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

Abstract

The invention relates to a method for manufacturing an electrode alloy sheet, a method for manufacturing a battery, an electrode alloy sheet, and a battery. The method for manufacturing an electrode alloy sheet includes: attaching polyvinylidene fluoride to a plurality of active material particles to produce a plurality of PVdF-carrying active material particles; mixing the plurality of active substance particles with PVdF with a plurality of polytetrafluoroethylene particles to prepare a mixture; and applying pressure to the mixture, and fiberizing the plurality of polytetrafluoroethylene particles. Wherein the mixture does not contain a solvent. The preparation of the mixture is carried out at a temperature of 80 DEG C to 150 DEG C. The fibration is carried out at 160 DEG C or less.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a manufacturing method of an electrode mixture sheet, a manufacturing method of a battery, an electrode mixture sheet, and a battery. BACKGROUND

[0002] As a manufacturing method of an electrode of a lithium ion secondary battery, a dry method is known. In the dry method, a self-supporting electrode mixture sheet containing active material particles and a binder is produced without using a solvent. The obtained electrode mixture sheet is integrated with a current collector to obtain an electrode. By “self-supporting”, it is meant that the shape can be maintained without a support.

[0003] As a manufacturing method of an electrode employing the dry method, a method of using a resin having a property of causing fiberization (fibrillation) when a shear force is imparted as a binder has been proposed.

[0004] Japanese Patent Application Publication No. 2022-003694 discloses a manufacturing method of 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 film mixture containing dry carbon particles and dry fibrillatable binder particles (e.g., polytetrafluoroethylene) is formed. In the second step, the binder in the dry electrode film mixture is super-fibrillated by a super-fibrillation treatment (e.g., mechanical shearing treatment), and a super-fibrillation matrix is formed in the electrode film mixture. In the third step, the super-fibrillated electrode film mixture is subjected to a calendering treatment, and a self-supporting super-fibrillation electrode film is formed. Japanese Patent Application Publication No. 2022-003694 does not disclose a treatment temperature of the super-fibrillation treatment (e.g., mechanical shearing treatment). SUMMARY

[0005] If damage (e.g., breakage or cracking, etc.) occurs in the electrode mixture sheet, the battery performance can decrease. Therefore, an electrode mixture sheet that is less likely to be damaged (i.e., an electrode mixture sheet having excellent tensile strength) is needed.

[0006] The present disclosure was completed in view of the above-described actual situation.

[0007] An embodiment of the present disclosure aims to provide a manufacturing method of an electrode mixture sheet having excellent tensile strength, and a manufacturing method of a battery including the manufacturing method of the electrode mixture sheet.

[0008] Another embodiment of the present disclosure aims to provide an electrode mixture sheet capable of improving the unit charge capacity of a battery, and a battery including the electrode mixture sheet.

[0009] Means for solving the problem

[0010] The means for solving the above-mentioned problems include the following implementation methods.

[0011] <1> A method for manufacturing an electrode composite sheet includes: attaching polyvinylidene fluoride (PVDF) to a plurality of active material particles to form a plurality of PVDF-containing active material particles; mixing the plurality of PVDF-containing active material particles with a plurality of polytetrafluoroethylene (PTFE) particles to form a mixture; applying pressure to the mixture to fiberize the plurality of PTFE particles, wherein the mixture is solvent-free, the mixture is formed at 80°C to 150°C, and the fiberization is carried out at 160°C or below.

[0012] <2> The method for manufacturing the electrode composite sheet according to <1> above, wherein the mixture is manufactured at 80°C to 120°C.

[0013] <3> A method for manufacturing a battery, comprising manufacturing an electrode composite sheet using the method for manufacturing an electrode composite sheet according to <1> or <2> above.

[0014] <4> Electrode composite sheet, comprising multiple active material particles, polyvinylidene fluoride, and multiple polytetrafluoroethylene fibers, wherein the polyvinylidene fluoride content is 5% by mass or more relative to the total amount of the multiple active material particles, the polyvinylidene fluoride, and the multiple polytetrafluoroethylene fibers.

[0015] <5> Battery, comprising an electrode composite sheet according to <4> above.

[0016] According to one embodiment of the present disclosure, a method for manufacturing an electrode composite sheet having excellent tensile strength and a method for manufacturing a battery including the method for manufacturing the electrode composite sheet can be provided.

[0017] According to another embodiment of this disclosure, an electrode composite sheet capable of increasing the unit charge capacity of a battery and a battery comprising the electrode composite sheet can be provided. Attached Figure Description

[0018] Based on the following figures, exemplary embodiments of the present invention will be described in detail, wherein:

[0019] Figure 1 Scanning electron microscope (SEM) images of the surface of the mixtures of Examples 1-2.

[0020] Figure 2 Scanning electron microscope (SEM) images of the surfaces of the mixtures of Comparative Examples 1-2. Detailed Implementation

[0021] In this disclosure, the numerical range represented by "~" refers to the range in which the values ​​recorded before and after "~" are respectively the minimum and maximum values. In the numerical ranges recorded in stages in this disclosure, the upper or lower limit value recorded in a certain numerical range can be replaced by the upper or lower limit value of other numerical ranges recorded in stages. In the numerical ranges recorded in this disclosure, the upper or lower limit value recorded in a certain numerical range can be replaced by the value shown in the embodiments. In this disclosure, a combination of two or more preferred solutions is a more preferred solution. In this disclosure, regarding the amount of each component, in the case of multiple substances corresponding to each component, unless otherwise specified, it means the total amount of multiple substances. In this disclosure, the term "process" not only refers to an independent process, but also includes any process that achieves its intended purpose when it cannot be clearly distinguished from other processes.

[0022] (1) Manufacturing method of electrode composite sheet

[0023] The method for manufacturing the electrode composite sheet disclosed herein includes: attaching polyvinylidene fluoride (hereinafter also referred to as "PVdF") to a plurality of active material particles to produce a plurality of PVdF-containing particles (hereinafter also referred to as "composite process"); mixing the plurality of PVdF-containing particles with a plurality of polytetrafluoroethylene (hereinafter also referred to as "PTFE") particles to produce a mixture (hereinafter also referred to as "mixing process"); and applying pressure to the mixture to fiberize the plurality of polytetrafluoroethylene particles (hereinafter also referred to as "fiberization process").

[0024] The mixture is solvent-free. The mixture is prepared at 80°C to 150°C (i.e., the mixing process). The fiberization process is then carried out at 160°C or below (i.e., the fiberization process). The compounding process, mixing process, and fiberization process are performed sequentially.

[0025] In this disclosure, the term "electrode composite sheet" refers to a self-standing sheet containing active material particles. "The mixture is solvent-free" indicates that the electrode composite sheet is manufactured using a dry process.

[0026] The method for manufacturing the electrode composite sheet disclosed herein has the above-described structure, and therefore exhibits excellent tensile strength. This effect is presumably based on the following reasons, but is not limited thereto.

[0027] The manufacturing method disclosed herein includes a compounding step and a mixing step. The mixing step of this disclosure differs from conventional methods in that it is performed while heating (i.e., at 80°C to 150°C). Therefore, the multiple PTFE particles in the mixture are more easily dispersed compared to the first, second, or third scenarios. "First scenario" refers to the case where the mixing step is performed while heating at a temperature outside the range of 80°C to 150°C. "Second scenario" refers to the case where multiple active material particles, PVdF, and multiple PTFE particles are mixed without performing the compounding step. "Third scenario" refers to the case where multiple active material particles, PVdF, and multiple PTFE fibrous materials (hereinafter also referred to as "PTFE fibrous materials") are mixed. If the multiple PTFE particles in the mixture are dispersed, the PTFE fibrous materials easily entangle with the PVdF-containing particles through the fibrousization step. As a result, it is speculated that the tensile strength of the obtained electrode composite sheet is improved.

[0028] Furthermore, in the manufacturing method of this disclosure, no solvent is used when manufacturing the electrode composite sheet. Therefore, the manufacturing method of this disclosure has excellent biocompatibility and environmental friendliness. Moreover, in the manufacturing method of this disclosure, there is no need to perform a solvent evaporation step after film formation. As a result, the manufacturing efficiency of the manufacturing method of this disclosure is excellent.

[0029] The electrode composite sheet manufactured using the method disclosed herein is used as the electrode composite layer (positive electrode composite layer or negative electrode composite layer) of the electrode in a battery. There is no particular limitation on the type of battery; 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, or 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 located between the positive and negative electrodes and conducts ions. Examples of ion-conducting media include non-aqueous electrolytes, non-aqueous gel electrolytes, solid ion-conducting polymers, or inorganic solid electrolytes.

[0030] (1.1) Composite process

[0031] In the compounding process, PVdF is attached to multiple active material particles to create multiple particles with PVdF. Through the implementation of the compounding process, the multiple PTFE particles in the mixture are easily dispersed during the mixing process.

[0032] The term "active material particles" refers to particles composed of positive electrode active materials (hereinafter also referred to as "positive electrode active material particles") or particles composed of negative electrode active materials (hereinafter also referred to as "negative electrode active material particles").

[0033] There are no particular limitations on the method for attaching PVdF to multiple active material particles (hereinafter also referred to as the "attachment method"), and any known method may be used. Examples of attachment methods include stirring, spray drying, freeze drying, atomic layer deposition (ALD), ion plating, or sputtering.

[0034] There are no particular limitations on the adhesion conditions (such as temperature or time), which can be appropriately selected according to the adhesion method. The compounding process can be carried out while cooling the adherend to keep the multiple active material particles and PVdF (hereinafter also referred to as "adhesive") at 23°C.

[0035] (1.1.1) Active substance particles

[0036] The active material particles are either negative electrode active material particles or positive electrode active material particles.

[0037] The negative electrode active material can be any known negative electrode active material used in lithium-ion secondary batteries. Examples of negative electrode active materials include carbon (e.g., natural graphite, artificial graphite) or compounds that can be alloyed with lithium (e.g., silicon, or tin). The negative electrode active material can be a single type or two or more types.

[0038] The positive electrode active material can be any known positive electrode active material used in lithium-ion secondary batteries. Examples of positive electrode active materials include lithium transition metal composite oxides. Examples of lithium transition metal composite oxides include compounds represented by LiMO2 (where M is a transition metal selected from at least one of Ni, Co, and Mn), LiMn2O4, or LiMPO4 (where M is Fe, Co, Ni, or Mn). The positive electrode active material can be a single type or two or more types.

[0039] There are no particular restrictions on the volume average particle size of the active material particles, which can be 5 μm to 30 μm. "Volume average particle size" refers to the value when the cumulative particle size distribution from the small diameter side in the volume standard particle size distribution determined by laser diffraction and scattering method becomes 50% (D50).

[0040] (1.1.2)PVdF

[0041] PVdF has adhesive properties. PVdF can adhere to the entire surface of active material particles or only a portion of their surface.

[0042] There is no particular limitation on the amount of PVdF relative to the total amount of multiple active material particles; it can be 3% to 15% by mass, 5% to 15% by mass, or 5% to 10% by mass.

[0043] (1.1.3) Conductive additives

[0044] In the compounding process, conductive additives can be mixed in addition to PVdF and active material particles. There are no particular limitations on conductive additives; examples include carbon materials. Examples of carbon materials include carbon black (acetylene black, pyrolytic carbon black, or furnace black), carbon nanotubes, or graphite.

[0045] (1.2) Mixing process

[0046] In the mixing process, multiple PVdF-containing particles are mixed with multiple PTFE particles to create a mixture. This disperses the multiple PTFE particles in the mixture. As a result, compared to mixing multiple PVdF-containing particles with multiple PTFE fibers, an electrode composite sheet with superior tensile strength is obtained.

[0047] "PTFE particles" refers to particles composed of PTFE. "Particles" indicates that they are not fibers. Specifically, "particles" means an aspect ratio of 5 or higher. "Fibers" means an aspect ratio of less than 5. PTFE particles generally consist of multiple molecular chains aggregated into a lamellar structure resembling ribbons (plates). When shear force is applied to PTFE particles, the lamellar structure breaks down, and the PTFE particles become fibrous. That is, through shear force, PTFE particles transform into PTFE fibers. "PTFE fibers" includes PTFE that has completely transformed into fibers and PTFE particles that have partially transformed into fibers. The mixing process is carried out using a heating device. The "temperature" in the mixing process refers to the set temperature of the heating device.

[0048] In the mixing process, a known mixing apparatus is used to stir multiple PVdF particles and multiple PTFE particles, and a known heating apparatus is used to heat the stirred mixture.

[0049] The mixing process is carried out at 80°C to 150°C. If the mixing temperature is below 80°C, it is possible that an electrode composite sheet with excellent tensile strength will not be obtained. If the mixing temperature exceeds 150°C, part of the PVDF will melt, and the adhesiveness of the PVDF may decrease. As a result, it is possible that an electrode composite sheet with excellent tensile strength will not be obtained.

[0050] The mixing process is preferably carried out at 80°C to 120°C. This results in an electrode composite sheet with superior tensile strength.

[0051] There is no particular limitation on the mixing speed of the mixing device; it can be 1000 rpm to 6000 rpm, or 2000 rpm to 4000 rpm. There is no particular limitation on the mixing time of the mixing device; it can be 1 minute to 60 minutes, or 10 minutes to 20 minutes.

[0052] (1.2.1) PTFE particles

[0053] Through the fiberization process, PTFE particles are transformed into PTFE fibers, which improves the tensile strength of the electrode composite sheet.

[0054] In the mixing process, at least a portion of a plurality of PTFE particles can be fibrous. In this case, a granule can be produced. The granule comprises a plurality of active material particles and PTFE fibers bonded to at least a portion of the active material particles.

[0055] There is no particular limitation on the amount of PTFE particles relative to the total amount of multiple active material particles; it can be 1% to 10% by mass, 2% to 8% by mass, or 3% to 6% by mass.

[0056] (1.2.2) Other resins

[0057] During the mixing process, other resins different from those containing PVdF and PTFE particles may be added and mixed. In other words, the mixture may further contain other resins. Examples of other resins include polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepoxychlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, or polymethacrylate, etc.

[0058] (1.3) Fiberization process

[0059] In the fiberization process, pressure is applied to the mixture to fiberize multiple PTFE particles.

[0060] The fiberizing process is carried out using a pressure device. The "temperature" of the fiberizing process is achieved using a pressure device (such as a calendering device or a pressing device). The "temperature" of the fiberizing process refers to the surface temperature of the surface of the pressure device that is in contact with the mixture.

[0061] There are no particular limitations on the method of applying pressure to the mixture (hereinafter also referred to as the "pressurization method"), and examples include calendering and pressing. In calendering, a known calendering apparatus is used to calender the mixture. In pressing, a known pressing apparatus is used to press the mixture. The calendering apparatus includes a pair of metal rollers and a heating device for heating the pair of metal rollers. The pressing apparatus includes a pair of metal plates and a heating device for heating the pair of metal plates. The mixture can be formed into a sheet while simultaneously fiberizing multiple PTFE particles. The thickness of the electrode composite sheet can be 50 μm to 300 μm.

[0062] The fiberization process is carried out at temperatures below 160°C (i.e., below the melting point of PVDF). If the temperature of the fiberization process exceeds 160°C, it may not yield electrode composite sheets with excellent tensile strength.

[0063] From the viewpoint of improving the electrode composite sheet, the temperature of the fiberization process 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.

[0064] The pressure applied to the mixture only needs to be the pressure that imparts shear force to the PTFE particles, and should be appropriately selected depending on the type of pressing method. When the pressing method is calendering, the linear pressure can be 0.1 t / cm to 1.0 t / cm, or 0.2 t / cm to 0.6 t / cm.

[0065] (2) Battery manufacturing method

[0066] The battery manufacturing method disclosed herein includes fabricating an electrode assembly sheet (hereinafter also referred to as the "electrode assembly sheet fabrication process") using the electrode assembly sheet manufacturing method of this disclosure. A battery is thus obtained.

[0067] The electrode composite sheet manufacturing process is the same as the method exemplified as the electrode composite sheet manufacturing method of this disclosure.

[0068] The battery manufacturing method disclosed herein may include other steps different from the electrode assembly sheet fabrication step. These other steps are known steps for manufacturing batteries. The other steps are appropriately selected based on the type of battery described above.

[0069] (3) Electrode composite sheet

[0070] The electrode composite sheet disclosed herein comprises a plurality of active material particles, polyvinylidene fluoride (PVDF), and a plurality of polytetrafluoroethylene (PTFE) fibrous materials. The PVDF content is 5% by mass or more relative to the total amount of the plurality of active material particles, the PVDF, and the PTFE fibrous materials (hereinafter also referred to as the "three total amounts").

[0071] The electrode composite sheet has the above-described structure, thus improving the battery's unit charge capacity. "Unit charge capacity" refers to the charge capacity of the battery per 1g of active material particles. This effect is presumed to be based on the following reasons, but is not limited to them.

[0072] In the case of lithium-ion secondary batteries with non-aqueous electrolytes, if the PVDF content is 5% by mass or more, the amount of solid electrolyte interphase (SEI) film formed on the surface of the electrodes with electrode composite sheets is suppressed during battery charging and discharging. That is, SEI film thickening is suppressed. This, in turn, suppresses the increase in battery resistance caused by charging and discharging. As a result, it is speculated that the electrode composite sheets can improve the battery's unit charge capacity.

[0073] The electrode composite sheet is in sheet form. There is no particular limitation on the thickness of the electrode composite sheet, which can be 50 μm to 300 μm. The electrode composite sheet is preferably manufactured using the electrode composite sheet manufacturing method disclosed herein.

[0074] The electrode composite sheet comprises a plurality of active material particles, PVDF, and a plurality of PTFE fibers, and may further comprise, if desired, at least one of conductive additives and other resins. The active material particles, conductive additives, and other resins may be the same substances exemplified in the method of manufacturing the electrode composite sheet of this disclosure.

[0075] The proportion of various active material particles relative to the total amount of the electrode composite sheet is not particularly limited, and can be 85% to 94% by mass. The proportion of PVdF relative to the total amount of the three substances is 5% by mass or more. The proportion of PVdF can be 15% by mass or less, or 10% by mass or less. The proportion of various PTFE fibrous materials relative to the total amount of the three substances is not particularly limited, and can be 1% to 10% by mass, 2% to 8% by mass, or 3% to 6% by mass. When the electrode composite sheet contains conductive additives, the proportion of conductive additives relative to the total amount of the electrode composite sheet can be 0.1% to 3.0% by mass. When the electrode composite sheet contains other resins, the proportion of other resins relative to the total amount of the electrode composite sheet can be 0.1% to 10.0% by mass.

[0076] (3.1) Applications

[0077] Electrode composite sheets are used as electrodes. Specifically, the electrode composite sheet is integrated with the current collector, thereby serving as an electrode composite layer. From the viewpoint of SEI film formation, the electrode composite sheet is preferably used as a negative electrode composite layer. The electrode composite sheet can be directly connected to the current collector, or an electrode layer can exist between the electrode composite sheet and the current collector. The electrode layer is the same as the electrode composite sheet, except that the content of the adhesive (i.e., PVDF, PTFE fibers, and other resins) is lower than that of the adhesive in the electrode composite sheet. The content of the adhesive in the electrode layer relative to the total amount of the electrode layer can be 0% by mass. The current collector can be a known current collector (e.g., aluminum foil, or copper foil). The method of integrating the electrode composite sheet with the current collector can be a known method (e.g., a method using a roller press or a flat press).

[0078] (4) Battery

[0079] The battery disclosed herein includes the electrode composite sheet of this disclosure. The battery of this disclosure achieves the same functional effects as the electrode composite sheet of this disclosure. The types of batteries disclosed herein are equivalent to those exemplified in the manufacturing method of the electrode composite sheet of this disclosure.

[0080] The following describes a lithium secondary battery (hereinafter also referred to as a "non-aqueous battery") that uses the electrode composite sheet disclosed herein as the negative electrode active material layer and uses a non-aqueous electrolyte.

[0081] (4.1) Non-water batteries

[0082] A non-aqueous battery includes: a negative electrode, a positive electrode, a membrane (separator) disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0083] (4.1.1) Negative electrode

[0084] The negative electrode has a negative electrode composite layer and a negative electrode current collector (e.g., copper foil). The negative electrode composite layer is laminated on at least one main surface of the negative electrode current collector. The negative electrode composite layer is the negative electrode composite sheet of this disclosure.

[0085] (4.1.2) Positive electrode

[0086] The positive electrode has a positive electrode composite layer and a positive electrode current collector (e.g., aluminum foil). The positive electrode composite layer is laminated on at least one main surface of the positive electrode current collector. The positive electrode composite layer contains a positive electrode active material and may further contain at least one of a conductive additive, PVdF, and other resins. The positive electrode active material, conductive additive, and other resins may be equivalent to those exemplified in the method of manufacturing the electrode composite sheet of this disclosure.

[0087] (4.1.3) Diaphragm

[0088] Examples of membranes include porous resin sheets or nonwoven fabrics. Examples of materials for porous resin sheets include polyolefins (polypropylene, polyethylene, etc.). Examples of materials for nonwoven fabrics include polypropylene, polyethylene terephthalate, methylcellulose, etc. The membrane can have a known composition.

[0089] (4.1.4) Non-aqueous electrolyte

[0090] Non-aqueous electrolytes may contain non-aqueous solvents and lithium salts. 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). Non-aqueous electrolytes may contain additives (e.g., vinylene carbonate, lithium bis(oxalate)borate, etc.).

[0091] (4.1.5) Outer shell

[0092] Non-aqueous batteries typically have a casing. The casing houses the positive electrode, negative electrode, separator, and non-aqueous electrolyte. There are no particular limitations on the casing; examples include laminated films (e.g., aluminum sheets) and battery canisters (e.g., cylindrical, square, coin-shaped).

[0093] Example

[0094] The present disclosure is illustrated in more detail below with reference to the embodiments, but the invention of the present disclosure is not limited to these embodiments.

[0095] [1] Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3

[0096] [1.1] Example 1-1

[0097] [1.1.1] Composite Process

[0098] Multiple graphite particles were prepared as multiple negative electrode active material particles. The volume average particle size of the multiple graphite particles was 20 μm.

[0099] As the first mixing unit, an "MP mixer" (manufactured by Nippon Kogyo Co., Ltd.) was prepared. The "MP mixer" has a spherical tank (mixing vessel), stirring blades, and a cooling device. The cooling device can cool the spherical tank by circulating cooling water.

[0100] 92.2 parts by mass of multiple negative electrode active material particles and 4.8 parts by mass of PVdF were added to the first mixing device and mixed. At this time, the cooling device cooled the spherical container to maintain it at 23°C. The mixing speed (set rotation speed of the stirring blades) was 10,000 rpm. The mixing time (rotation time of the stirring blades) was 2 minutes. Thus, multiple negative electrode active material particles with PVdF adhering to their surface (hereinafter also referred to as the "complex") were obtained.

[0101] [1.1.2] Mixing process

[0102] PTFE powder was prepared. Visual inspection confirmed that the particles constituting the PTFE powder were spherical.

[0103] As a second mixing device, a mixer equipped with a heating device (BALANCE GRAN "BG-2L" manufactured by Freund-Turbo Corporation) was prepared. The "BG-2L" has a mixing tank, stirring blades, and a heating device. The heating device heats the mixing tank.

[0104] 97.0 parts by weight of the composite and 3.0 parts by weight of PTFE powder were added to a second mixing device and mixed. At this time, a heating device was used to heat the mixing tank. The heating device was set to 100°C. The mixing speed (set rotation speed of the stirring blades) was 3000 rpm. The mixing time (stirring time of the stirring blades) was 15 minutes. A mixture was thus obtained. The mixture contained negative electrode active material particles bonded with PTFE fibrous material. The mass ratio of the mixture (negative electrode active material particles / PVdF / PTFE) was 92.2 / 4.8 / 3.0.

[0105] The surface of the mixture was observed using scanning electron microscopy (SEM). The PTFE was confirmed to be fibrous. Multiple PTFE fibrous structures were confirmed to be entangled within the negative electrode active material particles.

[0106] [1.1.3] Fiberization process

[0107] The mixture was calendered using a roller press. The surface temperature of the rollers in the roller press was 160°C. The linear pressing rate was 0.4 t / cm. This yielded an electrode composite sheet. The thickness of the electrode composite sheet was approximately 200 μm.

[0108] The surface of the electrode composite sheet was observed using scanning electron microscopy (SEM). The PTFE was confirmed to be fibrous. The PTFE in the electrode composite sheet was more fibrous compared to the PTFE in the mixture. It was confirmed that the fibrous strands of multiple PTFE particles were more entangled with the negative electrode active material particles compared to the mixture.

[0109] [1.2] Examples 1-2 to 1-6

[0110] Except for changes to the set temperature, set speed, and rotation time of the mixing process as shown in Table 1, electrode composite sheets were obtained in the same manner as in Example 1-1.

[0111] The surfaces of the mixtures and electrode composite sheets obtained in Examples 1-2 to 1-6 were observed using scanning electron microscopy (SEM). In both the mixtures and electrode composite sheets, the PTFE was confirmed to be fibrous. The PTFE in the electrode composite sheets was more fibrous than that in the mixtures. It was confirmed that, compared to the mixtures, the fibrous components of the PTFE in the electrode composite sheets were more entangled with the negative electrode active material particles.

[0112] SEM images of the surface of the mixtures from Examples 1-2 are shown below. Figure 1 .

[0113] [1.3] Comparative Example 1-1

[0114] Except that the mixing process was changed to the mixing process described below, electrode composite sheets were obtained in the same manner as in Example 1-1.

[0115] The surfaces of the mixture and electrode composite sheets were observed using scanning electron microscopy (SEM). PTFE was confirmed to be fibrous in both the mixture and electrode composite sheets. Multiple PTFE fibrous structures were confirmed to be entangled within the negative electrode active material particles.

[0116] [1.3.1] Mixing process

[0117] In Comparative Example 1-1, 3.0 parts by weight of PTFE powder were further added to the first mixing unit after the compounding process and mixed. At this time, the cooling unit cooled the spherical container to maintain it at 23°C. The mixing speed (set rotation speed of the stirring blades) was 300 rpm. The mixing time (stirring time of the stirring blades) was 60 seconds. An intermediate was thus obtained. The intermediate did not contain negative electrode active material particles with fibrous PTFE bound together.

[0118] The intermediate material is added to the second mixing device and mixed. At this time, the heating device heats the mixing tank. The heating device is set to 50°C. The mixing speed (set rotation speed of the stirring blades) is 5000 rpm. The mixing time (rotation time of the stirring blades) is 15 minutes. Thus, a mixture is obtained. The mixture contains negative electrode active material particles with fibrous PTFE bonded to them. The mass ratio of the mixture (negative electrode active material particles / PVdF / PTFE) is 92.2 / 4.8 / 3.0.

[0119] [1.4] Comparative Examples 1-2 to 1-3

[0120] Except that the set temperature, set speed and rotation time of the mixing process were changed to those shown in Table 1, electrode composite sheets were obtained in the same manner as in Comparative Example 1-1.

[0121] The surfaces of the mixtures and electrode composite sheets obtained in Comparative Examples 1-2 to 1-3 were observed using scanning electron microscopy (SEM). In the mixtures and electrode composite sheets, PTFE was confirmed to be fibrous. Multiple PTFE fibrous structures were confirmed to be entangled within the negative electrode active material particles.

[0122] SEM images of the surfaces of the mixtures from Comparative Examples 1-2 are shown below. Figure 2 .

[0123] [1.5] Tensile strength determination

[0124] Rectangular test pieces were prepared by cutting electrode composite sheets. The width of the test piece was 35 mm. The length of the test piece was 31 mm. Tensile tests were performed on the test pieces using a texture analyzer (manufactured by Eiko Seiki Co., Ltd.). The tensile speed was 2 mm / s. The maximum load (F) required to cause the test piece to break was determined. Using the maximum load (F), the tensile strength was calculated using the following formula (i). The test results are shown in Table 1. The permissible (acceptable) tensile strength is greater than 0.5 MPa.

[0125] Equation (i): Tensile strength (MPa) = F(g) × 0.0098 / (thickness (mm) × width (mm))

[0126] Table 1

[0127]

[0128] In Comparative Examples 1-1 to 1-2, the mixing process was not carried out at 80°C to 150°C. Therefore, the tensile strength of the resulting electrode composite sheet did not exceed 0.5 MPa. As a result, it can be concluded that the manufacturing method of the electrode composite sheet in Comparative Examples 1-1 to 1-2 is not a "manufacturing method of an electrode composite sheet with excellent tensile strength".

[0129] In Examples 1-1 to 1-6, the mixing process was carried out at 80°C to 150°C, and the fiberization process was carried out at 160°C or below. Therefore, the tensile strength of the obtained electrode composite sheet was greater than 0.5 MPa. As a result, it can be concluded that the manufacturing method of the electrode composite sheet in Examples 1-1 to 1-6 is "a method for manufacturing an electrode composite sheet with excellent tensile strength".

[0130] Comparing Examples 1-1 to 1-6, the tensile strength of Examples 1-1 to 1-3 is higher than that of Examples 1-4 to 1-6. This indicates that performing the mixing process at 80°C to 120°C yields electrode composite sheets with higher tensile strength. The main reason for the lower tensile strength in Examples 1-4 to 1-6 is believed to be that at a mixing temperature of 150°C, the added heat of stirring caused PVdF (melting point 160°C) to melt.

[0131] [2] Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-2

[0132] [2.1] Electrode composite sheet

[0133] 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, electrode composite sheets were obtained in the same manner as in Examples 1-1.

[0134] [2.2] Evaluation

[0135] Using the obtained electrode composite sheet, a small battery cell was fabricated using the following method.

[0136] [2.2.1] Negative electrode

[0137] A copper foil (thickness: 8μm) was prepared as the negative electrode current collector. The electrode composite sheet was then bonded to the negative electrode current collector using a flatbed press. The load was 5t. The surface temperature of the two flat plates of the press was 160℃. This yielded the negative electrode.

[0138] [2.2.2] Positive electrode

[0139] NCM (lithium nickel cobalt manganese oxide) was prepared as multiple 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 the positive electrode current collector.

[0140] A positive electrode composite paste was prepared by mixing 97.5 parts by mass of multiple positive electrode active material particles, 1.5 parts by mass of conductive additive, 1 part by mass of PVdF, and a solvent. The positive electrode composite paste was then coated onto the positive electrode current collector, dried, and pressed. This yielded the positive electrode.

[0141] [2.2.3] Non-aqueous electrolyte

[0142] As a non-aqueous electrolyte, a mixture of a mixed solvent and LiPF6 as a supporting salt was prepared. 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.

[0143] [2.2.4] Assembly

[0144] A small battery cell was fabricated using a negative electrode, a positive electrode, and a non-aqueous electrolyte.

[0145] [2.2.5] Determination

[0146] Using a small battery cell, CCCV (cutoff current: 1 / 20C) was performed at a current of 0.3C within the range of 4.25V to 2.5V to determine the charging capacity (mAh). The measured charging capacity (mAh) was divided by the mass (g) of the negative electrode active material to calculate the "unit charging capacity (mAh / g)". The results are shown in Table 2. The permissible (acceptable) unit charging capacity (mAh / g) is 192 mAh / g or higher.

[0147] Table 2

[0148]

[0149] In Comparative Examples 2-1 and 2-2, the PVdF content of the electrode composite sheet was not more than 5% by mass. Therefore, the unit charge capacity of the small battery cell was not more than 192 mAh / g. As a result, it can be concluded that the electrode composite sheets of Comparative Examples 2-1 and 2-2 are not "electrode composite sheets that can improve the unit charge capacity of the battery".

[0150] In Examples 2-1 to 2-3, the PVdF content of the electrode composite sheet was 5% by mass or more. Therefore, the unit charge capacity of the small battery cell was 192 mAh / g or more. As a result, the electrode composite sheets of Examples 2-1 to 2-3 are "electrode composite sheets capable of improving the unit charge capacity of the battery".

Claims

1. A method for manufacturing electrode composite sheets, comprising: Polyvinylidene fluoride is attached to multiple active material particles to create multiple active material particles with PVdF. A mixture is prepared by mixing multiple PVdF-containing active material particles with multiple polytetrafluoroethylene particles; and Pressure is applied to the mixture to fiberize the plurality of polytetrafluoroethylene particles. The mixture is solvent-free, and the mixture is prepared at 80°C to 150°C, and the fiberization is carried out at 160°C or below.

2. The method for manufacturing the electrode composite sheet according to claim 1, wherein, The mixture is prepared at 80°C to 120°C.

3. A method for manufacturing a battery, comprising manufacturing an electrode composite sheet using the method for manufacturing an electrode composite sheet as described in claim 1 or 2.

4. Electrode composite sheet, comprising multiple active material particles, polyvinylidene fluoride, and multiple polytetrafluoroethylene fibrous materials. The polyvinylidene fluoride content is 5% by mass or more relative to the total amount of the plurality of active material particles, the polyvinylidene fluoride and the plurality of polytetrafluoroethylene fibers.

5. A battery comprising the electrode composite sheet of claim 4.

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