KR20180020784A - Electrode for lithium secondary battery and Method for preparing the same - Google Patents

Abstract

The present invention relates to an electrode for a lithium secondary battery to improve adhesion of the electrode by securing uniform distribution of a polymer binder even if a high loading electrode is used. The electrode for a lithium secondary battery comprises: an electrode current collector; and an electrode compound layer formed on the electrode current collector and including an electrode active material, a conductor and a polymer binder. The loading amount of the electrode compound layer is 250 mg/25cm^2 or more. The grain size (D50) of a complex formed as a plurality of electrode active material particles and the polymer binder are coupled is 1.5 to 8 times the grain size (D50) of the electrode active material.

Description

[0001] The present invention relates to an electrode for a lithium secondary battery,

The present invention relates to an electrode for a lithium secondary battery having a high capacity characteristic and a method for manufacturing the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low discharge rate is commercialized and widely used.

The lithium secondary battery includes a positive electrode including a positive electrode active material on at least one surface of a positive electrode collector, a negative electrode including a negative electrode active material on at least one surface of the negative electrode collector, and a separator interposed between the positive electrode and the negative electrode, A conductive material is added to improve the energy density of the conductive material. In addition, as interest in environmental issues grows, the market for high-capacity battery-use devices such as electric vehicles and hybrid electric vehicles, which can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, There is a demand for designing a high-capacity electrode for manufacturing a lithium secondary battery having high energy density, high output and high discharge voltage as a power source of these devices.

In order to design the high loading electrode, the amount of active material is increased, and a high loading electrode having a thick electrode has been attempted. As the thickness of the electrode increases, the polymer binder moves to the surface of the electrode together with the solvent during the manufacturing process of the electrode, and the polymer binder is unevenly distributed in the thickness direction.

An object of the present invention is to provide an electrode for a lithium secondary battery capable of achieving uniform distribution of a polymer binder by selecting an optimum polymer binder in consideration of processability in a high loading electrode and a method for producing the same.

According to an aspect of the present invention, there is provided an electrode current collector, And an electrode mixture layer formed on one surface of the electrode current collector and including an electrode active material, a conductive material, and a polymer binder, wherein the loading amount of the electrode mixture layer is 250 mg / 25 cm ² or more And a particle size (D50) of a composite formed by combining a plurality of electrode active material particles and a polymer binder is 1.5 to 8 times the particle size (D50) of the electrode active material.

Preferably, the particle size (D50) of the composite may be from 30 m to 250 m.

Preferably, the particle size (D50) of the composite may range from 45 [mu] m to 195 [mu] m.

Preferably, the electrode active material and the polymeric binder may be contained in a weight ratio of 97: 3 to 99: 1.

Preferably, the electrode may be a cathode or a cathode.

Preferably, the thickness of the electrode mixture layer may be 70 占 퐉 to 200 占 퐉.

Preferably, the particle surface of the electrode active material can be subjected to hydrophilization treatment.

According to another aspect of the present invention, an electrode active material and a polymeric binder are dispersed in a solvent so that a particle size (D50) of a composite of an electrode active material and a polymeric binder is 1.5 to 8 times the particle size (D50) , Selecting a polymeric binder; Dispersing the selected polymeric binder, the electrode active material, and the conductive material in a solvent to prepare an electrode slurry; Applying the electrode slurry to one surface of an electrode current collector at a loading amount of 250 mg / 25 cm ² or more; And drying the electrode slurry applied on the current collector. The present invention also provides a method of manufacturing an electrode for a lithium secondary battery.

Preferably, the particle size (D50) of the composite may be from 30 m to 250 m.

Preferably, the solvent may be an organic solvent or an aqueous base.

Preferably, when the solvent is an aqueous solvent, the electrode slurry may further include a thickener.

The electrode according to one aspect of the present invention can uniformly distribute the polymer binder even when a high loading electrode is used, can prevent the electrode active material from being separated, and can improve the performance of the battery due to the reduced resistance.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given above, serve to further the understanding of the technical idea of the invention, It should not be construed as limited.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the measurement results of adhesive strength of electrodes manufactured according to Examples and Comparative Examples of the present invention. FIG.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely examples of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents And variations are possible.

In the case of the conventional high loading electrode, as the thickness of the electrode becomes thick, the polymer binder moves to the surface of the electrode together with the solvent during the manufacturing process of the electrode, and the polymer binder is dispersed unevenly There was a problem. In order to solve this problem, a method of comparing the affinity between the polymer binder and the solvent has been proposed, and there has been a problem that the measurement is not easy.

(D50) of a composite of an electrode active material and a polymeric binder when the electrode active material and a polymeric binder are mixed with each other after the particle size of the electrode active material and the polymeric binder are mixed and dispersed in a solvent when only the electrode active material is dispersed in a solvent, The affinity of the polymeric binder to the solvent was evaluated by the measurement, and it was experimentally confirmed that the distribution of the polymeric binder was uniformly improved by using the polymeric binder capable of providing the optimum affinity.

Like the conventional electrode, the electrode for a lithium secondary battery of the present invention comprises an electrode collector; And an electrode mixture layer formed on one surface of the electrode current collector and including an electrode active material, a conductive material, and a polymeric binder.

In the electrode for a lithium secondary battery according to one aspect of the present invention, the loading amount of the electrode mixture layer is 250 mg / 25 cm ² or more, and the particle size (D50) of the composite formed by combining a plurality of electrode active material particles and a polymeric binder, Of the particle size (D50). In the present invention, by selecting a polymer binder whose particle size (D50) of the composite of the electrode active material and the polymeric binder has a range of 1.5 to 8 times the particle size (D50) of the electrode active material in the high loading electrode, The uniform distribution of the polymeric binder can be achieved. When the particle size (D50) of the composite is smaller than 1.5 times the particle size (D50) of the electrode active material, there is a problem that migration of the polymer binder occurs strongly due to too strong affinity with the solvent. When the particle size (D50) is larger than 8 times the particle size (D50) of the electrode active material, the affinity with the solvent is lowered and coagulation occurs in the production of the electrode slurry, which makes it difficult to produce the electrode. Preferably, the loading amount of the electrode mix layer may be 300 to 500 mg / 25 cm ² , and the particle size (D50) of the composite may be 1.8 to 7.8 times the particle size (D50) of the electrode active material.

In the electrode for a lithium secondary battery according to an embodiment of the present invention, the particle size (D50) of the composite may be 30 μm to 250 μm, preferably 45 μm to 195 μm.

The electrode active material according to an embodiment of the present invention may be a negative electrode active material or a positive electrode active material.

The cathode active material may be a lithium-containing oxide, and a lithium-containing transition metal oxide may be preferably used. For example, the lithium-containing transition metal _{oxides, Li x CoO 2 (0.5 <} x <1.3), Li x NiO 2 (0.5 <x <1.3), Li x MnO 2 (0.5 <x <1.3), Li x _{Mn 2 O 4 (0.5 <x} <1.3), Li x (Ni a Co b Mn c) O2 (0.5 <x <1.3, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Li x Ni 1-y Co y O 2 (0.5 <x <1.3, 0 <y <1), Li x Co 1 - y Mn y O 2 (0.5 <x <1.3, 0≤ y <1), Li _x Ni _{1 -y} Mn _y O ₂ (0.5 <x <1.3, 0≤y <1), Li _x (Ni _a Co _b Mn _c ) O 4 <2, 0 <b <2 , 0 <c <2, a + b + c = 2), Li x Mn 2 - z Ni z O4 (0.5 <x <1.3, 0 <z <2), Li x Mn _{2 - z Co z O 4 (} 0.5 <x <1.3, 0 <z <2), Li x CoPO 4 (0.5 <x <1.3) and Li _x FePO ₄ is selected from the group consisting of (0.5 <x <1.3) Or a mixture of two or more of them, and the lithium-containing transition metal oxide may be coated with a metal such as aluminum (Al) or a metal oxide. In addition to the lithium-containing transition metal oxide, sulfide, selenide and halide may also be used.

The negative electrode active material may be a lithium metal, a carbonaceous material, a metal compound, or a mixture thereof, which is capable of occluding and releasing lithium ions.

Concretely, as the carbon material, both low-crystalline carbon and highly-crystalline carbon may be used. Examples of low crystalline carbon are soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, kishgraphite, pyrolytic carbon, liquid crystal pitch carbon fiber mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes.

Examples of the metal compound include metal elements such as Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, , And the like. These metal compounds can be used in any form such as a single body, an alloy, an oxide (TiO ₂ , SnO _2, etc.), a nitride, a sulfide, a boride and an alloy with lithium, but an alloy with a single body, alloy, It can be increased in capacity. Among them, it may contain at least one element selected from Si, Ge and Sn, and it may further increase the capacity of the battery including at least one element selected from Si and Sn.

The polymeric binder of the present invention is a component that assists in binding of an electrode active material and a conductive material and bonding to a current collector and has a particle size (D50) of a composite formed by bonding with an electrode active material is 1.5 to 8 For example, polyvinylidene fluoride (PVDF), hexafluoro propylene (HFP), polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluoride), polyvinylidene fluoride polyvinylidene fluoride-co-hexafluoro propylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethyle ne-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, But are not limited to, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, An acrylonitrile-styrene-butadiene copolymer, and a polyimide, or a mixture of two or more thereof. The electrode active material and the polymeric binder may be contained in a weight ratio of 97: 3 to 99: 1.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as 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 and the like can be used. Preferably, the conductive material may be acetylene black.

In the electrode for a lithium secondary battery according to another aspect of the present invention, the electrode mixture layer may further include a thickening agent. Carboxymethylcellulose (CMC) may be used as the thickening agent, and those having a molecular weight of 400,000 to 200,000 may be used.

The electrode material mixture layer may have a thickness of 70 mu m to 200 mu m.

The electrode current collector according to an embodiment of the present invention may be a positive current collector or a negative current collector.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and examples thereof include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the negative electrode current collector may have a surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

In addition, the electrode active material according to another aspect of the present invention may be one in which the surface of the particles is hydrophilized.

The electrode active material may be subjected to a mechanical treatment to hydrophilize the particle surface, and the mechanical treatment may be a treatment simultaneously applying compressive force and shear force. The mechanical treatment is preferably applied to the surface of the electrode active material, and the particle shape of the electrode active material particle is preferably not destroyed. Specifically, it is preferable to suppress the rate of decrease of the average particle diameter of the electrode active material particles by the mechanical treatment to 20% or less.

Preferably, the electrode active material may be a mixture of mechanically treated graphite and a non-mechanically treated carbonaceous material.

A method of manufacturing an electrode for a lithium secondary battery according to another aspect of the present invention comprises dispersing an electrode active material and a polymeric binder in a solvent so that a particle size (D50) of a composite of an electrode active material and a polymeric binder is smaller than a particle size (D50) Selecting a polymeric binder such that the polymeric binder is 1.5 to 8 times larger than the polymeric binder; Dispersing the selected polymeric binder, the electrode active material, and the conductive material in a solvent to prepare an electrode slurry; Applying the electrode slurry to at least one surface of the electrode current collector at a loading amount of 250 mg / 25 cm ² or more; And drying the electrode slurry applied on the current collector.

The particle size (D50) of the composite may range from 30 [mu] m to 250 [mu] m.

The solvent may be an organic solvent or an aqueous solvent, depending on the selected polymeric binder.

The organic solvent may be a conventionally known solvent, for example, a cyclic carbonate system with or without a halogen substituent; Linear carbonate system; Ester-based, nitrile-based, phosphate-based solvents, or mixtures thereof. For example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, acetic acid Methyl, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate and butyl propionate or mixtures thereof.

The aqueous solvent may be at least one selected from the group consisting of water, methanol, ethanol, ethylene glycol, diethylene glycol, and glycerol. When an aqueous solvent is used as the solvent, the slurry may further contain a thickener. The thickening agent may include any one selected from the group consisting of a cellulosic compound, polyvinyl alcohol, and polyacrylic acid, or a mixture of two or more thereof.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the above-described embodiments. The embodiments of the present invention are provided so that those skilled in the art can explain the present invention more clearly and completely.

Example 1

Artificial graphite (having a tap density of 0.9 g / cc or less) and styrene butadiene rubber (SBR) as a polymer binder were prepared as an electrode active material. The artificial graphite and SBR were dispersed in water at a weight ratio of 98: 2 and the particle size (D50) of the composite of artificial graphite and SBR was measured. The particle size (D50) of the composite was 45 탆, (D50).

Applied to the copper foil to the artificial graphite 96.8% by weight, styrene-butadiene rubber 2% by weight, and 1.2 wt% carboxymethyl cellulose was dispersed in water to prepare an electrode slurry, these electrode slurry as a loading dose of 300 mg / 25cm ² And then dried and rolled for 10 hours or more in a vacuum oven at 100 캜 to prepare an electrode having a thickness of 107 탆.

Example 2

The same electrode as in Example 1 was prepared except that the particle size (D50) of the composite of artificial graphite and SBR was 195 占 퐉 and the particle size (D50) of artificial graphite was 7.8 times.

Comparative Example 1

The same electrode as in Example 1 was prepared except that the particle size (D50) of the composite of artificial graphite and SBR was 25 mu m and the particle size (D50) of artificial graphite was the same.

Comparative Example 2

The same electrode slurry as in Example 1 was prepared except that the particle size (D50) of the composite of artificial graphite and SBR was 290 占 퐉 and the particle size (D50) of the artificial graphite was 11.6 times. Such an electrode slurry had an agglomeration phenomenon, making it impossible to produce an electrode.

Cathode adhesion measurement

The adhesive strength of the negative electrode material mixture layer was measured using the electrodes prepared according to Examples 1 and 2 and Comparative Example 1, and the measured results are shown in FIG. The specific measurement method is as follows.

1. Place a double-sided tape on the slide glass and place the electrode on it.

2. Tape and peel off the other side of the electrode, and measure the thickness of the electrode.

3. The peeling was repeated until the thickness became 10% of the electrode thickness, and the adhesive strength to the thickness of the cathode was measured.

Referring to FIG. 1, it can be seen that the adhesiveness of the electrodes of Examples 1 and 2 is improved compared to the comparative example, and the binder is uniformly distributed as compared with Comparative Example.

Claims (11)

Electrode collector; And an electrode mixture layer formed on one surface of the electrode current collector and including an electrode active material, a conductive material, and a polymeric binder,
Particle size (D50) of the electrode loading of the anode mix layer is 250 mg / 25cm ² or more, a plurality of electrode active material particles and the polymer composite, the binder is formed by the combination is characterized in that 1.5 to 8 times the particle size (D50) of the electrode active material Wherein the electrode is a lithium secondary battery. The method according to claim 1,
Wherein the composite has a particle size (D50) of 30 占 퐉 to 250 占 퐉. The method according to claim 1,
Wherein the composite has a particle size (D50) of 45 m to 195 m. The method according to claim 1,
Wherein the electrode active material and the polymeric binder are contained in a weight ratio of 97: 3 to 99: 1. The method according to claim 1,
Wherein the electrode is a positive electrode or a negative electrode. The method according to claim 1,
Wherein the electrode mixture layer has a thickness of 70 占 퐉 to 200 占 퐉. The method according to claim 1,
Wherein the surface of the particle of the electrode active material is hydrophilized. Dispersing the electrode active material and the polymer binder in a solvent so that the particle size (D50) of the composite of the electrode active material and the polymer binder is 1.5 to 8 times the particle size (D50) of the electrode active material;
Dispersing the selected polymeric binder, the electrode active material, and the conductive material in a solvent to prepare an electrode slurry;
Applying the electrode slurry to one surface of an electrode current collector at a loading amount of 250 mg / 25 cm ² or more; And
And drying the electrode slurry applied on the current collector. 9. The method of claim 8,
Wherein the composite has a particle size (D50) of 30 占 퐉 to 250 占 퐉. 9. The method of claim 8,
Wherein the solvent is an organic solvent or an aqueous solvent. 10. The method of claim 9,
Wherein when the solvent is an aqueous solvent, the electrode slurry further comprises a thickening agent.

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