KR102527927B1 - Electrode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

In the present invention, an electrode mixture including a bimodal type electrode active material composed of large and small particles having different average particle diameters, a conductive material, and a binder is formed on a current collector, and a 0.1 to 2.0 μm thick primer coating layer, the allele: small particle weight ratio is 6: 4 to 8: 2, the average particle diameter (D50) of the allele: average particle diameter (D50) ratio of the allele is 4.3: 1 to 2: 1 phosphorus, relates to an electrode for a lithium secondary battery.

Description

Electrode for lithium secondary battery and lithium secondary battery employing the same

The present invention relates to an electrode for a lithium secondary battery and a lithium secondary battery employing the same.

Lithium secondary battery is a type of secondary battery in which charging and discharging are performed by intercalation and desorption of lithium ions within the battery. Conversely, during discharge, the lithium ions inserted into the negative electrode move toward the positive electrode and are inserted into the active material of the positive electrode. Such a "lithium" secondary battery has advantages of high energy density, large electromotive force, and high capacity, and is widely used as a power source for mobile phones, laptop computers, and the like.

The "lithium" secondary battery is usually composed of a positive electrode, a negative electrode, a separator and an electrolyte solution. As described above, the positive electrode and the negative electrode include a positive electrode active material and a negative electrode active material capable of intercalating and deintercalating lithium ions. A separator prevents physical “cell” contact between the anode and the cathode. Instead, the movement of ions through the separator is free. The electrolyte serves as a passage through which ions can freely move between the anode and the cathode.

On the other hand, in the lithium secondary battery, an active material is coated with a constant thickness on each of the positive and negative current collectors, and a separator is interposed between the current collectors to form a jelly roll or cylindrical shape. It can be produced by accommodating the manufactured electrode assembly in a cylindrical, prismatic can or pouch and sealing it.

Meanwhile, in the process of manufacturing the battery as described above, in the process of coating the electrode mixture on the current collector, a rolling process is performed. At this time, stress is applied to the current collector from the electrode mixture, and cracks occur in the current collector. There may be. When a crack occurs on the current collector, the electron movement path is reduced and cell resistance increases, which may adversely affect the lifespan characteristics and high rate charge/discharge characteristics of the battery.

In addition, when the crack is severe, complete disconnection may occur in the current collector, and when complete disconnection occurs, an electrode tab portion forming an electrode is blocked, resulting in loss of function of the battery cell itself.

The present invention has been made to solve the above problems, and the present invention is a bimodal type electrode active material composed of large particles and small particles having different average particle diameters, a conductive material, and an electrode mixture including a binder on a current collector. formed in, and the ratio of the weight ratio of the large particles to the small particles and the average particle diameter (D50) of the large particles to the average particle diameter (D50) of the small particles is within a specific range, and when a primer layer is provided between the electrode mixture and the current collector, the electrode It is intended to provide an electrode for a lithium secondary battery that not only improves rollability in a rolling process during the manufacturing process, but also effectively prevents cracks that may occur in the electrode during a winding process, and a lithium secondary battery employing the same.

In the present specification, an electrode mixture including a bimodal type electrode active material composed of large and small particles having different average particle diameters, a conductive material, and a binder is formed on a current collector,

A primer coating layer having a thickness of 0.1 to 2.0 μm is included between the electrode mixture and the current collector,

The allele: the weight ratio of the small particles is 6: 4 to 8: 2, the average particle diameter (D50) of the alleles: the average particle diameter (D50) ratio of the small particles is 4.3: 1 to 2: 1, a lithium secondary battery electrode is provided do.

In addition, in the present specification, a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, wherein at least one electrode selected from the positive electrode and the negative electrode is an electrode for the lithium secondary battery is provided.

Hereinafter, an electrode for a lithium secondary battery and a lithium secondary battery according to specific embodiments of the present invention will be described in more detail.

As described above, according to one embodiment of the present invention, an electrode mixture including a bimodal type electrode active material composed of large particles and small particles having different average particle diameters, a conductive material, and a binder is formed on the current collector. become,

A primer coating layer having a thickness of 0.1 to 2.0 μm is included between the electrode mixture and the current collector,

The allele: the weight ratio of the small particles is 6: 4 to 8: 2, the average particle diameter (D50) of the alleles: the average particle diameter (D50) ratio of the small particles is 4.3: 1 to 2: 1, a lithium secondary battery electrode is provided It can be.

In an electrode for a lithium secondary battery, the present inventors configure electrode active material particles in an electrode mixture formed on a current collector in a bimodal form composed of large particles and small particles, and the large particle: small particle weight ratio and average particle diameter of the large particles (D50): When the ratio of the average particle diameter (D50) of small particles is within a specific range, and a primer layer is provided between the electrode mixture and the current collector, not only the rolling property is improved in the rolling process during the electrode manufacturing process, but also the winding ( It was confirmed through experiments that effectively preventing cracks that may occur in electrodes in the winding process was completed, and the invention was completed.

In the electrode for a lithium secondary battery according to one embodiment of the present invention, the electrode active material in the electrode mixture formed on the current collector is in a bimodal form consisting of large particles and small particles having different average particle diameters, and the weight ratio of large particles to small particles Is 6: 4 to 8: 2, or 7: 3 to 8: 2, and the ratio of the average particle diameter (D50) of the alleles: the average particle diameter (D50) of the small particles is 4.3: 1 to 2: 1, or 4: 1 to It may be 2.5:1.

In general, according to the prior art, when manufacturing an electrode, it is possible to improve the volume density and improve rollability by using large and small particles having an average particle diameter as electrode active materials, and in particular, the particle size of small particles (d _small ) / particle size of large particles (d It is known that the smaller the diameter ratio (d _s /d _l ) measured by _large ), the better the packing effect during rolling is. However, when the active material particles are well packed and come into direct contact with the current collector, for example, as shown in FIG. 2, the stress applied to the current collector relatively increases in the winding process performed after rolling, There is a problem in that cracks are generated in the cell, cell resistance is increased due to a reduction in the electron movement path, and adversely affects the lifespan characteristics and high-rate charge/discharge characteristics of the battery.

In addition, when the crack is severe, as shown in FIG. 4 exemplarily, the electrode may be completely disconnected, and in this case, the electrode tab portion forming the electrode is blocked and the battery cell itself may lose its function. existed.

However, according to the present invention, the electrode active material is configured in a bimodal form consisting of large particles and small particles having different average particle diameters, but the large: small particle weight ratio and average particle diameter (D50) of small particles: average particle diameter of small particles (D50) When the ratio is configured to be within a specific range, the rollability is improved in the rolling process through the improvement of the volume density, while minimizing the stress applied to the electrode to effectively prevent cracks that may occur in the electrode in the winding process You can do it. Therefore, it is possible to prevent the shortening of the life of the battery and the deterioration of the high-rate charge/discharge characteristics due to cracks, and further prevent the loss of the function of the blocking cell itself in advance.

Specifically, the allele according to an embodiment of the present invention: the weight ratio of small particles is 6: 4 to 8: 2, and the average particle diameter (D50) of the allele: average particle diameter (D50) ratio of the allele is 4.3: 1 to 2 : can be 1. The filling density is sufficiently secured within the weight ratio range and average particle diameter ratio of the large particles to small particles to improve rollability in the rolling process, and at the same time to lower the stress applied to the current collector to effectively crack cracks that may occur on the current collector in the winding process be able to prevent

The average particle diameter (D50) of alleles according to one embodiment of the present invention may be 13 to 15 μm, or 14 to 15 μm, and the average particle diameter (D50) of small particles according to another embodiment of the present invention is 3.5 to 15 μm. It may be 6.5 μm, or 4 to 6 μm. The average particle diameter (D50) of these large/small particles can be measured according to a conventional number average particle diameter measurement method, and can be calculated from the result by measuring the number distribution for each particle diameter using a particle size analyzer well known to those skilled in the art. there is. .

On the other hand, in the electrode for a lithium secondary battery according to an embodiment of the present invention, the average particle diameter (D50) value of all the particles of the electrode active material having a bimodal form composed of large and small particles having different average particle diameters is 9 to 9 11 μm, or 9.5 to 10.5 μm, and the standard deviation (SD) of the particle size may be greater than 0 and less than or equal to 2, or 0.1 to 1.5.

Meanwhile, in the electrode for a lithium secondary battery according to an embodiment of the present invention, a primer coating layer having a thickness of 0.1 to 2.0 μm may be included between the electrode mixture and the current collector. As such, in the lithium secondary battery electrode manufactured according to an embodiment of the present invention, an example of a schematic diagram briefly showing a structure in which a primer coating layer is formed between the current collector and the positive electrode mixture is shown in FIG. 3 .

Specifically, the primer coating layer is positioned between the current collector and the electrode mixture, and increases bonding strength between the current collector and the electrode mixture to prevent the electrode mixture layer from being separated from the current collector during charging and discharging of the battery. Furthermore, since the primer coating layer is provided, the stress applied to the current collector by the electrode mixture including the electrode active material particles due to the pressure applied during the rolling and winding process can be buffered, thereby further preventing cracks in the electrode current collector. can be effectively prevented.

On the other hand, the primer coating layer according to an embodiment of the present invention is not particularly limited as long as it can perform the above role, but as an example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydrogel Roxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluoro rubber, etc. It may be selected from various copolymers, etc., but in detail, it may be a polymer of the same type as the binder included in the electrode mixture in terms of ease of manufacture and mutual adhesion between the primer coating layer and the electrode mixture layer.

Meanwhile, the primer coating layer may be formed by a wet method, for example, a gravure roll-coating method, but is not particularly limited.

Meanwhile, according to an embodiment of the present invention, at least one type of electrode selected from the positive electrode and the negative electrode includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the lithium secondary battery electrode is the lithium secondary battery. A battery may be provided.

The positive electrode or the negative electrode is composed of a current collector and an electrode mixture formed on the current collector, and the electrode mixture may include an electrode active material, a conductive material, and a binder.

The current collector is a metal having high conductivity, and the electrode mixture slurry can be easily adhered to, and the current collector is not limited as long as it is non-reactive in the voltage range of the battery. When the current collector is a positive electrode current collector, it may be, for example, a foil made of aluminum, nickel, or a combination thereof, or may be a laminate of substrates made of the above materials. When the current collector is an anode current collector, it may be a foil made of copper, gold, nickel, copper alloy, or a combination thereof, or may be a laminate of substrates made of the above materials.

Meanwhile, when the electrode active material of the electrode mixture is a positive electrode active material, a positive electrode active material capable of intercalating and deintercalating lithium, for example, a manganese spinel-based active material or lithium metal oxide may be used. Among the lithium metal oxides, lithium-cobalt-based oxides containing cobalt or manganese, lithium-manganese-based oxides, lithium-nickel-manganese-based oxides, lithium-manganese-cobalt-based oxides, and lithium-nickel-manganese-cobalt-based oxides, etc. can be used

Meanwhile, when the electrode active material of the electrode mixture is an anode active material, an anode active material capable of intercalating and deintercalating lithium, such as lithium metal, a carbon material, a metal compound, and a mixture thereof may be used. For example, both low crystalline carbon and high crystalline carbon may be used as the carbon material. The low crystalline carbon may be at least one selected from soft carbon and hard carbon, and the high crystalline carbon may be natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch. At least one type of high-temperature calcined carbon consisting of mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes can

On the other hand, the metal compound is Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, Ba, etc. It may be a compound containing one or more types of metal elements. These metal compounds can be used in any form, such as simple elements, alloys, oxides (TiO ₂ , SnO _{2 ,} etc.), nitrides, sulfides, borides, alloys with lithium, etc. It can be high-capacity. Among them, one or more elements selected from Si, Ge, and Sn may be contained, and more specifically, one or more elements selected from Si and Sn may be included in order to increase the capacity of the battery.

On the other hand, the conductive material has conductivity without causing side reactions with other elements of the battery. Specific examples of the conductive material include graphite such as natural graphite or artificial graphite; carbon black such as carbon black (super-p), 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 whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; It may be a conductive material such as a polyphenylene derivative.

On the other hand, the binder is a component that assists in the binding of the electrode active material and the conductive material and the binding to the current collector. Specific examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, and polymethylmethacrylate. , polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) , sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and the like.

An electrode according to an embodiment of the present invention may be manufactured by applying an electrode mixture in which the above-described electrode active material, conductive material, and binder are mixed on a current collector having a primer coating layer formed thereon. Specifically, an electrode is manufactured by applying an electrode mixture on a current collector on which a primer coating layer is formed and then pressing. Specifically, in the rolling process, the electrode current collector coated with the electrode mixture is passed between two or more rotating rolls, and through this process, the electrode mixture can be well adhered to the electrode current collector. Meanwhile, the two or more rotating rolls may be in a high temperature state. On the other hand, after the rolling process as described above, a step of drying it may be further included.

Among the electrodes prepared as described above, the positive electrode mixture may be coated on a current collector in a thickness of 30 μm to 180 μm, more specifically, in a thickness of 50 μm to 150 μm. A sufficient amount of the positive electrode (active material) is secured within the thickness range of the “positive electrode” mixture, so that the “battery” capacity is prevented from being reduced, and cycle characteristics or rate characteristics can be improved.

Among the electrodes prepared as described above, the negative electrode mixture may be coated on a current collector with a thickness of 1 μm to 180 μm, more specifically, 30 μm to 150 μm. When the material satisfies this thickness range within the thickness range of the above negative electrode mixture, a sufficient amount of active material in the negative electrode active material layer is secured, and the reduction in battery capacity can be prevented, and cycle characteristics or rate characteristics can be improved. .

On the other hand, in one embodiment of the present invention, a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, and at least one electrode selected from the positive electrode and the negative electrode is the electrode for the lithium secondary battery. is provided.

The electrode for a lithium secondary battery described above may be a positive electrode or a negative electrode.

On the other hand, the separator is interposed between the positive electrode and the negative electrode and outside the positive electrode or the negative electrode in a state where the positive electrode and the negative electrode plate are not wound, and when the positive electrode and the negative electrode are wound together with the separator, the positive electrode or negative electrode located outside Prevent contact with the negative electrode or the positive electrode located inside. On the other hand, in the case of the electrode for a lithium secondary battery configured according to the present invention, the occurrence of cracks in the electrode in the winding process is effectively suppressed.

As the separator, a polymeric porous substrate commonly used as a separator in the art may be used, and is not particularly limited. For example, a polyolefin-based porous substrate; or a group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfite, and polyethylene naphthalene. It may be a porous substrate formed of any one selected from or a mixture of two or more of them, and the polyolefin-based porous substrate can be used as long as it is a commonly used polyolefin-based porous substrate. More specifically, a membrane formed of polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high-molecular-weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, each alone or a mixture thereof. ) or non-woven fabric.

As described above, when the positive electrode, the negative electrode, and the separator are prepared, a jelly roll is formed by winding the electrode assembly, dried, stored in a battery case, and electrolyte solution is injected into the battery case. Meanwhile, the type of the battery case is not particularly limited, but may be, for example, a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

Meanwhile, the electrolyte solution may be a non-aqueous electrolyte solution including an organic solvent and an electrolyte salt, and as the organic solvent, those commonly used in electrolyte solutions for lithium secondary batteries may be used without limitation. Representatively, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methyl carbonate Mate (MF), gamma-butyrolactone (γ-BL; butyrolactone), sulfolane (sulfolane) and methyl acetate (MA; methyl acetate) Any one selected from the group consisting of, or a mixture of two or more of them can be used However, it is not limited thereto.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they dissociate lithium salts in the electrolyte well. A non-aqueous electrolyte having high electrical conductivity can be prepared by mixing and using a low-viscosity, low-dielectric constant linear carbonate such as carbonate in an appropriate ratio.

In addition, the electrolyte salt contained in the non-aqueous electrolyte of the present invention, as an anion, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- _, CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- ,SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may include any one selected from the group consisting of. Here, non-limiting examples of the electrolyte salt include 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 ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carbonate, lithium 4phenylborate, and the like may be used, but are not limited thereto.

The above description is merely an example of the technical idea of the present invention, and various modifications and variations can be made to those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed according to the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

In the case of a lithium secondary battery to which the electrode for a lithium secondary battery of the present invention is applied, rollability is improved in a rolling process during the electrode manufacturing process, and cracks that may occur in the electrode during a winding process are effectively prevented.

Accordingly, there is little concern about an increase in cell resistance, a decrease in battery lifespan characteristics, and high rate charge/discharge characteristics, and complete disconnection due to cracks in the electrodes is prevented, thereby preventing loss of battery cell function.

1 shows the results of measuring stress applied to a cathode current collector for a lithium secondary battery manufactured according to Example 1 of the present invention.
2 shows the results of measuring the stress applied to the cathode current collector for a lithium secondary battery prepared according to Comparative Example 1 of the present invention.
3 is a schematic diagram schematically illustrating a structure in which a primer coating layer is formed between a current collector and a positive electrode mixture in an electrode for a lithium secondary battery manufactured according to an embodiment of the present invention.
4 is a photograph showing that an electrode crack occurs when the electrode manufactured according to Comparative Example 1 is wound.

Since the present invention can have various changes and various forms, specific embodiments will be exemplified and described in detail below. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Hereinafter, the actions and effects of the present invention will be described in more detail through specific examples of the present invention. However, these embodiments are only presented as examples of the invention, and the scope of the invention is not determined thereby.

Example 1: electrode manufacturing

A binder solution was prepared by dissolving a binder (polyvinylidene fluoride, 10% by weight) in N-methylpyrrolidone (NMP) solvent, and then the binder solution and acetylene black conductive material (super C65, average Particle diameter (D50) 30 nm) was mixed and stirred for 3 minutes at 1500 rpm.

Subsequently, lithium cobalt oxide (LiCoO ₂ ) in which large particles having an average particle diameter (D50) of 15 μm and small particles having an average particle diameter (D50) of 5 μm were mixed in a weight ratio of 8:2 was prepared, and the conductive material: positive electrode active material were mixed at a volume ratio of 0.19:1, and then mixed at 1500 rpm for 5 minutes to prepare a positive electrode active material slurry (solid content: 80% by weight). At this time, the average particle diameter of all the particles of the positive electrode active material was 10 μm.

Meanwhile, SBR and polyvinylidene fluoride were mixed in a weight ratio of 1:10 and added to water to prepare a composition for preparing a primer coating layer.

Next, the composition for preparing a primer coating layer was applied to a thickness of 0.5 μm by a gravure-roll coating method on an aluminum foil having a thickness of 15 μm, and then, 6.3 mg of the prepared cathode active material slurry was applied on the primer coating layer using a comma coater. / cm 2 and dried with hot air to prepare a positive electrode (total thickness of 107.2 μm, positive electrode mixture layer thickness of 92 μm) including the first positive electrode mixture layer having a porosity of 65% by volume.

A roll press equipment (CIS Co. Ltd, DLC-CLPCA-2020) equipped with two upper and lower rolls was prepared, and the gap between the two upper and lower rolls was set to be 85 μm. .

A positive electrode including a positive electrode mixture layer having a porosity of 55% by volume by primary rolling while passing the aluminum foil on which the positive electrode mixture layer was formed between the two rolls at room temperature (total thickness 85 ㎛, positive electrode mixture layer thickness 77 ㎛) Manufacturing did After the first rolling, the prepared positive electrode was allowed to stand for 1 hour. Next, the gap between the upper roll and the lower roll is set to a thickness of 67 μm, and then secondary rolling is performed while passing the anode prepared after the primary rolling to a positive electrode including a positive electrode mixture layer having a porosity of 40% by volume ( A total thickness of 67 μm and a cathode mixture layer thickness of 52 μm) were prepared. Then, the positive electrode manufactured after the secondary rolling was left to stand for 1 hour. Next, third rolling was performed at the same roll interval as the second rolling step to prepare a positive electrode (total thickness: 67 μm, positive electrode mixture layer thickness: 52 μm) including a positive electrode mixture layer having a porosity of 40% by volume.

The prepared positive electrode includes a bimodal positive electrode active material and a conductive material having different sizes.

Example 2

An electrode was prepared in the same manner as in Example 1, except that large particles having an average particle diameter (D50) of 15 μm and small particles having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 7:3.

comparative example One

An electrode was prepared in the same manner as in Example 1, except that large particles having an average particle diameter (D50) of 15 μm and small particles having an average particle diameter (D50) of 5 μm were mixed at a weight ratio of 9:1.

comparative example 2

An electrode was prepared in the same manner as in Example 1, except that large particles having an average particle diameter (D50) of 15 μm and small particles having an average particle diameter (D50) of 5 μm were mixed in a weight ratio of 5:5.

comparative example 3

Electrodes were manufactured in the same manner as in Example 1, except that large particles having an average particle diameter (D50) of 15 μm and small particles having an average particle diameter (D50) of 3 μm were used.

comparative example 4

Electrodes were manufactured in the same manner as in Example 1, except that large particles having an average particle diameter (D50) of 13 μm and small particles having an average particle diameter (D50) of 7 μm were used.

[ Experimental example ]

Experimental example 1: Stress evaluation on anode

In the cathodes for lithium secondary batteries prepared according to Example 1 and Comparative Example 1, the stress applied to each cathode current collector was measured, and the measurement results are shown in FIGS. 1 and 2, respectively. Referring to FIGS. 1 and 2 , in Example 1, it was confirmed that the stress applied to the electrode current collector was relatively reduced compared to Comparative Example 1.

Experimental example 2: whole house crack Occurrence measurement

For Examples 1 and 2 and Comparative Examples 1 to 4, whether or not cracks occurred in the positive electrode current collector was evaluated according to the following criteria. The evaluation results are summarized in Table 1 below:

* crack occurrence evaluation criteria

X: In the manufactured electrode, cracks do not occur in the electrode current collector

△: In the manufactured electrode, cracks occur in the electrode current collector, but disconnection of the electrode current collector does not occur

O: In the manufactured electrode, cracks and disconnection occurred in the electrode current collector (Example: Fig. 4)

Crack occurrence Example 1 X Example 2 X Comparative Example 1 △ Comparative Example 2 O Comparative Example 3 O Comparative Example 4 O

As shown in Table 1, in Examples 1 and 2, the stress applied to the electrode current collector is reduced and cracks do not occur on the electrode current collector, whereas in Comparative Examples 1 to 4, cracks and further disconnection of the electrode current collector It has been confirmed that this occurs

Claims (10)

An electrode mixture including a bimodal electrode active material composed of large and small particles having different average particle diameters, a conductive material, and a binder is formed on a positive electrode current collector,
A primer coating layer having a thickness of 0.1 to 2.0 μm is included between the electrode mixture and the positive electrode current collector,
The electrode active material includes lithium-cobalt-based oxide, the positive electrode current collector includes aluminum, and the primer coating layer includes a polymer having the same polymer as the binder of the electrode mixture,
The allele: the weight ratio of the small particles is 6: 4 to 8: 2, the average particle diameter (D50) of the allele: the average particle diameter (D50) ratio of the small particles is 4.3: 1 to 2: 1, lithium secondary battery electrode. According to claim 1,
The average particle diameter (D50) of the allele is a lithium secondary battery electrode of 13 to 15㎛. According to claim 1,
The average particle diameter (D50) of the small particles is a lithium secondary battery electrode of 3.5 to 6.5㎛. According to claim 1,
The average particle diameter (D50) value of all the particles of the electrode active material having a bimodal form composed of large and small particles having different average particle diameters is 9 to 11 μm, and the standard deviation (SD) of the particle diameter is greater than 0 and less than 2 , Electrodes for lithium secondary batteries. delete delete According to claim 1,
An electrode for a lithium secondary battery in which a positive electrode mixture is formed on the positive electrode current collector to a thickness of 30 μm to 180 μm. delete According to claim 1,
The primer coating layer is polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, poly An electrode for a lithium secondary battery comprising at least one polymer selected from the group consisting of propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the electrode for a lithium secondary battery according to claim 1.

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