Manufacturing method for the negative electrode plate of a lithium-ion secondary battery

Abstract

To optimize the orientation of the negative electrode active material within the negative electrode plate of a lithium-ion secondary battery, thereby reducing the diffusion resistance within the negative electrode plate. [Solution] A method for manufacturing a negative electrode plate of a lithium-ion secondary battery, comprising a coating step in which a negative electrode mixture paste 260 containing a negative electrode active material 261 made of graphite and a negative electrode solvent 263 is coated onto a negative electrode current collector foil 25, and after coating, a magnetic field is formed on the negative electrode mixture paste 260 using magnetic field applying devices 130a and 130b to increase the degree of orientation of the negative electrode active material 261; and a drying step following the coating step in which the negative electrode mixture paste 260 is cured to form a negative electrode mixture layer 26, wherein in the drying step, a magnetic field is formed from the negative electrode current collector foil 25 side using a magnetic field applying device 130c to optimize the orientation of the negative electrode active material 261.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a negative electrode plate for a lithium-ion secondary battery, and more specifically, to a method for manufacturing a negative electrode plate for a lithium-ion secondary battery in which the negative electrode active material is oriented by magnetic force. [Background technology]

[0002] A lithium-ion secondary battery comprises a positive electrode, a negative electrode, and a separator impregnated with an electrolyte, which is interposed between these two electrodes. + Charging and discharging occur as lithium moves back and forth between the positive and negative electrodes. The negative electrode composite layer of a typical negative electrode in this type of lithium-ion secondary battery contains a negative electrode active material that can reversibly intercept and release lithium ions. For example, graphite is used as the negative electrode active material. Graphite has a layered crystalline structure, and charging and discharging are effectively achieved by intercepting lithium ions into the interlayers and releasing lithium ions from the interlayers. Such negative electrode active materials generally have a flattened shape rather than a perfect sphere. Therefore, the diffusion resistance within the electrode plate changes depending on its orientation, so it is preferable to orient the negative electrode active material in a direction that minimizes diffusion resistance.

[0003] Here, "degree of orientation" refers to the angle formed between the layer surface of the layered negative electrode active material and the surface of the negative electrode current collector foil. Therefore, in the secondary battery described in Patent Document 1, the negative electrode active material layer has a relatively high degree of graphite orientation in the surface region of the negative electrode active material layer, so lithium ions Li that have moved from the positive electrode + Charge carriers such as ions can easily enter the interlayers of graphite. As a result, the intercalation of charge carriers into and out of the interlayers of graphite proceeds smoothly.

[0004] Furthermore, the degree of graphite orientation is relatively low in the internal region of the negative electrode active material layer. Therefore, for example, during the rolling process, the stress generated during rolling is relieved, preventing cracks and fissures in the graphite that may occur during rolling. Such a secondary battery may have a high initial capacity and excellent output characteristics due to the orientation of the negative electrode active material. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-137879 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the inventors have found that while conventional techniques increase the orientation of the surface anode active material during drying to suppress diffusion resistance, the orientation of the anode active material near the anode current collector foil decreases again during the drying process. In particular, the basis weight [mg / cm²] of the anode composite paste during coating. 2 This tendency is particularly pronounced when [the value] is high.

[0007] The problem that the present invention's method for manufacturing a negative electrode plate of a lithium-ion secondary battery aims to solve is to optimize the orientation of the negative electrode active material within the negative electrode plate and reduce the diffusion resistance within the negative electrode plate. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a method for manufacturing a negative electrode plate of a lithium-ion secondary battery, comprising: a coating step of coating a negative electrode composite paste containing a flattened negative electrode active material that exhibits magnetism to a magnetic field onto a negative electrode current collector foil, and forming a magnetic field on the negative electrode composite paste to increase the degree of orientation of the negative electrode active material; and a drying step following the coating step of curing the negative electrode composite paste to form a negative electrode composite layer, wherein in the drying step, a magnetic field is formed at least from the negative electrode current collector foil side.

[0009] In the drying process, a magnetic field can be formed only from the negative electrode current collector foil side, and the negative electrode plate can also be heated from the surface side, which is the opposite side of the negative electrode current collector foil side. In addition, the magnetic field in the drying process can also be formed from both sides of the negative electrode composite paste.

[0010] The magnetic field in the coating process can also be formed from both sides of the negative electrode composite paste after coating. The basis weight of the negative electrode composite layer is 16 [mg / cm 2 or more, and the viscosity of the negative electrode composite paste can be 2400 [mPa·s(@1 / s)] or less.

[0011] The degree of orientation of the negative electrode active material on the negative electrode current collector foil side can be 39 [°] or more in terms of the azimuth angle [°], which is the deviation angle of the layer plane of the negative electrode active material with respect to the plane perpendicular to the thickness direction of the negative electrode current collector foil.

[0012] In the drying process, a magnet with a magnetic flux density of 0.4 [T] or more in the magnetic field can be arranged with the distance between the electrode plate and the magnet being 1 [mm] or less, and the negative electrode plate can be arranged for 3.8 [sec] or more.

[0013] The azimuth angle [°] on the negative electrode current collector foil side can be in the range of 98 to 102 [%] with respect to the azimuth angle [°] on the side opposite to the negative electrode current collector foil. When the negative electrode active material is graphite, it can be preferably implemented.

Advantages of the Invention

[0014] According to the method for manufacturing a negative electrode plate of a lithium ion secondary battery of the present invention, there is an effect that the orientation of the negative electrode active material in the negative electrode plate can be optimized and the diffusion resistance in the negative electrode plate can be reduced.

Brief Description of the Drawings

[0015] [Figure 1] It is a perspective view showing a schematic configuration of a cell of a lithium ion secondary battery. [Figure 2] It is a view showing a part of the electrode body developed. [Figure 3] It is a view showing the process of forming the negative electrode active material layer. [Figure 4]This is a conceptual diagram illustrating the "azimuth angle" as defined in this invention. [Figure 5] This is a flowchart showing the procedure for manufacturing the negative electrode plate of the lithium-ion secondary battery according to this embodiment. [Figure 6] (a) to (f) are schematic diagrams of the manufacturing method for the negative electrode plate of the lithium-ion secondary battery of this embodiment. [Figure 7] This is a micrograph showing the azimuth angle θ[°] of the negative electrode plate of the lithium-ion secondary battery of this embodiment. [Figure 8] This graph shows the relationship between the azimuth angle θ [°] and the diffusion resistance ratio [%]. [Figure 9] (a) to (f) are schematic diagrams of conventional methods for manufacturing the negative electrode plate of a lithium-ion secondary battery. [Figure 10] This is a micrograph showing the azimuth angle θ[°] of the negative electrode plate of a conventional lithium-ion secondary battery. [Modes for carrying out the invention]

[0016] Hereinafter, the method for manufacturing the negative electrode plate of the lithium-ion secondary battery of the present invention will be described with reference to Figures 1 to 10, using an embodiment of the method for manufacturing the negative electrode plate 24 of the lithium-ion secondary battery 10 as an example. Note that this embodiment is just one example of the present invention and does not limit the present invention.

[0017] (Summary of this embodiment) In recent years, there has been a demand for further increases in the battery capacity [Ah] of the lithium-ion secondary battery 10 shown (see Figure 1). To this end, the negative electrode composite layer 26 is made thicker and the amount of negative electrode active material 261 is increased (see Figures 2 and 4). That is, the basis weight [mg / cm²] of the negative electrode composite paste 260 relative to the negative electrode current collector foil 25. 2 It was proposed to increase the amount of the negative electrode composite layer 26. By making the negative electrode composite layer 26 thicker in this way, the amount of negative electrode active material 261 that contributes to the battery capacity can be increased.

[0018] Figures 9(a) to 9(f) are schematic diagrams of a conventional method for manufacturing a negative electrode plate of a lithium-ion secondary battery. As shown in Figure 9(a), the negative electrode active material 261 is displaceably held in a negative electrode composite paste 260 whose viscosity has been reduced with a negative electrode solvent 263. Then, as shown in Figure 9(b), a magnetic field is formed on the negative electrode composite paste 260 by magnetic field applying devices 130a and 130b to orient the negative electrode active material 261. Then, in this oriented state, it is dried with hot air by a drying device 140 as shown in Figure 9(c). At this time, as shown in Figure 9(d), the magnetic field disappears, so even if the orientation on the surface side is maintained in the initial stage of the drying process, the orientation of the negative electrode active material 261 is disrupted by gravity in the negative electrode composite paste 260 on the negative electrode current collector foil 25 side, where the viscosity is low. The drying process is completed in the state shown in Figure 9(e), and the negative electrode solvent 263 vaporizes. As a result, as shown in Figure 9(f), the negative electrode composite layer 26 is completed with the orientation of the negative electrode active material 261 on the negative electrode current collector foil 25 side disrupted and hardened.

[0019] Therefore, even if conventional technology could increase the battery capacity [Ah] by increasing the amount of negative electrode active material 261, lithium ion Li + The diffusion resistance for the ions to diffuse increases. In other words, as the negative electrode composite layer 26 becomes thicker, the lithium ions exchanged via the surface of the negative electrode plate 24 become thicker. + However, if the negative electrode active material 261 near the negative electrode current collector foil 25, which is located deep within the battery, is not oriented, the diffusion resistance will increase. This leads to a problem where the input / output characteristics of the battery deteriorate. Therefore, in this embodiment, this problem is solved by providing the following configuration.

[0020] In the manufacturing method of the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment, as shown in Figures 3, 5, and 6, a negative electrode composite paste 260 containing a negative electrode active material 261 made of graphite is applied to the negative electrode current collector foil 25 in a coating step. In this coating step, a magnetic field is formed on the negative electrode composite paste 260 to increase the degree of orientation of the negative electrode active material 261. Furthermore, in the drying step following the coating step, the negative electrode composite paste 260 is cured to form a negative electrode composite layer 26. A characteristic feature of this drying step is that a magnetic field is formed from the negative electrode current collector foil 25 side.

[0021] According to the manufacturing method of the negative electrode plate 24 of the lithium-ion secondary battery 10 having such a configuration, the orientation of the negative electrode active material 261 within the negative electrode plate 24 can be optimized. By optimizing the orientation of the negative electrode active material 261, the lithium ions within the negative electrode plate 24 Li + This has the effect of reducing the diffusion resistance and improving the input / output characteristics of the battery.

[0022] <Orientation degree (azimuth angle θ)> Here, the "degree of orientation" in this embodiment will be explained. Figure 4 is a conceptual diagram illustrating the "azimuth angle" as used in this invention. The graphite used as the negative electrode active material 261 of the lithium-ion secondary battery 10 is not a perfect sphere but has a flattened shape, so when considered in cross-section, it is elliptical rather than a perfect circle. In this specification, the "azimuth angle θ[°]" is defined as the angle of deviation made between the direction parallel to the layer surface 261a of the negative electrode active material 261 and the direction perpendicular to the thickness direction of the surface of the negative electrode current collector foil 25, using the direction parallel to the surface as a reference.

[0023] When the negative electrode active material 261 is in a "lying down" position, that is, when the azimuth angle θ[°] is small, the pore path is formed by wrapping around the negative electrode active material 261, resulting in a longer pore path length and a greater degree of curvature. Therefore, the diffusion distance from the surface of the negative electrode composite layer 26 to the vicinity of the negative electrode current collector foil 25 is long, and the diffusion resistance is high. On the other hand, when the negative electrode active material 261 is in an "upright" position, that is, when the azimuth angle θ[°] is large, the degree of curvature is small, and the diffusion distance from the surface of the negative electrode composite layer 26 to the vicinity of the negative electrode current collector foil 25 is short, thus reducing the diffusion resistance.

[0024] Therefore, in this embodiment, when the "azimuth angle θ[°]" is large, the "degree of orientation" is said to be high or large, and the diffusion resistance of the negative electrode active material 261 becomes small. On the other hand, when the "azimuth angle θ[°]" is small, the "degree of orientation" is said to be low or small, and the diffusion resistance of the negative electrode active material 261 increases.

[0025] The azimuth angle θ [°] is, for example, determined from a micrograph, and the outer diameters of a plurality of negative electrode active materials 261 are measured to calculate the median average (d 50 ). In the present application, the "azimuth angle θ [°]" shall refer to such a median average (d 50 ).

[0026] Therefore, as described in Patent Document 1, by applying a magnetic field to the negative electrode composite paste 260 after coating so that the azimuth angle θ of the negative electrode active material 261 increases, the diffusion resistance of the negative electrode active material 261 decreases.

[0027] <Features of the present embodiment> However, experiments by the present inventors have revealed that in the prior art disclosed in Patent Document 1, the negative electrode active material 261 cannot be properly oriented. This was particularly prominent when the basis weight [mg / cm 2 of the negative electrode composite paste 260 was high and the viscosity [Pa·s(@1 / s)] was low in order to increase the battery capacity. That is, the inventors obtained the finding that the orientation degree of the negative electrode active material 261 near the negative electrode current collector foil 25, which 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the inventors have created a magnetic field even during the drying process after the coating process to prevent the azimuth angle θ[°] of the negative electrode active material 261 near the negative electrode current collector foil 25 from decreasing again due to gravity or other reasons. Note that in the drying process, since the drying device 140 is located on the negative electrode composite layer 26 side, it is not possible to place magnets on both sides of the negative electrode plate 24 as in the coating process (see Figure 3). The inventors have found that in the drying process, the surface side of the negative electrode composite layer 26 (opposite the negative electrode current collector foil 25) dries quickly and the degree of orientation is fixed. On the other hand, the side of the negative electrode current collector foil 25 is difficult to dry and the viscosity does not increase. Therefore, in the manufacturing method of the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment, in the coating process, a negative electrode composite paste 260 containing the negative electrode active material 261 is coated onto the negative electrode current collector foil 25. After coating, a magnetic field is formed on both sides of the negative electrode composite paste 260 in the thickness direction to increase the orientation of the negative electrode active material 261. Following the coating process, the drying process hardens the negative electrode composite paste 260 to form the negative electrode composite layer 26. In this drying process, a magnetic field is formed only from the negative electrode current collector foil 25 side.

[0029] It was found that by configuring it in this way, it is possible to maintain a well-balanced state of increased orientation of the negative electrode active material 261 not only on the surface side of the negative electrode composite layer 26, but also on the negative electrode current collector foil 25 side.

[0030] As a result, the manufacturing method for the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment has the effect of optimizing the orientation of the negative electrode active material 261 within the negative electrode plate 24 and reducing the diffusion resistance within the negative electrode plate 24.

[0031] (Configuration of this embodiment) <Lithium-ion secondary battery 10 of this embodiment> First, an example of the lithium-ion secondary battery 10, which is the premise of this embodiment, will be described. Note that this embodiment is not limited to the lithium-ion secondary battery 10.

[0032] Figure 1 is a perspective view showing the schematic configuration of the cell of the lithium-ion secondary battery 10 of this embodiment. Figure 2 is a diagram showing a part of the electrode body 20 unfolded. As shown in Figure 1, the lithium-ion secondary battery 10 is a cell battery that, when combined with multiple lithium-ion secondary batteries 10, is enclosed in a resin or metal case to form a battery pack. The battery pack is used in hybrid vehicles and electric vehicles. For this purpose, the positive electrode plate 21 and the negative electrode plate 24 are laminated with a separator 27, wound together, and pressed to form a plate-shaped electrode body 20.

[0033] The lithium-ion secondary battery 10 comprises a battery case 11 and a cover 12. The battery case 11 is a rectangular parallelepiped with an opening on its upper side. The cover 12 seals the opening of the battery case 11. The battery case 11 and the cover 12 are made of a metal such as aluminum or an aluminum alloy. The lithium-ion secondary battery 10 is formed as a sealed battery case by attaching the cover 12 to the battery case 11.

[0034] The cover 12 is provided with a negative electrode external terminal 13A and a positive electrode external terminal 13B. The negative electrode external terminal 13A and the positive electrode external terminal 13B are used for charging and discharging power. The electrode body 20 is housed inside the battery case 11. The negative electrode side current collector 20A, which is the negative electrode end of the electrode body 20, is electrically connected to the negative electrode external terminal 13A via the negative electrode side current collector member 14A. The positive electrode side current collector 20B, which is the positive electrode end of the electrode body 20, is electrically connected to the positive electrode external terminal 13B via the positive electrode side current collector member 14B. In addition, a non-aqueous electrolyte is injected into the battery case 11 through the injection hole. Note that the shapes of the negative electrode external terminal 13A and the positive electrode external terminal 13B are not limited to the shapes shown in Figure 1, but may be any shape.

[0035] <Electrode body 20> As shown in Figure 2, the electrode body 20 is a flat wound body formed by winding a laminate in which long positive electrode plates 21 and negative electrode plates 24 are stacked with separators 27 in between. The positive electrode plate 21, negative electrode plate 24, and separator 27 are stacked so that their respective longitudinal directions coincide with the longitudinal direction D1. Before winding, the laminate is stacked in the order of positive electrode plate 21, separator 27, negative electrode plate 24, and separator 27.

[0036] <Positive plate 21> The positive electrode plate 21 comprises a positive electrode current collector foil 22 and a positive electrode composite layer 23. The positive electrode current collector foil 22 is a foil-shaped positive electrode substrate formed in an elongated shape. The positive electrode composite layer 23 is provided on each of two opposing surfaces of the positive electrode current collector foil 22. The positive electrode current collector foil 22 has an uncoated positive electrode side portion 22A at one end in the width direction D2 where the positive electrode composite layer 23 is not formed and the positive electrode current collector foil 22 is exposed.

[0037] The positive electrode current collector foil 22 is made of a metal foil composed of aluminum or an alloy mainly composed of aluminum. The positive electrode current collector foil 22 functions as a current collector foil at the positive electrode. In the state of the wound body, the uncoated positive electrode side portion 22A of the positive electrode current collector foil 22 is pressed against each other by opposing surfaces to form the positive electrode side current collector portion 20B.

[0038] The positive electrode composite layer 23 is a cured form of a liquid positive electrode composite paste. The positive electrode composite paste contains a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode composite layer 23 is formed when the positive electrode composite paste dries and the positive electrode solvent vaporizes. Therefore, the positive electrode composite layer 23 contains a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0039] The positive electrode active material is lithium ion Li, which is the charge carrier in the lithium-ion secondary battery 10. +A lithium-containing composite oxide capable of intercalating and releasing lithium is used. The lithium-containing composite oxide is an oxide containing lithium and other metallic elements other than lithium. The other metallic elements other than lithium are at least one selected from the group consisting of, for example, nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide.

[0040] For example, lithium-containing composite oxides include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganeseate (LiMn2O4). Another example is lithium-containing composite oxide, a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, which is lithium nickel-cobalt-manganate (LiNiCoMnO2). Yet another example is lithium iron phosphate (LiFePO4).

[0041] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. Examples of positive electrode conductive materials include carbon black such as acetylene black and Ketjenblack, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite. The positive electrode binder is an example of a resin component contained in the positive electrode composite paste. Examples of positive electrode binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR).

[0042] The positive electrode plate 21 may also be provided with an insulating layer at the boundary between the uncoated positive electrode portion 22A and the positive electrode composite layer 23. The insulating layer comprises an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0043] <Negative electrode plate 24> The negative electrode plate 24 comprises a negative electrode current collector foil 25 and a negative electrode composite layer 26. The negative electrode current collector foil 25 is a foil-shaped negative electrode substrate formed in an elongated shape. The negative electrode composite layer 26 is provided on each of two opposing surfaces of the negative electrode current collector foil 25. The negative electrode current collector foil 25 has a negative electrode side uncoated portion 25A at one end in the width direction D2, which is located opposite the positive electrode side uncoated portion 22A, where the negative electrode composite layer 26 is not formed and the negative electrode current collector foil 25 is exposed.

[0044] The negative electrode current collector foil 25 is made of a metal foil composed of copper or an alloy mainly composed of copper. The negative electrode current collector foil 25 functions as a current collector at the negative electrode. In the state of the wound body, the uncoated negative electrode side portion 25A has opposing surfaces pressed against each other to form the negative electrode side current collector portion 20A.

[0045] The negative electrode composite layer 26 is a cured form of a liquid negative electrode composite paste 260. The negative electrode composite paste 260 contains a negative electrode active material 261, a negative electrode solvent 263, as well as a negative electrode binder (not shown), a negative electrode thickener, and additives. The negative electrode composite layer 26 is formed when the negative electrode composite paste 260 is dried with hot air during the drying process, causing the negative electrode solvent 263 to vaporize. Therefore, the negative electrode composite layer 26 contains the negative electrode active material 261, a negative electrode binder, and a negative electrode thickener as an additive. The negative electrode composite layer 26 may further contain additives such as a conductive material.

[0046] The negative electrode active material 261 is lithium ion Li + It is a material capable of intercalating and releasing. The negative electrode active material 261 can be, for example, graphite, non-graphitizable carbon, easily graphitizable carbon, carbon nanotubes, or other carbon materials. In this embodiment, the negative electrode active material 261 can be any material whose orientation can be changed by a magnetic field.

[0047] The negative electrode solvent 263 is, for example, water. As an example of a negative electrode thickener, CMC (carboxymethylcellulose) can be used as a thickener containing a sodium salt. The negative electrode binder can be the same as the positive electrode binder. As an example of a negative electrode binder, SAR (styrene-acrylic acid copolymer) can be used as a binder containing a sodium salt.

[0048] <Separator 27> The separator 27 prevents contact between the positive electrode plate 21 and the negative electrode plate 24, and holds the non-aqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the ends in the width direction D2 of the separator 27 toward the center.

[0049] The separator 27 is a nonwoven fabric made of polypropylene or the like. As the separator 27, for example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, and ion-conductive polymer electrolyte membranes can be used.

[0050] <Nonaqueous electrolyte> A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc., can be used. As the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, LiBOB (lithium bisoxalate borate), etc., can be used.

[0051] In this embodiment, ethylene carbonate is used as the non-aqueous electrolyte. <Manufacturing equipment 500 for negative electrode plate 24> Figure 3 shows a manufacturing apparatus 500 that embodies a method for manufacturing the negative electrode plate 24 of a lithium-ion secondary battery 10. This manufacturing apparatus 500 includes a travel path 110, a supply unit 112, a recovery unit 114, a coating device 120, magnetic field application devices 130a to 130c, and a drying device 140.

[0052] The travel path 110 is the path through which the negative electrode current collector foil 25 travels. In this embodiment, a plurality of guide rollers 116 are arranged along a predetermined path through which the negative electrode current collector foil 25 travels. In this embodiment, the negative electrode current collector foil 25 is stretched sequentially across the plurality of guide rollers 116, and a predetermined tension is applied to the negative electrode current collector foil 25. Some of the guide rollers 116 are fitted with a drive device (not shown) that rotates the roller. The negative electrode current collector foil 25 can be transported by rotating these guide rollers 116 in one direction.

[0053] At the starting end of the travel path 110, a supply unit 112 is provided for supplying negative electrode current collector foil 25. The supply unit 112 contains negative electrode current collector foil 25 that has been pre-wound onto a winding core 112A. An appropriate amount of negative electrode current collector foil 25 is supplied from the supply unit 112 to the travel path 110 as needed. At the end of the travel path 110, a recovery unit 114 is provided for recovering the negative electrode current collector foil 25. The recovery unit 114 winds the negative electrode current collector foil 25, which has undergone predetermined processing in the travel path 110, onto a winding core 114A. A coating device 120, a magnetic field application device 130, and a drying device 140 are arranged in that order along the travel path 110.

[0054] The coating apparatus 120, which embodies the coating process, is a device that applies negative electrode composite paste 260 to the negative electrode current collector foil 25. In this embodiment, the coating apparatus 120 is configured to apply the negative electrode composite paste 260 in the longitudinal direction of the elongated negative electrode current collector foil 25. An example of such a coating apparatus is a die coater coating machine. In the coating apparatus 120, which is a die coater coating machine, the negative electrode composite paste 260 is contained in a tank 122, and the negative electrode composite paste 260 sucked up by a pump 124 is supplied to a die 126. Then, while being conveyed by the rotation of a backup roll 128, it passes through the gap (coating gap) between the backup roll 128 and the die 126, forming a coating film of negative electrode composite paste 260 on the surface of the negative electrode current collector foil 25 from the die 126. The coating apparatus 120, which consists of such a die coater coating machine, can continuously coat the negative electrode composite paste 260 in the longitudinal direction of the negative electrode current collector foil 25 while adjusting the basis weight of the coating film made of the negative electrode composite paste 260.

[0055] <Manufacturing method for the negative electrode plate 24 of the lithium-ion secondary battery 10> Figure 5 is a flowchart showing the procedure for manufacturing the negative electrode plate 24 of the lithium-ion secondary battery 10 according to this embodiment. Figure 6 is a schematic diagram of the manufacturing method of the negative electrode plate 24 of the lithium-ion secondary battery 10 according to this embodiment.

[0056] Next, the procedure for manufacturing the negative electrode plate 24 of the lithium-ion secondary battery 10 using the manufacturing apparatus 500 described above will be explained with reference to Figure 3. <Set of negative electrode current collector foil 25 (S1)> When the manufacturing method for the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment is started, first the negative electrode current collector foil 25 is set in the manufacturing apparatus 500 (S1). Here, the long negative electrode current collector foil 25 wound on a winding core 112A is set in the supply unit 112 and pulled out, and while tension is applied by the guide rollers 116, 116 of the travel path 110, it is wrapped around the backup roll 128. The negative electrode current collector foil 25 is brought into close contact with the backup roll 128 and inverted. The inverted negative electrode current collector foil 25 is wound up and recovered by the winding core 114A of the recovery unit 114 while tension is applied by the guide rollers 116.

[0057] <Negative electrode composite paste coating (S2)> Next, as part of the coating process, the negative electrode current collector foil 25, set in the travel path 110, is coated with negative electrode composite paste 260 while being transported. This procedure constitutes part of the coating process in this embodiment. Here, the negative electrode composite paste 260 is adjusted in composition, its viscosity is adjusted to, for example, 2400 [mPa·s (@1 / s)], and it is stored in the tank 122. The negative electrode composite paste 260 stored in the tank 122 is pumped to the die 126 by the pump 124. The gap [mm] between the die 126 and the negative electrode current collector foil 25, which is transported at a predetermined speed [m / s] in close contact with the backup roll 128, is adjusted, and the basis weight is, for example, 16 [mg / cm]. 2 Discharge volume [cm] greater than or equal to [cm] 2 At [ / s], the negative electrode composite paste 260 is discharged. Here, as shown in Figure 6(a), the negative electrode active material 261 is dispersed in the negative electrode solvent 263 of the negative electrode composite paste 260 in a random orientation, in other words, in a direction where the azimuth angle θ[°] is not fixed. That is, the negative electrode active material 261 is not oriented in a specific orientation. In other words, the degree of orientation is low.

[0058] <Orientation of negative electrode active material 261 (S3)> Next, in the coating process, a magnetic field applying device 130a, consisting of a permanent magnet, is placed on the surface side of the negative electrode composite paste 260, and a magnetic field applying device 130b, also consisting of a permanent magnet, is placed on the negative electrode current collector foil 25 side. As a result, as shown in Figure 6(b), a magnetic field is formed between the magnetic field applying device 130a and the magnetic field applying device 130b with the negative electrode composite paste 260 in between. Here, in Figure 4, the direction of the magnetic field is assumed to be from top to bottom (from magnetic field applying device 130a to magnetic field applying device 130b). In this case, due to diamagnetism, the negative electrode active material 261 shown in Figure 4 is held upright by the magnetic field, that is, the azimuth angle θ[°] becomes large, and the degree of orientation increases.

[0059] <Drying while orienting the negative electrode active material 261 (S4)> After the coating process described above is completed, the azimuth angle θ[°] of the negative electrode active material 261 in the negative electrode mixture paste 260 is large. At the start of the drying process, the viscosity [mPa·s(@1 / s)] of the negative electrode mixture paste 260 is low, and the azimuth angle θ[°] of the negative electrode active material 261 is still fluid and not fixed.

[0060] Next, the process moves from coating to drying. In this procedure, a magnetic field is first formed on the negative electrode mixture paste 260 to orient the negative electrode active material 261, and then it is heated and dried with hot air (S4).

[0061] As shown in Figure 3, in the drying process, the drying device 140 is positioned on the surface side of the anode composite paste 260 before solidification and the paste is transported. In the drying device 140 of this embodiment, hot air is blown onto the surface side of the anode composite paste 260 to vaporize the anode solvent 263 in the anode composite paste 260, thereby hardening the anode composite paste 260.

[0062] Furthermore, a magnetic field generating device 130c is installed on the negative electrode current collector foil 25 side. As shown in Figure 6(c), the magnetic field of the magnetic field generating device 130c is formed in the vertical direction on the negative electrode active material 261 on the negative electrode current collector foil 25 side. In the initial stages of the drying process, the viscosity [mPa·s (@1 / s)] of the negative electrode composite paste 260 is low, and the azimuth angle θ [°] of the negative electrode active material 261 is still fluid and not fixed. Also, due to the influence of gravity, if left as is, the layer surface 261a will gradually become horizontal, that is, the azimuth angle θ [°] will change to a small value.

[0063] However, the magnetic field formed by the magnetic field generating device 130c is formed in the vertical direction in the negative electrode active material 261 on the negative electrode current collector foil 25 side. Therefore, the azimuth angle θ[°] of the negative electrode active material 261 is maintained at a high value due to diamagnetism depending on the direction of the magnetic field.

[0064] With the azimuth angle θ[°] maintained at a high value in this manner, the viscosity [mPa·s(@1 / s)] of the negative electrode composite paste 260 gradually increases due to the drying device 140. <Dispel the magnetic field and continue heating (S5)> In the drying process, drying continues using the drying device 140. When the viscosity [mPa·s(@1 / s)] of the negative electrode composite paste 260 reaches a certain value using the drying device 140, the orientation of the negative electrode active material 261 is fixed, and the azimuth angle θ[°] is maintained at a high value. Once the orientation of the negative electrode active material 261 is fixed in this way, the magnetic field from the magnetic field applying device 130c is eliminated as shown in Figure 6(d), but drying by the drying device 140 continues.

[0065] In this embodiment, during the drying process, the magnetic field applying device 130c places a magnet with a magnetic flux density of 0.4 [T] or more at a position where the distance between the electrode plate and the magnet is 1 [mm] or less. In addition, the negative electrode plate 24 is transported so as to be in position for 3.8 [sec] or more.

[0066] Furthermore, drying by the drying apparatus 140 continues, and as shown in Figure 6(e), once the negative electrode solvent 263 has completely vaporized, the negative electrode composite paste 260 hardens, and drying by the drying apparatus 140 is terminated as shown in Figure 6(f). As shown in Figure 3, the negative electrode plate 24 after the drying process is completed is wound onto the winding core 114A of the recovery unit 114 and recovered as the negative electrode plate 24 after the drying process is completed.

[0067] <Shaping press process (S6)> In the shaping press process (S6), the negative electrode plate 24, after the drying process has been completed, is transported and pressed with a pair of roller presses (not shown) at a predetermined gap to set its thickness to a predetermined value.

[0068] <Forming process (S7)> The negative electrode plate 24, after the shaping press process (S6) is completed, is cut into the designed shape in the shaping process (S7). In this embodiment, the negative electrode composite paste 260 is applied to both sides of the negative electrode current collector foil 25, which is twice the width of the negative electrode plate 24, leaving the uncoated portion 25A on the negative electrode side as shown in Figure 2. Then, it is divided in half at the center in the width direction.

[0069] This completes the negative electrode plate 24 (end). Subsequently, the negative electrode plate 24 is laminated with the positive electrode plate 21 and the separator 27, wound up, and press-formed to form the electrode body 20.

[0070] (Operation of this embodiment) <Magnetic field formation during the drying process> Figure 7 is a micrograph showing the azimuth angle θ[°] of the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment. The photograph shows a cross-section obtained by cutting the completed negative electrode plate 24 in the thickness direction. In this embodiment, the "surface side" of the negative electrode composite layer 26 or negative electrode composite paste 260 refers to the area above the center in the height direction (thickness direction) in the figure. Similarly, the "negative electrode current collector foil 25 side" refers to the area below the center in the height direction in the figure. The plate was then divided in the thickness direction, and multiple samples were randomly extracted from the micrographs of each region. The longitudinal orientation of the graphite particles, which are the negative electrode active material 261, was visually measured, and its median mean (d 50 ) was calculated. In this way, the median mean (d) of the azimuth angle θ[°] was calculated. 50 When the azimuth angle was calculated, it was found to be θ = 64° on the surface side and also θ = 64° on the negative electrode current collector foil 25 side, yielding roughly the same result. From these results, the average azimuth angle θ of the completed negative electrode composite layer 26 was 64° in all cases, showing a high value.

[0071] Figure 10 is a micrograph showing the azimuth angle θ [°] of the negative electrode plate 24 of a conventional lithium-ion secondary battery 10, shown for comparison with the negative electrode plate 24 of this embodiment in Figure 7. Divided in half in the thickness direction, the median mean (d 50 When the azimuth angle was calculated, the azimuth angle θ was 43° on the surface side and 29° on the negative electrode current collector foil 25 side, showing a significant difference between the surface side and the negative electrode current collector foil 25 side. On the surface side, the azimuth angle θ was 43°, indicating that despite forming a magnetic field in a similar process during the coating process, the azimuth angle θ decreased during the subsequent drying process. Furthermore, on the negative electrode current collector foil 25 side, the azimuth angle θ was 29°, and as the inventors had anticipated, a particularly large decrease in the azimuth angle θ was observed on the negative electrode current collector foil 25 side.

[0072] These comparisons confirmed that forming a magnetic field during the drying process is effective. <Azimuth angle θ[°] and diffusion resistance ratio[%]> Figure 8 is a graph showing the relationship between the azimuth angle θ [°] and the diffusion resistance ratio [%]. The diffusion resistance ratio [%] is shown when the diffusion resistance when the negative electrode active material 261 is not oriented is set to 100 [%]. The horizontal axis represents the azimuth angle θ [°], and the vertical axis represents the diffusion resistance ratio [%].

[0073] Here, representative plot points P1 to P3 are shown for illustrative purposes. In actual tests, many plot points are obtained. Plot points P1 to P3 represent the median mean (d) of the overall azimuth angle θ [°] of the negative electrode composite layer 26. 50 This graph plots the diffusion resistance ratio [%] at ). The relationship between the azimuth angle θ [°] and the diffusion resistance ratio [%] shows a strong correlation and is generally expressed as a linear function. Therefore, graph L1 is the straight line identified by regression analysis based on these plotted points P1 to P3.

[0074] At plot point P1, when the negative electrode active material 261 was not oriented, the azimuth angle θ[°] was approximately 26.6[°]. At this azimuth angle θ=26.6[°], the lithium ion Li + Let the diffusion resistance be 100.

[0075] In this embodiment, if the diffusion resistance ratio [%] is reduced by 10 [%] to 90 [%] in order to achieve an effective effect, it is derived that the azimuth angle θ at which this can be achieved is approximately 39 [°] or greater. Furthermore, if the diffusion resistance ratio [%] is reduced by 20 [%] to 80 [%], it is derived that the azimuth angle θ at which this can be achieved is approximately 50 [°].

[0076] From the above measurements, it is most ideal for the azimuth angle θ[°] to be θ≧64[°] or greater, as obtained in the embodiment. Furthermore, it is desirable to set the azimuth angle θ[°] to θ≧50[°] to achieve a high effect. It was also found that setting the azimuth angle θ[°] to θ≧39[°] can achieve a sufficient effect. At a minimum, it was found that the azimuth angle θ[°] must be θ≧27[°] to achieve at least an effect.

[0077] (Effects of this embodiment) (1) The method for manufacturing the negative electrode plate 24 of the lithium-ion secondary battery 10 of this embodiment has the effect of optimizing the orientation of the negative electrode active material 261 in the negative electrode plate 24 and reducing the diffusion resistance in the negative electrode plate 24.

[0078] (2) In the drying process, a magnetic field is formed at least from the negative electrode current collector foil 25 side. Therefore, especially in the initial stages of the drying process, when the viscosity [mPa·s (@1 / s)] of the negative electrode composite paste 260 is low, it is possible to suppress the decrease in the azimuth angle θ [°] due to gravity.

[0079] (3) In the drying process, a magnetic field is formed only on the negative electrode current collector foil 25 side, and the negative electrode plate 24 is heated from the surface side opposite to the negative electrode current collector foil 25 side. Therefore, there is no magnetic field application device on the surface side, and it can be dried quickly by the hot air of the drying device 140. In addition, the decrease in the azimuth angle θ[°] of the negative electrode active material 261 on the negative electrode current collector foil 25 side, which is particularly prone to decrease due to gravity, can be effectively suppressed by the magnetic field application device 130c.

[0080] (4) The magnetic field in the coating process is formed from both sides of the negative electrode mixture paste 260 by magnetic field applying devices 130a and 130b after coating. This has the effect of forming a magnetic field with a strong magnetic flux density over the entire negative electrode mixture paste 260.

[0081] (5) In this embodiment, the basis weight of the negative electrode composite layer 26 is 16 [mg / cm²] 2 The viscosity of the negative electrode composite paste 260 is 2400 [mPa·s (@1 / s)] or less. Even under conditions such as a negative electrode composite paste 260 with low viscosity and large basis weight, this embodiment has the effect of effectively optimizing orientation and suppressing diffusion resistance.

[0082] (6) In this embodiment, θ ≥ 64 [°], and lithium ion Li +This ideally suppresses diffusion resistance. Furthermore, setting the azimuth angle θ[°] to θ≧50[°] can suppress diffusion resistance by more than 20%. Setting the azimuth angle θ[°] to θ≧39[°] can suppress diffusion resistance by more than 10%. At least an azimuth angle θ≧27[°] is sufficient to achieve the desired effect.

[0083] (7) In this embodiment, during the drying process, a magnet with a magnetic flux density of 0.4 [T] or more in the magnetic field is used, with the distance between the negative electrode plate 24 and the magnet of the magnetic field applying device 130c being 1 [mm] or less, and the negative electrode plate 24 being positioned for 3.8 [sec] or more. This has the effect of forming a strong magnetic field and sufficiently reducing the azimuth angle θ [°].

[0084] (8) The azimuth angle θ[°] on the negative electrode current collector foil 25 side is set to be in the range of 98 to 102[%] of the azimuth angle θ[°] on the surface layer side. This has the effect of effectively suppressing the diffusion resistance of the negative electrode composite layer 26 in a well-balanced manner overall.

[0085] (modified version) The above embodiments are just one example of how the present invention can be implemented, and can be modified as follows. Furthermore, these modifications do not limit the present invention.

[0086] ○In this embodiment, the surface side of the negative electrode composite layer 26 and the negative electrode current collector foil 25 side are distinguished in a 1:1 ratio in the thickness direction, but this is illustrative and the present invention is not limited. For example, the rate of change in the degree of orientation over time due to viscosity [mPa·s (@1 / s)] and the change in viscosity [mPa·s (@1 / s)] due to drying can be appropriately changed by those skilled in the art, for example, to 1:9 or 9:1. Also, for example, in addition to the surface side and the negative electrode current collector foil 25 side, an intermediate section can be provided, and the invention can be carried out by dividing it into three parts such as surface side:intermediate section:negative electrode current collector foil 25 side = 2:6:2. In short, if the degree of orientation of the entire negative electrode composite layer 26 can be controlled in a balanced manner, the problems of the present invention can be solved.

[0087] ○In the coating process of this embodiment, the configuration is not limited as long as the azimuth angle θ[°] of the negative electrode active material 261 can be oriented to be sufficiently large. For example, in the coating process of this embodiment, a magnetic field is formed by sandwiching the negative electrode composite paste 260 with magnetic field applying devices 130a and 130b. However, if a sufficient magnetic field can be formed over the entire negative electrode composite paste 260, either magnetic field applying device 130a or 130b alone may suffice.

[0088] ○In this embodiment, in the coating process, a magnetic field is formed to orient the negative electrode mixture paste 260 after application. However, for example, a magnetic field may be formed at the discharge section of the die 126 to orient the negative electrode mixture paste 260 simultaneously during coating.

[0089] ○In this embodiment, the configuration is not limited as long as drying can be performed while appropriately maintaining the orientation during the drying process. For example, in this embodiment, a magnetic field is formed by a magnetic field applying device 130c located on the negative electrode current collector foil 25 side during the drying process, but magnetic field applying devices 130 may be arranged above and below, similar to the coating process, to achieve orientation.

[0090] ○In this embodiment, the drying process is performed by drying with hot air, but drying may be performed by other methods such as infrared irradiation or heating with a coil. ○Although permanent magnets are used as examples in magnetic field generating devices 130a to c, magnetic fields can also be formed using electromagnets, and are not limited to these.

[0091] Furthermore, in the drying process, the negative electrode plate 24 may be arranged to surround the coil to form a magnetic field, and the coil may be heated to dry the negative electrode composite paste 260.

[0092] ○In this embodiment, a lithium-ion secondary battery 10, which is a plate-shaped cell battery for use in vehicles, is used as an example, but the invention is not limited to this and can be implemented in other shapes and applications such as cylindrical or stationary. Furthermore, in the electrode body 20 of this embodiment, a long positive electrode plate 21, a negative electrode plate 24, and a separator 27 are stacked, wound, and pressed, but a configuration in which a flat positive electrode plate 21, a negative electrode plate 24, and a separator 27 are stacked is also acceptable.

[0093] The drawings are for illustrative purposes only and may omit numbers or exaggerate dimensional balances for ease of explanation; however, they are not limited to these drawings.

[0094] ○The flowchart shown in Figure 5 is an example of the present invention, and the steps can be added, deleted, rearranged, or rearranged to carry it out. ○The various numerical values ​​and ranges are examples only and can be optimized and implemented by those skilled in the art.

[0095] ○The composition and material properties of the lithium-ion secondary battery 10 exemplified are examples of the present invention and can be optimized and implemented by those skilled in the art. The manufacturing apparatus 500 shown in Figure 3 is an example of a negative electrode plate 24, and its configuration is not limited to that of conveying, for example, a horizontal conveyor.

[0096] ○This embodiment is one embodiment of the present invention, and it goes without saying that, as long as it does not depart from the scope of the claims, it is not limited to this embodiment and can be implemented by those skilled in the art by adding, deleting, or modifying its configuration. [Explanation of Symbols]

[0097] P1~P3...Plot points L1...Graph D1... Longitudinal direction D2…Width direction 10…Lithium-ion rechargeable battery 11…Battery case 12... Lid 13A... Negative external terminal 13B... Positive external terminal 14A... Negative electrode current collector 20...Electrode body 20A... Negative electrode current collector 20B…Positive side current collector 21…Positive plate 22...Positive current collector foil 22A...Unpainted area on the positive electrode side 23…Positive electrode composite layer 24... Negative plate 25... Negative electrode current collector foil 25A...Unpainted area on the negative electrode side 26…Negative electrode composite material layer 260... Negative electrode composite paste 261...Negative electrode active material 261a…Layer plane 261b... Edge section 263... Negative electrode solvent 27... Separator 110...Route 112...Supply section 112A...winding core 114... Recovery Department 114A...Core 116... Guide roller 120... Coating device 122... Tank 124... Pump 126...Dai 128... Backup role 130 (130a~130c)... Magnetic field application device 140...Drying equipment 500...Manufacturing equipment

Claims

1. A method for manufacturing a negative electrode plate of a lithium-ion secondary battery, comprising: a coating step of coating a negative electrode composite paste containing a flattened negative electrode active material that exhibits magnetism to a magnetic field onto a negative electrode current collector foil, and forming a magnetic field on the negative electrode composite paste to increase the degree of orientation of the negative electrode active material; and a drying step following the coating step of curing the negative electrode composite paste to form a negative electrode composite layer, wherein A method for manufacturing a negative electrode plate of a lithium-ion secondary battery, characterized in that a magnetic field is formed at least from the negative electrode current collector foil side during the drying process.

2. In the drying process, a magnetic field is formed only from the negative electrode current collector foil side, A method for manufacturing a negative electrode plate of a lithium-ion secondary battery according to claim 1, characterized in that the negative electrode plate is heated from the surface side which is opposite to the negative electrode current collector foil side of the negative electrode plate.

3. The method for manufacturing a negative electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the magnetic field in the drying step is formed from both sides of the negative electrode composite paste.

4. The method for manufacturing a negative electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the magnetic field in the coating step is formed from both sides of the negative electrode composite paste after coating.

5. The basis weight of the negative electrode composite layer is 16 [mg / cm²] ２ The method for manufacturing a negative electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the negative electrode composite paste is 2400 [mPa·s (@1 / s)] or less, and the viscosity of the negative electrode composite paste is 2400 [mPa·s (@1 / s)] or less.

6. The method for manufacturing a negative electrode plate of a lithium-ion secondary battery according to claim 1, characterized in that the degree of orientation of the negative electrode active material on the negative electrode current collector foil side is such that the azimuth angle [°] which is the angle of declination of the layer surface of the negative electrode active material with respect to a plane perpendicular to the thickness direction of the negative electrode current collector foil is 39 [°] or more.

7. The method for manufacturing a negative electrode plate of a lithium-ion secondary battery according to claim 1, characterized in that, in the drying step, a magnet having a magnetic flux density of 0.4 [T] or more in the magnetic field is arranged such that the distance between the electrode plate and the magnet is 1 [mm] or less, and the negative electrode plate is arranged for 3.8 [sec] or more.

8. The method for manufacturing a negative electrode plate of a lithium-ion secondary battery according to claim 6, characterized in that the azimuth angle [°] on the negative electrode current collector foil side is in the range of 98 to 102 [%] of the azimuth angle [°] on the opposite side of the negative electrode current collector foil.

9. A method for manufacturing a negative electrode plate for a lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that the negative electrode active material is graphite.

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