Electrode and method for manufacturing electrode

Abstract

Provided is an electrode with which tensile strength is improved by improving PTFE in-plane dispersibility. An electrode according to one embodiment of the present disclosure comprises: a core material; and an electrode combined material that is layered onto surfaces of the core material. The electrode combined material comprises an active substance and PTFE. In an image illustrating a composition distribution obtained upon measuring a surface of the electrode combined material using energy dispersion-type X-ray analysis, the standard deviation of the area ratio of PTFE in 30 adjacent sections having a size of 150 μｍ × 133 μｍ is 6% or less. When the electrode combined material is divided into three equal parts in the thickness direction to create, from the core material side, a first region, a second region, and a third region, the content (a) of PTFE in the first region, the content (b) of PTFE in the second region, and the content (c) of PTFE in the third region satisfy (c-a) / (a+b+c)≦±10%.

Description

[Technical Field]

[0001] The present disclosure relates to electrodes and methods for manufacturing electrodes. [Background technology]

[0002] Electrodes for nonaqueous electrolyte secondary batteries such as lithium-ion batteries are generally produced by a wet method in which an electrode mixture slurry containing an active material, a binder, and the like is applied to the surface of a metal foil core material, and the resulting coating is then dried and compressed. This method presents a problem of the tendency for the binder to migrate during drying. When binder migration occurs, the amount of binder is greater on the surface side of the coating film (electrode mixture layer) than on the core material side, resulting in a bias in the distribution of the binder in the thickness direction of the electrode mixture layer.

[0003] In recent years, a dry method has been investigated in which an electrode mixture is stretched and formed into a sheet to produce an electrode mixture sheet, and the sheet is then attached to a core material to produce an electrode. Patent Document 1 discloses an electrode film (electrode mixture) produced by mixing an active material, a fibrillating binder such as polytetrafluoroethylene (PTFE), and a conductive material using a mill, and then treating the mixture under high pressure and large shearing force for a long period of time to fibrillate the PTFE. The content of fibrillated PTFE in the electrode mixture is described as 5% to 7% by weight. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-512872 Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of research by the present inventors, it was found that, as disclosed in Patent Document 1, when the PTFE content is relatively high and a large shear force is applied to the electrode composite for a long period of time, the conductive material adheres to the PTFE rather than to the active material, and the PTFE aggregates, making it impossible to uniformly disperse the PTFE even when the electrode composite is stretched and shaped into a sheet. Poor in-plane dispersion of PTFE can reduce the tensile strength of the electrode composite. The technology disclosed in Patent Document 1 does not consider how to prevent a decrease in the tensile strength of the electrode composite, and there is still room for improvement.

[0006] Therefore, an object of the present disclosure is to provide an electrode having improved tensile strength by improving the in-plane dispersion of PTFE. [Means for solving the problem]

[0007] An electrode according to one embodiment of the present disclosure comprises a core material and an electrode composite laminated on the surface of the core material, the electrode composite comprising an active material and PTFE, and in an image showing the composition distribution obtained when the surface of the electrode composite is measured using energy dispersive X-ray analysis, the standard deviation of the area ratio of PTFE in 30 adjacent sections of 150 μm × 133 μm in size is 6% or less, and when the electrode composite is divided into three equal parts in the thickness direction into a first region, a second region, and a third region from the core material side, the PTFE content (a) in the first region, the PTFE content (b) in the second region, and the PTFE content (c) in the third region satisfy (ca) / (a+b+c)≦±10%.

[0008] A method for manufacturing an electrode according to one embodiment of the present disclosure is characterized by including a mixing step of mixing an active material, a conductive material, and PTFE to produce electrode composite particles having a solid content of substantially 100%, a stretching step of passing the electrode composite particles between rolls two or more times to mix and stretch them to produce an electrode composite sheet, and a laminating step of laminating the electrode composite sheet to a core material to produce an electrode. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, the tensile strength of an electrode can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of an electrode according to an embodiment. [Figure 2] FIG. 1A is a diagram showing a mixing step, and FIG. 1B is a diagram showing a stretching step in a manufacturing process of an electrode that is one example of an embodiment. [Figure 3] 1A to 1C are diagrams illustrating a bonding step in a manufacturing process of an electrode according to an embodiment.

[0011] Hereinafter, embodiments of an electrode and an electrode manufacturing method according to the present disclosure will be described in detail. The embodiments described below are merely examples, and the present disclosure is not limited to the following embodiments. Furthermore, the drawings referred to in the description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings should be determined in consideration of the following description.

[0012] [electrode] The electrode according to the present disclosure is suitable for non-aqueous electrolyte secondary batteries such as lithium ion batteries, but can also be applied to batteries containing aqueous electrolytes or power storage devices such as capacitors. The following description will be given taking as an example an electrode for a non-aqueous electrolyte secondary battery (particularly when applied to a positive electrode).

[0013] FIG. 1 is a cross-sectional view of an electrode according to an embodiment. Electrode 10 includes a core material 11 and an electrode composite material 12 laminated on the surface of the core material. As shown in FIG. 1, electrode 10 may include electrode composite material 12 on both sides of core material 11. Electrode 10 may be a long electrode constituting a wound electrode body, or a rectangular electrode constituting a laminated electrode body. Electrode 10 may be used as the positive electrode, the negative electrode, or both of a nonaqueous electrolyte secondary battery.

[0014] The core material 11 may be a metal foil or a film with a metal layer formed on its surface. The thickness of the core material 11 is, for example, 5 μm to 20 μm. In the case of a positive electrode, the core material 11 may be a metal foil containing aluminum as its main component. In the case of a negative electrode, the core material 11 may be a metal foil containing copper as its main component. In this specification, the term "main component" refers to the component with the highest mass ratio. The core material 11 may be an aluminum foil that is substantially 100% aluminum, or a copper foil that is substantially 100% copper.

[0015] The electrode mixture 12 contains an active material and polytetrafluoroethylene (PTFE). The thickness of the electrode mixture 12 is, for example, 30 μm to 120 μm, and preferably 50 μm to 100 μm. The electrode mixture 12 may contain a conductive material. Examples of the conductive material contained in the electrode mixture 12 include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), and graphite. The particle diameter of the conductive material is, for example, 0.01 μm to 0.1 μm. This allows the conductive material to penetrate and adhere to recesses on the surface of the positive electrode active material. The content of the conductive material in the electrode mixture 12 can be, for example, 0.5% by mass to 5.0% by mass.

[0016] Lithium transition metal composite oxides are generally used for the positive electrode active material (positive electrode active material). Metal elements contained in the lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, at least one of Ni, Co, and Mn is preferably contained. Carbon-based active materials, such as natural graphite (e.g., flake graphite, lump graphite, and amorphous graphite), and artificial graphite (e.g., massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB)), are used for the negative electrode active material. Alternatively, Si-based active materials that can be alloyed with lithium may be used for the negative electrode active material. The active material is the main component of the electrode mixture 12, and the content of the active material in the electrode mixture 12 is preferably 85% to 99% by mass, and more preferably 90% to 99% by mass.

[0017] The positive electrode active material is, for example, a secondary particle formed by the aggregation of multiple primary particles. This creates irregularities on the surface of the positive electrode active material, allowing the conductive material to penetrate and adhere to the recesses of these irregularities as described above. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The positive electrode active material is a particle having a volume-based median diameter (D50) of, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and more preferably 7 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also referred to as the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrack-Bell Corporation) using water as a dispersion medium.

[0018] The PTFE is a dry powder, not a powder dispersed in a dispersion such as water. This allows the electrode mixture to be produced by a dry process described below. The electrode mixture 12 may contain, in addition to PTFE, a binder such as polyvinylidene fluoride (PVdF) that does not fibrillate. The electrode mixture 12 may also contain a fibrillating binder other than PTFE, as long as it does not impair the objectives of the present disclosure.

[0019] The PTFE content in the electrode mixture 12 is preferably 0.05% by mass to 5% by mass, and more preferably 1% by mass to 3% by mass. This range is preferable from the viewpoint of improving battery characteristics, since it prevents the conductive material from adhering to the PTFE and allows a large amount of conductive material to be present on the surface of the active material. The PTFE adheres to the particle surfaces of the active material and is entangled with the active material. In other words, the active material is held in place by the PTFE present in a network.

[0020] PTFE includes fibrillated (fiberized) PTFE fibers. The PTFE fibers are formed by fibrillating a PTFE raw material (PTFE particles) belonging to a fibrillable fine powder through a mixing step described below. The median diameter of the PTFE fibers is preferably 2 μm to 20 μm. The median diameter of the PTFE fibers can be measured with a particle size distribution analyzer. A median diameter of the PTFE fibers of 2 μm to 20 μm means that the PTFE fibers are finely divided into PTFE particles.

[0021] As described above, most PTFE particles are fibrillated to form PTFE fibers, but PTFE may also contain PTFE particles that remain unfibrillated. The PTFE particles may be secondary particles. The average particle size of the PTFE particles is, for example, 100 μm to 700 μm, preferably 100 μm to 500 μm, and more preferably 100 μm to 400 μm. The average particle size of the PTFE particles can be determined by observing the particles of the PTFE raw material with an SEM. Specifically, the external shapes of 100 randomly selected particles are identified, and the major axis (longest diameter) of each of the 100 particles is determined, and the average value thereof is taken as the average particle size of the PTFE particles.

[0022] In an image showing the composition distribution obtained by measuring the surface of the electrode composite 12 using energy dispersive X-ray analysis (EDS), the standard deviation of the PTFE area ratio in 30 adjacent sections measuring 150 μm × 133 μm is 6% or less, preferably 5% or less, and more preferably 4% or less. If the standard deviation of the PTFE area ratio is 6% or less, the tensile strength can be improved due to the good in-plane dispersion of PTFE. The lower limit of the standard deviation of the PTFE area ratio is, for example, 1%.

[0023] In 30 adjacent sections each having a size of 150 μm × 133 μm, the area ratio of PTFE preferably has a maximum value of 23% or less and a minimum value of 0.1% or more. The maximum value is more preferably 21% or less, and particularly preferably 16% or less. The minimum value is more preferably 1% or more, and particularly preferably 3% or more.

[0024] The 30 adjacent sections each having a size of 150 μm × 133 μm may be, for example, a configuration in which two sections each having a size of 150 μm in length and 133 μm in width are arranged in the vertical direction and 15 sections are arranged in the horizontal direction. For example, by analyzing a field of view having a size of 300 μm in length and 399 μm in width at once with EDS, and performing the same EDS analysis on five adjacent fields in the horizontal direction, and dividing one field into two sections in the vertical direction and three sections in the horizontal direction, 30 sections each having a size of 150 μm × 133 μm may be formed. When analyzing five fields of view, there may be a mutually overlapping portion in two adjacent fields of view.

[0025] The area ratio of PTFE in each section can be calculated, for example, as follows.

[0026] <Method for Calculating Area Ratio of PTFE> (1) Using EDS, obtain a mapping image in which regions where carbon elements are present (C regions) and regions where fluorine elements are present (F regions) are mapped. Adjust the magnification of EDS so that the image has a size of 300 μm in length and 399 μm in width. (2) Import the mapping image into a computer, and using image analysis software (for example, ImageJ manufactured by the National Institutes of Health, USA), obtain a composite image in which the overlapping portion between the C region and the F region is defined as the region where PTFE is present (PTFE region). (3) Using the image analysis software, perform binarization processing on the composite image to obtain a binarized processed image in which the PTFE region in the image is colored green and the other regions (blank regions) are colored black. (4) Divide the binarized image vertically into two sections and horizontally into three sections to create six sections, and calculate the area of ​​the PTFE region and the area of ​​the blank region for each section. (5) The area ratio of PTFE in each section can be calculated based on the following formula. PTFE area ratio = PTFE area / (PTFE area + blank area) x 100

[0027] When the electrode mixture 12 is divided into three equal parts in the thickness direction, namely, a first region, a second region, and a third region from the core material 11 side, the PTFE content (a) in the first region, the PTFE content (b) in the second region, and the PTFE content (c) in the third region preferably satisfy (ca) / (a+b+c)≦±10%, and more preferably satisfy (ca) / (a+b+c)≦±5%. This allows the PTFE to be distributed substantially uniformly throughout the electrode mixture 12, even in the thickness direction, without being distributed unevenly in only a portion of the electrode mixture 12. By using a dry process described below, the PTFE can be distributed substantially uniformly throughout the electrode mixture 12.

[0028] The electrode 10 may further include an adhesive layer between the core material 11 and the electrode mixture 12, which has the function of adhering the core material 11 and the electrode mixture 12 together. The thickness of the adhesive layer is, for example, 1 μm to 10 μm. The adhesive layer may contain a conductive material and a binder, and may be conductive due to the conductive material. Examples of the conductive material contained in the adhesive layer include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotubes (CNT), and graphite. The conductive material preferably has a small particle diameter and a large specific surface area. This makes it easier for the adhesive layer to form a structure. The specific surface area of ​​the conductive material is, for example, 100 m 2 / g~150m 2 / g range. Examples of binders contained in the adhesive layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. PVdF is preferred as the binder contained in the adhesive layer. The adhesive layer can be produced, for example, by applying a slurry containing a conductive material, a binder, and the like to the surface of the core material 11, drying the coating, and then compressing it. The adhesive layer can also be produced on the surface of the core material 11 by dip coating or spray coating.

[0029] The content of the conductive material in the adhesive layer is preferably 40% by mass to 80% by mass, more preferably 45% by mass to 75% by mass, and particularly preferably 50% by mass to 71% by mass. By making the content of the conductive material in the adhesive layer relatively large in this way, it is possible to reduce the interfacial resistance. If the amount of conductive material is too large, the strength of the adhesive layer itself decreases and the layer structure becomes brittle, which inhibits conductivity between the electrode mixture 12 and the core material 11.

[0030] [Electrode manufacturing method] The method for manufacturing the electrode 10 will be described in more detail below. While the method for manufacturing a positive electrode will be exemplified below, this method can also be applied to the manufacture of a negative electrode. In the case of a negative electrode, a negative electrode active material is used instead of a positive electrode active material.

[0031] 2 and 3 are diagrams schematically illustrating the manufacturing process of an electrode 10, which is an example of an embodiment. The manufacturing method of the electrode 10 includes a mixing step shown in FIG. 2(a), a stretching step shown in FIG. 2(b), and a laminating step shown in FIG. 3. In the mixing step, an active material and PTFE are mixed to prepare electrode mixture particles 12a having a solid content concentration of substantially 100%. In the stretching step, the electrode mixture particles 12a are kneaded and stretched to form a sheet, thereby preparing an electrode mixture sheet 12b. In the laminating step, the electrode mixture sheet 12b is laminated to a core material 11 to produce an electrode.

[0032] The method for manufacturing electrode 10 is a dry process for manufacturing electrode 10 using electrode mixture 12 having a solid content concentration of substantially 100%. The dry process is a process in which active material particles and binder particles are mixed without using a solvent, that is, the active material and binder are mixed in a state in which the solid content concentration of the active material and binder is substantially 100%. The method for manufacturing electrode 10 according to the present disclosure does not require the use of a solvent as in conventional methods for manufacturing electrode 10. Not requiring the use of a solvent not only means that a solvent is not required as a raw material, but also means that a solvent drying process is not required, and exhaust equipment and the like related to the drying process are also not required.

[0033] In the mixing step, raw materials such as the active material, PTFE, and conductive material are mixed in a mixer 20 to produce electrode mixture particles 12a. The mixer 20 can be, for example, a conventional mechanical agitator mixer. Specific examples of suitable mixers 20 include devices capable of applying mechanical shearing force, such as cutter mills, pin mills, bead mills, microparticle compositers (devices in which shearing force is generated between a specially shaped rotor rotating at high speed inside a tank and an impact plate), granulators, and kneaders such as twin-screw extrusion mixers and planetary mixers. Cutter mills, microparticle compositers, granulators, and twin-screw extrusion mixers are preferred. This allows PTFE to be fibrillated while the raw materials are being mixed. The processing time for the mixing step (the time during which shearing force is applied to the materials) is preferably within a few minutes, for example, 0.5 to 10 minutes. If the processing time is too long, the amount of conductive material incorporated into PTFE increases. This adversely affects battery characteristics, such as a significant decrease in the conductivity of the electrode mixture sheet and an increase in resistance.

[0034] The mixing step may include a step of mixing an active material with a conductive material to prepare a coated active material, and a step of mixing the coated active material with PTFE. Using a coated active material prepared by mixing an active material with a conductive material can shorten the time required to mix the coated active material with PTFE. This reduces the amount of conductive material incorporated into PTFE. It is preferable that the surface of the coated active material has irregularities, and the conductive material penetrates and adheres to the recesses in the irregularities. This makes it difficult for the conductive material on the surface of the coated active material to be absorbed by PTFE during the mixing process of the coated active material and PTFE.

[0035] Mechanofusion, for example, may be used as a method for dry-mixing the active material and conductive material. Mechanofusion is a dry processing method carried out in a mechanofusion reactor, which has a cylindrical chamber equipped with a compression tool and rotates at high speed. The conductive material and active material are placed in the chamber, and by rotating the chamber, the particles are pressed against each other and against the chamber wall. The use of a compression tool and the generation of centrifugal force by high-speed rotation promotes adhesion and bonding between the conductive material and the active material. Examples of mechanofusion reactors include the "Nobilta" (registered trademark) or "Mechanofusion" (registered trademark) pulverizers manufactured by Hosokawa Micron Corporation (Japan), the "Hybridizer" (trademark) pulverizer manufactured by Nara Machinery Works, Ltd., the "Balance Gran" manufactured by Freund-Turbo Corporation, and the "COMPOSI" manufactured by Nippon Coke & Engineering Co., Ltd.

[0036] Next, in the stretching step, as shown in FIG. 2(b), the electrode mixture particles 12a are kneaded and stretched using a pair of rolls 22 to form a sheet. The pair of rolls 22 are arranged with a predetermined gap between them and rotate in the same direction. The electrode mixture particles 12a are supplied to the gap between the pair of rolls 22, whereby they are compressed by the pair of rolls 22 and stretched into a sheet. The linear pressure applied by the pair of rolls 22 is, for example, 1 t / cm to 3 t / cm. The pair of rolls 22 have, for example, the same roll diameter. The temperature of the pair of rolls 22 is not particularly limited and may be, for example, room temperature or higher.

[0037] The obtained electrode mixture sheet 12b is passed again between the pair of rolls 22, whereby the PTFE is loosened and dispersed. In other words, by passing the electrode mixture particles 12a between the pair of rolls 22 two or more times, the in-plane dispersibility of the PTFE is improved. The number of times that the electrode mixture particles 12a and the electrode mixture sheet 12b formed from the electrode mixture particles 12a are passed between the pair of rolls 22 is preferably 2 to 50 times, more preferably 3 to 40 times, and particularly preferably 5 to 20 times. The stretching step is not limited to a method using only one pair of rolls, and may include a step of stretching using another pair of rolls having a different roll diameter, peripheral speed, gap, etc.

[0038] The thickness of the electrode mixture sheet 12b obtained after the stretching step can be controlled by, for example, the gap between the pair of rolls 22, the peripheral speed, the number of stretching treatments, etc. In the stretching step, it is preferable to form the electrode mixture particles 12a into a sheet using a pair of rolls 22 whose peripheral speed ratio differs by at least two times. By making the peripheral speed ratio of the pair of rolls 22 different, for example, it becomes easier to make the electrode mixture sheet 12b thinner, improving productivity. The active material density of the electrode mixture sheet 12b is, for example, 3.6 g / cm 3 ~4.0g / cm 3 be.

[0039] Next, in the bonding step, as shown in FIG. 3, the electrode mixture sheet 12b is bonded to the core material 11, thereby obtaining an electrode 10 in which a mixture layer made of the electrode mixture 12 is provided on the surface of the core material 11. Although FIG. 3 shows a state in which the electrode mixture 12 is bonded to only one surface of the core material 11, it is preferable that the electrode mixture 12 is bonded to both surfaces of the core material 11. Two sheets of the electrode mixture 12 may be bonded to both surfaces of the core material 11 simultaneously, or one sheet may be bonded to one surface of the core material 11 and then the other sheet may be bonded to the other surface. Alternatively, the electrode mixture sheet 12b may be bonded to the core material 11 via an adhesive layer.

[0040] In the laminating step, the electrode mixture sheet 12b is laminated onto the surface of the core material 11 using a pair of rolls 24. The pair of rolls 24, for example, have the same roll diameter, are arranged with a predetermined gap between them, and rotate in the same direction at the same peripheral speed. The temperature of the pair of rolls 24 is, for example, 25°C to 300°C. The linear pressure applied by the pair of rolls 24 is preferably 0.1 t / cm to 5 t / cm, and more preferably 0.2 t / cm to 3 t / cm. [Example]

[0041] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0042] Example 1 [Preparation of positive electrode composite particles (mixing step)] A lithium transition metal composite oxide, acetylene black (AB), and PTFE particles were charged into a mixer (Osaka Chemical, Wonder Crusher) in a mass ratio of 100:1:2 and mixed for 5 minutes at room temperature at a rotation speed of 3. The rotation speed of the Wonder Crusher was 28,000 rpm, the maximum rotation speed at 10. This mixing process yielded positive electrode composite particles in which the positive electrode active material and PTFE were uniformly dispersed. The resulting positive electrode composite had a solids concentration of 100%.

[0043] [Preparation of positive electrode composite sheet (stretching step)] The resulting positive electrode composite particles were passed through a pair of rolls five times to be kneaded and stretched to produce a positive electrode composite sheet. The peripheral speed ratio of the rolls was set to 1:3, and the thickness of the positive electrode composite sheet was adjusted to approximately 100 μm.

[0044] [Measurement of tensile strength] The tensile strength of the positive electrode composite sheet was evaluated using a universal testing machine (SDMK-1000-D) (20 mm / min). The test piece was 12.5 mm wide and 122 mm long.

[0045] <Example 2> A positive electrode mixture sheet was produced and evaluated in the same manner as in Example 1, except that the number of times the positive electrode mixture particles were passed between the pair of rolls was set to 10 times.

[0046] Example 3 A positive electrode mixture sheet was produced and evaluated in the same manner as in Example 1, except that the number of times the positive electrode mixture particles were passed between the pair of rolls was set to 20 times.

[0047] <Comparative Example> A positive electrode mixture sheet was produced and evaluated in the same manner as in Example 1, except that the positive electrode mixture particles were passed between the pair of rolls once.

[0048] The results of the tensile strength measurements for the Examples and Comparative Examples are shown in Table 1. Table 1 also shows the number of times the positive electrode composite particles were passed between the pair of rolls (number of roll passes), as well as the standard deviation, maximum value, and minimum value of the area ratio of PTFE on the electrode composite surface calculated using the above method. Table 2 also shows the PTFE content (a) in the first region, the PTFE content (b) in the second region, the PTFE content (c) in the third region, and the value of (c a ) / (a + b + c) for the Examples and Comparative Examples.

[0049] [Table 1]

[0050] [Table 2]

[0051] As shown in Table 1, the positive electrode mixture sheets of the Examples had higher tensile strength than the positive electrode mixture sheets of the Comparative Examples. The positive electrode mixture sheets of the Comparative Examples had low tensile strengths that were too low to measure. Furthermore, as shown in Table 2, in the positive electrode mixture sheets of the Examples, PTFE was present almost uniformly throughout the entire electrode mixture, even in the thickness direction. [Explanation of symbols]

[0052] 10 electrode, 11 core material, 12 electrode mixture, 12a electrode mixture particles, 12b electrode mixture sheet, 20 mixer, 22, 24 rolls

Claims

1. An electrode including a core material and an electrode mixture laminated on a surface of the core material, the electrode mixture contains an active material and PTFE, In an image showing a composition distribution obtained by measuring the surface of the electrode mixture using energy dispersive X-ray analysis, the standard deviation of the area ratio of the PTFE in 30 adjacent sections each having a size of 150 μm × 133 μm is 6% or less; An electrode in which, when the electrode mixture is divided into three equal parts in the thickness direction, resulting in a first region, a second region, and a third region from the core material side, the PTFE content (a) in the first region, the PTFE content (b) in the second region, and the PTFE content (c) in the third region satisfy (c-a) / (a+b+c)≦±10%.

2. 2. The electrode according to claim 1, wherein the area ratio of the PTFE in the 30 adjacent sections each having a size of 150 μm×133 μm has a maximum value of 23% or less and a minimum value of 0.1% or more.

3. The electrode according to claim 1 or 2, wherein the content of the PTFE in the electrode mixture is 0.05% by mass to 5% by mass.

4. The electrode according to any one of claims 1 to 3, further comprising an adhesive layer between the core material and the electrode mixture, the adhesive layer having a function of adhering the core material and the electrode mixture.

5. a mixing step of mixing an active material, a conductive material, and PTFE to prepare electrode mixture particles having a solids concentration of substantially 100%; a stretching step of passing the electrode mixture particles between a pair of rolls two or more times to knead and stretch them to prepare an electrode mixture sheet; and a laminating step of laminating the electrode mixture sheet to a core material to produce an electrode.

6. The mixing step comprises: mixing the active material and the conductive material to prepare a coated active material; The method for manufacturing an electrode according to claim 5 , further comprising the step of mixing the coated active material with the PTFE.

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