Electrode

Abstract

Provided is an electrode in which transfer failure at the time of manufacturing of an electrode mixture is suppressed. An electrode according to one embodiment of the present disclosure comprises a core material, and an electrode mixture that is deposited onto a surface of the core material. The electrode mixture includes: an active material including a first active material having a circularity of less than 0.96 in the average particle diameter, and a second active material having a circularity of 0.96 or greater in the average particle diameter; an electroconductive material; and a fibrous binder. The mixing ratio of the first active material and the second active material is within the range of 0.1:99.9 to 74.9:25.1 in terms of mass ratio.

Description

electrode

[0001] The present disclosure relates to electrodes, and in particular to electrodes manufactured by dry processes.

[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 binder amount becomes greater on the surface side of the coating (electrode mixture layer) than on the core material side, resulting in a biased distribution of the binder in the thickness direction of the electrode mixture layer.

[0003] In recent years, a dry method has been studied in which an electrode mixture is rolled 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 particulate binder, and a conductive material using a mill, and then treating the mixture under high pressure and large shear force for a long period of time to fibrillate the binder.

[0004] Special table 2019-512872 publication

[0005] As a result of investigations by the present inventors, it was found that, depending on the shape of the active material, PTFE may not disperse but aggregate in the electrode mixture, resulting in poor transfer to the roll and making it impossible to form the electrode mixture. The techniques disclosed in publicly known documents such as Patent Document 1 do not consider how to deal with poor transfer of the electrode mixture, and there is still room for improvement.

[0006] Therefore, an object of the present disclosure is to provide an electrode that suppresses transfer defects during the production of an electrode mixture.

[0007] An electrode according to one aspect of the present disclosure includes a core material and an electrode composite laminated on a surface of the core material, the electrode composite including active materials including a first active material having a circularity at an average particle diameter of less than 0.96 and a second active material having a circularity at an average particle diameter of 0.96 or more, a conductive material, and a fibrous binder, and the mixing ratio of the first active material to the second active material is in the range of 0.1:99.9 to 74.9:25.1 by mass ratio.

[0008] According to one aspect of the present disclosure, transfer defects are suppressed and the productivity of electrode mixtures is improved.

[0009] Fig. 1 is a cross-sectional view of an electrode according to an embodiment; Fig. 2 is a diagram showing a mixing step in a manufacturing process of an electrode according to an embodiment; Fig. 3 is a diagram showing a rolling step in a manufacturing process of an electrode according to an embodiment; Fig. 4 is a diagram showing a compression step in a manufacturing process of an electrode according to an embodiment; Fig. 5 is a diagram showing a bonding step in a manufacturing process of an electrode according to an embodiment.

[0010] Hereinafter, embodiments of the positive electrode and nonaqueous electrolyte secondary battery 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.

[0011] [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. Note that 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).

[0012] FIG. 1 is a cross-sectional view of an electrode according to an embodiment. The electrode 10 includes a core material 11 and an electrode composite material 12 laminated on the surface of the core material 11. As shown in FIG. 1, the electrode 10 may include the electrode composite material 12 on both sides of the core material 11. The electrode 10 may be a long electrode constituting a wound electrode body, or a rectangular electrode constituting a laminated electrode body. The electrode 10 may be used as a positive electrode, a negative electrode, or both of a nonaqueous electrolyte secondary battery.

[0013] 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 whose main component is aluminum. In the case of a negative electrode, the core material 11 may be a metal foil whose main component is copper. 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.

[0014] The electrode mixture 12 includes an active material, a conductive material, and a fibrous binder. The active material, conductive material, and fibrous binder may be in powder form. The thickness of the electrode mixture 12 is, for example, 30 μm to 120 μm, preferably 50 μm to 100 μm. Examples of conductive materials included in the electrode mixture 12 include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphite, and other carbon materials. 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.

[0015] A lithium transition metal composite oxide is generally used as the positive electrode active material (positive electrode active material). Examples of metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one of Ni, Co, and Mn. For the negative electrode active material (negative electrode active material), a carbon-based active material such as natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB) is used. In addition, a Si-based active material that alloys with lithium may also be used as 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% by mass to 99% by mass, and more preferably 90% by mass to 99% by mass.

[0016] The active material includes a first active material having a circularity of less than 0.96 at its average particle diameter, and a second active material having a circularity of 0.96 or more at its average particle diameter. The greater the circularity, the closer the particle shape is to a sphere, and when the circularity is 1, the particle is considered to be a perfect sphere. The circularity is calculated from a particle image obtained by placing a sample in a measurement system and irradiating the sample flow with a strobe light. The perimeter of a circle having the same area as the particle image and the perimeter of the particle image are determined by image processing the particle image obtained by measuring the particle shape, and the circularity is calculated using the following formula: Circularity = perimeter of a circle having the same area as the particle image / perimeter of the particle image

[0017] In this specification, the average particle size refers to the volume-based median diameter (D50). 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 called the median diameter. The particle size distribution of the active material can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell Co., Ltd.) using water as a dispersion medium.

[0018] The average particle size of the first active material may be smaller than that of the second active material. The average particle size of the first active material is, for example, in the range of 1 μm to 10 μm, and the average particle size of the second active material is, for example, in the range of 10 μm to 20 μm. By including the first active material and the second active material having different average particle sizes, the filling rate of the active material is increased, and the density of the electrode mixture can be increased.

[0019] The mixing ratio of the first active material to the second active material is preferably in the range of 0.1:99.9 to 74.9:25.1 by mass, more preferably in the range of 0.1:99.9 to 50:50, and even more preferably in the range of 0.1:99.9 to 25:75. By mixing the first active material and the second active material satisfying the above circularity within this range, transfer defects are suppressed and the productivity of the electrode mixture is improved. Note that the active material contained in the electrode mixture may be composed only of the first active material and the second active material, or may contain active materials other than the first active material and the second active material.

[0020] The first active material is, for example, a single-crystal particle, and the second active material is, for example, a polycrystalline particle. A single-crystal particle is a particle composed of a single crystal structure, and a polycrystalline particle is a secondary particle formed by aggregation of single-crystal particles (primary particles) having a small particle diameter. The particle diameter of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle diameter of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM).

[0021] Single-crystal particles generally have a lower circularity than polycrystalline particles, and increasing the content of single-crystal particles in an electrode mixture can result in poor transfer during the production of the electrode mixture, reducing productivity. On the other hand, polycrystalline particles can cause cracks between the primary particles during repeated charging and discharging of a battery, reducing battery capacity and battery durability. Mixing the first active material, which is single-crystal particles, and the second active material, which is polycrystalline particles, in the above ratio can specifically improve the productivity of the electrode mixture while also improving battery durability.

[0022] The fibrous binder contained in the electrode mixture 12 includes, for example, fibrillated polytetrafluoroethylene (PTFE). The fibrous binder 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. Note that the electrode mixture 12 may also include, in addition to the fibrous binder, a binder such as non-fibrillated polyvinylidene fluoride (PVdF).

[0023] The PTFE fibrous degree is preferably more than 1.3% by mass, more preferably 2.5% by mass or more. This can more significantly suppress transfer defects during the production of electrode composites. The upper limit of the PTFE fibrous degree is not particularly limited, but is, for example, 10% by mass. The PTFE fibrous degree can be calculated as follows.

[0024] <Method for calculating the degree of fibrous content of PTFE> (1) The surface of the electrode composite is observed by energy dispersive X-ray spectroscopy (EDX), and a mapping image is obtained in which the carbon element region (C region), the oxygen element region (O region), the fluorine element region (F region), and the transition metal element (e.g., Ni) contained in the active material region (hereinafter, Ni region) are mapped. The magnification of the EDX is adjusted to obtain an image measuring 300 μm long x 400 μm wide. (2) The mapping image is imported into a computer, and image analysis software (e.g., ImageJ, manufactured by the National Institutes of Health) is used to obtain a first composite image in which the overlapping areas of the Ni, C, and O regions are designated as "areas where active material and conductive material exist (areas where the target exists)," a second composite image in which the overlapping areas of the Ni, C, F, and O regions are designated as "areas where fiberized PTFE and conductive material exist on the active material (areas where the target exists)," and a third composite image in which the overlapping areas of the C, F, and O regions are designated as "areas where aggregated PTFE and conductive material exist (areas where the target exists)." (3) Using image analysis software, the number of pixels occupied by the "area where the target exists" in each of the first to third composite images is calculated, and the area ratio of the fiberized portion is calculated using the following formula. The area ratio (%) of the fibrous portion = the area where the object exists in the second composite image / (the area where the object exists in the first composite image + the area where the object exists in the second composite image + the area where the object exists in the third composite image) (4) In the second composite image, the ratio of fluorine element to all elements is calculated to obtain the "amount of F present in the fibrous portion (mass%)". (5) From the "area ratio (%) of the fibrous portion" and "amount of F present in the fibrous portion (mass%)" obtained above, the fibrous degree of PTFE is calculated based on the following formula: PTFE fibrous degree (mass%) = area ratio of the fibrous portion × amount of F present in the fibrous portion (6) The above (1) to (5) were performed for each of two different locations on the electrode composite, and the average of the obtained values ​​was taken as the fibrous degree of PTFE (mass%) in the electrode composite.

[0025] The content of the fibrous binder in the electrode mixture 12 is, for example, 0.1% by mass to 3% by mass relative to 100 parts by mass of the active material. The fibrous binder 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 fibrous binder present in a mesh-like structure.

[0026] The fibrous binder can be produced by fibrillating a fibrillable fine powder PTFE raw material (PTFE particles) using a dry grinder such as a jet mill grinder. The PTFE raw material may be secondary particles. The particle diameter of the PTFE raw material is, for example, 100 μm to 700 μm, preferably 100 μm to 500 μm, and more preferably 100 μm to 400 μm. The particle diameter of the PTFE raw material can be determined by observing the PTFE raw material particles with an SEM. Specifically, the outer 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 is taken as the particle diameter of the PTFE raw material.

[0027] The median diameter (D50) of the fibrous binder is preferably 2 μm to 20 μm. The median diameter of the fibrous binder of 2 μm to 20 μm means that the fibrous binder has a size that is finer than the PTFE particles of the PTFE raw material.

[0028] 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 content (a) of the fibrous binder in the first region, the content (b) of the fibrous binder in the second region, and the content (c) of the fibrous binder in the third region preferably satisfy (c-a) / (a+b+c)≦±10%, and more preferably satisfy (c-a) / (a+b+c)≦±5%. This allows the fibrous binder to be present substantially uniformly throughout the electrode mixture 12, rather than being present only in part of the electrode mixture 12.

[0029] [Electrode Manufacturing Method] A method for manufacturing the electrode 10 will be described below. While a method for manufacturing a positive electrode is exemplified below, this manufacturing 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.

[0030] 2 to 5 are diagrams schematically illustrating the manufacturing process of an electrode 10 according to an embodiment. The manufacturing method of the electrode 10 includes a mixing step shown in FIG. 2, a rolling step shown in FIG. 3, a compression step shown in FIG. 4, and a lamination step shown in FIG. 5. In the mixing step, an active material and a fibrous binder are mixed to produce electrode mixture particles 12a having a solids concentration of substantially 100%. In the rolling step, the electrode mixture particles 12a are rolled and formed into a sheet to produce an electrode mixture sheet 12b. In the compression step, the electrode mixture sheet 12b is compressed to produce a high-density electrode mixture sheet 12c. In the lamination step, the high-density electrode mixture sheet 12c is laminated to a core material 11 to produce an electrode.

[0031] The method for manufacturing the electrode 10 is a dry process for manufacturing the electrode 10 using an electrode mixture 12 having a solids 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 solids concentration of the active material and binder is substantially 100%. The method for manufacturing the electrode 10 according to the present disclosure does not require the use of a solvent as in conventional methods for manufacturing the 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.

[0032] In the mixing step shown in FIG. 2, raw materials such as an active material, a fibrous binder, and a conductive material are mixed in a mixer 20 to produce electrode composite particles 12a. By including a first active material and a second active material in the active material, PTFE is appropriately fiberized, thereby suppressing poor transfer to the roll in the rolling step described below. The mixer 20 can be, for example, a conventional mechanical agitation mixer. Specific examples of suitable mixers 20 include devices capable of applying mechanical shear force, such as cutter mills, pin mills, bead mills, microparticle composite devices (devices in which shear 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 composite devices, granulators, and twin-screw extrusion mixers are preferred. This allows the fibrous binder to be further fibrillated while mixing the raw materials. The processing time of the mixing step (the time during which shear force is applied to the materials) is preferably within a few minutes, for example, 0.5 to 10 minutes. If the treatment time is too long, the amount of conductive material absorbed into the fibrous binder increases, which adversely affects the battery characteristics, such as significantly reducing the conductivity of the electrode mixture sheet and increasing the resistance.

[0033] The mixing step may include a step of mixing an active material and a conductive material to prepare a coated active material, and a step of mixing the coated active material and a fibrous binder. By using a coated active material prepared by mixing an active material and a conductive material, the time required to mix the coated active material and the fibrous binder can be shortened. This reduces the amount of conductive material incorporated into the fibrous binder. It is preferable that the surface of the coated active material has irregularities, and that the conductive material penetrates and adheres to the recesses in the irregularities. This makes it less likely that the conductive material on the surface of the coated active material will be taken up by the fibrous binder during the mixing process of the coated active material and the fibrous binder.

[0034] The mechanofusion method may be used as a method for dry-mixing the active material and the conductive material. The mechanofusion method is a dry processing method carried out in a mechanofusion reactor having a cylindrical chamber equipped with a compression tool and rotating 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) pulverizer or "Mechanofusion" (registered trademark) pulverizer manufactured by Hosokawa Micron Corporation (Japan), the "Hybridizer" (registered 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.

[0035] Next, in the rolling step, as shown in FIG. 3 , the electrode mixture particles 12 a supplied from a hopper 21 are rolled using two rolls 22 to form a sheet. The two rolls 22 are arranged with a predetermined gap between them and rotate in the same direction. The electrode mixture particles 12 a are supplied to the gap between the two rolls 22 and compressed by the two rolls 22 to be stretched into a sheet. If the electrode mixture sheet 12 b does not adhere to one of the rolls 22, the electrode mixture sheet 12 b cannot be properly fed to the subsequent process. Therefore, the electrode mixture sheet 12 b must be transferable to the rolls 22. The two rolls 22 have, for example, the same roll diameter. The obtained electrode mixture sheet 12 b may be passed through the gap between the two rolls 22 multiple times, or may be stretched one or more times using another roll with a different roll diameter, peripheral speed, gap, etc. Alternatively, the rolls may be heated to heat-press the electrode mixture particles 12 a.

[0036] The thickness of the electrode mixture sheet 12b can be controlled by, for example, the gap between the two rolls 22, the peripheral speed, the number of times of stretching, etc. In the rolling step, it is preferable to form the electrode mixture particles 12a into a sheet using two rolls 22 whose peripheral speed ratio differs by at least two times. By making the peripheral speed ratio of the two rolls 22 different, for example, it becomes easier to thin the electrode mixture sheet 12b, improving productivity.

[0037] Next, in the compression step, as shown in FIG. 4, the electrode mixture sheet 12b is compressed using two rolls 24 to produce a high-density electrode mixture sheet 12c. The two 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 two rolls 24 may apply a linear pressure of, for example, 1 t / cm to 5 t / cm. The temperature of the two rolls 24 is not particularly limited and may be, for example, room temperature. The active material density of the high-density electrode mixture sheet 12c is, for example, 3.6 g / cm. ３ ~4.0 g / cm ３ is.

[0038] Next, in the lamination step, as shown in Fig. 5, the high-density electrode mixture sheet 12c is laminated 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. 5 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 be 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 at the same time, 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.

[0039] In the laminating step, two rolls 26 are used to laminate the high-density electrode mixture sheet 12c onto the surface of the core material 11. The two rolls 26, 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 two rolls 26 is, for example, 50°C to 300°C. The linear pressure applied by the two rolls 26 is preferably 0.1 t / cm to 2 t / cm, and more preferably 0.2 t / cm to 1 t / cm.

[0040] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0041] Example 1 [Preparation of Cathode Composite Particles (Mixing Step)] As the first active material, an NCM-based (Ni-Co-Mn-based) lithium transition metal composite oxide having an average particle size (D50) of 4.5 μm and a circularity at the average particle size of 0.950 was used. Using a NOB300-Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation, 100 parts by mass of the lithium transition metal composite oxide and 0.9 parts by mass of carbon black (CB) were mixed in a Nobilta pulverizer for 5 minutes to prepare a carbon-coated first active material. As the second active material, an NCA-based (Ni-Co-Al-based) lithium transition metal composite oxide having an average particle size (D50) of 11.4 μm and a circularity at the average particle size of 0.972 was used. In the same manner as the first active material, the surface of the second active material was coated with CB to prepare a carbon-coated second active material.

[0042] Next, the carbon-coated first active material and the carbon-coated second active material were mixed in a mass ratio of 25:75 to prepare a carbon-coated positive electrode active material. This carbon-coated positive electrode active material and a fibrous binder were added to a mixer (Osaka Chemical, Wonder Crusher) in a mass ratio of 100.9:0.8 and mixed at room temperature for 2 minutes at a rotation speed of 3. The rotation speed of the Wonder Crusher was 28,000 rpm, the maximum rotation speed of 10. The resulting positive electrode composite particles had a solids concentration of 100%.

[0043] [Preparation of Positive Electrode Composite Sheet (Rolling Step)] The obtained positive electrode composite particles were passed through two rolls and rolled to prepare a positive electrode composite sheet. The width of the hopper supplying the positive electrode composite particles was 110 mm. The gap between the two rolls was 500 μm, and the pressure between the two rolls was 0.5 t. The speeds of the two rolls were 2.5 m / min and 10 m / min, respectively, resulting in a peripheral speed ratio of 1:4.

[0044] [Evaluation of Transferability] The transferability of the prepared positive electrode mixture sheet was visually evaluated based on the following evaluation criteria: ◯: 90% or more of the positive electrode mixture sheet was transferred to the roll surface Δ: 75% or more of the positive electrode mixture sheet was transferred to the roll surface ×: Less than 75% of the positive electrode mixture sheet was transferred to the roll surface

[0045] Example 2 A positive electrode composite sheet was prepared and evaluated in the same manner as in Example 1, except that in the mixing step, the mixing ratio of the carbon-coated first active material and the carbon-coated second active material was changed to 50:50 by mass ratio.

[0046] Comparative Example 1: Only the carbon-coated first active material was used as the carbon-coated positive electrode active material. That is, the mixing ratio of the carbon-coated first active material to the carbon-coated second active material was changed to 100:0 by mass. Aside from this, a positive electrode composite sheet was produced in the same manner as in Example 1, and evaluation was performed.

[0047] <Comparative Example 2> A positive electrode composite sheet was prepared and evaluated in the same manner as in Example 1, except that in the mixing step, the mixing ratio of the carbon-coated first active material and the carbon-coated second active material was changed to 75:25 by mass ratio.

[0048] <Reference Example> Only the carbon-coated second active material was used as the carbon-coated positive electrode active material. That is, the mixing ratio of the carbon-coated first active material to the carbon-coated second active material was changed to 0:100 by mass. A positive electrode composite sheet was prepared and evaluated in the same manner as in Example 1 except for this.

[0049] Table 1 shows the evaluation results and the degree of PTFE fiberization for the Examples, Comparative Examples, and Reference Examples.

[0050]

[0051] As shown in Table 1, the positive electrode composite sheet of the Example had better transferability than the positive electrode composite sheet of the Comparative Example. Furthermore, the degree of fiberization in the Example was greater than that in the Comparative Example, and a good correlation was obtained between the degree of fiberization of PTFE and the transferability of the positive electrode composite sheet. The positive electrode composite sheet of the Reference Example had good transferability, but because it did not contain single-crystal particles, the battery durability was poor compared to the Examples.

[0052] The present disclosure is further described by the following embodiments. Configuration 1: An electrode including a core material and an electrode composite laminated on a surface of the core material, wherein the electrode composite includes an active material including a first active material having a circularity of less than 0.96 in its average particle diameter and a second active material having a circularity of 0.96 or more in its average particle diameter, a conductive material, and a fibrous binder, wherein the mixing ratio of the first active material to the second active material is in the range of 0.1:99.9 to 74.9:25.1 by mass. Configuration 2: The electrode according to Configuration 1, wherein the fibrous binder includes polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is greater than 1.3 mass%. Configuration 3: The electrode according to Configuration 1, wherein the fibrous binder includes polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is 2.5 mass% or more. Configuration 4: The electrode according to any one of configurations 1 to 3, wherein the first active material is a single-crystal particle, and the second active material is a polycrystalline particle.Configuration 5: The electrode according to any one of configurations 1 to 4, wherein the average particle diameter of the first active material is smaller than the average particle diameter of the second active material.Configuration 6: The electrode according to any one of configurations 1 to 5, wherein, when the electrode mixture 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 content (a) of the fibrous binder in the first region, the content (b) of the fibrous binder in the second region, and the content (c) of the fibrous binder in the third region satisfy (c - a) / (a + b + c) ≦ ± 10%.

[0053] 10 Electrode, 11 Core material, 12 Electrode mixture, 12a Electrode mixture particles, 12b Electrode mixture sheet, 12c High-density electrode mixture sheet, 14 Active material, 20 Mixer, 21 Hopper, 22, 24, 26 Roll

Claims

1. An electrode comprising a core material and an electrode composite layered on the surface of the core material, wherein the electrode composite comprises active materials including a first active material having a circularity of less than 0.96 in its average particle diameter and a second active material having a circularity of 0.96 or more in its average particle diameter, a conductive material, and a fibrous binder, wherein the mixing ratio of the first active material to the second active material is in the range of 0.1:99.9 to 74.9:25.1 by mass ratio.

2. The electrode according to claim 1, wherein the fibrous binder contains polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is greater than 1.3% by mass.

3. The electrode according to claim 1, wherein the fibrous binder contains polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is 2.5 mass % or more.

4. The electrode of claim 1, wherein the first active material is a single crystal particle and the second active material is a polycrystalline particle.

5. The electrode according to claim 1, wherein the average particle size of the first active material is smaller than the average particle size of the second active material.

6. The electrode according to claim 1, wherein when the electrode mixture 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 content (a) of the fibrous binder in the first region, the content (b) of the fibrous binder in the second region, and the content (c) of the fibrous binder in the third region satisfy (c-a) / (a+b+c)≦±10%.

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