Method for manufacturing electrode sheets

Abstract

This invention provides a technology for manufacturing electrode sheets while suppressing or avoiding damage to active material particles. [Solution] A method for manufacturing an electrode sheet is provided. This manufacturing method comprises the steps of: preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated; and preparing an electrode composite mixture containing the binder mixture and active material particles.

Description

[Technical Field]

[0001] The technology disclosed herein relates to a method for manufacturing an electrode sheet. [Background technology]

[0002] A dry process is known as a method for manufacturing electrode sheets for secondary batteries (Patent Document 1). This process involves mixing a dry particulate non-fibrillated binder with an active material to form a dry bulk active mixture, then using high-shear mixing to form a dry structural binder mixture by mixing a dry fibrillable binder (hereinafter also referred to as a fibrillated binder) with an active material, and finally mixing these mixtures to form a dry electrode composite mixture, from which a dry self-supporting electrode sheet is manufactured. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-37911 [Overview of the project] [Problems that the invention aims to solve]

[0004] Generally, by high-shear mixing a dry fibrillation binder with active material particles, the dry fibrillation binder can be fibrillated, forming a dry binder mixture that contributes to the self-supporting nature of the electrode sheet. However, it has been found that such shear forces may cause damage to the active material particles, such as fragmentation or surface delamination. As a result, for example, the resistance value of the electrode sheet may deteriorate.

[0005] This specification provides a technique for manufacturing electrode sheets while suppressing or avoiding damage to active material particles. [Means for solving the problem]

[0006] The inventors have found that a fibrillable first binder can be fibrillated by using non-active, non-fibrillated particles as a medium or aid for fibrillation. The disclosure herein is based on this finding.

[0007] The technology disclosed herein relates to a method for manufacturing an electrode sheet. This manufacturing method comprises the step of mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated to prepare a binder mixture containing the fibrillated first binder. Furthermore, it comprises the step of manufacturing an electrode composite mixture containing the binder mixture and active material particles.

[0008] According to this manufacturing method, the first binder is fibrillated in the presence of non-fibrillated particles, which are inactive material particles, to obtain a binder mixture. Subsequently, an electrode composite mixture containing the binder mixture after fibrillation of the first binder and active material particles is prepared. Therefore, shear forces and other forces associated with the fibrillation of the first binder are suppressed or avoided from being applied to the active material particles, thereby suppressing or avoiding damage to the active material particles. As a result, deterioration of resistance values ​​and other properties in the electrode sheet due to damage to the active material particles is avoided. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a manufacturing scheme for electrode sheets using an electrode sheet manufacturing method. [Figure 2] This figure shows an example of a secondary battery equipped with an electrode sheet as the positive electrode. [Figure 3] This figure shows the evaluation results of the powder resistance values ​​of the electrode mixture prepared in the example. [Modes for carrying out the invention]

[0010] The method for manufacturing an electrode sheet disclosed in this specification (hereinafter, also simply referred to as this manufacturing method) can include, as described above, a step of preparing the binder mixture and a step of preparing the electrode composite mixture. This manufacturing method can also adopt the following aspects.

[0011] Another aspect of this manufacturing method is that the step of preparing the binder mixture includes performing it at a temperature below or lower than the melting point of the material contained in the non-fibrillated particles. By doing so, the particle form of the non-fibrillated particles is maintained in this step, and a shearing force can be effectively applied to the first binder.

[0012] Another aspect of this manufacturing method is that the active material particles may include a core portion containing the active material and a coating layer covering at least a part of the core portion. By doing so, particularly, the application of a high shearing force to the coating layer is suppressed or avoided, and the function of the coating layer is likely to be maintained. In this aspect, the coating layer may have electronic conductivity. By maintaining the function of the coating layer having electronic conductivity, the deterioration of the resistance value of the electrode sheet is effectively suppressed.

[0013] Another aspect of this manufacturing method is that the non-fibrillated particles may be components of the electrode sheet. By using non-fibrillated particles that are non-active material particles and are components of the electrode sheet, the electrode sheet can be efficiently manufactured while avoiding damage to the active material particles, etc. The non-fibrillated particles may be a second binder. By doing so, the first binder is easily fibrillated, and the binder mixture can be efficiently manufactured.

[0014] Another aspect of this manufacturing method is that the average particle diameter (D 50 ) of the non-fibrillated particles may be 7 μm or more. When the average particle diameter of the non-fibrillated particles is 7 μm or more, it is easy to mix with an effective amount of work for fibrillating the first binder, and it is easier to apply a shearing force for fibrillating to the first binder.

[0015] Another aspect of this manufacturing method is that the step of preparing the binder mixture includes mixing with a first amount of work, and the step of preparing the electrode composite mixture may include mixing with a second amount of work lower than the first amount of work. By doing so, suppression or avoidance of damage to the active material particles can be surely achieved.

[0016] Another aspect of this manufacturing method may include performing the step of preparing the binder mixture and the step of preparing the electrode composite mixture by a dry process. By doing so, the electrode sheet can be manufactured by omitting the process operations associated with using a solvent.

[0017] Another aspect of this manufacturing method may include a step of producing an electrode sheet using the electrode composite mixture.

[0018] According to this specification, a manufacturing method of an electrode binder mixture, which includes a step of preparing the binder mixture, is also provided. Also, a manufacturing method of an electrode composite mixture, which includes a step of preparing the binder mixture and a step of preparing the electrode composite mixture, is also provided.

[0019] Hereinafter, this manufacturing method will be described with reference to the drawings as appropriate. FIG. 1 shows an outline of the scheme of this manufacturing method, and FIG. 2 shows an example of a positive electrode and a secondary battery including an electrode sheet to be manufactured by this manufacturing method. In this specification, the electrode sheet is, for example, an electrode sheet constituting a positive electrode or a negative electrode of a lithium ion secondary battery. Also, in this specification, the electrode sheet is, for example, a self-supporting electrode sheet. In this specification, substances or materials expressed including the term "particles" such as fibrillated particles, non-fibrillated particles, and active material particles are all concepts including powders composed of a plurality of particles.

[0020] (Method for manufacturing an electrode sheet) The following describes, using examples, a method for manufacturing an electrode (positive electrode) sheet 2 that constitutes the positive electrode 14 of a lithium-ion secondary battery (hereinafter simply referred to as a secondary battery) 10. Unless otherwise specified, the various aspects of this manufacturing method are common to both the electrode sheet 2 for the positive electrode and the electrode sheet for the negative electrode.

[0021] Figure 2 shows an overview of the secondary battery 10. As shown in Figure 2, the secondary battery 10 comprises a positive electrode 14 and a negative electrode 16 provided on both sides of a separator 12. The separator 12 is made of a known material such as a polyolefin microporous membrane with fine pores formed therein. The separator 12 is impregnated with a liquid electrolyte containing a lithium salt such as lithium hexafluoride phosphate, using an organic solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC) as a medium. Alternatively, the separator 12 may be a solid electrolyte layer. The positive electrode 14 comprises a positive electrode composite layer 14a, which is an electrode sheet 2, and a positive electrode current collector layer 14b. The negative electrode 16 comprises a negative electrode composite layer 16a and a negative electrode current collector layer 16b. The positive electrode current collector layer 14b and the negative electrode current collector layer 16b can each be made of known materials as appropriate.

[0022] (Preparation process of binder mixture) As shown in Figure 1, the present manufacturing method includes a step (S10) of mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, in order to prepare a binder mixture containing the fibrillated first binder.

[0023] (First binder) The first fibrillable binder is a binder that becomes fibrous (fibrillated) when a shear force is applied. For example, a fibrous binder that is aggregated but becomes fibrous (fibrillated) when a certain shear force is applied. The particle shape of the first binder is not particularly limited. The first binder can be any binder known as an electrode binder for secondary batteries that has a fibrillable binder structure.

[0024] The first binder is not particularly limited, but examples include polytetrafluoroethylene (PTFE), polyolefins, polyalkylenes, polyethers, styrene-butadiene, polysiloxanes and polysiloxane copolymers, branched polyethers, polyvinyl ethers, and copolymers thereof. Another example of the first binder is cellulose containing carboxyalkyl cellulose, such as carboxymethylcellulose (CMC). Furthermore, examples of polyolefins as the first binder include polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), and copolymers thereof. Other examples of the first binder include polyvinyl chloride, poly(phenylene oxide) (PPO), block copolymers containing poly(ethylene oxide) (PEO) and PPO, and fluorine-containing polymers such as polydimethylsiloxane (PDMS). One or more of these can be used as the first binder. For example, the first binder is one or more selected from PTFE, PVDF, and CMC, and is PTFE and / or PVDF, and is PTFE.

[0025] The average particle size of the first binder is not particularly limited, but for example, it is between 5 μm and 50 μm. Within this range, fibrillation is easily achieved in this preparation process due to the presence of non-fibrillated particles. The average particle size may also be, for example, between 10 μm and 40 μm, between 15 μm and 35 μm, or between 20 μm and 30 μm. The average particle size of the first binder is the particle size (D) at which the cumulative value of 50% of the volume-based particle size distribution measured by laser diffraction-scattering is obtained. 50 It can be measured as follows:

[0026] (Non-fibrillated particles) Non-fibrillated particles are non-active material particles that cannot be fibrillated. Here, non-active material particles are particles that do not function as active material in the electrode sheet 2 to be manufactured. When the electrode sheet 2 is a positive electrode sheet, the active material particles are the various positive electrode active material particles described later. Therefore, non-active material particles include particles that are not such positive electrode active materials. When the electrode sheet 2 is a negative electrode sheet, non-active material particles include particles that are not negative electrode active material particles described later.

[0027] Non-fibrillated particles are particles that cannot be fibrillated. For non-fibrillated particles, particles with a structure that is not fibrillated or is difficult to fibrillate by shear force, etc., can be used as appropriate.

[0028] Non-fibrillated particles are preferable as components of electrode sheet 2 because the binder mixture can be used directly in the electrode composite mixture preparation process. Examples of components include other binders other than the first binder and conductive additives. The other binder is an example of the second binder in this specification.

[0029] Other binders include binders of the same or different types as the first binder, which are not fibrillable. Even if the polymer is of the same type as the first binder, if it is not fibrillable, it can be used as non-fibrillable particles. By using other binders as non-fibrillable particles, shear force tends to be more easily applied to the first binder, and binder mixtures containing binders of the same type but different forms, or two or more types of binders, can be efficiently obtained.

[0030] Other binders already described include the various binders that can be used as the first binder already described. Other binders other than the first binder include cellulose or cellulose derivatives (except CMC). Examples of cellulose derivatives include cellulose esters such as cellulose acetate, cellulose ethers such as methylcellulose, ethylcellulose, hydroxypropylcellulose (HPC), and hydroxyethylcellulose (HEC), and carboxyalkylcelluloses such as cellulose nitrate, carboxyethylcellulose, carboxypropylcellulose, and carboxyisopropylcellulose. Cellulose may also be a salt. The base constituting the salt may be selected from sodium, ammonium, or lithium. Other binders that are non-fibrillated particles may be one or more selected from these other binders. Examples of other binders include CMC and / or PVDF, or PVDF.

[0031] Furthermore, while there are no particular limitations, any conductive additive that can be used as a conductive additive in electrode sheet 2 may be used as appropriate. Examples of conductive additives include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; carbon materials such as graphene and carbon nanotubes; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. One or more of these non-fibrillated particles can be used as conductive additives.

[0032] Non-fibrillated particles are preferably of an average particle size of 7 μm or more. This is because an average particle size of 7 μm or more makes it easier to mix with a workload that allows for sufficient shear force to be applied to the first binder to enable fibrillation. According to the inventors, when the average particle size of the non-fibrillated particles is 6 μm or less, mixing can only be performed at a maximum of about 0.7 J per 100 g of the mixture, making it difficult to apply shear force to the first binder. On the other hand, when the average particle size of the non-fibrillated particles is between 7 μm and 20 μm, mixing can be performed with a workload of 1 J or more and up to about 8.2 J per 100 g of the mixture, making it easier to apply shear force to enable fibrillation of the first binder. In this specification, the total workload in the mixing operation can be obtained from the cumulative power amount obtained by accumulating the instantaneous power required for mixing in the equipment used for the mixing operation over the mixing time. The cumulative energy per 100g of the mixture can be obtained as the amount of work done during the mixing operation (per 100g).

[0033] The average particle diameter of non-fibrillated particles can be, for example, 8 μm or more, 9 μm or more, 10 μm or more, 11 μm or more, 12 μm or more, or 14 μm or more. The average particle diameter can also be, for example, 30 μm or less, 25 μm or less, 20 μm or less, 18 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 12 μm or less, or 10 μm or less. The range of the average particle diameter of non-fibrillated particles is 10 μm or more and 30 μm or less, and can be 10 μm or more and 20 μm or less. The average particle diameter of non-fibrillated particles may be greater than the average particle diameter of the first binder. The average particle diameter of non-fibrillated particles is the particle diameter (D) of the 50% cumulative value in the volume-based particle size distribution measured by laser diffraction-scattering. 50 It can be measured as follows:

[0034] As a mixed material for obtaining a binder mixture, in addition to the first binder and non-fibrillated particles, other binders or other conductive additives that do not constitute non-fibrillated particles may be appropriately included as needed.

[0035] The content of the first binder in the mixed material is preferably 90% by mass or less of the total mass of the mixed material, taking into account the dispersibility of the fibrillated first binder. For example, it may be 85% by mass or less, or 80% by mass or less. The first binder may be, for example, 70% by mass or more, 75% by mass or more, or 80% by mass or more. The total mass of non-fibrillated particles in the mixed material may be, for example, 10% by mass or more, 15% by mass or more, 20% by mass or more, or for example, 30% by mass or less, 25% by mass or less, or 20% by mass or less.

[0036] In this step, the first binder and non-fibrillated particles are mixed (shear mixing) to fibrillate the first binder. For example, it is sufficient to mix at least a portion of the first binder in a way that makes it fibrillable. Fibrillating the first binder itself is a well-known technique, and those skilled in the art can appropriately mix the first binder in a way that makes it fibrillable depending on the type of first binder and the mixing method. The degree of fibrillation of the first binder intended in this step is not particularly limited, but for example, it is sufficient to fibrillate the first binder so that a self-supporting electrode sheet 2 can be formed by the first binder and non-fibrillated particles.

[0037] Such shear mixing is not particularly limited, but for example, it is done at a work rate of 1 J or more per 100 g of the mixing material (to be mixed). For example, it could also be 2 J or more, 3 J or more, 4 J or more, 5 J or more, 6 J or more, or 8 J or more. The upper limit is not particularly limited, but for example, it could be 15 J or less, 14 J or less, 12 J or less, 10 J or less, or 9 J or less. With such a work rate, the first binder is more easily subjected to the shear force necessary to fibrillate it. Note that such a work rate is just an example of the first work rate disclosed herein. Specifically, the type of mixing apparatus is appropriately selected, and its rotation speed and time are adjusted to achieve such a work rate.

[0038] Furthermore, it is sometimes preferable to perform the mixing in this process at a temperature that facilitates fibrillation of the first binder. For example, if the first binder is PTFE, the process may be carried out at 40°C or higher. The temperature in shear mixing can be determined by appropriately performing fibrillation on the first binder used.

[0039] Furthermore, it is preferable that the mixing temperature in this process be below or lower than the melting point of the constituent material of the non-fibrillated particles. This tends to make it easier to apply shear force to the first binder. Also, since the first binder is fibrillated using the non-fibrillated particles as a medium or auxiliary material, the non-fibrillated particles can be maintained. When the non-fibrillated particles are other binders such as PVDF, the melting point of PVDF is 177°C, so the process should be carried out at 177°C or below or less than 177°C.

[0040] For example, considering the type of binder used in secondary batteries, this mixing process is carried out at temperatures such as 40°C to 150°C, 50°C to 140°C, 60°C to 140°C, 80°C to 120°C, and 90°C to 110°C. This allows for effective fibrillation of the first binder.

[0041] The mixing operation in this process is not particularly limited, but any known mixing device that can be used for shear mixing can be used as appropriate, including various kneaders such as pressure kneaders equipped with rotating bodies such as rolls, rotors, paddles, blades, gears, and screws, as well as Banbury mixers, Henschel mixers, twin-screw extruders, and various mills such as jet mills, roller mills, and hammer mills. For example, when using a kneader, the mixing operation is performed for a period of, for example, 10 to 1200 seconds, typically about 20 to 40 seconds.

[0042] This process allows for the production of a binder mixture containing a fibrillated first binder. The resulting binder mixture may have a composition depending on the composition of the mixed materials.

[0043] (Preparation Process of Electrode Composite Material Mixture) Next, a process (S20) of preparing an electrode composite material mixture containing a binder mixture and active material particles is carried out. In this process, the binder mixture and the active material particles are mixed to prepare the electrode composite material mixture.

[0044] (Active Material Particles) As the active material particles, when the electrode sheet 2 is a positive electrode sheet, active material particles known as positive electrode active materials can be used. Although not particularly limited, for example, metal oxides, metal sulfides, or lithium metal oxides can be mentioned. Typically, layered rock salt type lithium-containing oxides and olivine type lithium iron phosphate compounds can be mentioned. Examples of the layered rock salt type lithium-containing oxides include LiCoO2 (LCO), Li(Ni 0.6 Co 0.2 Mn 0.2 )O2 and other NCM-based oxides that can be represented by the general formula LiNi x Co y Mn z O2 (where x + y + z = 1), LiNi 0.8 Co 0.15 Al 0.05 O2 and other NCA-based oxides that can be represented by the general formula LiNi a Co b Al c O2 (where a + b + c = 1). Examples of the olivine type lithium iron phosphate compounds include lithium iron phosphate (LiFePO4, LFP), lithium manganese iron phosphate (LiMn (1-d) F d PO4, LMFP), lithium manganese phosphate (LiMnPO4, LMP), etc. As the active material particles of the positive electrode sheet, one or more of these can be used.

[0045] When electrode sheet 2 is a negative electrode sheet, known active material particles can be used as the negative electrode active material. While not particularly limited, examples include carbon-based materials and metallic materials. Examples of carbon-based materials include natural or artificial graphite, graphene, acetylene black, carbon fibers, and carbon nanotubes. Examples of metallic materials include tin, silicon, titanium, metallic bamboo, lithium, and lithium alloys. Furthermore, SiC and lithium-titanium composite oxides are also possible. One or more of these can be used as the active material particles for the negative electrode sheet.

[0046] The active material particles are not particularly limited, but may comprise a core containing the active material and a coating layer covering at least a portion of the core. Such active material particles are particularly susceptible to damage to the coating layer during shear mixing, which can impair its function. Therefore, it is beneficial to adapt this manufacturing method to positive electrode sheets containing such positive electrode active material particles. Known active material particles of this type can be used. For example, positive electrode active material particles may include particles with a carbon coating layer on the surface of olivine-type lithium iron phosphate compound (LFP, LMP, LMFP) particles that have excellent electronic conductivity. Furthermore, nano-sized metal particles may be supported. Negative electrode active material particles may include particles with a carbon coating layer made of pyrolytic carbon or crystalline carbon on the surface of graphite particles or the like.

[0047] The ratio of the coating layer to the core particles is not particularly limited and can be set as appropriate. For example, it may be preferable to have a ratio of 0.01% by mass or more and 1.20% by mass or less. Alternatively, it may be 0.10% by mass or more and 0.30% by mass or less. The thickness of the coating layer is not particularly limited, but may be, for example, 0.1 nm to 10 nm or 0.5 nm to 3 nm.

[0048] The average particle diameter of the active material particles is not particularly limited, but can be, for example, 2 μm to 50 μm. In this manufacturing method, since the active material particles are not a medium for fibrillating the first binder, their average particle diameter is not limited to the range in which they effectively function as a fibrillating medium. For example, the average particle diameter of the active material particles may be smaller than the average particle diameter of the first binder and the non-fibrillated particles. The average particle diameter of the active material particles can also be, for example, 2 μm to 20 μm, 3 μm to 15 μm, or 5 μm to 10 μm. The average particle diameter of the active material particles is the particle diameter (D) at which the cumulative value of 50% of the volume-based particle size distribution measured by laser diffraction-scattering is obtained. 50 It can be measured as follows:

[0049] The mixed material for the electrode composite used in the mixing operation in this process may include, in addition to the binder mixture and active material particles obtained in the preceding process, other binders, conductive additives, etc., as appropriate. The other binders and conductive additives have already been described in the preceding process. It is preferable that the total mass of the binder be between 2% and 20% by mass relative to the total mass of the mixed material for the electrode composite. For example, the binder may be between 2% and 10% by mass, or between 2% and 8% by mass.

[0050] The mixing operation in this step only requires mixing the binder mixture and active material particles at a lower workload than the workload performed in the preceding binder mixture preparation step (shear mixing). This suppresses or avoids damage to the active material particles. Since the effective amount of the first binder has already been fibrillated in the preceding binder mixture preparation step, this step does not require shear mixing to fibrillate the first binder. The mixing in this step is not particularly limited, but for example, it is mixed so as to impart a workload of less than 1 J per 100 g of the mixed material. For example, it could also be 0.9 J or less, 0.8 J or less, 0.7 J or less, 0.6 J or less, 0.5 J or less, or 0.4 J or less. Such workloads are examples of the second workloads disclosed herein. Specifically, the type of mixing apparatus is selected, and the rotation speed and time in the mixing apparatus are adjusted to achieve such workloads.

[0051] The mixing operation in this process is not particularly limited, but any mixing device capable of simple mixing, as described above, can be used as appropriate. For example, when using a mixer, the mixing operation is performed for a period of 10 to 1200 seconds, typically around 40 to 80 seconds.

[0052] By performing this process, an electrode mixture containing a fibrillated first binder, a material based on non-fibrillated particles such as the binder and / or conductive additive, and active material particles can be obtained. When this electrode mixture is subjected to sheet formation (or, for example, film formation) by calendering or press forming, the sheet formation process is facilitated or processing by a dry process is made possible due to the active material particle retention function exhibited by the first binder.

[0053] (Electrode sheet manufacturing process) This manufacturing method may further include a step (S30) of forming the electrode mixture into a sheet (film) to produce an electrode sheet 2. The thickness of the final electrode sheet 2 is not particularly limited, but for example, it is made to a thickness such that the final thickness of the positive electrode 14 or negative electrode 16 is approximately 10 μm to 500 μm. The thickness of the electrode sheet 2 is not particularly limited, but is approximately 100 μm to 2000 μm or 100 μm to 1000 μm. The sheeting process is not particularly limited, but for example, it can be done by calendering, in which the electrode mixture is supplied between rotating rollers without using a support and sheeted while being heated and pressed. Alternatively, it can be done by press processing, in which the electrode mixture is supplied to a suitable mold and heated and pressed.

[0054] The resulting electrode sheet 2 holds active material particles, as well as other binders and conductive additives, by a fibrillated first binder, and can constitute a self-supporting electrode sheet that can stand on its own without a support.

[0055] Furthermore, the process can also include a step of manufacturing a secondary battery 10 comprising a positive electrode 14, a negative electrode 16, and a separator 12 using such electrode sheet 2. This makes it possible to obtain a secondary battery 10 with a positive electrode 14 in which damage to the active material particles is suppressed and the impairment of electrode characteristics is suppressed or avoided. If the electrode sheet 2 is a negative electrode sheet, it is possible to obtain a secondary battery 10 with a negative electrode 16 in which the impairment of electrode characteristics is suppressed or avoided.

[0056] Furthermore, the binder mixture preparation step and the electrode composite mixture preparation step in the manufacturing method described above can be carried out as a dry process without using a solvent as a dispersion medium for the binder and electrode components such as active material particles. The dry process is advantageous in terms of improving the manufacturing efficiency of the electrode sheet 2. However, this manufacturing method does not necessarily eliminate the use of solvents entirely in the above steps. It does not preclude the use of small amounts of solvent as needed, as long as it does not impair the advantages of the dry process.

[0057] In the above description, a method for manufacturing an electrode sheet has been described. However, according to this specification, a method for manufacturing an electrode binder mixture is provided, comprising a step of preparing a binder mixture. A method for manufacturing an electrode composite mixture is also provided, comprising a step of preparing a binder mixture and a step of preparing an electrode composite mixture. Furthermore, a method for manufacturing an electrode is also provided, comprising a step of preparing a binder mixture, a step of preparing an electrode composite mixture, a step of manufacturing an electrode sheet using the electrode composite mixture, and a step of manufacturing a secondary battery in which the electrode sheet is at least one electrode. Various aspects of the steps and elements described in this manufacturing method apply to the various steps and elements in these manufacturing methods, etc.

[0058] This specification clearly includes the following components: [1] A method for manufacturing an electrode sheet, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, A manufacturing method comprising the step of preparing an electrode composite mixture containing the binder mixture and active material particles. [2] The manufacturing method according to [1], wherein the step of preparing the binder mixture is carried out at a temperature below or lower than the melting point of the material contained in the non-fibrillated particles. [3] The manufacturing method according to [1] or [2], wherein the active material particle comprises a core containing the active material and a coating layer covering at least a part of the core. [4] The coating layer is an electronically conductive coating layer, as described in [3]. [5] The manufacturing method according to any one of [1] to [4], wherein the non-fibrillated particles include components of the electrode sheet. [6] The non-fibrillated particles are manufactured according to any of [1] to [6], comprising a second binder. [7] The average particle size of the non-fibrillated particles (D 50The manufacturing method according to any one of [1] to [6], wherein the diameter is 7 μm or larger. [8] A manufacturing method according to any one of [1] to [7], wherein the step of preparing the binder mixture comprises mixing the first binder at a first work rate, and the step of preparing the electrode mixture comprises mixing at a second work rate lower than the first work rate. [9] A manufacturing method according to any one of [1] to [8], comprising performing the binder mixture preparation step and the electrode composite mixture preparation step by dry process.

[10] The manufacturing method according to any one of [1] to [9], further comprising the step of preparing an electrode sheet using the electrode composite mixture.

[11] A method for producing an electrode binder mixture, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated. A manufacturing method that includes the following features.

[12] A method for producing an electrode composite mixture, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, A step of preparing an electrode composite mixture containing the binder mixture and active material particles, A manufacturing method that includes the following features.

[13] A method for manufacturing a secondary battery, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, A step of preparing an electrode composite mixture containing the binder mixture and active material particles, A step of preparing an electrode sheet using the aforementioned electrode composite mixture, A step of manufacturing a secondary battery in which the electrode sheet is used as at least one electrode, A manufacturing method that includes the following features. [Examples]

[0059] The following describes embodiments that embody the disclosures of this specification, but these embodiments are for illustrative purposes only and are not limiting.

[0060] (Fabrication of the electrode sheet in the example) (1) Preparation of binder mixture As a material for the binder mixture, PTFE powder (average particle size (D) is used as a fibrillable binder. 50 :25μm)) and non-fibrillated particles, PVDF powder (average particle size (D 50 A PTFE powder with a particle size of 15 μm was used in a mass ratio of 5:1. These materials were placed in a kneader capable of shear mixing, and a mixing operation (shear mixing) was performed at a workload (4.6 J per 100 g of mixed material) sufficient to cause the PTFE powder in the mixed material to be approximately fibrillated, thereby preparing a binder mixture.

[0061] (2) Preparation of electrode composite mixture The active material is carbon-coated LFP (carbon coating layer thickness: 2 nm, carbon content (relative to LFP): 0.22 mass%, average particle size D 50 An electrode composite mixture was prepared using a 7.3 μm particle. Six parts by mass of the binder mixture prepared in (1) and 94 parts by mass of LFP were placed in a mixer, and the mixing operation was performed at a workload (0.4 J per 100 g) sufficient to simply mix these materials, thereby preparing the electrode composite mixture.

[0062] (3) Preparation of electrode sheets Using the electrode composite mixture of the example, the electrode sheet of the example was prepared by calendering.

[0063] (Preparation of the electrode composite mixture for the comparative example) As a comparative example, a comparative electrode mixture was prepared using the same PTFE powder, PVDF powder, and LFP as the fibrillated binder, non-fibrillated particles, and active material particles as in the above examples, by performing the following procedure.

[0064] (1) Preparation of electrode composite mixture One part by mass of PVDF powder, which had been pre-milled by jet pulverization, five parts by mass of PTFE powder, and 94 parts by mass of LFP were placed in the same kneader as in the example, and a mixing operation (shear mixing) was performed at 0.4 J per 100 g of the mixed material to prepare the electrode composite mixture of the comparative example.

[0065] (2) Preparation of electrode sheets An electrode sheet of the comparative example was prepared by calendering using the electrode mixture of the comparative example.

[0066] (evaluation) (1) Self-supporting nature of the electrode sheet The electrode sheets in both the examples and comparative examples maintained their intended three-dimensional shape.

[0067] (2) Evaluation of carbon coat damage in LFP using AES Only the LFPs from the electrode mixtures of the examples and comparative examples were extracted, and the LFP surfaces were analyzed by AES (Auger electron spectroscopy). As a result, in the LFPs of the electrode mixture of the examples, Auger electrons based on carbon atoms originating from the carbon coating were detected, and Auger spectroscopy based on Mn and Fe originating from nuclear particles was hardly observed. In contrast, in the LFPs of the electrode mixture of the comparative examples, Auger electrons based on carbon atoms could not be detected, but Auger electrons based on Mn and Fe were detected.

[0068] These results indicate that in the electrode mixture of the examples, the carbon coating of the LFP was maintained on the LFP without damage. In contrast, in shear mixing that causes fibrillation of PTFE, the carbon coating of the LFP was almost completely removed.

[0069] (3) Evaluation of powder resistivity Density of electrode composite mixtures in the examples and comparative examples: 2.0 g / cm³ 3Test specimens were prepared by pressing them, and the electrical resistance of these specimens was measured. The results are shown in Figure 3. As shown in Figure 3, the electrode mixture of the example had a resistance of 15.1 Ω·cm, while the electrode mixture of the comparative example had a resistance of 68.8 Ω·cm. As a control example, an electrode mixture composition prepared by mixing 1 part by mass of PVDF powder, 5 parts by mass of PTFE powder, and 94 parts by mass of LFP using the mixer used in the mixing operation for preparing the electrode mixture of the example, with a workload (0.4 J per 100 g of mixed material) sufficient to simply mix them, was measured using the same procedure as above, and the resistance value was 14.7 Ω·cm.

[0070] The resistance value of the electrode mixture in the example was similar to that of the symmetrical example, indicating that the carbon coating on the LFP was functioning properly in the example's electrode mixture. In contrast, the resistance value of the electrode mixture in the comparative example increased significantly, indicating that the carbon coating on the LFP had peeled off and was not performing its intended function.

[0071] From the above, it was found that the fibrillation binder can be sufficiently fibrillated by shear mixing in the presence of non-active and non-fibrillated particles, and that a dry, self-supporting electrode can be fabricated. From this, it was found that fibrillating the fibrillation binder in the absence of active material particles is useful for suppressing or avoiding damage to the active material particles and allowing the active material particles to perform their function.

[0072] The technical elements described herein or in the drawings demonstrate technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated herein or in the drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness in itself. [Explanation of Symbols]

[0073] 2 electrode sheets, 10 electrodes, 12 separators, 14 positive electrode, 16 negative electrode

Claims

1. A method for manufacturing an electrode sheet, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, A manufacturing method comprising the step of preparing an electrode composite mixture containing the binder mixture and active material particles.

2. The manufacturing method according to claim 1, wherein the step of preparing the binder mixture is carried out at a temperature below or lower than the melting point of the material contained in the non-fibrillated particles.

3. The manufacturing method according to claim 1, wherein the active material particle comprises a core containing the active material and a coating layer covering at least a portion of the core.

4. The manufacturing method according to claim 3, wherein the coating layer has electronic conductivity.

5. The manufacturing method according to claim 1, wherein the non-fibrillated particles include components of the electrode sheet.

6. The method for producing the non-fibrillated particles according to claim 1, wherein the non-fibrillated particles include a second binder.

7. The average particle size (D) of the non-fibrillated particles ５０ The manufacturing method according to claim 1, wherein the diameter is 7 μm or more.

8. The manufacturing method according to claim 1, wherein the step of preparing the binder mixture includes mixing at a first work rate, and the step of preparing the electrode mixture includes mixing at a second work rate lower than the first work rate.

9. The manufacturing method according to claim 1, comprising performing the binder mixture preparation step and the electrode composite mixture preparation step by dry process.

10. Furthermore, the process involves manufacturing an electrode sheet using the electrode composite mixture, A manufacturing method according to any one of claims 1 to 9, comprising:

11. A method for manufacturing an electrode binder mixture, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated. A manufacturing method that includes the following features.

12. A method for producing an electrode composite mixture, A step of preparing a binder mixture containing the fibrillated first binder by mixing a fibrillable first binder with non-fibrillable particles which are inactive material particles that cannot be fibrillated, A step of preparing the electrode composite mixture containing the binder mixture and active material particles, A manufacturing method that includes the following features.

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