Method for manufacturing secondary batteries or all-solid-state batteries

Abstract

This technology prevents aggregation of active material particles for secondary batteries and carbon nanotubes (CNTs), allowing for the formation of electrode layers with a small amount of binder. [Solution] The CNTs are dispersed in a solvent that does not aggregate. The CNT dispersion is turned into liquid particles using an independent spraying device, etc., and is brought into contact with active material particles on a heated object to evaporate the solvent and form an electrode thin film layer in contact with the CNTs. Binder spray particles are then scattered and attached on top of this to form a thin film electrode layer in which at least some of the active material particles, conductive additives, and binder are bound together.

Description

Technical Field

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

Background Art

[0002] The secondary battery of the present invention includes all-solid-state batteries and semi-solid-state batteries having safety, high energy density, charge-discharge cycle number, and high durability. With the increase in electric vehicles (EVs), the production volume of lithium-ion batteries (LIBs) has been increasing rapidly. On the other hand, from the aspects of safety and battery performance such as energy density, all-solid-state batteries using solid electrolytes such as sulfide-based and oxide-based that do not use solvent-type electrolytes have been in the spotlight. In addition, the production and development of sodium batteries, potassium batteries, zinc batteries, etc. using safe aqueous electrolytes are being carried out.

[0003] Ion conduction in the secondary battery in the present invention can be selected from lithium, sodium, potassium, zinc, and others, and does not limit the type of battery. Materials for secondary battery electrodes and electrolyte formation can be selected from powders, fibers, and liquid materials. The active material particles of the positive electrode can be selected from ternary systems, iron phosphate, Prussian blue, manganese oxide, etc. The negative electrode active material can also be selected from graphite, silicon, etc., and the negative electrode can also be a lithium plate or a zinc plate. The active material particles and conductive aids such as CNTs need to form the electrode in a desired dispersed state. Those particles and fibers may be made into independent dispersions or slurries and the electrode may be formed by a plurality of means, or may be made into a dispersion or slurry composed of a composite material and the electrode may be formed.

[0004] The binder may be fine particles or fibers. For example, by fibrillating PTFE, the active material particles and composite materials with carbonanotubes (CNTs) can be fixedly bonded by pressing or heat pressing. Since the particles and fibers of the active material particles, conductive additives such as CNTs, and binders have poor affinity for solvents such as water, it is desirable to improve their water dispersibility by plasma treatment so that they can be dispersed in water or other solvents. Polymer-based dispersants that remain on the surface of the active material particles, CNTs, and other particles and fibers that form the electrode layer and hinder the conduction of ions and electrons should be removed as much as possible. Therefore, the dispersibility of particles should be improved in a way that does not affect the degradation of battery performance.

[0005] Even if the weight ratio of particles is high in the dispersion or slurry of plasma-treated particles or fibers such as CNTs and a solvent such as water, and precipitation occurs, this problem can be solved by employing a method, for example, Japanese Patent Application Publication No. 2021-194581, invented by the present inventor, to rapidly move the slurry between, for example, two containers. This method stabilizes and maintains the viscosity of the slurry by applying a constant shear force, thus enabling a constant discharge rate per unit time. Therefore, the fibers can easily and accurately form networks to reinforce the electrode structure. The fiber binder can be composited with graphene or single-walled carbon nanotubes to create a conductive binder. As a result, the adhesion between interfaces, such as between the current collector and the electrode, or between the electrode and electrolyte particles in the case of all-solid-state batteries, can be improved and resistance can be reduced.

[0006] By dispersing CNTs, particularly SWCNTs, with a dispersant or solvent, a dispersion with a solid weight percentage of 1% or less of SWCNTs can be formed that does not aggregate, and this dispersion can then be applied to the target object. In addition, cellulose nanofibers can be effectively used in addition to binders such as SBR at the negative electrode.

[0007] Nanoparticles, nanofibers, and carbon nanotubes (CNTs), especially single-walled carbon nanotubes (SWCNTs) with a diameter of around 2 nanometers, tended to aggregate when they contained high-viscosity cathode liquids or binder solutions, thus preventing them from realizing their full potential. More specifically, PVDF and PTFE are used as binders for electrode slurries, particularly for forming the positive electrode of secondary batteries, and NMP (n-methylpyrrolidone) and the like are used as solvents that can dissolve these binders.

[0008] Generally, the positive electrode of a secondary battery uses a high-viscosity composite slurry with a weight-to-solids ratio of about 55 to 75%, consisting of active material particles, a binder, a conductive additive, and a solvent. In this case, it was difficult to achieve a uniform dispersion state of single-walled carbon nanotubes (WWNTs), which have a diameter of about 2 nanometers and a length of several tens of micrometers or more. Furthermore, using high-boiling-point solvents such as NMP resulted in long drying times even after coating. Therefore, achieving uniform dispersion of WWNTs in high-viscosity liquids and binder solutions presented many challenges.

[0009] A major challenge with secondary batteries has been the inability to fully utilize the potential of active material particles, electrolyte particles, and conductive additives. One example is the aggregation of nanomaterials. While the surface area increases with finer particles, the finer the particles and fibers, the more prone they are to aggregation. This was particularly noticeable with SWCNTs; even when well dispersed with a dispersant to create a dispersion of less than 1 wt.%, they tended to aggregate when mixed with high-viscosity, high-solids slurry. On the other hand, slurries containing solid particles of several micrometers or larger with high specific gravity tended to have high viscosity because they would precipitate severely unless the viscosity was increased.

[0010] Furthermore, since the binder acts as an insulator except for adhesion between active material particles, conductive additives, and electrolyte particles at desired locations, it is best to use only a small amount. For example, it should be 3% by weight or less, preferably 2% or less, relative to the total solid content of the electrode layer. If a larger amount of binder is desired, this invention recommends reducing the ratio of the solution to zero or less and increasing the amount of fibrous material, such as fibrillated fibrous binder, from the viewpoint of insulation. This allows for partial contact or adhesion to the active material. Moreover, in this invention, in order to form a good electrode structure, it is desirable to form the binder and polymer electrolyte into a fibrous network structure in which active material particles, conductive additives, and, if necessary, electrolytes are densely arranged in the desired dispersion state within the network.

[0011] Furthermore, it is particularly important to improve conductivity and adhesion at the interface between the current collector and the electrode layer. This invention allows the binder and conductive additives such as CNTs to be efficiently bonded to each liquid particle by impact, thereby creating a conductive binder layer. The interface needs to be dense to reduce electrical resistance, and this invention makes that possible. Therefore, in this invention, liquid CNTs and binders can be dispersed well and applied as particles, such as a spray, to the interface of a heated current collector, impacting it and instantly evaporating the solvent to create a good interface. As a result, the main electrode layer can be coated at high speed using die coating or roll coating and then laminated.

[0012] In this invention, the distance between the spray or particle generator and the heating means can be increased, thus solving the problem of heat being transferred to the particle generator head.

[0013] Reference 1 discloses a method for electroforming an all-solid-state battery by mixing electrode active material particles, a solid electrolyte, and a first binder with a first solvent to produce a primary slurry, drying the primary slurry to produce a mixed powder, and mixing the mixed powder with a conductive material and a second binder with a second solvent to produce a secondary slurry, which is then coated onto a current collector. It states that when 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 create many triple contact points. The first binder is PVDF, 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, such as SBR. The first binder is not to be dissolved in the second solvent.

[0014] Reference 2 proposes a method for forming an electrode layer by creating a binder layer consisting of a binder and a solvent on aluminum foil, drying it, and then creating an electrode layer on top of that using a binder-less slurry consisting of active material particles, a conductive additive, and a solvent, and drying it.

[0015] In reference 1, the risk of dead material due to the conductive material is reduced because the first binder solution and the conductive material do not come into contact. However, since the composite powder consisting of the active material, electrolyte, and binder is intended not to dissolve in the second solvent, it is not possible to allow the conductive material to penetrate into the powder and come into contact with it, thereby increasing the number of triple points.

[0016] 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 dry film thickness of typical LIB electrodes is around 100 μm, and without bonding or reinforcing networks such as binders or fibers, the electrode layer structure changes over time due to repeated charging and discharging. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] Special Publication 2022-512483 [Patent Document 2] Japanese Patent Publication No. 2012-174401 [Overview of the project] [Problems that the invention aims to solve]

[0018] As mentioned above, in order to obtain the best effect using the same electrode material, the following problems must be solved. 1. Maximize the potential of electrode materials. 2. Form an electrode layer while maintaining the dispersion state by making the slurry of particularly fine active material particles or conductive additive dispersions such as SWCNTs into a slurry or conductive additive dispersion with little or no aggregation. 3. At least a part of the active material particles, SWCNT, etc. in the formed electrode layer is fixed or reinforced with a binder to be stabilized over time.

Means for Solving the Problems

[0019] To solve the above problems, the present invention has the following content.

[0020] The present invention relates to a method for manufacturing a secondary battery or an all-solid-state battery, comprising forming a composite electrode layer by applying a dispersion or slurry made of an electrode active material particle, an electrolyte particle, a conductive aid, and a binder selected from a current collector, an electrode layer, an electrolyte layer, and a separator with a solvent, and forming an active material dispersion or slurry with the active material particles and at least the solvent, and preparing a conductive aid dispersion with a conductive aid selected from carbon nanotubes, carbon nanofibers, graphene, and carbon particles and at least the solvent, and preparing a liquid binder selected from binder microparticles, fibrous binders, binder solutions, emulsions, and solvents, and converting the active material dispersion or slurry, the conductive aid dispersion, and the liquid binder into liquid particles with an independent spray or particle generator to form a jet flow or a pulsed jet flow, and combining the respective jet flows or pulsed jet flows and colliding them with an object in the air or to a heated object to apply or collide them with the heated object in order or in any order to form a thin film layer and evaporate the solvent to stack and apply at least the same dispersion or slurry in multiple layers, thereby forming an electrode layer.

[0021] The present invention provides a method for manufacturing a secondary battery or an all-solid-state battery, characterized in that an electrode layer is formed by the following steps: forming a dispersion or slurry composed of the active material particles and at least a solvent, and a dispersion composed of carbon nanotubes and a solvent into a composite material dispersion or slurry; converting the composite material dispersion or slurry into liquid particles by a spray or particle generator to form a jet flow or a pulsed jet flow; converting the liquid binder into liquid particles by a spray or particle generator to form a jet flow or a pulsed jet flow; merging the respective jet flows or pulsed jet flows between the air or a heated object and colliding them with the object to apply or collide them with the heated object in order or in any order to form a thin film layer, evaporating the solvent, and laminating and applying at least the same dispersion or slurry in multiple layers.

[0022] The present invention provides a method for manufacturing a secondary battery or an all-solid-state battery, characterized in that the formation of the secondary battery electrode layer is the formation of the all-solid-state battery electrode layer, and includes the step of adding an electrolyte particle dispersion or an electrolyte particle slurry and converting it into liquid particles by a spray or particle generator to form a jet flow or a pulsed jet flow. The respective jet flows or pulsed jet flows are merged between the air or a heated object and collided with the object to apply or collided with the heated object in order or in any order to form a thin film layer, evaporating the solvent, and laminating and applying at least the same dispersion or slurry in multiple layers to form an electrode layer.

[0023] The present invention provides a method for manufacturing a secondary battery or an all-solid-state battery, characterized in that the conductive auxiliary agent is single-walled carbon nanotubes, and the solid content of the binder is 3% or less of the total solid content weight of the electrode layer.

[0024] The present invention provides a method for manufacturing a secondary battery or an all-solid-state battery, comprising forming an electrode layer on a current collector by selecting electrode active material particles, a solid electrolyte, a conductive additive, and a binder, comprising the steps of: preparing a binder-free slurry by selecting active material particles or composite particles in which at least a portion of the active material particles is coated with a solid electrolyte, and solid electrolyte particles, and at least a solvent; preparing a binder-free conductive additive dispersion by selecting at least carbon nanotubes and at least a solvent; and selecting from binder fine particles, fibrous binder, binder solution, emulsion, and solvent. The present invention provides a method for manufacturing a secondary battery or an all-solid-state battery, characterized by the steps of: creating a liquid binder; adding compressed gas to the slurry, dispersion, and liquid binder using an independent spray or particle generator to turn them into liquid particles and form a jet stream or pulsed jet stream; mixing and adhering the jet stream or pulsed jet stream to a heated object before it reaches the object, or layering the respective jet streams onto the heated object sequentially or in any order; and forming an electrode layer in which at least a portion of the composite electrode layer is fixed with the binder. [Brief explanation of the drawing]

[0025] [Figure 1] This is a schematic diagram showing the sequential layering of an active material particle slurry, a conductive additive dispersion, and a liquid binder using a particle generating device such as a spray. [Figure 2] This is a schematic diagram showing the sequential layering of active material particle slurry, conductive additive dispersion, and liquid binder solvent onto a thin film composite layer, using a particle generating device such as a spray head. [Figure 3] This is a schematic diagram showing the process of impact mixing and coating of an active material particle slurry, a conductive additive dispersion, and a liquid binder using a particle generating device such as a sprayer (hereinafter referred to as a spray head). [Modes for carrying out the invention]

[0026] The secondary battery of this invention will be described in detail below.

[0027] Prior document 2 proposes a method for manufacturing lithium-ion secondary batteries using an organic solvent-based composite paste electrode plate, which allows for lower viscosity even with the same solid content in the binderless case, enables efficient production, reduces the amount of organic solvent used, and increases the adhesion strength between the current collector and the electrode active material layer. The present invention can apply these advantages.

[0028] Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the following embodiments are merely examples to facilitate understanding of the invention and do not preclude additions, substitutions, modifications, etc., that can be implemented by those skilled in the art without departing from the technical spirit of the present invention.

[0029] The drawings schematically illustrate preferred embodiments of the present invention.

[0030] In Figure 1, representative spray heads 1, 2, and 3 of the particle generator deliver conductive additive dispersions, active material particle dispersions or slurries, or liquid polymers as liquid particle jets 101, 102, and 103 or pulsed jets, which collide with the heated object 4. A thin film is formed, and the solvent evaporates instantaneously, creating a composite layer in which each component adheres closely. Each dispersion may be moved between two syringes (not shown), or it may be supplied to the heads while being moved by a circulation device.

[0031] In Figure 2, a conductive additive dispersion, active material particle dispersion, slurry, or liquid polymer particles are ejected from spray heads 21, 22, and 23 as a jet stream or pulsed jet stream onto an electrode thin film composite layer 20 dispersed on a heated object 24 to a desired state, forming a new thin film composite layer. The thin film composite layer can be selected from 2 to 300 layers. For high-speed production lines, the inventors can use, for example, JP7411250 as an extension of the present invention.

[0032] In Figure 3, the ejected streams 31, 32, and 33 merge in the air 330 and adhere to the heated object 34 to form an electrode layer 350. The electrode layer 350 may be made as a thin film and stacked in layers of 2 to 300, and the coating weight per layer can also be increased. The confluence system can transport multiple fluids through a multi-pipe system, discharging each dispersion or slurry from its end face. Compressed gas is ejected from the outermost channel, stretching the liquids inside and, if necessary, swirling them to create particles for mixing and application. Furthermore, another compressed gas can be collided with the ejected flow to further refine the particles and improve mixing.

[0033] Thus, the method of the present invention does not involve the preparation of a dispersion or slurry by adding a binder solution, particularly for active material particles and SWCNTs, and therefore can prevent the aggregation of particles and fibers. Furthermore, the binder can be structured so that it does not form a continuous insulating layer within the electrode layer.

[0034] Therefore, the active material particles, with aggregation suppressed, are ejected from a particle generator while maintaining the desired dispersion or slurry state and dried on the target object. In this process, for example, a CNT dispersion with a solid content of 1% or less by weight is converted into liquid particles and applied to the desired area, and the solvent is instantly dried by heating the target object. To stabilize the contact or bonding between the active material particles and between the active material particles and CNTs over time, a minimum amount of binder is scattered as liquid particles only in the necessary areas, dried, and allowed to adhere.

[0035] To prevent the aggregation of electrolyte particles and CNTs, especially SWCNTs, the materials are prepared as independent, low-viscosity dispersions or slurries that can be handled individually. Furthermore, even solvents with high boiling points, such as NMP, will instantly evaporate upon impact with an object heated to 60 to 120°C if the solvent film is compressed to less than 1 micrometer. Treating the object's surface with plasma or other means to increase surface tension is beneficial, as it allows even solvents with poor wettability to level into a thin film. For this reason, a binder solution with a low solid content concentration is preferable. In the case of all-solid-state batteries with high electrode press pressure, and when using fibrillated fluorine-based materials, dispersion can be achieved with a poor solvent such as n-heptane, which allows for faster solvent evaporation.

[0036] As described above, the present invention makes it possible to maximize the potential of each material, thereby enabling the manufacture of secondary batteries, including all-solid-state batteries with excellent battery performance. [Examples]

[0037] The present invention can be suitably applied to fields such as solar cells, fuel cells, water electrolysis, secondary batteries, semiconductors, electronics, pharmaceuticals, food, and chemicals. In particular, it can be applied to dispersion coating of quantum dots with other materials. [Explanation of symbols]

[0038] 1, 21, 31, Sprayhead #1 2, 22, 32, Sprayhead #2 3, 23, 33 Sprayhead #3 4, 24, 34 Objects 5. Conductive additive thin film dispersion layer 6. Active material particle thin film layer 7. Binder particle dotted layer 20 Thin film composite layer 101, 201, 301 Jet or pulsed jet (conductive additive) 102, 202, 302 Jet or pulsed jet (active material particles) 103, 203, 303 Jet or pulsed jet (binder) 330 Merging 350 Mixed material layer

Claims

1. A method for manufacturing a secondary battery or an all-solid-state battery, comprising applying a dispersion or slurry of electrode active material particles, electrolyte particles, a conductive additive, and a binder, selected from current collectors, electrode layers, electrolyte layers, and separators, in a solvent, to form an composite electrode layer, wherein the method comprises the steps of: preparing an active material dispersion or slurry with active material particles and at least a solvent; preparing a conductive additive dispersion with a conductive additive selected from carbon nanotubes, carbon nanofibers, graphene, and carbon particles and at least a solvent; and using binder fine particles, fibrous binder, binder solution, emulsion, and solvent. A method for manufacturing a secondary battery or an all-solid-state battery, characterized by forming an electrode layer by: a step of selecting and creating a liquid binder; a step of turning the active material particle dispersion or slurry, the conductive additive dispersion, and the liquid binder into liquid particles using an independent spray or particle generator to form a jet stream or pulsed jet stream; and a step of merging each of the jet streams or pulsed jet streams between the air or a heated object and impacting the object to coat it, or impacting heated objects sequentially or in any order to form a thin film layer, evaporating the solvent, and applying multiple layers of at least the same dispersion or slurry.

2. A method for manufacturing a secondary battery or all-solid-state battery according to claim 1, characterized by forming an electrode layer by: a step of making a dispersion or slurry comprising the active material particles and at least a solvent, and a dispersion comprising carbon nanotubes and a solvent into an aggregate dispersion or slurry; a step of making the aggregate dispersion or slurry into liquid particles using a spray or particle generator and forming it into a jet stream or pulsed jet stream; a step of making the liquid binder into liquid particles using a spray or particle generator and forming it into a jet stream or pulsed jet stream; and a step of merging each of the jet streams or pulsed jet streams between the air or a heated object and impacting the object to coat it, or impacting heated objects sequentially or in no particular order to form a thin film layer and evaporating the solvent, thereby coating at least multiple layers of the same dispersion or slurry.

3. A method for manufacturing a secondary battery or all-solid-state battery according to claim 1, comprising the steps of: adding an electrolyte particle dispersion or electrolyte particle slurry and turning it into liquid particles using a spray or particle generator to form a jet stream or pulsed jet stream; and merging each of the jet streams or pulsed jet streams between the air or a heated object and impacting the object to coat it, or impacting heated objects sequentially or in any order to form a thin film layer and evaporating the solvent to coat at least multiple layers of the same dispersion or slurry.

4. A method for manufacturing a secondary battery or an all-solid-state battery according to claim 1, characterized in that the conductive additive is a single-walled carbon nanotube and the solid content of the binder is 3 percent or less of the total solid content weight of the electrode layer.

5. A method for manufacturing a secondary battery or an all-solid-state battery, comprising forming an electrode layer on a current collector by selecting electrode active material particles, a solid electrolyte, a conductive additive, and a binder, comprising the steps of: preparing a binder-free slurry by selecting active material particles or composite particles in which at least a portion of the active material particles is coated with a solid electrolyte, and solid electrolyte particles, and at least a solvent; preparing a binder-free conductive additive dispersion by at least carbon nanotubes and at least a solvent; and using binder fine particles, fibrous binder, binder solution, emulsion, and solvent. A method for manufacturing a secondary battery or an all-solid-state battery, characterized by the steps of: selecting and preparing a liquid binder; adding compressed gas to the slurry, dispersion, and liquid binder using an independent spray or particle generator to form liquid particles and then ejecting them as a jet stream or pulsed jet stream; mixing and adhering the jet stream or pulsed jet stream to a heated object before it reaches the object, or layering the respective jet streams onto the heated object sequentially or in no particular order; and forming an electrode layer in which at least a portion of the composite electrode layer is fixed with the binder.

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