Electrode and method for manufacturing electrode

Abstract

An electrode is an electrode in which an electrode composite material is layered on a surface of a core material, the electrode composite material including: a coated active material in which a conductive material is attached to a surface of an active material, and a PTFE powder, a coverage of the conductive material on the surface of the coated active material being 10% to 60%, a composite material resistance of the electrode composite material being 20 Ωcm or less, and when the electrode composite material is divided into three in a thickness direction and is provided as a first region, a second region, and a third region from the side of the core material, a content (a) of the PTFE powder in the first region, a content (b) of the PTFE powder in the second region, and a content (c) of the PTFE powder in the third region satisfy -10% ≤ (c-a) / (a+b+c) ≤ 10%.

Description

Technical Field

[0001] This invention relates to electrodes and methods for manufacturing electrodes. Background Technology

[0002] Electrodes for non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally manufactured using a wet process by coating an electrode composite slurry containing active materials and binders onto the surface of a core material, which is then dried and compressed. In this process, there is a problem of binder migration during the drying of the coating. When binder migration occurs, the amount of binder material closer to the surface than the core material side of the coating (electrode composite layer) increases, causing a deviation in the distribution of binder material along the thickness direction of the electrode composite layer.

[0003] In recent years, a dry method for manufacturing electrodes has been studied, which involves calendering electrode composite materials into sheets to produce electrode composite sheets and then bonding these sheets onto a core material. Patent Document 1 discloses an electrode film (electrode composite material) produced by mixing an active material, a particulate binder material, and a conductive material using a grinding mill and then subjecting the mixture to high pressure and large shear force for an extended period of time, thereby fibrillating the binder material.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2019-512872 Summary of the Invention

[0007] The inventors' research results show that, as disclosed in Patent Document 1, when a large shear force is applied to the electrode composite material for a long time, the conductive material adheres to the binder material instead of the active material, thereby significantly reducing the resistance of the composite material, resulting in a decrease in the discharge capacity of the battery.

[0008] One aspect of the present invention relates to an electrode in which an electrode composite material is laminated on the surface of a core material. The electrode composite material comprises: a coated active material on which a conductive material is attached to the surface of an active material, and PTFE powder. The coverage of the conductive material on the surface of the coated active material is 10% to 60%. The composite material resistivity of the electrode composite material is less than 20 Ωcm. When the electrode composite material is divided into three equal parts along the thickness direction and designated as a first region, a second region, and a third region from the core material side, the PTFE powder content (a) in the first region, the PTFE powder content (b) in the second region, and the PTFE powder content (c) in the third region satisfy -10% ≤ (ca) / (a+b+c) ≤ 10%.

[0009] One aspect of the present invention relates to a method for manufacturing an electrode comprising: a mixing step of mixing an active material coated with a conductive material on the surface of an active material and PTFE powder to produce electrode composite material particles with a solid content substantially 100%; a calendering step of producing an electrode composite material sheet by calendering the electrode composite material particles into a sheet shape; and a bonding step of producing an electrode by bonding the electrode composite material sheet onto a core material.

[0010] According to one aspect of the present invention, electrodes with low resistivity of composite materials can be obtained, thereby improving the discharge capacity of the battery. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of an electrode as an example of an implementation method.

[0012] Figure 2 This is a diagram showing a schematic of a mechanical fusion reaction apparatus for producing a coated active substance, as an example of an embodiment.

[0013] Figure 3 (a) is a diagram showing the mixing steps in the electrode manufacturing process as an example of an implementation method. Figure 3 (b) is a diagram representing the rolling process.

[0014] Figure 4 This diagram illustrates the bonding step in the manufacturing process of an electrode, as an example of an implementation method. Detailed Implementation

[0015] Hereinafter, embodiments of the electrode and electrode manufacturing method according to the present invention will be described in detail. The embodiments described below are merely examples, and the present invention is not limited to the embodiments described below. In addition, the accompanying drawings referred to in the description of the embodiments are schematic illustrations, and the size ratios of the constituent elements depicted in the drawings should be determined with reference to the following description.

[0016] [electrode]

[0017] The electrode involved in this invention is preferably used in non-aqueous electrolyte secondary batteries such as lithium-ion batteries, but it can also be used in energy storage devices such as batteries or capacitors containing aqueous electrolytes. It should be noted that the following description uses an electrode for a non-aqueous electrolyte secondary battery (particularly suitable for the positive electrode) as an example.

[0018] Figure 1 This is a cross-sectional view of an electrode as an example of an embodiment. Electrode 10 includes a core material 11 and an electrode composite material 12 disposed on the surface of the core material 11. (As...) Figure 1As shown, electrode 10 may also include electrode composite material 12 on both sides of core material 11. Electrode 10 may be a strip-shaped electrode constituting a wound electrode body, or a rectangular electrode constituting a stacked electrode body. It should be noted that electrode 10 can be used as the positive electrode, negative electrode, or both of non-aqueous electrolyte secondary batteries.

[0019] The core material 11 can be a metal foil or a thin 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 can be a metal foil with aluminum as the main component. In the case of a negative electrode, a metal foil with copper as the main component can be used. In this specification, the main component refers to the component with the highest mass ratio. The core material 11 can be an aluminum foil that is substantially 100% aluminum or a copper foil that is substantially 100% copper.

[0020] The electrode composite material 12 comprises a coated active material and PTFE powder. The thickness of the electrode composite material 12 is, for example, 30 μm to 120 μm, preferably 50 μm to 100 μm. In addition to PTFE powder, the electrode composite material 12 may also contain a binder material such as non-fiberized polyvinylidene fluoride (PVdF).

[0021] The coated active material is an active material with a conductive material attached to its surface. The coverage of the conductive material on the surface of the coated active material is preferably 10% to 60%, more preferably 20% to 60%. Because the coverage of the conductive material is very high, the battery characteristics of the electrode can be improved. Preferably, the surface of the coated active material has irregularities, and the conductive material penetrates and adheres to the recesses within these irregularities. Therefore, during the mixing treatment of the coated active material and PTFE powder (described later), the conductive material on the surface of the coated active material is less likely to be carried away by the PTFE powder. As described later, by keeping the mixing treatment time of the PTFE powder with the active material and the conductive material relatively short, the coverage of the conductive material can be improved. If the mixing treatment is short, the increase or decrease in the conductive material before and after the mixing treatment is ±5% or less.

[0022] The coated active material can be prepared by dry mixing the active material with a conductive material. As a method of dry mixing, for example, mechanical fusion can be used. Mechanical fusion refers to... Figure 2The mechanical fusion reaction apparatus 15 shown is a dry processing method performed by a cylindrical chamber 16 with a compression device 17 inside and rotating at high speed. The rotation speed is usually faster than 1000 rpm. By placing conductive material and active substance into the chamber 16 and rotating the chamber 16, the particles are squeezed against each other and against the walls of the chamber 16. When the compression device 17 is used and centrifugal force is generated by high-speed rotation, the adhesion and bonding of conductive material and active substance are promoted. Examples of mechanical fusion reaction apparatus 15 include the "NOBILTA" (registered trademark) pulverizer or "MECHANO FUSION" (registered trademark) pulverizer manufactured by Hosokawa Micron Co., Ltd. (Japan), the "Hybridizer" (trademark) pulverizer manufactured by Nara Machinery Co., Ltd., the "BALANCE GRAN" manufactured by Freund-Turbo Corporation, and the "COMPOSI" manufactured by NIPPON COKE & ENGINEERING CO.,LTD.

[0023] The positive electrode active material (positive electrode active material) generally uses lithium transition metal composite oxide. 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. Preferably, it contains at least one of Ni, Co, and Mn. The negative electrode active material (negative electrode active material) uses carbon-based active materials such as natural graphite (e.g., flake graphite, block graphite, amorphous graphite), artificial graphite (MAG), and graphitized mesophase carbon microspheres (MCMB). Alternatively, Si-based active materials alloyed with lithium can be used as the negative electrode active material. The active material is the main component of the electrode composite material 12, and the content of the active material in the electrode composite material 12 is preferably 85% to 99% by mass, more preferably 90% to 99% by mass.

[0024] The positive electrode active material is, for example, a secondary particle formed by the aggregation of multiple primary particles. Thus, the surface of the positive electrode active material has irregularities, and as described above, conductive material can penetrate and adhere to the recesses within these irregularities. 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 circumcircle in a particle image observed by a scanning electron microscope (SEM). The positive electrode active material has a median particle size (D50) on a volume basis, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 refers to the particle size from the smallest side of the cumulative frequency in the volume-based particle size distribution, also known as the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction-type particle size distribution measuring device (e.g., MT3000II manufactured by Macquarie Corporation) with water as the dispersion medium.

[0025] Examples of conductive materials included in the electrode composite material 12 include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNTs), and graphite. The particle size of the conductive material is, for example, 0.01 μm to 0.1 μm. This allows it to penetrate and adhere to the recesses on the surface of the positive electrode active material. The content of the conductive material in the electrode composite material 12 is, for example, 0.5% to 5.0% by mass.

[0026] PTFE powder is included as a binder in the electrode composite material 12. The PTFE powder is in a dry state, rather than being dispersed in a dispersion such as water. Therefore, the electrode composite material can be manufactured by the dry method described later.

[0027] The PTFE powder content in the electrode composite material 12 is, for example, 0.5% to 5.0% by mass. The PTFE powder adheres to the particle surface of the coated active material and becomes entangled with it. In other words, the coated active material is retained by the PTFE powder existing in a mesh-like structure.

[0028] As one example of an embodiment, the PTFE powder contains fibrous particles with an aspect ratio of 1.5 or higher in a proportion of 20% to 60% relative to all particles. Furthermore, the average long axis dimension of these fibrous particles is 1 μm to 20 μm (hereinafter, these fibrous particles of this shape are referred to as fibrous particle A). Using this PTFE powder, electrode composite sheets with good formability and high tensile strength can be manufactured. The proportion of fibrous particle A relative to all particles can be calculated as follows. It should be noted that the proportion of fibrous particle B relative to all particles, described later, can also be determined using the same method.

[0029] (1) Use a scanning electron microscope (SEM) to photograph the PTFE powder containing fibrous particles A. The magnification can be set to, for example, 300 to 1000 times.

[0030] (2) Import the captured images into the computer and use image analysis software such as ImageJ to divide all particles into fibrous particles A and particles with an aspect ratio of less than 1.5.

[0031] (3) Divide the number of fibrous particles A by the total number of particles, that is, the sum of the number of fibrous particles A and the number of particles with an aspect ratio less than 1.5, to calculate the proportion of fibrous particles A relative to all particles.

[0032] The average major axis dimension of fibrous particle A can be calculated in the same way as the calculation of the proportion of fibrous particle A to all particles. This is done by analyzing SEM images using image analysis software, measuring the major axis dimensions (major axis lengths) of 100 fibrous particles with an aspect ratio of 1.5 or greater, and averaging the measured values. It should be noted that the average minor axis dimension of fibrous particle B, described later, can also be measured using the same method.

[0033] The average aspect ratio of fibrous particle A can be between 2 and 20. The average aspect ratio of fibrous particle A can be calculated similarly to the average major axis dimension described above by analyzing SEM images using image analysis software, measuring the aspect ratio (major axis / minor axis) of 100 fibrous particles with an aspect ratio of 1.5 or higher, and averaging the measured values. It should be noted that the average aspect ratio of fibrous particle B, described later, can also be measured using the same method.

[0034] PTFE powder containing fibrous particles A can be produced by fibrillating PTFE raw materials (PTFE particles) that are capable of fibrillation (fibrillation) into fine powder using a dry mill such as a jet mill. The PTFE raw material can be secondary particles. The average particle size 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 average particle size of the PTFE raw material can be determined by observing the particles of the PTFE raw material using SEM. Specifically, based on the shape of 100 randomly selected particles, the major diameter (longest diameter) of each of the 100 particles is determined, and their average value is set as the average particle size of the PTFE raw material. When producing PTFE powder containing fibrous particles A using a jet mill, the proportion of fibrous particles A relative to all particles can be adjusted to 20% to 60% by appropriately adjusting the PTFE raw material supply speed, milling pressure, etc.

[0035] As another example of the embodiment, the PTFE powder contains fibrous particles with an aspect ratio of 5 or more in a proportion of 60% or more relative to all particles. Preferably, the PTFE powder contains fibrous particles with an aspect ratio of 5 or more in a proportion of 80% or more relative to all particles. Furthermore, the average minor axis dimension of these fibrous particles is 1 μm to 20 μm (hereinafter, fibrous particles of this shape are referred to as fibrous particle B). By using this PTFE powder, electrode composite sheets with good formability and high fracture strength can be manufactured.

[0036] PTFE powder containing fibrous particles B can be produced by fibrillating PTFE raw materials (PTFE particles) that are capable of fibrillation (fibrillation) into fine powder using a dry mill such as an air jet mill. The PTFE raw material can be the same as that used to produce PTFE powder containing the aforementioned fibrous particles A. When producing PTFE powder containing fibrous particles B using an air jet mill, the proportion of fibrous particles B relative to all particles can be adjusted to 60% or more by appropriately adjusting the PTFE raw material supply speed, blade rotation speed, or gap.

[0037] The median particle size of the PTFE powder containing fibrous particles A and / or B is preferably 2 μm to 20 μm. The median particle size can be determined using a particle size analyzer. The median particle size of the PTFE powder containing fibrous particles A and / or B being 2 μm to 20 μm means that the PTFE powder containing fibrous particles A and / or B represents the size of the PTFE particles from the PTFE raw material after micronization.

[0038] The composite material resistance of electrode composite material 12 is less than 20 Ωcm. This improves the battery's discharge capacity. The composite material resistance refers only to the resistance of electrode composite material 12. The composite material resistance can be measured, for example, using an electrode resistance measuring system manufactured by HIOKI Electric Co., Ltd., as follows.

[0039] (1) Prepare electrodes 10 cut to size 20mm×50mm.

[0040] (2) Measure the thickness of the electrode composite material 12 and the core material 11, and input them into the measurement conditions as measurement parameters.

[0041] (3) Select a suitable range of main current and voltage.

[0042] (4) Set electrode 10 in the specified position, make the probe contact, and measure the resistance of the composite material.

[0043] When the electrode composite material 12 is divided into three equal parts along its thickness direction and designated as the first, second, and third regions from the core material 11 side, the PTFE powder content (a) in the first region, the PTFE powder content (b) in the second region, and the PTFE powder content (c) in the third region satisfy -10% ≤ (ca) / (a+b+c) ≤ 10%, more preferably -5% ≤ (ca) / (a+b+c) ≤ 5%. That is, by making the difference between the PTFE powder content (a) in the first region near the surface and the PTFE powder content (c) in the third region near the core material 11 within ±10% of the total PTFE powder content (a+b+c), preferably within ±5%, the PTFE powder is not biased towards a part of the electrode composite material 12 but is present substantially uniformly throughout the whole.

[0044] The electrode composite material 12 is preferably a mixture formed by uniformly dispersing the coated active material and PTFE powder. Furthermore, the electrode composite material 12 preferably has few particle cracks in the active material, and most of the conductive material adheres to the particle surface of the active material to form conductive pathways between particles. That is, the electrode composite material 12 needs to be manufactured in a way that suppresses particle cracking of the active material while the amount of conductive material adhering to the particle surface of the active material is not reduced due to the PTFE powder carrying away the conductive material. According to the manufacturing method described later, a high-quality electrode composite material 12 that meets these conditions can be manufactured.

[0045] [Electrode manufacturing method]

[0046] The manufacturing method of electrode 10 will be described in further detail below. Although the manufacturing method of the positive electrode is illustrated below, this method is equally applicable to the manufacturing of the negative electrode. In the case of the negative electrode, a negative electrode active material is used instead of the positive electrode active material.

[0047] Figure 3 and Figure 4 This diagram schematically illustrates the manufacturing process of electrode 10 as an example of an embodiment. The manufacturing method of electrode 10 includes... Figure 3 The mixing steps shown in (a) Figure 3 The rolling steps shown in (b) and Figure 4 The bonding steps are shown below. In the mixing step, the coated active material and PTFE powder are mixed to produce electrode composite material particles 12a with a solid content of substantially 100%. In the calendering step, the electrode composite material particles 12a are calendered into sheets to produce electrode composite material sheets. In the bonding step, the electrode is fabricated by bonding the electrode composite material sheets onto the core material.

[0048] The method for manufacturing electrode 10 is a dry process using an electrode composite material 12 with a solid content concentration of substantially 100%. A dry process is a process in which active material particles and binder material particles are mixed without the use of solvents; that is, the mixing is carried out when the solid content concentration of the active material and binder material is substantially 100% by mass. The method for manufacturing electrode 10 according to the present invention does not require the use of solvents as in conventional electrode 10 manufacturing methods. The term "not requiring solvents" refers not only to the elimination of the need for solvent as a raw material, but also to the elimination of the need for a solvent drying process, and the elimination of exhaust equipment and the like associated with the drying process.

[0049] In the mixing step, raw materials such as the coated active material and PTFE powder are mixed in mixer 20 to produce electrode composite material particles 12a. By using the coated active material prepared by mixing the active material and the conductive material, the mixing time for obtaining an electrode composite material with a uniform dispersion of the coated active material and PTFE powder can be shortened. In cases where a long mixing process is performed, the conductive material is carried away by the binder material, and the coverage of the conductive material on the surface of the active material is less than 10%. By using the coated active material, the dispersibility of the constituent materials can be improved, thereby reducing the resistance of the composite material. In addition, by shortening the mixing time, cracking of the active material during the mixing process can be suppressed. It should be noted that the active material contained in the electrode may include substances that crack during the mixing process and substances that crack during the calendering step described later.

[0050] As the mixer 20, a conventionally known mechanical mixing mixer can be used, for example. Specific examples of suitable mixers 20 include shredders, pin pulverizers, bead mills, microparticle compounding devices (devices that generate shear force between a specially shaped rotor rotating at high speed inside a tank and a collision plate), granulators, twin-screw extruders, and planetary mixers, etc., preferably shredders, microparticle compounding devices, granulators, or twin-screw extruders. This allows for the further fibrillation of the PTFE powder while mixing the raw materials. The processing time of the mixing step (the time for applying shear force to the material) is preferably within a few minutes, for example, it can be set to 0.5 minutes to 4 minutes. If the processing time is too long, the amount of conductive material carried away by the PTFE powder increases. In this case, the conductivity of the electrode composite sheet decreases significantly while the resistance increases, adversely affecting the battery characteristics. Furthermore, since the longer the processing time, the more PTFE fibrillates, if excessive fibrillation occurs, the tensile strength of the sheet decreases. Since the PTFE powder contains a specified amount of fibrillated fibrous particles A and / or fibrous particles B, a processing time of 0.5 minutes or more can cause the PTFE powder to adhere to the surface of the active material particles and become entangled with the active material.

[0051] like Figure 3 As shown in (b), in the calendering step, electrode composite material particles 12a are calendered using two rollers 22 to form a sheet. The two rollers 22 are spaced apart by a predetermined gap and rotate in the same direction. The electrode composite material particles 12a are fed into the gap between the two rollers 22, thereby being compressed and stretched into a sheet by the two rollers 22. The two rollers 22 have, for example, the same roller diameter. The resulting electrode composite material sheet 12b can be passed through the gap between the two rollers 22 multiple times, or it can be stretched more than once using other rollers with different roller diameters, rotation speeds, gaps, etc. Alternatively, the rollers can be heated to hot-press the electrode composite material particles 12a.

[0052] The thickness of the electrode composite sheet 12b can be controlled, for example, by the gap between the two rollers 22, the rotational speed, and the number of stretching processes. In the calendering step, it is preferable to use two rollers 22 with a rotational speed ratio that differs by more than twice to form the electrode composite particles 12a into a sheet. By using a different rotational speed ratio between the two rollers 22, for example, thinning of the electrode composite sheet 12b becomes easier, and productivity is improved.

[0053] Next, as Figure 4 As shown, in the bonding step, by bonding the electrode composite material sheet 12b onto the core material 11, an electrode 10 is obtained with a composite material layer composed of the electrode composite material 12 disposed on the surface of the core material 11. Figure 4 The diagram shows a state where the electrode composite material 12 is bonded to only one side of the core material 11. Preferably, the electrode composite material 12 is bonded to both sides of the core material 11. Two electrode composite materials 12 can be bonded to both sides of the core material 11 simultaneously, or one can be bonded to one side of the core material 11 and then the other can be bonded to the other side.

[0054] In the bonding step, two rollers 24 are used to bond the electrode composite sheet 12b onto the surface of the core material 11. The two rollers 24, for example, have the same roller diameter, are spaced apart by a predetermined gap, and rotate in the same direction at the same speed. The two rollers 24 are preferably heated to a predetermined temperature and subjected to a predetermined pressure.

[0055] <Example>

[0056] The present invention will be further illustrated below by way of examples, but the present invention is not limited to these examples.

[0057] <Example>

[0058] [Conductive material coating treatment on the surface of the positive electrode active material]

[0059] A carbon-coated positive electrode active material was prepared by mixing 1000g of lithium transition metal composite oxide and 10g of acetylene black (AB) in a NOB300® NOBILTA (registered trademark) pulverizer manufactured by Hosokawa Micron Co., Ltd. for 5 minutes. The carbon (conductive material) coverage in this carbon-coated positive electrode active material was 51.5%.

[0060] [Preparation of Cathode Composite Material Particles (Mixing Steps)]

[0061] As the PTFE powder, a powder containing fibrous particles with an aspect ratio of 1.5 or greater at a proportion of 33% relative to all particles, and with an average long axis dimension of 8.3 μm for the fibrous particles, was used. The aforementioned carbon-coated positive electrode active material and this PTFE powder were added to a mixer (Osaka Chemical, Wonder Crusher) at a mass ratio of 101:4 and mixed at room temperature for 5 minutes at a speed of scale 5. It should be noted that the maximum speed of the Wonder Crusher at scale 10 is 28,000 rpm. This mixing process yielded positive electrode composite particles with uniform dispersion of the carbon-coated positive electrode active material and PTFE powder. The solids content of the obtained positive electrode composite material was 100%.

[0062] [Fabrication of Cathode Composite Material Sheets (Calendar Steps)]

[0063] The obtained cathode composite material particles are calendered between two rollers to produce cathode composite material sheets. The rotational speed ratio of the two rollers is set to 1:3, and the thickness of the cathode composite material sheet is adjusted to approximately 100 μm.

[0064] [Positive electrode fabrication (bonding steps)]

[0065] The positive electrode composite material sheet prepared in Example 1-1 was placed on the surface of the positive electrode core material. The laminate of the positive electrode composite material sheet and the positive electrode core material was stamped using two rollers (linear pressure: 1.0 t / cm) to obtain the positive electrode. Aluminum alloy foil was used as the core material. The resistivity of the composite material was 18.2 Ωcm.

[0066] [Preparation of non-aqueous electrolytes]

[0067] A non-aqueous electrolyte was prepared by dissolving LiPF6, which serves as the electrolyte salt, in a non-aqueous solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:3.

[0068] [Preparation of the experimental battery]

[0069] Aluminum leads are installed on the positive electrode, and nickel leads are installed on the lithium metal foil used as the negative electrode. The positive and negative electrodes are wound into a spiral shape with a polyolefin separator in between, and then radially stamped to form a flat, wound electrode body. This electrode body is housed in an outer casing made of aluminum laminates, and after injecting the non-aqueous electrolyte, the opening of the outer casing is sealed to obtain a test battery for evaluation.

[0070] [Evaluation of initial discharge capacity]

[0071] For the test battery described above, at a temperature of 25°C, it was charged at a constant current of 0.5C until the battery voltage reached 4.2V. Then, it was charged at a constant voltage of 4.2V until the current value reached 1 / 50C. Finally, it was discharged at a constant current of 0.5C until the battery voltage reached 2.5V. The discharge capacity at this point was set as the initial discharge capacity.

[0072] <Comparative Example>

[0073] Without performing conductive material coating treatment on the surface of the positive electrode active material, in the preparation of the positive electrode composite particles (mixing step), lithium transition metal composite oxide, AB, and PTFE powder were added to a mixer at a mass ratio of 100:1:4. Otherwise, the test cells were prepared and evaluated in the same manner as in the examples. The carbon (conductive material) coating rate on the surface of the positive electrode active material before the mixing step was 0%. Furthermore, the resistivity of the positive electrode composite particles was 55.1 Ωcm.

[0074] The initial discharge capacities of the examples and comparative examples are shown in Table 1. The discharge capacities of the comparative examples are values ​​expressed relative to the discharge capacities of the examples, which are set to 100. Table 1 also shows whether or not a conductive material coating treatment was applied to the surface of the positive electrode active material, the value of the composite material resistance, and the content (a, b, c) of the binder material in regions 1, 2, and 3 of the positive electrode composite material. It should be noted that, for the comparative examples, the content (a, b, c) of the binder material in regions 1, 2, and 3 was not measured.

[0075] [Table 1]

[0076]

[0077] As shown in Table 1, the test cells of the embodiments have a larger initial discharge capacity compared to the test cells of the comparative examples. It can be inferred that because the positive electrode of the embodiments has a higher coverage of conductive material on the surface of the positive electrode active material compared to the positive electrode of the comparative examples, the resistance of the composite material is lower than that of the positive electrode of the comparative examples, resulting in a higher initial discharge capacity.

[0078] Explanation of reference numerals in the attached figures

[0079] 10 electrodes

[0080] 11 core material

[0081] 12 Electrode Composite Materials

[0082] 12a Electrode Composite Particles

[0083] 12b electrode composite sheet

[0084] 15 Mechanical Fusion Reaction Device

[0085] 16 chambers

[0086] 17. Compression equipment

[0087] 20 Mixers

[0088] 22, 24 rolls

Claims

1. An electrode comprising an electrode composite material laminated on the surface of a core material, the electrode composite material comprising: an active material coated with a conductive material on its surface, and PTFE powder. The coverage of the conductive material on the surface of the coated active material is 10% to 60%. The resistivity of the electrode composite material is below 20 Ωcm. When the electrode composite material is divided into three equal parts along its thickness direction, and designated as region 1, region 2, and region 3 starting from the core material side, the PTFE powder content (a) in region 1, the PTFE powder content (b) in region 2, and the PTFE powder content (c) in region 3 satisfy -10% ≤ (ca) / (a+b+c) ≤ 10%. The PTFE powder is any one of the following: (1) the PTFE powder contains fibrous particles with an aspect ratio of 1.5 or more in a proportion of 20% to 60% relative to all particles, and the average major axis dimension of the fibrous particles is 1 μm to 20 μm; or (2) the PTFE powder contains fibrous particles with an aspect ratio of 5 or more in a proportion of 60% or more relative to all particles, and the average minor axis dimension of the fibrous particles is 1 μm to 20 μm.

2. The electrode according to claim 1, wherein, The surface of the coated active material has irregularities, and the conductive material penetrates and adheres to the recesses in the irregularities.

3. The electrode according to claim 1, wherein, The active material is a positive electrode active material.

4. A method for manufacturing an electrode according to any one of claims 1 to 3, comprising: In the mixing step, the active material coated with conductive material and PTFE powder are mixed to produce electrode composite material particles with a solid component concentration of 100%. The calendering step involves calendering the electrode composite material particles into sheets to produce electrode composite material sheets; and The bonding step involves bonding the electrode composite sheet onto the core material to fabricate the electrode.

5. The method for manufacturing the electrode according to claim 4, wherein, The coating active material is obtained by dry mixing the active material and the conductive material.

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