PTFE powder, method for producing electrode, and electrode

Abstract

In a dry state, the PTFE powder comprises fibrous particles having an aspect ratio of 1.5 or greater, with respect to the total particles, at a ratio of 20% to 60%, and the average major axis size of the fibrous particles is 1 μm to 20 μm. Furthermore, in another embodiment of the present invention, in a dry state, the fibrous particles having an aspect ratio of 5 or greater, with respect to the total particles, at a ratio of 60% or greater, and the average minor axis size of the fibrous particles is 1 μm to 20 μm.

Description

Technical Field

[0001] The present invention relates to a PTFE powder, a method for producing an electrode, and the electrode, and in particular to a PTFE powder, a method for producing an electrode, and the electrode suitable for non-aqueous electrolyte secondary batteries such as lithium ion batteries. Background Art

[0002] The electrode of the non-aqueous electrolyte secondary battery such as lithium ion battery is generally by coating the electrode composite material slurry including active material, binding material etc. on the surface of the core material as metal foil, and the wet method of drying and compressing is made to film.In this case, there is the problem of migration that easily causes the binding material to move in the drying of film.If the migration of binding material occurs, then the amount of binding material on the surface side becomes more than the core material side of film (electrode composite material layer), and the distribution of binding material in the thickness direction of electrode composite material layer produces uneven.

[0003] In recent years, a dry method has been studied in which an electrode composite material is formed into a sheet by rolling and shaping the electrode composite material, and the sheet is laminated to a core material to produce an electrode. Patent Document 1 discloses that an active material, a granular binder, and a conductive material are mixed in a mill, and then a high shear force is applied to the mixture at high pressure for a long time, thereby fibrillating the binder material to produce an electrode film (electrode composite material).

[0004] Prior art literature

[0005] Patent Literature

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

[0007] In the production of electrodes using a dry process that does not use solvents, for example, the degree of fibrillation of the binder and the mixing state of the materials that make up the electrode composite material significantly affect the formability and fracture strength of the electrode composite material sheet. The present inventors' research results indicate that, as disclosed in Patent Document 1, applying a large shear force to the electrode composite material and treating it for a long time deteriorates the formability of the electrode composite material sheet and significantly reduces its fracture strength.

[0008] In the PTFE powder of one embodiment of the present invention, in a dry state, the proportion of fibrous particles having an aspect ratio of 1.5 or greater relative to all particles is 20% to 60%, and the average major axis size of the fibrous particles is 1 μm to 20 μm.

[0009] In another embodiment of the PTFE powder of the present invention, in a dry state, the proportion of fibrous particles having an aspect ratio of 5 or greater relative to all particles is 60% or greater, and the average minor axis size of the fibrous particles is 1 μm to 20 μm.

[0010] One embodiment of the present invention provides a method for manufacturing an electrode, which includes: a mixing step of mixing the above-mentioned PTFE powder, active material and conductive material to produce an electrode composite material having a solid content concentration of substantially 100%; a rolling step of rolling the electrode composite material into a sheet to produce an electrode composite material sheet; and a bonding step of bonding the electrode composite material sheet to a core material to produce an electrode.

[0011] An electrode in one embodiment of the present invention has an electrode composite material comprising the above-mentioned PTFE powder, active material and conductive material stacked on the surface of a core material, wherein the coverage of the conductive material on the surface of the active material is 10% to 60%. When the electrode composite material is divided into three equal parts in the thickness direction and set as the first region, the second region and the third region from the core material side, the content of PTFE powder in the first region (a), the content of PTFE powder in the second region (b), and the content of PTFE powder in the third region (c) satisfy (ca) / (a+b+c)≤±10%.

[0012] According to one embodiment of the present invention, an electrode composite material sheet with excellent formability and high fracture strength can be produced. Furthermore, the electrode composite material sheet of the present invention has a high coverage rate of the conductive material with respect to the active material, thereby improving the battery characteristics of the electrode by using the electrode composite material sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A cross-sectional view of an electrode according to an example of an embodiment.

[0014] Figure 2 In the process of manufacturing an electrode according to an example of an embodiment, (a) shows a mixing step, and (b) shows a rolling step.

[0015] Figure 3 This is a diagram showing a bonding step in the electrode manufacturing process according to an example of the embodiment. DETAILED DESCRIPTION

[0016] The following describes in detail the embodiments of the electrode manufacturing method and the electrode composite material of the present invention. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. In addition, the drawings referenced in the description of the embodiment are schematically described, and the dimensional ratios of the components depicted in the drawings should be judged with reference to the following description.

[0017] [PTFE (polytetrafluoroethylene) powder]

[0018] PTFE powder is included in the electrode composite material as a binding material and can also be called battery PTFE powder. PTFE powder can also be used for positive electrodes. PTFE powder is a powder in a dry state, not a powder dispersed in a dispersion system such as water. Thus, the electrode composite material can be made using a dry method described later.

[0019] As an example of an embodiment, for PTFE powder, fibrous particles with an aspect ratio of 1.5 or more are included in a ratio of 20% to 60% relative to all particles. In addition, the average major axis size of the fibrous particles is 1 μm to 20 μm (hereinafter, the fibrous particles of this shape are referred to as fibrous particles A). By using this PTFE powder, an electrode composite material sheet with good formability and high fracture strength can be produced. The ratio of fibrous particles A to all particles can be calculated as follows. It should be noted that the ratio of fibrous particles B to all particles described later can also be measured using the same method.

[0020] (1) Use a scanning electron microscope (SEM) to photograph the PTFE powder containing the fibrous particles A. The photographic magnification may be, for example, 300 to 1000 times.

[0021] (2) The captured images were recorded in a computer and all particles were divided into fibrous particles A and particles with an aspect ratio of less than 1.5 using image analysis software such as ImageJ.

[0022] (3) The number of fibrous particles A is divided by the number of all particles, that is, the total number of fibrous particles A and particles with an aspect ratio of less than 1.5, to calculate the ratio of fibrous particles A to all particles.

[0023] The average major axis size of the fibrous particles A can be calculated similarly to the calculation of the ratio of the fibrous particles A to the total number of particles described above by analyzing SEM images using image analysis software, measuring the major axis size (major axis length) 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 size of the fibrous particles B described below can also be measured using the same method.

[0024] The average aspect ratio of the fibrous particles A can be 2 to 20. The average aspect ratio of the fibrous particles A can be calculated similarly to the above-described average major axis dimension 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 greater, and averaging the measured values. It should be noted that the average aspect ratio of the fibrous particles B described below can also be measured using the same method.

[0025] For PTFE powder containing fibrous particles A, it can be made by fibrillating a PTFE raw material (PTFE particles) that is a fine powder capable of fibrillation (fibrillation) using a dry pulverizer such as a jet mill. The PTFE raw material can be a secondary particle. 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 obtained by observing the particles of the PTFE raw material with a SEM. Specifically, based on the outer shape of 100 particles selected at random, the major diameter (longest diameter) of each of the 100 particles is obtained, and their average value is used as the average particle size of the PTFE raw material. When making PTFE powder containing fibrous particles A with a jet mill, the ratio of fibrous particles A relative to all particles can be adjusted to 20% to 60% by appropriately adjusting the supply speed, crushing pressure, etc. of the PTFE raw material.

[0026] In another embodiment, the PTFE powder comprises fibrous particles having an aspect ratio of 5 or greater at a ratio of 60% or greater relative to the total particles. The PTFE powder preferably comprises fibrous particles having an aspect ratio of 5 or greater at a ratio of 80% or greater relative to the total particles. In addition, the average minor axis size of the fibrous particles is 1 μm to 20 μm (hereinafter, fibrous particles of this shape are referred to as fibrous particles B). By using this PTFE powder, an electrode composite material sheet with good formability and high fracture strength can be produced.

[0027] The PTFE powder containing fibrous particles B can be produced by fibrillating a PTFE raw material (PTFE particles) that is a fine powder capable of being fibrillated (fibrillated) using a dry pulverizer such as an airflow pulverizer. The PTFE raw material can be the same as that used to produce the PTFE powder containing the above-mentioned fibrous particles A. When using an airflow pulverizer to produce the PTFE powder containing fibrous particles B, the proportion of fibrous particles B relative to the total particles can be adjusted to 60% or more by appropriately adjusting the feed rate of the PTFE raw material, the rotational speed of the blades, the gap, etc.

[0028] The median particle size of the PTFE powder containing fibrous particles A and / or B is preferably 2 to 20 μm. The median particle size can be measured using a particle size distribution analyzer. The median particle size of the PTFE powder containing fibrous particles A and / or B is 2 to 20 μm, indicating that the PTFE powder containing fibrous particles A and / or B has been micronized relative to the PTFE particles of the PTFE raw material.

[0029] [electrode]

[0030] The electrode of the present invention is suitable for non-aqueous electrolyte secondary batteries such as lithium ion batteries, but can also be applied to storage devices such as batteries or capacitors containing aqueous electrolytes. It should be noted that the following description is based on the electrode for non-aqueous electrolyte secondary batteries (especially when suitable for positive electrodes) as an example.

[0031] Figure 1 FIG. 1 is a cross-sectional view of an electrode according to an embodiment of the present invention. The electrode 10 includes a core material 11 and an electrode composite material 12 provided on the surface of the core material 11. Figure 1 As shown, the electrode 10 may also include an electrode composite material 12 on both sides of the core material 11. The electrode 10 may be a long strip electrode constituting a wound electrode body or a rectangular electrode constituting a stacked electrode body. It should be noted that the electrode 10 can be used as a positive electrode, a negative electrode, or both of the positive and negative electrodes of a non-aqueous electrolyte secondary battery.

[0032] The core material 11 can be made of metal foil, a film with a metal layer formed on the surface, or the like. 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 made of a metal foil having aluminum as its main component. In the case of a negative electrode, a metal foil having copper as its main component can be used. In this specification, the main component refers to the constituent with the highest mass ratio. The core material 11 can be an aluminum foil containing substantially 100% aluminum, or a copper foil containing substantially 100% copper.

[0033] The electrode composite material 12 comprises PTFE powder, an active material and a conductive material. 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 include a binding material such as unfibrillated polyvinylidene fluoride (PVdF). The electrode composite material 12 is composed of the active material as the main component. The content of the active material is preferably 85% by mass to 99% by mass relative to the mass of the electrode composite material 12, and more preferably 90% by mass to 99% by mass.

[0034] In the active material of the positive electrode (positive electrode active material), lithium transition metal composite oxides are generally used. As the metal elements contained in the lithium transition metal composite oxide, Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. can be mentioned. Among them, it is preferred to contain at least one of Ni, Co, and Mn. In the active material of the negative electrode (negative electrode active material), natural graphite such as flaky graphite, bulk graphite, and earthy graphite, blocky artificial graphite (MAG), graphitized mesophase carbon microbeads (MCMB) and other artificial graphite are used. In addition, Si-based active materials alloyed with lithium can also be used as the negative electrode active material.

[0035] Examples of the conductive material contained in the electrode composite material 12 include carbon materials such as carbon black (CB), acetylene black (AB), Ketjen black, and graphite. The content of the conductive material relative to the mass of the electrode composite material 12 is, for example, 0.5% to 5.0% by mass.

[0036] The coverage of the conductive material on the active material surface is preferably 10% to 60%, more preferably 20% to 60%. A sufficiently high coverage of the conductive material can improve the battery properties of the electrode. As described later, the coverage of the conductive material can be increased by shortening the mixing time of the PTFE powder, the active material, and the conductive material.

[0037] The content of the PTFE powder relative to the mass of 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 active material and entangles with the active material. In other words, the positive electrode active material is maintained by the PTFE powder in a mesh-like form. By including a predetermined amount of fibrous particles A and / or fibrous particles B in the PTFE powder, an electrode composite material sheet with good formability and high fracture strength can be produced.

[0038] When the electrode composite material 12 is divided into three equal parts along the thickness direction, and the electrode composite material 12 is divided into a first region, a second region, and a third region 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 (ca) / (a+b+c) ≤ ±10%, preferably (ca) / (a+b+c) ≤ ±5%. In other words, by ensuring that 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 is within the range of ±10%, preferably within the range of ±5%, relative to the total PTFE powder content (a+b+c), the PTFE powder can be present substantially uniformly throughout the electrode composite material 12 without being distributed throughout a portion of the electrode composite material 12.

[0039] The electrode composite material 12 preferably satisfies a peripheral speed ratio at break of 8 or more. The peripheral speed ratio at break of the electrode composite material 12 refers to the peripheral speed ratio at break when the test piece for measuring the peripheral speed ratio at break is formed. The peripheral speed ratio at break can be measured as follows: when the electrode composite particles are formed into a test piece, the peripheral speed ratio of a pair of forming rollers is changed to determine the peripheral speed ratio at which the piece breaks. "The peripheral speed ratio at break of the electrode composite material 12 preferably satisfies a peripheral speed ratio at break of 8 or more" means "The peripheral speed ratio at break when the test piece for measuring the peripheral speed ratio at break preferably satisfies a peripheral speed ratio at break of 8 or more". When the peripheral speed ratio at break of the electrode composite material 12 satisfies 8 or more, it can be determined that the fibrillation of the PTFE powder contained in the electrode composite material 12 is properly carried out, the electrode composite material 12 that satisfies this condition has excellent formability, and an electrode composite material 12 with high fracture strength can be produced from the electrode composite material 12 that satisfies this condition. The peripheral speed ratio at break is more preferably 9 or more, and further preferably 10 or more.

[0040] The method for measuring the peripheral velocity ratio at break of the electrode composite material 12 is as follows. The peripheral velocity ratio at break can be measured using the method described below. Figure 2 The electrode composite material particles 12a shown in (b) are rolled and formed into a sheet-shaped electrode composite material sheet 12b using the same apparatus. Figure 2 As shown in (b), two rollers are used to roll the electrode composite material particles 12a to form the electrode composite material 12 into a sheet. When the electrode composite material is formed into a sheet, the linear pressure of the two constant pressure rollers is fixed to about 0.03t / cm, the gap is fixed to 0μm, the circumferential speed of one roller is fixed to 5m / minute, and the circumferential speed ratio is changed from 1 to 10 one by one while the electrode composite material is sheeted. The smallest circumferential speed ratio among the circumferential speed ratios in which a fracture is confirmed in the sheet is used as the fracture circumferential speed ratio. It should be noted that the sheet of electrode composite material obtained when the fracture circumferential speed ratio of the electrode composite material is measured is equivalent to the test piece. In this specification, the test piece can also be replaced by an electrode composite material sheet.

[0041] The peripheral speed ratio is the ratio of the peripheral speed of one roller to the peripheral speed of the other roller, expressed as a ratio. The fracture peripheral speed ratio is the ratio of the peripheral speeds at the time the test piece breaks, expressed as a ratio of the peripheral speed of one roller to the peripheral speed of the other roller at the time the test piece breaks, expressed as a ratio of the peripheral speed of the other roller at the time the test piece breaks, expressed as a ratio of the peripheral speed of one roller to the peripheral speed of the other roller at the time the test piece breaks. A larger peripheral speed ratio between the two rollers increases the transverse shear force, making the test piece more susceptible to fracture. Therefore, a larger peripheral speed ratio at fracture indicates a higher fracture strength.

[0042] The electrode composite material 12 is preferably a mixture in which the active material, PTFE powder and conductive material are uniformly dispersed, and the fracture circumferential velocity ratio of the electrode composite material 12 becomes an indicator showing the dispersibility of the constituent materials. In addition, the electrode composite material 12 is preferably a mixture in which the particles of the active material are less broken and a large amount of conductive material is attached to the particle surface of the active material to form a conductive path between the particles. In other words, the electrode composite material 12 must be produced in such a way that the particles of the active material are suppressed from breaking and the amount of conductive material adhering to the particle surface of the active material by the conductive material is not reduced by the conductive material adsorbed into the PTFE powder. According to the manufacturing method described below, a high-quality electrode composite material 12 that meets such conditions can be produced.

[0043] [Method for manufacturing electrode]

[0044] The following describes the method for manufacturing the electrode 10 in further detail. While the following illustrates the method for manufacturing a positive electrode, this method is also applicable 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. Alternatively, the conductive material may not be added.

[0045] Figure 2 and Figure 3 The figure schematically shows the manufacturing process of the electrode 10 as an example of an embodiment. The manufacturing method of the electrode 10 includes Figure 2 (a) the mixing step, Figure 2 (b) the calendering step, and Figure 3 The laminating step is shown. In the mixing step, PTFE powder, active material, and conductive material are mixed to produce electrode composite material particles 12a having a solid content concentration of substantially 100%. In the rolling step, the electrode composite material particles 12a are rolled and formed into a sheet to produce an electrode composite material sheet. In the laminating step, the electrode composite material sheet is laminated to a core material to produce an electrode.

[0046] The manufacturing method of the electrode 10 is a dry process for manufacturing the electrode 10 using an electrode composite material 12 having a solid content concentration of substantially 100%. A dry process refers to a process in which active material particles and binding material particles are mixed without using a solvent, that is, the active material and the binding material are mixed in a state in which the solid content concentration is substantially 100%. The manufacturing method of the electrode 10 of the present invention does not require the use of a solvent as in the conventional manufacturing method of the electrode 10. The so-called "not requiring the use of a solvent" means not only that a simple raw material is not required, but also that a drying process for the solvent is not required, and exhaust equipment related to the drying process is also not required.

[0047] In the mixing step, raw materials such as PTFE powder, active material, and conductive material are mixed in a mixer 20 to produce electrode composite material particles 12a. In the mixing step, by using PTFE powder containing a specified amount of fibrous particles A and / or fibrous particles B to carry out a short-term mixing process, it is possible to improve the coverage of the conductive material on the surface of the active material while improving the dispersibility of the constituent materials, thereby improving the formability and fracture strength of the electrode composite material 12. The fracture circumferential velocity ratio of the electrode composite material 12 is preferably 8 or more. The fracture circumferential velocity ratio of the electrode composite material 12 becomes an index representing the dispersibility of the constituent materials and then the formability and fracture strength of the electrode composite material 12. It should be noted that, when a long-term mixing process is carried out, the conductive material is incorporated into the binding material, and the coverage of the conductive material on the active material surface is less than 10%. In addition, by using PTFE powder containing a specified amount of fibrous particles A and / or fibrous particles B, even a short-term mixing process can improve the dispersibility of the constituent materials, thereby suppressing the rupture of the active material during the mixing process. It should be noted that the active material contained in the electrode may include a material that may be broken during the mixing process or a material that may be broken during the rolling step described later.

[0048] In the mixing step, before the active material and the conductive material are put into the mixer 20, the conductive material may be preliminarily attached to the surface of the active material by a mechanical mixing method or the like. By preliminarily attaching the conductive material to the surface of the active material, the mixing process in the mixer 40 can be set to a short time for obtaining a state in which the raw materials other than the conductive material are dispersed. The mechanical mixing method is a dry treatment method performed in a mechanical mixing reaction device having a compression tool and blades inside and a cylindrical chamber that rotates at high speed. The rotation speed is usually faster than 1000 rpm. By placing the conductive material and the active material in the chamber and rotating the chamber, the particles are squeezed against each other and squeezed by the chamber wall. When a compression tool is used and centrifugal force is generated by high-speed rotation, the adhesion and bonding of the conductive material and the active material are promoted. Examples of mechanical mixing reaction apparatuses include the "Nobilta" (registered trademark) pulverizer and the "MechanoFusion" (registered trademark) pulverizer manufactured by Hosokawa Micron Corporation (Japan), the "Hybridiser" (trademark) pulverizer manufactured by Nara Machinery Manufacturing Co., Ltd., the "Balance Gran" manufactured by Freund-Turbo Corporation, and the "COMPOSI" manufactured by Nippon Coke & Engineering, Co., Ltd.

[0049] As the mixer 40, for example, a conventionally known mechanical stirring mixer can be used. As a specific example of a suitable mixer 40, a device that can impart mechanical shear force, a shredder, a pin mill, a bead mill, a microparticle composite device (a device that generates shear force between a rotor with a special shape that can rotate at high speed inside a tank and a collision plate), a granulator, a twin-screw extruder, a planetary mixer, etc. can be cited, preferably a shredder, a microparticle composite device, a granulator, a twin-screw extruder. Thus, the PTFE powder can be further fibrillated while mixing the raw materials. The processing time of the mixing step (the time when shear force is applied to the material) is preferably within a few minutes, for example, it can be 0.5 minutes to 4 minutes. Since the PTFE powder contains a predetermined amount of fibrous particles A and / or fibrous particles B that have been fibrillated, if the processing time is more than 0.5 minutes, the PTFE powder can be attached to the particle surface of the active material and entangled with the active material. When the processing time is too long, the amount of conductive material incorporated into the PTFE powder increases. In this case, the conductivity of the electrode composite material sheet is greatly reduced, the resistance increases, etc., which has an adverse effect on battery characteristics. In addition, the longer the treatment time, the more the fibrillation of PTFE proceeds. Therefore, if the fibrillation proceeds excessively, the breaking strength of the sheet becomes lower.

[0050] like Figure 2 As shown in (b), in the calendering step, two rollers 22 are used to calender the electrode composite material particles 12a and form them into a sheet. The two rollers 22 are arranged at a predetermined gap and rotate in the same direction. The electrode composite material particles 12a are supplied to the gap between the two rollers 22, thereby being compressed by the two rollers 22 and stretched into a sheet. The two rollers 22 have, for example, the same roller diameter. The obtained electrode composite material sheet 12b can pass through the gap between the two rollers 22 multiple times, or can be stretched more than once using other rollers with different roller diameters, peripheral speeds, gaps, etc. In addition, the rollers can be heated to perform heat pressing on the electrode composite material particles 12a.

[0051] The thickness of the electrode composite material sheet 12b can be controlled by, for example, the gap between the two rollers 22, the peripheral speed, the number of stretching treatments, etc. In the calendering step, it is preferred to use two rollers 22 with a peripheral speed ratio that is more than 2 times different to form the electrode composite material particles 12a into a sheet. By making the peripheral speed ratio of the two rollers 22 different, it is easier to make the electrode composite material sheet 12b into a thin film, and productivity is improved. The peripheral speed ratio of the two rollers 22 is more preferably 2.5 times or more, and can also be 3 times or more. It should be noted that the greater the peripheral speed ratio, the greater the shear force acting on the electrode composite material sheet 12b, and therefore, a high breaking strength is required for the electrode composite material sheet 12b.

[0052] Then, if Figure 3As shown, in the laminating step, the electrode composite material sheet 12 b is laminated to the core material 11 , thereby obtaining the electrode 10 having the composite material layer including the electrode composite material 12 provided on the surface of the core material 11 . Figure 3 , the electrode composite material 12 is bonded to only one surface of the core material 11, but it is preferred that the electrode composite material 12 be bonded to both surfaces of the core material 11. Two sheets of the electrode composite material 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.

[0053] In the laminating step, two rollers 24 are used to laminate the electrode composite material sheet 12b to the surface of the core material 11. The two rollers 24 have, for example, the same roller diameter, are arranged with a predetermined gap therebetween, and rotate in the same direction at the same peripheral speed. The two rollers 24 are preferably heated to a predetermined temperature and applied with a predetermined pressure.

[0054] <Example>

[0055] Hereinafter, the present invention will be further described with reference to Examples, but the present invention is not limited to these Examples.

[0056] <Example 1-1>

[0057] [Production of PTFE powder]

[0058] A PTFE raw material (PTFE particles) having an average particle size of 343 μm was pulverized using a jet mill at a feed rate of 3 kg / h and a pulverization pressure of 0.6 MPa to obtain a PTFE powder having a median particle size of 15.4 μm.

[0059] [Adhesion treatment of conductive material on the surface of positive electrode active material]

[0060] Using NOB300® Nobilta (registered trademark) manufactured by Hosokawa Micron Corporation, 1000 g of the lithium transition metal composite oxide and 10 g of acetylene black (AB) were mixed in a NOBILTA grinder for 5 minutes to prepare a carbon-attached positive electrode active material.

[0061] [Preparation of positive electrode composite material particles]

[0062] The carbon-coated positive electrode active material and PTFE powder were placed in a mixer (Wonder Crusher, manufactured by Osaka Chemical) at a mass ratio of 101:4 and mixed for 2 minutes at room temperature at a speed of dial 5. The Wonder Crusher speed was set to 28,000 rpm, the maximum speed on dial 10. This mixing process yielded positive electrode composite material particles in which the positive electrode active material, PTFE powder, and AB were uniformly dispersed. The resulting positive electrode composite material had a solids concentration of 100%.

[0063] [Production of positive electrode composite material sheet]

[0064] The obtained positive electrode composite material particles were passed between two rolls and rolled to produce a positive electrode composite material sheet. The peripheral speed ratio of the two rolls was set to 1:3, and the thickness of the positive electrode composite material sheet was adjusted to about 100 μm.

[0065] The obtained positive electrode composite material particles and positive electrode composite material sheets were evaluated for breaking strength and film-forming properties (appearance) of the sheets by the following methods. The evaluation results are shown in Table 1 together with the state of the PTFE powder.

[0066] [Evaluation of breaking strength]

[0067] Different from the preparation of the positive electrode composite material sheet, a test piece was formed to measure the fracture peripheral velocity ratio and evaluate the fracture strength. The test piece was formed as follows: the positive electrode composite material particles were Figure 2 (b) During sheeting, the linear pressure between two constant pressure rollers was constant at approximately 0.03 t / cm, the gap was constant at 0 μm, and the peripheral speed of one roller was constant at 5 m / min. The peripheral speed ratio was varied from 1 to 10, and the sheet was formed. The minimum peripheral speed ratio at which the sheet broke was defined as the peripheral speed ratio at break, and the sheet's breaking strength was evaluated. The peripheral speed ratio at break was measured multiple times, and the average of the minimum peripheral speed ratios at which the sheet broke during each measurement was defined as the peripheral speed ratio at break.

[0068] [Evaluation of film-forming properties]

[0069] The resulting positive electrode composite material sheets were visually observed to evaluate film-forming properties based on the presence of white streaks due to poor PTFE powder dispersion and the condition of the sheet at the ends. The presence of white streaks was evaluated as 0 if the PTFE powder was uniformly dispersed with almost no white streaks observed, and as x if the PTFE powder was uniformly dispersed. "Many white streaks and significant fibrous PTFE non-uniformity" indicated insufficient fibrillization of the PTFE, with white streaks observed due to the presence of large PTFE particles. Regarding the sheet condition at the ends, a 0 was evaluated if the sheets formed equally well at both ends perpendicular to the stretching direction of the positive electrode composite material sheet as at the center, and x was evaluated if the ends were powdery and insufficiently formed. "Powdery at the ends and insufficiently formed" indicates that the pressure during rolling was lower at the ends than at the center, resulting in insufficient compression and insufficient forming, resulting in a powdery state. The evaluation results for the presence of white streaks and the sheet condition at the ends are shown in Table 1 under "White Streaks" and "Ends."

[0070] <Example 1-2>

[0071] In the production of PTFE powder, a jet mill was used instead of a jet mill, and pulverization was carried out in a continuous process at a feed rate of 20 kg / h, a rotation speed of 8000 rpm, and a gap of 2 mm. Positive electrode composite material particles and positive electrode composite material sheets were produced and evaluated in the same manner as in Example 1. The median particle size of the resulting PTFE powder was 9.3 μm.

[0072] <Comparative Example 1-1>

[0073] Positive electrode composite material particles and positive electrode composite material sheets were prepared and evaluated in the same manner as in Example 1 except that PTFE powder was not prepared and untreated PTFE raw material was used for preparing positive electrode composite material particles.

[0074] <Comparative Example 1-2>

[0075] In the production of PTFE powder, an air flow mill was used instead of a jet mill, and the powder was crushed in a continuous process under the conditions of a supply rate of 10 kg / h, a rotation speed of 5000 rpm, and a gap of 5 mm. Otherwise, positive electrode composite material particles and positive electrode composite material sheets were produced in the same manner as in Example 1 and evaluated.

[0076] <Comparative Examples 1-3>

[0077] In the production of PTFE powder, a dry bead mill was used instead of a jet mill, and the powder was crushed in a continuous process at a flow rate of 0.4 L / min, a peripheral speed of 14 m / s, and a bead diameter of φ1.0 mm. In addition, positive electrode composite material particles and positive electrode composite material sheets were prepared in the same manner as in Example 1 and evaluated.

[0078] <Comparative Examples 1-4>

[0079] In the preparation of PTFE powder, a wet bead mill was used instead of a jet mill, ethanol was used as the solvent in a batch process, and ZrO2 beads with a diameter of 2.0 mm were used for 60 minutes. Otherwise, positive electrode composite material particles and positive electrode composite material sheets were prepared and evaluated in the same manner as in Example 1.

[0080] [Table 1]

[0081]

[0082] The evaluation results shown in Table 1 show that the positive electrode composite material sheets of Examples have better film-forming properties (appearance) and higher breaking strength than the positive electrode composite material sheets of Comparative Examples.

[0083] <Example 2-1>

[0084] [Production of positive electrode]

[0085] The positive electrode composite material sheet prepared in Example 1-1 was placed on the surface of the positive electrode core material, and the stack of the positive electrode composite material sheet and the positive electrode core material was pressed using two rollers (linear pressure: 1.0 t / cm) to obtain a positive electrode. Aluminum alloy foil was used as the core material.

[0086] <Example 2-2>

[0087] A positive electrode was produced in the same manner as in Example 2-1, except that the PTFE powder obtained in Example 1-2 was used instead of the PTFE powder obtained in Example 1-1 in the production of positive electrode composite material particles.

[0088] <Example 2-3>

[0089] In the preparation of the positive electrode composite material particles, a positive electrode was prepared in the same manner as in Example 2-2 except that the rotation speed of the mixer was changed to dial 3.

[0090] <Example 2-4>

[0091] In the preparation of the positive electrode composite material particles, a positive electrode was prepared in the same manner as in Example 2-2 except that the rotation speed of the mixer was changed to dial 1.

[0092] <Example 2-5>

[0093] In the preparation of the positive electrode composite material particles, a positive electrode was prepared in the same manner as in Example 2-2 except that the rotation speed of the mixer was changed to dial 1 and the mixing time was changed to 1 minute.

[0094] <Comparative Example 2-1>

[0095] In the preparation of positive electrode composite material particles, a positive electrode was prepared in the same manner as in Example 2-1 except that the PTFE powder obtained in Comparative Example 1-1 was used instead of the PTFE powder obtained in Example 1-1 and the mixing time was changed to 5 minutes.

[0096] For the positive electrodes obtained in Examples and Comparative Examples, the binder contents in the first, second, and third regions of the positive electrode composite materials and the AB coverage on the surface of the active material were evaluated. The evaluation results are shown in Table 2 together with the preparation conditions of the positive electrode composite material particles.

[0097] [Table 2]

[0098]

[0099] The evaluation results shown in Table 2 show that the coverage of the conductive material on the active material surface of the positive electrodes of the examples is 10% to 60%, and the content of the PTFE powder in the first region (a), the content of the PTFE powder in the second region (b), and the content of the PTFE powder in the third region (c) satisfy (ca) / (a+b+c)≤±10%. On the other hand, the coverage of the conductive material on the active material surface of the positive electrodes of the comparative examples is less than 10%. Therefore, it can be inferred that the positive electrodes of the examples, due to the high coverage of the conductive material on the positive electrode active material, can improve the battery characteristics of the electrode compared to the positive electrodes of the comparative examples.

[0100] In Examples 2-5, the positive electrodes were produced at a lower mixing speed and shorter mixing time than in the other examples. This demonstrates that lower mixing speeds and shorter mixing times can achieve higher conductive coverage. On the other hand, shorter mixing times are more likely to affect the dispersibility of the composite material particles, compared to the binder content in the first, second, and third regions.

[0101] Description of Reference Numerals

[0102] 10 electrodes

[0103] 11 core material

[0104] 12 Electrode composite materials

[0105] 12a Electrode composite material particles

[0106] 12b electrode composite material sheet

[0107] 20 mixer

[0108] 22, 24 rollers

Claims

1. A PTFE powder, which is a PTFE powder in a dry state, The fibrous PTFE particles having an aspect ratio of 1.5 or greater are contained in a ratio of 20% to 60% relative to the total particles. The average major axis size of the fibrous PTFE particles is 1 μm to 20 μm.

2. The PTFE powder according to claim 1, wherein The average aspect ratio of the fibrous PTFE particles is 2-20.

3. The PTFE powder according to claim 1 or 2, wherein the median particle size is 2 μm to 20 μm. 4 . The PTFE powder according to claim 1 , which is used as a binder for a positive electrode of a non-aqueous electrolyte secondary battery.

5. A PTFE powder, which is a PTFE powder in a dry state, The fibrous PTFE particles having an aspect ratio of 5 or greater are contained at a ratio of 60% or greater relative to the total particles. The average minor axis size of the fibrous PTFE particles is 1 μm to 20 μm. The median particle size of the PTFE powder is 2 μm to 20 μm. 6 . The PTFE powder according to claim 5 , which is used as a binder for a positive electrode of a non-aqueous electrolyte secondary battery.

7. A method for manufacturing an electrode, comprising: A mixing step of mixing the PTFE powder, active material and conductive material according to any one of claims 1 to 6 to prepare electrode composite material particles with a solid content concentration of 100%; a calendering step of calendering the electrode composite material particles to form a sheet to produce an electrode composite material sheet; and a laminating step of laminating the electrode composite material sheet to the core material to produce the electrode, The content of the active material is 85% to 99% by mass relative to the mass of the electrode composite material. The content of the PTFE powder is 0.5% to 5.0% by mass relative to the mass of the electrode composite material. The content of the conductive material is 0.5% to 5.0% by mass relative to the mass of the electrode composite material. The thickness of the electrode composite material is 30 μm to 120 μm.

8. The method for manufacturing an electrode according to claim 7, wherein: In the calendering step, the electrode composite material particles are formed into a sheet shape using two rolls having a peripheral speed ratio that differs by more than 2 times.

9. An electrode comprising an electrode composite material comprising the PTFE powder according to any one of claims 1 to 6, an active material, and a conductive material laminated on the surface of a core material, The coverage rate of the conductive material on the surface of the active material is 10% to 60%. When the electrode composite material is divided into three equal parts along the thickness direction and is divided into a first region, a second region, and a third region from the core material side, the content (a) of the PTFE powder in the first region, the content (b) of the PTFE powder in the second region, and the content (c) of the PTFE powder in the third region satisfy (ca) / (a+b+c)≤±10%, The content of the active material is 85% to 99% by mass relative to the mass of the electrode composite material. The content of the PTFE powder is 0.5% to 5.0% by mass relative to the mass of the electrode composite material. The content of the conductive material is 0.5% to 5.0% by mass relative to the mass of the electrode composite material. The thickness of the electrode composite material is 30 μm to 120 μm.

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