KR102613287B1 - Method for Manufacturing an Electrode in which a Carbon nanotube is Applied as a Conductive Material, an Electrode Manufactured by the Method, and a Secondary Battery Including the Electrode - Google Patents

Abstract

The present invention relates to a method for manufacturing an electrode using carbon nanotubes (CNT) as a conductive material, an electrode manufactured thereby, and a secondary battery including this electrode. The method for manufacturing an electrode according to the present invention is ( a) manufacturing step of an electrode active material slurry prepared by dispersing an electrode active material, a conductive material, and a binder in a dispersion medium, and using carbon nanotubes (carbon nanotubes) as a conductive material; (b) drying the electrode active material slurry to remove the dispersion medium to prepare an active material powder whose surface is covered with carbon nanotubes; and (c) manufacturing an electrode by applying and pressing the active material powder to one or both sides of a current collector. The electrode manufactured in this way basically has excellent conductive performance even with a small content of conductive material, and the binder distribution is uniform, which improves the adhesion of the electrode and improves high output and rapid charging characteristics.

Description

Method for manufacturing an electrode using carbon nanotubes as a conductive material, an electrode manufactured thereby, and a secondary battery including the electrode , and a Secondary Battery Including the Electrode}

The present invention relates to a method of manufacturing an electrode using carbon nanotubes (Carbon nanotubes, CNT) as a conductive material, an electrode manufactured thereby, and a secondary battery containing this electrode. More specifically, it relates to a method of manufacturing an electrode using carbon nanotubes (CNTs) as a conductive material. By using a dry method of electrodes, it is possible to efficiently manufacture electrodes that basically have excellent conductive performance even with a small content, but also improve high output and rapid charging characteristics due to uniform binder distribution in the thickness direction compared to electrodes made by wet manufacturing methods. It is about manufacturing method.

Recently, as the demand for portable electronic products such as laptops, video cameras, and portable phones has rapidly increased, and as the development of electric vehicles, energy storage batteries, robots, and satellites has begun, high-performance secondary batteries capable of repeated charging and discharging have been developed. Research is actively underway.

Currently commercialized secondary batteries include nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, and lithium secondary batteries. Among these, lithium secondary batteries have little memory effect compared to nickel-based secondary batteries, so they can be freely charged and discharged. It is receiving attention for its extremely low self-discharge rate and high energy density.

Generally, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated in an electrode assembly consisting of a positive electrode containing lithium transition metal oxide as an electrode active material, a negative electrode containing a carbon-based active material, and a separator. Typically, the positive electrode is manufactured by coating and drying a positive electrode mixture containing lithium transition metal oxide on a current collector such as aluminum foil, and the negative electrode is manufactured by coating and drying the negative electrode mixture containing a carbon-based active material on a current collector such as copper foil. It is manufactured.

In general, high-density electrodes are formed by molding electrode active material particles having a size of several ㎛ to tens of ㎛ using a high-pressure press, so the particles are deformed, the space between the particles is reduced, and electrolyte permeability is likely to be reduced.

To solve this problem, conductive materials with excellent electrical conductivity and strength are used when manufacturing electrodes. When using a conductive material when manufacturing an electrode, the conductive material is dispersed between compressed electrode active materials, thereby maintaining micropores between the active material particles, facilitating penetration of the electrolyte solution, and reducing resistance within the electrode due to excellent conductivity.

Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Carbon derivatives such as carbon nanotubes and fullerene, conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives can be used, and among these conductive materials, the use of carbon nanotubes, a fibrous carbon-based conductive material that can further reduce electrode resistance by forming an electrically conductive path within the electrode, is increasing. .

Carbon nanotubes, a type of fine carbon fiber, are tubular carbon with a diameter of 1 μm or less, and are expected to be applied and commercialized in various fields due to high conductivity, tensile strength, and heat resistance due to their specific structure.

Even when manufacturing an electrode by applying carbon nanotubes as a conductive material, the electrode mixture prepared by dispersing the electrode active material, conductive material, binder, etc. in a dispersion medium is coated and dried on a current collector as in the conventional electrode manufacturing method. When drying the mixture layer coated on the current collector, the dispersion medium in the mixture layer evaporates and a movement phenomenon occurs in which the binder rises to the surface along with the dispersion medium. As a result, the distribution of the binder in the mixture layer, especially in the layer thickness direction, occurs. There are problems such as the binder distribution becomes uneven, the adhesion of the electrode deteriorates, and the input/output characteristics of the battery deteriorate.

In addition, as secondary batteries with excellent performance such as high capacity, high output, long life, and fast charging are increasingly required, the amount of active material in the electrode mixture is increasing, and the amount of binder and conductive material is relatively reduced, resulting in less binder. The need to demonstrate excellent adhesion even with the use of and excellent conductive performance even with the use of a small amount of conductive materials is even more urgent.

Meanwhile, in order to solve the problem caused by the movement of the binder as described above, a dry electrode technology that manufactures electrodes through powder mixing without a dispersion medium has been proposed. The dry manufacturing method is a method of manufacturing an electrode by drying an electrode slurry containing an electrode active material and then coating the obtained powdery electrode material on a current collector. Since coating is performed after drying, the solvent evaporates and the binder and conductor are removed. By preventing the phenomenon of ash being lifted to the surface of the electrode, the uniformity of the binder in the thickness direction is increased, which is advantageous for output and rapid charging.

However, despite the usefulness of this dry manufacturing technology, it was not easy to apply carbon nanotubes as a conductive material. This is because carbon nanotubes tend to aggregate due to strong mutual Van de Waals forces, making it particularly difficult to uniformly disperse the carbon nanotubes. If carbon nanotubes are directly mixed with other electrode materials or electrode slurry without a separate process, the carbon nanotubes may not be uniformly dispersed and may be exposed to the electrode surface in a partially agglomerated form, acting as a conductive material within the electrode active material. Problems may arise in performance.

Patent Document 1 (WO 2009/044856) relates to an electrochemical device electrode that can obtain an electrode for an electric double layer capacitor with high conductivity and low internal resistance and a manufacturing method thereof, which involves assembling an electrode active material, a conductive additive, and a binder. A process of obtaining granulated particles, a process of mixing the granulated particles and a fibrous conductive additive to obtain an electrode material containing a fibrous conductive additive on the outside of the granulated particles, and a process of dry molding the electrode material to form an active material layer. , and a method of manufacturing an electrode for an electric double layer capacitor including a process of laminating the active material layer and the current collector. In addition, in Patent Document 1, a slurry is prepared by stirring and mixing high-purity activated carbon powder as an electrode active material, acetylene black as a particulate conductive aid, an aqueous dispersion of an acrylate polymer as a binder, and an aqueous solution of ammonium salt of carboxymethylcellulose and distilled water as a dispersant. Then, this slurry is spray-dried and granulated using a spray dryer to obtain granulated particles, and then the granulated particles are mixed with aluminum fiber (or carbon nanofiber, carbon nanotube, etc.) as a fibrous conductive agent using a high-speed mixer to form a surface. An example is described in which composite particles to which a fibrous conductive additive is attached are obtained, the obtained composite particles are then roll-pressed to form a sheet-shaped active material layer, and this is laminated on a separately prepared current collector to produce a sheet-shaped electrode. .

However, in Patent Document 1, it is only described that the dried granulated particles and the fibrous conductive additive are mixed at high speed to obtain composite particles with the fibrous conductive additive attached to the surface, and there is a specific method of coating the surface of the particles with the fibrous conductive additive. The method is no longer disclosed in detail. According to what the present inventor actually confirmed, there was a problem in that dry mixing as in Patent Document 1 did not disperse the carbon nanotubes uniformly among the electrode materials and resulted in poor electrode characteristics due to agglomeration. Therefore, Patent Document 1 has some technical significance in solving the problem caused by the movement of the binder as described above, but there are limitations as a technology for applying tubular or fibrous conductive materials such as carbon nanotubes to the dry manufacturing method.

International Publication WO 2009/044856 Korean Patent Publication No. 10-2017-0111730

Accordingly, the present invention is intended to solve the problems of the prior art as described above. By using carbon nanotubes instead of spherical conductive materials and allowing the carbon nanotubes to thinly and evenly cover the surface of the active material, excellent conductive performance is basically secured even with a small content. However, the purpose is to provide a method of manufacturing an electrode that can efficiently manufacture an electrode with improved high output and rapid charging characteristics due to uniform binder distribution in the thickness direction compared to the wet manufacturing electrode.

In addition, the present invention has a further object to provide an electrode manufactured by the above-described manufacturing method and a secondary battery including the electrode.

The method for manufacturing an electrode for secondary batteries according to the present invention to achieve the above object is,

(a) manufacturing step of an electrode active material slurry prepared by dispersing an electrode active material, a conductive material, and a binder in a dispersion medium, and using carbon nanotubes (CNTs) as a conductive material;

(b) drying the electrode active material slurry to remove the dispersion medium to prepare an active material powder whose surface is covered with carbon nanotubes; and

(c) manufacturing an electrode by applying and pressing the active material powder to one or both sides of a current collector.

According to a preferred embodiment of the present invention, in step (b), the dispersion medium may be removed from the electrode active material slurry by spray drying or freeze drying.

According to a preferred embodiment of the present invention, the particle diameter of the active material powder may be 10 to 300 μm, more preferably 50 to 150 μm.

According to a preferred embodiment of the present invention, the average length of the carbon nanotubes may be 0.1 ㎛ to 100 ㎛, more preferably 1 ㎛ to 20 ㎛.

According to a preferred embodiment of the present invention, the carbon nanotubes of the present invention may have an average diameter of 0.4 nm to 20 nm.

According to a preferred embodiment of the present invention, the solid content excluding the dispersion medium may be 10 to 40 parts by weight based on 100 parts by weight of the electrode active material slurry.

In addition, the secondary battery according to the present invention is characterized in that one or both of the positive electrode and the negative electrode are electrodes manufactured according to the present invention described above in the secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte.

According to the present invention, by using carbon nanotubes instead of conventional spherical conductive materials, excellent conductive performance can be achieved even with a small content of the conductive material, and thus the energy density can be increased by a relative increase in the amount of active material used. . In addition, in the present invention, compared to the powder mixing method, superior conductive performance can be achieved by wrapping carbon nanotubes thinly and evenly on the surface of the active material, and the adhesion of the electrode is improved by distributing the binder particularly evenly in the thickness direction compared to the wet manufacturing method. This results in improved high-output characteristics and fast charging characteristics.

Figure 1a is an SEM photograph obtained after dyeing the cross section of the electrode in Example 1 of the present invention.
Figure 1b shows the binder distribution ratio measured for each region by dividing the image in Figure 1a into nine regions in the thickness direction.
Figure 2a is an SEM photograph obtained after dyeing the cross section of the electrode of Comparative Example 1.
Figure 2b shows the binder distribution ratio measured for each region by dividing the image in Figure 2a into nine regions in the thickness direction.

Hereinafter, the present invention will be described in more detail. The details, examples, and drawings described below merely exemplify embodiments of the present invention, and the present invention should not be construed as being limited to these descriptions or contents.

The method for manufacturing an electrode for secondary batteries according to the present invention is,

(a) a manufacturing step of an electrode active material slurry prepared by dispersing an electrode active material, a conductive material, and a binder in a dispersion medium, and using carbon nanotubes (CNTs) as a conductive material (hereinafter, sometimes abbreviated as step (a));

(b) drying the electrode active material slurry to remove the dispersion medium to produce an active material powder whose surface is covered with carbon nanotubes (hereinafter abbreviated as step (b)); and

(c) manufacturing an electrode by applying and pressing the active material powder to one or both sides of a current collector (hereinafter, sometimes abbreviated as step (c)).

In a typical electrode manufacturing method, an electrode active material slurry is prepared, coated on an electrode current collector, and then dried and rolled to manufacture an electrode. However, in the manufacturing method of the present invention, the prepared electrode active material slurry is first dried and powdered. Then, this powder is applied to the current collector and pressed to produce an electrode.

In the present invention, which performs the process in this order, the advantage is that the active material, carbon nanotubes (conductive material), etc. are dispersed using a dispersion medium in the manufacturing step of the electrode active material slurry, so that the carbon nanotubes can be uniformly wrapped around the surface of the active material. By drying the prepared active material slurry before applying it to the current collector, there is no room for movement of the binder rising to the surface of the active material layer as the dispersion medium evaporates, resulting in an even distribution of the binder within the electrode. There is. Accordingly, excellent conductive performance can be secured, while the adhesion of the electrode is improved and high output characteristics and fast charging characteristics are improved.

The electrode active material used in step (a) of the present invention, carbon nanotubes as a conductive material, binder, dispersion medium, etc. are common ones known in the art and are not particularly limited. The solid content excluding the dispersion medium is usually 5 to 50 parts by weight, preferably 10 to 40 parts by weight, and most preferably 20 to 30 parts by weight, based on 100 parts by weight of the electrode active material slurry. If the solid content exceeds 50 parts by weight, it is undesirable in terms of dispersibility of the conductive material, and if it is less than 5 parts by weight, it is undesirable in terms of productivity.

Since the electrode manufacturing method of the present invention can be applied to both positive and negative electrodes, the electrode active material may be a positive electrode active material or a negative electrode active material. Specifically, the positive electrode active material is a lithium transition metal oxide and includes two or more transition metals, for example, lithium cobalt oxide (LiCoO ₂ ) substituted with one or more transition metals, lithium nickel oxide (LiNiO ₂ ), etc. Layered compounds; Lithium manganese oxide substituted with one or more transition metals; Chemical formula LiNi _{1 - y} MyO ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga and contains one or more of the above elements, 0.01≤≤y≤≤0.7) Lithium nickel-based oxide expressed as; Li _{1 + z} Ni _{1 / 3} Co _{1 / 3} Mn _{1 / 3} O ₂ , Li _{1 + z} Ni _{0 . 4} Mn _{0 . 4} Co _{0 . 2} O ₂ , etc. Li _{1 + z} Ni _b Mn _c Co _{1 - (b+c+d)} M _d O _(2-e) Ae (where -0.5≤z≤≤0.5, 0.1≤≤b≤≤0.8 , 0.1≤≤c≤≤0.8, 0≤≤d≤≤0.2, 0≤≤e≤≤0.2, b+c+d<1, M is Al, Mg, Cr, Ti, Si or Y, and A = Lithium nickel cobalt manganese composite oxide expressed as F, P or Cl); Chemical formula Li _{1 + x M 1 - y} M' _y PO _{4 - z} (Here, M = transition metal, specifically Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, -0.5≤≤x≤≤+0.5, 0≤ and olivine-based lithium metal phosphate expressed as ≤y≤≤0.5, 0≤≤z≤≤0.1.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt, and Ti, which can be alloyed with lithium, and compounds containing these elements; Complexes of metals and their compounds with carbon and graphite materials; Lithium-containing nitride, etc. can be mentioned.

The binder includes, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, chlorotrifluoroethylene (CTFE), and polyacrylonitrile ( polyacrylonitrile), polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, poly It may be one or more selected from the group consisting of acrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber.

The dispersion medium is not particularly limited as long as it is a liquid at room temperature and pressure, and may be any one or a mixture of two or more selected from the group consisting of water, alcohol-based compounds, amide-based compounds, ketone-based compounds, ether-based compounds, and lactam-based compounds. You can. Specifically, water; Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol, and hexanol; Ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone, and cycloheptanone; Methyl ethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, din-amyl ether, diisoamyl ether, methylpropyl ether, methyl isopropyl ether, methyl butyl ether, ethers such as ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether, and tetrahydrofuran; amides such as diethyl formamide, dimethylacetamide, N-methyl-2-pyrrolidone, and dimethylimidazolidinone; Lactones such as gamma-butyrolactone and delta-butyrolactone; Lactams such as beta-lactam may be mentioned, but are not limited to these alone, and two or more types of dispersion media may be used in mixture.

The carbon nanotube (CNT) has a graphite layer rolled into a single or multiple layer, and is characterized by high conductivity and a large surface area. Raw materials for carbon nanotubes are not particularly limited as long as they contain carbon, and include graphite such as natural graphite and artificial graphite used as general conductive materials, carbon black, acetylene black, Ketjen black, channel black, furnace black, and lamps. In addition to carbon-based materials such as carbon black such as black and summer black, aromatic hydrocarbons such as benzene, toluene, or xylene (o-xylene, m-xylene, p-xylene) can also be used.

In a specific embodiment, the average length of the carbon nanotubes may be 0.1 ㎛ to 100 ㎛, preferably 1 ㎛ to 50 ㎛, and most preferably 20 ㎛ to 30 ㎛. If the average length of the carbon nanotubes outside the above range is longer than 100 ㎛, dispersibility may be reduced due to agglomeration, and if it is less than 0.1 ㎛, it is difficult to secure the desired physical properties, which is not desirable.

Additionally, the average diameter of the carbon nanotubes may be, for example, 0.4 nm to 20 nm. Carbon nanotubes may be single-walled or multiwalled; in the case of single-wall, the average diameter is 0.4 nm to 2 nm, and in the case of multiwall, the average diameter is 10 nm to 20 nm. It is common. If the average diameter of the carbon nanotubes is outside the above range and is less than 0.4 nm, it may be difficult to secure the desired conductivity and even form a single wall, and if the average diameter of the carbon nanotubes is larger than 20 nm, it is substantially time and cost This is undesirable as it increases.

In addition to the electrode active material, conductive material, binder, and dispersion medium, the electrode active material slurry may further include a viscosity modifier and/or filler. These viscosity modifiers and fillers may be appropriately selected and used among those known in the art. .

In a preferred embodiment of the present invention, the drying in step (b) is preferably performed by spray drying or freeze drying. This drying method suppresses the movement of the binder in the active material slurry even during the formation stage of the active material powder, making it possible to manufacture an active material powder in which the binder is evenly distributed.

The particle diameter of the active material powder obtained by drying the electrode active material slurry and removing the dispersion medium may be 10 to 300 μm, preferably 30 to 200 μm, and most preferably 50 to 150 μm.

The spray drying method is a drying method that obtains a powder-like product by spraying and dispersing a material containing liquid such as moisture in hot air and drying it rapidly while returning it with hot air. It can be performed using a spray dryer known in the industry. . This drying method is preferable because drying is performed rapidly and the temperature of the material does not rise relatively high, so side effects caused by heating can be prevented and movement of the binder in the slurry can be suppressed.

The hot air temperature during spray drying is usually 80 to 250°C, preferably 100 to 200°C. In the spray drying method, the method of blowing hot air is not particularly limited, for example, a method in which the hot air and the spray direction coexist in the horizontal direction, a method in which the spray is sprayed from the top of the drying tower and descends with the hot air, and the sprayed water and hot air are A method of countercurrent contact, where the sprayed enemy first flows in parallel with the hot air and then falls due to gravity, makes countercurrent contact.

The freeze-drying method is a drying method in which the electrode active material slurry is frozen by cooling it to a low temperature below the freezing point of the dispersion medium, and then the dispersion medium is removed by sublimation by reducing the pressure to a high vacuum degree below the vapor pressure, preventing denaturation of the material due to heat, This is desirable because it can suppress the movement of the binder in the slurry.

In a preferred embodiment of the present invention, the freezing is preferably performed for 0.5 to 12 hours at a temperature of -40°C to -0.1°C, which is below the freezing point of the dispersion medium, and at normal pressure.

The sublimation is preferably carried out at a pressure of 1.4×10 ^-5 to 6.2×10 ^-3 kgf/cm2, which is lower than the vapor pressure of the dispersion medium, and at a temperature higher than the temperature at the time of freezing, at 0°C to 20°C.

The current collector used in step (c) of the present invention may be a positive electrode current collector or a negative electrode current collector, and is generally made to have a thickness of 3 ㎛ to 500 ㎛, and has a high durability without causing chemical changes in the battery. There is no particular limitation as long as it has conductivity, but examples of the positive electrode current collector include, for example, stainless steel, aluminum (Al), nickel (Ni), titanium (Ti), calcined carbon, or carbon on the surface of aluminum or stainless steel. Those surface-treated with nickel, titanium, silver, etc. can be used, and the negative electrode current collector includes, for example, stainless steel, aluminum (Al), nickel (Ni), titanium (Ti), fired carbon, or aluminum. Surface treatment of stainless steel with carbon, nickel, titanium, silver, etc. can be used.

The application and pressurization of the active material powder in step (c) is not particularly limited and can be performed by conventional methods known in the art. For example, the active material powder is supplied to the roll-type pressing device using a supply device such as a screw feeder, and the electrode is rolled, or the active material powder is spread on the current collector, the thickness is adjusted by picking the active material powder with a blade, etc., and then the electrode is rolled. It can be rolled. At this time, the temperature during rolling is usually 0°C to 200°C. The linear pressure during rolling may be 0.5 to 3.5 ton/cm, more preferably 1 to 3 ton/cm, and most preferably 1 to 2 ton/cm. If the linear pressure during rolling is less than 0.5 ton/cm, it is undesirable in terms of electrode uniformity, and if the linear pressure exceeds 3.5 ton/cm, the electrode may break.

The number of rolling of the dried coating portion is preferably 1 to 3 times. If the number of rolling exceeds 3 times, it is not desirable because there is a risk that the electrode mixture may break.

In addition, the present invention provides an electrode manufactured by the above-described manufacturing method and a secondary battery including the same. The secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, One or both of the anode and the cathode are characterized in that they are electrodes manufactured according to the present invention described above.

Carbon-based negative electrode active materials are commonly used in the production of negative electrodes, and since carbon-based active materials themselves have a certain degree of electrical conductivity, carbon nanotubes are generally evaluated as more useful in the production of positive electrodes than negative electrodes. Therefore, if the manufacturing method of the present invention is used when manufacturing an anode, the effect of improving the electrical characteristics of the electrode while uniformizing the distribution ratio of the binder in the thickness direction of the electrode can be better expressed compared to the cathode.

Matters related to the separator, electrolyte, etc. that constitute the secondary battery of the present invention are commonly known in the art and can be used in the present invention without any particular limitation, and those skilled in the art can easily understand and acquire the matters and invent the present invention. Since they can be used, detailed descriptions of them are omitted. In this regard, for example, patent document 2 (Korean Patent Publication No. 10-2017-0111730) applied by the present applicant may be referred to, and the entire contents of this document are included in the present invention to the extent that they do not contradict the present invention. Quoting for reference

Hereinafter, the present invention will be described in more detail through examples. The following examples are only intended to specifically illustrate the present invention, so it goes without saying that the scope of the present invention is not limited by these examples.

Example 1 (Manufacture of anode)

LiNi ₀ as the positive electrode active material _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ (average particle diameter: 14㎛), PVDF as a binder, and carbon nanotubes (diameter: 10~20nm, length: 20~30㎛, bundle type CNT, source: LG Chemical) as a conductive material in the ratio of 97:1.5: A positive electrode slurry (solids concentration: 25%) to form a positive electrode active material layer was prepared by mixing and dispersing in N-methyl pyrrolidone (NMP), a dispersion medium, at a weight ratio of 1.5.

The positive electrode slurry was dried using a spray drying method to remove the dispersion medium, thereby obtaining an active material powder (particle diameter: 50-150㎛) whose surface was covered with carbon nanotubes. At this time, spray drying was performed using a spray dryer (OC-16; Okawara Chemical) using a rotating disk atomizer (diameter 65 mm) at a rotation speed of 25,000 rpm, a hot air temperature of 150°C, and a particle recovery outlet temperature of 90°C.

A positive electrode was manufactured by applying the obtained active material particles to the cross section of aluminum foil (thickness: 20㎛) and pressing to form a positive electrode active material layer with a thickness of 150㎛.

Comparative example 1 (Manufacture of anode)

A positive electrode was manufactured by applying, drying, and rolling the positive electrode slurry prepared in Example 1 to the cross section of aluminum foil (thickness: 20 μm) without drying it to form a positive electrode active material layer (thickness: 150 μm).

<Experimental example> Measurement of distribution ratio of binder

In order to confirm the uniformity of distribution of the binder in the thickness direction in the electrodes of Example 1 and Comparative Example 1, the active material, voids, and binder were dyed on the cross section of each electrode (anode) of Example 1 and Comparative Example 1. Afterwards, SEM images were obtained. The obtained SEM images are as shown in FIG. 1A (Example) and FIG. 2A (Comparative Example). In the SEM image, the green area represents the active material, the red area represents the void, and the white area represents the binder. After dividing the SEM image into 9 regions in the thickness direction, the ratio of the area occupied by the binder in each region was calculated as the binder distribution ratio using the AVIZ0 program. The distribution ratio of the binder measured in this way is shown in Table 1 and Figures 1b (Example) and Figure 2b (Comparative Example).

area Binder ratio (%)
Example 1 (Figure 1b) Comparative Example 1 (Figure 2b) upper floor One 10.0 17.4 2 11.5 21.0 3 10.7 12.1 bout 32.1 50.5 middle layer 4 13.1 12.0 5 11.3 9.5 6 10.4 8.5 bout 34.8 30.0 substratum 7 10.8 8.5 8 11.2 6.0 9 11.1 5.0 bout 33.1 19.5

As can be seen from FIGS. 1A to 2B and Table 1, in the electrode of Comparative Example 1, as the binder moves toward the top of the electrode and gets closer to the current collector, the distribution ratio of the binder decreases, so that the binder is distributed throughout the electrode in the thickness direction. Although it is non-uniformly distributed, it can be confirmed that the binder is uniformly distributed in the upper/middle/lower layers within the electrode according to the present invention.

Although it can naturally be predicted that the adhesive strength of the electrode according to the present invention will be superior from the distribution state of the binder as described above, the adhesive strength between the current collector and the active material layer was actually measured for the electrodes manufactured in Example 1 and Comparative Example 1, respectively. did. The adhesion was measured by cutting the surface of the manufactured electrode, fixing it on a slide glass, and then measuring the 180-degree peeling strength while peeling off the current collector. The evaluation was made by measuring the peeling strength of five or more pieces and determining the average value. The results are shown in Table 2.

Adhesion (gf/2cm) Example 1 20.3 Comparative Example 1 11.9

As can be seen from the above examples and comparative examples, according to the present invention, it can be confirmed that the distribution of the binder in the electrode active material layer, especially the distribution in the thickness direction, is uniform, thereby improving the adhesion of the electrode.

As explained in detail above, the present invention can basically secure excellent conductive performance even with a small content of conductive material, and by uniformly distributing the binder in the electrode active material layer, energy density can be increased, high output characteristics, and rapid speed can be achieved. It is very useful industrially because it can improve charging characteristics.

Meanwhile, although the present invention has been described in detail with reference to specific embodiments and examples above, based on these contents, modifications to various other forms, replacement of materials, etc., changes in dimensions, and additional changes may be made without departing from the scope of the present invention. It will be obvious to those skilled in the art that components can be added, etc.

Claims (9)

(a) manufacturing step of an electrode active material slurry prepared by dispersing an electrode active material, a conductive material, and a binder in a dispersion medium, and using carbon nanotubes (CNTs) as a conductive material;
(b) drying the electrode active material slurry to remove the dispersion medium to prepare an active material powder whose surface is covered with carbon nanotubes; and
(c) manufacturing an electrode by applying and pressing the active material powder to one or both sides of a current collector,
The carbon nanotubes have an average length of 0.1 ㎛ to 100 ㎛, an average diameter of 0.4 nm to 20 nm,
In step (b), the dispersion medium is removed by spray drying or freeze drying,
No drying process is performed in step (c),
When the electrode cross section is divided into 9 regions in the thickness direction of the electrode, the ratio of the binder area in each region to the binder area of the entire electrode cross section is 10.0% to 13.1% (however, the ratio of the binder area in each of the 9 regions is 10.0% to 13.1% A method of manufacturing an electrode for a secondary battery, characterized in that the total is 100%.
delete According to claim 1,
A method of manufacturing an electrode for a secondary battery, characterized in that the particle diameter of the active material powder is 50 to 150㎛.
delete delete According to claim 1,
A method for manufacturing an electrode for a secondary battery, characterized in that the solid content excluding the dispersion medium is 10 to 40 parts by weight based on 100 parts by weight of the electrode active material slurry.
Manufactured according to claim 1,
When the electrode cross section is divided into 9 regions in the thickness direction of the electrode, the ratio of the binder area in each region to the binder area of the entire electrode cross section is 10.0% to 13.1% (however, the ratio of the binder area in each of the 9 regions is 10.0% to 13.1% A secondary battery electrode characterized in that the total is 100%.
In a secondary battery comprising an anode, a cathode, a separator, and an electrolyte,
One or both of the anode and cathode are prepared according to claim 1,
When the electrode cross section is divided into 9 regions in the thickness direction of the electrode, the ratio of the binder area in each region to the binder area of the entire electrode cross section is 10.0% to 13.1% (however, the ratio of the binder area in each of the 9 regions is 10.0% to 13.1% The total of is 100%) A secondary battery characterized in that it is an electrode. delete