Method for manufacturing a negative electrode and apparatus for manufacturing a negative electrode

Abstract

The present invention provides a method for manufacturing a negative electrode that can improve the degree of orientation of graphite, which is the negative electrode active material. [Solution] A method for manufacturing a negative electrode, comprising the steps of: supplying a negative electrode composite material containing a negative electrode active material containing graphite to a metal foil as a current collector; and applying a magnetic field to the negative electrode active material in which the magnetic field lines are oriented perpendicular to the surface of the metal foil, wherein in the step of applying the magnetic field to the negative electrode active material, a plurality of magnets are arranged at predetermined intervals along the transport direction while the metal foil is transported in the transport direction, and the magnetic field is continuously applied by the plurality of magnets.

Description

[Technical Field]

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

[0002] Various technologies have been proposed regarding methods for manufacturing batteries, as disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-73970 [Patent Document 2] International Publication No. 2012 / 124033 [Patent Document 3] Special Publication No. 6-103530 [Overview of the project] [Problems that the invention aims to solve]

[0004] Graphite, used as a negative electrode active material, has a structure in which many layers of six-membered carbon rings are stacked, and during charging, ions such as lithium ions are inserted between the layers. Generally, the in-plane direction of the layers of six-membered rings in graphite is represented by the (002) plane, and the stacking direction of the layers of six-membered rings is represented by the direction of the (110) plane. During charging, ions such as lithium ions penetrate between the layers from near the edges of the layers of six-membered rings in the in-plane direction of the layers, i.e., along the (002) plane. Therefore, because the (002) plane of the graphite is oriented toward the positive electrode, the penetration of ions into the graphite and the diffusion of ions from the graphite proceed efficiently.

[0005] 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 serving as a current collector, and applying a magnetic field in which the magnetic field lines are oriented perpendicular to the surface of the metal foil to which the negative electrode mixture has been supplied. In the manufacturing method described in Patent Document 1, the graphite, which is the negative electrode active material, is oriented in the magnetic field application step. Patent Document 1 states that the shorter the time the magnetic field is applied in the magnetic field application step, the better, and that it is desirable for the graphite to be sufficiently oriented in a short time of about 0.5 seconds, and that the strength of the magnetic field in the magnetic field application step should be 1.0[T] or higher, preferably 1.5[T] or higher, and even more preferably 2.0[T] or higher. However, there is room for improvement in the magnetic field application step in order to increase the degree of orientation of the graphite in the negative electrode.

[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, which is the negative electrode active material. [Means for solving the problem]

[0007] In other words, this disclosure includes the following aspects: <1> A method for manufacturing a negative electrode, A process of supplying a negative electrode mixture containing a negative electrode active material containing graphite to a metal foil used as a current collector, The process includes applying a magnetic field to the negative electrode active material, in which the magnetic field lines are oriented perpendicular to the surface of the metal foil. A method for manufacturing a negative electrode, comprising the step of applying the magnetic field to the negative electrode active material, wherein, while conveying the metal foil in the conveying direction, a plurality of magnets are arranged at predetermined intervals along the conveying direction, and the magnetic field is continuously applied by the plurality of magnets.

[0008] <2> The process further comprises the step of drying the negative electrode mixture after the step of applying the magnetic field, <1> A method for manufacturing the negative electrode described above.

[0009] <3> The basis weight of the negative electrode composite material is 25 mg / cm 2 or more, and the method for manufacturing a negative electrode according to <1> or <2>.

[0010] <4> The time for applying the magnetic field is 0.36 seconds or more and 5.04 seconds or less, In the step of applying the magnetic field, the time for the metal foil to pass through each magnet is 0.18 seconds, and the method for manufacturing a negative electrode according to any one of <1> to <3>.

[0011] <5> A manufacturing apparatus for a negative electrode, A supply unit that supplies a negative electrode composite material containing a negative electrode active material containing graphite to a metal foil as a current collector, A magnetic field application unit that applies a magnetic field in a direction perpendicular to the surface of the metal foil to the negative electrode active material, and has, In the magnetic field application unit, a plurality of magnets for applying the magnetic field are arranged at predetermined intervals along the conveyance direction of the metal foil, and a manufacturing apparatus for a negative electrode.

Advantages of the Invention

[0012] According to the present disclosure, it is possible to improve the degree of orientation of graphite, which is a negative electrode active material.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a step of applying a magnetic field in the manufacturing method of the present disclosure. [Figure 2] FIG. 2 is a diagram showing an example of the manufacturing apparatus of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional schematic diagram showing a step of applying a magnetic field in a comparative example. [Figure 4] FIG. 4 is a graph showing the relationship between the magnetic field application time and the degree of orientation in an example and a comparative example.

Embodiments for Carrying Out the Invention

[0014] Embodiments of this disclosure are described below. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (e.g., general configuration and manufacturing process of the negative electrode that do not characterize 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 content disclosed herein and common technical knowledge in the art. Furthermore, the dimensions (length, width, thickness, etc.) shown in the diagram do not necessarily reflect the actual dimensions.

[0015] 1. Manufacturing method This disclosure provides a method for manufacturing a negative electrode, comprising the steps of: supplying a negative electrode composite material containing a negative electrode active material containing graphite to a metal foil serving as a current collector (hereinafter sometimes referred to as the negative electrode composite material supply step); and applying a magnetic field to the negative electrode active material in which the magnetic field lines are oriented perpendicular to the surface of the metal foil (hereinafter sometimes referred to as the magnetic field application step), wherein in the step of applying the magnetic field to the negative electrode active material, a plurality of magnets are arranged at predetermined intervals along the transport direction while the metal foil is transported in the transport direction, and the magnetic field is continuously applied by the plurality of magnets. The following describes each step.

[0016] [Negative electrode composite material supply process] The negative electrode composite material supply process involves supplying a negative electrode composite material containing graphite-containing negative electrode active material to a metal foil that serves as a current collector. The negative electrode composite material forms a negative electrode layer containing the negative electrode active material.

[0017] The metal foil functions as a current collector for the negative electrode. Furthermore, the metal foil must not hinder the orientation of the graphite during the subsequent magnetic field application process. Specific examples of metal foil include aluminum foil and copper foil. The metal foil may also be an alloy foil, and may contain materials other than metal. The shape of the metal foil is not particularly limited and may be the same as that of metal foil used in conventional anode manufacturing. For example, it may be in the form of a long sheet. The thickness of the metal foil is not particularly limited.

[0018] The negative electrode composite material contains at least graphite as the negative electrode active material, and may also contain other negative electrode active materials, or may contain only graphite as the negative electrode active material. The graphite can be any material that can absorb and release ions such as lithium ions, and whose edge portions that serve as ion entry points are oriented when a magnetic field is applied. The graphite may have a layered structure in which multiple hexagonal plate-like crystals are stacked to form multiple layers, and specific examples include natural graphite, artificial graphite, amorphous carbon of natural graphite, and amorphous carbon of artificial graphite. Conventionally known materials can be appropriately used as negative electrode active materials other than graphite. The graphite content in the negative electrode mixture may be, for example, 80% by mass or more and 99% by mass or less of the total graphite content in the negative electrode layer, or 90% by mass or more and 97.95% or less of the total graphite content in the negative electrode layer. Here, an amount of 80% by mass or more of graphite content in the total graphite content in the negative electrode layer means that the amount of graphite that accounts for 80% by mass or more of the total negative electrode layer formed after volatile components such as solvents contained in the negative electrode mixture have been removed is 80% by mass or more. The same applies to components other than graphite and solvents.

[0019] The negative electrode mixture may contain other components besides the negative electrode active material, such as a binder. Examples of binders include styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polytetrafluoroethylene (PTFE), polyethylene (PE), polyacrylic acid (PAA), and polyvinylidene fluoride (PVdF). The materials exemplified above as binders may also be used to function as thickeners or other additives for the negative electrode mixture, in addition to their function as binders. The binder content in the negative electrode composite material may be, for example, an amount such that the binder content relative to the entire negative electrode layer is 0.4% by mass or more and 10% by mass or less, or an amount such that it is 0.4% by mass or more and 5% by mass or less.

[0020] Furthermore, the negative electrode composite material may also contain a conductive material as another component. Examples of conductive materials include carbon nanotubes (CNTs), acetylene black, carbon black, and Ketjenblack. The content of the conductive material is not particularly limited; for example, the content of the conductive material relative to the entire negative electrode layer may be 0.05% by mass or more, 1% by mass or less, or 0.5% by mass or less.

[0021] The negative electrode mixture may contain a solvent for dispersing the above components. Examples of solvents include organic solvents such as N-methylpyrrolidone (NMP), pyrrolidone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, dimethylformamide, and dimethylacetamide. Alternatively, it may be water or a water-based mixed solvent. As solvents other than water that constitute the mixed solvent, organic solvents that can be uniformly mixed with water (such as lower alcohols and lower ketones) can be appropriately selected and used. The solvent content in the negative electrode mixture is not particularly limited.

[0022] The orientation of graphite in the negative electrode mixture is usually higher when the viscosity of the negative electrode mixture is lower. However, in the manufacturing method of this disclosure, the orientation of graphite is high, so the graphite can be sufficiently oriented without lowering the viscosity of the negative electrode mixture. Therefore, the negative electrode mixture can be used, for example, at a shear rate of 0.01 s. -1 It may also be a slurry (paste) having a high viscosity of 100,000 mPa·s or more.

[0023] The method for supplying the negative electrode mixture to the metal foil is not particularly limited, and a general method can be used, such as a coating method using an applicator like a die coater. The fact that graphite orientation can be ensured even when using a high-viscosity negative electrode mixture, i.e., a negative electrode mixture with a low solvent content, means that it is possible to achieve both a thick negative electrode and high graphite orientation. According to the manufacturing method of this disclosure, the basis weight of the negative electrode mixture is 25 mg / cm³. 2 The above is possible. The basis weight of the negative electrode composite material is 200 mg / cm³. 2The following may also be acceptable: 100 mg / cm³ 2 It may also be less than 40 mg / cm³ 2 The following is also acceptable.

[0024] [Magnetic field application process] The magnetic field application step is a step of applying a magnetic field to the negative electrode active material in the negative electrode mixture supplied onto the metal foil (current collector) in the negative electrode mixture supply step, wherein the magnetic field lines are oriented perpendicular to the surface of the metal foil, and the process involves conveying the metal foil in the conveying direction while arranging a plurality of magnets at predetermined intervals along the conveying direction, and continuously applying the magnetic field with the plurality of magnets. By applying a magnetic field with magnetic field lines oriented perpendicular to the surface of the metal foil, the graphite (negative electrode active material) on the metal foil is oriented so that its interlayer surface (002) is parallel to the magnetic field lines.

[0025] As a result of the diligent research conducted by this researcher, it was discovered that the degree of orientation of graphite on the metal foil can be improved by arranging multiple magnets at predetermined intervals in the direction of transport of the metal foil (hereinafter sometimes simply referred to as the transport direction), thereby creating a magnetic field distribution in which the magnetic fields of adjacent magnets are continuous. Specifically, the researchers compared (1) a case in which a magnetic field is applied by leaving the metal foil supplied with the negative electrode mixture (containing graphite) stationary in front of a single magnet (see Figure 3) with (2) a case in which a magnetic field is applied by transporting the metal foil supplied with the negative electrode mixture (containing graphite) along multiple magnets arranged at predetermined intervals (see Figure 1). As a result, it was confirmed that the degree of graphite orientation was higher in case (2), where multiple magnets were arranged at predetermined intervals, even with the same application time.

[0026] Here, the magnetic field distribution pattern formed in the magnetic field application step of the manufacturing method of the present disclosure will be explained with reference to Figure 1. Figure 1 is a schematic diagram showing an example of the magnetic field application step in the manufacturing method of the present disclosure. In Figure 1, a negative electrode composite material 20 is supplied onto a metal foil 10, which is a current collector. The magnets that form a magnetic field with magnetic field lines oriented perpendicular to the surface of the metal foil 10 are a plurality of magnets 132A, 132B, and 132C arranged at predetermined intervals along the transport direction of the metal foil 10. Here, "perpendicular direction" does not have to be perfectly perpendicular, and a predetermined error is permitted. Magnets 132A to 132C are pairs of magnets (hereinafter sometimes referred to as magnet units) consisting of magnets 132A1 and 132A2, magnets 132B1 and 132B2, and magnets 132C1 and 132C2, and are arranged so as to sandwich the metal foil 10 between each magnet unit. Furthermore, each magnet unit is positioned such that one side (132A1, 132B1, 132C1) faces the metal foil 10 as the north pole, and the other side (132A2, 132B2, 132C2) faces as the south pole.

[0027] The adjacent magnets 132 are arranged with a predetermined spacing D between them, and their magnetic field distributions form a continuous magnetic field distribution pattern. Specifically, each magnet 132A, 132B, and 132C forms a magnetic field distribution with a strong magnetic field (positive flux) and a weak reverse magnetic field (negative flux), as shown in Figure 1. By arranging these multiple magnets with spacing D, a continuous magnetic field distribution is formed between adjacent magnets. Due to this continuous magnetic field distribution pattern, a strong magnetic field and a weak reverse magnetic field are continuously and repeatedly applied to the graphite on the metal foil. As a result, acceleration is applied to the graphite on the metal foil, and the mobility of the graphite within the negative electrode composite is thought to increase. Therefore, compared to the case where the metal foil is placed stationary relative to a single magnet unit 132A, as shown in Figure 3, and the magnetic field formed only by the magnet unit 132A is applied to the graphite in the negative electrode composite, the degree of orientation of the graphite is thought to be higher according to the method of this disclosure.

[0028] As described above, the manufacturing method of this disclosure makes it possible to improve the degree of orientation of the active material, graphite, and as a result, it is possible to provide a negative electrode with excellent ion diffusion (ionic conductivity). Furthermore, the manufacturing method disclosed herein has the advantage of shortening the manufacturing time of the negative electrode because it is possible to orient the graphite in a shorter time compared to conventional methods. In addition, even if the viscosity of the negative electrode mixture is high, the degree of graphite orientation can be increased, making it easy to apply a thick negative electrode and shortening the drying process time of the electrode mixture. Moreover, because a high-viscosity negative electrode mixture can be used, the occurrence of sagging when supplying the negative electrode mixture to the metal foil can also be suppressed.

[0029] The number of magnets arranged along the transport direction is not particularly limited, as long as there are multiple magnets (two or more), and can be appropriately selected according to the magnetic force of each magnet, the viscosity and basis weight of the negative electrode composite on the metal foil, etc. For example, there may be three or more, five or more, or eight or more. The magnet used in the embodiment shown in Figure 1 is a magnet unit consisting of a pair of magnets, arranged so that one is the north pole and the other is the south pole relative to the metal foil. However, in this disclosure, the magnet does not necessarily have to be a magnet unit. By using such a magnet unit, a strong magnetic field can be applied. In this disclosure, although the magnet unit consists of a pair of magnets, it is treated as a single magnet, and a single magnet unit is not treated as multiple magnets. Multiple magnets are arranged along the transport direction, and the pair of magnets constituting a single magnet unit are usually arranged so as to intersect with the transport direction.

[0030] Furthermore, in Figure 1, each magnet unit 132 is arranged so that the south pole faces the lower side of the metal foil 10 and the north pole faces the upper side of the metal foil 10 (the side where the negative electrode composite material 20 is supplied). However, the orientation of the south and north poles is not limited to this configuration and can be selected as appropriate. The type of magnet is not particularly limited; for example, it could be a permanent magnet or an electromagnet.

[0031] Multiple magnets are arranged at predetermined intervals along the transport direction. If the magnets are placed without spacing, a negative magnetic field will not be formed, and a sufficient magnetic field application effect cannot be obtained. On the other hand, it is thought that the magnetic field application effect does not change as long as the spacing between the magnets is greater than the length of each magnet in the transport direction. The distance between the magnets can be set as appropriate; for example, it may be 1 mm or more, 1 cm or more, or 10 cm or less. The length of each magnet in the transport direction is not particularly limited, but if it is too long, the magnetic force will decrease around the middle of the magnet's transport length. Therefore, it should be set appropriately considering the magnetic force of the magnets, etc. The strength of the magnetic field formed by each magnet may be such that, for example, the maximum value of the magnetic flux density of the strong magnetic field is 0.5T or more, 0.75T or more, or 1.0T or more.

[0032] The duration for applying the magnetic field depends on the strength of the magnetic field formed by the magnet, but it may be, for example, 0.36 seconds or longer, or 5.04 seconds or shorter. The time for applying the magnetic field here is the sum of the time the metal foil passes through each magnet. The time the metal foil passes through one magnet may be, for example, 0.1 seconds or more, 0.15 seconds or more, or 0.18 seconds or more. Specific conditions for applying a magnetic field include, for example, a configuration where the magnetic field is applied for a duration of 0.36 seconds or more and 5.04 seconds or less, and the time it takes for the metal foil to pass through each magnet is 0.18 seconds.

[0033] [Drying process] The drying process is the process of drying the negative electrode mixture. The drying method is not particularly limited as long as it can dry and remove the solvent in the negative electrode mixture, and known methods can be used. For example, hot air drying and infrared drying can be used. As described above, the method of this disclosure makes it possible to use a negative electrode mixture with a small amount of solvent and high viscosity, so it can be said that the drying process can be shortened and simplified compared to conventional methods. The drying process is usually carried out after the magnetic field application process. This is because it is not possible to orient the graphite in the negative electrode mixture after it has been dried.

[0034] [others] The method for manufacturing a negative electrode according to this disclosure may include steps other than the negative electrode composite material supply step, magnetic field application step, and drying step described above. An example of other steps is a rolling step in which the negative electrode layer obtained in the drying step is rolled. The rolling method can be selected from known methods such as roll press and plate press. The negative electrode provided by the manufacturing method of this disclosure can be used, for example, in a battery such as a lithium-ion battery. 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. 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.

[0035] 2. Manufacturing equipment This disclosure provides a negative electrode manufacturing apparatus comprising: a supply unit (hereinafter sometimes referred to as a material supply unit) that supplies a negative electrode composite containing a negative electrode active material including graphite to a metal foil serving as a current collector; and a magnetic field application unit that applies a magnetic field to the negative electrode active material with magnetic field lines oriented perpendicular to the surface of the metal foil, wherein a plurality of magnets for applying the magnetic field are arranged at predetermined intervals along the transport direction of the metal foil in the magnetic field application unit.

[0036] The anode manufacturing apparatus of this disclosure will be described below with reference to Figure 2. Figure 2 is a diagram showing an example of the anode manufacturing apparatus of this disclosure. Note that, regarding the anode manufacturing apparatus of this disclosure, explanations that overlap with the manufacturing method of this disclosure may be omitted here. In Figure 2, the negative electrode manufacturing apparatus 100 includes a transport path 110, a metal foil supply unit 112, a recovery unit 114, an asphalt mixture supply unit 120, a magnetic field application unit 130, a drying unit 140, and a rolling unit 150.

[0037] The transport path 110 is a path for transporting the metal foil (current collector) 10. In the embodiment shown in Figure 2, a plurality of guide rollers 116 are arranged along the path for transporting the metal foil 10. The metal foil 10 is stretched over these guide rollers 116, and a predetermined tension is applied to the metal foil 10. At the beginning of the transport path 110, there is a metal foil supply unit 112 for supplying the metal foil 10. The metal foil supply unit 112 supplies the long metal foil 10, which is wound in a roll shape on a winding core 112A, to the transport path 110 by the rotation of the winding core 112A. At the end of the transport path 110, there is a recovery unit 114 for recovering the metal foil 10. The recovery unit 114 winds the metal foil 10, which has undergone predetermined processing in the transport path 110, onto a winding core 114A. Along the transport path 110, the asphalt supply unit 120, the magnetic field application unit 130, the drying unit 140, and the rolling unit 150 are arranged in that order.

[0038] The asphalt mixture supply unit 120 supplies a negative electrode mixture 20 containing a negative electrode active material including graphite to the metal foil 10, which serves as a current collector. In the embodiment shown in Figure 2, the asphalt mixture supply unit 120 is a die coater coating machine that applies the negative electrode mixture 20 along the longitudinal direction of the long metal foil 10. In the asphalt mixture supply unit 120, the negative electrode mixture 20 contained in the tank 122 is sucked in by the pump 124 and supplied to the die 126. The metal foil 10 is then transported by the rotation of the backup roll 128, passing through the gap between the backup roll 128 and the die 126, forming a coating film of the negative electrode mixture 20 on the surface of the metal foil 10 from the die 126.

[0039] The magnetic field applying unit 130 applies a magnetic field to the negative electrode active material in the negative electrode composite material 20 supplied onto the metal foil 10 by the composite material supply unit 120, with the magnetic field lines oriented perpendicular to the surface of the metal foil 10. Multiple magnets 132 for applying the magnetic field are arranged at predetermined intervals along the transport direction of the metal foil 10. In the embodiment shown in Figure 2, a plurality of magnets 132A, 132B, and 132C are arranged at predetermined intervals along the transport direction of the metal foil 10. As in Figure 1, each of the magnets 132A to 132C is a magnet unit consisting of a pair of magnets, and is arranged so as to sandwich the metal foil 10 between the magnet units. Furthermore, the magnet units are arranged such that one (132A1, 132B1, 132C1) is the north pole and the other (132A2, 132B2, 132C2) is the south pole when facing the metal foil 10. These magnets 132A to 132C continuously apply a magnetic field to the graphite (negative electrode active material) on the metal foil 10 as it is transported along the transport path 110, with magnetic field lines oriented perpendicular to the surface of the metal foil 10.

[0040] The metal foil 10, to which a magnetic field has been applied by the magnetic field application unit 130, is transported along the transport path 110 to the drying unit 140. In the drying unit 140, the negative electrode composite material 20 on the metal foil 10 is dried to obtain the negative electrode layer 30. The metal foil 10 with the formed negative electrode layer 30 is transported along the transport path 110 to the rolling unit 150. In the rolling unit 150, the negative electrode layer 30 is rolled (pressed). In this embodiment shown in Figure 2, a roll press machine is used. [Examples]

[0041] (Examples 1-7) A negative electrode composite material (paste) was prepared by mixing and dispersing artificial graphite (negative electrode active material), CMC (thickener), SBR (binder), and CNT paste (conductive material) in a planetary mixer. The composition ratio of the negative electrode composite material was set to artificial graphite / CMC / SBR / CNT paste = 97.95 / 0.4 / 1.6 / 0.05 by mass ratio. The obtained negative electrode composite material was subjected to a shear rate of 0.01 s. -1 The viscosity was 212530 mPa·s. The applicator coated the negative electrode composite material on a Cu foil serving as a current collector. The coating amount was 27.8 mg / cm per-sided basis 2 was set.

[0042] Next, as shown in FIG. 1, the Cu foil with the negative electrode composite material was conveyed between a plurality of magnet units arranged at predetermined intervals along the conveyance direction of the Cu foil, and a magnetic field was continuously applied to the graphite in the negative electrode composite material. Each magnet unit was arranged such that one magnet faced the S pole and the other magnet faced the N pole with respect to the surface of the Cu foil. Each magnet unit had a length of 50 mm in the conveyance direction and a maximum value of the magnetic flux density of the strong magnetic field of 1 T, and had a magnetic field distribution as shown in FIG. 1. The plurality of magnet units were arranged side by side in the conveyance direction at an interval such that the magnetic fields of adjacent magnet units were continuous as shown in FIG. 1. The number of magnet units in each example was as shown in Table 1. Further, the Cu foil was conveyed so as to pass between the magnet units in 0.18 seconds. The magnetic field application time shown in Table 1 was calculated from the number of magnet units × 0.18 (s).

[0043] After the magnetic field application, the negative electrode composite material was dried. For the dried negative electrode, X-ray diffraction (XRD) measurement was performed, and the peak intensities of the 110 plane and the 002 plane were measured. The relative ratio (110 / 002) of the peak intensity of the 110 plane to the peak intensity of the 002 plane was calculated as the orientation degree. The results are shown in Table 1 and FIG. 4. Furthermore, by roll pressing, the negative electrode density was set to 1.25 g / cm 3 was set.

[0044] (Comparative Example 1) In the example, the negative electrode was produced and XRD measurement was carried out in the same manner except that the magnetic field application was not performed. The orientation degree of the negative electrode is shown in Table 1 and FIG. 4. (Comparative Examples 2 to 4) In the example, the negative electrode was produced and XRD measurement was carried out in the same manner except that the Cu foil with the negative electrode composite material was left standing between one magnet unit for a predetermined time as shown in FIG. 3 to apply a magnetic field to the graphite in the negative electrode composite material. The magnetic field application time is shown in Table 1, and the orientation degree of the negative electrode is shown in Table 1 and FIG. 4.

[0045] [Table 1]

[0046] As shown in Table 1 and Figure 4, the examples showed a higher degree of orientation compared to the comparative example, even with the same magnetic field application time. That is, it was confirmed that the method of this disclosure allows for a reduction in the magnetic field application time. Furthermore, the shear rate was 0.01 s. -1 It was found that even when using a high-viscosity negative electrode composite material with a viscosity of 100,000 mPa·s or more, there is an effect of improving the degree of orientation. [Explanation of Symbols]

[0047] 10…metal foil 20…Negative electrode composite material 30 ... Negative electrode layer 100...Negative electrode manufacturing equipment 110 ... Transport route 112...Metal foil supply section 112A ... core 114 ... Recovery Department 114A ... core 116 ... Guide roller 120…Mixed material supply section 122... Tank 124 ... pump 126... 128... Backup role 130 ... Magnetic field application section 132, 132A, 132B, 132C… Magnets D... Distance between magnets 140...Drying section 150 ... Rolling section

Claims

1. A method for manufacturing a negative electrode, A process of supplying a negative electrode mixture containing a negative electrode active material containing graphite to a metal foil used as a current collector, The process includes applying a magnetic field to the negative electrode active material, in which the magnetic field lines are oriented perpendicular to the surface of the metal foil. A method for manufacturing a negative electrode, comprising the step of applying the magnetic field to the negative electrode active material, wherein, while conveying the metal foil in the conveying direction, a plurality of magnets are arranged at predetermined intervals along the conveying direction, and the magnetic field is continuously applied by the plurality of magnets.

2. The method for manufacturing a negative electrode according to claim 1, further comprising the step of drying the negative electrode composite material after the step of applying the magnetic field.

3. The basis weight of the aforementioned negative electrode composite material is 25 mg / cm². ２ The method for manufacturing a negative electrode according to claim 1 is as described above.

4. The time for applying the magnetic field is 0.36 seconds or more and 5.04 seconds or less. The method for manufacturing a negative electrode according to claim 1, wherein in the step of applying the magnetic field, the time it takes for the metal foil to pass through each magnet is 0.18 seconds.

5. A negative electrode manufacturing apparatus, A supply unit that supplies a negative electrode mixture containing a negative electrode active material containing graphite to a metal foil that serves as a current collector, The negative electrode active material has a magnetic field applying unit that applies a magnetic field to the metal foil surface with magnetic field lines oriented perpendicular to the surface of the metal foil, A negative electrode manufacturing apparatus, wherein the magnetic field applying section has a plurality of magnets arranged at predetermined intervals along the transport direction of the metal foil for applying the magnetic field.

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