WO2025164452A1 - Electrode - Google Patents

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

This disclosure relates to electrodes, and in particular to electrodes manufactured by a dry process.

Electrodes for non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally produced using a wet method in which an electrode mixture slurry containing active material, binder, etc. 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 in that the binder is prone to migration while the coating is drying. When binder migration occurs, the amount of binder is greater on the surface side of the coating (electrode mixture layer) than on the core material side, resulting in an uneven distribution of binder across the thickness of the electrode mixture layer.

In recent years, a dry method has been investigated in which an electrode composite sheet is produced by rolling an electrode composite into a sheet, and then this sheet is attached to a core material to manufacture an electrode. Patent Document 1 discloses an electrode film (electrode composite) produced by mixing an active material, a particulate binder, and a conductive material using a mill, and then applying a large shear force under high pressure to the mixture for a long period of time to fibrillate the binder.

Special table 2019-512872 publication

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

Therefore, the object of this disclosure is to provide an electrode that suppresses transfer defects during the production of electrode composites.

An electrode according to one embodiment of the present disclosure includes a core material and an electrode composite laminated on the surface of the core material. The electrode composite includes active materials including 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; a conductive material; and a fibrous binder. 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.

According to one aspect of the present disclosure, transfer defects are suppressed and the productivity of electrode composites is improved.

FIG. 2 is a cross-sectional view of an electrode according to an embodiment. 1A to 1C are diagrams illustrating a mixing step in a manufacturing process of an electrode according to an embodiment. 3A to 3C are diagrams illustrating a rolling step in a manufacturing process of an electrode according to an embodiment. 1A to 1C are diagrams illustrating a compression step in a manufacturing process of an electrode according to an embodiment. 1A to 1C are diagrams illustrating a bonding step in a manufacturing process of an electrode according to an embodiment.

Embodiments of the positive electrode and nonaqueous electrolyte secondary battery according to the present disclosure are described in detail below. 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 light of the following description.

[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).

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 that constitutes a wound electrode body, or a rectangular electrode that constitutes a laminated electrode body. The electrode 10 may be used as the positive electrode, negative electrode, or both, of a non-aqueous electrolyte secondary battery.

The core material 11 can be made of 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. For the positive electrode, the core material 11 can be made of metal foil whose main component is aluminum. For the negative electrode, the core material 11 can be made of metal foil whose main component is copper. In this specification, "main component" means the component with the highest mass ratio. The core material 11 can be aluminum foil that is essentially 100% aluminum, or copper foil that is essentially 100% copper.

The electrode mixture 12 contains 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, and preferably 50 μm to 100 μm. Examples of conductive materials contained 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 conductive material content in the electrode mixture 12 can be, for example, 0.5% to 5.0% by mass.

A lithium transition metal composite oxide is generally used as the positive electrode active material (positive electrode active material). 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, W, etc. Among these, it is preferable to contain at least one of Ni, Co, and Mn. 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 as the negative electrode active material. 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 active material content in the electrode mixture 12 is preferably 85% to 99% by mass, and more preferably 90% to 99% by mass.

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 greater at its average particle diameter. The greater the circularity, the closer the particle shape is to a sphere, and a circularity of 1 is considered a perfect sphere. The circularity is calculated from particle images 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 of the particle image obtained by measuring the particle shape, and the circularity is calculated using the following formula:
Circularity = perimeter of a circle with the same area as the particle image / perimeter of the particle image

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 a 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 (for example, the MT3000II manufactured by Microtrac-Bell Corporation) using water as the dispersion medium.

The average particle diameter of the first active material may be smaller than the average particle diameter of the second active material. The average particle diameter of the first active material is, for example, in the range of 1 μm to 10 μm, and the average particle diameter of the second active material is, for example, in the range of 10 μm to 20 μm. By including a first active material and a second active material with different average particle diameters, the filling rate of the active material is increased, allowing for a higher density electrode composite.

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 and second active materials that satisfy the above circularity within this range, transfer defects are suppressed and the productivity of the electrode mixture is improved. The active material contained in the electrode mixture may consist only of the first and second active materials, or may contain active materials other than the first and second active materials.

The first active material is, for example, a single-crystal particle, and the second active material is, for example, a polycrystalline particle. Single-crystal particles are particles composed of a single crystal structure, and polycrystalline particles are secondary particles formed by the aggregation of single-crystal particles (primary particles) with small particle diameters. The particle diameter of the primary particles that make up 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).

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, when a battery is repeatedly charged and discharged, cracks can form between the primary particles of polycrystalline particles, reducing battery capacity and battery durability. By mixing the first active material, which is single-crystal particles, and the second active material, which is polycrystalline particles, in the above ratio, it is possible to specifically improve the productivity of the electrode mixture while also improving battery durability.

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 using the dry process described below. Note that, in addition to the fibrous binder, the electrode mixture 12 may also include a binder such as non-fibrillated polyvinylidene fluoride (PVdF).

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

<Method for calculating the degree of PTFE fibrosis>
(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 region, C region, and O region are designated as "areas where active material and conductive material exist (areas where the target object exists)," a second composite image in which the overlapping areas of the Ni region, C region, F region, and O region are designated as "areas where fiberized PTFE and conductive material exist on the active material (areas where the target object exists)," and a third composite image in which the overlapping areas of the C region, F region, and O region are designated as "areas where aggregated PTFE and conductive material exist (areas where the target object exists)."
(3) Using image analysis software, the number of pixels occupied by the "region where the object exists" in each of the first to third composite images is calculated, and the area ratio of the fibrous portion is calculated using the following formula.
Area ratio (%) of fibrous portion = area where the object exists in the second composite image / (area where the object exists in the first composite image + area where the object exists in the second composite image + 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 (mass %) present in the fibrous portion."
(5) From the "area ratio (%) of the fibrous part" and "amount of F present in the fibrous part (mass%)" obtained above, calculate the degree of fibrous part of PTFE according to the following formula:
PTFE fibrosis degree (mass%) = area ratio of fibrous part × amount of F present in fibrous part (6) The above (1) to (5) were carried out for each of two different parts of the electrode composite, and the average value of the obtained values was taken as the PTFE fibrosis degree (mass%) in the electrode composite.

The content of the fibrous binder in the electrode mixture 12 is, for example, 0.1% to 3% by mass per 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.

The fibrous binder can be produced by fibrillating PTFE raw material (PTFE particles), a fine powder that can be fibrillated, 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 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 is taken as the particle diameter of the PTFE raw material.

The median diameter (D50) of the fibrous binder is preferably 2 μm to 20 μm. A median diameter of 2 μm to 20 μm means that the fibrous binder is a finely powdered size relative to the PTFE particles in the PTFE raw material.

When the electrode mixture 12 is divided into three equal parts in the thickness direction, starting from the core material 11 side, into a first region, a second region, and a third region, the content of the fibrous binder in the first region (a), the content of the fibrous binder in the second region (b), and the content of the fibrous binder in the third region (c) 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 distributed unevenly in only a portion of the electrode mixture 12.

[Electrode manufacturing method]
A method for manufacturing the electrode 10 will be described below. While a method for manufacturing a positive electrode will be 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.

FIGS. 2 to 5 are schematic diagrams 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 rolling step shown in FIG. 3, a compression step shown in FIG. 4, and a laminating step shown in FIG. 5. In the mixing step, an active material and a fibrous binder are mixed to produce electrode mixture particles 12a with 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 laminating step, the high-density electrode mixture sheet 12c is laminated to a core material 11 to produce an electrode.

The method for manufacturing electrode 10 is a dry process in which electrode 10 is manufactured using electrode mixture 12 with a solids concentration of substantially 100%. A dry process is a process in which active material particles and binder particles are mixed without using a solvent; in other words, the active material and binder are mixed in a state in which the solids concentration 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 it is not necessary 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.

In the mixing step shown in Figure 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, the PTFE is properly fiberized, suppressing poor transfer to the roll in the rolling step described below. The mixer 20 can be, for example, a conventional mechanical stirring 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 the raw materials are mixed. The processing time for 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 processing time is too long, the amount of conductive material absorbed into the fibrous binder increases. In this case, the conductivity of the electrode mixture sheet decreases significantly, increasing resistance and adversely affecting battery characteristics.

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 a fibrous binder. By using a coated active material prepared by mixing an active material with a conductive material, the time required to mix the coated active material with the fibrous binder can be shortened. This reduces the amount of conductive material taken up by 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 these 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.

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 inside 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 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.

Next, in the rolling step, as shown in FIG. 3, the electrode mixture particles 12a supplied from the 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 12a are supplied to the gap between the two rolls 22, where they are compressed and stretched into a sheet. If the electrode mixture sheet 12b does not adhere to one of the rolls 22, it will not be able to be properly fed to the subsequent process. Therefore, the electrode mixture sheet 12b must be transferable to the rolls 22. The two rolls 22 have, for example, the same roll diameter. The obtained electrode mixture sheet 12b 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 12a.

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

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 to 4.0 ^g /cm.

Next, in the lamination step, as shown in Figure 5, the high-density electrode composite sheet 12c is laminated to the core material 11, thereby obtaining an electrode 10 in which a composite layer made of the electrode composite 12 is provided on the surface of the core material 11. While Figure 5 shows the electrode composite 12 bonded to only one surface of the core material 11, it is preferable that the electrode composite 12 be bonded to both surfaces of the core material 11. Two sheets of electrode composite 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.

In the laminating step, two rolls 26 are used to laminate the high-density electrode composite sheet 12c to 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.

The present disclosure will be further explained below using examples, but the present disclosure is not limited to these examples.

Example 1
[Preparation of Positive Electrode Composite Particles (Mixing Step)]
The first active material was 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. 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 produce a carbon-coated first active material. The second active material was 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. The surface of the second active material was coated with CB in the same manner as the first active material to produce a carbon-coated second active material.

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 placed in a mixer (Wonder Crusher, manufactured by Osaka Chemical) 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 at 10. The resulting positive electrode composite particles had a solids concentration of 100%.

[Preparation of positive electrode composite sheet (rolling step)]
The obtained positive electrode composite particles were passed through two rolls and rolled to produce 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.

[Evaluation of transferability]
The prepared positive electrode mixture sheets were visually inspected for transferability based on the following evaluation criteria.
◯: 90% or more of the positive electrode mixture sheet was transferred to the roll surface. △: 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.

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.

<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. A positive electrode composite sheet was prepared and evaluated in the same manner as in Example 1 except for this.

<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.

<Reference example>
As the carbon-coated positive electrode active material, only the carbon-coated second active material was used. 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.

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

As shown in Table 1, the positive electrode mixture sheet of the Example had better transferability than the positive electrode mixture 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 the PTFE and the transferability of the positive electrode mixture sheet. The positive electrode mixture sheet of the Reference Example had good transferability, but because it did not contain single-crystal particles, the battery durability was poorer than that of the Example.

The present disclosure is further illustrated by the following embodiments.
Configuration 1:
An electrode including a core material and an electrode mixture laminated on 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 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;
The electrode, 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.
Configuration 2:
2. The electrode of claim 1, wherein the fibrous binder comprises polytetrafluoroethylene, and the polytetrafluoroethylene has a fiberization degree of greater than 1.3 wt.%.
Configuration 3:
2. The electrode of claim 1, wherein the fibrous binder comprises polytetrafluoroethylene, and the polytetrafluoroethylene has a degree of fiberization of 2.5% by mass or more.
Configuration 4:
4. The electrode of 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:
5. The electrode of any one of configurations 1 to 4, wherein the average particle size of the first active material is smaller than the average particle size of the second active material.
Configuration 6:
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%.

10 Electrode, 11 Core material, 12 Electrode composite, 12a Electrode composite particles, 12b Electrode composite sheet, 12c High-density electrode composite sheet, 14 Active material, 20 Mixer, 21 Hopper, 22, 24, 26 Rolls

Claims (6)

An electrode including a core material and an electrode mixture laminated on 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 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;
The electrode, 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. The electrode described in claim 1, wherein the fibrous binder contains polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is greater than 1.3% by mass. The electrode described in claim 1, wherein the fibrous binder contains polytetrafluoroethylene, and the degree of fiberization of the polytetrafluoroethylene is 2.5 mass% or more. The electrode described in claim 1, wherein the first active material is single-crystal particles and the second active material is polycrystalline particles. The electrode described in claim 1, wherein the average particle diameter of the first active material is smaller than the average particle diameter of the second active material. 2. The electrode according to claim 1, wherein when the electrode mixture is divided into three equal parts in a 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%.