Battery electrode and manufacturing method therefor

Abstract

This battery electrode comprises: a current collector; and an electrode composite layer that is disposed on the current collector and includes active material particles and a binder. The electrode composite layer includes: a first electrode composite layer disposed directly on the current collector; and a second electrode composite layer disposed directly or indirectly on the first electrode composite layer. In at least the second electrode composite layer, at least a portion of the binder is fibrillated. The degree to which the binder in the second electrode composite layer is fibrillated is higher than the degree to which the binder in the first electrode composite layer is fibrillated.

Description

Battery electrode and method for manufacturing the same

[0001] The technology disclosed in this specification relates to a battery electrode and a method for manufacturing the same.

[0002] Japanese Patent Application Laid-Open No. 2022-003694 describes a battery electrode. This electrode includes a current collector and an electrode mixture layer disposed on the current collector. The electrode mixture layer contains active material particles and a binder, and the binder is fibrillated. It is known that the mechanical strength of the electrode mixture layer is improved by fibrillating the binder. In particular, in the electrode described in Patent Document 1, the degree of fibrillation of the binder is high, which is called super fibrillation. Thereby, even when a relatively small amount of binder is used, the mechanical strength required for the electrode mixture layer can be realized.

[0003] In the electrode mixture layer, as the degree of fibrillation of the binder increases, more of the surface of the active material particles is covered by the binder. Since the binder does not have conductivity, there may be a problem that the interfacial resistance between the current collector and the electrode mixture layer increases as the surface of the active material particles is covered by the binder. That is, there is a trade-off problem that when the degree of fibrillating the binder is increased, the mechanical strength of the electrode mixture layer is improved while the electrical characteristics of the electrode are degraded.

[0004] In view of the above situation, this specification provides a technique for reducing the interfacial resistance between the current collector and the electrode mixture layer while maintaining the mechanical strength of the electrode mixture layer.

[0005] The technology disclosed herein is embodied in the electrodes of a battery. In a first embodiment thereof, the electrode comprises a current collector and an electrode composite layer disposed on the current collector, comprising active material particles and a binder. The electrode composite layer includes a first electrode composite layer disposed directly on the current collector and a second electrode composite layer disposed directly or indirectly on the first electrode composite layer. In at least the second electrode composite layer, at least a portion of the binder is fibrillated. The degree to which the binder in the second electrode composite layer is fibrillated is higher than the degree to which the binder in the first electrode composite layer is fibrillated.

[0006] In the above electrode, a first electrode material layer and a second electrode material layer are used as the electrode material layer. The first electrode material layer is directly placed on the current collector, and the second electrode material layer is placed directly or indirectly on the first electrode material layer. The degree to which the binder of the second electrode material layer is fibrillated is higher than the degree to which the binder of the first electrode material layer is fibrillated. That is, the degree to which the binder of the first electrode material layer is fibrillated is lower than the degree to which the binder of the second electrode material layer is fibrillated, or the binder of the first electrode material layer is not fibrillated. Therefore, the interfacial resistance between the current collector and the electrode material layer can be reduced. In addition, the fibrillation of the binder of the second electrode material layer improves the mechanical strength of the electrode material layer.

[0007] In a second embodiment, the thickness dimension of the first electrode composite layer may be 10% or more and 90% or less of the thickness dimension of the electrode composite layer in the first embodiment. With this configuration, the interfacial resistance between the current collector and the electrode composite layer can be reduced while maintaining the mechanical strength of the electrode composite layer.

[0008] In a third embodiment, in the first or second embodiment, the thickness of the second electrode composite layer may be 10% or more and 90% or less of the thickness of the front electrode composite layer. With such a configuration, the interfacial resistance between the current collector and the electrode composite layer can be reduced while improving the mechanical strength of the electrode composite layer.

[0009] In a fourth embodiment, in any of the first to third embodiments, the binder may include at least a first binder material. In this case, at least in the second electrode composite layer, the first binder material may be fibrillated. With this configuration, the fibrillation of the first binder material in the second negative electrode composite layer can improve the mechanical strength of the electrode composite layer.

[0010] In a fifth embodiment, in the fourth embodiment, the first binder material in the first electrode composite layer does not need to be fibrillated. With this configuration, the interfacial resistance between the current collector and the electrode composite layer can be reduced.

[0011] In the sixth embodiment, in the fourth or fifth embodiment, the first binder material may include at least one selected from the group consisting of polytetrafluoroethylene cellulose, acrylic resin, and ultra-high molecular weight polyethylene.

[0012] In the seventh embodiment, in any of the fourth to sixth embodiments, the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the second electrode composite layer may be greater than the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the first electrode composite layer. With this configuration, the second electrode composite layer can maintain the mechanical strength of the electrode composite layer, while the first electrode composite layer can reduce the interfacial resistance between the current collector and the electrode composite layer.

[0013] In the eighth aspect, in the seventh aspect, the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the second electrode composite layer may be greater than three times the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the first electrode composite layer.

[0014] In the ninth embodiment, in the seventh or eighth embodiment, the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the first electrode composite layer may be 5% or less, and the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the second electrode composite layer may be 10% or more. With such a configuration, the interfacial resistance between the current collector and the electrode composite layer can be reduced while maintaining the mechanical strength of the electrode composite layer.

[0015] The technology disclosed herein is also embodied in a method for manufacturing electrodes for a battery. Specifically, in a tenth embodiment, the method for manufacturing electrodes for a battery comprises the steps of: preparing a first electrode mixture by mixing first active material particles with at least a first binder; preparing a first electrode mixture sheet by forming the first electrode mixture into a sheet; preparing a second electrode mixture by mixing second active material particles with at least a second binder; preparing a second electrode mixture paste in which the second binder is fibrillated by kneading the second electrode mixture; preparing a second electrode mixture sheet by forming the second electrode mixture paste into a sheet; and stacking the first electrode mixture sheet and the second electrode mixture sheet on a current collector. In the stacking step, the first electrode mixture sheet is directly stacked on the current collector.

[0016] According to the above manufacturing method, the degree to which the binder of the second electrode composite sheet is fibrillated can be made higher than the degree to which the binder of the first electrode composite sheet is fibrillated. Then, by stacking these electrode composite sheets on a current collector, the electrode of the first embodiment described above can be manufactured.

[0017] In the eleventh embodiment, in the tenth embodiment, the shear force applied to the second binder in the step of preparing the second electrode composite mixture may be greater than the shear force applied to the second binder in the step of preparing the second electrode composite mixture. With this configuration, by applying a relatively large shear force to the second binder in the preparation of the second electrode composite mixture, the degree of fibrillation of the second binder can be increased.

[0018] In the twelfth embodiment, in the step of preparing the second electrode mixture in the tenth or eleventh embodiment, the shear force applied to the second binder may be greater than the shear force applied to the first binder in the step of preparing the first electrode mixture. With this configuration, by applying a relatively large shear force to the second binder in the preparation of the second electrode mixture, the degree of fibrillation of the second binder can be increased.

[0019] In the thirteenth embodiment, in any of the tenth to twelfth embodiments, the first binder and the second binder may each contain a first binder material. In this case, the first binder material may be fibrillated in the process of preparing the second electrode mixture. With this configuration, the mechanical strength of the electrode mixture layer can be improved by fibrillating the first binder material of the second negative electrode mixture layer.

[0020] In the 14th embodiment, in any of the 10th to 13th embodiments, the step of stacking the materials may include the steps of manufacturing an electrode material sheet by integrating a first electrode material sheet and a second electrode material sheet, and integrating the current collector and the electrode material sheet so that the first electrode material sheet contacts the current collector. With this configuration, the current collector and the electrode material sheet can be integrated after manufacturing an electrode material sheet in which the first electrode material sheet and the second electrode material sheet are integrated.

[0021] In the fifteenth embodiment, the step of manufacturing the electrode composite sheet in the fourteenth embodiment may include a step of heating and pressurizing the overlapping first electrode composite sheet and the second electrode composite sheet to a predetermined temperature or higher. In this case, at least one of the first binder and the second binder may contain a second binder material whose melting temperature is lower than the predetermined temperature. With this configuration, the first electrode composite sheet and the second electrode composite sheet can be joined more firmly by the melting and solidification of the second binder material.

[0022] The technology disclosed herein is also embodied in electrodes of other batteries. Specifically, in a sixteenth embodiment, the electrode of a battery comprises a current collector and an electrode composite layer disposed on the current collector, comprising active material particles and a binder. The electrode composite layer includes a first electrode composite layer disposed directly on the current collector and a second electrode composite layer disposed directly or indirectly on the first electrode composite layer. The binder comprises at least a first binder material, and in at least the second electrode composite layer, the first binder material is fibrillated. The area ratio occupied by the first binder material in a magnified cross-sectional image of the second electrode composite layer is greater than the area ratio occupied by the first binder material in a magnified cross-sectional image of the first electrode composite layer.

[0023] In the above electrode, a first electrode composite layer and a second electrode composite layer are used as the electrode composite layer. The first electrode composite layer is directly placed on the current collector, and the second electrode composite layer is placed directly or indirectly on the first electrode composite layer. In a cross-sectional image of the second electrode composite layer viewed under magnification, the area ratio occupied by the first binder material is larger than the area ratio occupied by the first binder material in a cross-sectional image of the first electrode composite layer viewed under magnification. That is, the area ratio occupied by the first binder material in a cross-sectional image of the first electrode composite layer is smaller than the area ratio occupied by the first binder material in a cross-sectional image of the second electrode composite layer viewed under magnification. Therefore, the interfacial resistance between the current collector and the electrode composite layer can be reduced. In addition, the fibrillation of the binder in the second electrode composite layer improves the mechanical strength of the electrode composite layer.

[0024] A schematic diagram showing the configuration of the battery 100 in Example 1.

[0025] Enlarged view of section II in Figure 1.

[0026] Enlarged view of section III in Figure 2.

[0027] Enlarged view of section IV in Figure 3.

[0028] Enlarged view of section V in Figure 2.

[0029] Enlarged view of section VI in Figure 5.

[0030] The cross-sectional image obtained by magnifying the inside of the first negative electrode composite layer 16 shows the relationship between the area ratio occupied by the first binder material 20a and the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16.

[0031] This shows the relationship between the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 and the tensile strength of the negative electrode composite layer 14.

[0032] This shows the relationship between the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14, and the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16.

[0033] A flowchart illustrating the manufacturing method of the negative electrode 10.

[0034] A diagram illustrating the process of preparing a first negative electrode composite mixture 44 (or a second negative electrode composite mixture 52) by mixing a first binder material 42a (or a first binder material 50a) and a second binder material 42b (or a second binder material 50b) with negative electrode active material particles 40 (or negative electrode active material particles 48) using a mixer 200.

[0035] A diagram illustrating the process of producing a first negative electrode composite sheet 46 (or second negative electrode composite sheet 56) by forming a first negative electrode composite mixture 44 (or second negative electrode composite mixture kneaded 54) into a sheet using a press device 206.

[0036] A diagram illustrating the process of producing a second negative electrode mixture 54 in which the first binder material 50a is fibrillated by kneading the second negative electrode mixture 52 using a kneader 210.

[0037] A diagram for explaining the process of producing the negative electrode composite sheet 58 by integrating the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 using the pressing device 216.

[0038] A diagram for explaining the process of integrating the negative electrode current collector 12 and the negative electrode composite sheet 58 so that the first negative electrode composite sheet 46 contacts the negative electrode current collector 12 using the pressing device 222.

[0039] Shows the relationship between the heating temperature when integrating the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56, and the tensile strength of the negative electrode composite sheet 58 produced by being pressed at that heating temperature.

[0040] Shows the tensile strength of the negative electrode composite sheet 58 produced by integrating the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 using each of the roll pressing device and the flat pressing device.

[0041] A diagram schematically showing the configuration of the battery 300 of Example 2.

[0042] Hereinafter, representative and non-limiting specific examples of the present invention will be described in detail with reference to the drawings. This detailed description is merely intended to show those skilled in the art the details for implementing preferred examples of the present invention, and is not intended to limit the scope of the present invention. In addition, the additional features and inventions disclosed below can be used separately or together with other features and inventions in order to provide improved electrodes for batteries and their manufacturing methods.

[0043] Also, the combinations of features and steps disclosed in the following detailed description are not essential for implementing the present invention in the broadest sense, and are described only for the purpose of explaining representative specific examples of the present invention. Furthermore, the various features of the above and below representative specific examples, as well as the various features described in the independent and dependent claims, do not have to be combined as described in the specific examples here or in the order listed when providing additional and useful embodiments of the present invention.

[0044] All features described in this specification and / or the claims are intended to be disclosed separately and independently of each other, as limitations to the initial disclosure and the claimed subject matter, apart from the configuration of the features described in the examples and / or claims. Further, all descriptions of numerical ranges and groups or collections are made with the intention of disclosing intermediate configurations as limitations to the initial disclosure and the claimed subject matter.

[0045] (Example 1) Referring to the drawings, the negative electrode 10 of this example and the battery 100 in which it is employed will be described. The battery 100 is, for example, a lithium ion secondary battery. Although it will be described in detail later, the battery 100 in this example is a bipolar type lithium ion secondary battery. The battery 100 can be mounted on a vehicle, for example, and used as a power source for driving the vehicle wheels.

[0046] As shown in FIG. 1, the battery 100 includes a plurality of bipolar electrodes 102, a plurality of separators 104, a positive electrode side end electrode 110, and a negative electrode side end electrode 120. Each of the bipolar electrodes 102 is arranged parallel to the X-axis and the Y-axis. The plurality of bipolar electrodes 102 are stacked along the Z-axis direction. Here, the X-axis, the Y-axis, and the Z-axis are orthogonal to each other. Although not particularly limited, the battery 100 may further include a sealing body or the like arranged to surround the periphery of the battery 100 when the battery 100 is viewed in the stacking direction.

[0047] As shown in FIG. 1, the bipolar electrode 102 includes a negative electrode 10 and a positive electrode 30. The negative electrode 10 includes a negative electrode current collector 12 and a negative electrode composite material layer 14. The negative electrode current collector 12 is a conductive sheet. The negative electrode current collector 12 is, for example, a copper foil. The thickness dimension of the negative electrode current collector 12 is, for example, 5 μm or more and 50 μm or less. The negative electrode composite material layer 14 is arranged on the upper surface of the negative electrode current collector 12 (that is, the surface on the positive Z-axis side). The thickness dimension of the negative electrode 10 is, for example, 10 μm or more and 500 μm or less.

[0048] As shown in Figure 2, the negative electrode composite layer 14 comprises a first negative electrode composite layer 16 and a second negative electrode composite layer 22. The first negative electrode composite layer 16 is directly positioned on the upper surface of the negative electrode current collector 12 (i.e., the surface on the positive Z-axis side). The second negative electrode composite layer 22 is directly positioned on the upper surface of the first negative electrode composite layer 16 (i.e., the surface on the positive Z-axis side).

[0049] As shown in Figures 3 and 4, the first negative electrode composite layer 16 comprises negative electrode active material particles 18 and a binder 20. As shown in Figures 5 and 6, the second negative electrode composite layer 22 similarly comprises negative electrode active material particles 24 and a binder 26.

[0050] The negative electrode active material particles 18 and 24 include, for example, carbon materials such as graphite, hard carbon, and soft carbon, materials that form alloys with lithium such as silicon (Si), and lithium alloys of these materials (e.g., Li Ｘ Examples of materials include M, where M is C, Si, Sn, Sb, Al, Mg, Ti, Bi, Ge, Pb, or P, and X is a natural number. The negative electrode active material particles 18 and 24 may be composed of a single type of material or multiple types of materials. The average particle diameter of the negative electrode active material particles 18 and 24 is not particularly limited, but for example, it is 5 μm or more and 50 μm or less. The average particle diameter referred to here means the particle diameter at 50% of the cumulative value (D50) in the volume-based particle size distribution measured by laser diffraction and scattering.

[0051] Binders 20 and 26 bind the negative electrode active material particles 18 and 24 together. Binders 20 and 26 include first binder materials 20a and 26a and second binder materials 20b and 26b. The first binder materials 20a and 26a are materials that can be fibrillated by the application of shear force. Examples of the first binder materials 20a and 26a include polytetrafluoroethylene (PTFE), cellulose, acrylic resin, and ultra-high molecular weight polyethylene. In this embodiment, the first binder materials 20a and 26a are PTFE. The second binder materials 20b and 26b are materials that melt at a lower temperature than the first binder materials 20a and 26a. Examples of the second binder materials 20b and 26b include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF-HFP), and polyacrylic acid. In this embodiment, the second binder materials 20b and 26b are PVdF.

[0052] As shown in Figure 1, the positive electrode 30 comprises a positive electrode current collector 32 and a positive electrode composite layer 34. The positive electrode current collector 32 is a conductive sheet. For example, the positive electrode current collector 32 is aluminum foil. The thickness of the positive electrode current collector 32 is, for example, 5 μm or more and 50 μm or less. The positive electrode composite layer 34 is arranged on the lower surface of the positive electrode current collector 32 (i.e., the surface on the negative Z-axis side). The negative electrode current collector 12 is arranged on the upper surface of the positive electrode current collector 32 (i.e., the surface on the positive Z-axis side). The positive electrode current collector 32 is joined to the negative electrode current collector 12 by a bonding body. The thickness of the positive electrode 30 is, for example, 10 μm or more and 500 μm or less.

[0053] The separator 104 is positioned between the negative electrode 10 of one bipolar electrode 102 and the positive electrode 30 of another adjacent bipolar electrode 102. Therefore, the negative electrode 10 of one bipolar electrode 102 faces the positive electrode 30 of another adjacent bipolar electrode 102 on one side of the stacking direction (i.e., the positive Z-axis direction), with the separator 104 in between. The positive electrode 30 of one bipolar electrode 102 faces the negative electrode 10 of another adjacent bipolar electrode 102 on the other side of the stacking direction (i.e., the negative Z-axis direction), with the separator 104 in between. The separator 104 prevents short circuits between the negative electrode 10 and positive electrode 30 of adjacent bipolar electrodes 102 while allowing charge carriers such as lithium ions to pass through.

[0054] The positive electrode end electrode 110 comprises a positive electrode end current collector 112 and a positive electrode end composite layer 114. The positive electrode end current collector 112 is a conductive sheet. For example, the positive electrode end current collector 112 is aluminum foil. The thickness of the positive electrode end current collector 112 is, for example, 5 μm or more and 50 μm or less. The positive electrode end composite layer 114 is arranged on the lower surface of the positive electrode end current collector 112 (i.e., the surface on the negative Z-axis side). The positive electrode end composite layer 114 faces the negative electrode 10 of the bipolar electrode 102, with the separator 104 in between.

[0055] The negative electrode end electrode 120 comprises a negative electrode end current collector 122 and a negative electrode end composite layer 124. The negative electrode end current collector 122 is a conductive sheet. The negative electrode end current collector 122 is, for example, copper foil. The thickness of the negative electrode end current collector 122 is, for example, 5 μm or more and 50 μm or less. The negative electrode end composite layer 124 is arranged on the upper surface of the negative electrode end current collector 122 (i.e., the surface on the positive Z-axis side). The negative electrode end composite layer 124 faces the positive electrode 30 of the bipolar electrode 102, with the separator 104 in between.

[0056] In the battery 100 described above, for example, in the negative electrode composite layer 14, the higher the degree to which the binders 20 and 26 are fibrillated, the more of the surface of the negative electrode active material particles 18 and 24 is covered by the binders 20 and 26. Since the binders 20 and 26 are not conductive, the more the surface of the negative electrode active material particles 18 and 24 is covered by the binders 20 and 26, the greater the problem of increased interfacial resistance between the negative electrode current collector 12 and the negative electrode composite layer 14. In other words, increasing the degree to which the binders 20 and 26 are fibrillated improves the mechanical strength of the negative electrode composite layer 14, but there is a trade-off problem in that the electrical characteristics of the negative electrode decrease.

[0057] In relation to the above, in the battery 100 of this embodiment, as shown in Figures 5 and 6, the first binder material 26a in the second negative electrode composite layer 22 is fibrillated. On the other hand, as shown in Figures 3 and 4, the first binder material 20a in the first negative electrode composite layer 16 is not fibrillated. Thus, the degree to which the first binder material 26a in the second negative electrode composite layer 22 is fibrillated is higher than the degree to which the first binder material 20a in the first negative electrode composite layer 16 is fibrillated. With this configuration, the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 can be reduced. Furthermore, since the first binder material 26a in the second negative electrode composite layer 22 is fibrillated, the mechanical strength of the negative electrode composite layer 14 can be improved.

[0058] Whether or not the first binder materials 20a and 26a are fibrillated, and the degree of fibrillation, can be determined from magnified images acquired, for example, by a microscope or scanning electron microscope. For example, the degree of fibrillation of the first binder materials 20a and 26a can be quantified using the aspect ratio of the first binder materials 20a and 26a in the magnified image. Here, as shown in Figures 4 and 6, the aspect ratio of the first binder materials 20a and 26a is the ratio of the major axis lengths L2 and L4 of the first binder materials 20a and 26a to the minor axis lengths L1 and L3 of the first binder materials 20a and 26a. The minor axis lengths L1 and L3 and the major axis lengths L2 and L4 of the first binder materials 20a and 26a can be measured using magnified images acquired, for example, by a microscope or scanning electron microscope. Furthermore, the higher the average aspect ratio, the higher the degree to which the first binder materials 20a and 26a are fibrillated. On the other hand, when the average aspect ratio of the first binder materials 20a and 26a is, for example, 5 or less, the first binder materials 20a and 26a can be evaluated as not being fibrillated. In other words, in this specification, the first binder material is evaluated as being fibrillated when the average aspect ratio of the first binder material is greater than 5.

[0059] The degree to which the first binder materials 20a and 26a in each negative electrode composite layer 16 and 22 are fibrillated can also be quantified using the area ratio occupied by the first binder materials 20a and 26a in a cross-sectional image obtained by magnifying the inside of each negative electrode composite layer 16 and 22 (for example, Figures 3 and 5). This is because the higher the degree to which the first binder materials 20a and 26a are fibrillated, the larger the area ratio occupied by the first binder materials 20a and 26a in the cross-sectional image. Here, the area ratio occupied by the first binder material 20a in a cross-sectional image obtained by magnifying the inside of each negative electrode composite layer 16 and 22 means the average value of the area ratio occupied by the first binder material 20a in at least three different cross-sectional images obtained by magnifying the inside of each negative electrode composite layer 16 and 22. The cross-sectional images obtained by magnifying the inside of each negative electrode composite layer 16 and 22 can be acquired, for example, by a microscope, a scanning electron microscope, etc. The magnification ratio used when observing the inside of each negative electrode composite layer 16, 22 is set so that approximately 5 to 10 negative electrode active material particles 18, 24 can be observed on each side of the cross-sectional image.

[0060] The inventors of the present invention have found that, as shown in Figure 7, when the area ratio occupied by the first binder material 20a in a cross-sectional image obtained by magnifying the inside of the first negative electrode composite layer 16 exceeds 5%, the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 becomes relatively high. Therefore, from the viewpoint of reducing the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16, it is preferable that the area ratio occupied by the first binder material 20a in a cross-sectional image obtained by magnifying the inside of the first negative electrode composite layer 16 is 5% or less. Furthermore, from the viewpoint of improving the mechanical strength of the negative electrode composite layer 14, it is considered preferable that the area ratio occupied by the first binder material 20a in a cross-sectional image obtained by magnifying the inside of the second negative electrode composite layer 22 is 10% or more. The interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 can be measured, for example, using an electrode resistance measurement system (HIOKI RM2610).

[0061] Therefore, from the viewpoint of maintaining the mechanical strength of the negative electrode composite layer 14 while reducing the interfacial resistance between the negative electrode current collector 12 and the negative electrode composite layer 14, it is preferable that the area ratio occupied by the first binder material 26a in a magnified cross-sectional image of the second negative electrode composite layer 22 is greater than the area ratio occupied by the first binder material 20a in a magnified cross-sectional image of the first negative electrode composite layer 16. Furthermore, it is considered more preferable that the area ratio occupied by the first binder material 20a in a magnified cross-sectional image of the second negative electrode composite layer 22 is greater than three times the area ratio occupied by the first binder material 20a in a magnified cross-sectional image of the first negative electrode composite layer 16.

[0062] In addition, as shown in Figures 8 and 9, the inventors of the present invention measured the tensile strength of the negative electrode composite layer 14 and the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 was changed. Based on the above results, the area ratio occupied by the first binder material 20a in a magnified cross-sectional image of the inside of the first negative electrode composite layer 16 was set to 1.5%. Also, the area ratio occupied by the first binder material 26a in a magnified cross-sectional image of the inside of the second negative electrode composite layer 22 was set to 14.5%.

[0063] As shown in Figure 8, when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 is 0% (i.e., when the second negative electrode composite layer 22 is absent), the tensile strength of the negative electrode composite layer 14 is relatively low. In contrast, when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 is 10% or more, the tensile strength of the negative electrode composite layer 14 is significantly improved. Furthermore, when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 is 100% (i.e., when the first negative electrode composite layer 16 is absent), the tensile strength of the negative electrode composite layer 14 becomes very high.

[0064] As shown in Figure 9, when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 is 100% (i.e., when the first negative electrode composite layer 16 is absent), the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 is relatively high. In contrast, when the ratio of the thickness dimension of the second negative electrode composite layer 22 to the thickness dimension of the negative electrode composite layer 14 is 90% or less, the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 decreases significantly.

[0065] Based on these results, from the viewpoint of improving the tensile strength of the negative electrode composite layer 14 while reducing the interfacial resistance between the negative electrode current collector 12 and the negative electrode composite layer 14, it is preferable that the thickness dimension of the second negative electrode composite layer 22 be 10% or more and 90% or less of the thickness dimension of the negative electrode composite layer 14. Furthermore, it is preferable that the thickness dimension of the first negative electrode composite layer 16 be 10% or more and 90% or less of the thickness dimension of the negative electrode composite layer 14. In this way, by adjusting the thickness dimensions of the negative electrode composite layers 16 and 22 relative to the thickness dimension of the negative electrode composite layer 14, it is possible to reduce the interfacial resistance between the negative electrode current collector 12 and the negative electrode composite layer 14 while maintaining the mechanical strength of the negative electrode composite layer 14.

[0066] In the above-described embodiment, the binders 20 and 26 include first binder materials 20a and 26a. In this case, the first binder material 26a is fibrillated in the second negative electrode composite layer 22. With this configuration, the fibrillation of the first binder material 26a in the second negative electrode composite layer 22 improves the mechanical strength of the negative electrode composite layer 14.

[0067] In the above-described embodiment, the first binder material 20a in the first negative electrode composite layer 16 is not fibrillated. With this configuration, the interfacial resistance between the negative electrode current collector 12 and the negative electrode composite layer 14 can be reduced.

[0068] In the above-described embodiment, the first binder materials 20a and 26a include at least one selected from the group consisting of polytetrafluoroethylene cellulose, acrylic resin, and ultra-high molecular weight polyethylene.

[0069] Next, a method for manufacturing the negative electrode 10 will be described. In this manufacturing method, the negative electrode 10 can be produced without using a solvent. In other words, this manufacturing method is a so-called dry process.

[0070] As shown in Figure 10, the manufacturing method includes a step of producing a first negative electrode composite mixture 44 by mixing a binder 42 with negative electrode active material particles 40 (S10). In this step, as shown in Figure 11, for example, a mixer 200 is used. The mixer 200 mixes the negative electrode active material particles 40 and the binder 42 introduced into the container 204 by rotating the blade 202. The binder 42 includes a first binder material 42a and a second binder material 42b. In this specification, the negative electrode active material particles 40 and the binder 42 used to produce the first negative electrode composite mixture 44 may be referred to as the first negative electrode active material particles and the first binder, respectively.

[0071] As a specific example, in step S10 described above, graphite, PTFE (manufactured by Chemours), and PVdF (manufactured by Arkema) may be put into a mixer (manufactured by Nippon Coke Co., Ltd., MP5B), mixed at 300 rpm for 180 seconds, and then mixed at 3000 rpm for 8 minutes. Here, graphite is an example of negative electrode active material particles 40, PTFE is an example of the first binder material 42a, and PVdF is an example of the second binder material 42b. The weight ratio of graphite:PTFE:PVdF may be 94.5:3.0:2.5.

[0072] Thus, in this embodiment, the mixer 200 gradually increases the rotation speed of the blade 202, mixing the negative electrode active material particles 40 and the binder 42 at two different rotation speeds. However, the mixer 200 does not necessarily have to increase the rotation speed of the blade 202 in two stages. In other embodiments, the rotation speed of the blade 202 may be constant or increased in three or more stages. Also, in S10, the mixer 200 is not necessarily used. In other embodiments, other mixing devices such as blenders or mills may be used instead of the mixer 200.

[0073] As shown in Figure 10, the manufacturing method further includes a step of producing a first negative electrode composite sheet 46 by forming the first negative electrode composite mixture 44 into a sheet (S12). In this step, as shown in Figure 12, for example, a press device 206 is used. The press device 206 is equipped with a pair of rollers 208. The first negative electrode composite mixture 44 is formed into a sheet by being rolled by the pair of rollers 208 as it passes between them. As a specific example, in step S12, the first negative electrode composite mixture 44 may be rolled with a linear pressure of 0.4 t / cm using a roll press device (SA-602, manufactured by Tester Industries Co., Ltd.). This produces the first negative electrode composite sheet 46. The first negative electrode composite sheet 46 in this embodiment is a self-supporting electrode composite sheet. A self-supporting electrode composite sheet, as used here, means an electrode composite sheet that is supported by itself without requiring a support (for example, a current collector).

[0074] As shown in Figure 10, the manufacturing method further comprises a step of producing a second negative electrode composite mixture 52 by mixing a binder 50 with negative electrode active material particles 48 (S14). In this step, as shown in Figure 11, for example, a mixer 200 is used. The mixer 200 mixes the negative electrode active material particles 48 and the binder 50 introduced into the container 204 by rotating the blade 202. The binder 50 includes a first binder material 50a and a second binder material 50b. In this specification, the negative electrode active material particles 48 and the binder 50 used to produce the second negative electrode composite mixture 52 may be referred to as the first negative electrode active material particles and the first binder, respectively.

[0075] As a specific example, in step S14 described above, graphite, PTFE (manufactured by Chemours), and PVdF (manufactured by Arkema) may be put into a mixer (manufactured by Nippon Coke Co., Ltd., MP5B), mixed at 300 rpm for 180 seconds, and then mixed at 3000 rpm for 8 minutes. Here, graphite is an example of negative electrode active material particles 48, PTFE is an example of the first binder material 50a, and PVdF is an example of the second binder material 50b. The weight ratio of graphite:PTFE:PVdF may be 94.5:3.0:2.5. Thus, S14 can be carried out in the same manner as S10 described above.

[0076] As shown in Figure 10, the manufacturing method further includes a step of producing a second anode composite mixture 54 by kneading the second anode composite mixture 52 (S16). In this step, as shown in Figure 13, for example, a kneader 210 is used. The kneader 210 applies a shear force to the second anode composite mixture 52 that exists between the blade 212 and the wall surface 214a of the container 214 by rotating the blade 212. Since the first binder material 50a is a material that can be fibrillated, the first binder material 50a constituting the second anode composite mixture 52 is fibrillated by the application of a shear force to the first binder material 50a. This improves the mechanical strength of the anode composite sheet 58.

[0077] As a specific example, in step S16 described above, the second negative electrode mixture 52 may be put into a kneader (manufactured by Nippon Spindle Manufacturing Co., Ltd., DSI-5 type) and kneaded for 180 seconds at 100°C and 10 rpm. Note that the kneader 210 is not necessarily required to be used in S16. In other embodiments, other mixers such as blenders or mills may be used instead of the kneader 210. Note that, although not particularly limited, the process in S18 may be carried out with the container 214 of the kneader 210 heated to a predetermined temperature.

[0078] As shown in Figure 10, the manufacturing method further includes a step of producing a second negative electrode composite sheet 56 by forming the second negative electrode composite mixture 54 into a sheet (S18). In this step, as shown in Figure 12, for example, a press device 206 is used. The second negative electrode composite mixture 54 is formed into a sheet by being rolled by a pair of rollers 208 as it passes between them. Specifically, in step S18, the second negative electrode composite mixture 54 may be rolled by a roll press device (SA-602, manufactured by Tester Industries Co., Ltd.) at a linear pressure of 0.4 t / cm. This produces the second negative electrode composite sheet 56. Thus, S18 is performed in the same manner as S12 described above. The second negative electrode composite sheet 56 in this embodiment is a self-supporting electrode composite sheet.

[0079] As shown in Figure 10, the manufacturing method further includes a step of producing a negative electrode composite sheet 58 by integrating a first negative electrode composite sheet 46 and a second negative electrode composite sheet 56 (S20). This step includes a step of heating the stacked first negative electrode composite sheet 46 and second negative electrode composite sheet 56 to a predetermined temperature and applying pressure. In S20, as shown in Figure 14, for example, a press device 216 is used. The press device 216 comprises a stage 218 and an upper die 220. With the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 stacked in this order on the stage 218, the upper die 220 is lowered. At this time, since the stage 218 and / or the upper die 220 are heated, the stacked first negative electrode composite sheet 46 and second negative electrode composite sheet 56 are heated to a predetermined temperature and applied pressure. As a specific example, in this process S20, the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 are heated to 160°C by a flat plate press (manufactured by AS ONE, model H300-05) at a rate of 0.2 t / cm ２ It may be pressurized with surface pressure.

[0080] The second binder materials 42b and 50b (here, PVdF) are materials that melt at a lower temperature than the first binder materials 42a and 50a (here, PTFE). The predetermined temperature mentioned above is above the melting temperature of the second binder materials 42b and 50b, and below the melting temperature of the first binder materials 42a and 50a. Therefore, when the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 are heated above the predetermined temperature, the second binder materials 42b and 50b melt and solidify, allowing the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 to be joined together. At this time, the first binder materials 42a and 50a do not melt, and are therefore maintained in a fibrillated state.

[0081] As shown in Figure 10, the manufacturing method further includes a step of producing a negative electrode 10 by integrating a negative electrode composite sheet 58 with a negative electrode current collector 12 (S22). In this step, as shown in Figure 15, for example, a press device 216 is used. The press device 216 comprises a stage 218 and an upper die 220. First, the negative electrode current collector 12 and the negative electrode composite sheet 58 are stacked on the stage 218 in that order. At this time, the negative electrode composite sheet 58 is stacked on the negative electrode current collector 12 such that the first negative electrode composite sheet 46 is in contact with the negative electrode current collector 12. In this state, the negative electrode current collector 12 and the negative electrode composite sheet 58 are integrated by lowering the upper die 220 toward the stage 218.

[0082] The aforementioned negative electrode 10 is manufactured by the manufacturing method described above. Specifically, the negative electrode composite sheet 58 shown in Figure 15 becomes the negative electrode composite layer 14 shown in Figures 1 and 2. The binder 42 shown in Figure 11 becomes the binder 20 of the first negative electrode composite layer 16 shown in Figure 3. More specifically, the first binder material 42a shown in Figure 11 becomes the first binder material 20a of the first negative electrode composite layer 16 shown in Figures 3 and 4, and the second binder material 42b shown in Figure 11 becomes the second binder material 20b of the first negative electrode composite layer 16 shown in Figure 3. Similarly, the binder 50 shown in Figure 11 becomes the binder 26 of the second negative electrode composite layer 22 shown in Figure 5. More specifically, the first binder material 50a shown in Figure 11 becomes the first binder material 26a of the second negative electrode composite layer 22 shown in Figures 5 and 6, and the second binder material 50b shown in Figure 11 becomes the second binder material 26b of the second negative electrode composite layer 22 shown in Figure 5. The negative electrode active material particles 40 shown in Figure 11 become the negative electrode active material particles 18 of the first negative electrode composite layer 16 shown in Figures 3 and 4, and the negative electrode active material particles 48 shown in Figure 11 become the negative electrode active material particles 24 of the second negative electrode composite layer 22 shown in Figures 5 and 6.

[0083] In the negative electrode 10 manufactured by the above-described manufacturing method, the degree to which the first binder material 26a of the second negative electrode composite layer 22 is fibrillated is higher than the degree to which the first binder material 20a of the first negative electrode composite layer 16 is fibrillated. Therefore, the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 can be reduced while maintaining the mechanical strength of the negative electrode composite layer 14.

[0084] In the manufacturing method described above, the shear force applied to the first binder material 50a of the binder 50 in the step of producing the second anode composite mixture 54 (S16) is greater than the shear force applied to the first binder material 50a of the binder 50 in the step of producing the second anode composite mixture 52 (S14). With this configuration, by applying a relatively large shear force to the first binder material 50a of the binder 50 in the production of the second anode composite mixture 54, the degree of fibrillation of the first binder material 50a of the binder 50 can be increased.

[0085] As an example, in the manufacturing method described above, in the step of producing the second anode composite mixture 54 (S16), the shear force applied to the first binder material 50a of the binder 50 is greater than the shear force applied to the first binder material 42a of the binder 42 in the step of producing the first anode composite mixture 44 (S10). With this configuration, by applying a relatively large shear force to the first binder material 50a of the binder 50 in the production of the second anode composite mixture 54, the degree of fibrillation of the first binder material 50a of the binder 50 can be increased.

[0086] In the manufacturing method described above, the binders 42 and 50 include first binder materials 42a and 50a. In this case, in the step of preparing the second anode composite mixture 54 (S16), the first binder material 50a is fibrillated. With this configuration, the fibrillation of the first binder material 50a in the second anode composite layer 22 improves the mechanical strength of the anode composite layer 14.

[0087] The manufacturing method described above includes the steps of: (S20) manufacturing a negative electrode composite sheet 58 by integrating a first negative electrode composite sheet 46 and a second negative electrode composite sheet 56; and (S22) integrating the negative electrode current collector 12 and the negative electrode composite sheet 58 so that the first negative electrode composite sheet 46 is in contact with the negative electrode current collector 12. As a result, the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 are stacked on the negative electrode current collector 12. The specific procedure for stacking the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 on the negative electrode current collector 12 is not particularly limited. In another embodiment, the first negative electrode composite sheet 46 may be stacked on the negative electrode current collector 12, and then the second negative electrode composite sheet 56 may be stacked thereafter. As long as the first negative electrode composite sheet 46 is directly laminated on the negative electrode current collector 12, the specific procedure for laminating the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 on the negative electrode current collector 12 can be freely designed.

[0088] The inventors of the present invention investigated the effect of the heating temperature of the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 in step S20 on the tensile strength of the negative electrode composite sheet 58 produced. Specifically, in S20, the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 were heated and pressed with a linear pressure of 0.4 t / cm using a roll press device (SA-602, manufactured by Tester Sangyo Co., Ltd.) to produce the negative electrode composite sheet 56. At this time, the heating temperature of the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 was changed in four ways to produce four negative electrode composite sheets 56. Each negative electrode composite sheet 56 was punched out with a punching die to produce a 4 mm wide dogbone-shaped sample piece. The thickness of the sample piece was approximately 5.6 mm. The measurement was performed using a Shimadzu AGS-X, a 50N load cell, and a 50N clip-type gripping device, with a gripping distance of approximately 4.0 mm and an initial strain rate of 0.33 mm / s (tensile speed of 1.3 mm / s).

[0089] The melting temperature of the PVdF used as the second binder materials 42b and 50b is around 150°C. As shown in Figure 16, when the heating temperature of the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 exceeds the melting temperature of the second binder materials 42b and 50b, the tensile strength of the negative electrode composite sheet 58 is significantly higher. If the melting temperature of the second binder materials 42b and 50b is lower than the heating temperature of the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56, the second binder materials 42b and 50b melt when the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 are heated. Subsequently, the solidification of the molten second binder materials 42b and 50b allows for a stronger bond between the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56, which is thought to significantly increase the tensile strength of the negative electrode composite sheet 58.

[0090] Based on this finding, in the manufacturing method described above, the step (S20) for producing the negative electrode composite sheet 58 includes a step of heating and pressurizing the stacked first negative electrode composite sheet 46 and second negative electrode composite sheet 56 to a predetermined temperature or higher. In this case, the binders 42 and 50 include second binder materials 42b and 50b, which have a melting temperature lower than the predetermined temperature. However, it is not necessary for both binders 42 and 50 to contain the second binder materials 42b and 50b. In another embodiment, only binder 42 may contain the second binder material 42b. Or, in yet another embodiment, only binder 50 may contain the second binder material 50b.

[0091] Furthermore, the inventors of the present invention investigated the effect of the press device used in process S20 on the tensile strength of the negative electrode composite sheet 58. Specifically, in S20, a flat plate press device (manufactured by AS ONE, model H300-05) was used to heat the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 to 160°C while applying a pressure of 0.2 t / cm². ２ The negative electrode composite sheet 58 was prepared by applying pressure with the specified surface pressure. The preparation and measurement conditions for the sample pieces were the same as described above.

[0092] As shown in Figure 17, the tensile strength of the negative electrode composite sheet 58 produced using a flat plate press was higher than that of the negative electrode composite sheet 58 produced using a roll press. Therefore, in the process of heating and pressurizing the overlapping first negative electrode composite sheet 46 and second negative electrode composite sheet 56 to a predetermined temperature or higher, it can be said that using a flat plate press is more advantageous than using a roll press. This is because, with a flat plate press, heating and pressurizing can be applied over the entire contact area between the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56, thereby more firmly bonding the first negative electrode composite sheet 46 and the second negative electrode composite sheet 56 via the second binder materials 42b and 50b.

[0093] (Example 2) The battery 300 of Example 2 will be described with reference to Figure 18. In the following, components identical to those in Example 1 will be denoted by the same reference numerals, and redundant explanations will be omitted here.

[0094] The battery 300 comprises a negative electrode 310, a positive electrode 330, and a separator 104. In this embodiment, each of the negative electrode 310 and the positive electrode 330 is a monopolar electrode. That is, the battery 300 in this embodiment is a monopolar lithium-ion secondary battery. The negative electrode 310 comprises a negative electrode current collector 12 and a negative electrode composite layer 14. The positive electrode 330 comprises a positive electrode current collector 32 and a positive electrode composite layer 34. The positive electrode current collector 32, positive electrode composite layer 34, separator 104, negative electrode composite layer 14, and negative electrode current collector 12 are stacked in this order from the negative Z-axis direction toward the positive Z-axis direction.

[0095] In the battery 300 of this embodiment, the negative electrode composite layer 14 has the same structure as the negative electrode composite layer 14 of Embodiment 1 shown in Figures 2-6. That is, the negative electrode composite layer 14 in this embodiment comprises a first negative electrode composite layer 16 and a second negative electrode composite layer 22. The first negative electrode composite layer 16 is directly disposed on the negative electrode current collector 12, and the second negative electrode composite layer 22 is directly disposed on the first negative electrode composite layer 16. Furthermore, the degree to which the first binder material 26a of the second negative electrode composite layer 22 is fibrillated is higher than the degree to which the first binder material 20a of the first negative electrode composite layer 16 is fibrillated. As a result, the interfacial resistance between the negative electrode current collector 12 and the first negative electrode composite layer 16 can be reduced. Furthermore, in the second negative electrode composite layer 22, the first binder material 26a is fibrillated, which improves the mechanical strength of the negative electrode composite layer 14.

[0096] In the above-described Examples 1 and 2, the technology was explained using the negative electrodes 10 and 310 of batteries 100 and 300 as examples. However, the technology disclosed herein is not necessarily limited to the negative electrodes 10 and 310 of batteries 100 and 300, but can also be applied to the positive electrodes 30 and 330 of batteries 100 and 300. Furthermore, the technology is not limited to lithium-ion secondary batteries, but can be similarly applied to electrodes (positive or negative) of any type of secondary battery, or to electrodes (positive or negative) of all-solid-state batteries.

[0097] In the above-described embodiments 1 and 2, the second negative electrode composite layer 22 is directly disposed on the first negative electrode composite layer 16. However, in another embodiment, the second negative electrode composite layer 22 may be indirectly disposed on the first negative electrode composite layer 16. In this case, for example, the negative electrode composite layer 14 further comprises a third negative electrode composite layer, and the second negative electrode composite layer may be disposed between the first negative electrode composite layer 16 and the second negative electrode composite layer 22.

[0098] In the above-described embodiments 1 and 2, binders 20 and 26 include first binder materials 20a and 26a and second binder materials 20b and 26b. However, it is not necessarily required that both binders 20 and 26 include both first binder materials 20a and 26a and second binder materials 20b and 26b. For example, binder 26 may include first binder material 26a and second binder material 26b, while binder 20 may include only second binder material 20b. In this case, the first negative electrode composite sheet 46 does not need to be a self-supporting film. Thus, binders 20 and 26 may include a single type of binder material.

[0099] As described above, the degree to which the first binder materials 20a and 26a in each negative electrode composite layer 16 and 22 are fibrillated can be quantified using the area ratio occupied by the first binder materials 20a and 26a in a cross-sectional image obtained by magnifying the inside of each negative electrode composite layer 16 and 22 (for example, Figures 3 and 5). Therefore, in the above-described examples 1 and 2, when the area ratio occupied by the first binder material 26a in a cross-sectional image obtained by magnifying the inside of the second negative electrode composite layer 22 is greater than the area ratio occupied by the first binder material 20a in a cross-sectional image obtained by magnifying the inside of the first negative electrode composite layer 16, it can be determined that the degree to which the first binder material 26a in the second negative electrode composite layer 22 is fibrillated is higher than the degree to which the first binder material 20a in the first negative electrode composite layer 16 is fibrillated.

Claims

1. An electrode for a battery, comprising: a current collector; and an electrode composite layer disposed on the current collector and containing active material particles and a binder, wherein the electrode composite layer includes a first electrode composite layer directly disposed on the current collector and a second electrode composite layer directly or indirectly disposed on the first electrode composite layer, wherein at least a portion of the binder in the second electrode composite layer is fibrillated, and the degree to which the binder in the second electrode composite layer is fibrillated is higher than the degree to which the binder in the first electrode composite layer is fibrillated.

2. The electrode according to claim 1, wherein the thickness dimension of the first electrode composite layer is 10% or more and 90% or less of the thickness dimension of the electrode composite layer.

3. The electrode according to claim 1 or 2, wherein the thickness dimension of the second electrode composite layer is 10% or more and 90% or less of the thickness dimension of the electrode composite layer.

4. The electrode according to any one of claims 1 to 3, wherein the binder comprises at least a first binder material, and in at least the second electrode composite layer, the first binder material is fibrillated.

5. The electrode according to claim 4, wherein the first binder material in the first electrode composite layer is not fibrillated.

6. The electrode according to claim 4 or 5, wherein the first binder material comprises at least one selected from the group consisting of polytetrafluoroethylene, cellulose, acrylic resin, and ultra-high molecular weight polyethylene.

7. The electrode according to any one of claims 4 to 6, wherein the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the second electrode composite layer is greater than the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the first electrode composite layer.

8. The electrode according to claim 7, wherein the area ratio occupied by the first binder material in the cross-sectional image obtained by magnifying the inside of the second electrode composite layer is greater than three times the area ratio occupied by the first binder material in the cross-sectional image obtained by magnifying the inside of the first electrode composite layer.

9. The electrode according to claim 7 or 8, wherein in the cross-sectional image obtained by magnifying the first electrode composite layer, the area ratio occupied by the first binder material is 5% or less, and in the cross-sectional image obtained by magnifying the second electrode composite layer, the area ratio occupied by the first binder material is 10% or more.

10. A method for manufacturing electrodes for a battery, comprising: a step of preparing a first electrode composite mixture by mixing first active material particles with at least a first binder; a step of preparing a first electrode composite sheet by forming the first electrode composite mixture into a sheet; a step of preparing a second electrode composite mixture by mixing second active material particles with at least a second binder; a step of preparing a second electrode composite mixture by kneading the second electrode composite mixture to prepare a second electrode composite mixture in which the second binder is fibrillated; a step of preparing a second electrode composite sheet by forming the second electrode composite mixture into a sheet; and a step of laminating the first electrode composite sheet and the second electrode composite sheet onto a current collector, wherein in the laminating step, the first electrode composite sheet is directly laminated onto the current collector.

11. The manufacturing method according to claim 10, wherein in the step of preparing the second electrode composite mixture, the shear force applied to the second binder is greater than the shear force applied to the second binder in the step of preparing the second electrode composite mixture.

12. The manufacturing method according to claim 11, wherein in the step of preparing the second electrode mixture, the shear force applied to the second binder is greater than the shear force applied to the first binder in the step of preparing the first electrode mixture.

13. The manufacturing method according to any one of claims 10 to 12, wherein each of the first binder and the second binder comprises a first binder material, and in the step of producing the second electrode mixture kneaded product, the first binder material is fibrillated.

14. The manufacturing method according to any one of claims 10 to 13, wherein the step of stacking and arranging comprises the steps of: manufacturing an electrode composite sheet by integrating the first electrode composite sheet and the second electrode composite sheet; and integrating the current collector and the electrode composite sheet so that the first electrode composite sheet contacts the current collector.

15. The manufacturing method according to claim 14, wherein the step of producing the electrode composite sheet includes a step of pressurizing the stacked first electrode composite sheet and the second electrode composite sheet while heating them to a predetermined temperature or higher, and at least one of the first binder and the second binder contains a second binder material having a melting temperature lower than the predetermined temperature.

16. An electrode for a battery, comprising: a current collector; and an electrode composite layer disposed on the current collector and containing active material particles and a binder, wherein the electrode composite layer includes a first electrode composite layer directly disposed on the current collector and a second electrode composite layer directly or indirectly disposed on the first electrode composite layer, the binder includes at least a first binder material, and at least in the second electrode composite layer, the first binder material is fibrillated, and the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the second electrode composite layer is greater than the area ratio occupied by the first binder material in a cross-sectional image obtained by magnifying the inside of the first electrode composite layer.

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