Self-supporting electrode membrane and manufacturing method thereof

Abstract

[Problem] To provide a technology that suppresses or avoids the increase in powder resistance in a self-supporting electrode film. [Solution] The self-supporting electrode film (4) comprises an active material particle (6) comprising an olivine-type positive electrode material having an electronically conductive material film (8), a conductive agent (10), a first polymer having a shape covering the electronically conductive material film, and a second polymer having a fibrillated shape.

Description

Technology Field

[0001] The technology disclosed in this specification relates to a self-supporting electrode film and a method for manufacturing the same, etc. Background Technology

[0002] Recently, self-standing electrode films are being manufactured by a dry process. For example, a self-standing electrode film is known to contain a composite binder containing polyvinylpyrrolidone (PVP) or polyethylene oxide (PEO) in addition to polytetrafluoroethylene (PTFE) (Patent Document 1). Patent Document 1 describes combining a mixture for an electrode film containing a composite binder, active material particles, and a conductive agent, then adding a small amount of solvent to the mixture, applying shear force to fibrillate the PTFE, and then pressing to form a self-standing electrode film. Prior art literature

[0003] Japanese Patent Publication No. 2024-26272 The problem to be solved

[0004] However, the method of Patent Document 1 uses a solvent, even though it is a dry process. Also, in a dry process, when a mixture for an electrode film is prepared by mixing a binder, active material particles, and a conductive agent, there were cases where a large frictional force occurred between the active material particles. When the active material particles have a coating such as an electronically conductive material, damage to this coating occurs, and as a result, the powder resistance of the electrode film increases.

[0005] The present specification provides a technique for suppressing or avoiding an increase in powder resistance in a self-supporting electrode film. means of solving the problem

[0006] One technology disclosed in this specification relates to a self-supporting electrode film. The self-supporting electrode film comprises an active material particle comprising an olivine-type positive electrode material having an electron-conducting material film, a conductive agent, a first polymer having a shape covering the electron-conducting material film, and a second polymer having a fibrillated shape.

[0007] According to the above self-supporting electrode film, the first polymer has a shape that covers the electronically conductive material film, thereby suppressing or avoiding damage to the electronically conductive material film. The second polymer has a fibrillated shape, thereby binding and integrating the active material particles and the conductive additive. As a result, the increase in powder resistance in the self-supporting electrode film is suppressed or improved.

[0008] In addition, another technology disclosed in this specification is implemented as a method for manufacturing an electrode sheet for a self-supporting electrode film. The manufacturing method comprises: a process of preparing a first mixture by mixing an active material particle comprising an olivine-type positive electrode material having an electronically conductive material film, a conductive additive, and a first polymer that does not fibrillate, in a state where the first polymer is fluidized; a process of preparing a second mixture by mixing the first mixture with a second polymer capable of fibrillation, in a state where the second polymer is fibrillated; and a process of manufacturing the electrode sheet using the second mixture.

[0009] In preparing the first mixture, the first mixture is prepared in a fluidized state of the first polymer. Because of this, the frictional force between the active material particles is reduced, and damage to the electronically conductive material film on the surface of the active material particles is suppressed or reduced. In addition, in preparing the second mixture, the active material particles having the electronically conductive material with suppressed damage and the conductive additive are bound and integrated by the second polymer in which the conductive additive is fibrillated. Because of this, the increase in the powder resistance of the electrode sheet and the self-supporting electrode film can be suppressed or improved.

[0010] In addition, when preparing the first mixture, the use of a solvent can be avoided by mixing the first polymer in a fluidized state. Brief explanation of the drawing

[0011] FIG. 1 is a cross-sectional view showing an example of the structure of an electrode disclosed in this specification. FIG. 2 is a process diagram showing an example of a method for manufacturing an electrode sheet disclosed in the present specification. Specific details for implementing the invention

[0012] The self-supporting electrode film and the method for manufacturing the same disclosed in this specification are as described above, but these disclosures may adopt the following aspects.

[0013] Another aspect of the above-described self-standing electrode film comprises that the first polymer has a melting point of 60°C or higher and 260°C or lower. By using such a first polymer, the first polymer melts and becomes fluid during the manufacturing process of the above-described self-standing electrode film, thereby easily reducing the frictional force between active material particles. Such a first polymer is easy to form a shape that covers the above-described electronically conductive material film.

[0014] Another aspect of the above-described self-supporting electrode film comprises that the first polymer is one or more selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride, ethylene carbonate, polyethylene, polypropylene, polystyrene, ABS resin, polyacrylate, polymethacrylate, polyvinyl alcohol, and polycarbonate. These polymers may exhibit fluidity at a temperature of 60°C or higher and 260°C or lower. The first polymer may be one or more selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, and polyvinylidene fluoride. These polymers may have ionic conductivity and may be able to suppress the decrease in lithium ion conductivity.

[0015] Another aspect of the above-described self-supporting electrode film comprises containing the first polymer in an amount of 0.1 mass% or more and 3.0 mass% or less with respect to the total mass of the above-described self-supporting electrode film. By doing so, the frictional force between the active material particles can be effectively reduced, while suppressing or avoiding an increase in powder resistance in the above-described self-supporting electrode film.

[0016] Another aspect of the above-described self-supporting electrode membrane is that the second polymer may include polytetrafluoroethylene. By doing so, the fibrillated second polymer effectively binds and integrates the self-supporting electrode membrane.

[0017] The disclosure of this specification includes an electrode having any of the above-mentioned self-supporting electrode films. Additionally, the disclosure of this specification includes a secondary battery having said electrode.

[0018] Another embodiment of the method for manufacturing the electrode sheet described above includes the first polymer having a melting point of 60°C or higher and 260°C or lower. By having the first polymer having a melting point within the above temperature range, the first polymer can be easily fluidized by heating, making it easier to reduce the frictional force between the active material particles. Furthermore, in this embodiment, the process of preparing the second mixture may include mixing the first mixture and the second polymer while the first polymer is fluidized. By doing so, even when preparing the second mixture, the first polymer is fluidized to reduce the frictional force between the active material particles, thereby suppressing damage to the electronically conductive material film.

[0019] The disclosure of this specification also includes a method for manufacturing an electrode having a self-supporting electrode film. More specifically, the method may comprise a process of preparing a first mixture by mixing an active material particle having an olivine-type positive electrode material having an electron-conductive material film, a conductive additive, and a first polymer that does not fibrillate, in a state where the first polymer is fluidized; a process of preparing a second mixture by mixing the first mixture with a second polymer capable of fibrillation, in a state where the second polymer is fibrillated; a process of manufacturing an electrode sheet using the second mixture; and a process of manufacturing the electrode having the self-supporting electrode film by bonding the electrode sheet to a current collector.

[0020] Hereinafter, with appropriate reference to the drawings, a self-supporting electrode film and an electrode, and a method for manufacturing an electrode sheet for a self-supporting electrode film, etc., will be described. Furthermore, in this specification, the self-supporting electrode film and the electrode are, for example, a self-supporting electrode film and a positive electrode constituting the positive electrode of a lithium-ion secondary battery.

[0021] (Self-supporting electrode membrane and electrode)

[0022] FIG. 1 shows an example of a cross-section of a positive electrode (2) of a lithium-ion secondary battery (hereinafter simply referred to as a secondary battery). The positive electrode (2) is provided with a self-supporting electrode film (hereinafter also simply referred to as an electrode film) (4) and a current collector (20). The current collector (20) is not specifically limited, but examples include aluminum foil or nickel. Additionally, although not shown, the secondary battery is provided with a separator containing an electrolyte and a negative electrode. The separator is composed of a known material such as a polyolefin-based microporous membrane having fine pores formed therein. The separator is impregnated with a liquid electrolyte containing a lithium salt, such as lithium hexafluorophosphate, using an organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC) as a medium. In addition, a solid electrolyte layer may be used instead of these. The negative electrode of the secondary battery may be provided with a negative electrode film and a current collector made of appropriately known materials and compositions.

[0023] As shown in FIG. 1, the electrode film (4) comprises active material particles (6), a conductive agent (10), a first polymer (12), and a second polymer (14).

[0024] (Active material particles)

[0025] The active material particles (6) may use particles containing known olivine-type positive electrode materials. As olivine-type positive electrode materials, lithium iron phosphate (LiFePO4, LFP) and lithium iron manganese phosphate (LiMn (1-d) Examples include FePO4 (LMFP), lithium manganese phosphate (LiMnPO4, LMP), etc. As active material particles (6), one or more of these may be used. The active material particles (6) may have any average particle size. The active material particles (6) may have a form in which each particle is secondarily aggregated.

[0026] (Electronically conductive material film)

[0027] The active material particle (6) is provided with an electronically conductive material coating (hereinafter also simply referred to as a coating) (8) that covers at least a portion of its surface. The coating (8) contributes to improving the electronic conductivity of the active material particle (6). The electronically conductive material included in the coating (8) may be a known material. Examples of electronically conductive materials include carbon-based materials such as graphite and semigraphite, or nano-sized metal particle materials.

[0028] The film (8) is formed to cover at least a portion of the surface of the active material particle (6). In addition, even if the film (8) covers the entire surface of the active material particle (6), it is sufficient as long as the insertion and extraction of lithium ions are possible. The shape of the film (8) is not particularly limited. It may be a roughly uniform coating layer when the active material particle (6) is used as a core, or it may be formed by attaching a carbon-based material of any shape to the surface of the active material particle (6). The former may be, for example, a carbon-based material film obtained by carbonizing an organic material applied to the surface of the active material particle (6). The latter may be a film obtained by attaching a carbon-based material to the surface of the active material particle (6) through mechanochemical mixing, etc.

[0029] The thickness of the film (8) is not specifically limited. For example, it may be 0.1 nm or more and 10 nm or less, or 0.5 nm or more and 3 nm or less.

[0030] (Challenge Jose)

[0031] The conductive agent (10) is a agent for improving the electronic conductivity of the electrode film (4). The conductive agent (10) is dispersed and retained in the electrode film (4), but, for example, it may be interposed between active material particles (6) coated with the first polymer (12) or attached to the surface thereof and dispersed and retained.

[0032] As for the conductive agent (10), it is not specifically limited and various known conductive agents may be used. Examples of conductive agents (10) include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; carbon materials such as graphene or carbon nanotubes; fluorocarbon; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. As for the carbon nanotube, for example, single-walled carbon nanotubes (SW-CNT) and multi-walled carbon nanotubes (MW-CNT) including double-walled carbon nanotubes may be preferred. One or more of these may be used as the conductive agent (10).

[0033] The content of the conductive agent (10) in the electrode film (4) is not specifically limited, but, for example, is 0.01 mass% or more and 5 mass% or less of the total mass of the electrode film (4). Also, for example, it is 1.0 mass% or more and 3.0 mass% or less, and 1.0 mass% or more and 2.0 mass% or less.

[0034] (First polymer)

[0035] The first polymer (12) may be included in the electrode film (4) in a form that covers the film (8). The first polymer (12) may cover part or all of the film (8) to the extent that it does not impair the function of the film (8).

[0036] The first polymer (12) has a shape that covers the film (8), so that in the electrode film (4), damage to the active material particles (6) is suppressed in addition to damage to the film (8). It is understood that by including the first polymer (12) in the electrode film (4) in this shape, the frictional force between the active material particles (6) is reduced when mixed with the conductive agent (10), and thus damage to the film (8) is suppressed. In addition, damage to the active material particles (6) themselves is also suppressed. Therefore, by including the first polymer (12) in this shape, the decrease in the powder resistance of the electrode film (4) is suppressed.

[0037] The first polymer (12) is a polymer that does not fibrillate, as it covers the film (8) on the surface of the active material particles (6). In addition, it is preferable that the first polymer (12) has a melting point of 60°C or higher and 260°C or lower. By having a melting point in this temperature range, the first polymer (12) is easily fluidized, and the frictional force between the active material particles (6) is effectively reduced.

[0038] The melting point of the first polymer (12) is, for example, 70°C or higher, 75°C or higher, 80°C or higher, 90°C or higher, and also 240°C or lower, 230°C or lower, 220°C or lower, and 200°C or lower. In addition to the above range, the range of the melting point of the first polymer (12) can be set by appropriately combining the lower and upper temperature limits described above. For example, 60°C or higher and 240°C or lower, 60°C or higher and 200°C or lower, 60°C or higher and 180°C or lower, and 60°C or higher and 120°C or lower.

[0039] The first polymer (12) is not specifically limited as long as it is fluidized and, for example, interposed to cover the film (8) of the active material particles (6), thereby reducing the frictional force between the active material particles (6) and coating them. Examples of the first polymer (12) include polyethylene oxide (PEO), polypropylene oxide, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride, ethylene carbonate, polyethylene, polypropylene, polystyrene, ABS resin, polyacrylate, polymethacrylate, polyvinyl alcohol, and polycarbonate. One or more of these may be used. The first polymer (12) may also function as a binder in the electrode film (4).

[0040] The first polymer (12) may be one or more selected from the group consisting of PEO, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, and polyvinylidene fluoride. These polymers have ionic conductivity and can suppress the decrease in lithium ion conductivity.

[0041] Herein, each of the above polymers comprises, for example, homopolymers and copolymers each comprising a basic structural unit based on the name of the polymer and a structural unit to which the basic structural unit is modified. For example, PEO comprises homopolymers and copolymers having structural units derived from ethylene oxide and / or their modified structural units, and may have various forms such as straight chains, comb-shaped, cross-linked types, etc. Such polymers are known to those skilled in the art and can be appropriately obtained or manufactured by those skilled in the art.

[0042] For example, as the first polymer (12), PEO such as a homopolymer of structural units derived from ethylene oxide with a number average molecular weight of 3,000 or more and 10,000,000 or less can be used. The number average molecular weight of such PEO is, for example, 3,000 or more and 50,000 or less, 8,000 or more and 50,000 or less, and 10,000 or more and 30,000 or less.

[0043] The content of the first polymer (12) in the electrode film (4) is not specifically limited and is sufficient as long as it can suppress damage to the coating (8). For example, if the content of the first polymer (12) is 0.1 mass% or more and 3.0 mass% or less relative to the total mass of the electrode film (4), it may be effective in reducing frictional force during the production of the electrode film (4), protecting the coating (8), and suppressing the decrease in powder resistance in the electrode film (4). For example, it is 0.5 mass% or more, 0.7 mass% or more, 0.8 mass% or more, 1.0 mass% or more, 1.5 mass% or more, and 2.0 mass% or more. Also, it is 2.5 mass% or less, 2.0 mass% or less, 1.5 mass% or less, and 1.2 mass% or less. The range of the content of the first polymer (12) can be set by appropriately combining the lower and upper limits in addition to the above range. For example, 0.7 mass% or more and 3.0 mass% or less, 0.8 mass% or more and 2.0 mass% or less, 0.8 mass% or more and 1.5 mass% or less, and 0.8 mass% or more and 1.2 mass% or less.

[0044] (Second polymer)

[0045] The electrode film (4) includes a second polymer (14). In the electrode film (4), the second polymer (14) has a fibrillated form. For example, the second polymer (14) exists in a fibrillated state and is wound fibrously on the outside of the active material particle (6) that is coated with the film (8).

[0046] As the second polymer (14), a fibrillable polymer is used. When a shear force is applied to the second polymer (14), the second polymer (14) becomes fibrillated. The fibrillated second polymer (14) wraps around the active material particles (6) and the conductive agent (10), restrains them, and imparts mechanical strength to the electrode film (4).

[0047] The second polymer (14) can be used without special limitation as long as it is a fibrillable polymer. Fibrillable polymers are well known to those skilled in the art. Examples of the second polymer (14) include polytetrafluoroethylene (PTFE), polyolefin, polyalkylene, polyether, styrene-butadiene, polysiloxane and copolymer of polysiloxane, branched polyether, polyvinyl ether, and copolymers thereof. As the second polymer (14), cellulose containing carboxyalkylcellulose, such as carboxymethylcellulose (CMC), may also be used. One or more of these may be used as the second polymer (14). For example, it is preferable that the second polymer (14) be PTFE. This is because PTFE has excellent fibrillability and binder performance.

[0048] It is preferable that the second polymer (14) be capable of fibrillation at a temperature of 60°C or higher and 260°C or lower. This temperature range corresponds to the temperature range of the preferred melting point of the first polymer (12). Since the second polymer (14) can be fibrillated within the range in which the first polymer (12) used is fluidized, a lubricating effect by the first polymer (12) may be expected when the active material particles (6), etc., are composited by the second polymer (14). Furthermore, it is preferable that the second polymer (14) has heat resistance at the temperature in which the first polymer (12) is fluidized. From this perspective, it is preferable that the second polymer (14) has a melting point exceeding, for example, 260°C.

[0049] The content of the second polymer (14) in the electrode film (4) is not specifically limited and can be integrated by binding the electrode film (4). For example, the content of the second polymer (14) is 1.0 mass% or more and 10 mass% or less with respect to the total mass of the electrode film (4). Also, for example, it is 1.5 mass% or more, 2.0 mass% or more, 2.5 mass% or more, and 3.0 mass% or more. Also, it is 8.0 mass% or less, 6.0 mass% or less, and 5.0 mass% or less. In addition to the above ranges, the range of the content of the second polymer (14) can be set by appropriately combining these lower and upper limits. For example, it is 1.5 mass% or more and 5.0 mass% or less, 2.0 mass% or more and 5.0 mass% or less, and 2.5 mass% or more and 4.5 mass% or less.

[0050] In addition, the electrode film (4) may, if necessary, contain a polymer that functions as a binder between the active material particles (6), the conductive agent (10), and the current collector (20). For example, in addition to the first polymer (12) and the second polymer (14) mentioned above, known polymers that can be used for this type of electrode may be used. These polymers may be in the form of particles, etc.

[0051] The electrode film (4) described above has a thickness of, for example, 10 μm or more and 500 μm or less, and forms a positive electrode (2) together with a current collector (20).

[0052] According to this positive electrode (2), in the electrode film (4), the first polymer (12) has a shape that covers the film (8). According to this shape, damage to the film (8) is suppressed, and the increase in powder resistance is suppressed. From this shape of the first polymer (12), it is understood that when preparing a mixture for the electrode film (4), the first polymer (12) is interposed to cover the film (8), thereby reducing the frictional force between the active material particles (6). For this reason, even if the electrode film (4) is formed by a dry process using a fibrillated second polymer (14), damage to the film (8) is suppressed during that process.

[0053] In addition, the second polymer (14) is generally uniformly dispersed in the electrode film (4) with respect to the active material particles (6) having a coating (8) and the conductive agent (10). Furthermore, the coating (8) of the active material particles (6) can be constrained to be wound in a fibrous manner from the outside. In this respect as well, the increase in powder resistance is suppressed.

[0054] Next, a method for manufacturing an electrode sheet for manufacturing such an electrode film (4) will be explained with appropriate reference to FIG. 2. Additionally, the electrode sheet is laminated onto a current collector (20) and, appropriately, integrated by a heat press or the like to form the electrode film (4). FIG. 2 shows an example of a method for manufacturing an electrode sheet.

[0055] This manufacturing method comprises a process S10 for preparing a first mixture, a process S20 for preparing a second mixture using the first mixture, and a process S30 for producing an electrode sheet for an electrode film (4) using the second mixture.

[0056] (Process S10 for preparing the first mixture)

[0057] Process S10 comprises preparing a first mixture by mixing an active material particle (6) having a film (8), a conductive agent (10), and a first polymer (12) that does not fibrillate. It is preferable that the first mixture does not contain a second polymer (14) capable of fibrillation. As a result of including the second polymer (14), the protection and lubricity of the film (8) by the first polymer (12) may be reduced. Consequently, it becomes difficult for the first polymer (12) to form a shape that covers the film (8), and the film (8) becomes prone to damage. Additionally, the uniformity of dispersion of the second polymer (14) and the conductive agent (10) may be reduced.

[0058] The first mixture may comprise active material particles (6), a conductive agent (10), and a first polymer (12), and may be a mixture having at least the first polymer (12) covering the surface of the active material particles (6), that is, the surface of the electronically conductive material film (8). In process S10, the first mixture can be obtained by mixing these materials to be mixed in a state where the first polymer (12) is fluidized. For example, when using a polymer with a melting point of 60°C or higher and 260°C or lower, the first mixture can be obtained by mixing under a suitable shear force at a temperature of 60°C or higher and 260°C or lower, which is the temperature at which the polymer melts and becomes fluidized.

[0059] As the first polymer (12) is melted and fluidized, the frictional force between the active material particles (6) is reduced. This effect is thought to be because the first polymer (12) has a shape that covers the film (8) during mixing. By fluidizing and using the first polymer (12), it functions as a lubricant during the mixing of the active material particles (6) and the conductive agent (10) without using a solvent, and the mixing can be facilitated. As a result, damage to the film (8) during mixing with the conductive agent (10) is suppressed.

[0060] Process S10 may include multiple steps as long as the first mixture is obtained. For example, the active material particles (6) and the first polymer (12) may be mixed in advance while the first polymer (12) is in a fluidized state to form a shape covering the surface of the film (8) with the first polymer (12), and then, the first polymer (12) may be maintained in a fluidized state while adding and mixing a conductive agent (10). By doing so, strong frictional force applied to the film (8) can be effectively suppressed.

[0061] In preparing the first mixture, the conductive agent (10) and the first polymer (12) may be used within the range of contents already described with respect to the total mass of the second mixture to be finally obtained. Also, the amount of active material particles (6) may be used such that it is the remainder other than the conductive agent (10), the first polymer (12), and the second polymer (14) with respect to the total mass of the second mixture.

[0062] Process S10 can be carried out using a known mixing device. Examples of known mixing devices that can be used for shear mixing include various kneaders such as a pressure kneader equipped with a roller, rotor, paddle, blade, gear, screw, etc. as a rotating body, as well as Banbury mixers, Henschel mixers, twin-screw extruders, and various mills such as jet mills, roller mills, and hammer mills. A person skilled in the art can appropriately set mixing conditions, such as shear force and mixing time, so that a proper mixing state of the active material particles (6) and the conductive agent (10) is obtained.

[0063] (Process S20 for preparing the second mixture)

[0064] Process S20 includes mixing a first mixture with a fibrillable second polymer (14) to prepare a second mixture having the second polymer (14) in a fibrillated state.

[0065] The second mixture is a mixture in which the second polymer (14) is in a fibrillated state in addition to the active material particles (6) derived from the first mixture, the conductive agent (10), and the first polymer (12). The second mixture can be obtained by mixing these materials to be mixed so as to fibrillate the second polymer (14).

[0066] After preparing the first mixture, a second polymer (14) is added and mixed to enable fibrillation, thereby obtaining a second mixture having a structure similar to or similar to that of the electrode film (4). That is, in the second mixture, the first polymer (12) has a form covering the film (8) of the active material particles (6), and the second polymer (14) has a fibrillated form. In addition, the second polymer (14) restrains the active material particles (6) so that they are wound in a fibrous shape from the outside.

[0067] Process S20 is preferably performed in a state where the first polymer (12) is melted and fluidized, just like in Process S10. That is, based on the melting point of the first polymer (12), it is preferable to mix at a temperature of 60°C or higher and 260°C or lower. By doing so, in Process S20, the first polymer (12) functions as a lubricant, making the mixing of Process S20 easier and suppressing damage to the film (8).

[0068] In preparing the second mixture, the second polymer may be used in the range of the previously described content with respect to the total mass of the second mixture to be finally obtained.

[0069] Process S20 can be carried out using a known mixing device, just like process S10. A person skilled in the art can appropriately set mixing conditions, such as shear force and mixing time, so that the fibrillation of the second polymer (14) and the proper mixing state of the materials to be mixed are obtained.

[0070] (Process S30 for manufacturing an electrode sheet for an electrode film)

[0071] Process S30 includes manufacturing an electrode sheet for manufacturing an electrode film (4) using the second mixture. Here, the thickness of the electrode sheet is approximately 10 μm or more and 2000 μm or less, or 10 μm or more and 1000 μm or less. The sheeting process is not particularly limited. For example, without using a support, the second mixture may be supplied between rotating rollers and formed into a sheet by calendering while hot pressing. Alternatively, the electrode composite mixture may be supplied to a suitable mold and formed into a sheet by press pressing.

[0072] The resulting electrode sheet has active material particles (6), conductive additives (10), a first polymer (12), and a second polymer (14) in the same form as those in the electrode film (4) described above, and has a predetermined mechanical strength. Because of this, it is possible to form an electrode film (4) that can stand on its own without a support.

[0073] In addition, a positive electrode (2) and a secondary battery can be manufactured using such an electrode sheet. First, a current collector (20) and an electrode sheet are laminated. Furthermore, the electrode sheet is compressed by applying pressure at a predetermined temperature, etc., to a thickness of approximately 10 μm or more and 500 μm or less, thereby forming an electrode film (4). At the same time as obtaining the electrode film (4), a positive electrode (2) in which the electrode film (4) is integrated with the current collector (20) can be obtained. A secondary battery equipped with a positive electrode (2) can be manufactured appropriately by a known method.

[0074] In the electrode film (4) obtained in this way, damage to the film (8) on the surface of the active material particle (6) is suppressed, and damage to the electronic conductivity is suppressed. Because of this, a secondary battery having a positive electrode (2) and a positive electrode (2) can be obtained that exhibits good electrode characteristics.

[0075] In the above description, the electrode film (4), etc., have been described; however, according to the present specification, in addition to the electrode sheet which is a precursor of the electrode film (4), a positive electrode (2) having the electrode film (4) and a secondary battery having the positive electrode (2) are also provided. Furthermore, in the above description, a method for manufacturing an electrode sheet for the electrode film (4) has been described; however, according to the present specification, a method for manufacturing a mixture for an electrode film is also provided, comprising a process for preparing a first mixture and a process for preparing a second mixture. In addition to the process in the method for manufacturing an electrode sheet, a method for manufacturing an electrode is also provided, comprising a process for manufacturing an electrode film (4) using the electrode sheet. In addition to the method for manufacturing an electrode, a method for manufacturing a secondary battery is also provided, comprising a process for manufacturing a secondary battery.

[0076] It is evident that the present specification includes the following components.

[0077] [1] Active material particles comprising an olivine-type positive electrode material having an electronically conductive material film, and

[0078] Challenge Joze and,

[0079] A first polymer having a shape covering the above-mentioned electronically conductive material film, and

[0080] Second polymer having a fibrillated form

[0081] A self-supporting electrode membrane having

[0082] [2] The first polymer described above is a self-supporting electrode film described in [1], having a melting point of 60°C or higher and 260°C or lower.

[0083] [3] The first polymer is one or more selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride, ethylene carbonate, polyethylene, polypropylene, polystyrene, ABS resin, polyacrylate, polyvinyl alcohol and polycarbonate, and is a self-supporting electrode membrane as described in [1] or [2].

[0084] [4] A self-supporting electrode film described in any one of [1] to [3] containing the first polymer in an amount of 0.1 mass% or more and 3.0 mass% or less with respect to the total mass of the self-supporting electrode film.

[0085] [5] The second polymer described above is a self-supporting electrode membrane comprising polytetrafluoroethylene, as described in any one of [1] to [4].

[0086] [6] An electrode having the above-mentioned self-supporting electrode membrane as described in any of [1] to [5].

[0087] [7] A secondary battery having the electrode described in [6].

[0088] [8] As a method for manufacturing an electrode sheet for a self-supporting electrode membrane,

[0089] A process of preparing a first mixture by mixing an active material particle comprising an olivine-type positive electrode material having an electronically conductive material film, a conductive additive, and a first polymer that does not fibrillate, while the first polymer is in a fluidized state;

[0090] A process of mixing the first mixture with a second polymer capable of fibrillation to prepare a second mixture having the second polymer in a fibrillated state, and

[0091] A process for manufacturing the electrode sheet using the second mixture above.

[0092] A manufacturing method comprising

[0093] [9] The first polymer described above has a melting point of 60°C or higher and 260°C or lower, according to the manufacturing method described in [8].

[0094]

[10] The process of preparing the second mixture described above comprises mixing the first mixture and the second polymer while the first polymer is in a fluidized state, as described in [8] or [9].

[0095]

[11] A method for manufacturing an electrode having a self-supporting electrode membrane,

[0096] A process of preparing a first mixture by mixing an active material particle comprising an olivine-type positive electrode material having an electronically conductive material film, a conductive additive, and a first polymer that does not fibrillate, while the first polymer is in a fluidized state;

[0097] A process of mixing the first mixture with a second polymer capable of fibrillation to prepare a second mixture having the second polymer in a fibrillated state, and

[0098] A process for manufacturing an electrode sheet for the self-supporting electrode membrane using the second mixture above, and

[0099] A process of manufacturing the electrode having the self-supporting electrode film by bonding the electrode sheet to a current collector.

[0100] A manufacturing method comprising

[0101] [Example]

[0102] Hereinafter, embodiments embodying the disclosure of this specification will be described, but these embodiments are not limited to explaining the disclosure of this specification.

[0103] In this embodiment, a mixture for an electrode film of a positive electrode of a lithium-ion secondary battery was prepared by the following method, an electrode sheet was fabricated, and the powder resistance was measured.

[0104] For the preparation of the mixture, LFP (lithium iron phosphate) was used as the olivine-type positive electrode material (active material particle) having a carbon coat, MW-CNT as the conductive additive, PEO (number average molecular weight about 20,000, melting point 60°C) as the first polymer, and PTFE as the second polymer.

[0105] (Example 1)

[0106] The mixture for the electrode film of Example 1 was prepared by including active material particles, a conductive additive, and a first polymer, and by preparing a first mixture that does not include a second polymer, and then by preparing a second mixture as a mixture for the electrode film that also includes the second polymer. In addition, the mass ratio of each material in the second mixture was set so that active material particles / conductive additive / PEO / PTFE was 94.1 / 1.5 / 1.0 / 3.4.

[0107] First, active material particles (LFP), conductive aid (MW-CNT), and first polymer (PEO) were mixed in the above mass ratio, and a first mixture was obtained by mixing using a kneader under mixing conditions of 80°C, 60 rpm, and 600 seconds.

[0108] Next, a second polymer (PTFE) was added to the first mixture in the above mass ratio, and the mixture was mixed using the kneader under mixing conditions of 160°C, 60 rpm, and 30 seconds to obtain a second mixture for an electrode film.

[0109] The second mixture was also molded using a calender device at 160°C, with a roll clearance of 340 μm, a roll 1 speed of 1.8 m / sec, and a roll 2 speed of 2.4 m / sec to obtain an electrode sheet. For a sample prepared from this electrode sheet by a predetermined method, the volume resistivity (Ω·cm) was measured according to the standard method of powder resistance measurement. The results are shown in Table 1. For reference, the total power required to obtain the first and second mixtures in the kneader is also shown as processing energy.

[0110] (Comparative Example 1)

[0111] As Comparative Example 1, the first polymer (PEO) was not used in the first mixture, and the mixing conditions were the same as those in Example 1, except that the mass ratio of active material particles was increased instead of the first polymer. The first mixture, the second mixture, and the electrode sheet of Comparative Example 1 were obtained, and the volume resistivity was measured in the same manner as in Example 1. In addition, in Comparative Example 1, the mass ratio of each material (active material particles / conductive aid / PTFE) in the second mixture was 95.1 / 1.5 / 3.4. The results are shown in Table 1.

[0112] (Comparative Example 2)

[0113] As Comparative Example 2, the active material particles / conductive aid / PEO / PTFE of the entire material were initially blended in a mass ratio of the second mixture (94.1 / 1.5 / 1.0 / 3.4), and the second mixture was obtained by mixing under the mixing conditions of the first mixture (80°C, 60 rpm, and 600 seconds) and subsequently under the mixing conditions of the second mixture (160°C, 60 rpm, and 30 seconds), and an electrode sheet was obtained in the same manner as in Example 1. The volume resistivity was measured in the same manner as in Example 1. The results are also shown in Table 1.

[0114] In addition, through Example 1, Comparative Examples 1 and 2, since mixing was performed at 80°C, which exceeds the melting point of the first polymer (PEO), the first polymer (PEO) was in a melted and fluidized state at either mixing step.

[0115] [Table 1]

[0116]

[0117] As shown in Table 1, Example 1 exhibited the lowest volume resistivity and also had the minimum processing energy. In addition, when the cross-section of the electrode sheet in Example 1 was observed using a transmission electron microscope, the first polymer, PEO, had a structure covering the carbon coat of the active material particles, and the second polymer, PTFE, was generally uniformly dispersed with respect to the active material particles having the carbon coat and the conductive additive, CNT. Furthermore, the PTFE restrained the active material particles to be wound in a fibrous manner from the outside.

[0118] In contrast, in Comparative Example 1, the volume resistivity was clearly increased and the processing energy was also increased. This indicates that in the absence of the first polymer (PEO), a large shear force is generated during mixing, and the carbon coating layer on the active material particles is damaged as the second mixture is prepared step by step.

[0119] In addition, in Comparative Example 2, the volume resistivity was significantly higher than that of Comparative Example 1, and the processing energy was also increased. This was thought to be because, when using the first polymer (PEO) and mixing it all at once, the lubricating function of the first polymer due to fluidization in the presence of the second polymer (PTFE) could not be fully exerted, which promoted damage to the carbon coating on the surface of the active material particles and also reduced the dispersibility of the conductive aid.

[0120] From the above, it was found that by using a first polymer such as PEO, which can be melted and fluidized, to pre-mix active material particles and a conductive additive to prepare a first mixture, and then adding a second polymer such as PTFE, which can be fibrillated to prepare a second mixture, an electrode sheet and an electrode film are obtained in which damage to the carbon coat is suppressed and the dispersibility of the conductive additive is also secured.

[0121] The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings is capable of achieving multiple objectives simultaneously, and achieving one of those objectives itself constitutes technical utility. Explanation of the symbols

[0122] 2 Positive electrode, 4 Self-supporting electrode film, 6 Active material particle, 8 Electronically conductive material film, 10 Conductive agent, 12 First polymer, 14 Second polymer, 20 Current collector

Claims

Claim 1 A self-supporting electrode film comprising an active material particle including an olivine-type positive electrode material having an electronically conductive material film, a conductive agent, a first polymer having a shape covering the electronically conductive material film, and a second polymer having a fibrillated shape. Claim 2 In claim 1, the first polymer is a self-supporting electrode film having a melting point of 60°C or higher and 260°C or lower. Claim 3 In claim 2, the first polymer is one or more selected from the group consisting of polyethylene oxide, polyacrylonitrile, polyvinyl chloride, polymethyl methacrylate, polyvinylidene fluoride, ethylene carbonate, polyethylene, polypropylene, polystyrene, ABS resin, polyacrylate, polyvinyl alcohol, and polycarbonate, forming a self-supporting electrode membrane. Claim 4 A self-supporting electrode film according to claim 1, wherein the first polymer is contained in an amount of 0.1 mass% or more and 3.0 mass% or less with respect to the total mass of the self-supporting electrode film. Claim 5 In claim 1, the second polymer comprises polytetrafluoroethylene, forming a self-supporting electrode membrane. Claim 6 An electrode having a self-supporting electrode membrane as described in claim 1. Claim 7 A secondary battery having the electrode described in claim 6. Claim 8 A method for manufacturing an electrode sheet for a self-supporting electrode film, comprising: a process of preparing a first mixture by mixing an active material particle comprising an olivine-type positive electrode material having an electronically conductive material film, a conductive additive, and a first polymer that does not fibrillate, in a state where the first polymer is fluidized; a process of preparing a second mixture by mixing the first mixture with a second polymer capable of fibrillation, in a state where the second polymer is fibrillated; and a process of manufacturing the electrode sheet using the second mixture. Claim 9 A method of manufacturing according to claim 8, wherein the first polymer has a melting point of 60°C or higher and 260°C or lower. Claim 10 A manufacturing method according to claim 8, wherein the process of preparing the second mixture comprises mixing the first mixture and the second polymer while the first polymer is in a fluidized state. Claim 11 A method for manufacturing an electrode having a self-standing electrode film, comprising: a process of preparing a first mixture by mixing an active material particle comprising an olivine-type positive electrode material having an electron-conductive material film, a conductive additive, and a first polymer that does not fibrillate, in a state where the first polymer is fluidized; a process of preparing a second mixture by mixing the first mixture with a second polymer capable of fibrillation, wherein the second polymer is in a fibrillated state; a process of manufacturing an electrode sheet for the self-standing electrode film using the second mixture; and a process of manufacturing the electrode having the self-standing electrode film by bonding the electrode sheet to a current collector.

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