Method for manufacturing electrode mixture sheet, method for manufacturing battery, electrode mixture sheet, and battery

Abstract

To provide a method for manufacturing an electrode mixture sheet having excellent tensile strength.SOLUTION: The method for manufacturing an electrode mixture sheet according to the present disclosure includes: attaching polyvinylidene fluoride to a plurality of active material particles to produce a plurality of PVdF-attached active material particles; mixing the plurality of PVdF-attached active material particles with a plurality of polytetrafluoroethylene particles to produce a mixture; and applying pressure to the mixture to fibrillate the plurality of polytetrafluoroethylene particles. The mixture contains no solvent. Producing the mixture is performed at 80°C to 150°C. The fibrillation is performed at 160°C or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrode mixture sheet, a method for manufacturing a battery, an electrode mixture sheet, and a battery. [Background technology]

[0002] A dry process is known as a method for manufacturing electrodes for lithium-ion secondary batteries. In this process, a self-supporting electrode mixture sheet containing active material particles and a binder is produced without using a solvent. The resulting electrode mixture sheet is integrated with a current collector to obtain an electrode. The term "self-supporting" refers to the ability to maintain its shape without a support.

[0003] As a method for manufacturing an electrode by a dry method, a method has been proposed in which a resin that has the property of becoming fibrous (fibrillated) when a shear force is applied is used as a binder.

[0004] Patent Document 1 discloses a method for manufacturing an electrode film (hereinafter also referred to as "electrode"). The manufacturing method includes a first step, a second step, and a third step. In the first step, a first dry electrode mixture is formed containing dried carbon particles and dried fibrillizable binder particles (e.g., polytetrafluoroethylene). In the second step, the binder in the dried electrode film mixture is ultrafibrillated by an ultrafibrillation treatment (e.g., mechanical shearing treatment) to form an ultrafibrillated matrix in the electrode film mixture. In the third step, the ultrafibrillated electrode film mixture is calendered to form a free-standing ultrafibrillated electrode film. Patent Document 1 does not disclose the treatment temperature for the ultrafibrillation treatment (e.g., mechanical shearing treatment). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-003694 Summary of the Invention [Problem to be solved by the invention]

[0006] If an electrode mixture sheet is damaged (for example, broken or cracked), the battery performance may be reduced. Therefore, there is a demand for an electrode mixture sheet that is less susceptible to damage (i.e., an electrode mixture sheet having excellent tensile strength).

[0007] The present disclosure has been made in consideration of the above circumstances. An object of one embodiment of the present disclosure is to provide a method for manufacturing an electrode mixture sheet having excellent tensile strength, and a method for manufacturing a battery including the method for manufacturing the electrode mixture sheet. Another problem to be solved by another embodiment of the present disclosure is to provide an electrode mixture sheet capable of improving the unit charge capacity of a battery, and a battery including the electrode mixture sheet. [Means for solving the problem]

[0008] The means for solving the above problems include the following embodiments. <1> attaching polyvinylidene fluoride to a plurality of active material particles to form a plurality of PVdF-coated active material particles; mixing a plurality of the PVdF-attached active material particles with a plurality of polytetrafluoroethylene particles to prepare a mixture; applying pressure to the mixture to fiberize the polytetrafluoroethylene particles; Including, the mixture is solvent-free; preparing the mixture is carried out at 80°C to 150°C; A method for producing an electrode mixture sheet, wherein the pre-fiberization is carried out at 160°C or less. <2> The step of preparing the mixture is carried out at a temperature of 80°C to 120°C. <1> A method for producing the electrode mixture sheet according to claim 1. <3> The aforementioned <1> or <2> A method for manufacturing a battery, comprising producing an electrode mixture sheet by the method for manufacturing an electrode mixture sheet according to claim 1. <4> The battery includes a plurality of active material particles, polyvinylidene fluoride, and a plurality of polytetrafluoroethylene fibrous materials, an electrode mixture sheet, wherein a content ratio of the polyvinylidene fluoride relative to the total amount of the active material particles, the polyvinylidene fluoride, and the polytetrafluoroethylene fibrous substances is 5 mass % or more; <5> The aforementioned <4> A battery comprising the electrode mixture sheet according to claim 1. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, there are provided a method for manufacturing an electrode mixture sheet having excellent tensile strength, and a method for manufacturing a battery including the method for manufacturing the electrode mixture sheet. According to another embodiment of the present disclosure, there are provided an electrode mixture sheet capable of improving the unit charge capacity of a battery, and a battery including the electrode mixture sheet. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a scanning electron microscope (SEM) image of the surface of the mixture of Example 1-2. [Figure 2] FIG. 2 is a scanning electron microscope (SEM) image of the surface of the mixture of Comparative Example 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when multiple substances corresponding to each component are present, the amount of each component means the total amount of multiple substances unless otherwise specified. In the present disclosure, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0012] (1) Manufacturing method of electrode composite sheet The method for producing an electrode mixture sheet according to the present disclosure includes: Adhering polyvinylidene fluoride (hereinafter also referred to as "PVdF") to a plurality of active material particles to prepare a plurality of PVdF-attached particles (hereinafter also referred to as "composite step"); mixing a plurality of the PVdF-attached particles with a plurality of polytetrafluoroethylene (hereinafter also referred to as "PTFE") particles to prepare a mixture (hereinafter also referred to as "mixing step"); and applying pressure to the mixture to fiberize the plurality of polytetrafluoroethylene particles (hereinafter also referred to as the "fiberization step"). The mixture does not contain a solvent. The preparation of the mixture (i.e., the mixing step) is carried out at 80°C to 150°C. The fiberization (i.e., the fiberization step) is carried out at 160°C or lower. The compounding step, the mixing step, and the fiberization step are carried out in this order.

[0013] In the present disclosure, the term "electrode mixture sheet" refers to a self-supporting sheet containing active material particles. The term "the mixture does not contain a solvent" indicates that the manufacturing method of the electrode mixture sheet is a dry method.

[0014] The method for producing an electrode mixture sheet according to the present disclosure has the above-described configuration, and therefore has excellent tensile strength. This effect is presumably due to, but not limited to, the following reasons. The manufacturing method of the present disclosure includes a compounding step and a mixing step. Unlike conventional methods, the mixing step of the present disclosure is performed while heating (i.e., at 80°C to 150°C). Therefore, the PTFE particles in the mixture are more easily dispersed than in the first, second, or third cases. "Case 1" refers to a case where the mixing step is performed while heating at a temperature outside the range of 80°C to 150°C. "Case 2" refers to a case where multiple active material particles, PVdF, and multiple PTFE particles are mixed without performing the compounding step. "Case 3" refers to a case where multiple active material particles, PVdF, and multiple PTFE fibrous materials (hereinafter also referred to as "PTFE fibrous materials") are mixed. If the PTFE particles in the mixture are dispersed, the PTFE fibrous materials are more likely to become entangled with the PVdF-attached particles when the fiberizing step is performed. As a result, it is presumed that the tensile strength of the resulting electrode mixture sheet is improved.

[0015] In addition, the manufacturing method of the present disclosure does not use a solvent when manufacturing the electrode mixture sheet. Therefore, the manufacturing method of the present disclosure has excellent affinity with living organisms and the environment. Furthermore, the manufacturing method of the present disclosure does not require a step of volatilizing the solvent after film formation. As a result, the manufacturing method of the present disclosure has excellent manufacturing efficiency.

[0016] The electrode mixture sheet produced by the electrode mixture sheet manufacturing method of the present disclosure is used as an electrode mixture layer (positive electrode mixture layer or negative electrode mixture layer) of a battery electrode. The type of battery is not particularly limited, and examples include lithium ion secondary batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, cobalt-titanium lithium secondary batteries, and sodium-ion secondary batteries. A lithium ion secondary battery includes a negative electrode, a positive electrode, and an ion-conducting medium. The ion-conducting medium is interposed between the positive electrode and the negative electrode and conducts carrier ions. Examples of the ion-conducting medium include a nonaqueous electrolyte, a nonaqueous gel electrolyte, a solid ion-conducting polymer, and an inorganic solid electrolyte.

[0017] (1.1) Composite process In the compounding step, PVdF is attached to a plurality of active material particles to produce a plurality of PVdF-attached particles. By carrying out the compounding step, the plurality of PTFE particles in the mixture are easily dispersed in the mixing step.

[0018] The term "active material particles" refers to particles made of a positive electrode active material (hereinafter also referred to as "positive electrode active material particles") or particles made of a negative electrode active material (hereinafter also referred to as "negative electrode active material particles").

[0019] The method for adhering PVdF to the active material particles (hereinafter also referred to as the "adhering method") is not particularly limited and may be any known method, such as stirring, spray drying, freeze drying, atomic layer deposition (ALD), ion plating, or sputtering.

[0020] The adhesion conditions (e.g., temperature, time, etc.) are not particularly limited and are appropriately selected depending on the adhesion method. The composite step may be carried out while cooling the adhesion material so that the plurality of active material particles and PVdF (hereinafter also referred to as "adhesion material") are kept at 23°C.

[0021] (1.1.1) Active material particles The active material particles are negative electrode active material particles or positive electrode active material particles.

[0022] The negative electrode active material may be a known negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include carbon (e.g., natural graphite, artificial graphite), and compounds that can be alloyed with lithium (e.g., silicon, tin, etc.). The negative electrode active material may be one type alone or two or more types. The positive electrode active material may be a known positive electrode active material for lithium ion secondary batteries. Examples of the positive electrode active material include lithium transition metal composite oxides. Examples of the lithium transition metal composite oxides include a compound represented by LiMO2 (wherein M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), LiMn2O4, or LiMPO4 (wherein M is Fe, Co, Ni, or Mn). The positive electrode active material may be one type alone or two or more types.

[0023] The volume average particle diameter of the active material particles is not particularly limited and may be 5 μm to 30 μm. The "volume average particle diameter" refers to the value (D50) at which the cumulative total from the small diameter side reaches 50% in the volume-based particle size distribution measured by a laser diffraction / scattering method.

[0024] (1.1.2)PVdF PVdF has adhesive properties and may be attached to the entire surface of the active material particles or to only a portion of the surface of the active material particles.

[0025] The amount of PVdF mixed relative to the total amount of the multiple active material particles is not particularly limited, and may be 3% by mass to 15% by mass, 5% by mass to 15% by mass, or 5% by mass to 10% by mass.

[0026] (1.1.3) Conductive additive In the composite process, a conductive additive may be mixed in addition to the PVdF and active material particles. The conductive additive is not particularly limited, and examples thereof include carbon materials. Examples of the carbon material include carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes, and graphite.

[0027] (1.2) Mixing process In the mixing step, a plurality of PVdF-attached particles and a plurality of PTFE particles are mixed to prepare a mixture. This allows the plurality of PTFE particles to be dispersed in the mixture. As a result, an electrode mixture sheet having superior tensile strength can be obtained compared to the case where a plurality of PVdF-attached particles and a plurality of PTFE fibrous materials are mixed.

[0028] "Polytetrafluoroethylene particles" refers to particles made of PTFE. "Particles" refers to particles that are not fibers. Specifically, "particles" refers to particles with an aspect ratio of 5 or more. "Fibers" refers to particles with an aspect ratio of less than 5. PTFE particles generally have a lamellar structure in which multiple molecular chains are gathered in ribbon-like (flat) shapes. When shear force is applied to PTFE particles, the lamellar structure melts and the PTFE particles become fibrous. In other words, PTFE particles are transformed into PTFE fibrous materials by shear force. "PTFE fibrous materials" include PTFE that has completely transformed into fibers and PTFE in which some PTFE particles have transformed into fibers. The mixing process is carried out using a heating device. The "temperature" during the mixing process refers to the set temperature of the heating device.

[0029] In the mixing step, a known mixing device for stirring the plurality of PVdF-attached particles and the plurality of PTFE particles, and a known heating device for heating the mixture being stirred are used.

[0030] The mixing step is carried out at 80°C to 150°C. If the temperature in the mixing step is lower than 80°C, an electrode mixture sheet having excellent tensile strength may not be obtained. If the temperature in the mixing step is higher than 150°C, a portion of the PVDF may melt, causing a decrease in the adhesiveness of the PVDF. As a result, an electrode mixture sheet having excellent tensile strength may not be obtained. The mixing step is preferably carried out at a temperature of 80° C. to 120° C. This makes it possible to obtain an electrode mixture sheet having superior tensile strength.

[0031] The mixing speed of the mixer is not particularly limited and may be 1000 rpm (revolutions per minute) to 6000 rpm, or 2000 rpm to 4000 rpm. The mixing time of the mixer is not particularly limited and may be 1 minute to 60 minutes, or 10 minutes to 20 minutes.

[0032] (1.2.1)PTFE particles The PTFE particles are converted into PTFE fibrous materials by the fiberization step, which improves the tensile strength of the electrode mixture sheet.

[0033] In the mixing step, at least a portion of the PTFE particles may be fibrous. In this case, a granule may be produced. The granule includes a plurality of active material particles and PTFE fibrous material bound to at least a portion of the active material particles.

[0034] The amount of PTFE particles mixed relative to the total amount of multiple active material particles is not particularly limited, and may be 1% by mass to 10% by mass, 2% by mass to 8% by mass, or 3% by mass to 6% by mass.

[0035] (1.2.2) Other resins In the mixing step, a resin other than the PVdF-attached particles and the PTFE particles may be added and mixed. In other words, the mixture may further contain another resin. Examples of the other resin include polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, and polymethacrylate.

[0036] (1.3) Fiberization process In the fiberization step, pressure is applied to the mixture to fiberize the PTFE particles.

[0037] The fiberization process is carried out using a pressure device. The "temperature" of the fiberization process is carried out using a pressure device (e.g., a rolling device or a press device). The "temperature" of the fiberization process refers to the surface temperature of the surface of the pressure device that comes into contact with the mixture.

[0038] The method of applying pressure to the mixture (hereinafter also referred to as "pressurizing method") is not particularly limited, and examples thereof include rolling and pressing. In rolling, a known rolling device is used to roll the mixture. In pressing, a known pressing device is used to press the mixture. The rolling device includes a pair of metal rolls and a heating device that heats the pair of metal rolls. The pressing device includes a pair of metal plates and a heating device that heats the pair of metal plates. The mixture may be formed into a sheet at the same time as the plurality of PTFE particles are fiberized. The thickness of the electrode mixture sheet may be 50 μm to 300 μm.

[0039] The fiberization step is carried out at 160° C. or lower (i.e., a temperature below the melting point of PVDF). If the temperature in the fiberization step exceeds 160° C., an electrode mixture sheet having excellent tensile strength may not be obtained. From the viewpoint of improving the electrode mixture sheet, the temperature in the fiberization step is preferably 50°C or higher, more preferably 100°C or higher, even more preferably 130°C or higher, and particularly preferably 150°C or higher.

[0040] The pressure applied to the mixture may be any pressure that applies shear force to the PTFE particles, and is appropriately selected depending on the type of pressurizing method, etc. When the pressurizing method is rolling, the linear pressure may be 0.1 t / cm to 1.0 t / cm, or 0.2 t / cm to 0.6 t / cm.

[0041] (2) Battery manufacturing method The method for producing a battery according to the present disclosure includes producing an electrode mixture sheet by the method for producing an electrode mixture sheet according to the present disclosure (hereinafter also referred to as an "electrode mixture sheet production step"). This produces a battery.

[0042] The electrode mixture sheet preparation step is the same as the method exemplified as the electrode mixture sheet production method of the present disclosure.

[0043] The battery manufacturing method of the present disclosure may include other steps different from the electrode mixture sheet manufacturing step. The other steps are known steps for manufacturing a battery. The other steps are appropriately selected depending on the type of battery described above, etc.

[0044] (3) Electrode composite sheet The electrode mixture sheet of the present disclosure includes a plurality of active material particles, polyvinylidene fluoride, and a plurality of polytetrafluoroethylene fibrous materials, wherein the content of the polyvinylidene fluoride relative to the total amount of the plurality of active material particles, the polyvinylidene fluoride, and the plurality of polytetrafluoroethylene fibrous materials (hereinafter also referred to as the "total amount of the three") is 5 mass% or more.

[0045] The electrode mixture sheet has the above-described structure, which can improve the unit charge capacity of the battery. "Unit charge capacity" refers to the battery charge capacity per 1 g of active material particles. This effect is presumed to be due to, but not limited to, the following reasons. When the battery is a lithium-ion secondary battery containing a nonaqueous electrolyte solution, if the PVDF content is 5% by mass or more, the amount of solid electrolyte interphase (SEI) film formed on the surface of the electrode containing the electrode mixture sheet during charging and discharging of the battery is suppressed. In other words, the thickness of the SEI film is suppressed. This suppresses the increase in battery resistance due to charging and discharging of the battery. As a result, it is presumed that the electrode mixture sheet can improve the unit charge capacity of the battery.

[0046] The electrode mixture sheet is a sheet-like object. The thickness of the electrode mixture sheet is not particularly limited and may be 50 μm to 300 μm. The electrode mixture sheet is suitably produced by the electrode mixture sheet production method of the present disclosure.

[0047] The electrode mixture sheet includes a plurality of active material particles, PVDF, and a plurality of PTFE fibrous materials, and may further include at least one of a conductive additive and another resin, as necessary. Examples of the active material particles, conductive additive, and other resin include those similar to those exemplified in the manufacturing method of the electrode mixture sheet of the present disclosure.

[0048] The content ratio of the multiple active material particles relative to the total amount of the electrode mixture sheet is not particularly limited and may be 85% by mass to 94% by mass. The content ratio of PVdF relative to the total amount of the three materials is 5% by mass or more. The content ratio of PVdF may be 15% by mass or less, or may be 10% by mass or less. The content ratio of the multiple PTFE fibrous materials relative to the total amount of the three materials is not particularly limited and may be 1% by mass to 10% by mass, 2% by mass to 8% by mass, or 3% by mass to 6% by mass. When the electrode mixture sheet contains a conductive additive, the content ratio of the conductive additive relative to the total amount of the electrode mixture sheet may be 0.1% by mass to 3.0% by mass. When the electrode mixture sheet contains another resin, the content ratio of the other resin relative to the total amount of the electrode mixture sheet may be 0.1% by mass to 10.0% by mass.

[0049] (3.1) Purpose The electrode mixture sheet is used for an electrode. Specifically, the electrode mixture sheet is integrated with a current collector and used as an electrode mixture layer. From the viewpoint of forming an SEI film, the electrode mixture sheet is preferably used as a negative electrode mixture layer. The electrode mixture sheet may be in direct contact with the current collector, or an electrode layer may be interposed between the electrode mixture sheet and the current collector. The electrode layer is similar to the electrode mixture sheet except that the binder content (i.e., PVDF, PTFE fiber, and other resins) is lower than the binder content of the electrode mixture sheet. The binder content of the electrode layer relative to the total amount of the electrode layer may be 0 mass%. The current collector may be a known current collector (e.g., aluminum foil, copper foil, etc.). The electrode mixture sheet and the current collector may be integrated by any known method (e.g., a method using a roll press or a plate press, etc.).

[0050] (4)Battery The battery of the present disclosure includes the electrode mixture sheet of the present disclosure. The battery of the present disclosure achieves the same effects as the electrode mixture sheet of the present disclosure. Examples of the types of the battery of the present disclosure include those similar to those exemplified in the manufacturing method of the electrode mixture sheet of the present disclosure.

[0051] Hereinafter, a lithium secondary battery (hereinafter also referred to as "nonaqueous battery") using the electrode mixture sheet of the present disclosure as a negative electrode active material layer and using a nonaqueous electrolyte solution will be described.

[0052] (4.1) Nonaqueous batteries The non-aqueous battery includes a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0053] (4.1.1) Negative electrode The negative electrode has a negative electrode mixture layer and a negative electrode current collector (e.g., copper foil, etc.). The negative electrode mixture layer is laminated on at least one main surface of the negative electrode current collector. The negative electrode mixture layer is the negative electrode mixture sheet of the present disclosure.

[0054] (4.1.2) Positive electrode The positive electrode has a positive electrode mixture layer and a positive electrode current collector (e.g., aluminum foil, etc.). The positive electrode mixture layer is laminated on at least one main surface of the positive electrode current collector. The positive electrode mixture layer contains a positive electrode active material and may further contain at least one of a conductive additive, PVdF, and another resin. Examples of the positive electrode active material, the conductive additive, and the other resin include those similar to those exemplified in the manufacturing method of the electrode mixture sheet of the present disclosure.

[0055] (4.1.3) Separators The separator may be, for example, a porous resin sheet or a nonwoven fabric. The porous resin sheet may be made of, for example, polyolefin (polypropylene, polyethylene, etc.). The nonwoven fabric may be made of, for example, polypropylene, polyethylene terephthalate, methyl cellulose, etc. The separator may have a known configuration.

[0056] (4.1.4) Non-aqueous electrolyte The non-aqueous electrolyte may contain a non-aqueous solvent and a lithium salt. Examples of lithium salts include LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2. Examples of non-aqueous solvents include cyclic carbonates (e.g., ethylene carbonate), chain carbonates (e.g., dimethyl carbonate, ethyl methyl carbonate), cyclic esters (e.g., γ-butyrolactone, γ-valerolactone), chain esters (e.g., methyl formate, methyl acetate), and ethers (e.g., dimethoxyethane, ethoxymethoxyethane). The non-aqueous electrolyte may contain additives (e.g., vinylene carbonate, lithium bis(oxalato)borate, etc.).

[0057] (4.1.5) Case A nonaqueous battery typically has a case that houses a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The case is not particularly limited, and examples thereof include a laminate film (e.g., an aluminum sheet) and a battery can (e.g., a cylindrical, prismatic, or coin-shaped can). [Example]

[0058] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.

[0059] [1] Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3 [1.1] Example 1-1 [1.1.1] Composite process A plurality of graphite particles were prepared as the plurality of negative electrode active material particles, and the plurality of graphite particles had a volume average particle diameter of 20 μm.

[0060] An "MP Mixer" (manufactured by Nippon Coke and Engineering Co., Ltd.) was prepared as the first mixing device. The "MP Mixer" has a spherical tank (mixing tank), a stirring blade, and a cooling device. The cooling device can cool the spherical tank by circulating cooling water.

[0061] 92.2 parts by mass of a plurality of negative electrode active material particles and 4.8 parts by mass of PVdF were charged into a first mixer and mixed. During this, the cooling device cooled the spherical tank so that the temperature of the spherical tank was maintained at 23°C. The mixing speed (set rotation speed of the stirring blade) was 10,000 rpm. The mixing time (rotation time of the stirring blade) was 2 minutes. This resulted in the production of a plurality of negative electrode active material particles with PVdF attached to their surfaces (hereinafter also referred to as a "composite").

[0062] [1.1.2] Mixing process A PTFE powder was prepared. It was visually confirmed that the particles constituting the PTFE powder were spherical.

[0063] A mixer with a heater (Balance Gran "BG-2L" manufactured by Freund-Turbo Corporation) was prepared as the second mixing device. The "BG-2L" has a mixing tank, agitator blades, and a heating device. The heating device can heat the mixing tank.

[0064] 97.0 parts by mass of the composite and 3.0 parts by mass of PTFE powder were charged into a second mixer and mixed. At this time, the heating device heated the mixing tank. The set temperature of the heating device was 100°C. The mixing speed (set rotation speed of the stirring blade) was 3000 rpm. The mixing time (stirring time of the stirring blade) was 15 minutes. A mixture was thus obtained. The mixture contained negative electrode active material particles bound with PTFE fibrous material. The mass ratio of the mixture composition (negative electrode active material particles / PVdF / PTFE) was 92.2 / 4.8 / 3.0.

[0065] The surface of the resulting mixture was observed with a scanning electron microscope (SEM). It was confirmed that the PTFE was fibrous. It was also confirmed that multiple PTFE fibers were entangled with the negative electrode active material particles.

[0066] [1.1.3] Fiberization process The mixture was rolled using a roll press. The surface temperature of the rolls of the roll press was 160°C. The linear pressure was 0.4 t / cm. This resulted in an electrode mixture sheet. The thickness of the electrode mixture sheet was approximately 200 μm.

[0067] The surface of the obtained electrode mixture sheet was observed with a scanning electron microscope (SEM). It was confirmed that the PTFE was fibrous. The PTFE in the electrode mixture sheet was more fibrous than the PTFE in the mixture. It was confirmed that multiple PTFE fibers were more entangled with the negative electrode active material particles than in the mixture.

[0068] [1.2] Examples 1-2 to 1-6 Except for changing the set temperature, set rotation speed, and rotation time in the mixing step as shown in Table 1, an electrode mixture sheet was obtained in the same manner as in Example 1-1.

[0069] The surfaces of the mixtures and electrode mixture sheets obtained in Examples 1-2 to 1-6 were observed with a scanning electron microscope (SEM). It was confirmed that the PTFE was fibrous in the mixtures and electrode mixture sheets. The PTFE in the electrode mixture sheets was more fibrous than the PTFE in the mixtures. It was confirmed that the multiple PTFE fibrous materials in the electrode mixture sheets were more entangled with the negative electrode active material particles than in the mixtures. An SEM image of the surface of the mixture of Example 1-2 is shown in FIG.

[0070] [1.3] Comparative Example 1-1 An electrode mixture sheet was obtained in the same manner as in Example 1-1, except that the mixing step was changed to the following mixing step. The surfaces of the resulting mixture and electrode mixture sheet were observed using a scanning electron microscope (SEM). It was confirmed that the PTFE in the mixture and electrode mixture sheet was fibrous. It was confirmed that multiple PTFE fibers were entangled with the negative electrode active material particles.

[0071] [1.3.1] Mixing process In Comparative Example 1-1, 3.0 parts by mass of PTFE powder was further added to the first mixer after the composite step was performed and mixed. During this process, the cooling device cooled the spherical tank so that the temperature of the spherical tank was maintained at 23°C. The mixing speed (set rotation speed of the stirring blade) was 300 rpm. The mixing time (stirring time of the stirring blade) was 60 seconds. This resulted in an intermediate. The intermediate did not contain negative electrode active material particles bound with PTFE fibrous materials.

[0072] The intermediate was added to the second mixture and mixed. At this time, the heating device heated the mixing tank. The set temperature of the heating device was 50°C. The mixing speed (set rotation speed of the stirring blade) was 5000 rpm. The mixing time (rotation time of the stirring blade) was 15 minutes. In this way, a mixture was obtained. The mixture contained negative electrode active material particles bound with PTFE fibrous material. The mass ratio of the mixture composition (negative electrode active material particles / PVdF / PTFE) was 92.2 / 4.8 / 3.0.

[0073] [1.4] Comparative Examples 1-2 to 1-3 Except for changing the set temperature, set rotation speed, and rotation time in the mixing step as shown in Table 1, an electrode mixture sheet was obtained in the same manner as in Comparative Example 1-1. The surfaces of the mixtures and electrode mixture sheets obtained in Comparative Examples 1-2 to 1-3 were observed with a scanning electron microscope (SEM). It was confirmed that the PTFE in the mixtures and electrode mixture sheets was fibrous. It was confirmed that a plurality of PTFE fibrous materials were entangled with the negative electrode active material particles. An SEM image of the surface of the mixture of Comparative Example 1-2 is shown in FIG.

[0074] [1.5] Tensile strength measurement The electrode mixture sheet was cut to prepare rectangular test pieces. The width of the test pieces was 35 mm. The length of the test pieces was 31 mm. The test pieces were set in a texture analyzer (manufactured by Eiko Seiki Co., Ltd.) and a tensile test was carried out. The tensile speed was 2 mm / sec. The maximum load (F) required to break the test pieces was measured. The tensile strength was calculated using the maximum load (F) according to the following formula (i). The measurement results are shown in Table 1. The allowable tensile strength is greater than 0.5 MPa. Formula (i): Tensile strength (MPa) = F (g) × 0.0098 / (thickness (mm) × width (mm))

[0075] [Table 1]

[0076] In Comparative Examples 1-1 and 1-2, the mixing step was not carried out at 80°C to 150°C. Therefore, the tensile strength of the obtained electrode mixture sheet did not exceed 0.5 MPa. As a result, it was found that the manufacturing methods of electrode mixture sheets in Comparative Examples 1-1 and 1-2 were not "manufacturing methods of electrode mixture sheets having excellent tensile strength."

[0077] In Examples 1-1 to 1-6, the mixing step was carried out at 80°C to 150°C, and the fiberization step was carried out at 160°C or lower. Therefore, the tensile strength of the obtained electrode mixture sheets exceeded 0.5 MPa. As a result, it was found that the manufacturing methods of electrode mixture sheets in Examples 1-1 to 1-6 were "manufacturing methods of electrode mixture sheets having excellent tensile strength."

[0078] Comparing Examples 1-1 to 1-6, the tensile strengths of Examples 1-1 to 1-3 were higher than those of Examples 1-4 to 1-6. This indicates that electrode mixture sheets with higher tensile strength can be obtained when the mixing step is performed at 80°C to 120°C. The main reason for the low tensile strengths of Examples 1-4 to 1-6 is thought to be that the mixing temperature of 150°C, combined with the heat of stirring, caused PVdF (melting point 160°C) to melt.

[0079] [2] Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-2 [2.1] Electrode composite sheet An electrode mixture sheet was obtained in the same manner as in Example 1-1, except that the mass ratio of the mixture composition (negative electrode active material particles / PVdF / PTFE) was changed to the mass ratio shown in Table 1.

[0080] [2.2] Evaluation Using the obtained electrode mixture sheet, a small cell was produced by the following method.

[0081] [2.2.1] Negative electrode Copper foil (thickness: 8 μm) was prepared as a negative electrode current collector. The electrode mixture sheet and the negative electrode current collector were bonded together using a flat plate press. The load was 5 tons. The surface temperature of the pair of flat plates of the flat plate press was 160°C. This produced a negative electrode.

[0082] [2.2.2] Positive electrode NCM (nickel cobalt manganese oxide) was prepared as a plurality of positive electrode active material particles. Acetylene black was prepared as a conductive additive. PVdF was prepared as a binder. Aluminum foil (thickness: 12 μm) was prepared as a positive electrode current collector. A positive electrode composite paste was prepared by mixing 97.5 parts by mass of a plurality of positive electrode active material particles, 1.5 parts by mass of a conductive additive, 1 part by mass of PVdF, and a solvent. The positive electrode composite paste was applied to a negative electrode current collector, dried, and pressed. A positive electrode was thus obtained.

[0083] [2.2.3] Non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by mixing a mixed solvent with LiPF6 as a supporting electrolyte. The mixed solvent consisted of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The volume ratio of the mixed solvent (EC:DMC:EMC) was 30:34:36. The concentration of LiPF6 was 1.14 mol / L.

[0084] 2.2.4 Assembly A small cell was fabricated using the negative electrode, the positive electrode, and the non-aqueous electrolyte.

[0085] 2.2.5 Measurement Using a small cell, CCCV (cut current: 1 / 20 C) was performed at a current value of 0.3 C in the range of 4.25 V to 2.5 V, and the charge capacity (mAh) was measured. The measured charge capacity (mAh) was divided by the mass (g) of the negative electrode active material to calculate the "unit charge capacity (mAh / g)." The results are shown in Table 2. The allowable unit charge capacity (mAh / g) is 192 mAh / g or more.

[0086] [Table 2]

[0087] In Comparative Examples 2-1 and 2-2, the PVdF content of the electrode mixture sheets was not 5% by mass or more. Therefore, the unit charge capacity of the small cells was not 192 mAh / g or more. As a result, it was found that the electrode mixture sheets of Comparative Examples 2-1 and 2-2 were not "electrode mixture sheets that can improve the unit charge capacity of a battery."

[0088] In Examples 2-1 to 2-3, the PVdF content in the electrode mixture sheets was 5% by mass or more. Therefore, the unit charge capacity of the small cells was 192 mAh / g or more. As a result, it was found that the electrode mixture sheets of Examples 2-1 to 2-3 were "electrode mixture sheets capable of improving the unit charge capacity of batteries."

Claims

1. Adhering polyvinylidene fluoride to a plurality of active material particles to produce a plurality of PVdF-coated active material particles; mixing a plurality of the PVdF-attached active material particles with a plurality of polytetrafluoroethylene particles to prepare a mixture; applying pressure to the mixture to fiberize the polytetrafluoroethylene particles; Including, the mixture is solvent-free; forming the mixture is carried out at 80°C to 150°C; A method for producing an electrode mixture sheet, wherein the pre-fiberization is carried out at 160°C or less.

2. The method for producing an electrode mixture sheet according to claim 1, wherein preparing the mixture is carried out at 80°C to 120°C.

3. A method for manufacturing a battery, comprising producing an electrode mixture sheet by the method for manufacturing an electrode mixture sheet according to claim 1 or 2.

4. The battery includes a plurality of active material particles, polyvinylidene fluoride, and a plurality of polytetrafluoroethylene fibrous materials, an electrode mixture sheet in which a content ratio of the polyvinylidene fluoride relative to a total amount of the plurality of active material particles, the polyvinylidene fluoride, and the plurality of polytetrafluoroethylene fibrous substances is 5 mass % or more;

5. A battery comprising the electrode mixture sheet according to claim 4.

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