Method for manufacturing secondary battery and method for manufacturing all-solid-state battery

Abstract

To form a uniformly dispersed structure electrode layer of active material particles for a secondary battery, carbon nanotubes (CNT) and a binder.SOLUTION: The active material particles and the CNTs are independently dispersed in a solvent. Atomized particles are formed by each independent spray means or the like, and collide with and adhere to a heated object to form an electrode mixture layer in which CNTs are uniformly brought into contact with active material particles or the like. To keep the stability with time of an electrode layer by sticking binder sprayed particles to at least a part of active material particles and a conductive assistant of the electrode layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery and a method for manufacturing an all-solid-state battery. [Background technology]

[0002] With the increase in electric vehicles (EVs), the production volume of lithium-ion batteries (LIBs) is rapidly increasing. Meanwhile, from the perspectives of safety and battery performance such as energy density, all-solid-state batteries that use solid electrolytes rather than solvent-type electrolytes are attracting attention. In addition, secondary batteries that use safe aqueous electrolytes, such as sodium batteries, potassium batteries, and zinc batteries, are being manufactured and developed, mainly for stationary use.

[0003] The secondary battery of the present invention includes an all-solid-state battery and a semi-solid-state battery, which are likely to be safe and have a high energy density. The solid electrolyte of the all-solid-state battery of the present invention may be of any type, such as a polymer, oxide, or sulfide. Furthermore, the present invention does not limit the type of secondary battery. The electrode active material for a lithium-ion secondary battery (LIB) can be lithium cobalt oxide (LCO), LMO, NCA, LNO, or ternary NCM or NMC containing lithium ions, or iron phosphate (LFP) for the positive electrode. The negative electrode can be selected from graphite, carbon, or silicon, or can be a lithium metal plate. Sodium batteries often use prussianin blue for the positive electrode and hard carbon for the negative electrode. Zinc secondary batteries often use nickel oxide, manganese oxide, or the like for the positive electrode, and the negative electrode can be a zinc metal plate. The present invention does not limit the type of battery or the materials for the positive and negative electrodes.

[0004] Therefore, the electrode layer forming material can be selected from powder, fiber, and liquid, or they may be formed into an electrode by a single means or a combination of means. Electrodes can be formed using the binder alone or as a slurry containing the binder and a solvent. The binder can be a fine particle, and a fibrous material containing fibrillated fibers can form a network that reinforces the electrode structure in addition to bonding the active material and CNTs. Binder fibers can be combined with carbon fine particles, graphene, single-walled carbon nanotubes, etc. to form a conductive binder, forming a conductive network. To reduce adhesion and resistance, a conductive binder structure can be used to increase the adhesion between the interface, for example, between the current collector and the electrode, thereby reducing resistance. Electrode active material particles, electrolyte particles, and conductive additives such as carbon nanotubes (CNTs) can be dispersed in a solvent or dispersant that does not dissolve the binder, including fibrillated binder fibers, and applied to the target object as a slurry or colloid.

[0005] Nanoparticles, nanofibers, and CNTs, especially single-phase carbon nanotubes (SWCNTs) with diameters of around 2 nanometers, tend to aggregate when made into high-viscosity positive electrode liquids, especially composite slurries containing fluorine-based binder solutions, preventing the SWCNTs from realizing their full potential. In particular, PVDF and PTFE are used as binders in electrode slurries for forming the positive electrode of secondary batteries, and NMP (normal methylpyrrolidone) or, in rare cases, DMF are used as solvents that can dissolve these binders. Generally, secondary battery positive electrodes are handled using high-viscosity composite slurries consisting of active material particles, binders, conductive additives, and solvents, with a non-volatile content of approximately 55 to 75 wt.%. In these cases, it has been difficult to maintain a uniform dispersion of SWCNTs, which have diameters of approximately 2 nanometers and lengths of tens of micrometers or more. In particular, uniform dispersion of SWCNTs in positive electrode slurries, which use positive electrode active material particles, conductive additives such as CNTs, and fluorine-based binder solutions such as PVDF and PTFE, has been a challenge.

[0006] One of the major challenges facing electrodes is that the potential of active materials, electrolytes, conductive additives, etc. has not been fully utilized. One of the reasons for this is the problem of nanomaterials agglomerating, making it difficult to disperse uniformly in composites. The finer the nanoparticles or fibers, the larger the surface area, but they are also more prone to agglomeration. This is particularly noticeable with SWCNTs, which tend to change their dispersion state when mixed with composite slurries, even if they are well dispersed in a dispersion of 1 wt.% or less.

[0007] When the binder solution covers all areas except the desired adhesion between active material particles, conductive additives, and electrolyte particles, it forms an insulating coating. It is best to apply a small amount only to the desired areas, except for the adhesive strength within the electrode layer. Generally, when a binder solution or emulsion is mixed with active material, electrolyte particles, and conductive additives, the entire active material surface is coated. Therefore, the binder content is preferably 3 wt% or less of the total solids, and more preferably 2% or less. If a larger binder content is desired, this can be achieved by reducing the solids content of the solution or emulsion to 0 or as low as possible and increasing the binder microparticles or fibers, as proposed in this invention. For example, a desired amount of fibrillated binder fibers can be added so that they partially contact or entangle the active material. Furthermore, in this invention, to form a good electrode structure, the binder or polymer electrolyte can be formed into a fibrous network structure, and the active material particles, conductive additives, and, if necessary, solid electrolyte can be densely applied within the network in the desired dispersion state.

[0008] It is particularly important to reduce resistance and improve adhesion at the interface between the current collector and electrode layer. To achieve this, binders and conductive additives such as CNTs are collided with each other by impact, along with active material particles as needed, to form a conductive binder layer, resulting in a dense structure and reduced electrical resistance. Therefore, in the present invention, a thin film layer is formed at the interface by the above method, and a slurry or composite slurry mainly consisting of an active material can be applied at high speed by die coating, roll coating, etc. When laminating multiple times by die coating, etc., it is also possible to provide a desired dispersion of CNTs and binders by applying and laminating particles while coarsely dispersing CNTs or binder spray.

[0009] In the present invention, the spray means or particle generating means can be spaced apart from the heating means, which solves the problem of deformation of the coating tip of a die coater and the problem of promoting solvent evaporation while coating. When using a die coater at a distance, the inventors proposed an air-assisted method in JP 2021-034227, in which compressed gas is directed along the liquid film from both sides of the die head to support the coating. This method allows CNT spray particles, binder spray particles, etc. to come into contact with or collide with the liquid film before or after the liquid film is applied to the target object, allowing the coating to be achieved in the desired dispersed state. This also solves the following problems. 1. Create a process that maximizes the potential of electrode materials. 2. By making the slurry of particularly fine active material particles or the dispersion of conductive additives such as SWCNT into a slurry or dispersion of conductive additives with little or no aggregation, an electrode layer can be formed while maintaining the desired dispersion state. 3. At least a portion of the active material particles and SWCNTs in the formed electrode layer are fixed or reinforced with a binder to provide a structure that is stable over time.

[0010] Cited Document 1 discloses a method for manufacturing an electrode for an all-solid-state battery, which comprises mixing electrode active material particles, a solid electrolyte, and a first binder with a first solvent to prepare a primary slurry, drying the primary slurry to prepare a mixed powder, mixing the mixed powder with a conductive material and a second binder with a second solvent to prepare a secondary slurry, and coating the secondary slurry on a current collector. It states that when the electrode active material, solid electrolyte, conductive material, and binder are mixed simultaneously, electrode active material isolated by the conductive material (dead active material) is generated. Therefore, different types of binders are used at each stage, and conductive material is added only to the secondary slurry to prevent dead spots and generate many triple points of contact. The first binder is PVDF or similar, the first solvent is a non-aqueous solvent that dissolves fluorine-based binders such as NMP, and the second solvent is an aqueous solvent used for the second binder, SBR, etc. The first binder is designed not to dissolve in the second solvent.

[0011] Reference 2 proposes a method of forming an electrode layer by forming a binder layer consisting of a binder and a solvent on aluminum foil, drying it, and then forming an electrode layer on top of that using a binderless slurry consisting of active material particles, a conductive additive, and a solvent, and drying it.

[0012] In Reference 1, the first binder solution does not come into contact with the conductive material, so the risk of dead cells due to the conductive material is reduced. However, the composite powder consisting of the active material, electrolyte, and binder is designed to not dissolve in the second solvent, so it is difficult to make the conductive material penetrate into the powder and contact it, thereby increasing the triple point further.

[0013] In Reference 2, the binder layer is located at the interface between the aluminum foil and the electrode, so the issue of adhesion at the interface can be overcome. However, the issue of interfacial electrical resistance remains depending on the mixing ratio of the conductive material. Also, there is no disclosure of measures to ensure the stability of strength over time when the binderless electrode layer expands and contracts due to charging and discharging for a typical LIB positive electrode layer with a film thickness of around 100 μm. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Special Table 2022-512433 [Patent Document 2] Patent Publication No. 2012-17440 Summary of the Invention [Problem to be solved by the invention]

[0015] To obtain the best results using the same electrode material, the following problems must be solved: 1. The process will maximize the potential of electrode materials. 2. By converting particularly fine active material particle slurry or conductive additive dispersion liquid such as SWCNT into a slurry or conductive additive dispersion liquid with no or little aggregation, an electrode layer is formed while maintaining the desired dispersion state. 3. At least a portion of the active material particles and SWCNTs in the formed electrode layer are fixed or reinforced with a binder to provide a structure that is stable over time. [Means for solving the problem]

[0016] In order to solve the above problems, the present invention provides the following.

[0017] The present invention is a method for manufacturing a secondary battery in which an electrode layer is formed on a current collector from electrode active material particles, a conductive additive, and a binder, and the method includes a step of using the current collector or the electrode layer as a target object, a step of preparing an active material slurry from active material particles and at least a solvent, a step of preparing a conductive additive dispersion from at least carbon nanotubes and at least a solvent, a step of preparing a liquid binder selected from binder fine particles, a fibrous binder, a binder solution, an emulsion, and a solvent, and a step of spraying the slurry, dispersion, and liquid binder by independent spray means or The present invention provides a method for manufacturing a secondary battery, comprising the steps of: forming particles using a particle generating means to produce a jet stream or a pulsed jet stream; colliding the jet stream or pulsed jet stream of each of the slurry, dispersion, and liquid binder with the heated object to compress and promote evaporation of the solvent in the spread thin film; and laminating the jet stream or pulsed jet stream of each of the slurry, dispersion, and liquid binder multiple times in any order to form an electrode layer in which the binder adheres to at least part of the active material particles and at least part of the conductive additive in at least part of the electrode layer.

[0018] The present invention provides a method for producing a secondary battery, wherein the carbon nanotubes are single-walled carbon nanotubes, and the solid content of the binder is 3% or less by weight of the total solid content of the electrode layer.

[0019] The present invention provides a method for manufacturing a secondary battery, comprising the steps of: mixing an active material slurry comprising the active material particles and a solvent with a dispersion liquid comprising at least carbon nanotubes and a solvent to form a composite slurry; spraying the composite slurry into particles using a particle generating means to form a jet stream or a pulsed jet stream; spraying the liquid binder into particles using a particle generating means to form a jet stream or a pulsed jet stream; colliding the jet streams or pulsed jet streams of the composite slurry and the liquid binder with the heated object to promote solvent evaporation; and stacking the jet streams or pulsed jet streams multiple times in any order to form an electrode layer in which the binder adheres to the active material particles of at least some of the electrode layer and at least some of the conductive additive.

[0020] The present invention provides a method for producing a secondary battery, wherein the active material particle slurry is a slurry comprising active material particles, electrolyte particles, and at least a solvent, or a slurry comprising composite particles in which active material particles are at least partially coated with a solid electrolyte, and a solvent.

[0021] The present invention provides a method for manufacturing a secondary battery, characterized in that the active material slurry comprising active material particles and a solvent is a slurry comprising active material particles, solid electrolyte particles, and at least a solvent, or a slurry comprising composite particles in which at least a portion of the active material particles is coated with a solid electrolyte, and a solvent, and the method includes the steps of: mixing the active material slurry with a dispersion comprising at least carbon nanotubes and a solvent to form a composite slurry; spraying the composite slurry or forming a jet stream or a pulsed jet stream; spraying the liquid binder with a spray or particle generating means to form a jet stream or a pulsed jet stream; colliding the composite slurry jet stream or pulsed jet stream, the liquid binder jet stream or pulsed jet stream, with the heated object to promote solvent evaporation; and laminating the composite slurry and liquid binder jet stream or pulsed jet stream multiple times, in any order, to form an electrode layer in which the binder adheres to at least a portion of the active material particles, electrolyte particles, and conductive additive of at least a portion of the electrode layer. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic cross-sectional view showing how an active material particle slurry and a conductive additive dispersion are alternately layered using particle generating means such as a spray. [Figure 2] FIG. 2 is a schematic cross-sectional view showing how an active material particle slurry, a conductive additive dispersion, and a liquid binder are alternately layered by spray means or the like. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following describes preferred embodiments of the present invention with reference to the drawings. Note that the following embodiments are merely examples for facilitating understanding of the invention, and do not exclude additions, substitutions, modifications, and the like that can be implemented by those skilled in the art within the scope of the technical concept of the present invention.

[0024] The drawings show diagrammatically preferred embodiments of the invention.

[0025] 1, an object 1 is moved while being heated by a heating means (not shown). The heating means may be a heating table or a heating roll. Active material slurry is sprayed onto the target 1 from the first spray means 4, and spray particles 2' collide with the target 1 as a jet stream 8 or a pulsed jet stream, crushing the solvent into a thin film and promoting evaporation, thereby adhering the active material particles 2 to the target. Using a means that moves simultaneously with the target while adsorbing and heating the target is effective because it prevents a drop in the target's temperature due to the heat of vaporization caused by solvent evaporation. A dispersion of a conductive additive such as SWCNTs is sprayed onto the active material particles 2 from the second spray means 5, and spray particles 3' collide with the target as a jet stream 9 or a pulsed jet stream, crushing the spray particles into a thin film and promoting solvent evaporation, allowing the conductive additive 3 such as SWCNTs to contact or entangle with the active material particles without agglomeration.

[0026] The spray can be made into fine particles by a particle generating means, which are then moved and ejected using a carrier gas or the like, or ejected in a pulsed manner. The particle generating means can be a spray or two-fluid spray, and the spray particles can be moved together using a carrier gas such as compressed gas, or the spray particles can be collided with a rotating body from close range to generate fine particles with an average particle diameter of, for example, several μm, which can then be moved using compressed gas. A particle generating device using a bubbler is also acceptable, and any generating means is acceptable.

[0027] By adding binder fine particles or a binder solution or emulsion with a low solid content, for example, 1 wt. % or less, to the active material particle slurry, an electrode layer can be formed without affecting the dispersion of the active material particles.

[0028] 2, first spray means 14, second spray means 15, and third spray means 17 spray jets 18, 19, and 20 or pulsed jets consisting of active material slurry spray particles 12', conductive additive spray particles 13', and liquid binder spray particles 16', respectively, onto the heated object 11 in sequence or random order, promoting solvent evaporation and bringing the conductive additive such as SWCNTs into contact with or entangled with the active material particles in a desired dispersed state. The liquid binder spray particles are then deposited on the object, active material particles, and conductive additive at desired locations to form an electrode layer.

[0029] In this invention, the target material is not limited to aluminum or copper foil, but can also be a material with a network formed from polymer fibers or carbon fibers, since the binder content is kept to an extremely small amount of 0% or less than 1 wt.% of the electrode solids. The network substrate can be a nonwoven fabric with a low basis weight. Alternatively, an electrode can be formed by applying an electrode material to a metal foil current collector using a different material and a different method, such as electrospinning, to form a network while fiberizing the liquid material. [Industrial Applicability]

[0030] This invention can be applied not only to secondary batteries but also to supercapacitors. For insulating layers that also serve as heat dissipation layers in the field of semiconductors, which are highly integrated and generate a lot of heat, a thermally conductive dispersion liquid consisting of, for example, diamond nanoparticles and a solvent can be sprayed onto a heated object using a particle generating means such as a spray, and a dispersion liquid consisting of a nano-inorganic binder or a nano-organic binder / nano-inorganic binder hybrid binder and a solvent can be sprayed as a jet or pulsed jet and allowed to collide with the heated object, forming an insulating thin film layer with densely arranged diamond nanoparticles. [Explanation of symbols]

[0031] 1, 11 Object 2, 12 Active material particles 2', 12' spray particles (active material particles) 3, 13 Conductive additive (CNT) 3', 13' Spray particles (conductive additive) 4, 14 First spray means 5, 15 Second spray means 8 Spout flow (active material) 9. Jet flow (conductive additive) 16 Binder 16' Spray particles (binder) 17 Third spray means 18 Jet stream 19 Ejected grains 20 ejected grains

Claims

1. A method for manufacturing a secondary battery in which an electrode layer is formed on a current collector from electrode active material particles, a conductive additive, and a binder, the method comprising the steps of: using the current collector or the electrode layer as a target; preparing an active material slurry from active material particles and at least a solvent; preparing a conductive additive dispersion from at least carbon nanotubes and at least a solvent; preparing a liquid binder selected from binder fine particles, a fibrous binder, a binder solution, an emulsion, and a solvent; and spraying the slurry, dispersion, and liquid binder by separate spray means or a spraying method. a step of forming particles by particle generating means to form a jet stream or a pulsed jet stream of the slurry, dispersion, and liquid binder; a step of causing the jet stream or pulsed jet stream of each of the slurry, dispersion, and liquid binder to collide with the heated object and pressurize it to promote evaporation of the solvent in the spread thin film; and a step of laminating the jet stream or pulsed jet stream of each of the slurry, dispersion, and liquid binder multiple times in any order to form an electrode layer in which the binder adheres to at least a portion of the active material particles and the conductive additive of at least a portion of the electrode layer.

2. 2. The method for manufacturing a secondary battery according to claim 1, wherein the carbon nanotubes are single-walled carbon nanotubes, and the solid content of the binder is 3% or less by weight of the total solid content of the electrode layer.

3. 2. The method for manufacturing a secondary battery according to claim 1, comprising the steps of: mixing an active material slurry comprising the active material particles and a solvent with a dispersion liquid comprising at least carbon nanotubes and a solvent to form a composite slurry; forming particles from the composite slurry using a spray or particle generating means to form a jet stream or a pulsed jet stream; forming particles from the liquid binder using a spray or particle generating means to form a jet stream or a pulsed jet stream; colliding the jet streams or pulsed jet streams of the composite slurry and the liquid binder with the heated object to promote solvent evaporation; and stacking the jet streams or pulsed jet streams in order or in any order a plurality of times to form an electrode layer in which the binder adheres to the active material particles of at least some of the electrode layer and at least some of the conductive additive.

4. 2. The method for producing a secondary battery according to claim 1, wherein the active material particle slurry is a slurry consisting of active material particles, electrolyte particles, and at least a solvent, or a slurry consisting of composite particles in which active material particles are at least partially coated with a solid electrolyte, and a solvent.

5. 2. The method for manufacturing a secondary battery according to claim 1, wherein the active material slurry comprising active material particles and a solvent is a slurry comprising active material particles, solid electrolyte particles, and at least a solvent, or a slurry comprising composite particles in which at least a portion of the active material particles is coated with a solid electrolyte, and a solvent, and the method comprises the steps of: mixing the active material slurry and a dispersion liquid comprising at least carbon nanotubes and a solvent to form a composite slurry; spraying or particle generating means to form particles of the composite slurry into a jet stream or a pulsed jet stream; spraying or particle generating means to form particles of the liquid binder into a jet stream or a pulsed jet stream; colliding the composite slurry jet stream or pulsed jet stream and the liquid binder jet stream or pulsed jet stream with the heated object to promote solvent evaporation; and laminating the jet stream or pulsed jet stream of the composite slurry and the liquid binder multiple times in any order or in any order to form an electrode layer in which the binder adheres to at least a portion of the active material particles, electrolyte particles, and conductive additive of at least a portion of the electrode layer.

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