Method for manufacturing secondary battery

Abstract

To reduce variation in orientation after application of magnetic flux.SOLUTION: When a secondary battery is manufactured, a magnetic flux is applied to a negative electrode composite material applied to an electrode sheet serving as a negative electrode plate to control the orientation of a negative electrode active material contained in the negative electrode composite material. The negative electrode active material is mainly composed of graphite whose surface is coated with an amorphous material. In addition, the relationship between the raw material specific surface area of the negative electrode active material as a raw material of the negative electrode mixture, the magnetic field intensity at the time of applying the magnetic flux, and the orientation of the negative electrode active material after applying the magnetic flux is stored in the database DB. Further, the raw material specific surface area of the negative electrode active material used for manufacturing the electrode sheet is measured. Then, the magnetic field intensity corresponding to the measurement value Sxd of the raw material specific surface area is set based on the database DB so that the orientation of the negative electrode active material after applying the magnetic flux becomes the control target value γ 0.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Conventionally, as described in Patent Document 1, for example, there is a secondary battery manufacturing apparatus that applies a magnetic flux to a negative electrode composite coated on an electrode sheet to control the orientation of the negative electrode active material contained in the negative electrode composite. For example, in the case of a negative electrode composite using hexagonal plate-shaped graphite as the negative electrode active material, applying a magnetic flux perpendicular to the electrode sheet causes the scale-shaped negative electrode active material to be oriented along the direction of the applied magnetic flux, i.e., standing upright on the substrate of the electrode sheet, which serves as a current collector. This facilitates the movement of ions within the negative electrode composite, ensuring excellent battery performance.

[0003] Furthermore, for example, Patent Documents 2 and 3 disclose a negative electrode active material in which graphite is used as a core and the core graphite is coated with an amorphous or low-crystalline carbon material. In other words, by adopting such a configuration, the reaction between the negative electrode active material and the electrolyte is suppressed. This allows for improvements in so-called high-rate characteristics, such as a large discharge capacity and excellent rapid charge / discharge characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-104840 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-107029 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-63321 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the magnetic field generated by the application of magnetic flux in the negative electrode composite acts on the core graphite of the negative electrode active material. Furthermore, the ratio of carbon material covering the core graphite, i.e., the so-called coating ratio, is not necessarily constant for the negative electrode active material used as the raw material for the negative electrode composite. This may result in variations in the results of orientation control by the application of magnetic flux. [Means for solving the problem]

[0006] Various aspects of the method for manufacturing a secondary battery that solves the above problems will be described. Aspect 1 is a method for manufacturing a secondary battery in which a magnetic flux is applied to a negative electrode composite coated on an electrode sheet that serves as a negative electrode plate of the secondary battery, thereby controlling the orientation of a negative electrode active material contained in the negative electrode composite, and the negative electrode active material is mainly composed of graphite whose surface is coated with an amorphous body. The method includes: storing in a database a relationship between a raw material specific surface area, which is the specific surface area of ​​the negative electrode active material that is a raw material for the negative electrode composite, the magnetic field strength at the time of application of magnetic flux, and the orientation of the negative electrode active material after application of magnetic flux; and measuring the raw material specific surface area of ​​the negative electrode active material used in manufacturing the electrode sheet, and setting the magnetic field strength according to the measured value of the raw material specific surface area based on the database so that the orientation of the negative electrode active material after application of magnetic flux becomes a control target value.

[0007] According to the above configuration, the measured value of the specific surface area of ​​the raw material can be used to substitute for the coating ratio of the negative electrode active material used in the raw material, specifically, the so-called coated graphite that is its main component. This allows for a simple configuration to easily set the magnetic field strength so that the orientation after magnetic flux application reaches the control target value. As a result, even if the coating ratio is not necessarily constant, the variation in the orientation after magnetic flux application can be reduced.

[0008] A second aspect is the method for manufacturing a secondary battery according to the first aspect, wherein the value that defines the magnetic field strength is set to a distance between the negative electrode composite and the magnet when the magnetic flux is applied. According to the above configuration, the magnetic field strength when the magnetic flux is applied can be easily adjusted with a simple configuration.

[0009] Aspect 3 is the method for producing a secondary battery according to Aspect 1 or Aspect 2, wherein the database includes a specific surface area / orientation database that stores a relationship between the specific surface area of ​​the raw material and the orientation of the negative electrode active material when the magnetic field strength is the same, and a magnetic field strength / orientation database that stores a relationship between the magnetic field strength and the orientation of the negative electrode active material for each specific surface area of ​​the raw material.

[0010] According to the above configuration, by referring to the specific surface area / orientation database and the magnetic field strength / orientation database, it is possible to easily set the magnetic field strength according to the measured value of the specific surface area of ​​the raw material so that the orientation after magnetic flux application becomes the control target value.

[0011] Aspect 4 is the method for producing a secondary battery according to Aspect 3, wherein the specific surface area of ​​the core graphite coated on the amorphous body is defined as a core specific surface area, and the specific surface area / orientation database maintains a relationship between the raw material specific surface area and the orientation of the negative electrode active material for each core specific surface area.

[0012] According to the above configuration, differences in the specific surface area of ​​the raw material are likely to be directly reflected in differences in the coating ratio, thereby ensuring the validity of using the specific surface area of ​​the raw material as a substitute variable for the coating ratio.

[0013] Aspect 5 is the method for producing a secondary battery according to Aspect 3 or Aspect 4, wherein the magnetic field strength / orientation database maintains a relationship between the magnetic field strength and the orientation of the negative electrode active material for each degree of sphericity of the nuclear graphite coated on the amorphous body.

[0014] In other words, when the core graphite has been subjected to a spheroidizing treatment, the higher the spheroidization degree, the less susceptible it is to the effects of a magnetic field. Therefore, by adopting such a configuration, it is possible to set the magnetic field strength according to the measured value of the raw material specific surface area so that the orientation after application of the magnetic flux reaches the control target value with greater precision.

[0015] Aspect 6 is the method for producing a secondary battery according to any one of Aspects 1 to 5, wherein the relationship between the raw material specific surface area, the magnetic field strength, and the orientation of the negative electrode active material used as the raw material is registered in the database.

[0016] According to the above configuration, the database is updated as new data is registered, and this allows the magnetic field strength to be set according to the measured value of the specific surface area of ​​the raw material so that the orientation after magnetic flux application reaches the control target value with greater accuracy.

[0017] A seventh aspect is the method for producing a secondary battery according to any one of the first to sixth aspects, wherein the ratio of a horizontal component of the negative electrode active material along the electrode sheet to a vertical component perpendicular to the electrode sheet is set as a value of the orientation of the negative electrode active material.

[0018] That is, when a magnetic flux perpendicular to the electrode sheet is applied, the vertical component of the negative electrode active material in the negative electrode composite increases. Furthermore, as a result, the negative electrode active material in the negative electrode composite oriented by the application of the magnetic flux appears to stand upright on the substrate of the electrode sheet. As a result, ions can move more easily within the negative electrode composite, improving battery performance. Therefore, the above configuration allows for accurate evaluation of the orientation of the negative electrode active material controlled by the application of the magnetic flux. [Effects of the Invention]

[0019] According to the present invention, it is possible to reduce variations in the orientation after application of a magnetic flux. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of a secondary battery. [Figure 2] FIG. 2 is an exploded view of the electrode assembly. [Figure 3] FIG. 3 is a side view of the secondary battery. [Figure 4]FIG. 4 is a flowchart showing the procedure for manufacturing an electrode sheet that will become a negative electrode plate. [Figure 5] FIG. 5 is an explanatory diagram that schematically shows the alignment state before the application of magnetic flux. [Figure 6] FIG. 6 is an explanatory diagram that schematically shows the application of magnetic flux using a magnet and the alignment state after the application of magnetic flux. [Figure 7] FIG. 7 is a graph showing the relationship between the coating ratio and the specific surface area of ​​coated graphite, which is the main component of the negative electrode active material. [Figure 8] FIG. 8 is a graph illustrating the configuration of the specific surface area / orientation database. [Figure 9] FIG. 9 is a graph illustrating the configuration of the magnetic field strength / orientation database. [Figure 10] FIG. 10 is a flowchart showing the procedure for setting the magnetic field strength based on the measured value of the specific surface area of ​​the raw material and the control target value of the orientation. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of a method for manufacturing a secondary battery will be described with reference to the drawings. <Lithium-ion secondary battery> 1, the secondary battery 1 includes an electrode assembly 10 in which a positive electrode 3, a negative electrode 4, and a separator 5 are integrated, and a case 20 that houses the electrode assembly 10. The secondary battery 1 of this embodiment has a configuration as a lithium ion secondary battery in which the electrode assembly 10 inside the case 20 is impregnated with a non-aqueous electrolyte solution (not shown).

[0022] More specifically, in the secondary battery 1 of this embodiment, the positive electrode 3, the negative electrode 4, and the separator 5 are stacked in a sheet-like outer shape. Then, by winding up the stack of the positive electrode 3, the negative electrode 4, and the separator 5, an electrode assembly 10 is formed in which the positive and negative electrodes and the separators 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4.

[0023] The case 20 of this embodiment includes a case body 21 in the shape of a flat, generally rectangular box, and a lid member 22 that closes an open end 21x of the case body 21. The electrode body 10 of this embodiment has a flat outer shape that corresponds to the box shape of the case 20.

[0024] <Electrode sheet and electrode body> More specifically, as shown in FIG. 2, in the secondary battery 1 of this embodiment, the positive electrode 3 and the negative electrode 4 each have a configuration as an electrode sheet 35 including a current collector 31 having a sheet-like outer shape and an electrode active material layer 32 laminated on this current collector 31.

[0025] Specifically, for the electrode sheet 35P for the positive electrode 3, a paste-like positive electrode mixture 37P containing a lithium transition metal oxide as the positive electrode active material is applied to a substrate 36P made of aluminum or the like that constitutes the positive electrode current collector 31P. For the electrode sheet 35N for the negative electrode 4, a slurry-like negative electrode mixture 37N containing a carbon-based material as the negative electrode active material is applied to a substrate 36N made of copper or the like that constitutes the negative electrode current collector 31N. Furthermore, each of the electrode mixtures 37 for the positive electrode 3 and the negative electrode 4 contains a binder. In the secondary battery 1 of this embodiment, the electrode mixture 37 applied to the substrate 36 dries to form a corresponding positive electrode active material layer 32P and a corresponding negative electrode active material layer 32N on the positive and negative electrode sheets 35P and 35N, respectively.

[0026] Furthermore, in the secondary battery 1 of this embodiment, the positive and negative electrode sheets 35P, 35N are each shaped like a strip. The electrode assembly 10 of this embodiment has a configuration as a wound body in which the positive and negative electrode sheets 35P, 35N, stacked with the separator 5 sandwiched therebetween, are wound around a winding axis 10x extending in the width direction of the strip (the left-right direction in FIG. 2).

[0027] 2, the separator 5 and each electrode sheet 35 are wound in such a way that the electrode sheet 35P constituting the positive electrode 3 is wound on the inside. However, this figure is one example showing the structure of the electrode assembly 10, and the separator 5 and each electrode sheet 35 may also be wound in such a way that the electrode sheet 35N constituting the negative electrode 4 is wound on the inside. This determines whether the electrode sheet 35 arranged on the outermost shell of the electrode assembly 10 is the electrode sheet 35P constituting the positive electrode 3 or the electrode sheet 35N constituting the negative electrode 4.

[0028] 1 to 3, the lid member 22 of the case 20 is provided with a positive electrode terminal 38P and a negative electrode terminal 38N that protrude outside the case 20. Furthermore, each electrode sheet 35 has an uncoated portion 39 where the electrode active material layer 32 is not formed on the current collector 31. The secondary battery 1 of this embodiment is configured so that, utilizing these uncoated portions 39, the electrode sheet 35P constituting the positive electrode 3 and the positive electrode terminal 38P are electrically connected, and the electrode sheet 35N constituting the negative electrode 4 and the negative electrode terminal 38N are electrically connected.

[0029] Specifically, the electrode body 10 of this embodiment is housed in the case 20 with its winding axis 10x aligned along the longitudinal direction (left-right direction in FIG. 1 ) of the lid member 22, which is an elongated, generally rectangular plate. Furthermore, in this state, an uncoated portion 39P of an electrode sheet 35P constituting the positive electrode 3 is connected to a positive electrode terminal 38P via a connecting member 40P. Similarly, an uncoated portion 39N of an electrode sheet 35N constituting the negative electrode 4 is connected to a negative electrode terminal 38N via a connecting member 40N.

[0030] Furthermore, an electrolyte solution 45 is poured into the case 20. That is, the electrolyte solution 45 of the secondary battery 1 configured as a lithium ion secondary battery is one in which a lithium salt serving as a supporting salt is dissolved in an organic solvent. Thus, the secondary battery 1 of this embodiment is configured such that the electrode assembly 10 sealed in the case 20 is impregnated with the electrolyte solution 45.

[0031] <Manufacturing process of electrode sheet that becomes negative electrode plate> As shown in FIG. 4, in the secondary battery 1 of this embodiment, in the manufacturing process of the electrode sheet 35N on the negative electrode 4 side, i.e., the negative electrode plate, first, the negative electrode active material that is the raw material of the negative electrode composite 37N and the binder and other additives thereto are mixed (step 101).

[0032] Specifically, in the secondary battery 1 of this embodiment, the negative electrode active material is so-called coated graphite, which is primarily composed of graphite whose surface is coated with an amorphous material. More specifically, the core graphite that forms the core of this coated graphite is, for example, a core graphite of hexagonal plate-shaped crystals that has been subjected to a spheroidizing process. Furthermore, the coating material that covers the surface of this core graphite can be a carbon material that forms the amorphous material, such as a pitch material such as coal tar pitch. Furthermore, the binder added to the negative electrode composite can be, for example, styrene-butadiene rubber (SBR).

[0033] Next, the prepared negative electrode composite 37N is kneaded (step 102). Furthermore, the kneaded negative electrode composite 37N is coated on the substrate 36N that constitutes the negative electrode current collector 31N of the electrode sheet 35N on the negative electrode 4 side (step 103). Furthermore, in the secondary battery 1 of this embodiment, a magnetic flux is applied to the negative electrode composite 37N coated on the electrode sheet 35N, a process generally referred to as "magnetic field orientation" (step 104). Furthermore, after this magnetic field orientation process, a drying process (step 105) of the negative electrode composite 37N coated on the substrate 36N and a pressing process of the electrode sheet 35N are performed (step 106). Then, in the secondary battery 1 of this embodiment, a cutting process (step 107) is performed after the pressing process, and the electrode sheet 35N for the negative electrode 4 shaped into a strip-like foil as described above is manufactured (see FIG. 2).

[0034] The pressing step of step 106 is a step of increasing the adhesive strength of the negative electrode composite 37N to the substrate 36N by pressing the electrode sheet 35N, which has the negative electrode composite 37N coated on the substrate 36N, in the thickness direction. Furthermore, during the manufacture of the electrode sheet 35N on the negative electrode 4 side, the electrode sheet 35N is wound around multiple rolls (not shown) and continuously transported in the length direction of its strip shape. In this way, the secondary battery 1 of this embodiment is configured so that the steps 103 to 107, i.e., "coating," "magnetic field alignment," "drying," "pressing," and "cutting," are performed continuously.

[0035] Furthermore, in the secondary battery 1 of this embodiment, when manufacturing the electrode sheet 35P on the positive electrode 3 side, i.e., the positive electrode plate, substantially the same steps as those in the manufacturing process of the negative electrode plate are also sequentially performed. Therefore, a detailed description of the manufacturing process of the positive electrode plate will be omitted.

[0036] <Magnetic field orientation: Orientation effect by applying magnetic flux> Furthermore, as shown in FIGS. 5 and 6, in the secondary battery 1 of this embodiment, when manufacturing the electrode sheet 35N that becomes the negative electrode plate 50, a magnetic flux is applied to the coated negative electrode composite 37N to control the orientation of the negative electrode active material 60 contained in this negative electrode composite 37N.

[0037] That is, for example, if the main component of the negative electrode active material 60 contained in the negative electrode composite 37N is a hexagonal plate-shaped graphite nucleus, the flat shape based on the scale shape of the graphite nucleus will be oriented along the direction of magnetic flux application. In other words, when magnetic flux is applied in a direction perpendicular to the electrode sheet 35N, the negative electrode active material 60 in the negative electrode composite 37N will stand upright on the substrate 36N that becomes the negative electrode current collector 31N (see FIG. 6). The secondary battery 1 of this embodiment is configured to ensure excellent battery performance by the resulting change in so-called tortuosity, that is, by facilitating the movement of ions in the negative electrode composite 37N.

[0038] 5, for ease of explanation, the orientation of the negative electrode active material 60 in this orientation state before the application of magnetic flux is depicted as being approximately "horizontal," but the orientation of the negative electrode active material 60 after the application of negative electrode composite 37N and before the application of magnetic flux is random. Similarly, for ease of explanation, in FIG. 6, the "vertical" orientation of the negative electrode active material 60 is emphasized as the orientation state after the application of magnetic flux shown in FIG.

[0039] <Effects of coating ratio and magnetic field orientation of coated graphite used as negative electrode active material> As described above, in the secondary battery 1 of this embodiment, coated graphite 70, which is mainly composed of graphite whose surface is coated with an amorphous material, is used as the negative electrode active material 60. When such coated graphite 70 is used for the negative electrode active material 60, the effect of the magnetic field orientation changes depending on the ratio of the amorphous material that forms the coating material 70c that covers the core graphite 70a, that is, the coating ratio.

[0040] That is, as described above, when magnetic field orientation is performed on the negative electrode composite 37N coated on the electrode sheet 35N (see FIG. 4 , step 104), the magnetic field in the negative electrode composite 37N formed by application of magnetic flux acts on the core graphite 70a of the coating graphite 70 used in the negative electrode active material 60. Then, for example, when the coating graphite 70 used in the negative electrode active material 60 has a flat shape based on the shape of the core graphite 70a, such as the flake shape described above, a high orientation effect can be obtained by application of the magnetic flux.

[0041] However, by covering the surface of the core graphite 70a with the coating material 70c, the coated graphite 70 becomes less susceptible to the influence of the magnetic field. In particular, when the coating ratio of the coated graphite 70 is high, the shape of the coated graphite 70 becomes spherical due to the increase in the amount of coating material 70c attached to the surface of the core graphite 70a. This tends to reduce the orientation effect caused by the application of the magnetic flux.

[0042] <Coating rate and specific surface area of ​​coated graphite> It is also known that the specific surface area of ​​the coated graphite 70 decreases as the coating ratio of the coated graphite 70 increases. That is, the coating material 70c attached to the surface of the core graphite 70a fills in the minute irregularities present on the surface, smoothing the surface of the core graphite 70a. As a result, it is presumed that the specific surface area of ​​the coated graphite 70 decreases.

[0043] FIG. 7 is a graph of data (see Table 1 in Patent Document 3) showing the relationship between the coating ratio α and the specific surface area S of coated graphite 70. In FIG. 7, the unit of specific surface area S is "square meters / gram" (same below). Furthermore, the coating ratio α is the weight percentage of coating material 70c in coated graphite 70 (same below). In this example as well, it can be seen that the higher the coating ratio α of coated graphite 70, the lower its specific surface area S.

[0044] The specific surface area of ​​a porous powder such as the negative electrode active material 60 is measured, for example, by a gas adsorption measurement method using the BET equation, that is, the BET method. The adsorbed gas is, for example, nitrogen. The specific surface area measured by the BET method is generally referred to as the "BET specific surface area."

[0045] <Measurement of the specific surface area of ​​the raw material and setting the magnetic field strength according to the measured value of the specific surface area of ​​the raw material> In consideration of this, in the secondary battery 1 of this embodiment, when manufacturing the electrode sheet 35N that becomes the negative electrode plate 50, the specific surface area S of the negative electrode active material 60 that serves as the raw material for the negative electrode composite 37N, i.e., the raw material specific surface area Sx, is measured. Note that the measurement of the raw material specific surface area Sx is performed before the kneading step, for example, before the raw materials are mixed (see FIG. 4, step 101). The measurement of the raw material specific surface area Sx uses the BET method described above. Then, based on the measurement value of the raw material specific surface area Sx, the magnetic field strength of the magnetic field orientation step (see FIG. 4, step 104), i.e., the magnetic field strength when applying a magnetic flux to the negative electrode composite 37N coated on the electrode sheet 35N, is set.

[0046] That is, during the manufacture of the electrode sheet 35N, it is difficult to individually measure the coating ratio α of the coated graphite 70, which is the main component of the negative electrode active material 60 that is the raw material of the negative electrode composite 37N, for example, for each lot or each production run. Therefore, in the secondary battery 1 of this embodiment, based on the relationship between the coating ratio α and the specific surface area S of the coated graphite 70 as described above (see FIG. 7 ), the raw material specific surface area Sx is used as a substitute variable for the coating ratio α. This allows for setting an appropriate magnetic field strength depending on the orientation effect upon magnetic flux application, that is, the ease of orientation, which changes depending on the coating ratio α, thereby making it less likely that variations will occur in the orientation of the negative electrode active material 60 after the magnetic flux is applied.

[0047] Specifically, in the secondary battery 1 of this embodiment, before manufacturing the electrode sheet 35N that will become the negative electrode plate 50, the relationships between the raw material specific surface area Sx, the magnetic field strength when magnetic flux is applied, and the orientation of the negative electrode active material 60 after the magnetic flux is applied are stored in a database in advance. Then, by referring to this database for the measured value of the raw material specific surface area Sx, the magnetic field strength is set according to the measured value of the raw material specific surface area Sx so that the orientation of the negative electrode active material 60 after the magnetic flux is applied reaches the control target value.

[0048] <Specific surface area / orientation database> More specifically, as shown in FIG. 8, the secondary battery 1 of this embodiment uses, as its database DB, a specific surface area / orientation database DB1 that maintains the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 when the magnetic field strength is the same.

[0049] In the secondary battery 1 of this embodiment, the orientation γ of the negative electrode active material 60 contained in the negative electrode composite 37N is defined as the ratio of the horizontal component of the negative electrode active material 60 along the electrode sheet 35N to the vertical component perpendicular to the electrode sheet 35N. Specifically, the value of the horizontal component (plane index: 002) measured using X-ray diffraction (XRD) divided by the vertical component (plane index: 110) is defined as the orientation γ (γ = horizontal component value / vertical component value). That is, before the application of magnetic flux, the vertical component of the negative electrode active material 60 in the negative electrode composite 37N increases due to magnetic field orientation. Therefore, in the secondary battery 1 of this embodiment, the smaller the value of the orientation γ, the greater the orientation effect due to the application of magnetic flux.

[0050] Furthermore, the magnetic field strength when the magnetic flux is applied is determined by the distance δ between the magnet 80, which is disposed at a distance from the surface 37s of the negative electrode composite material 37N coated on the electrode sheet 35N, during the magnetic field orientation. The value of orientation γ shown in Fig. 8 is the value when the distance δ between the magnet 80 and the negative electrode composite material 37N during the magnetic flux application is set to "1 mm" (δ = 1 mm).

[0051] Furthermore, FIG. 8 shows data D1 to D3 for negative electrode active materials 60 having different raw material specific surface areas Sx, as a relationship between the raw material specific surface area Sx stored in the specific surface area / orientation database DB1 and the orientation γ of the negative electrode active material 60. Furthermore, the negative electrode active materials 60 shown in data D1 to D3 all have the same specific surface area S of the core graphite 70a of the coated graphite 70, which is their main component, i.e., the core specific surface area. Therefore, differences in the raw material specific surface area Sx are likely to be directly reflected in differences in the coating ratio α. This ensures the validity of using the raw material specific surface area Sx as a substitute variable for the coating ratio α.

[0052] Specifically, the data D1 to D3 in the specific surface area / orientation database DB1 shown in FIG. 8 have raw material specific surface area Sx values ​​of "3.57," "3.06," and "2.8," respectively. Furthermore, the orientation γ values ​​for each of the data D1 to D3 are "34.476," "49.979," and "55," respectively. From each of the data D1 to D3, it can be seen that the larger the raw material specific surface area Sx value, that is, the lower the coating ratio α of the coated graphite 70, the main component, the smaller the orientation γ value, with a substantially constant gradient. The effect of magnetic field orientation according to the raw material specific surface area Sx can be confirmed.

[0053] <Magnetic field strength / orientation database> Furthermore, as shown in FIG. 9, in the secondary battery 1 of this embodiment, a magnetic field strength / orientation database DB2 is used as the database DB, which stores the relationship between the magnetic field strength and the orientation γ of the negative electrode active material 60 for each raw material specific surface area Sx.

[0054] More specifically, graph L1 illustrated in Fig. 9 shows the relationship between the orientation γ and the distance δ between negative electrode composite 37N and magnet 80, which determines the magnetic field strength when magnetic flux is applied, for negative electrode active material 60 having a raw material specific surface area Sx value of "3.57" shown in data D1 in Fig. 8. Graph L2 also illustrated in Fig. 9 shows the relationship between the orientation γ and the distance δ between negative electrode composite 37N and magnet 80, which determines the magnetic field strength when magnetic flux is applied, for negative electrode active material 60 having a raw material specific surface area Sx value of "3.06" shown in data D2 in Fig. 8.

[0055] Specifically, for negative electrode active material 60 with a raw material specific surface area Sx of 3.57, the orientation γ values ​​are 34.23, 34.476, and 134.59 when the distance δ between negative electrode composite 37N and magnet 80 is 0.5 mm, 1 mm, and 3 mm, respectively. Similarly, for negative electrode active material 60 with a raw material specific surface area Sx of 3.06, the orientation γ values ​​are 46.76, 49.979, and 90.837 when the distance δ between negative electrode composite 37N and magnet 80 is 0.5 mm, 1 mm, and 3 mm, respectively. The waveforms of graphs L1 and L2 in FIG. 9 represent approximations of the relationship between magnetic field strength and orientation γ plotted on two-dimensional coordinates for each raw material specific surface area Sx.

[0056] Furthermore, these graphs L1 and L2 have different waveform slopes based on the difference in the raw material specific surface area Sx. In other words, the rate of change in orientation γ, which changes depending on the distance δ between the negative electrode composite 37N and the magnet 80, which determines the magnetic field strength when the magnetic flux is applied, is different. Specifically, the negative electrode active material 60 with a larger raw material specific surface area Sx shown in graph L1 has a larger rate of change in orientation γ depending on the magnetic field strength than the negative electrode active material 60 with a smaller raw material specific surface area Sx shown in graph L2. In other words, the negative electrode active material 60 with a larger raw material specific surface area Sx is more susceptible to the influence of magnetic field strength. Based on the relationship stored in the magnetic field strength / orientation database DB2, it is possible to estimate the rate of change in orientation γ depending on the magnetic field strength for the negative electrode active material 60 used to manufacture the electrode sheet 35N from the measured value of the raw material specific surface area Sx.

[0057] <Estimation of the rate of change of orientation γ> That is, for example, suppose that the negative electrode active material 60 used to manufacture the electrode sheet 35N has a core specific surface area substantially equal to that of the negative electrode active material 60 shown in each of data D1 to D3 in FIG. 8, and that the measured raw material specific surface area Sx is close to the raw material specific surface area Sx of data D1. In this case, the rate of change of the orientation γ with respect to the magnetic field strength of the negative electrode active material 60 used to manufacture the electrode sheet 35N also has a value close to that of the negative electrode active material 60 of data D1. In other words, it can be estimated that the value of the orientation γ changes with the magnetic field strength when the magnetic flux is applied, with a slope close to that of graph L1 in FIG. 9.

[0058] Furthermore, for example, suppose that the measured raw material specific surface area Sx is close to the raw material specific surface area Sx of data D2. In this case, the rate of change of the orientation γ according to the magnetic field strength of the negative electrode active material 60 used in manufacturing the electrode sheet 35N also has a value close to that of the negative electrode active material 60 of data D2. In other words, it can be estimated that the value of the orientation γ according to the magnetic field strength when the magnetic flux is applied changes with a slope close to that of graph L2 in FIG.

[0059] Furthermore, even if the measured raw material specific surface area Sx does not necessarily match the value stored in the database DB, such as when the measured raw material specific surface area Sx lies between the raw material specific surface area Sx of data D1 and the raw material specific surface area Sx of data D2, estimation by linear interpolation is possible. That is, based on the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 stored in the specific surface area / orientation database DB1 as shown in graph L0 in FIG. 8, the rate of change in the orientation γ corresponding to the measured raw material specific surface area Sx can be estimated. Specifically, based on the magnetic field strength / orientation database DB2, a graph with a slope corresponding to the rate of change estimated by linear interpolation can be displayed, for example, as shown in FIG. 9. In this case, the specific surface area / orientation database DB1 stores the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 when the distance δ from the magnet 80 is set to "0.5 mm" and "3 mm," enabling more accurate linear interpolation. In the secondary battery 1 of this embodiment, this makes it possible to set the magnetic field strength according to the measured value of the raw material specific surface area Sx so that the orientation γ of the negative electrode active material 60 after application of magnetic flux becomes the control target value γ0.

[0060] <Operation of this embodiment> That is, as shown in the flowchart of FIG. 10 , when manufacturing an electrode sheet 35N that becomes a negative electrode plate 50, the raw material specific surface area Sx of the negative electrode active material 60 that is the raw material of the negative electrode composite 37N is measured (measured value Sxd, step 201). Next, the control target value of the magnetic field orientation (see FIG. 4 , step 104), that is, the preset control target value γ0 of the orientation γ of the negative electrode active material 60 after application of magnetic flux to the negative electrode composite 37N coated on the electrode sheet 35N, is read (step 202). Note that the control target value γ0 of the orientation γ may have a certain range. Furthermore, the control target value γ0 of the orientation γ and the measured value Sxd of the raw material specific surface area Sx are referenced in a database DB related to the raw material specific surface area Sx, the magnetic field strength during magnetic flux application, and the orientation of the negative electrode active material after magnetic flux application (step 203). More specifically, as described above, the specific surface area / orientation database DB1 and the magnetic field strength / orientation database DB2 are referenced, and the distance δ between the negative electrode composite 37N and the magnet 80 according to the measured value Sxd of the raw material specific surface area Sx is calculated as a value that defines the magnetic field strength when magnetic flux is applied (step 204).

[0061] For example, suppose that the control target value γ0 of the orientation γ is "50" and the measured value Sxd of the raw material specific surface area Sx is "3.6." In this case, by referring to the database DB, it can be estimated that the negative electrode active material 60 used in manufacturing the electrode sheet 35N has characteristics close to the stored data D1 (see FIGS. 8 and 9). As a result, "1 mm" is derived as the distance δ from the magnet 80 at which the orientation γ after application of the magnetic flux reaches the control target value γ0.

[0062] <Effects of this embodiment> Next, the effects of this embodiment will be described. (1) When manufacturing the secondary battery 1, a magnetic flux is applied to a negative electrode composite 37N coated on an electrode sheet 35N that will become a negative electrode plate 50, thereby controlling the orientation of the negative electrode active material 60 contained in the negative electrode composite 37N. The negative electrode active material 60 is primarily composed of graphite whose surface is coated with an amorphous material. A database DB stores the relationship between the raw material specific surface area Sx of the negative electrode active material 60 that is the raw material for the negative electrode composite 37N, the magnetic field strength during magnetic flux application, and the orientation γ of the negative electrode active material 60 after magnetic flux application. Furthermore, the raw material specific surface area Sx of the negative electrode active material 60 used in manufacturing the electrode sheet 35N is measured. Based on the database DB, the magnetic field strength is set according to the measured value Sxd of the raw material specific surface area Sx so that the orientation γ of the negative electrode active material 60 after magnetic flux application reaches a control target value γ0.

[0063] According to the above configuration, the measured value Sxd of the raw material specific surface area Sx can be used as a substitute for the coating ratio α of the negative electrode active material 60 used in the raw material, specifically, the coated graphite 70 that is its main component. This allows for a simple configuration to easily set the magnetic field strength such that the orientation γ after magnetic flux application reaches the control target value γ0. As a result, even if the coating ratio α is not necessarily constant, the variation in the orientation γ after magnetic flux application can be reduced.

[0064] (2) The distance δ between negative electrode composite material 37N and magnet 80 when magnetic flux is applied is set as a value that defines the magnetic field strength. According to the above configuration, the magnetic field strength when the magnetic flux is applied can be easily adjusted with a simple configuration.

[0065] (3) As the database DB, a specific surface area / orientation database DB1 is used, which holds the relationship between the specific surface area Sx of raw materials and the orientation γ when the magnetic field strength is the same. In addition to this specific surface area / orientation database DB1, a magnetic field strength / orientation database DB2 is used, which holds the relationship between the magnetic field strength and the orientation γ for each raw material specific surface area Sx.

[0066] According to the above configuration, by referring to the specific surface area / orientation database DB1 and the magnetic field strength / orientation database DB2, it is possible to easily set the magnetic field strength according to the measured value Sxd of the raw material specific surface area Sx so that the orientation γ after magnetic flux application becomes the control target value γ0.

[0067] (4) The core specific surface area is defined as the specific surface area S of core graphite 70a, which is the core of coated graphite 70 coated with amorphous coating material 70c. The specific surface area / orientation database DB1 stores the relationship between the raw material specific surface area Sx and the orientation γ for a plurality of negative electrode active materials 60 having the same core specific surface area but different raw material specific surface areas Sx.

[0068] According to the above configuration, differences in the raw material specific surface area Sx tend to directly appear in differences in the coating ratio α, thereby ensuring the validity of using the raw material specific surface area Sx as a substitute variable for the coating ratio α.

[0069] (5) The ratio of the horizontal component of the negative electrode active material 60 along the electrode sheet 35N to the vertical component perpendicular to the electrode sheet 35N is defined as the orientation γ value of the negative electrode active material 60. That is, when magnetically oriented, the negative electrode active material 60 in the negative electrode composite 37N is subjected to magnetic flux perpendicular to the electrode sheet 35N, increasing its vertical component. This causes the negative electrode active material 60 in the negative electrode composite 37N, oriented by the application of magnetic flux, to appear to stand upright on the substrate 36N of the electrode sheet 35N. This facilitates ion migration within the negative electrode composite 37N, improving battery performance. Therefore, the above configuration allows accurate evaluation of the orientation γ of the negative electrode active material 60, which is controlled by the application of magnetic flux.

[0070] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0071] In the above embodiment, a preset control target value γ0 of the orientation γ is read out, but the timing for setting this control target value γ0 is arbitrary. For example, it may be configured to be set during the manufacturing process of the electrode sheet 35N.

[0072] In the above embodiment, the value of the orientation γ was determined by dividing the value of the horizontal component measured using X-ray diffraction by the value of the vertical component (γ = horizontal component value / vertical component value). However, this is not limiting, and the value of the vertical component divided by the value of the horizontal component may also be determined as the value of the orientation γ. Furthermore, the definition and calculation method of the orientation γ may be changed as desired, as long as it is possible to determine the extent to which the vertical component is included.

[0073] In the above embodiment, the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 stored in the specific surface area / orientation database DB1 is exemplified as a case where the magnetic field strength is the same. However, this is not limiting, and a configuration in which the relationship between the raw material specific surface area Sx and the orientation γ is stored for each of different values ​​of magnetic field strength may be used. This makes it possible to set the magnetic field strength according to the measured value Sxd of the raw material specific surface area Sx so that the orientation γ after magnetic flux application reaches the control target value γ0 with greater accuracy.

[0074] In the above embodiment, the specific surface area / orientation database DB1 has been configured to store data D1 to D3 for the negative electrode active material 60 having the same nucleus specific surface area as the relationship between the raw material specific surface area Sx and the orientation γ. However, this is not limiting. The specific surface area / orientation database DB1 does not necessarily have to store the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 for a specific nucleus specific surface area. It is more preferable to store the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60 for each different nucleus specific surface area. This reinforces the validity of using the raw material specific surface area Sx as a substitute variable for the coating ratio α. Furthermore, any classification may be used to store the relationship between the raw material specific surface area Sx and the orientation γ of the negative electrode active material 60, as long as it reinforces the validity of using the raw material specific surface area Sx as a substitute variable.

[0075] Alternatively, the magnetic field strength and the orientation γ of the negative electrode active material 60 may be stored in the magnetic field strength / orientation database DB2 for each degree of sphericity of the core graphite 70a coated with the amorphous coating material 70c. That is, when the core graphite 70a is subjected to a sphericity treatment, the higher the sphericity, the less susceptible it is to the effects of the magnetic field. The sphericity may be calculated by any method. In this case, the higher the sphericity, the more round the graphite is. By adopting such a configuration, the magnetic field strength can be set according to the measured value Sxd of the raw material specific surface area Sx so that the orientation γ after magnetic flux application reaches the control target value γ0 with greater accuracy.

[0076] In the above embodiment, the value that defines the magnetic field strength is set to the distance δ between the negative electrode composite 37N and the magnet 80 when the magnetic flux is applied. However, this is not limiting, and the strength, size, etc. of the magnet 80 used for magnetic field orientation may be used as the value that defines the magnetic field strength.

[0077] The magnet 80 used for magnetic field orientation is not limited to a permanent magnet, and an electromagnet may be used. In this case, the magnetic field strength may be determined by, for example, setting the amount of current flowing through the electromagnet or the number of turns of the magnet coil.

[0078] After the electrode sheet 35N that becomes the negative electrode plate 50 is manufactured, the relationship between the raw material specific surface area Sx, magnetic field strength, and orientation γ for the negative electrode active material 60 used as the raw material for the negative electrode composite 37N may be registered in a database DB. By adopting such a configuration, the database DB is updated sequentially with the registration of new data. This makes it possible to set the magnetic field strength according to the measured value Sxd of the raw material specific surface area Sx so that the orientation γ after magnetic flux application reaches the control target value γ0 with greater accuracy.

[0079] In the above embodiment, the databases DB are a specific surface area / orientation database DB1 and a magnetic field strength / orientation database DB2. However, the configuration of the databases DB is not limited to this, and may be changed as desired. For example, the databases DB may be configured to hold the relationship between the raw material specific surface area Sx, the magnetic field strength when magnetic flux is applied, and the orientation of the negative electrode active material 60 after magnetic flux application in the form of a three-dimensional map or a higher-dimensional map.

[0080] If the orientation γ of the negative electrode active material 60 after application of the magnetic flux deviates from the control target value γ0, the pressing pressure may be adjusted in the pressing process of the electrode sheet 35N, which is performed after drying the negative electrode composite 37N. That is, the stronger the pressing pressure, the more horizontally oriented the negative electrode active material 60 tends to be in the negative electrode composite 37N after pressing. This reduces the variation in the orientation γ in downstream processes in the manufacturing process of the electrode sheet 35N, i.e., in a state closer to the finished state.

[0081] In the above embodiment, the coating material 70c covering the core graphite 70a of the coated graphite 70 used in the negative electrode active material 60 is amorphous. However, the coating material 70c may be a low-crystalline carbon material.

[0082] The terminal shapes of the positive electrode terminal 38P and the negative electrode terminal 38N are not limited to the shapes shown in FIG. 1 and may be changed arbitrarily. <Additional Notes> Next, the technical ideas that can be understood from the above-described embodiment and modified examples will be described.

[0083] (A) A magnetic flux is applied to the negative electrode composite using an electromagnet, and the amount of current flowing through the electromagnet is set as a value that defines the magnetic field strength, thereby making it possible to easily adjust the magnetic field strength when the magnetic flux is applied with a simple configuration.

[0084] (ii) The specific surface area is the BET specific surface area. This allows the specific surface area of ​​the raw material to be measured with high accuracy. As a result, with a simple configuration, it is possible to easily set the magnetic field strength according to the measured value of the specific surface area of ​​the raw material so that the orientation γ after magnetic flux application reaches the control target value. [Explanation of symbols]

[0085] 1…Secondary battery 35N...electrode sheet 37N…Negative electrode composite material 50...Negative electrode plate 60...Negative electrode active material Sx…Raw material specific surface area Sxd: Measurement value γ...Orientation γ0: Control target value DB...database

Claims

1. A method for manufacturing a secondary battery, comprising: applying a magnetic flux to a negative electrode composite coated on an electrode sheet that serves as a negative electrode plate of the secondary battery, thereby controlling the orientation of a negative electrode active material contained in the negative electrode composite; and wherein a main component of the negative electrode active material is graphite whose surface is coated with an amorphous body, A relationship between a raw material specific surface area, which is a specific surface area of ​​the negative electrode active material that is a raw material of the negative electrode composite, a magnetic field strength when a magnetic flux is applied, and an orientation of the negative electrode active material after the magnetic flux is applied is stored in a database; By measuring the raw material specific surface area of ​​the negative electrode active material used to manufacture the electrode sheet, The magnetic field intensity is set based on the database in accordance with the measured value of the specific surface area of ​​the raw material so that the orientation of the negative electrode active material after the application of the magnetic flux reaches a control target value. A method for manufacturing a secondary battery.

2. The method for manufacturing a secondary battery according to claim 1 , wherein the value that defines the magnetic field strength is set by setting the distance between the negative electrode composite material and the magnet when the magnetic flux is applied.

3. The database comprises: a specific surface area / orientation database that stores a relationship between the specific surface area of ​​the raw material and the orientation of the negative electrode active material when the magnetic field intensity is the same; a magnetic field strength / orientation database that stores a relationship between the magnetic field strength and the orientation of the negative electrode active material for each specific surface area of ​​the raw material. The method for manufacturing the secondary battery according to claim 1 or 2.

4. The specific surface area of ​​the core graphite coated on the amorphous body is defined as the core specific surface area, The method for manufacturing a secondary battery according to claim 3 , wherein the specific surface area / orientation database holds a relationship between the specific surface area of ​​the raw material and the orientation of the negative electrode active material for each of the core specific surface areas.

5. The magnetic field strength / orientation database stores the relationship between the magnetic field strength and the orientation of the negative electrode active material for each degree of sphericity of the core graphite coated on the amorphous body. The method for manufacturing a secondary battery according to claim 3 .

6. For the negative electrode active material used as the raw material, the relationship between the raw material specific surface area, the magnetic field strength, and the orientation of the negative electrode active material is registered in the database. The method for manufacturing the secondary battery according to claim 1 or 2.

7. The ratio of the horizontal component of the negative electrode active material along the electrode sheet to the vertical component perpendicular to the electrode sheet is defined as the orientation value of the negative electrode active material. The method for manufacturing the secondary battery according to claim 1 or 2.

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