Anode manufacturing method

Abstract

The present invention provides a method for manufacturing a negative electrode that can improve the degree of orientation of graphite in the negative electrode mixture. [Solution] A method for manufacturing a negative electrode, comprising the steps of supplying a negative electrode mixture containing graphite to a metal foil as a current collector, and applying a magnetic field to the negative electrode mixture supplied to the metal foil, wherein the step of supplying the negative electrode mixture is a step of supplying the negative electrode mixture to the metal foil being conveyed along the outer surface of a magnet roll as a backup roll, and the step of applying a magnetic field includes a first magnetic field application step in which the magnet roll applies a magnetic field to the negative electrode mixture, and a second magnetic field application step in which a magnetic field is further applied to the negative electrode mixture after the metal foil supplied with the negative electrode mixture has passed through the magnet roll.

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a method for manufacturing a lithium-ion secondary battery, which includes the steps of supplying a negative electrode mixture containing graphite to a metal foil used as a current collector, and applying a magnetic field to the negative electrode mixture. One embodiment of this method discloses an embodiment in which the back roll supporting the metal foil is a magnetic field roll.

[0003] Patent Document 2 discloses a magnetic roll in which multiple magnetic pole pieces are installed along the circumferential direction. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-073970 [Patent Document 2] Special Publication No. 6-105644 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] As disclosed in Patent Document 1, when graphite in a negative electrode mixture is oriented using only a magnetic roll, the orientation occurs in the high shear rate region (low viscosity), which improves the degree of orientation. However, because the orientation time is insufficient, it is difficult to obtain a negative electrode with a high degree of orientation.

[0006] This disclosure has been made in view of the above circumstances, and its main purpose is to provide a method for manufacturing a negative electrode that can improve the degree of orientation of graphite in the negative electrode mixture. [Means for solving the problem]

[0007] In other words, this disclosure includes the following aspects: <1> A process of supplying a negative electrode mixture containing graphite to a metal foil used as a current collector, A step of applying a magnetic field to the negative electrode mixture supplied to the metal foil, A method for manufacturing a negative electrode having the following characteristics: The step of supplying the negative electrode mixture is a step of supplying the negative electrode mixture to the metal foil that is conveyed along the outer surface of a magnet roll acting as a backup roll, A method for manufacturing a negative electrode, comprising: a first magnetic field application step in which the magnet roll applies a magnetic field to the negative electrode mixture; and a second magnetic field application step in which, after the metal foil to which the negative electrode mixture has been supplied has passed the magnet roll, a further magnetic field is applied to the negative electrode mixture.

[0008] <2> In the first magnetic field application step, the angle at which the magnet roll grips the metal foil to which the negative electrode mixture is supplied is 90 degrees or more and 350 degrees or less. <1> A method for manufacturing the negative electrode described above.

[0009] <3> In the first magnetic field application step, the angle at which the magnet roll grips the metal foil to which the negative electrode mixture is supplied is 180 degrees or more and 350 degrees or less. <1> A method for manufacturing the negative electrode described above. [Effects of the Invention]

[0010] According to this disclosure, the degree of orientation of graphite in the negative electrode mixture can be increased. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows an example of the configuration of a negative electrode manufacturing apparatus. [Figure 2] Figure 2 shows another example of the configuration of a negative electrode manufacturing apparatus. [Figure 3] Figure 3 shows yet another example of the configuration of a negative electrode manufacturing apparatus. [Figure 4]FIG. 4 is a diagram showing a specific example of a magnet roll. [Figure 5] FIG. 5 is a graph showing an example of the relationship between the shear rate and viscosity of the negative electrode binder. [Figure 6] FIG. 6 is a graph showing the relationship between the degree of orientation and the magnetic field application time of negative electrode samples 1 to 7.

Embodiments for Carrying Out the Invention

[0012] Conventionally, in order to increase the degree of orientation of graphite in the negative electrode binder by magnetic field orientation, for example, the viscosity of the negative electrode binder is decreased, the conveyance speed of the metal foil as the current collector is decreased to increase the orientation time, or the size of the magnet for magnetic field orientation is increased. In the manufacturing method of the present disclosure, a magnet roll is used as a backup roll for supporting the metal foil, and a first magnetic field application step of applying a magnetic field to the negative electrode binder immediately after coating on the metal foil is performed by the magnet roll. Thereafter, a second magnetic field application step of applying a further magnetic field to the negative electrode binder on the metal foil after passing through the magnet roll is performed. In the manufacturing method of the present disclosure, since the degree of orientation of graphite in the negative electrode binder can be further increased by the second magnetic field application step after the graphite in the negative electrode binder is oriented by the first magnetic field application step, the degree of orientation of graphite in the negative electrode binder can be improved as compared with the conventional method. Further, in the first magnetic field application step, by applying a magnetic field to the negative electrode binder in a low-viscosity state in the high shear rate region, the degree of orientation of graphite in the negative electrode binder can be increased in a shorter time than when a magnetic field is applied to the negative electrode binder in a high-viscosity state. Therefore, in the manufacturing method of the present disclosure, the magnetic field application time (orientation time) for achieving a sufficient degree of orientation of graphite in the negative electrode binder can be shortened. Furthermore, in the manufacturing method of the present disclosure, since the degree of orientation of graphite in the negative electrode binder can be sufficiently increased by the first and second magnetic field application steps, it is not necessary to lower the viscosity of the negative electrode binder. Therefore, the negative electrode binder can be made thicker. For example, the basis weight after drying of the negative electrode binder can be 25 mg / cm 2 or more (for example, 25 to 100 mg / cm 2 ). Also, by not lowering the viscosity of the negative electrode binder, sagging at the coating edge can be suppressed. Furthermore, in the manufacturing method of this disclosure, since the backup roll is a magnet for applying the magnetic field in the first magnetic field application step, there is no need to place a large magnet for applying the magnetic field. Also, by performing the first magnetic field application step and the second magnetic field application step, the graphite in the negative electrode mixture can be oriented to a sufficient degree even if the magnetic field application means used in the second magnetic field application step is reduced in size. Therefore, the manufacturing method of this disclosure can achieve miniaturization of the apparatus and cost reduction.

[0013] The embodiments of this disclosure will be described below with reference to the drawings, but this disclosure is not limited to the embodiments described herein. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. The same reference numerals are used for members or parts that perform the same function, and redundant explanations may be omitted or simplified. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (for example, the general configuration and manufacturing process of anode manufacturing equipment not characterized by this disclosure) can be understood as design matters for those skilled in the art based on the prior art. This disclosure can be implemented based on the contents disclosed herein and common technical knowledge in the art.

[0014] Figure 1 shows the configuration of a negative electrode manufacturing apparatus used in one embodiment of the present disclosure. The negative electrode manufacturing apparatus 100 shown in Figure 1 comprises 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.

[0015] The metal foil supply unit 10 unwinds the metal foil 1 (for example, copper foil) that has been wound onto the winding core 11 and supplies it to the travel path 12. The travel path 12 may be equipped with guides 13 to allow the metal foil 1 to travel along a predetermined path.

[0016] In the first magnetic field application unit 20, a first magnetic field application step is performed in which a negative electrode mixture 2 containing graphite is supplied to the metal foil 1, and a magnet roll 21, which acts as a backup roll supporting the metal foil 1, applies a magnetic field to the negative electrode mixture 2 supplied to the metal foil 1.

[0017] Negative electrode mixture 2 is a paste-like mixture containing graphite as the negative electrode active material. The viscosity of negative electrode mixture 2 is, for example, that of a shear rate of 0.01 s. -1 When measured under these conditions, the result is 1.0 × 10 5 mPa·s ~5.0 × 10 5 It may be around mPa·s, or a shear rate of 100 s -1 When measured under these conditions, the result is 1.0 × 10 3 mPa·s ~5.0 × 10 3 It can be around mPa·s.

[0018] The graphite contained in negative electrode mixture 2 can be any material that is oriented by a magnetic field. The graphite has a layered structure in which hexagonal plate-like crystals are stacked to form multiple layers. Specifically, natural graphite, artificial graphite, or carbon-based materials such as amorphous carbon can be used.

[0019] The negative electrode mixture 2 may further contain a binder such as styrene-butadiene rubber (SBR), a conductive additive such as vapor-grown carbon fiber (VGCF) or carbon nanotubes (CNT), a thickener such as carboxymethylcellulose (CMC), or a solvent.

[0020] The first magnetic field applying unit 20 includes a magnet roll 21 as a backup roll for the metal foil 1 and a die 22 that discharges the negative electrode mixture 2. The magnet roll 21 is disposed along the traveling path 12, is a roller that supports the metal foil 1, and is also a magnet that applies a magnetic field to the negative electrode mixture 2 on the metal foil 1. The die 22 is provided to face the magnet roll 21, and discharges and supplies the negative electrode mixture 2 to the metal foil 1 conveyed along the outer peripheral surface of the magnet roll 21. In the first magnetic field applying unit 20, simultaneously with the supply of the negative electrode mixture ② to the metal foil 1, the magnet roll 21 that supports the metal foil 1 applies a magnetic field to the negative electrode mixture 2 on the metal foil 1. Therefore, in the high shear rate region during coating (for example, the region where the shear rate may be 100 s -1 or higher, and may also be the region of 100 s -1 to 600 s -1 ), a magnetic field can be applied to the negative electrode mixture 2, and as a result, the degree of orientation of graphite in the negative electrode mixture 2 can be increased in a short time.

[0021] In the first magnetic field application step, the time during which a magnetic field is applied to the negative electrode mixture 2 on the metal foil 1 (i.e., orientation time) can be increased by increasing the gripping angle of the magnet roll 21 with respect to the metal foil 1 to which the negative electrode mixture 2 is supplied, without reducing the transport speed of the metal foil 1. Here, the gripping angle of the magnet roll 21 with respect to the metal foil 1 to which the negative electrode mixture 2 is supplied is the angle with respect to the center point of the cross-section of the magnet roll 21, between the starting point where the metal foil 1 contacts the magnet roll 21 while holding the negative electrode mixture 2 on its surface, and the ending point where it begins to move away from the magnet roll 21. The starting point of the above gripping angle may be the position of the discharge port of the die 22. The above gripping angle can be used as an indicator of the size of the magnetic field application area or orientation time in the first magnetic field application step. The above-mentioned gripping angle may be, for example, 90 degrees or more, 120 degrees or more, 180 degrees or more, 200 degrees or more, or 270 degrees or more, while from the viewpoint of ease of manufacturing, it may be 350 degrees or less, 300 degrees or less, 270 degrees or less, or 200 degrees or less. For example, by increasing the above-mentioned gripping angle from 90 degrees to 270 degrees, the orientation time in the first magnetic field application step can be increased threefold. Furthermore, in the manufacturing method of this disclosure, as described above, it is not necessary to reduce the viscosity of the negative electrode mixture 2, so the above-mentioned gripping angle can be increased. Figures 2 and 3 show examples of configurations for a negative electrode manufacturing apparatus with an increased gripping angle compared to the negative electrode manufacturing apparatus 100 shown in Figure 1. In Figures 1, 2, and 3, the gripping angle is denoted as α.

[0022] As the magnet roll 21, for example, a magnet roll 21A shown in Figure 4 can be used, in which multiple magnetic pole portions 23 are arranged such that south poles and north poles are alternately arranged along the circumferential direction and the south poles and north poles face each other. Note that the arrows shown in Figure 4 indicate the direction of magnetic flux. Furthermore, a magnet roll having magnetic pole portions 23 and non-magnetic material portions 24 can also be used. An example of a magnet roll having magnetic pole portions 23 and non-magnetic material portions 24 is a magnet roll in which, as shown in Figure 4, a plurality of magnetic pole portions 23 are arranged so that S poles and N poles are alternately arranged along the circumferential direction and S poles and N poles face each other, and in which a portion of the magnetic pole portions 23 are replaced with non-magnetic material portions 24. By using such a magnet roll in which a portion is composed of non-magnetic material portions, it is possible to orient the graphite in the negative electrode mixture 2 into a pattern orientation along the transport direction of the metal foil 1. Note that even if the second magnetic field application step is performed after the pattern orientation in the first magnetic field application step, the pattern orientation can be achieved due to the difference in magnetic field application time. For example, the pattern orientation may be performed at the center or edge of the negative electrode to match the unevenness of the reaction of the negative electrode, or the orientation may be in any pattern. In a magnet roll having a magnetic pole portion 23 and a non-magnetic material portion 24, the area ratio (magnetic pole portion:non-magnetic material portion) of the magnetic pole portion 23 and the non-magnetic material portion 24 in a cross section perpendicular to the roll axis may be set to, for example, 95:5 to 80:20, from the viewpoint of ensuring a sufficient magnetic field application area in the first magnetic field application step and from the viewpoint of achieving a desired pattern orientation.

[0023] In the second magnetic field application unit 30, a second magnetic field application step is performed to further apply a magnetic field to the negative electrode mixture 2 after the metal foil 1 to which the negative electrode mixture 2 has been supplied has passed through the magnet roll 21. The second magnetic field application step is performed in a relatively low shear rate region (for example, when the shear rate is 0.01 s) after a predetermined time has elapsed since coating. -1 The following regions may be included, or 0.01s -1 ~0.05s -1 This may be a region of ) in which a magnetic field is applied to the negative electrode mixture 2 to orient the graphite in the negative electrode mixture 2. The means for applying a magnetic field in the second magnetic field application unit 30 is not particularly limited. In the manufacturing method of this disclosure, orientation is performed by the first magnetic field application step, so even if the means for applying a magnetic field in the second magnetic field application unit 30 is reduced in size, the graphite in the negative electrode mixture can be oriented to a sufficient degree. The means for applying a magnetic field in the second magnetic field application unit 30 may be, for example, a pair of magnets 31 arranged opposite each other so as to sandwich the metal foil 1 that travels along the travel path 12, as shown in Figure 1. In this case, the pair of magnets 31 arranged opposite each other so as to sandwich the metal foil 1 are arranged so that one is the south pole and the other is the north pole toward the metal foil 1. The magnets 31 may be, for example, permanent magnets or electromagnets that generate magnetic force by the action of electricity.

[0024] The manufacturing method of the present disclosure includes at least the first magnetic field application step and the second magnetic field application step as steps for applying a magnetic field to a negative electrode mixture 2 supplied to a metal foil 1. In the manufacturing method of this disclosure, 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 may be a magnetic field in which the magnetic field lines are directed in a direction perpendicular to the surface of the metal foil 1 to which the negative electrode mixture 2 is supplied. The "perpendicular direction" referred to here does not have to be perfectly perpendicular, but should be approximately perpendicular.

[0025] The drying section 40 is provided with a drying oven 41 along the travel path 12. The drying oven 41 applies heat to the negative electrode mixture 2, which has been subjected to a magnetic field in the first magnetic field application section 30 and the second magnetic field application section 40, to dry the negative electrode mixture 2.

[0026] The negative electrode obtained by the manufacturing method of this disclosure can be used in batteries such as lithium-ion batteries. By increasing the degree of orientation of graphite in the negative electrode mixture using the manufacturing method of this disclosure, the diffusivity of ions such as lithium ions in the negative electrode of a battery can be improved. The battery using the negative electrode obtained by the manufacturing method of this disclosure may be a primary battery or a secondary battery, and more preferably a secondary battery, because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. The shape of the battery is not particularly limited and may be, for example, coin-type, cylindrical, prismatic, sheet-type, button-type, flat-type, or stacked-type.

[0027] 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 automobiles, and diesel automobiles. In particular, they may be used as power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric automobiles (BEVs). Furthermore, the batteries may be used as power sources for mobile devices other than vehicles (e.g., railways, ships, aircraft), or as power sources for electrical products such as information processing devices.

[0028] <Evaluation Test> The following tests were conducted to investigate the relationship between the viscosity (shear rate) of the negative electrode mixture and the degree of orientation of graphite in the negative electrode mixture.

[0029] A paste-like anode mixture was obtained by mixing and dispersing artificial graphite as the anode active material, CMC as a thickening agent, SBR as a binder, and CNT paste as a conductive additive in a planetary mixer in a mass ratio (active material / thickening agent / binder / conductive additive) of 97.95 / 0.4 / 1.6 / 0.05 (wt%).

[0030] The obtained negative electrode mixture had a shear rate of 0.01 s. -1 ~1000s -1 The viscosity was measured within the specified range. Figure 5 shows a graph of the relationship between the shear rate and viscosity of the negative electrode mixture. Shear rate 0.01 s -1 The viscosity of the negative electrode mixture measured under these conditions was 212530 mPa·s.

[0031] (Negative electrode sample 1) After placing a magnetic field orientation magnet (magnetic flux density 500 mT) under the glass plate, the surface of the glass plate on the opposite side from the magnet was treated with an applicator to obtain a dry surface weight of 27.8 mg / cm² on one side. 2 The negative electrode mixture obtained above was applied in such a manner, and the negative electrode mixture was dried 2 seconds after application to form a negative electrode mixture layer (i.e., magnetic field application time 2 seconds), thereby producing negative electrode sample 1.

[0032] (Negative electrode samples 2 and 3) Anode sample 2 and anode sample 3 were prepared in the same manner as anode sample 1, except that the time from coating to drying of the anode mixture (magnetic field application time) was changed. The magnetic field application time was changed from 2 seconds to 5 seconds for anode sample 2, and from 2 seconds to 20 seconds for anode sample 3.

[0033] (Negative electrode sample 4) On the surface of the glass plate, the basis weight on one side after drying was 27.8 mg / cm² using an applicator. 2 The negative electrode mixture obtained above was applied in such a manner, and after a predetermined time had elapsed, a magnetic field orientation magnet (magnetic flux density 500 mT) was placed under the glass plate (on the opposite side from the side to which the negative electrode mixture was applied). Two seconds after the magnet was placed, the negative electrode mixture was dried to form a negative electrode mixture layer (i.e., magnetic field application time 2 seconds), and negative electrode sample 4 was prepared.

[0034] (Negative electrode samples 5 and 6) Anode sample 5 and anode sample 6 were prepared in the same manner as anode sample 4, except that the arrangement of the magnets and the time from the arrangement of the magnets to the drying of the anode mixture (magnetic field application time) were changed. The magnetic field application time was changed from 2 seconds to 5 seconds for anode sample 5, and from 2 seconds to 20 seconds for anode sample 6.

[0035] (Negative electrode sample 7) A negative electrode sample 7 was prepared in the same manner as negative electrode sample 1, except that a magnet for magnetic field orientation was not placed under the glass plate.

[0036] For negative electrode samples 1, 2, and 3, a magnetic field was applied to the negative electrode mixture simultaneously with the coating of the negative electrode mixture, similar to the first magnetic field application step in the manufacturing method of this disclosure, thereby orienting the graphite in the negative electrode mixture in a high shear rate region. On the other hand, for negative electrode samples 4, 5, and 6, a magnetic field was applied after a predetermined time had elapsed since the coating of the negative electrode mixture, thereby orienting the graphite in the negative electrode mixture in a relatively low shear rate region. No magnetic field was applied to negative electrode sample 7.

[0037] XRD (X-ray diffraction) was used to measure the peak intensities of the (110) plane and the (002) plane of each negative electrode sample, and the ratio (110 / 002) of these intensities was calculated to determine the degree of orientation. Figure 6 shows a graph of the correspondence between the degree of orientation of negative electrode samples 1 to 7 and the magnetic field application time. In Figure 6, the horizontal axis represents the magnetic field application time, and the vertical axis represents the degree of orientation. Negative electrode samples 1, 2, and 3 are shown as "This Disclosure," negative electrode samples 4, 5, and 6 are shown as "Conventional," and negative electrode sample 7 is shown as "No Magnet." As shown in Figure 6, when comparing the degree of orientation of negative electrode samples 1, 2, and 3 with that of negative electrode samples 4, 5, and 6 for the same magnetic field application time, the degree of orientation of negative electrode samples 1, 2, and 3 was higher than that of negative electrode samples 4, 5, and 6, respectively.

[0038] The color of each negative electrode sample was measured, and the L value (brightness) was determined. The L values ​​of negative electrode samples 1, 2, and 3 were compared with the L values ​​of negative electrode samples 4, 5, and 6, with 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, respectively. Since the L value is strongly correlated with the degree of orientation, the comparison of the L values ​​also indicated that the degree of orientation of negative electrode samples 1, 2, and 3 was higher than that of negative electrode samples 4, 5, and 6, respectively.

[0039] The above demonstrates that the degree of orientation of graphite in the negative electrode mixture can be easily increased by oriented it in a high shear rate region. Therefore, the manufacturing method of this disclosure includes a first magnetic field application step of applying a magnetic field to the negative electrode mixture in a high shear rate region immediately after coating, thereby shortening the magnetic field application time (orientation time) required to achieve a sufficient degree of orientation of graphite in the negative electrode mixture.

[0040] The manufacturing method disclosed herein involves a second magnetic field application step following a first magnetic field application step. In the first magnetic field application step, a magnetic field is applied to the anode mixture in a low viscosity state immediately after coating to increase its degree of orientation. Subsequently, the degree of orientation can be further increased in the second magnetic field application step. Therefore, the degree of orientation can be improved compared to conventional methods. [Explanation of symbols]

[0041] 1…metal foil 2 ... Negative electrode mixture 10...Metal foil supply section 11... core 12 ...Route 13… Guide 20 ...First magnetic field application unit 21, 21A, 21B... Magnetic Roll 22... 23...Magnetic pole part 24...Nonmagnetic material section 30 ...Second magnetic field application section 31... Magnet 40...Drying section 41...Drying oven 100...Negative electrode manufacturing equipment

Claims

1. A process of supplying a negative electrode mixture containing graphite to a metal foil used as a current collector, A step of applying a magnetic field to the negative electrode mixture supplied to the metal foil, A method for manufacturing a negative electrode having the following characteristics: The step of supplying the negative electrode mixture is a step of supplying the negative electrode mixture to the metal foil that is conveyed along the outer surface of a magnet roll acting as a backup roll, A method for manufacturing a negative electrode, comprising: a first magnetic field application step in which the magnet roll applies a magnetic field to the negative electrode mixture; and a second magnetic field application step in which, after the metal foil to which the negative electrode mixture is supplied has passed the magnet roll, a magnetic field is further applied to the negative electrode mixture.

2. The method for manufacturing a negative electrode according to claim 1, wherein in the first magnetic field application step, the angle at which the magnet roll embraces the metal foil to which the negative electrode mixture is 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 at which the magnet roll embraces the metal foil to which the negative electrode mixture is supplied is 180 degrees or more and 350 degrees or less.

Images