KR102196750B1 - Method of manufacturing electrode comprising two-layer structure - Google Patents

Abstract

In the present invention, (i) preparing a first electrode mixture slurry for forming a first active material layer, coating the first electrode mixture slurry on an electrode current collector, drying, and rolling to form a first active material layer; And (ii) preparing a second electrode mixture slurry for forming a second active material layer, coating the second electrode mixture slurry on the first active material layer, and laminating; A method is provided, and an electrochemical device including an electrode manufactured by such a method can satisfy the recent demand for secondary batteries of high capacity and high density.

Description

Method of manufacturing electrode comprising two-layer structure

The present invention relates to a method of manufacturing an electrode having a two-layer structure.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries exhibit high energy density and operating potential, long cycle life, and low self-discharge rate. Batteries are commercialized and widely used.

In addition, as interest in environmental issues has increased in recent years, electric vehicles (EV) and hybrid electric vehicles (HEV) that can replace vehicles that use fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. There is a lot of research on the back. As a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), lithium secondary batteries having high energy density, high discharge voltage, and output stability are mainly studied and used.

In recent years, such a lithium secondary battery has a tendency to become wider and thicker for higher capacity and higher density, and thus, an applied current value is also increasing.

On the other hand, when the lithium secondary battery is repeatedly charged and discharged, deterioration of the battery occurs due to side reactions such as decomposition of an electrolyte solution, and in particular, there is a problem that side reaction products are intensively generated between the negative electrode and the separator.

An object of the present invention is to solve the problems of the prior art and technical problems that have been requested from the past.

That is, in the present invention, it is intended to provide a method of manufacturing an electrode that enables rapid movement of lithium ions and secures a high energy density.

In addition, the present invention is to provide a secondary battery in which the generation of side reaction products between the cathode and the separator including the electrode prepared above and the electrode is reduced.

According to an aspect of the present invention, a method of manufacturing an electrode for a secondary battery in which an active material layer is formed on one or both sides of a current collector, comprising: (i) preparing a first electrode mixture slurry for forming a first active material layer, and Coating the first electrode mixture slurry on the entire surface, drying and rolling to form a first active material layer; And (ii) preparing a second electrode mixture slurry for forming a second active material layer, applying the second electrode mixture slurry to the first active material layer, and laminating; A method is provided.

The second electrode mixture slurry may have a viscosity ranging from 1 centipoise to 1000 centipoise.

The second electrode mixture slurry may be applied to the first active material layer by spray coating or inkjet printing.

The application of the second electrode mixture slurry may be performed in a lamination process line.

The electrode may be a negative electrode, and the second active material layer may be lithium titanium oxide (LTO) represented by the following formula:

[Formula 1]

Li _a Ti _b O ₄

In the above formula, 0.5≤a≤3 and 1≤b≤2.5.

The electrode for a secondary battery according to an aspect of the present invention includes a first active material layer and a second active material layer, and a high energy density is secured by the first active material layer, and lithium ions are formed by the second active material layer. Since rapid movement is ensured, from this, it is possible to provide a secondary battery that satisfies the high capacity and high density required in the art.

In addition, since it is possible to increase the capacity and density of the secondary battery by the predetermined manufacturing method according to the present invention, there is an advantage of a wide range of options for active material particle size and electrode structure design.

In addition, since lithium ions can quickly move into the electrode, lithium ions that have not diffused from the negative electrode surface to the negative electrode active material and the negative electrode react with the electrolyte, thereby reducing generation of by-products generated between the negative electrode and the separator. This effect is more effective in a high-capacity battery. As the current value (current density) increases due to the high capacity of the battery, the amount of lithium ions applied to the surface of the negative electrode increases, and the amount of lithium ions that cannot diffuse into the negative electrode active material and the negative electrode is increased. Because there are more.

In addition, on the side of the equipment for applying the second electrode mixture slurry for forming the second active material layer, since it is possible to apply the second electrode mixture slurry in the existing lamination process line, facilities or spaces for applying the second electrode mixture slurry are saved. There is an advantage that there is no need to provide additional.

1A schematically shows a process of laminating a positive electrode, a negative electrode, and a separator after applying a second electrode mixture slurry to a negative electrode in one embodiment of the present invention.
1B is a cross-sectional view schematically showing an embodiment in which a first active material layer is formed on a current collector in one embodiment of the present invention.
1C is a cross-sectional view schematically showing an embodiment in which a first active material layer is formed on a current collector and a second active material layer is formed on the first active material layer in one embodiment of the present invention.

According to an aspect of the present invention, there is provided an electrode for a secondary battery in which an active material layer is coated on one or both surfaces of an electrode current collector, comprising: an electrode current collector; A first active material layer applied on the current collector; And a second active material layer coated on the first active material layer, wherein the second active material layer is a high-power layer having a high lithium ion diffusion rate.

The electrode may be an anode or a cathode.

It is preferable that the first active material layer is designed to secure a high energy density, and the second active material layer is designed to secure faster movement of lithium ions. In the present invention, not only requirements related to electrode components to satisfy the above object, but also a method of manufacturing an electrode is presented.

According to another aspect of the present invention, as a method of manufacturing an electrode for a secondary battery in which an active material layer is formed on one or both sides of a current collector, (i) a first electrode mixture slurry for forming a first active material layer is prepared, and the electrode collector Coating the first electrode mixture slurry on the entire surface, drying and rolling to form a first active material layer; And (ii) preparing a second electrode mixture slurry for forming a second active material layer, coating the second electrode mixture slurry on the first active material layer, and laminating; A manufacturing method is provided.

In the present invention, the positive electrode active material of the first and second active material layers constituting the positive electrode is 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 manganese oxides such as the formula Li _{1 + x} Mn _{2 - x} O ₄ (wherein x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, etc.; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _{2 - x} MxO ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, A lithium manganese composite oxide represented by Cu or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _{2 - x} O ₄ ; LiMn ₂ O _{4 wherein} part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like may be mentioned, but the present invention is not limited thereto.

In the present invention, the negative electrode active material of the first active material layer and the second active material layer constituting the negative electrode may include, for example, carbon such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _{1 - x} Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal composite oxides such as Al, B, P, Si, elements of groups 1, 2, and 3 of the periodic table, halogen, 0<x≦1;1≦y≦3;1≦z≦8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ and Metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide or the like can be used.

In a preferred embodiment, when the electrode is a negative electrode, the negative active material constituting the second active material layer may be lithium titanium oxide (LTO) represented by the following formula.

[Formula 1]

Li _a Ti _b O ₄

In the above formula, 0.5≤a≤3 and 1≤b≤2.5.

Non-limiting examples of the lithium titanium oxide, Li _{0 . 8} Ti _{2 . 2} O ₄ , Li _{2 . 67} Ti _{1 . 33} O ₄ , LiTi ₂ O ₄ , Li _{1 . 33} Ti _{1 . 67} O ₄ , Li _{1 . 14} Ti _{1 . 71} O ₄ etc.

In the negative electrode and the positive electrode, the active material constituting the second active material layer is the aforementioned active material, and more preferably has an average particle diameter of 0.2 to 10 µm. If the average particle diameter is less than 0.2 µm, a very large amount of solvent is required when forming the slurry, making drying after coating difficult in the lamination process, and desorption may occur in subsequent processes due to low adhesion between active materials, and the average particle diameter is If it is larger than 10 μm, the diffusion distance of lithium ions in the active material becomes longer, so that the diffusion rate of lithium ions in the second active material layer decreases, so that the composition effect of the double layer disappears.

In the negative electrode and the positive electrode, the first and second active material layers may include a conductive material, a binder, and a filler in addition to the active material, and may further include other additives used in the art, if necessary.

The conductive material may be included in an amount of 1 to 50% by weight of the total components constituting the active material layer.

Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that aids in binding of the active material to the conductive material and bonding to the current collector, and is added in an amount of 1 to 50% by weight to the total components constituting the active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component that suppresses the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefin-based polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

The thickness of the first active material layer in the positive electrode and the negative electrode is not particularly limited, but it is more preferable because it is possible to ensure a balance between energy density and output when having a thickness in the range of 25 μm to 150 μm. When the second active material layer has a thickness in the range of 2 to 30 μm, it is possible to secure a high rate of lithium ions, so it is preferable.

The positive electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface treatment of carbon, nickel, titanium, silver, or the like may be used on the surface of. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics are possible.

The negative electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. For example, carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, and the like may be used. In addition, like the positive electrode current collector, it is possible to enhance the bonding strength of the negative electrode active material by forming fine irregularities on the surface thereof, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

As described above, in another aspect of the present invention, as a method of manufacturing an electrode for a secondary battery in which an active material layer is formed on one or both sides of a current collector, (i) a first electrode mixture slurry for forming a first active material layer is prepared. And coating the first electrode mixture slurry on an electrode current collector, drying and rolling to form a first active material layer; And (ii) preparing a second electrode mixture slurry for forming a second active material layer, coating the second electrode mixture slurry on the first active material layer, and laminating; Methods are also provided.

To prepare the electrode mixture slurry, an active material, a conductive material, a binder, a filler, and other additives, if necessary, are added to the solvent. For the active material, the conductive material, the binder, and the filler, refer to the above description. To prepare the first electrode mixture slurry, an active material selected as the first active material is added, and to prepare the second electrode mixture slurry, an active material selected as the second active material is added.

It is preferable that the solvent used to form the electrode mixture slurry has a solubility index similar to that of the binder polymer to be used, and has a low boiling point. This is because mixing can be made uniformly, and then the solvent can be easily removed. Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N It may be one or a mixture of two or more selected from the group consisting of -methyl-2-pyrrolidone, NMP) and cyclohexane.

The first electrode mixture slurry is used in a conventional coating method used in the art, such as dip coating, die coating, roll coating, comma coating, or a combination thereof. It is coated on one or both sides of the current collector.

Subsequently, the first electrode mixture slurry is dried at a temperature of 20 to 300°C. If necessary, firing can be performed at 300 to 800°C in an inert gas atmosphere such as Ar or N ₂ .

Then, the first active material layer formed from the above is rolled. When the second electrode mixture slurry is applied without rolling the first active material layer, the first active material layer may be peeled off. Rolling of the first active material layer may be performed by a method commonly used in the art, such as a roll press. Rolling may be performed at a pressure of 1 MPa to 50 MPa and a temperature of 10 to 60°C.

The electrode formed from the above and on which the first active material layer is formed may be wound and stored as necessary.

Next, a second electrode mixture slurry is prepared. It is preferable that the second electrode mixture slurry has a viscosity in the range of 1000 centipoise. In terms of the manufacturing process and battery performance, the lower limit of the viscosity of the second electrode mixture slurry is not particularly limited, and when the components constituting the slurry are considered, the second electrode mixture slurry may have a viscosity of 2 centipoise or more. If the viscosity of the second electrode mixture slurry is greater than 1000 centipoise, the second electrode mixture slurry is not sprayed from the nozzle or it is difficult to form a uniform layer during coating.

The second electrode mixture slurry is applied to the first active material layer. The application process of the second electrode mixture slurry is performed in a process line for lamination by interposing a separator between the positive electrode, the negative electrode, and the positive electrode and the negative electrode, thereby eliminating the need for additional facilities or space for forming the second active material layer. I can make it. To this end, it is preferable to apply the second electrode mixture slurry to the first active material layer by a method such as spray coating or inkjet printing. In the case of using die coating or comma coating, it is difficult to apply the second electrode mixture slurry to the first active material layer in a lamination process line without additional equipment or space. As the second electrode mixture slurry is applied to the first active material layer in the lamination process line, productivity of battery manufacturing may be improved and facility space may be reduced. Meanwhile, since the lamination process is applied immediately after the second electrode mixture slurry is applied, the second electrode mixture slurry may be dried by heat and pressure applied in the lamination process to form a second active material layer. For example, lamination may be performed at a temperature of 30 to 150° C., a pressure of 98,000 to 490,000 N/cm ² , or both. Accordingly, a separate process for drying the second electrode mixture slurry is not required, thereby simplifying the process.

An embodiment of such a process line according to the present invention is schematically illustrated in FIG. 1A, and according to an aspect of the present invention, a cathode is presented as an electrode made of two active material layers.

In FIG. 1A, the cathode 100 is prepared in a wound state. The negative electrode 100 is in a state in which the first active material layer 120 is coated, dried, and rolled on both sides of the electrode current collector 110 as shown in FIG. 1B. The coating was performed using dip coating, die coating, roll coating, comma coating, or a combination thereof, and then drying was performed at a temperature of 20 to 300°C. Rolling was carried out at a pressure of 1 MPa to 50 MPa and a temperature of 10 to 60°C. Immediately before the negative electrode 100 is laminated with the separator 200 and the positive electrode 300, by spray 400, a second negative electrode mixture slurry (not shown) having a viscosity of 1 to 1000 centipoise is added to the negative electrode ( 100), more specifically, it is applied on the first active material layer of the negative electrode. The second negative electrode mixture slurry preferably contains LTO particles. As the second electrode mixture slurry is applied by a spray method, the burden on additional facilities or space for forming the second active material layer is minimized, and an existing process line can be utilized. Subsequently, the laminate in the state in which the separator is interposed between the cathode and the anode is laminated while passing through the heater chamber 510 and the roller 520. The lamination is carried out at a temperature of 30 to 150° C., a pressure of 98,000 to 490,000 N/cm ² , or both. Accordingly, the negative electrode has a structure including an electrode current collector 110, a first active material layer 120, and a second active material layer 130, as shown in FIG. 1C. In FIG. 1A, '600' is a cutting machine that cuts each of the separator, the cathode, and the anode.

The present invention also provides a secondary battery including the electrode, in detail, a lithium secondary battery.

The lithium secondary battery may have a structure in which an electrolyte solution containing a lithium salt is impregnated into an electrode assembly in which a separator is interposed between the positive electrode and the negative electrode.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 µm, and the thickness is generally 5 to 300 µm. Examples of such separation membranes include olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity; Sheets or non-woven fabrics made of glass fiber or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing electrolyte is composed of an electrolyte solution and a lithium salt, and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used as the electrolyte, but is not limited thereto.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid tryster, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbo Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate and ethyl propionate may be used.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymerization agent or the like containing an ionic dissociating group may be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ may be used.

The lithium salt is a material that is easily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

In addition, for the purpose of improving charge/discharge properties and flame retardancy, the electrolyte solution includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, and nitro. Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included in order to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), and the like may be further included.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , and LiN(SO ₂ CF ₃ ) ₂ are used in the cyclic carbonate of EC or PC as a highly dielectric solvent and DEC, DMC or EMC as a low viscosity solvent. The lithium salt-containing non-aqueous electrolyte may be prepared by adding it to a mixed solvent of linear carbonate.

The present invention also provides a battery module including the secondary battery as a unit cell, a battery pack including the battery module, and provides a device including the battery pack.

In particular, the battery pack can be used as a power source for mid- to large-sized devices that require high temperature stability, long cycle characteristics, and high rate characteristics.

The device may include, for example, a power tool that is driven and moved by an electric motor; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); Electric golf cart; Power storage systems, etc., but are not limited thereto.

Claims (5)

Preparing a first electrode mixture slurry for forming a first active material layer, coating the first electrode mixture slurry on an electrode current collector, drying, and rolling to form a first active material layer; And
Preparing a second electrode mixture slurry for forming a second active material layer, and coating the second electrode mixture slurry on the first active material layer; Including,
The coating of the second electrode mixture slurry is performed in a lamination process line of the anode, the cathode, and the separator,
When the electrode is an anode,
Further comprising the step of laminating by interposing a separator between the result of the second electrode mixture slurry coated and the negative electrode,
When the electrode is a cathode,
Further comprising the step of laminating by interposing a separator between the result of coating the second electrode mixture slurry and the anode,
The method of manufacturing a secondary battery, characterized in that the second electrode mixture slurry is dried by the heat and pressure applied in the laminating step to form a second active material layer.
The method of claim 1,
The method of manufacturing a secondary battery, wherein the second electrode mixture slurry has a viscosity ranging from 1 centipoise to 1000 centipoise.
The method of claim 1,
A method of manufacturing a secondary battery, wherein the second electrode mixture slurry is coated on the first active material layer by spray coating or inkjet printing.
delete The method of claim 1,
The electrode is a cathode,
Method for manufacturing a secondary battery, characterized in that the second active material layer is lithium titanium oxide (LTO) represented by the following formula:
[Formula 1]
Li _a Ti _b O ₄
In the above formula, 0.5≤a≤3 and 1≤b≤2.5.

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