WO2025193055A1 - Electrode composition for manufacturing dry electrode, dry electrode formed using electrode composition, secondary battery comprising dry electrode, and dry electrode manufacturing method and device using electrode composition - Google Patents

Abstract

A technology of the present invention relates to a dry electrode, which is an electrode manufactured using a dry method, and, more particularly, to: an electrode composition for manufacturing a dry electrode, the composition being a new composition capable of simplifying a manufacturing process and providing a better quality dry electrode by omitting a process that is essential in the prior art in order to manufacture an electrode without a solvent by using a dry method; a dry electrode formed using the electrode composition; a secondary battery comprising the dry electrode; and a dry electrode manufacturing method and device using the electrode composition.

Description

Electrode composition for manufacturing a dry electrode, a dry electrode formed with the electrode composition, a secondary battery including the dry electrode, and a method and device for manufacturing a dry electrode using the electrode composition

This invention was supported by the following national research and development project.

[Project ID] 1415187718

[Assignment Number] 20023145

Ministry of Trade, Industry and Energy

[Name of Project Management (Specialist) Agency] Korea Industrial Technology Evaluation and Planning Institute

[Research Project Name] Material and Components Technology Development

[Research Project Name] Development of a Binder and Manufacturing Process for a Dry Process for Reducing Carbon in Secondary Battery Applications

The present invention relates to a technology related to a dry electrode, which is an electrode manufactured by a dry method, and more specifically, to a novel electrode composition for manufacturing a dry electrode, which simplifies the manufacturing process by omitting a process that was essential in the prior art for manufacturing an electrode without a solvent by a dry method and provides a dry electrode of excellent quality, a dry electrode formed by the electrode composition, a secondary battery including the dry electrode, and a method and device for manufacturing a dry electrode using the electrode composition.

Secondary batteries, such as lithium-ion batteries, are electrical storage devices that operate through electrochemical reactions in electrode layers composed of active materials, conductive materials, and binders. The electrochemical properties of secondary batteries are determined by various factors, including the type and content of each component, their compositional ratio, and the electrode manufacturing method.

Conventionally, electrode manufacturing methods involve mixing and dispersing all components in a solvent to create a uniform electrode composition slurry, which is then applied to a metal plate as a current collector and dried to produce an electrode with a certain thickness (wet electrode method). Because this method has been used for a long time, the manufacturing process is already stable and the yield is very high. However, this method has many inconveniences in the manufacturing process, such as the mandatory installation of a drying chamber for solvent removal and the need to recover all evaporated solvent to prevent air pollution. Consequently, the equipment and manufacturing costs are high.

To address these shortcomings, a dry process has recently been proposed. This method involves mixing all components—active material, conductive agent, and binder—in a solvent-free dry process, forming electrode sheets that are then directly attached to metal plates. This method eliminates the need for a drying furnace and, consequently, a solvent recovery device, significantly reducing overall costs. However, the dry process presents challenges, including the difficulty in uniformly mixing all components without solvents and the difficulty in producing electrodes with uniform thickness.

Typically, particulate polytetrafluoroethylene (PTFE) is used in the manufacture of dry electrodes using a dry method. This is because PTFE is known to fiberize (become thinner and longer) when subjected to shear force, effectively binding the active material and conductive additives. The conventional method for manufacturing dry electrodes comprises the steps of: (1) preparing a kneaded material (compound) by putting all of the components of the electrode, i.e., the active material, binder, and conductive additive, into a kneader (e.g., internal mixer; kneader) and kneading them; (2) a grinding step for grinding the kneaded material into an appropriate size to create particles suitable for calendering; (3) a calendering step for manufacturing a dry electrode sheet using a calender; and (4) a step for attaching the dry electrode sheet onto a metal plate. The dry electrode is manufactured through the following steps (hereinafter referred to as the "kneading/grinding/calendering method").

The above-described dry electrode manufacturing method, namely the kneading/grinding/calendering method, is possible because it uses PTFE as a binder. However, PTFE particles, known by the trade name Teflon, are a fluorinated polymer and are known to have high releasability and poor adhesion to other substances. Furthermore, there is the problem of requiring very high pressure to make the dry electrode less than a certain thickness, for example, less than 100 microns. In particular, even if a dry electrode is manufactured by applying high pressure, the shrinkage and expansion caused by the temperature change during repeated charge and discharge processes cause minute gaps between the components in the electrode layer, increasing the possibility of the electrode layer peeling off from the metal plate, which serves as the current collector. This leads to various problems, such as a decline in the electrochemical properties of the dry electrode.

To overcome these problems of poor adhesion and difficulty in making electrodes thin, there may be a way to complement the shortcomings of PTFE by mixing PTFE with other types of binders currently used as binders for secondary batteries. However, mixing PTFE with other binders for secondary batteries that have good adhesion, such as polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), or acrylonitrile copolymers, will interfere with the fiberization of PTFE, making dry electrode manufacturing very difficult. For example, if PTFE particles and acrylonitrile copolymer binder particles are dry blended at a weight ratio of 50:50 to create a binder mixture and then kneaded, the kneading will not proceed to the extent that torque is applied during the kneading operation. Furthermore, if this mixture is passed through a calendaring roll, it will crumble and fall down as it passes through the roll, preventing the formation of a dry electrode sheet. Ultimately, in the case of an electrode composition containing PTFE, the content of the adhesive binder must be increased to increase the adhesiveness of the dry electrode, but in this case, there is a problem that manufacturing a dry electrode sheet becomes very difficult.

Therefore, there is an urgent need for a technology that can maintain surface forming ability when manufacturing dry electrodes by mixing a significant amount of PTFE with other binders and easily manufacture dry electrodes without using a batch-type kneading/grinding method, a dry electrode manufactured using such a technology, and a secondary battery including the same.

Accordingly, the purpose of the present invention is to provide a novel electrode composition for manufacturing a dry electrode, which can improve the adhesive strength with the electrode plate of a dry electrode and the bonding strength between each component within the electrode without reducing the surface forming ability of the dry electrode sheet during the manufacturing of the dry electrode.

Another object of the present invention is to provide a dry electrode manufacturing method and device that can increase economic efficiency by simplifying the manufacturing process by omitting the process that was essential in the prior art using the electrode composition for manufacturing the dry electrode described above and provide a dry electrode of better quality.

Another object of the present invention is to provide a dry electrode having excellent adhesive strength with a metal electrode plate as a current collector and excellent bonding strength between each component in the electrode by using an electrode composition for manufacturing a dry electrode having the above-described configuration, and to provide a secondary battery including the electrode capable of effectively maintaining stable electrochemical characteristics.

The purpose of the present invention is not limited to the purposes mentioned above, and even if not explicitly mentioned, the purpose of the invention that can be recognized by a person of ordinary skill in the art from the description of the detailed description of the invention described below may also be included.

In order to achieve the above-described object of the present invention, the present invention provides an electrode composition for manufacturing a dry electrode, which comprises 90-98 wt% of an active material, 1.0-5 wt% of a binder, and 1.0-5 wt% of a surface forming agent.

In a preferred embodiment, the surface forming agent is a nanomaterial having at least one shape selected from the group consisting of a tube shape, a ribbon shape, and a fiber shape.

In a preferred embodiment, the surface forming agent is at least one carbonaceous nanomaterial selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, few-walled carbon nanotubes, branched carbon nanotubes, carbon nanoribbons, and carbon nanofibers, or at least one non-carbonaceous nanomaterial selected from the group consisting of boron nitride nanotubes, boron nitride nanoribbons, and aramid nanofibers.

In a preferred embodiment, the surface forming agent is a carbon nanotube in the form of a lump or bundle having a size of 0.2-50 microns.

In a preferred embodiment, the carbon nanotube has an aspect ratio of 100 or more.

In a preferred embodiment, the active material has a coating layer formed on the surface thereof made of carbon-based nanomaterials.

In a preferred embodiment, the binder comprises a fiberizable fluorine-based resin and another binder resin.

In a preferred embodiment, the fiberizable fluorine resin is polytetrafluoroethylene (PTFE).

In a preferred embodiment, the binder is a simple mixture of the fiberizable fluorinated resin and another binder resin, or a core-shell structure composite binder formed such that a core made of the fiberizable fluorinated resin and a shell made of another binder resin surround the core.

In a preferred embodiment, the other binder resin is a copolymer comprising at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer; or at least one selected from the group consisting of acrylonitrile-based monomers, carboxyl-based monomers, and glycol-based monomers.

In a preferred embodiment, the carboxylic monomer is at least one selected from the group consisting of acrylic acid, acrylate, maleic acid, and maleic anhydride.

In a preferred embodiment, the other binder resin is an acrylonitrile-ethylene glycol-maleic acid copolymer.

In a preferred embodiment, the content of the fiberizable fluorine resin included in the binder is 80% by weight or less of the total weight of the binder.

In a preferred embodiment, the content of the fiberizable fluorine resin included in the binder is 50% by weight or less of the total weight of the binder.

In a preferred embodiment, the surface-forming agent further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, and graphene nanoplates, per 100 parts by weight of the surface-forming agent.

In addition, the present invention provides a method for manufacturing a dry electrode, including a step of preparing an electrode composition for manufacturing a dry electrode by stirring and mixing an active material, a binder, and a surface forming agent; a calendering step of manufacturing an electrode material layer sheet by calendering the electrode composition; and a rolling step of attaching the electrode material layer sheet to a support film or a metal electrode plate and then rolling it.

In a preferred embodiment, the calendaring step and the rolling step are performed continuously on the same line.

In a preferred embodiment, the calendering roll is heated to 50°C to 200°C when performing the calendering.

In a preferred embodiment, the electrode composition for manufacturing a dry electrode is any one of the electrode compositions for manufacturing a dry electrode described above.

In a preferred embodiment, the content of the fiberizable fluorine resin included in the binder in the electrode composition for manufacturing the dry electrode is 80% by weight or less of the total weight of the binder.

In a preferred embodiment, the electrode composition for manufacturing a dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates per 100 parts by weight of the surface-forming agent.

In addition, the present invention provides a dry electrode manufacturing device comprising: a stirring device for stirring and mixing an electrode composition for manufacturing a dry electrode, including an active material, a binder, and a surface forming agent; a calender device for forming the stirred and mixed electrode composition into an electrode material layer sheet; and a rolling device for attaching and pressing the electrode material layer sheet by positioning it on at least one surface of a support film or a metal electrode plate.

In a preferred embodiment, the calendar device is set to a heating condition of 50°C to 200°C.

In a preferred embodiment, the calendar device and the rolling device are located on the same line.

In a preferred embodiment, the electrode composition for manufacturing a dry electrode is any one of the electrode compositions for manufacturing a dry electrode described above.

In a preferred embodiment, the content of the fiberizable fluorine resin included in the binder in the electrode composition for manufacturing the dry electrode is 80% by weight or less of the total weight of the binder.

In a preferred embodiment, the electrode composition for manufacturing a dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates per 100 parts by weight of the surface-forming agent.

In addition, the present invention provides a dry electrode comprising any one of the above-described electrode compositions for manufacturing a dry electrode.

In a preferred embodiment, the content of the fiberizable fluorine resin included in the binder in the electrode composition for manufacturing the dry electrode is 80% by weight or less of the total weight of the binder.

In a preferred embodiment, the electrode composition for manufacturing a dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates per 100 parts by weight of the surface-forming agent.

In addition, the present invention provides a secondary battery including the above-described dry electrode.

The electrode composition for manufacturing a dry electrode of the present invention described above can improve the adhesive strength with the electrode plate of the dry electrode and the bonding strength between each component in the electrode without reducing the surface forming ability of the dry electrode sheet during the manufacturing of the dry electrode.

In addition, according to the dry electrode manufacturing method and device of the present invention, by using the electrode composition for manufacturing the dry electrode described above, the kneading process and the grinding process, which are processes essential in the prior art, are omitted, thereby simplifying the manufacturing process, and in order to improve adhesiveness, a considerable amount of a binder for existing secondary batteries is mixed in order to minimize the content of PTFE, so that a dry electrode can be easily manufactured, thereby increasing economic efficiency and providing a dry electrode of superior quality.

In addition, the dry electrode of the present invention has excellent adhesive strength with a metal electrode plate as a current collector and bonding strength between each component in the electrode by using the electrode composition for manufacturing a dry electrode having the above-described configuration, and also has the effect of improving long-term life characteristics, and the secondary battery of the present invention can effectively maintain stable electrochemical characteristics by including the dry electrode.

These technical effects of the present invention are not limited to the scope mentioned above, and effects of the invention that can be recognized by a person having ordinary skill in the art from the description of specific contents for implementing the invention described below, even if not explicitly mentioned, are also naturally included.

Figure 1 is an actual appearance of a dry electrode material layer sheet according to an embodiment of the present invention (surface forming agent: untreated carbon nanotubes).

Figure 2 is an actual appearance of a dry electrode material layer sheet according to an embodiment of the present invention (surface forming agent: boron nitride nanotube).

Figure 3 is a cross-sectional photograph of a dry electrode formed using an electrode composition for manufacturing a dry electrode according to an embodiment of the present invention.

Figure 4 shows the results of electrochemical impedance spectroscopy (EIS) measurement of a coin cell according to an embodiment of the present invention.

Figure 5 shows the results of a charge/discharge cycle test of a coin cell including a dry electrode according to an embodiment of the present invention.

The terminology used herein is merely used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the description of the invention, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

While terms like "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component."

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

When interpreting components, even if there is no explicit description, they are interpreted as including the tolerance range. In particular, when terms such as "about" or "substantially" are used, they may be interpreted as meaning at or near that value when manufacturing and material tolerances inherent to the meaning stated are provided.

When describing a temporal relationship, for example, when the temporal order is described as ‘after’, ‘following’, ‘next to’, ‘before’, etc., it also includes cases where it is not continuous, unless ‘right away’ or ‘directly’ is used.

Hereinafter, the technical configuration of the present invention will be described in detail with reference to the attached drawings and preferred embodiments.

However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Throughout the specification, the same reference numbers are used to designate the same components. Furthermore, in describing the present invention, detailed descriptions of known components or functions will be omitted if they are deemed to obscure the gist of the present invention.

The technical features of the present invention are a novel electrode composition for manufacturing a dry electrode, which simplifies the manufacturing process by omitting the kneading process and the grinding process, which are processes essential in the prior art when manufacturing a dry electrode, and improves the adhesive strength with the electrode plate of the dry electrode and the bonding strength between each component in the electrode without reducing the surface forming ability of the dry electrode sheet, a dry electrode formed with the electrode composition, a secondary battery including the dry electrode, and a method and device for manufacturing a dry electrode using the electrode composition.

As is known, since dry electrodes are manufactured in a dry manner without a solvent, the most important requirement when selecting a binder is the ability to form an electrode surface by dry processing. The polymer suitable for this condition is PTFE. PTFE is a polymer that stretches and becomes thin and long when a shear force is applied, i.e., fibers, and is therefore used as a binder for manufacturing dry electrodes. However, PTFE has the disadvantage of poor adhesion to other materials due to its high releasability. Although PTFE can be made to adhere together with the active material and conductive additives by applying high pressure, there is a high possibility that interfacial peeling will occur at the interface between each component in the dry electrode and the electrode plate when repeated expansion/contraction due to heating/cooling during use in a secondary battery. This can ultimately lead to a decline in electrochemical performance during charge/discharge cycle tests, and there was a problem that it could generate hydrogen fluoride, a toxic gas, in the event of a fire.

In order to prevent these problems, it is desirable to replace PTFE, which is a binder for dry processes, with another binder, or, if PTFE cannot be completely replaced, to minimize the PTFE content by using a mixed binder in which PTFE is mixed with another binder. However, other binders that are to be mixed with PTFE are almost impossible to fiberize like PTFE, so not only cannot other binders replace PTFE, but also, mixing another binder with PTFE causes a problem in that the sheet forming ability is rapidly reduced. However, the present invention includes an electrode sheeting agent in the electrode composition during the manufacture of a dry electrode, thereby improving the sheet forming ability of the dry electrode to the extent that the calendaring process can be performed directly without performing the kneading process and the grinding process, which are pretreatment processes for fiberization, even when the content of the fiberizing polymer, i.e. PTFE, which had to be used at 100 wt% in the prior art, is used at 80 wt% or less, preferably 50 wt% or less, and more preferably 30 wt% or less.

Accordingly, the electrode composition for manufacturing a dry electrode of the present invention comprises 90-98 wt% of an active material, 1.0-5 wt% of a binder, and 1.0-5 wt% of a planarizing agent. The composition ratio of each component is experimentally determined, and if it is below the lower limit of each component, the effect of each component is not realized, which is disadvantageous, and if it exceeds the upper limit, each component is used excessively more than necessary, which reduces economic feasibility or causes electrochemical performance to not be realized properly, which is disadvantageous. Specifically, if the binder content is low, less than 1.0 wt%, the electrode surface is not properly formed during the manufacture of the electrode, which is disadvantageous, and if the content is 5 wt% or more, the electrode surface of the dry electrode is well formed, but the active material content is relatively low, making it difficult to realize electric capacity, which may be disadvantageous. In the case of the planarizing agent, if the content is less than 1.0 wt%, the planarizing ability is reduced, which is disadvantageous, and if it is 5 wt% or more, the tubular planarizing agent is too abundant, which may result in an unclean appearance and many defects, which may be disadvantageous.

First, in the electrode composition for manufacturing a dry electrode of the present invention, the active material may be a positive electrode active material or a negative electrode active material, and may be any one selected from the group consisting of alkali metal elements, alkaline earth metal elements, manganese, nickel, cobalt, aluminum, iron, phosphorus, tin, titanium, graphite, silicon, silicon oxide, sulfur, and combinations thereof. Here, the alkali metal element may be any one selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and francium, and the alkaline earth metal element may be any one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). If necessary, as described below, when the surface forming agent is a carbon-based nanomaterial, the active material may have a structure further including a coating layer formed on its surface.

In addition, in the electrode composition for manufacturing a dry electrode of the present invention, the surface forming agent may be a thin and long nanomaterial having a diameter in the nanometer range and a length in the several to several hundred microns range. In particular, the surface forming agent is not intended to improve surface adhesion properties, but rather is used together with each component forming the electrode, i.e., the active material and the binder, to cause these components to become entangled with each other, i.e., to form a surface or sheet, and therefore may be a nanomaterial having one or more shapes selected from the group consisting of a tube shape, a ribbon shape, and a fiber shape.

In one embodiment, the sheet-forming agent may be at least one carbon-based nanomaterial selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, few-walled carbon nanotubes, branched carbon nanotubes, carbon nanoribbons, and carbon nanofibers; or at least one non-carbon-based nanomaterial selected from the group consisting of boron nitride nanotubes, boron nitride nanoribbons, and aramid nanofibers. However, since non-carbon-based nanomaterials are electrically insulating materials, when they are used as sheet-forming agents, a conductive additive must be added separately. However, when carbon-based nanomaterials are used as sheet-forming agents, the carbon-based nanomaterials themselves have good electrical conductivity, so a separate conductive additive does not need to be used, and various surface treatment techniques are possible, so they can be significantly advantageous compared to other sheet-forming agents.

As described above, the surface-forming agent in the present invention is not intended to control surface properties, so it may be used as is without any special surface treatment. However, it is advantageous to use the surface of the surface-forming agent by surface-treating it to enhance the adhesiveness of the surface-forming agent, to impart surface chemical bonding or other functionalities, or to use a method of pretreating the surface-forming agent so that it is uniformly attached to the surface of the active material, thereby enabling the production of a more uniform dry electrode sheet. For example, when using carbon nanotubes as the surface-forming agent, it is advantageous to use an active material surface-coated with a small amount of carbon nanotubes, thereby enabling the dry electrode sheet to have more uniform electrical conductivity.

In particular, the surface-forming agent of the present invention may be carbon nanotubes in the form of lumps (particles) or bundles having a size of 0.2 to 200 microns. If the size of the particles or bundles is 0.2 microns or less, the size is too small, which causes a problem in that the surface-forming ability is significantly reduced, and if it is 200 microns or more, the particles are too large, which hinders surface formation, which is rather disadvantageous. Preferably, the carbon nanotubes may be particles or bundles having a size of 1 to 50 microns. At this time, the carbon nanotubes are nanomaterials having an aspect ratio of 100 or more, and are at least one selected from the group consisting of carbon nanotubes such as single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, few-walled carbon nanotubes, and branched carbon nanotubes.

In addition, in the electrode composition for manufacturing a dry electrode of the present invention, the binder includes a fiberizable fluorine-based resin and another binder resin to supplement the adhesiveness, which is a shortcoming of the fiberizable fluorine-based resin, and the form thereof may be two types: a first form which is a simple mixture of a fiberizable fluorine-based resin and another binder resin, or a second form which is a core-shell structure composite binder formed so that a core made of a fiberizable fluorine-based resin and a shell made of another binder resin surround the core. At this time, the fluorine-based resin capable of fiberization may be polytetrafluoroethylene (PTFE), and as for other binder resins, basically all types of secondary battery binders may be used as long as they have adhesive properties that can be mixed with the fluorine-based resin particles. As an example, the binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose, styrene-butadiene copolymers, and acrylonitrile-butadiene copolymers; or a copolymer including at least one selected from the group consisting of acrylonitrile-based monomers, carboxyl-based monomers, and glycol-based monomers.

In the electrode composition for manufacturing a dry electrode of the present invention, a simple mixture of a first type of binder, such as PTFE, a fluorine-based resin particle, and another binder resin having excellent adhesive properties can be manufactured using a simple dry blending method and a wet solution mixing method. In one embodiment, the dry blending method is a method of manufacturing a binder mixture or binder blend by simply mixing PTFE and another binder resin having excellent adhesive properties in a dry blender. Although a mixed binder of the first type can be obtained using a simple dry blending device, since PTFE is a binder in the form of particles, there is a restriction that the other binder resin to be mixed with it must also be a binder resin in the form of particles having at least a similar or identical size, which makes manufacturing inconvenient. In addition, since PTFE particles readily fiberize when manufacturing dry electrodes, while other binder resins are polymer materials that do not fiberize, the first type of binder that is simply mixed has PTFE particles and other binder particles separately, so fiberization necessary for surface formation is partially achieved, and therefore the surface forming ability deteriorates in proportion to the content of the other mixed binder resin, so increasing the content of the other binder resin that can replace PTFE is inevitably limited.

On the other hand, in the electrode composition for manufacturing a dry electrode of the present invention, the second type of binder, a core-shell structure composite binder, has a shell shape in which fluorine-based resin particles, i.e., PTFE, form a core inside, and another binder resin with adhesive properties surrounds the outer surface thereof. In this core-shell structure composite binder, the fluorine-based resin particles inside provide planar forming ability during dry processing, and the adhesive other binder resin on the surface complements the adhesiveness of the dry electrode, so that it can function as a binder having both planar forming ability and adhesiveness. In addition, since it is not a structure in which different particles are mixed, but a single particle having a core-shell structure, unlike the binder mixture of the first type described above, even if a large amount of another binder resin is included, the fiberization of PTFE is not significantly hindered, so that the fiberization can be relatively uniform, and a relatively larger amount of fluorine-based resin can be replaced with another binder resin, which can be effective.

Looking more specifically at the core-shell structure composite binder, which is the second type of binder in the electrode composition for manufacturing a dry electrode of the present invention, first, the fluorine-based resin forming the core is not limited as long as it contains a fluorine component and is a polymer capable of being fiberized, but in particular, it may be polytetrafluoroethylene (PTFE), and the particle diameter may be 0.05-5.0 microns. If the particle size of the fluorine-based resin is less than 0.05 microns, the particles are too small, making it difficult to form fluorine-based resin particles or to form a fluorine-based resin dispersion, which is disadvantageous. If it is 5 microns or more, the total surface area of the fluorine-based resin particles becomes small, so that the content of other adhesive binder resins coated on the surface becomes low, making it difficult to impart adhesiveness, which is rather disadvantageous.

The other binder resin forming the shell can be any polymer compound that has adhesive properties and can be used as a binder for secondary batteries. The polymer that can be used as an electrode binder for a secondary battery can be a polymer that can be dissolved in organic or aqueous solvents, and can include one or more polymers. In one embodiment, it can be in the form of a homopolymer, such as polyvinylidene fluoride (PVDF), which is widely used as a binder for a positive electrode, or it can be a polymer in the form of a copolymer with various functions. One or more of these binders can be mixed and used, which is advantageous because the characteristics of each binder are complemented to produce a better effect.

Other binder resins forming a representative shell may be, but are not limited to, one or more selected from the group consisting of a cellulose polymer binder such as polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose, a flexible copolymer such as styrene-butadiene rubber or acrylonitrile-butadiene rubber, or a copolymer comprising one or more selected from the group consisting of acrylonitrile-based monomers, carboxyl-based monomers, and glycol-based monomers.

More specifically, a copolymer can be used, which is synthesized by copolymerizing a carboxylic monomer for imparting adhesiveness to another binder resin forming the shell and an acrylonitrile monomer for imparting stable electrochemical properties as a base, with a third monomer for imparting other functions. For example, when an acrylate monomer neutralized with a compound consisting of 2-6 carbons is copolymerized together, these components cause geometric hindrance, which makes the synthesized copolymer flexible and has strong adhesiveness. If this is used to manufacture a composite binder with a core-shell structure, a composite binder that is flexible and has strong adhesiveness can be obtained. Here, the carboxylic monomer may be one or more selected from the group consisting of acrylic acid, acrylate, maleic acid, and maleic anhydride, and in particular, the other binder resin forming the shell may be an acrylonitrile-ethylene glycol-maleic acid copolymer.

The core-shell structure composite binder of the above-described composition includes the steps of preparing a first binder dispersion by dispersing a fibrous fluorine-based resin in water; preparing a second binder solution by dissolving another binder resin having adhesive properties in a solvent; adding the second binder solution to the first binder dispersion while stirring; and a post-processing step of filtering, washing, and drying the resultant obtained after stirring is completed. Here, the step of preparing the first binder dispersion is performed by preparing an aqueous dispersion of fibrous fluorine-based resin particles, and a commercially available one may be used if necessary. The step of preparing the second binder solution may be performed by dissolving another binder resin having adhesive properties in an organic solvent to prepare the second binder solution. Here, the organic solvent is not limited as long as it can dissolve another binder resin, but as an example, either DMF or NMP may be used.

In particular, the content of the fluorine-based resin dispersed in the first binder dispersion and the other binder resin dissolved in the second binder solution can be prepared to have a weight ratio of 90 to 10:10 to 90, and through this mixing ratio, a core-shell structured composite binder in the form of a single particle can be finally obtained, that is, a fluorine-based resin particle inside which is surrounded by a layer of another binder resin having good adhesiveness on its outer surface. The stirring step can be performed by slowly adding the second binder solution to the first binder dispersion while stirring. The stirring conditions have also been experimentally established and can be performed by vigorously stirring for 20 minutes to 5 hours at a temperature of 20 to 70°C at a speed of 200 to 10,000 rpm. An increase in the stirring speed is advantageous because a smaller and more uniform composite binder can be obtained. Under conditions below the lower limit of the set stirring conditions, the core-shell structure reaction does not occur well or is difficult, which is disadvantageous, and under conditions exceeding the upper limit, the core-shell structure reaction is likely to be hindered, which is rather disadvantageous. The post-processing step is a process for obtaining core-shell structure composite binder particles generated in the stirring step, and can be performed by filtering the result obtained after stirring is completed, separating the core-shell structure composite binder particles from the solvent, washing, purifying, and then drying. Here, filtering and washing can be performed more than once.

Meanwhile, in the electrode composition for manufacturing a dry electrode of the present invention, the content of the fibrous fluorine-based resin (fibrous fluorine-based resin) included in the binder may be 30 wt% or less of the total weight of the binder. In the present invention, if necessary, the fibrous fluorine-based resin constituting the binder may be replaced with another binder resin up to 80 wt%. In the prior art, the binder included in the electrode composition for manufacturing a dry electrode is almost entirely composed of PTFE, and a pretreatment process was required to maintain the surface-forming ability of the dry electrode. However, the electrode composition for manufacturing a dry electrode of the present invention includes a surface-forming agent, so that even if the content of the fibrous fluorine-based resin included in the binder is reduced to a maximum of 20 wt%, an excellent dry electrode surface can be formed directly through a calendaring process without a pretreatment process.

In addition, the electrode composition for manufacturing a dry electrode of the present invention may further include, if necessary, 1 to 100 parts by weight of one or more conductive nanomaterials selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates, per 100 parts by weight of the surface-forming agent. In particular, when a non-carbonaceous nanomaterial is used as the surface-forming agent, it is essential to further add a conductive nanomaterial to enhance conductivity. However, when a carbonaceous nanomaterial, particularly a carbon nanotube, is used as the surface-forming agent, it is not essential as a component, but when a carbon nanotube having an aspect ratio of 100 or more is used as the surface-forming agent, additionally including a conductive nanomaterial having an aspect ratio of less than 100 can not only help disperse the carbon nanotubes, but also have the advantage of imparting higher conductivity.

Next, the dry electrode manufacturing method of the present invention includes a step of preparing an electrode composition for manufacturing a dry electrode by stirring and mixing an active material, a binder, and a surface forming agent; a calendering step of manufacturing an electrode material layer sheet by calendering the electrode composition; and a rolling step of attaching the electrode material layer sheet to a support film or a metal electrode plate and then rolling it. Here, the calendering step and the rolling step may be performed continuously on the same line.

First, in the step of preparing the electrode composition, the active material, binder, and surface forming agent are mixed and stirred without a solvent using one of various dry mixers selected from among low-speed and high-speed mixers, mixers that simultaneously implement revolution and rotation, Henschel mixers, extrusion mixers with single or multi-screws, mixers using ball mills, swing-type or twist-type mixers, and mortar-type mixers, thereby preparing an electrode composition for dry electrode manufacturing. At this time, the active material is any kind of active material that can be used for the positive electrode and the negative electrode, and in one embodiment, it may be one or more materials selected from alkali metal elements such as lithium or sodium, alkaline group elements such as calcium, manganese, nickel, cobalt, aluminum, iron, phosphorus, tin, carbon materials such as graphite, titanium, silicon, silicon oxide, sulfur, and combinations thereof. In the present invention, the electrode composition for the positive electrode of a lithium ion battery has been mainly described. However, it is self-evident that the technology of the present invention can be applied to manufacture dry electrodes in various types of secondary batteries, such as solid electrolyte batteries such as metal ion batteries, semi-solid electrolyte batteries, or sulfide-based all-solid-state batteries. The binder, as described above, is a mixture of a fibrous fluorine-based resin and another binder resin, and in particular, may be a core-shell structured composite binder. If necessary, the fibrous fluorine-based resin may be used in an amount of 30 wt% or less of the total binder weight. The surface-forming agent may be a nanomaterial having one or more shapes selected from the group consisting of a tube shape, a ribbon shape, and a fiber shape, as described above. When carbon nanotubes are used, the material itself has good electrical conductivity, so that a dry electrode with low surface resistance can be manufactured without using a separate conductive additive, which is advantageous. In addition, it is self-evident that the surface-forming agent of the present invention can be applied to manufacture dry electrodes for both positive and negative electrodes by appropriately selecting and using the types of active material and binder together.

The calendaring step is a process of forming a dry electrode surface, i.e., an electrode material layer sheet, using a prepared electrode composition for dry electrode manufacturing. When the electrode composition for dry electrode manufacturing is put into a device (calendering device, calendar machine) in which two rolls are interlocked and rotated, an electrode surface, i.e., an electrode material layer sheet of a certain thickness can be formed.

The calender rolls of the calendering machine are usually made of metal, but if necessary, the metal roll surface may be coated with a different material and used. During calendering, a dry electrode surface is well formed at room temperature. However, in some cases, depending on the composition of the binder included in the electrode composition for dry electrode manufacturing, heating the calender roll and passing it through the high-temperature roll may result in a better dry electrode surface than at room temperature. The temperature of the calender roll may vary depending on the calendering speed, but it can be heated in the range of 50-200℃. If the roll temperature is below 50℃, the temperature may be too low and the dry electrode surface may not be formed well. On the other hand, if the roll temperature exceeds 200℃, the binder on the electrode surface may melt, causing the dry electrode surface to stick to the roll or affecting the peripheral devices, which is rather disadvantageous. The pressure during calendering should be appropriately adjusted in consideration of the thickness and porosity of the electrode to be manufactured. Since this is something that can be easily figured out through trial and error by those in the industry, the present invention is not limited to any special conditions.

The rolling step involves attaching the electrode material layer sheet to a support film or metal plate and then rolling it. This can generally be performed using rolling rolls. In particular, by applying heat and pressure while passing between the rolling rolls, the characteristics of the electrode surface, such as thickness and porosity, can be finely controlled, ultimately producing a dry electrode.

When the calendering step and the rolling step are performed sequentially on the same line, the support film may be fed together in the calendering step and passed through the calender roll, or the electrode surface may be formed on the support film by another appropriate method and then passed through the rolling roll, or a metal plate (current collector) on which a primer layer is formed may be fed so that the electrode material layer sheet discharged from the calendering roll is placed on it and passed through the rolling roll, so that the electrode surface is attached to the plate.

At this time, the support film used in the manufacture of dry electrodes can be a polymer film made of polyester, polypropylene, nylon, polyimide, etc. with a thickness ranging from 10 to 100 microns. If the thickness of the support film is less than 10 microns, the film is difficult to handle, and if it is more than 100 microns, it is unnecessarily thick or economically disadvantageous. The surface of these support films can be a polymer film that has been surface-treated to have silicone or fluorine release properties so that the dry electrode layer can be easily peeled off in the subsequent process. In addition, the primer layer of the metal electrode plate on which the primer layer has been formed can be preheated to increase the adhesion between the primer layer formed on the metal electrode plate and the electrode material layer sheet (dry electrode layer). For continuous processing, the metal electrode plate on which the primer layer has been formed can be preheated to a temperature range of 50 to 200°C. If the preheating temperature is less than 50°C, the preheating effect is almost non-existent, and if it is more than 200°C, the primer layer may be overheated and damaged.

During the dry electrode manufacturing process, thermal or mechanical stress may occur, which may cause dimensional changes in the dry electrode or the presence of pores between the wound rolls. To prevent this, the wound dry electrode rolls can be aged at an appropriate temperature. Aging temperature is typically 30-80°C for 12-100 hours. The aging temperature and time are inversely proportional; lower aging temperatures require longer aging times, while higher temperatures require shorter aging times. If the aging temperature or time exceeds the above ranges, the aging effect may be reduced or the dry electrode may be damaged, which is actually disadvantageous.

Next, the dry electrode manufacturing device of the present invention comprises a stirring device for stirring and mixing an electrode composition for manufacturing a dry electrode, which comprises an active material, a binder, and a surface forming agent; a calender device for forming the stirred and mixed electrode composition into an electrode material layer sheet; and a rolling device for attaching and pressing the electrode material layer sheet by positioning it on at least one surface of a support film or a metal electrode plate. Here, the calender device and the rolling device may be installed so as to be positioned on the same line.

As described above, the dry electrode manufacturing device of the present invention has a technical feature in that it can manufacture a dry electrode by using an electrode composition for dry electrode manufacturing, even if it is configured with a stirring device, a calender device, and a rolling device without a kneading device and a crushing device that are essentially included in a conventional dry electrode manufacturing device. Since the stirring device, the calender device, and the rolling device can be devices of known configurations, a detailed description thereof will be omitted. However, it may constitute a technical feature of the present invention to install the electrode material layer sheet output from the calender device on the same line so that it can be directly fed into the rolling device, i.e., the rolling roll.

Examples 1 to 4

Electrode compositions 1 to 4 for manufacturing dry electrodes were prepared as follows. That is, the active material (NCM811), the surface-forming agent, and the binder were placed in a dry blender (powder mixer) in the mixing ratios shown in Table 1 and stirred at a speed of 2,000 rpm for 10 minutes to prepare electrode compositions 1 to 4 for manufacturing dry electrodes. Here, the surface-forming agent is a multi-walled carbon nanotube having a particle diameter of 20 microns, and the surface-forming agent was an as-received multi-walled carbon nanotube received from the manufacturer without separate pretreatment unless otherwise specified. The binder (first form) was obtained by placing PTFE and PVDF or PTFE and PAEM in a dry blender (powder mixer) in the mixing ratios shown in Table 1 and mixing at a speed of 2,000 rpm for 10 minutes.

NCM811 cotton forming agent Binder (Type 1) PTFE PVDF PAEM Example 1 95.0 2.0 1.5 1.5 Example 2 95.0 2.0 0.9 2.1 Example 3 95.0 2.0 1.5 1.5 Example 4 95.0 2.0 0.9 2.1

In Table 1, all composition ratios are in weight %, and are PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), and PAEM (acrylonitrile-ethylene glycol-maleic acid copolymer).

Examples 5 to 11

Electrode compositions 5 to 11 for manufacturing dry electrodes were prepared by performing the same method as Example 1, except that a core-shell structure composite binder of the second type, not the first type, was manufactured as follows and the mixing ratio as shown in Table 2 was used.

NCM811 cotton forming agent Binder (Type 2) Core-shell structure composite binder 1 Core-shell structure composite binder 2 Core: PTFE Shell: PVDF Core: PTFE Shell:PAEM Example 5 95.0 2.0 0.6 2.4 Example 6 95.0 2.0 1.5 1.5 Example 7 95.0 2.0 0.6 2.4 Example 8 95.0 2.0 1.5 1.5 Example 9 95.5 2.5 1.0 1.0 Example 10 96.0 2.0 1.6 0.4 Example 11 95.0 1.5 1.5 1.5

Core-shell structure composite binders 1 and 2 were prepared as follows.

① Step for preparing the first binder dispersion

A first binder dispersion was prepared in which PTFE particles having an average particle diameter of 250 nanometers (0.25 microns) were dispersed in water.

② Step for preparing the second binder solution

A second binder solution was created by dissolving PVDF or PAEM, which is used as a positive electrode binder in existing lithium-ion batteries, in NMP.

③ Stirring step

The second binder solution was slowly added to the first binder dispersion and stirred at a speed of 3,500 rpm for 30 minutes.

④Post-processing stage

The result obtained in the stirring step was filtered with a pressure filter, washed with distilled water twice, and then dried at 50 degrees Celsius to obtain light brown final reactants, core-shell structure composite binder 1 (core: PTFE + shell: PVDF) and core-shell structure composite binder 2 (core: PTFE + shell: PAEM).

Example 12

An electrode composition 12 for manufacturing a dry electrode was prepared by performing the same method as Example 11, except that a core-shell structure composite binder 3 was manufactured by mixing PAEM and PVDF in a weight ratio of 1:1 instead of using only PAEM when manufacturing a second binder solution for manufacturing a core-shell structure composite binder.

Example 13

An electrode composition 13 for manufacturing a dry electrode was obtained by performing the same method as Example 8, except that boron nitride nanotubes (BN Nanotube, NAIEEL Technology, Korea) were used as a surface forming agent.

Example 14

An electrode composition 14 for manufacturing a dry electrode was obtained by performing the same method as Example 8, except that aramid nanofiber, which is a polymer nanofiber, was used as a surface forming agent.

Example 15

An electrode composition 15 for manufacturing a dry electrode was obtained by performing the same method as Example 11, except that a coating layer was formed on the surface of the active material using 0.5 wt% of untreated multi-walled carbon nanotubes having a particle diameter of 20 microns and 1 wt% of untreated multi-walled carbon nanotubes having a particle diameter of 20 microns as a surface forming agent.

Comparative Examples 1 to 8

Comparative electrode compositions 1, 2, 4, and 6 to 7 were prepared using the same method as Example 1, except that the mixing ratios shown in Table 3 were used, and comparative electrode compositions 3 and 5 to 8 were prepared using the same method as Example 5. Since Comparative Examples 1 to 3 did not use a surface forming agent, 2 wt% of conductive carbon black was added.

NCM811 cotton forming agent PTFE Binder (Type 1) Binder (Type 2) Core-shell structure composite binder 2 PTFE PVDF PAEM Core: PTFE Shell: PAEM Comparative Example 1 95.0 0 3.0 Comparative Example 2 95.0 0 3.0 Comparative Example 3 95.0 0 0 1.5 1.5 Comparative Example 4 95.0 2.0 3.0 Comparative Example 5 96.5 0.5 1.5 1.5 Comparative Example 6 95.0 2.0 0.6 2.4 Comparative Example 7 95.0 2.0 0.6 2.4 Comparative Example 8 95.0 2.0 0.5 2.5

Examples 16 to 21

1. Preparation stage of electrode composition for dry electrode manufacturing

Electrode compositions 6, 8, 9, 11, 12 and 15 for manufacturing dry electrodes were prepared by performing the same method as in Examples 6, 8, 9, 11, 12 and 15.

2. Calendaring Step

Electrode compositions 6, 8, 9, 11, 12, and 15 for manufacturing dry electrodes were each introduced into a calendar device (roll diameter: 88 mm, roll temperature: room temperature (23°C), 10 rpm) at a loading amount (capacity per unit area) of about 4.2 mAh/㎠ to manufacture electrode material layer sheets 1 to 3 and 5 formed of electrode compositions 6, 8, 9, and 12 for manufacturing dry electrodes, respectively. In addition, electrode material layer sheets 4 and 6 were manufactured by performing the same method as electrode compositions 11 and 15 for manufacturing dry electrodes, except that the roll temperature of the calendar device was heated to 70°C.

3. Rolling stage

Electrode material layer sheets 1 to 6 were each pressed and attached to a primer layer (1 micron thick) of an aluminum electrode plate (12 microns thick), and passed through a rolling roll to manufacture positive electrode plates 1 to 6 (pressing pressure: 8 kgf/cm ² ). The capacity per unit area of these positive electrode plates 1 to 6 was adjusted to be approximately 4.0-4.5 mAh/cm ² .

Example 22

A positive electrode plate 7 was manufactured by performing the same method as Example 17, except that the aluminum electrode plate on which the primer layer was formed was heated at 150°C for about 3 seconds in the rolling step to preheat the primer layer and then the electrode material layer sheet 2 was attached.

Examples 23 to 29

Coin cells (CR2032 type) 1 to 7 of half-cell structure were manufactured using the manufactured positive electrode plates 1 to 7, respectively. At this time, lithium metal foil was used as the counter electrode, and the electrolyte was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 30/50/20, to which 5% fluoroethylene carbonate (FEC) was mixed, and then 1.15 mol of LiPF6 was dissolved to use as the electrolyte. The coin cells were manufactured according to the conventional half-cell structure coin cell manufacturing method in a glove box filled with argon gas.

Experimental Example 1

The manufacturing of dry electrodes by the calendering method is a method in which the electrode composition passes between calender rolls, thereby creating a dry electrode surface and controlling its thickness by adjusting the gap between the rolls. Therefore, if the electrode surface is not formed when passing between the first two rolls, the manufacturing of dry electrode surfaces by the calendering method is virtually impossible. Therefore, it is essential to ensure that the electrode composition is formed on the dry electrode surface as it passes through the calender rolls.

The evaluation of the surface forming ability of dry electrodes, i.e., the ease of manufacturing dry electrode sheets, was performed as follows. Except for the comparative electrode composition 2 obtained in comparative example 2, the electrode compositions 1 to 15 for manufacturing dry electrodes obtained in the above-described examples 1 to 15 and the comparative electrode compositions 1, 3 to 8 manufactured in comparative examples 1 and 3 to 8 were placed between the first two rolls of a calender without any separate pretreatment such as a kneading/grinding process and passed at a speed of ~3 meters per minute (~10 rpm) to evaluate whether an electrode surface (i.e., an electrode material layer sheet) of a certain thickness was formed, and the results are shown in Table 4. At this time, if an electrode surface of a certain thickness was formed well without crumbling, the surface forming ability was judged as good (“good”). If an electrode surface was not formed in the same process but crumbled and fell off, it was judged as defective (“bad”). If an electrode surface was formed but easily broke even with a weak impact, it was judged as average (“normal”).

division Roll temperature Kneading/grinding Surface forming power Example 1 Room temperature × well Example 2 Room temperature × well Example 3 Room temperature × well Example 4 Room temperature × well Example 5 Room temperature × commonly Example 6 Room temperature × well Example 7 Room temperature × well Example 8 Room temperature × well Example 9 Room temperature × well Example 10 Room temperature × well Example 11 Room temperature × well Example 12 Room temperature × well Example 13 Room temperature × well Example 14 Room temperature × well Example 15 70℃ × well Comparative Example 1 Room temperature × bad Comparative Example 2 Room temperature ○ well Comparative Example 3 Room temperature × bad Comparative Example 4 Room temperature × well Comparative Example 5 100℃ × bad Comparative Example 6 Room temperature × bad Comparative Example 7 Room temperature × bad Comparative Example 8 Room temperature × bad

From Table 4, it can be seen that the electrode composition for manufacturing a dry electrode manufactured according to an embodiment of the present invention has good planarization ability by including a planarizing agent even without kneading/grinding (see FIG. 1: an actual photograph of a dry electrode material layer sheet obtained by calendering the electrode composition of Example 8 (planarizing agent: untreated multi-walled carbon nanotubes). In the case of Comparative Examples 1 and 2 containing only PTFE as a binder, it can be seen that Comparative Example 2, which performed the kneading/grinding process in the same manner as the conventional method, formed an electrode surface and thus had good planarization ability, but Comparative Example 1, which did not perform the kneading/grinding process, had poor planarization ability because no electrode surface was formed. On the other hand, it can be seen that Comparative Example 4 had excellent planarization ability because an electrode surface was formed by including 2 wt% of the planarizing agent of the present invention even without performing the kneading/grinding process. Meanwhile, Comparative Example 3 is not a simple blend but a core-shell structure composite binder composed of PTFE:PAEM at a ratio of 50:50, and since it does not include a planarizing agent, it was found that even if the kneading/grinding process was performed as in Comparative Example 2, the electrode surface was not formed, resulting in poor planarizing ability. From Comparative Example 5, it was found that even if the kneading/grinding process was not performed and a planarizing agent was included, if the content of the planarizing agent was low, the planarizing ability was poor even when the calendar roll was heated. In addition, the results of Comparative Examples 6 to 8 show that even if a surface-forming agent is included in an appropriate amount, both a simple dry blend binder and a core-shell structured composite binder have poor surface-forming ability if the PTFE content in the binder is too low. From the results in Table 4, when the surface-forming agent of the present invention is used, (1) when PTFE alone is used, a dry electrode is well formed even at room temperature, (2) however, when PTFE is mixed and used with another binder, the surface-forming ability is rapidly reduced, (3) in this case, it can be confirmed that a dry electrode can be manufactured without difficulty even by a simple calendering method without a pretreatment step by using 1.0 wt% or more of the surface-forming agent and 2.0 wt% or more of the composite binder in parallel and, if necessary, a method of heating the calender roll, or by mixing one or more binders with PTFE as in Example 12.

In addition, it was confirmed that electrode surfaces were well formed even at room temperature through calendaring of electrode compositions 13 and 14 for manufacturing dry electrodes containing non-carbon nanomaterials (boron nitride nanotubes (Example 13), aramid nanofibers (Example 14)) as surface-forming agents (see Fig. 2: an actual photograph of a dry electrode material layer sheet obtained by calendaring the electrode composition of Example 13 (surface-forming agent: boron nitride nanotubes). Therefore, it can be seen that boron nitride nanotubes, which are nanomaterials having a shape similar to carbon nanotubes, or aramid nanofibers, which are polymers, can also be used as surface-forming agents, and nanomaterials having a shape similar to nanotubes, nanoribbons, nanofibers, or the like can be used as surface-forming agents for manufacturing dry electrode surfaces.

However, the surface resistance of the dry electrode surface itself manufactured using boron nitride nanotubes or aramid nanofibers is more than 10 ⁷ ohm/area, which is much higher than the surface resistance when carbon nanotubes are used as a surface former (Fig. 1: surface resistance: less than 10 ² ohm/area). This is because these nanomaterials themselves are nanomaterials with no electrical conductivity. Therefore, when boron nitride nanotubes or aramid nanofibers are used as a surface former, there is a disadvantage in that a conductive additive must be used separately. Therefore, it can be seen that it is much more effective to use carbon-based nanomaterials, such as carbon nanotubes, which have electrical conductivity in themselves, as a surface former.

In addition, it was confirmed that the carbon nanotubes, which are the carbon-based sheet-forming agents of the present invention, can be used to produce dry electrode sheets even when as-received multi-walled carbon nanotubes are used. This is because the intention of using carbon nanotubes in the present invention is not to improve the adhesion with other components of the electrode composition, but to utilize the characteristic of carbon nanotubes to be entangled with each other in a normal state due to their high aspect ratio. As a result, the present invention has a configuration in which a small amount of carbon nanotubes is added while significantly reducing the PTFE content, so that the active material and the binder are entangled with the carbon nanotubes, and accordingly, all components are entangled even by a simple calendaring method without a kneading/pulverizing process, so that an electrode material layer sheet is easily produced. Accordingly, the carbon nanotubes included in the present invention can sufficiently function as a surface forming agent even when they are untreated carbon nanotubes without separate surface treatment to improve adhesiveness, which can ultimately be said to be an economically very advantageous method for manufacturing dry electrode sheets and secondary batteries including the same.

In addition, comparing the results of Comparative Examples 6 and 7 and Examples 5 and 7, it can be seen that when a core-shell structured composite binder is used rather than a simple dry blend binder, a dry electrode is well formed even when about 80% of the PTFE is replaced with another adhesive binder. In the case of adhesive binders, the adhesiveness may differ depending on the binder, and it can also be seen that a core-shell structured composite binder using an acrylonitrile-ethylene glycol-maleic acid copolymer is more effective than polyvinylidene fluoride. Meanwhile, in the case of the same content of surface forming agent, it can be seen that when the content of PTFE is high in the ratio of the core and shell materials of the composite binder, that is, the ratio of PTFE and adhesive binder, the surface forming ability is better.

Experimental Example 2

In order to determine whether the temperature of the calendar roll during calendaring affects the surface forming ability and adhesive strength, calendaring was performed at different temperatures of the calendar roll for the electrode compositions 5 and 11 for dry electrode manufacturing manufactured in Examples 5 and 11 and the comparative electrode composition 8 manufactured in Comparative Example 8, and the surface forming ability and adhesive strength were evaluated. The results are shown in Table 5. Here, the adhesive strength refers to the degree to which the electrode layer is transferred to the tape when it is attached and removed with Scotch tape. Weak: A lot is transferred, Strong: A little is transferred.

Roll temperature (℃) Surface forming power Adhesion Electrode composition for manufacturing dry electrodes 5 70 well strength Electrode composition for manufacturing dry electrodes 11 70 well strength Comparative example electrode composition 8 100 well strength Electrode composition for manufacturing dry electrodes 5 40 commonly weakness

From Table 5, it can be confirmed that the electrode composition 5 has a better surface forming ability at 70°C than at 40°C. In addition, the comparative electrode composition 8 also showed poor surface forming ability when calendered at room temperature, but it can be confirmed that the dry electrode surface is good when the calender roll temperature is increased to 100°C. From this, it can be seen that the temperature of the calender roll is one of the very important factors during calendering. In particular, from the result that the surface forming ability of the electrode composition 5 for manufacturing a dry electrode obtained in Example 5 improved as the temperature of the calender roll increased from room temperature, 40°C, and 70°C during calendering, it can be seen that increasing the temperature of the calender roll during calendering is more effective in manufacturing a dry electrode surface, i.e., an electrode material layer sheet. Meanwhile, when an electrode composition using 0.5 wt% of carbon nanotubes for the surface coating of an active material and 1.0 wt% as a surface forming agent as in Example 15 was calendered at a roll temperature of 100°C or lower, both the surface forming ability and the adhesive strength were good. From this result, it is shown that when a portion of the carbon nanotubes is used for the surface coating of an active material, the carbon nanotubes used for the surface coating of the active material also help in the surface forming of the dry electrode surface.

Experimental Example 3

The adhesiveness, including the degree to which the dry electrode is attached to the aluminum plate and the cohesion of each component within the dry electrode, was evaluated for the positive electrodes 1 to 7 manufactured in Examples 16 to 22. To confirm the adhesiveness of the electrode layer, an adhesive test was performed using Scotch tape (3M Scotch Tape). If the electrode layer was not completely peeled off from the plate when the tape was attached and then peeled off on the electrode layer, the adhesion of the electrode to the plate was judged to be good. In addition, the cohesion between each component within the electrode was judged as “strong,” “average,” and “weak” based on the amount/slight amount of electrode layer material that was transferred to the tape when peeling the tape. This evaluation method is subjective and qualitative, but it is a method that can quickly evaluate adhesiveness.

As a result of the adhesive test, positive electrodes 1 to 6 were well adhered without peeling off from the aluminum electrode plate. In addition, it was observed that the amount of electrode layer material transferred to the tape was small, which confirmed that it exhibited relatively good bonding strength. As a result, it was determined that the adhesiveness of the dry electrode manufactured using the surface forming agent of the present invention was good. In addition, positive electrode plate 7 was manufactured by attaching a dry electrode to an aluminum electrode plate on which a primer layer was preheated, and as a result of the tape test, the electrode layer was well attached with almost no peeling off, and the bonding strength of the dry electrode layer was confirmed to be better than that of positive electrode plates 1 to 6. As a result, it can be seen that by preheating the primer layer and attaching the electrode material layer sheet, a dry electrode having more solid adhesive strength and bonding strength can be manufactured.

Experimental Example 4

Among the positive electrodes 1 to 7, the cross-section of positive electrode plate 2 was observed using an electron microscope, and the resulting photograph is shown in Fig. 3.

In Fig. 3, it can be seen that a clean electrode layer with few pores has been formed.

In this way, it can be seen that the dry electrode manufactured by rolling the electrode composition for manufacturing the dry electrode of the present invention, which is manufactured by calendering without pretreatment to manufacture an electrode material layer sheet, exhibits very excellent characteristics.

Experimental Example 5

The electrical conductivity of the positive electrode plates 1 to 7 was confirmed by measuring the surface resistance (measuring device: Mitsubishi Corporation, 4-point probe method, measuring tip shape: flat), and the results are shown in Table 6.

Surface resistance (ohm/area) Positive electrode plate 1 10 ¹ Positive electrode plate 2 10 ¹ Positive electrode plate 3 10 ¹ Positive electrode plate 4 10 ¹ Positive electrode plate 5 10 ¹ Positive electrode plate 6 10 ¹ Positive electrode plate 7 10 ¹

As a result of the surface resistance experiment, as shown in Table 6, since all of the positive electrodes 1 to 7 used carbon nanotubes in an amount of 1.5 wt% or more, the surface resistance of the dry electrode surface was measured to be several tens of ohms/area, that is, 10 ¹ ohms/area, showing very good surface resistance. In particular, in the case of positive electrode plate 6, which is an example in which some carbon nanotubes were first coated on the surface of the active material, it showed a lower surface resistance than the other positive electrode plates.

Experimental Example 6

First, EIS (electrochemical impedance spectroscopy) was performed on coin cell 2 including positive electrode plate 2, and the results are shown in Fig. 4. From Fig. 4, it can be confirmed that all types of resistance were measured to be on the order of tens of ohms.

In order to determine the electric capacity characteristics of the coin cells 1 to 7 manufactured in Examples 23 to 29, a charge/discharge cycle test was conducted, and the results, particularly those of coin cell 2 including positive electrode plate 2, are shown in Fig. 5.

The charge/discharge cycle test was initially performed at rates of 0.1, 0.1, and 0.33C, followed by a charge/discharge life test at a rate of 1.0C. In the charge/discharge cycle test of the present invention, the discharge capacity after 4 cycles was considered the initial capacity, and the capacity retention rate (%) was calculated by comparing these initial capacities with the discharge capacity after 50 cycles.

As shown in Fig. 5, the initial capacity was 186 mAh/g, and after 50 cycles, the capacity was 173 mAh/g, showing a capacity retention rate of approximately 93%, confirming excellent characteristics.

Although not shown, the charge/discharge life test results of the remaining coin cells (coin cells 1, 3-7) all showed an initial capacity of 183-187 mAh/g, a discharge capacity after 50 cycles of 170-174 mAh/g, and a capacity retention rate of 91-95%. In particular, the capacity retention rate was as high as approximately 96% for the positive electrode plate 6 and coin cell 6 manufactured with an active material obtained by pre-coating some of the carbon nanotubes on the surface of the active material. This is thought to be because the surface resistance of the positive electrode plate 6 including the carbon nanotubes, which have good electrical conductivity, is lower than that of the other positive electrode plates because they are uniformly coated on the surface of the active material.

From the experimental results described above, when a dry electrode is manufactured using an electrode composition for manufacturing a dry electrode including a planarizing agent, a significant amount of PTFE, a fluorinated resin binder that exhibits poor adhesiveness and severe attenuation of electric capacity, can be replaced with a binder that has good adhesiveness and electrochemical properties, thereby preparing an electrode composition with a minimized PTFE content, and it was confirmed that a dry electrode can be manufactured well even if the prepared electrode composition is calendered as is without any pretreatment such as kneading/pulverizing. In this way, the present invention improves the planarizing ability of the dry electrode to the extent that the calendering process can be performed directly without performing the kneading process and the pulverizing process, which are pretreatment steps for fiberization, on the prepared electrode composition by replacing the PTFE, a fiberizing polymer that had to be used at 100 wt% in the prior art, with another binder. In particular, when PTFE is contained in an amount of 15 wt% or more of the total weight of the binder, room temperature calendering is sufficiently effective, but when the PTFE content is low, less than 15 wt%, it was confirmed that high temperature calendering using a method of applying pressure while heating the calender roll is more effective.

Among the surface forming agents used in the electrode composition for manufacturing a dry electrode of the present invention, carbon-based nanomaterials including carbon nanotubes are nanomaterials with high electrical conductivity, so when carbon-based nanomaterials, especially carbon nanotubes, are used as a surface forming agent, the electrical conductivity of the dry electrode is excellent without using a separate conductive additive, so it can be much more effective than other types of surface forming agents.

In addition, in the electrode composition for manufacturing a dry electrode of the present invention, it is more effective to use a binder made in the form of a composite binder with a core-shell structure rather than a method of simply dry blending different binders in the other adhesive binder resin used in parallel with PTFE, as this can expand the range of PTFE substitution.

Meanwhile, as described above, the present invention has been described using two types of binders, including polyvinylidene fluoride and acrylonitrile-ethylene glycol-maleic acid copolymer, as adhesive binders. However, the scope of the present invention is not limited to the two binders, and it is clear that the better the adhesiveness of a binder, the more effective it is.

Although the present invention has been illustrated and described with reference to preferred embodiments as described above, it is not limited to the above embodiments, and various changes and modifications may be made by a person having ordinary skill in the art to which the invention pertains within a scope that does not depart from the spirit of the present invention.

Claims (31)

An electrode composition for manufacturing a dry electrode, comprising 90-98 wt% of an active material, 1.0-5 wt% of a binder, and 1.0-5 wt% of a surface-forming agent. In the first paragraph, An electrode composition for manufacturing a dry electrode, characterized in that the above-mentioned surface forming agent is a nanomaterial having at least one shape selected from the group consisting of a tube shape, a ribbon shape, and a fiber shape. In the second paragraph, An electrode composition for manufacturing a dry electrode, characterized in that the surface forming agent is at least one carbon-based nanomaterial selected from the group consisting of single-wall carbon nanotubes, double-wall carbon nanotubes, multi-wall carbon nanotubes, few-wall carbon nanotubes, branched carbon nanotubes, carbon nanoribbons, and carbon nanofibers, or at least one non-carbon-based nanomaterial selected from the group consisting of boron nitride nanotubes, boron nitride nanoribbons, and aramid nanofibers. In the third paragraph, An electrode composition for a dry electrode, characterized in that the above-mentioned surface forming agent is a carbon nanotube formed in the form of a lump or bundle having a size of 0.2-50 microns. In paragraph 4, An electrode composition for manufacturing a dry electrode, characterized in that the above carbon nanotube has an aspect ratio of 100 or more. In the first paragraph, The above active material is an electrode composition for manufacturing a dry electrode, characterized in that a coating layer composed of carbon nanomaterials is formed on the surface. In the first paragraph, An electrode composition for manufacturing a dry electrode, characterized in that the binder comprises a fluorine-based resin capable of fiberization and another binder resin. In paragraph 7, An electrode composition for manufacturing a dry electrode, characterized in that the above-mentioned fiberizable fluorine-based resin is polytetrafluoroethylene (PTFE). In paragraph 7, An electrode composition for manufacturing a dry electrode, characterized in that the binder is a core-shell structure composite binder formed by a simple mixture of the fiberizable fluorine-based resin and another binder resin or a core made of the fiberizable fluorine-based resin and a shell made of another binder resin surrounding the core. In paragraph 7, The above other binder resin is at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer; or An electrode composition for manufacturing a dry electrode, characterized in that it is a copolymer comprising at least one selected from the group consisting of an acrylonitrile-based monomer, a carboxyl-based monomer, and a glycol-based monomer. In paragraph 10, An electrode composition for manufacturing a dry electrode, characterized in that the above carboxylic monomer is at least one selected from the group consisting of acrylic acid, acrylate, maleic acid, and maleic anhydride. In paragraph 10, An electrode composition for manufacturing a dry electrode, characterized in that the above-mentioned other binder resin is an acrylonitrile-ethylene glycol-maleic acid copolymer. In any one of paragraphs 7 to 12, An electrode composition for manufacturing a dry electrode, characterized in that the content of the fiberizable fluorine resin included in the binder is 80% by weight or less of the total weight of the binder. In paragraph 13, An electrode composition for manufacturing a dry electrode, characterized in that the content of the fiberizable fluorine resin included in the binder is 50% by weight or less of the total weight of the binder. In any one of claims 1 to 12, An electrode composition for manufacturing a dry electrode, characterized in that it further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates per 100 parts by weight of the surface-forming agent. A step of preparing an electrode composition for manufacturing a dry electrode by stirring and mixing an active material, a binder, and a surface forming agent; A calendering step for manufacturing an electrode material layer sheet by calendering the above electrode composition; and A dry electrode manufacturing method comprising a rolling step of attaching the electrode material layer sheet to a support film or metal electrode plate and then rolling it. In paragraph 16, A dry electrode manufacturing method characterized in that the above-mentioned calendaring step and the above-mentioned rolling step are performed continuously on the same line. In paragraph 16, A dry electrode manufacturing method characterized in that the calendaring roll is heated to 50°C to 200°C when performing the above calendaring. In paragraph 16, A method for manufacturing a dry electrode, characterized in that the electrode composition for manufacturing a dry electrode is an electrode composition for manufacturing a dry electrode according to any one of claims 1 to 12. In paragraph 19, A dry electrode manufacturing method, characterized in that the content of a fiberizable fluorine resin included in the binder in the electrode composition for manufacturing the dry electrode is 50% by weight or less of the total weight of the binder. In paragraph 19, A method for manufacturing a dry electrode, characterized in that the electrode composition for manufacturing the dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplates, or graphene nanoplates per 100 parts by weight of a surface-forming agent. A stirring device for stirring and mixing an electrode composition for manufacturing a dry electrode, which includes an active material, a binder, and a surface forming agent; A calendar device for forming the above stirred and mixed electrode composition into an electrode material layer sheet; and A dry electrode manufacturing device comprising a rolling device that attaches and presses the electrode material layer sheet by positioning it on at least one surface of a support film or a metal electrode plate. In paragraph 22, A dry electrode manufacturing device characterized in that the above calendar device is set to a heating condition of 50°C to 200°C. In paragraph 22, A dry electrode manufacturing device characterized in that the above calendar device and the above rolling device are located on the same line. In paragraph 22, A dry electrode manufacturing device, characterized in that the electrode composition for manufacturing a dry electrode is an electrode composition for manufacturing a dry electrode according to any one of claims 1 to 12. In paragraph 22, A dry electrode manufacturing device, characterized in that the content of a fiberizable fluorine resin included in the binder in the electrode composition for manufacturing the dry electrode is 80% by weight or less of the total weight of the binder. In paragraph 22, A dry electrode manufacturing device characterized in that the electrode composition for manufacturing the dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplate, or graphene nanoplate per 100 parts by weight of the surface forming agent. A dry electrode comprising an electrode composition for manufacturing a dry electrode according to any one of claims 1 to 12. In paragraph 28, A dry electrode, characterized in that the content of a fluorine-based resin capable of fiberization included in the binder in the electrode composition for manufacturing the dry electrode is 80% by weight or less of the total weight of the binder. In paragraph 28, A dry electrode, characterized in that the electrode composition for manufacturing the above dry electrode further comprises 1 to 100 parts by weight of at least one selected from the group consisting of conductive carbon black, graphene, carbon nanoplate, or graphene nanoplate per 100 parts by weight of the surface forming agent. A secondary battery comprising a dry electrode according to claim 28.