WO2018199702A1 - Cathode, secondary battery comprising same, and method for manufacturing same cathode - Google Patents

Abstract

The present invention relates to a method for manufacturing a cathode, the method comprising the steps of: dry-mixing a cathode active material, a dry conductive material, and a dry binder to prepare a mixture; applying a high shear force to the mixture; arranging the mixture on a current collector; and rolling the current collector on which the mixture has been arranged, wherein the dry conductive material is at least one of a carbon nanotube and a carbon fiber, and the high shear force ranges from 50N to 1000N.

Description

A positive electrode, a secondary battery comprising the same, and a method of manufacturing the positive electrode

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0055638, filed April 28, 2017 and Korean Patent Application No. 10-2018-0049220, filed April 27, 2018, and All content disclosed in the literature of a Korean patent application is included as part of this specification.

Field of technology

The present invention relates to a positive electrode, a secondary battery including the same, and a method of manufacturing the positive electrode, and specifically, the method of manufacturing the positive electrode includes: preparing a mixture by dry mixing a positive electrode active material, a dry conductive material, and a dry binder; Applying a high shear force to the mixture; Disposing the mixture on a current collector; And rolling the current collector on which the mixture is disposed, wherein the dry conductive material is at least one of carbon nanotubes and carbon fibers, and the high shear force may be 50N to 1000N.

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 the most actively researched fields are power generation and storage using electrochemical reactions.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing. Recently, as the development and demand of portable devices such as portable computers, portable telephones, cameras, and the like, the demand for secondary batteries is rapidly increasing, and among such secondary batteries, high energy density, that is, high capacity lithium secondary batteries Much research has been done on the market and commercialized and widely used.

Generally, 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 and a conductive material. The conductive material may serve to decrease the resistance by increasing the electrical conductivity of the positive electrode.

On the other hand, during the charge and discharge of the secondary battery, the positive electrode repeats expansion and contraction, and the problem that the positive electrode structure collapses as the cycle continues. Thus, there are attempts to reduce the anode volume change in various ways. Japanese Laid-Open Patent Publication No. 2015-220225 discloses using carbon nanotubes as the conductive material to reduce the volume change of the positive electrode by combining the positive electrode active material and the conductive material.

However, all of these existing attempts have been made for the production of a positive electrode slurry using a solvent, and the positive electrode produced through the positive electrode slurry. Therefore, when considering the viscosity and the like suitable for the production process of the positive electrode, there is a problem that the upper limit of the content of the conductive material that can be introduced into the solvent and the upper limit of the solid content of the prepared positive electrode slurry.

In addition, when manufacturing the positive electrode through the positive electrode slurry using a solvent, it is necessary to dry the positive electrode slurry applied on the current collector to remove the solvent. In this process, the thickness of the cathode active material layer decreases, and there is a problem that a cathode active material layer having a uniform thickness is difficult to be manufactured.

Therefore, there is a demand for a method of manufacturing a cathode, which may increase the content of a conductive material in the anode, may be independent of the solid content, and minimize the thickness variation of the manufactured anode.

[Preceding technical literature]

[Patent Documents]

Japanese Laid-Open Patent Publication No. 2015-220225

One problem to be solved by the present invention is to provide a method for manufacturing a positive electrode that can increase the content of the conductive material in the positive electrode, can be independent of the solid content, the thickness variation of the prepared positive electrode can be minimized.

According to one embodiment of the present invention, dry mixing the positive electrode active material, the dry conductive material, and the dry binder to prepare a mixture; Applying a high shear force to the mixture; Disposing the mixture on a current collector; And rolling a current collector on which the mixture is disposed, wherein the dry conductive material is at least one of carbon nanotubes and carbon fibers, and has a high shear force of 50N to 1000N.

According to another embodiment of the present invention, a current collector and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer comprises a positive electrode active material, a dry conductive material, and a dry binder, the dry conductive The ash comprises at least one of carbon nanotubes and carbon fibers, and a cathode having a thickness variation of 0.001 μm to 5 μm is provided.

According to the positive electrode manufacturing method according to an embodiment of the present invention, since the positive electrode is manufactured by a dry method without using a solvent, it is possible to increase the content of the conductive material in the positive electrode, the positive electrode slurry manufacturing step is unnecessary, the solid content of the positive electrode slurry It may not be content. Accordingly, the process can be simplified, and the resistance of the manufactured anode can be minimized.

In addition, since the positive electrode according to another embodiment of the present invention is manufactured by the manufacturing method, the positive electrode active material layer may be minimized in thickness variation. Accordingly, the capacity variation of the battery can be reduced, and the life characteristics of the battery can be improved.

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

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

As used herein, the terms "comprise", "comprise" or "have" are intended to indicate that there is a feature, number, step, component, or combination thereof, that is, one or more other features, It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

<Anode>

A positive electrode according to an embodiment of the present invention includes a current collector, and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer includes a positive electrode active material, a dry conductive material, and a dry binder, the dry conductive Ash is at least one of carbon nanotubes and carbon fibers, the thickness of the positive electrode may be 0.001㎛ to 5㎛.

The current collector is not particularly limited as long as it is conductive without causing chemical change in the battery. For example, carbon, nickel, titanium, or carbon on aluminum or stainless steel surfaces may be used. The surface-treated with silver etc. can be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The positive electrode active material layer may be disposed on the current collector. Specifically, the positive electrode active material layer may be disposed on one side or both sides of the current collector.

The dry conductive material can impart conductivity to the anode. Here, the dry conductive material means a conductive material having a form such as powder without using a solvent.

The dry conductive material may include at least one of carbon nanotubes and carbon fibers, and specifically, at least one of carbon nanotubes and carbon fibers. The length of the carbon nanotubes and carbon fibers is larger than that of a conductive material such as a spherical or plate-shaped. In the carbon nanotubes and the carbon fiber, the long axis length, that is, the largest distance between two points in the carbon nanotubes or the carbon fibers may be referred to as a length. Since the length of the carbon nanotubes and carbon fibers is larger than that of a conventional general conductive material, the conductive network can be formed in the positive electrode active material layer, so that the resistance of the positive electrode can be reduced. In addition, the carbon nanotubes and the carbon fibers may be complexed with the positive electrode active material, thereby controlling the excessive change of the volume of the positive electrode active material during charging and discharging of the secondary battery. Through this, the lifespan and stability of the secondary battery may be improved.

The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term 'bundle type' herein refers to a plurality of carbon nanotube units aggregated (unless otherwise stated, the axes in the longitudinal direction of the carbon nanotube units are arranged side by side or entangled in substantially the same orientation). Secondary shape in the form of bundles, ropes, or ropes. The carbon nanotube unit has a graphite sheet having a nano size diameter cylinder shape, and has a sp ² bonding structure. In this case, the graphite surface may exhibit characteristics of a conductor or a semiconductor depending on the angle and structure of the surface. Carbon nanotube units are single-walled carbon nanotube (SWCNT) units, double-walled carbon nanotube (DWCNT) units and multi-walled carbon nanotubes (MWCNT) multi-walled carbon nanotube) monomers. Specifically, the carbon nanotube unit may be a multi-walled carbon nanotube unit. The multi-walled carbon nanotube unit has a lower energy required for dispersion than the single-walled carbon nanotube unit and the double-walled carbon nanotube unit, and is preferable in that it has a level of dispersion conditions that can be easily adjusted.

The average length of the carbon nanotubes may be 1㎛ to 100㎛, specifically 5㎛ to 50㎛. When the length range is satisfied, the conductivity of the electrode is excellent, and the flexibility of the electrode may be improved, thereby improving mechanical stability.

The average diameter of the carbon nanotube unit may be 5nm to 100nm, specifically 10nm to 50nm. When the diameter range is satisfied, the conductive material may be smoothly dispersed in the electrode, thereby improving the conductivity of the electrode. The diameter refers to the average diameter of the cross section that appears when the carbon nanotube unit is cut in the short axis direction among the major and minor axes of the carbon nanotube unit.

The average length of the carbon fiber may be 1㎛ to 50㎛, specifically 2㎛ to 10㎛. When the length range is satisfied, the conductivity of the electrode is excellent, and the flexibility of the electrode may be improved, thereby improving mechanical stability.

The average diameter of the carbon fiber may be 5nm to 500nm, specifically, may be 50nm to 300nm. When the diameter range is satisfied, the conductive material may be smoothly dispersed in the electrode, thereby improving the conductivity of the electrode. The carbon fiber may include carbon nanofibers. The diameter means the average diameter of the cross section that appears when the carbon fiber is cut in the short axis direction among the long axis and short axis of the carbon fiber.

The dry conductive material may be included in an amount of 1 wt% to 10 wt% based on the total weight of the mixture, and specifically, may be included in an amount of 2 wt% to 4 wt%. When the above range is satisfied, conductivity of the electrode is excellent, and flexibility of the electrode can be improved.

The cathode active material may be a cathode active material in which the cathode active material is commonly used. Specifically, the cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound 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 , Cu ₂ V ₂ O _7, and the like; LiNi _1-a2 M _a2 O ₂ comprising 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 , and the like, wherein M is Co, Mn, Al, Cu, Fe At least one selected from the group consisting of Mg, B, and Ga, and satisfies 0.01 ≦≦ a2 ≦≦ 0.5); 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 Lithium manganese composite oxide represented by ₃ MO ₈ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); Li part of the formula may be at least one selected from the group consisting of LiMn ₂ O ₄ substituted with alkaline earth metal ions. 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 dry binder serves to improve adhesion between the positive electrode active materials and adhesion between the positive electrode active material and the current collector. Here, the dry binder means a binder having a form such as powder without using a solvent. The dry binder is polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene Butadiene rubber (SBR), fluorine rubber, or at least one selected from the group consisting of various copolymers thereof. Further, through the application of high shear forces, in order to further smoothly agglomerate with the positive electrode active material and the dry conductive material to further improve the positive electrode adhesion, the dry binder may be polyvinylidene fluoride-hexafluoropropylene and polytetrafluoro. At least one of ethylene. The dry binder may be included in an amount of about 2 wt% to about 10 wt% based on the total weight of the cathode active material layer.

The thickness deviation of the positive electrode may be 5 μm or less, specifically 0.001 μm to 5 μm, and more specifically 0.01 μm to 4 μm. When the thickness deviation is more than 5 μm, the flatness of the cell may be lowered or the coating amount may be uneven when the battery is manufactured. The thickness deviation may be measured by the following method. The thickness was measured by applying a force of 0.5 N to 1.0 N using a 5 mm tip on the part and the other parts of the anode, and then measured the thickness deviation as an average of the difference between the thickness of the part and the thickness of the other parts. Can be. In the present invention, since the positive electrode is manufactured through a dry method without using a solvent, a problem of increasing thickness variation of the positive electrode in the presence of a solvent may be solved. Therefore, the thickness deviation of the positive electrode is derived by a manufacturing method which is one of the technical features of the present invention.

The electrode adhesive force of the positive electrode active material layer may be 35gf / 20mm to 200gf / 20mm, and specifically 50gf / 20mm to 150gf / 20mm. Since the positive electrode of this invention arrange | positions and rolls a positive electrode active material, a dry conductive material, and a dry binder on an electrical power collector, without using a solvent, an electrode adhesive force can satisfy the said range. The electrode adhesion may be measured by the following method. After punching the positive electrode into 20 mm x 150 mm and fixing the tape to the center of the 25 mm x 75 mm slide glass, the adhesive strength of the electrode can be measured by measuring the peeling strength of 90 degrees while peeling off the current collector using UTM.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery or a capacitor, and more specifically, may be a secondary battery.

The secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for 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 negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying 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, 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 thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) 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 typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point 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 optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing 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 may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in secondary batteries. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 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 and the like can 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 included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate 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 included. In this case, the additive may be included in 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (hybrid) It is useful for electric vehicle fields such as electric vehicle (HEV).

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 the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Method for producing a positive electrode according to another embodiment of the present invention comprises the steps of preparing a mixture by dry mixing a positive electrode active material, a dry conductive material, and a dry binder; Applying a high shear force to the mixture; Disposing the mixture on a current collector; And rolling the current collector on which the mixture is disposed, wherein the dry conductive material is at least one of carbon nanotubes and carbon fibers, and the high shear force may be 50N to 1000N. Since the positive electrode active material, the dry conductive material, and the dry binder are the same as those of the positive electrode active material, the dry conductive material, and the dry binder described above, description thereof is omitted.

The mixture may be prepared by dry mixing the positive electrode active material, the dry conductive material, and the dry binder.

The dry mixing means mixing without a solvent. The solvent generally means a solvent used for preparing a positive electrode slurry, and may be, for example, water, N-methyl-2-pyrrolidone (NMP), or the like. Although not necessarily limited thereto, the dry mixing may be performed by mixing the mixture at 600 rpm to 1800 rpm for 40 minutes to 60 minutes at room temperature or less using a stirring device.

The positive electrode manufacturing method of the present embodiment may include applying a high shear force to the mixture. The step of applying the high shear force may be performed before placing the mixture on the current collector. Applying the high shear force may include applying a high shear force by shear compressing the mixture. Specifically, when using a device for applying the shear force, for example Nobilta (Hosokawa micron Co., Ltd.), it is possible to apply a high shear force by shear compressing the mixture through the blade (blade) in the device. However, it is not necessarily limited to this method. When a high shear force is applied to the mixture, the positive electrode active material, the dry binder, and the dry conductive material (specifically, carbon nanotubes or carbon fibers) in the mixture may be entangled with each other, and thus, the dry conductive material and the positive electrode active material. Granules in which the dry binder is aggregated may be formed. Therefore, the positive electrode active material and the dry binder may be supported by the dry conductive materials by the presence of the particles, thereby increasing the bonding force between the positive electrode active material, the dry conductive material, and the dry binder. Accordingly, the process of disposing the mixture on the current collector can be facilitated, and the electrode adhesion of the manufactured positive electrode can be improved.

The high shear force may be 50N to 1000N, specifically 100N to 500N, more specifically may be 100N to 300N. The present invention applies a high shear force in the above range to induce entanglement of carbon nanotubes or carbon fibers.

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 on the current collector in a uniform thickness by a scattering method. More specifically, when using a scattering method, the mixture can be moved through a feeding roller, and when the mixture is applied to a current collector, a brush can be used to quantitatively apply the mixture. have.

The rolling of the current collector on which the mixture is disposed may include applying pressure to the current collector, wherein the pressure may include a compressive force. The pressure may be applied through a roll press method. The device for a roll press may include a roll for applying pressure to the mixture and the current collector and a belt for moving the current collector. The current collector is moved by a belt, while at the same time the mixture and current collector are under pressure from a roll. At this time, the pressure includes a compressive force. Before applying the pressure, the belt may be preheated to 50 ° C. to 100 ° C., so that heat can be transferred to the current collector on which the mixture is placed. In addition, when the pressure is applied, the temperature of the roll may be 50 ℃ to 150 ℃.

Hereinafter, preferred embodiments are provided to aid in understanding the present invention, but the above embodiments are merely illustrative of the present disclosure, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present disclosure. It is natural that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

Example 1 Preparation of Positive Electrode

96 g of Li [Ni _0.6 Mn _0.2 Co _0.2 ] O ₂ , the cathode active material particles, ₃ g of carbon nanotubes (bundle) having a unit diameter of 10 nm and a length of 50 μm as the conductive material, and PVDF-HFP 1.5 g, PTFE 1.5 g was mixed for 25 minutes at 1800 rpm without a solvent using a nobilta instrument (Hosokawa). Thereafter, a shear force of 250 N was applied to the mixture (Nobilta (Hosokawa micron)). Thereafter, the mixture was placed on one surface of an aluminum current collector having a thickness of 15 μm at a loading amount of 52 mg / cm ² using a scattering method to prepare a preliminary electrode. The preliminary electrode was placed on the belt of the roll press equipment and the belt was preheated to 60 ° C. Thereafter, the preliminary electrode was rolled with a roll at 60 ° C. to prepare a positive electrode of Example 1.

Example 2 Preparation of Positive Electrode

A positive electrode of Example 2 was prepared in the same manner as in Example 1, except that carbon fiber having a diameter of 150 nm and a length of 10 μm was used instead of 3 g of carbon nanotubes as a conductive material in Example 1.

Example 3: Preparation of Positive Electrode

A positive electrode of Example 3 was prepared in the same manner as in Example 1, except that carbon fibers having a diameter of 100 nm and a length of 5 μm were used instead of 3 g of carbon nanotubes in Example 1.

Example 4: Preparation of Positive Electrode

In Example 1, the positive electrode of Example 4 was prepared in the same manner as in Example 1, except that the carbon nanotubes were 80 μm in length.

Comparative Example 1: Preparation of Positive Electrode

96 g of Li [Ni _0.6 Mn _0.2 Co _0.2 ] O ₂ as the positive electrode active material particles, 3 g of carbon nanotubes having a diameter of 10 nm and a length of 50 μm as a conductive material, 1.5 g of PVDF-HFP as a binder and 1.5 g of PTFE After addition to phosphorus NMP, the mixture was stirred to prepare a positive electrode slurry having a mixture solid content of 65% by weight. The positive electrode slurry was applied on a surface of an aluminum current collector having a thickness of 350 μm with a loading of 52 mg / cm ² and then dried. The drying at this time was carried out in a convection oven at 60 ℃. Subsequently, the cathode slurry applied and dried was rolled through a roll at room temperature and dried in a vacuum oven at 80 ° C. for 12 hours to prepare a cathode of Comparative Example 1.

Comparative Example 2: Preparation of Positive Electrode

A positive electrode of Comparative Example 2 was prepared in the same manner as in Comparative Example 1, except that carbon fiber having a diameter of 150 nm and a length of 10 μm was used instead of 3 g of carbon nanotubes as a conductive material in Comparative Example 1.

Comparative Example 3: Preparation of Positive Electrode

A positive electrode of Comparative Example 3 was prepared in the same manner as in Example 1, except that the shear force was applied at 1200N instead of 250N.

Comparative Example 4: Preparation of Positive Electrode

A positive electrode of Comparative Example 4 was prepared in the same manner as in Example 1, except that the shear force was applied at 25N instead of 250N.

Experimental Example 1 Evaluation of Anode Adhesion

For each of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 4, the positive electrode was punched into 20 mm x 150 mm and fixed to the center of the 25 mm x 75 mm slide glass using a tape, and then the current collector was peeled off using UTM. 90 degree peel strength was measured. Evaluation was made into the average value by measuring five or more peeling strengths. This is shown in Table 1 below.

Experimental Example 2: Thickness Deviation of Anode

For each of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 4, a thickness of 1.0 N was applied using a 5 mm tip to a part of the positive electrode and the other parts separated by 10 mm from the one part to measure thickness. After the thickness (based on the thickness measurement: 100mm), after calculating the thickness deviation as an average of the difference between the thickness of the part and the thickness of the other parts, it is shown in Table 1.

Anode Adhesion (gf / 20mm) Thickness variation of anode (㎛) Example 1 65 4 Example 2 84 3 Example 3 115 2 Example 4 56 5 Comparative Example 1 15 7 Comparative Example 2 23 6 Comparative Example 3 21 6 Comparative Example 4 17 6.5

In the case of Examples 1 to 4, since the positive electrode was manufactured through a drying method, the thickness variation of the positive electrode was smaller than that of Comparative Examples 1 to 4, and it was confirmed that the positive electrode adhesive force was high.

Examples 5 to 8 and Comparative Examples 5 to 8: Preparation of a secondary battery

Using the positive electrodes prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the batteries of Examples 5 to 8 and Comparative Examples 5 to 8 were prepared, respectively. The specific manufacturing method is as follows.

(1) Preparation of Cathode

As a negative electrode active material, a natural graphite, a carbon black conductive material, and a PVdF binder were mixed in an N-methylpyrrolidone solvent in a ratio of 85: 10: 5 in a weight ratio to prepare a composition for forming a negative electrode, which was applied to a copper current collector to form a negative electrode. Was prepared.

(2) Preparation of Secondary Battery

An electrode assembly was prepared between the positive and negative electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 4 via a separator of porous polyethylene, and the electrode assembly was placed inside the case, and then the electrolyte solution was introduced into the case. Injected to prepare a lithium secondary battery. At this time, the electrolyte solution was dissolved 1.0M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). Through this, the secondary batteries of Examples 6 to 10 and Comparative Examples 5 to 8 were prepared.

Experimental Example 3: Evaluation of Capacity Retention Rate (Lifetime Characteristics)

Charging and discharging were performed on the secondary batteries of Examples 5 to 8 and Comparative Examples 5 to 8 to evaluate the capacity retention rate, which is shown in Table 2 below. One cycle and two cycles were charged and discharged at 0.1C, and charging and discharging were performed at 0.5C from 3 cycles to 49 cycles. The 50 cycles ended with charging (with lithium in the negative electrode).

Charging Conditions: CC (Constant Current) / CV (Constant Voltage) (5mV / 0.005C current cut-off)

Discharge condition: CC (constant current) condition 1.5 V

Dose retention rates were each derived by the following calculations.

Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) ×× 100

Capacity retention rate (%) Example 5 80 Example 6 82 Example 7 81 Example 8 77 Comparative Example 5 70 Comparative Example 6 73 Comparative Example 7 75 Comparative Example 8 73

In the case of Examples 5 to 8, since the capacity unevenness of the battery can be eliminated by using the positive electrode having a small thickness variation, it can be confirmed that the capacity retention rate is improved compared to Comparative Examples 5 to 8.

Claims (15)

A current collector, and a cathode active material layer disposed on the current collector, The positive electrode active material layer includes a positive electrode active material, a dry conductive material, and a dry binder, The dry conductive material is at least one of carbon nanotubes and carbon fibers, Anode with a thickness deviation of 5 μm or less. The method according to claim 1, Electrode adhesion of the positive electrode is 35gf / 20mm to 200gf / 20mm. The method according to claim 1, The dry conductive material is a positive electrode containing 1% to 10% by weight based on the total weight of the positive electrode active material layer. An anode of claim 1; cathode; A separator interposed between the anode and the cathode; And Secondary battery comprising an electrolyte. Dry mixing the positive electrode active material, the dry conductive material, and the dry binder to prepare a mixture; Applying a high shear force to the mixture; Disposing the mixture on a current collector; And Rolling the current collector on which the mixture is disposed; The dry conductive material is at least one of carbon nanotubes and carbon fibers, The high shear force is a method of producing a positive electrode 50N to 1000N. The method according to claim 5, The average length of the carbon nanotubes is 1㎛ 100㎛ manufacturing method of the positive electrode. The method according to claim 5, The carbon nanotubes are bundle-type carbon nanotubes in which a plurality of carbon nanotube units are aggregated. The diameter of the unit of the carbon nanotubes is 5nm to 100nm of a positive electrode manufacturing method. The method according to claim 5, The average length of the carbon fiber is 1㎛ 50㎛ manufacturing method of the positive electrode. The method according to claim 5, The carbon fiber has a diameter of 5nm to 500nm manufacturing method of the positive electrode. The method according to claim 5, The applying of the high shear force may include applying a high shear force by shear compressing the mixture. The method according to claim 5, Disposing the mixture, A method of manufacturing a positive electrode comprising disposing the mixture in a uniform thickness on the current collector by a scattering method. The method according to claim 5, Rolling the current collector in which the mixture is disposed, Positioning the current collector on which the mixture is disposed on a belt and rolling the current collector on which the mixture is disposed through a roll. The method according to claim 12, Positioning the current collector disposed on the belt on the mixture, Method for producing a negative electrode comprising preheating the belt to 50 ℃ to 100 ℃. The method according to claim 12, In the step of rolling the current collector on which the mixture is disposed through a roll, The temperature of the roll is 50 ℃ to 150 ℃ manufacturing method of the negative electrode. The method according to claim 5, And the dry binder is at least one of polyvinylidene fluoride-hexafluoropropylene and polytetrafluoroethylene.