.

[0046] In the manufacturing method disclosed herein, the magnetic field applied to the negative electrode mixture 2 is a magnetic field in which the magnetic field lines are directed toward the surface of the metal foil 1 to which the negative electrode mixture 2 is supplied. For example, it can be a magnetic field in which the magnetic field lines are directed in a direction orthogonal to the surface of the metal foil 1 to which the negative electrode mixture 2 is supplied. The "orthogonal direction" mentioned here does not have to be perfectly orthogonal, as long as it is approximately orthogonal.

[0047] A drying oven 41 is provided in the drying section 40 along the travel path 12. The drying oven 41 applies heat to the negative electrode mixture 2, which has been subjected to magnetic fields by the first magnetic field application section 20 and the second magnetic field application section 30, thereby drying the negative electrode mixture 2.

[0048] The negative electrode obtained by the manufacturing method of this disclosure can be used in batteries such as lithium-ion batteries. By utilizing the manufacturing method of this disclosure to improve the orientation degree of graphite in the negative electrode mixture, the diffusion of lithium-ion plasma in the negative electrode of the battery can be improved.

[0049] A battery using the negative electrode obtained by the manufacturing method of this disclosure can be a primary battery or a secondary battery, and can also be a secondary battery. Because it can be repeatedly charged and discharged, it is useful, for example, as a vehicle battery. The shape of the battery is not particularly limited, and can be, for example, coin-shaped, cylindrical, square, sheet-shaped, button-shaped, flat, or stacked.

[0050] Applications of batteries equipped with a negative electrode obtained by the manufacturing method of this disclosure include, for example, power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, they can also be used as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, the batteries can be used as power sources for mobile bodies other than vehicles (e.g., railways, ships, aircraft), and also as power sources for electrical appliances such as information processing devices.

[0051] <Evaluation Experiment>

[0052] To investigate the relationship between the viscosity (shear rate) of the negative electrode mixture and the orientation degree of graphite in the negative electrode mixture, the following experiment was conducted.

[0053] Artificial graphite as the negative electrode active material, CMC as the thickener, SBR as the binder, and CNT as the conductive additive were mixed and dispersed using a planetary mixer at a mass ratio (active material / thickener / binder / conductive additive) of 97.95 / 0.4 / 1.6 / 0.05 (wt%) to obtain a paste-like negative electrode mixture.

[0054] The shear rate of the obtained negative electrode mixture was measured to be 0.01 s. -1 ~1000s -1 The viscosity within the specified region. A graph showing the relationship between the shear rate and viscosity of the negative electrode mixture is shown below. Figure 5 As shown. At a shear rate of 0.01 s. -1 The viscosity of the negative electrode mixture was measured to be 212530 mPa·s under the specified conditions.

[0055] (Negative electrode sample 1)

[0056] After placing a magnetic field orientation magnet (magnetic flux density 500 mT) under a glass plate, a coating device is used on the surface of the glass plate on the opposite side from the side where the magnet is located, so that the weight per unit area of ​​the dried single-sided surface is 27.8 mg / cm². 2 The negative electrode mixture obtained above was applied in a manner that allowed it to dry for 2 seconds after application, thereby forming a negative electrode mixture layer (i.e., the magnetic field was applied for 2 seconds), and negative electrode sample 1 was produced.

[0057] (Negative electrode samples 2 and 3)

[0058] Except for changing the time from the application of the negative electrode mixture to drying (magnetic field application time), negative electrode samples 2 and 3 were prepared in the same manner as negative electrode sample 1. The magnetic field application time was changed from 2 seconds to 5 seconds in negative electrode sample 2 and from 2 seconds to 20 seconds in negative electrode sample 3.

[0059] (Negative electrode sample 4)

[0060] On the surface of the glass plate, using a dressing device, the weight per unit area of ​​the dried single side is 27.8 mg / cm². 2 The negative electrode agent obtained above was applied in a certain manner. After a specified time, a magnetic field orientation magnet (magnetic flux density 500mT) was placed below the glass plate (on the side opposite to the side with the negative electrode agent applied). The negative electrode agent was dried 2 seconds after the magnet was placed, thereby forming a negative electrode agent layer (i.e., the magnetic field was applied for 2 seconds), and negative electrode sample 4 was made.

[0061] (Negative electrode samples 5 and 6)

[0062] Except for changing the time from the placement of the magnet to the drying of the negative electrode mixture (magnetic field application time), negative electrode samples 5 and 6 were prepared in the same manner as negative electrode sample 4. The magnetic field application time was changed from 2 seconds to 5 seconds in negative electrode sample 5 and from 2 seconds to 20 seconds in negative electrode sample 6.

[0063] (Negative electrode sample 7)

[0064] Except that a magnetic field orientation magnet was not placed under the glass plate, negative electrode sample 7 was made in the same way as negative electrode sample 1.

[0065] Similar to the first magnetic field application step in the manufacturing method of this disclosure, negative electrode samples 1, 2, and 3 are oriented in a high shear rate region by applying a magnetic field to the negative electrode mixture simultaneously with the coating of the negative electrode mixture. On the other hand, negative electrode samples 4, 5, and 6 are oriented in a lower shear rate region by applying a magnetic field after a predetermined time following the coating of the negative electrode mixture. Negative electrode sample 7 is not subject to a magnetic field.

[0066] The peak intensities of the (110) plane and the (002) plane of each negative electrode sample were measured by XRD (X-ray diffraction), and their ratio (110 / 002) was calculated as the degree of orientation. Figure 6 A coordinate graph showing the relationship between the orientation degree of negative electrode samples 1–7 and the duration of magnetic field application. Figure 6 In this diagram, the horizontal axis represents the time the magnetic field is applied, the vertical axis represents the orientation degree, negative electrode samples 1, 2, and 3 are designated as "this disclosure," negative electrode samples 4, 5, and 6 are designated as "conventional," and negative electrode sample 7 is designated as "without magnet." Figure 6 As shown, when the orientation degrees of negative electrode samples 1, 2 and 3 are compared with those of negative electrode samples 4, 5 and 6 under the condition that the magnetic field is applied for the same time, the orientation degrees of negative electrode samples 1, 2 and 3 are higher than those of negative electrode samples 4, 5 and 6, respectively.

[0067] Colorimetric measurements were performed on each negative electrode sample to determine the L value (lightness). The L values ​​of negative electrode samples 1, 2, and 3 were compared with those of negative electrode samples 4, 5, and 6 after the same magnetic field application time. The results showed that the L values ​​of negative electrode samples 1, 2, and 3 were lower than those of negative electrode samples 4, 5, and 6. Since the L value is strongly correlated with orientation, the comparison of L values ​​also indicates that the orientation of negative electrode samples 1, 2, and 3 is higher than that of negative electrode samples 4, 5, and 6.

[0068] As shown above, by orienting the graphite in the negative electrode mixture in a high shear rate region, the degree of orientation can be easily improved. Therefore, in the manufacturing method of this disclosure, it is shown that by including a first magnetic field application step that applies a magnetic field to the negative electrode mixture in the high shear rate region immediately after coating, the magnetic field application time (orientation time) for achieving sufficient orientation of the graphite in the negative electrode mixture can be shortened.

[0069] The manufacturing method disclosed herein further performs a second magnetic field application step after the first magnetic field application step. Therefore, in the first magnetic field application step, a magnetic field can be applied to the negative electrode mixture in a low-viscosity state after it has just been coated to improve the orientation degree. Subsequently, the orientation degree is further improved in the next second magnetic field application step. Therefore, the orientation degree can be improved compared with conventional methods.

Claims

1. A method for manufacturing a negative electrode, comprising: The process of supplying a negative electrode mixture containing graphite to a metal foil serving as a current collector; and The process of applying a magnetic field to the negative electrode mixture supplied to the metal foil. The process of supplying the negative electrode mixture is the process of supplying the negative electrode mixture to the metal foil that is being conveyed along the outer peripheral surface of the magnetic roller, which serves as a support roller. The process of applying the magnetic field includes: a first magnetic field application process in which the magnetic roller applies a magnetic field to the negative electrode mixture; and a second magnetic field application process in which the metal foil, to which the negative electrode mixture has been supplied, further applies a magnetic field to the negative electrode mixture after it passes through the magnetic roller.

2. The method for manufacturing a negative electrode according to claim 1, wherein in the first magnetic field application step, the angle of wrap of the magnetic roller relative to the metal foil to which the negative electrode mixture has been supplied is 90 degrees or more and 350 degrees or less.

3. The method for manufacturing a negative electrode according to claim 1, wherein in the first magnetic field application step, the angle of wrap of the magnetic roller relative to the metal foil to which the negative electrode mixture has been supplied is 180 degrees or more and 350 degrees or less.

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