KR102520396B1 - Method for manufacturing positive electrode - Google Patents

Abstract

The present invention comprises the steps of dry mixing a cathode active material, a conductive material, and a binder to prepare a mixture; disposing the mixture on a current collector; and forming a cathode active material layer by rolling the current collector on which the mixture is disposed through a roll press method, wherein the binder is polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, and poly It relates to a method for manufacturing a cathode comprising at least one of tetrafluoroethylene and having a temperature of a roll used in the roll press method of 70° C. to 120° C.

Description

Manufacturing method of anode {METHOD FOR MANUFACTURING POSITIVE ELECTRODE}

The present invention relates to a method for manufacturing a positive electrode, and specifically, the method for manufacturing a positive electrode includes preparing a mixture by dry mixing a positive electrode active material, a conductive material, and a binder; disposing the mixture on a current collector; and forming a cathode active material layer by rolling the current collector on which the mixture is disposed through a roll press method, wherein the binder is polyvinylidene fluoride homopolymer (PVdF homopolymer), polyvinylidene fluoride-hexafluoro It includes at least one of polypropylene (PVdF-HFP) and polytetrafluoroethylene (PTFE), and the temperature of the roll used in the roll press may be 70 ° C to 120 ° C.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing, and as part of this, the most actively researched fields are power generation and storage using electrochemical reactions.

Currently, a secondary battery is a representative example of an electrochemical device using such electrochemical energy, and its use area is gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, mobile phones, and cameras increase, the demand for secondary batteries as an energy source is rapidly increasing. A lot of research has been done on it, and it is also commercialized and widely used.

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the positive electrode may include a positive electrode active material, a conductive material, and a binder.

A conventionally used cathode manufacturing method is a wet method using a solvent. Specifically, a typical wet method is to prepare a positive electrode slurry by adding a positive electrode active material, a conductive material, and a binder to a solvent and then mixing them to prepare a positive electrode slurry, and then coating the slurry on a current collector and drying the positive electrode slurry.

However, these existing attempts have a problem in that there are upper limits on the contents of the binder and the conductive material that can be added to the solvent and the upper limit on the solid content of the prepared positive electrode slurry when considering the viscosity suitable for the manufacturing process of the positive electrode.

In addition, when a positive electrode is manufactured using a positive electrode slurry using a solvent, the positive electrode slurry applied on the current collector must be dried to remove the solvent. In this process, the thickness of the positive electrode active material layer decreases, and it is difficult to manufacture a positive electrode active material layer having a uniform thickness.

In order to solve these problems, a method of manufacturing a positive active material layer by mixing a positive active material, a conductive material, and a binder in a dry state without using the solvent has been considered. However, when the above method is used, when the loading amount of the positive electrode active material layer is high, there is a problem in that the adhesive strength of the electrode is significantly lowered, so it is difficult to apply the above method.

Therefore, there is a need for a method for manufacturing a positive electrode that enables a positive electrode manufactured by a dry method without using a solvent to have sufficient electrode adhesive strength while including a high loading amount of the positive electrode active material layer.

One problem to be solved by the present invention is to provide a method for manufacturing a positive electrode in which a positive electrode manufactured by a dry method without using a solvent can have sufficient adhesion of the positive electrode active material layer while including a positive electrode active material layer having a high loading amount. .

According to one embodiment of the present invention, dry mixing a cathode active material, a conductive material, and a binder to prepare a mixture; disposing the mixture on a current collector; and forming a cathode active material layer by rolling the current collector on which the mixture is disposed through a roll press method, wherein the binder is polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, and poly A method for producing a cathode comprising at least one of tetrafluoroethylene and having a temperature of a roll used in the roll press method is 70° C. to 120° C. is provided.

According to the positive electrode manufacturing method according to an embodiment of the present invention, while using a dry method without using a solvent, a dry mixture for a positive electrode active material layer contains a specific binder, and the mixture is disposed through a roll at an appropriate temperature. Since the current collector is rolled, the prepared positive electrode active material layer can have a high loading amount and at the same time have sufficient adhesive strength (positive electrode adhesive strength) to the current collector.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

Terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, number, step, component, or combination thereof, but one or more other features or It should be understood that the presence or addition of numbers, steps, components, or combinations thereof is not precluded.

In this specification, the term "on" means a state in which another component exists on the surface of one component, and specifically includes both a state in contact with the surface of one component and a state in which it exists on the surface even if it does not come into contact with the surface. means that

A method of manufacturing a positive electrode according to an embodiment of the present invention includes preparing a mixture by dry mixing a positive electrode active material, a conductive material, and a binder; disposing the mixture on a current collector; and forming a cathode active material layer by rolling the current collector on which the mixture is disposed through a roll press method, wherein the binder is polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, and poly It contains at least one of tetrafluoroethylene, and the temperature of the roll used in the roll press method may be 70 °C to 120 °C.

In the step of preparing a mixture by dry mixing the cathode active material, the conductive material, and the binder, the dry mixing means mixing without a solvent. In other words, the dry mixing means mixing the cathode active material, the conductive material, and the binder without using a solvent. The solvent usually refers to a solvent used in preparing a cathode slurry, and may be, for example, water, N-methyl-2-pyrrolidone (NMP), or the like. The dry mixing may be performed by mixing at room temperature or lower at 600 rpm to 1800 rpm for 40 to 60 minutes using a stirring device.

The cathode active material may be a commonly used cathode active material. Specifically, the cathode active material may include layered compounds such as lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; lithium iron oxides such as LiFe ₃ O ₄ ; lithium manganese oxides such as Li _1+a1 Mn _2-a1 O ₄ (0≤a1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; LiNi _1-a2 M a2 O 2 including the _formula Li[Ni _0.6 Mn _0.2 Co _0.2 ] _{O 2} , Li[Ni _0.5 Mn _0.3 Co _0.2 ]O ₂ , etc., where M is Co, Mn, Al, Cu, Fe , Mg, at least one selected from the group consisting of B and Ga, and satisfies 0.01≤a2≤0.5) Ni site type lithium nickel oxide represented by; Formula LiMn _2-a3 M _a3 O ₂ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤a3≤0.1) or Li ₂ Mn ₃ MO ₈ (here, M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn.) Lithium manganese composite oxide represented by; It may be at least one selected from the group consisting of LiMn ₂ O ₄ in which a portion of Li in the formula is substituted with an alkaline earth metal ion. More specifically, the cathode active material may be at least one of Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ and Li[Ni _0.5 Mn _0.3 Co _0.2 ]O ₂ .

The conductive material may impart conductivity to the anode. The conductive material may be graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of them alone or a mixture of two or more may be used.

The binder may include at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, and polytetrafluoroethylene, and specifically, the polyvinylidene fluoride homopolymer, polyvinyl It may be made of at least one of leaden fluoride-hexafluoropropylene and polytetrafluoroethylene. The binder has a close relationship with the rolling process using a roll having a specific temperature of the present invention. Specifically, when a rolling process using a roll having a specific temperature of the present invention is applied while using the binder, the adhesive strength of the positive electrode active material layer can be improved, and cracks in the positive electrode active material layer can be suppressed. It can be. Here, the adhesive strength of the positive electrode active material layer means the adhesive strength between the positive electrode active material layer and the current collector.

The polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene may each be in the form of secondary particles in which primary particles are aggregated. The primary particle may have a particle diameter of 40 nm to 1000 nm, specifically 50 nm to 750 nm, and more specifically 100 nm to 500 nm. The size of the primary particles can be confirmed with a scanning electron microscope (SEM).

On the other hand, the average particle diameter (D ₅₀ ) of each of the polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene in the form of secondary particles may be 20 μm to 1000 μm, specifically 50 μm to 800 μm. It may be ㎛, and more specifically, it may be 100 ㎛ to 500 ㎛. When the above range is satisfied, the contact area of the binder contacting the cathode active material and the conductive material in the dry mixing process may be sufficient. Thereafter, when the positive electrode active material layer is formed by rolling with a roll at a specific temperature, the contact area within the positive electrode active material layer may be maintained at a desired level. Therefore, the adhesion of the positive electrode can be improved, and the resistance in the positive electrode active material layer can be uniform, so that the cycle characteristics of the battery can be improved. Meanwhile, in the present specification, the average particle diameter (D ₅₀ ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle diameter distribution curve of the particles. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle diameters of several millimeters in the submicron region, and can obtain results with high reproducibility and high resolution.

The polytetrafluoroethylene may be in the form of single particles rather than in the form of secondary particles. The average particle diameter (D ₅₀ ) of the polytetrafluoroethylene may be 0.2 mm to 3.0 mm, specifically 0.3 mm to 2.0 mm. When the above range is satisfied, the contact area of the binder contacting the cathode active material and the conductive material in the dry mixing process may be sufficient. Thereafter, when the positive electrode active material layer is formed by rolling with a roll at a specific temperature, the contact area within the positive electrode active material layer may be maintained at a desired level. Therefore, the adhesion of the positive electrode can be improved, and the resistance in the positive electrode active material layer can be uniform, so that the cycle characteristics of the battery can be improved.

The binder may be included in 0.5% by weight to 5.0% by weight based on the total weight of the mixture, specifically 1.0% by weight to 3.0% by weight, and more specifically 1.5% by weight to 2.0% by weight. . When the above range is satisfied, the positive electrode adhesive strength may be higher than that of the positive electrode manufactured by the wet method, and the positive electrode adhesive strength may be uniform within the positive electrode.

Prior to disposing the mixture on the current collector, applying a high shear force to the mixture may be performed. The applying of the high shear force may include applying a high shear force by shear-compressing the mixture. Specifically, when using a device for applying shear force, for example, Nobilta (Hosokawa micron company) or a twin screw extruder (Thermo KA company), the mixture is shear-compressed through a blade in the device to apply a high shear force can However, it is not necessarily limited to this method. When a high shear force is applied to the mixture, the binders in the mixture may become entangled with each other. Therefore, the positive electrode active material and the conductive material are supported by the binder, and bonding strength between the positive electrode active material, the conductive material, and the binder may increase. Accordingly, the process of disposing the mixture on the current collector is facilitated, and the adhesive strength of the prepared positive electrode active material layer can be further improved.

In the step of disposing the mixture on the current collector, the current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, sintering A surface treated with carbon, nickel, titanium, silver, or the like may be used on the surface of carbon or aluminum or stainless steel. In addition, the cathode current collector may have a thickness of typically 3 to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the current collector. The current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, non-woven material, etc., but is not limited thereto.

Disposing the mixture on the current collector may include disposing the mixture on the current collector in the following manner. Specifically, the mixture may be disposed with a uniform thickness on the current collector by a scattering method. More specifically, when using the scattering method, the mixture is moved through a feeding roller, and when the mixture is applied to the current collector, the mixture is applied in a quantity using a squeeze roll. can make it

The mixture is disposed on the current collector in a powder state, and is not disposed on the current collector after being prepared in a film state. Since the mixture may be disposed on the current collector in a powder state, contact between the current collector and the mixture may be increased compared to when the mixture is disposed in the form of a film, and thus, positive electrode adhesion may be further improved.

The mixture may be disposed on one side or both sides of the current collector. In order to arrange the mixture on both sides, the mixture may be applied to one surface of the current collector and then rolled to form a positive electrode active material layer on one surface, and then the mixture may be disposed on the other surface.

The mixture disposed on the current collector may be formed into a positive electrode active material layer through a rolling process. Specifically, the positive electrode active material layer may be formed by rolling the current collector on which the mixture is disposed, and the rolling may be performed by a roll press method.

In the roll press method, in a state in which two rolls are disposed above and below the current collector on which the mixture is disposed, pressure is applied to the current collector on which the mixture is disposed with the rolls, and at the same time, the current collector on which the mixture is disposed is horizontally Including moving in the direction

At this time, the temperature of the roll used in the roll press method may be 70 °C to 120 °C, specifically 75 °C to 100 °C, and more specifically 75 °C to 95 °C. The temperature of the roll is an optimum temperature considering that the binder is at least one of polyvinylidene fluoride-hexafluoropropylene and polytetrafluoroethylene. When the temperature of the roll is less than 70° C., the positive electrode active material layer is not smoothly adhered to the current collector because thermal melting of the binder does not occur properly. Conversely, when the temperature of the roll exceeds 120° C., the thermally melted binder becomes too hard after rolling, and thus the flexibility of the positive electrode is deteriorated, and thus cycle characteristics and safety of the battery may be deteriorated.

The loading amount of the positive electrode active material layer included in the positive electrode formed by this process may be 24 mg/cm ² or more, specifically 24 mg/cm ² to 80 mg/cm ² . A positive electrode active material layer prepared by a conventional wet process rather than the manufacturing method of the present invention generally has a loading amount of less than 24 mg/cm ² for good performance. However, according to the manufacturing method of the present invention, it is possible to manufacture a positive electrode including the positive electrode active material layer having a loading amount of 24 mg/cm ² or more. In addition, the capacity of the battery including the negative electrode may be improved based on the loading amount.

According to another embodiment of the present invention, it is similar to the manufacturing method of the positive electrode according to the above-described embodiment, but the manufacturing method of the positive electrode is applied to the surface of the current collector before the step of disposing the mixture on the current collector. A step of disposing a surface modification layer is further included, and the positive electrode active material layer is different in that it is disposed on the surface modification layer. Hereinafter, the above differences will be described.

The surface modification layer may be used to increase adhesion between the current collector and the cathode active material layer. In addition, the surface modification layer may enable the mixture in a powder state rather than a slurry state to be smoothly disposed on the current collector. Furthermore, during the roll press process, the surface modification layer does not move from the position where the mixture is disposed, so that the prepared positive electrode active material layer may have a more uniform thickness.

The surface modification layer may include at least one selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and carbon black, preferably may be styrene-butadiene rubber. When the surface modification layer includes the material, since the contact area between the mixture and the surface modification layer is large, anode adhesion may be further improved.

The surface modification layer may have a thickness of 1 μm to 10 μm, specifically 1 μm to 5 μm, and more specifically 1 μm to 2 μm. When the above range is satisfied, the anode adhesion may be sufficiently improved without an excessive increase in electrode thickness.

According to another embodiment of the present invention, a positive electrode manufactured by the method of manufacturing the positive electrode may be provided. Furthermore, according to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be a battery or a capacitor, and more specifically, a secondary battery.

The secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, the secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

In the secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. As an example, the negative electrode active material layer is formed by applying a composition for forming a negative electrode including a negative electrode active material, and optionally a binder and a conductive material on a negative electrode current collector and drying it, or by casting the composition for forming a negative electrode on a separate support, and then , It may be produced by laminating a film obtained by peeling from the support on a negative electrode current collector.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiO _x (0 < x < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one or a mixture of two or more of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is representative.

Also, the binder and the conductive material may be the same as those described in the foregoing positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement, and any separator used as a separator in a lithium secondary battery can be used without particular limitation, especially for the movement of ions in the electrolyte. It is preferable to have low resistance to the electrolyte and excellent ability to absorb the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single layer or multilayer structure.

In addition, the electrolyte used in the present invention includes an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a secondary battery. It is not.

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Among them, carbonate-based solvents are preferred, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high dielectric constant capable of increasing the charge and discharge performance of batteries, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

As the lithium salt, any compound capable of providing lithium ions used in a secondary battery may be used without particular limitation. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO _{4 , LiAlCl 4 ,} LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

The secondary battery may be used in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). Accordingly, according to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. The battery module or battery pack may include a power tool; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for one or more medium or large-sized devices among power storage systems.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the above embodiments are merely illustrative of the present description, and various changes and modifications are possible within the scope and spirit of the present description. It is obvious to those skilled in the art, Naturally, such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

Example 1: Preparation of positive electrode

Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ having an average particle diameter (D ₅₀ ) of 5 μm and 15 μm, respectively, was used as a cathode active material, and carbon black having an average particle diameter (D ₅₀ ) of 65 nm was used as a conductive material, PTFE in the form of single particles and having an average particle diameter (D ₅₀ ) of 1 mm was used as a binder.

The cathode active material, the conductive material, and the binder were mixed at a weight ratio of 96.5:1.5:2.0 at 1800 rpm for 25 minutes without a solvent using a Nobilta machine (Hosokawa Co.). Then, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa micron company)). Thereafter, the mixture was disposed on one surface of an aluminum current collector having a thickness of 15 μm using a scattering method to prepare a preliminary positive electrode. The preliminary positive electrode was placed on a belt of roll press equipment, and then, the positive electrode of Example 1 including a positive electrode active material layer was manufactured by rolling the preliminary positive electrode at a speed of 0.5 m/min using a roll at 75 ° C. . The loading amount of the positive electrode active material layer was 48 mg/cm ² .

Example 2: Preparation of positive electrode

The positive electrode of Example 2 was prepared in the same manner as in Example 1, except that PVdF-HFP having an average secondary particle diameter (D ₅₀ ) of 200 μm was used as a binder instead of the PTFE of Example 1. The loading amount of the positive electrode active material layer of the prepared positive electrode was 48 mg/cm ² .

Example 3: Preparation of positive electrode

The positive electrode of Example 3 was prepared in the same manner as in Example 1, except that PVdF homopolymer having an average secondary particle diameter (D ₅₀ ) of 200 μm was used as a binder instead of the PTFE of Example 1. The loading amount of the positive electrode active material layer of the prepared positive electrode was 48 mg/cm ² .

Example 4: Preparation of positive electrode

Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ having an average particle diameter (D ₅₀ ) of 5 μm and 15 μm, respectively, was used as a cathode active material, and carbon black having an average particle diameter (D ₅₀ ) of 65 nm was used as a conductive material, PVdF-HFP having an average secondary particle diameter (D ₅₀ ) of 200 μm was used as a binder.

A surface modification layer was formed by disposing SBR to a thickness of 2 μm by gravure coating on one surface of an aluminum current collector having a thickness of 15 μm.

Meanwhile, the cathode active material, the conductive material, and the binder were mixed at a weight ratio of 96.5:1.5:2 at 1800 rpm for 25 minutes without a solvent using a Nobilta machine (Hosokawa Co.). Then, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa micron company)). Thereafter, the mixture was disposed on the surface modification layer disposed on the current collector using a scattering method to prepare a preliminary positive electrode. The preliminary positive electrode was placed on a belt of roll press equipment, and then, the positive electrode of Example 4 including a positive electrode active material layer was manufactured by rolling the preliminary positive electrode at a speed of 0.5 m/min using a roll at 75 ° C. . The loading amount of the positive electrode active material layer was 48 mg/cm ² .

Comparative Example 1: Preparation of positive electrode

A positive electrode of Comparative Example 1 was prepared in the same manner as in Example 1, except that the roll temperature was 50 °C instead of 75 °C.

Comparative Example 2: Preparation of positive electrode

A positive electrode of Comparative Example 2 was prepared in the same manner as in Example 1, except that the roll temperature was 150 °C instead of 75 °C.

Comparative Example 3: Preparation of positive electrode

A positive electrode of Comparative Example 3 was prepared in the same manner as in Example 2, except that the roll temperature was 50 °C instead of 75 °C.

Comparative Example 4: Preparation of positive electrode

A positive electrode of Comparative Example 4 was prepared in the same manner as in Example 2, except that the roll temperature was 200 °C instead of 75 °C.

Comparative Example 5: Preparation of positive electrode

Li[Ni _0.6 Mn _0.2 Co _0.2 ]O ₂ having an average particle diameter (D ₅₀ ) of 5 μm and 15 μm, respectively, was used as a cathode active material, and carbon black having an average particle diameter (D ₅₀ ) of 65 nm was used as a conductive material, PVdF-HFP having an average secondary particle diameter (D ₅₀ ) of 200 μm was used as a binder.

The cathode active material, the conductive material, and the binder were mixed at a weight ratio of 96.5:1.5:2.0 at 1800 rpm for 25 minutes without a solvent using a Nobilta machine (Hosokawa Co.). Then, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa micron company)). Thereafter, a preliminary film having a thickness of 1000 μm was prepared using the mixture using a 2-roll press, and a film having a thickness of 500 μm was prepared using a 2-roll press. The loading amount of the film was 48 mg/cm ² .

Meanwhile, a surface modification layer was formed by disposing SBR to a thickness of 2 μm by gravure coating on one surface of an aluminum current collector having a thickness of 15 μm.

After placing the prepared film on the surface modification layer, it was rolled at a speed of 0.5 m/min using a roll at 75° C. to prepare a positive electrode of Comparative Example 5.

Comparative Example 6: Preparation of positive electrode

A positive electrode of Comparative Example 6 was prepared in the same manner as in Comparative Example 5, except that the roll temperature was 23 °C instead of 75 °C.

Experimental Example 1: Evaluation of Anode Adhesion

For each of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 6, the positive electrode was punched out to a size of 20 mm × 150 mm and fixed to the center of a 25 mm × 75 mm slide glass using tape, and then the current collector was peeled off using UTM. The 90 degree peel strength was measured. The evaluation was determined as an average value by measuring 5 or more peeling strengths. This is shown in Table 1 below.

Experimental Example 2: Anode Crack Evaluation

For each of the anodes of Examples 1 to 4 and Comparative Examples 1 to 6, the anode was punched out to a size of 20 mm × 150 mm, wound around a rod with a diameter of 10 mm, and whether or not cracks occurred (fail when not occurring, when not occurring). pass). Specifically, experiments were conducted 5 times for each of the Examples and Comparative Examples to evaluate whether or not cracks occurred.

Loading amount of positive electrode active material layer (mg/cm ² ) Anode adhesion (gf/15mm) Anode crack occurrence Example 1 48 12 Pass Example 2 48 24 Pass Example 3 48 22 Pass Example 4 48 32 Pass Comparative Example 1 48 9 Pass Comparative Example 2 48 11 Fail Comparative Example 3 48 10 Pass Comparative Example 4 48 13 Fail Comparative Example 5 48 9 Pass Comparative Example 6 48 3 Pass

Referring to Table 1, in the case of Examples 1 to 4 in which the roll temperature satisfies the temperature range of the present invention, Comparative Example 1 in which the roll temperature does not satisfy the above range (ex. 50 ° C, 150 ° C, 200 ° C) It can be seen that the anode adhesion is far superior to that of 4 to 4. In addition, in the case of Comparative Examples 2 and 4 to which the roll temperature of 150 ° C. or 200 ° C. was applied, it was confirmed that the flexibility of the positive active material layer was excessively reduced and cracks occurred.

On the other hand, unlike the present invention in which the dried mixture (powder form) was placed on the current collector and then rolled, Comparative Examples 5 and 6, in which the mixture was prepared as a film and placed on the current collector, showed poor positive electrode adhesion. there is.

Furthermore, referring to Examples 2 and 4, it can be confirmed that the positive electrode adhesive strength can be further improved in the case of the positive electrode to which the surface modification layer is introduced.

Claims (9)

Preparing a mixture by dry mixing a cathode active material, a conductive material, and a binder;
applying a shear force to the mixture;
disposing the mixture on a current collector using a scattering method; and
Forming a positive electrode active material layer by rolling the current collector on which the mixture is disposed through a roll press method,
The dry mixing is to mix the cathode active material, the conductive material, and the binder without using a solvent,
The binder includes at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene and polytetrafluoroethylene,
The method of manufacturing a positive electrode wherein the temperature of the roll used in the roll press method is 70 ° C to 120 ° C.
The method of claim 1,
The method of manufacturing a positive electrode wherein the temperature of the roll is 75 ° C to 100 ° C.
The method of claim 1,
The binder is a method of manufacturing a positive electrode included in 0.5% to 5.0% by weight based on the total weight of the mixture.
The method of claim 1,
In the step of preparing a mixture by dry mixing the cathode active material, the conductive material, and the binder,
The polyvinylidene fluoride homopolymer and polyvinylidene fluoride-hexafluoropropylene are in the form of secondary particles in which primary particles are aggregated, respectively,
The average particle diameter (D ₅₀ ) of the secondary particles is a method for producing a positive electrode of 20 μm to 1000 μm.
The method of claim 1,
In the step of preparing a mixture by dry mixing the cathode active material, the conductive material, and the binder,
The polytetrafluoroethylene is in the form of single particles,
The average particle diameter (D ₅₀ ) of the polytetrafluoroethylene is a method for producing a positive electrode of 0.2 mm to 3.0 mm.
The method of claim 1,
The method of manufacturing a positive electrode wherein the loading amount of the positive electrode active material layer is 24 mg / cm ² or more.
The method of claim 1,
Prior to disposing the mixture on the current collector,
Further comprising disposing a surface modification layer on the surface of the current collector,
The positive electrode active material layer is disposed on the surface modification layer,
The method of claim 1 , wherein the surface modification layer includes at least one selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, and carbon black.
The method of claim 7,
The thickness of the surface modification layer is 1㎛ to 10㎛ manufacturing method of the anode.
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