Binder for lithium secondary batteries and electrodes for lithium secondary batteries using the same

Abstract

A binder for a lithium secondary battery is provided, comprising composite particles of a polytetrafluoroethylene structure coated with an acrylic polymer. The binder for a lithium secondary battery according to an embodiment of the present invention not only solves problems such as agglomeration that may occur when handling conventional binders, but also has excellent physical properties such as low thickness deviation and high tensile strength when manufacturing an electrode. In addition, a battery using such an electrode has improved battery performance such as capacity retention.

Description

[Technical Field]

[0001] This invention relates to a binder for lithium secondary batteries and an electrode for lithium secondary batteries using the same. Specifically, it relates to a binder for lithium secondary batteries containing polytetrafluoroethylene modified with an acrylic polymer and an electrode for lithium secondary batteries using the same.

[0002] This application claims priority under Korean Patent Application No. 10-2022-0116479 dated September 15, 2022, and incorporates all the contents disclosed in the said Korean Patent Application as part of this Specification. [Background technology]

[0003] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly increasing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] During the manufacturing of electrodes for lithium secondary batteries, a mixture containing electrode active material, conductive material, and binder is produced by mixing the electrode active material. This mixture is then applied to an electrode current collector and pressurized through equipment such as a roll to produce the electrode. Binders such as polytetrafluoroethylene (PTFE) undergo shear force during roll pressurization, primarily at the surface in contact with the roll, leading to fibrous formation. This fibrous formation occurs in the direction of roll movement (Machine Direction, MD direction), and relatively, it is mainly formed around the binder located on the electrode surface. Even with binder fibrous formation, the electrode active material, conductive material, and binder located inside the electrode remain dispersed as small particles, which can lead to insufficient electrode durability. Electrode durability is a factor that can be related to electrode lifespan and directly affect battery performance.

[0005] The demands of users for secondary batteries with high energy density are increasing rapidly, and in this technical field, research on electrodes with a thick thickness (thick film electrodes) has been continuing. In the conventional traditional electrode manufacturing method of manufacturing electrodes by coating a slurry containing an electrode active material in a wet method, there is a phenomenon of movement of a conductive material and a binder to the upper part of the coating layer during drying. As a result, due to problems such as a decrease in conductivity and a low adhesive force between the current collector and the electrode active material, it is not easy to maintain the quality of the manufactured electrodes while increasing the thickness of the electrodes. Also, in a new electrode manufacturing method of manufacturing electrodes in a dry method, unless the functionality of the binder is maximally enhanced, the adhesive force between the particles of the electrode active material, the conductive material, and the binder becomes insufficient, and it is difficult to manufacture electrodes with high durability while having a thick thickness.

[0006] Therefore, the present inventor completed the present invention after continuous research on a plan to enhance the functionality of the binder and manufacture a thick film electrode with high durability while manufacturing electrodes in a dry method.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention aims to provide a binder for a lithium secondary battery containing polytetrafluoroethylene modified with an acrylic polymer that is easy to handle and can improve the functionality of the battery during application, and an electrode for a lithium secondary battery using the same.

Means for Solving the Problems

[0009] <。 According to the first aspect of the present invention, A binder for lithium secondary batteries is provided, comprising composite particles of a polytetrafluoroethylene structure coated with an acrylic polymer.

[0010] In one embodiment of the present invention, the average diameter of the composite particles is 0.01 μm to 2 μm.

[0011] In one embodiment of the present invention, the acrylic polymer is a monomer polymer comprising an alkyl acrylate, an alkyl methacrylate, or a combination thereof, wherein the alkyl has 1 to 10 carbon atoms.

[0012] In one embodiment of the present invention, the acrylic polymer has a glass transition temperature of 60°C to 150°C.

[0013] In one embodiment of the present invention, the acrylic polymer has a weight-average molecular weight of 10,000 g / mol to 300,000 g / mol.

[0014] In one embodiment of the present invention, the acrylic polymer contains 40% to 90% by weight of methyl methacrylate based on the total weight of the monomers.

[0015] In one embodiment of the present invention, the acrylic polymer is a monomer copolymer containing methyl methacrylate and n-butyl acrylate.

[0016] In one embodiment of the present invention, the acrylic polymer is coated onto polytetrafluoroethylene at an amount of 5% to 40% by weight, based on the total weight of the composite particles.

[0017] In one embodiment of the present invention, the n-butyl acrylate comprises 10 to 60 parts by weight based on 100 parts by weight of methyl methacrylate.

[0018] In one embodiment of the present invention, the monomer further comprises acrylic acid or methacrylic acid.

[0019] In one embodiment of the present invention, the acrylic acid or methacrylic acid is present in an amount of 0.1% to 40% by weight based on the total weight of the monomers.

[0020] In one embodiment of the present invention, the polytetrafluoroethylene has a standard specific gravity (SSG) of 2.3 or less.

[0021] According to a second aspect of the present invention, An electrode for a lithium secondary battery is provided, manufactured by mixing the aforementioned binder, electrode active material, and conductive material, and then pressurizing the mixture.

[0022] In one embodiment of the present invention, the binder is contained in the electrode at an amount of 0.1% to 10% by weight, based on the total weight of the binder, electrode active material, and conductive material. [Effects of the Invention]

[0023] A binder for lithium secondary batteries according to one embodiment of the present invention can solve problems such as aggregation that may occur when handling conventional binders by modifying polytetrafluoroethylene with an acrylic polymer.

[0024] Furthermore, electrodes manufactured using the binder have excellent physical properties due to their low thickness deviation and high tensile strength, and when such electrodes are applied to a battery, the battery's performance, such as capacity retention rate, can be improved. [Brief explanation of the drawing]

[0025] [Figure 1] These are TEM and TEM-EDX mapping images showing a composite particle binder with a polytetrafluoroethylene structure coated with an acrylic polymer according to one embodiment of the present invention. [Modes for carrying out the invention]

[0026] All embodiments provided in accordance with the present invention can be achieved by the following description. The following description should be understood to describe preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0027] If the measurement conditions and methods for any physical properties described herein are not specifically described, such physical properties shall be measured in accordance with the measurement conditions and methods commonly used by ordinary artisans in that field.

[0028] This invention provides a binder for lithium secondary batteries that contains polytetrafluoroethylene modified with an acrylic polymer. In the field of dry-process electrode manufacturing, polytetrafluoroethylene, which is commonly used as a binder, is a long-chain polymer that maintains a stable phase below the phase transition temperature of 19°C. However, at room temperature above 19°C, the twisted helical chains easily unravel, and fibrous formation easily progresses, resulting in the characteristic of mutual aggregation even when fine shear forces are applied. In particular, at room temperature around 25°C, above the phase transition temperature of 19°C, even under powder transport and stirring conditions where shear forces can be frequently applied, fine fibrous formation and aggregation easily occur, making uniform dispersion of the powder itself difficult during the dry-process electrode manufacturing process. Consequently, handling of the aforementioned polytetrafluoroethylene requires expensive maintenance costs for refrigerated transport and storage, and special attention is required regarding the working temperature. To solve these problems with polytetrafluoroethylene, this invention modifies polytetrafluoroethylene with an acrylic polymer.

[0029] While various methods exist for modifying polytetrafluoroethylene with an acrylic polymer, in one embodiment of the present invention, a composite particle with an acrylic polymer / polytetrafluoroethylene structure is provided by coating the outside of polytetrafluoroethylene particles with an acrylic polymer. The composite particle can also be represented as a core-shell structure, where the core is composed of polytetrafluoroethylene and the shell is composed of an acrylic polymer.

[0030] According to one embodiment of the present invention, when polytetrafluoroethylene particles are coated with an acrylic polymer, the problem of polytetrafluoroethylene aggregation can be resolved, and the polytetrafluoroethylene contained within can be a high-molecular-weight substance with a high degree of fiber formation. According to one embodiment of the present invention, the polytetrafluoroethylene has a standard specific gravity (SSG) of 2.3 or less. The standard specific gravity is the specific gravity defined by the measurement method according to Japanese Industrial Standard (JIS) K6892. Since the standard specific gravity shows an inverse correlation with the average molecular weight, a low standard specific gravity of the polytetrafluoroethylene means that the molecular weight is high. Considering that a higher molecular weight results in a better degree of fiber formation, the lower limit of the standard specific gravity range may not be that important, but it could be, for example, 2.0 or higher. The composite particles according to one embodiment of the present invention are easier to handle, so the standard specific gravity can be made as low as possible.

[0031] Figure 1 provides TEM (Transmission Electron Microscope) and TEM-EDX (Energy Dispersive X-ray Spectroscopy) mapping images showing a composite particle binder with a polytetrafluoroethylene structure coated with an acrylic polymer according to one embodiment of the present invention. As can be seen in Figure 1, the polytetrafluoroethylene coated with an acrylic polymer does not allow the polytetrafluoroethylene particles to aggregate with each other due to the acrylic polymer located on the outside, and the core-shell composite particles can be easily separated while maintaining their original shape. Such composite particles have high dispersibility when mixed with electrode active material and conductive material in the electrode active material layer, and can improve the binder application efficiency by forming fibers even at low concentrations.

[0032] According to one embodiment of the present invention, the average diameter of the composite particles is 0.01 μm to 2 μm. The average diameter was calculated by measuring the size of each particle distinguishable in the TEM analysis image and then taking the arithmetic mean of the measured values. Specifically, the average diameter of the composite particles may be 0.01 μm to 2 μm, 0.01 μm to 1.5 μm, or 0.01 μm to 1 μm. Such an average diameter of composite particles helps polytetrafluoroethylene to fiberize at an appropriate level while increasing the dispersibility of the composite particles in the electrode active material layer.

[0033] Since the polytetrafluoroethylene can easily agglomerate at room temperature, agglomeration may occur during the production of composite particles, making it difficult to control the particle size. Therefore, for ease of operation, the composite particles are produced by adding a dispersant to uniformly disperse the polytetrafluoroethylene, followed by coating with an acrylic polymer. Due to the characteristics of the production method, trace amounts of the dispersant may be detected between the polytetrafluoroethylene and the acrylic polymer. The polytetrafluoroethylene core and the acrylic polymer shell do not necessarily need to adhere strongly, and the presence of a dispersant has the advantage that even if the adhesion between the core and shell is not high, the core components can be released more easily when the shell melts / breaks. The dispersant is not particularly limited as long as it does not readily undergo side reactions with the polytetrafluoroethylene and the acrylic polymer and is a substance commonly used in the art. For example, nonionic surfactants of the ethylene glycol series can be used as the dispersant, and in particular, Tween 20, Tween 60, Tween 80, Brij L23, Brij 020, triton x-100, and tergitol 100X can be used.

[0034] The type of acrylic polymer in the composite particles is not particularly limited, as long as it can form a coating layer and prevent aggregation of polytetrafluoroethylene. According to one embodiment of the present invention, the acrylic polymer is a monomer polymer containing alkyl acrylate, alkyl methacrylate, or a combination thereof. In the acrylic polymer, the polymerization units of alkyl acrylate and alkyl methacrylate may be 20 mol% or more, 50 mol% or more, or 70 mol% or more. Here, the alkyl can be adjusted to an appropriate level considering the physical properties of the coating layer, and in one embodiment of the present invention, alkyl having 1 to 10 carbon atoms is used. The alkyl may be a linear or branched substituent, and may be a substituted or unsubstituted alkyl. The functional group substituted on the alkyl is not particularly limited, as long as it is commonly used in the art, and it is preferable that it is not highly reactive in relation to other components of the electrode active material layer, for example, alkyl functional groups such as methyl or ethyl, halogen functional groups such as fluorine, hydroxyl functional groups, alkoxy functional groups such as methoxy or ethoxy, epoxy functional groups, etc. can be used.

[0035] According to one embodiment of the present invention, the acrylate monomer that forms the acrylic polymer is selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, glycidyl acrylate, and combinations thereof, and the methacrylate monomer that forms the acrylic polymer is selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, glycidyl methacrylate, and combinations thereof, and the acrylate monomer and the methacrylate monomer can also be used in combination.

[0036] The acrylic polymer can be composed of one or more monomers, and if the monomers are two or more alkyl acrylates or alkyl methacrylates, it can become a copolymer. Therefore, in this specification, the term "polymer" can be interpreted as a concept that includes copolymers. The acrylic polymer is formed by the linking of monomers while the double bonds present in the acrylic monomers are broken into single bonds, and the monomer structure is maintained almost unchanged within the polymer. The arrangement of monomers in the copolymer is not necessarily limited to one of the following: random copolymer, alternating copolymer, or block copolymer, but random copolymer is often used as the primary arrangement.

[0037] The acrylic polymer, as a coating layer that prevents the aggregation of polytetrafluoroethylene, does not aggregate with other particles, has a certain level of durability, and has the functionality to stably maintain polytetrafluoroethylene within the coating layer until it is fibrousized through heating or pressurization. Furthermore, the acrylic polymer may have the functionality to reinforce the binding force between constituent components within a dry electrode. Due to the aforementioned functionality, the physical properties of the acrylic polymer may be adjusted to a certain level.

[0038] According to one embodiment of the present invention, the acrylic polymer has a glass transition temperature of 60°C to 150°C. The glass transition temperature is measured according to a standard measurement method using a Differential Scanning Calorimeter (DSC) (e.g., manufacturer: TA, product name: Q20). Specifically, the glass transition temperatures of the acrylic polymer are 60°C to 150°C, 65°C to 140°C, 70°C to 130°C, and 75°C to 120°C. Acrylic polymers having a glass transition temperature within these ranges can have superior functionality.

[0039] The weight-average molecular weight of the acrylic polymer may also affect its functionality. According to one embodiment of the present invention, the acrylic polymer has a weight-average molecular weight of 10,000 g / mol to 600,000 g / mol. Here, the weight-average molecular weight is a value converted relative to standard polymethyl methacrylate measured with a GPC (Gel Permeation Chromatograph) (e.g., manufacturer: Waters, product name: Alliance2695). Specifically, the weight-average molecular weight of the acrylic polymer is 10,000 g / mol to 600,000 g / mol, 10,000 g / mol to 300,000 g / mol, and 100,000 g / mol to 200,000 g / mol. Acrylic polymers having a weight-average molecular weight within the above range can have superior functionality.

[0040] The acrylic polymer's properties affecting its functionality can be adjusted by controlling the composition of the monomers that make up the polymer. Methyl methacrylate, as the main monomer constituting the acrylic polymer, can be included in the largest amount. According to one embodiment of the present invention, the acrylic polymer is a monomer copolymer containing 40% to 90% by weight of methyl methacrylate based on the total weight of the monomers. Specifically, the content of methyl methacrylate can be 40% to 90% by weight or 45% to 90% by weight. Based on methyl methacrylate, other types of monomers can be combined to adjust the properties of the acrylic polymer.

[0041] The methyl methacrylate can be combined with other compounds from the aforementioned acrylate or methacrylate monomers, excluding methyl methacrylate, to produce various types of acrylic polymers. According to one embodiment of the present invention, the acrylic polymer is a copolymer of monomers containing methyl methacrylate and n-butyl acrylate. The n-butyl acrylate contains an n-butyl group with three different carbon atoms compared to methyl methacrylate, and can be easily adjusted to the properties required in the present invention even in small amounts compared to other alkyl acrylates. According to one embodiment of the present invention, the n-butyl acrylate is contained in amounts of 10 to 60 parts by weight based on 100 parts by weight of methyl methacrylate. Within this range, more desirable properties can be achieved when polymerized with methyl methacrylate.

[0042] The acrylic polymer may further contain novel functional groups to have additional functionality, such as reinforcing the binding force between components in a dry electrode, even after the composite particles are broken down by heating or pressurizing and release the internal polytetrafluoroethylene. Such functional groups can be introduced into the acrylic polymer from monomers other than alkyl acrylates or alkyl methacrylates, and the functional groups may be carboxylic acids. According to one embodiment of the present invention, the monomers constituting the acrylic polymer further contain acrylic acid or methacrylic acid. According to one embodiment of the present invention, the acrylic acid or methacrylic acid is included in an amount of 40% by weight or less based on the total weight of the monomers. Specifically, the content of the acrylic acid or methacrylic acid may be 40% by weight or less, or 30% by weight or less. The acrylic acid or methacrylic acid is not an essential component but an optional component in that it is introduced to impart the aforementioned additional functionality, and therefore the lower limit of its content may include 0% by weight. However, if acrylic acid or methacrylic acid is included to ensure additional functionality, it can be included in amounts ranging from a very small amount of 0.1% by weight or more to the aforementioned upper limit, and can be included in the acrylic polymer in amounts of 0.1% to 40% by weight, 5% to 35% by weight, and 10% to 30% by weight, as examples. The acrylic acid or methacrylic acid, due to the carboxylic acid protruding from the outside of the coating layer, can enhance the bonding strength not only with polytetrafluoroethylene but also with the electrode active material or conductive material constituting the electrode.

[0043] Since the acrylic polymer does not have the property of easily forming fibers like polytetrafluoroethylene, it cannot be used as a binder to replace polytetrafluoroethylene. Therefore, the acrylic polymer is not required in large quantities as long as the aforementioned functionality can be ensured. According to one embodiment of the present invention, the acrylic polymer is coated onto polytetrafluoroethylene at an amount of 5% to 40% by weight, based on the total weight of the composite particles. The content of the acrylic polymer can be 5% to 40% by weight, 10% to 30% by weight, or 10% to 20% by weight. Within these ranges, it is possible to include a sufficient amount of polytetrafluoroethylene while fully achieving the purpose of introducing the acrylic polymer.

[0044] The manufacture of electrodes for lithium secondary batteries typically uses a wet process, where a mixture containing electrode active material is added to a solvent such as water or an organic solvent and applied to the electrode current collector in the form of a slurry, taking into consideration the processability of the mixture. However, increasing the electrode thickness is not easy due to problems such as binder migration during drying and low adhesion between the electrode current collector and the electrode active material. To solve these problems, research is ongoing on dry processes that do not use solvents during electrode manufacturing. Polytetrafluoroethylene has been used as a binder as one means of solving the problem of reduced binding strength between the electrode active material, conductive material, and binder during the dry process. This invention modifies the polytetrafluoroethylene binder with an acrylic polymer to enhance its usefulness, and specifically relates to the dry process for manufacturing electrodes for lithium secondary batteries.

[0045] According to the dry method, the electrode for a lithium secondary battery is manufactured by mixing and dispersing an electrode active material, a conductive material, and a binder, and then pressing them. As the binder, a composite particle binder according to an embodiment of the present invention is utilized. The electrode can be composed of an active layer and a current collector. The active layer means a layer containing an electrode active material, a conductive material, and a binder. The current collector not only supports the active layer but also plays a role of supplying electrons to the active layer, but there may be cases where the current collector is not necessarily included in the configuration by the active layer. Since the active layer contains an electrode active material, it has activity in the electrochemical reaction in the electrode. In terms of containing the electrode active material, and in terms of being formed by mixing the electrode active material layer, the electrode active material, the conductive material, and the binder, it can be expressed as a mixed layer. Also, in the case of all-solid-state batteries where recent research is actively underway, a solid electrolyte can be additionally included.

[0046] The electrode active material can become a positive electrode active material when applied to the positive electrode and a negative electrode active material when applied to the negative electrode. The positive electrode active material or the negative electrode active material is not particularly limited as long as it is generally used in the art.

[0047] According to an embodiment of the present invention, the positive electrode active material is a lithium transition metal oxide. In the lithium transition metal oxide, the transition metal is Li 1+x M y O 2+Z (0 ≦ x ≦ 5, 0 < y ≦ 2, 0 ≦ z ≦ 2) has a form, where M is selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, V, and combinations thereof, and is not particularly limited within the above range. More specifically, the lithium transition metal oxide is LiCoO2, LiNiO2, LiMnO2, Li2MnO3, LiMn2O4, Li(Ni a Co b Mn c )O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), LiNi 1-y Co y O2(0 < y < 1), LiCo 1-y Mny O2, LiNi 1-y Mn y O2 (O < y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4 (0 < z < 2), LiMn 2-z Co z O4 (0 < z < 2) and are selected from combinations thereof.

[0048] According to one embodiment of the present invention, the negative electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy; SiO βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, can be used. Typical examples of low-crystallinity carbon include soft carbon and hard carbon, while typical examples of high-crystallinity carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. Additionally, metal nanoparticles having lithium-affinity properties may be further included. These metal nanoparticles may be a combination of one or more elements selected from silver, gold, platinum, palladium, silicon, aluminum, bismuth, tin, indium, zinc, etc., and specifically, may be silver.

[0049] According to one embodiment of the present invention, the electrode active material is a lithium transition metal oxide having an average particle diameter of 5 μm to 30 μm. Specifically, the average particle diameter can be 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, 10 μm or more, 30 μm or less, 28 μm or less, 26 μm or less, 24 μm or less, 22 μm or less, 20 μm or less, and can range from 5 μm to 30 μm, 7 μm to 24 μm, or 10 μm to 20 μm.

[0050] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is constructed from, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, single-walled or multi-walled carbon nanotubes, carbon fibers, carbon nanofibers, graphene, activated carbon, and activated carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more.

[0051] The conductive material may be a carbon-based material or a metallic material, and the metallic material may include the aforementioned metal powder, metal fibers, conductive metal oxides, etc. The conductive material may be spherical or linear particles. If the conductive material is spherical particles, the average diameter of the particles may be 1 nm to 100 nm, specifically 5 nm to 70 nm, and more specifically 10 nm to 40 nm. If the conductive material is linear particles, the length of the linear particles may be 1 μm to 10 μm, specifically 2 μm to 9 μm, and more specifically 3 μm to 8 μm, and the diameter of the vertical cross-section may be 10 nm to 500 nm, specifically 50 nm to 350 nm, and more specifically 100 nm to 200 nm.

[0052] The binder plays a role in improving adhesion between electrode active material particles and the adhesion between the electrode active material and the electrode current collector. In one embodiment of the present invention, the aforementioned composite particles are used as a binder, and the composite particles, which do not easily aggregate, are mixed with the electrode active material and conductive material and uniformly dispersed. After this, the mixture is fibrousized and pressurized by equipment such as rolls, at which point the acrylic polymer coating layer is destroyed and the polytetrafluoroethylene inside is released, and fibrousization proceeds due to the applied shear force. Due to the excellent dispersibility of the composite particles in the active layer, the present invention can maximize the functionality of the binder. The acrylic polymer coating layer may also be destroyed by heating, and when heated and mixed, fibrousization of polytetrafluoroethylene may proceed simultaneously with the mixing.

[0053] According to one embodiment of the present invention, the binder is contained in the active layer at an amount of 0.1% to 10% by weight, specifically 0.5% to 5% by weight, and more specifically 1% to 3% by weight, based on the total weight of the electrode active material, conductive material, and binder. The present invention is significant in that it can increase the overall binding strength of the active layer even with a small amount of binder.

[0054] In one embodiment of the present invention, the electrode's shape can be fixed by the fibrous formation of the binder, meaning that an electrode current collector is not necessarily required. However, an electrode current collector can be utilized because it can provide a uniform electron transport path in relation to the battery's conductor and active layer. The electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. The electrode current collector can also typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the electrode current collector to enhance the adhesion of the electrode active material. For example, it can be used in various forms such as film, sheet, foil, net, porous material, foam, nonwoven fabric, etc. Furthermore, a primer-coated foil can be used for the electrode current collector, and the current collector material may include a surface layer coated with a mixture of conductive carbon material and binder.

[0055] The aforementioned electrodes can be applied to lithium secondary batteries. These lithium secondary batteries are generally manufactured by interposing a separation membrane between the positive and negative electrodes and then injecting an electrolyte, but they can be modified to various forms, such as by mixing in a solid electrolyte, as needed.

[0056] The separation membrane separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any membrane commonly used as a separation membrane in lithium secondary batteries can be used without particular limitations, and those with low resistance to electrolyte ion movement while exhibiting excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength can be used, and they can be selectively used in single-layer or multi-layer structures.

[0057] The aforementioned electrolyte includes, but is not limited to, liquid electrolytes and solid electrolytes that can be used in the manufacture of lithium secondary batteries.

[0058] Typically, liquid electrolytes can include organic solvents and lithium salts.

[0059] The organic solvent can be used without particular limitations as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene carbonate). A variety of solvents can be used, including carbonate solvents such as PC; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge-discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte can be excellently expressed by mixing the cyclic carbonate and the cyclic carbonate in a volume ratio of about 1:1 to about 1:9.

[0060] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0061] In addition to the electrolyte components, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0062] In one embodiment of the present invention, an electrode can also preferably be manufactured using a dry method, and a solid electrolyte can also be applied. The solid electrolyte may include an ion-conducting solid electrolyte material. The ion-conducting solid electrolyte material may include one or more polymer solid electrolytes and inorganic solid electrolytes. The polymer solid electrolyte may contain a polymer resin and a lithium salt, and may be a solid polymer electrolyte having the form of a mixture of a solvent-treated lithium salt and a polymer resin, or a polymer gel electrolyte in which an organic electrolyte containing an organic solvent and a lithium salt is incorporated into the polymer resin. Below, the ion-conducting solid electrolyte material will be described in detail to the extent that it does not overlap with the description of liquid electrolytes.

[0063] The solid polymer electrolyte may include, but is not limited to, one or more substances selected from the group consisting of polyether polymers, polycarbonate polymers, acrylate polymers, polysiloxane polymers, phosphazene polymers, polyethylene derivatives, alkylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups. Furthermore, the solid polymer electrolyte may include, but is not limited to, one or more substances selected from the group consisting of branched copolymers obtained by copolymerizing an amorphous polymer such as PMMA, polycarbonate, polysiloxane (pdms), and / or phosphazene with a PEO (polyethylene oxide) main chain as a copolymer, comb-like polymers, and crosslinked polymers.

[0064] The polymer gel electrolyte comprises an organic electrolyte containing a lithium salt and a polymer resin, wherein the organic electrolyte may be present in amounts of 60 to 400 parts by weight relative to the weight of the polymer resin. The polymer resin applied to the gel electrolyte may be one or more substances selected from the group consisting of, for example, PVC (Polyvinyl chloride), PMMA (Poly(methyl methacrylate)), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), but is not necessarily limited to these.

[0065] The inorganic solid electrolyte may include a sulfide-based solid electrolyte, a halide-based solid electrolyte, an oxide-based solid electrolyte, or one or more of these.

[0066] The sulfide-based solid electrolyte contains a sulfur atom among its electrolyte components and is not limited to any particular component. It may contain one or more of the following: crystalline solid electrolytes, amorphous solid electrolytes (vitreous solid electrolytes), and glass-ceramic solid electrolytes. Specific examples of the sulfide-based solid electrolyte include LPS-type sulfides containing sulfur and phosphorus, and Li 4-x Ge 1-x P x S4 (x is 0.1 to 2, specifically x is 3 / 4, 2 / 3), Li 10±1 MP2X 12 (M=Ge, Si, Sn, Al, X=S, Se), Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P 0.75 Examples include S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5 (where x is 70-80), Li2S-SiS2-Li3N, Li2S-P2S5-LiI, Li2S-SiS2-LiI, Li2S-B2S3-LiI, etc., but are not necessarily limited to these.

[0067] The aforementioned halide-based solid electrolyte may contain, but is not limited to, at least one of Li3YCl6 and Li3YBr6.

[0068] The oxide-based solid electrolyte is, for example, Li 3x La 2 / 3-x LLT systems with perovskite structures like TiO3, Li 14 LiSICON, such as Zn(GeO4)4, Li 1.3 Al 0.3 Ti 1.7 LATP systems like (PO4)3, (Li 1+x Ge 2-x Al x Appropriate selection and use of LAGP-based drugs such as (PO4)3) and phosphate-based drugs such as LiPON is possible, but the treatment is not necessarily limited to these.

[0069] As described above, the lithium secondary battery containing the electrode according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0070] Accordingly, according to another aspect of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The aforementioned battery modules or battery packs may include, but are not limited to, power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles (E-bikes, E-scooters, etc.); electric golf carts; urban air mobility (UAM); or power storage systems.

[0071] The following are preferred embodiments to aid in understanding the present invention, but these embodiments are provided to make the present invention easier to understand and are not limited thereto.

[0072] Manufacturing example (manufacturing of composite particles) Manufacturing Example 1: Uses an acrylic polymer polymerized with 100% by weight of methyl methacrylate monomer. A polytetrafluoroethylene aqueous dispersion (DISP30 from Chemours) was prepared, with an average particle diameter of 0.22 μm, a solid content concentration of 60%, and a standard specific gravity (SSG) of 2.22 after sintering.

[0073] Next, 1020.0 g of aqueous polytetrafluoroethylene dispersion and 1843.4 g of distilled water were placed in a 4 L reactor and stirred at a speed of 350 RPM while simultaneously bubbling with nitrogen to raise the temperature to 75°C. After reaching the polymerization temperature of 75°C, nitrogen bubbling was stopped, and 153 g of methyl methacrylate (MMA) was added dropwise to the reactor over 15 minutes. 15 minutes after the monomer was added, 10 g of distilled water and 0.77 g of aqueous ammonium persulfate were added dropwise to the reactor over approximately 10 minutes. After the polymerization reaction proceeded for 4 hours from the end of ammonium persulfate addition, the mixture was cooled to 30°C to obtain a white emulsion.

[0074] The white emulsion, after polymerization was complete, was diluted 1,000-fold, and its size was analyzed using NICOMP 380 (Entegris, dynamic light scattering method) and is shown in Table 1 below. For particle structure analysis, a drop of the emulsion diluted with water was placed on a transmission electron microscope (TEM) grid and dried at room temperature. The structure of the dried sample was analyzed using TEM / EDS (TECNAI TF20, FEI) at an acceleration voltage of 200kV and is shown in Figure 1 below.

[0075] Furthermore, the emulsified liquid was freeze-dried for 72 hours under conditions of -60°C and 10 mTorr to obtain a white powder.

[0076] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 100% by weight methyl methacrylate monomer, which is the substance that constitutes the exterior of the composite particles. w ): 543,000 g / mol, glass transition temperature (T g Composite particles with an average diameter of 0.3 μm were produced by coating polytetrafluoroethylene, the substance constituting the interior of the composite particles, with (120.2°C). In the produced composite particles, the weight ratio of polytetrafluoroethylene to acrylic polymer was 80:20.

[0077] Manufacturing Example 2: An acrylic polymer polymerized with 90% by weight of methyl methacrylate and 10% by weight of n-butyl acrylate monomer was used. The preparation was carried out in the same manner as in Preparation Example 1, except that a mixed monomer of 137.7 g of methyl methacrylate and 15.3 g of n-butyl acrylate and 0.21 g of the chain transfer agent n-octyl mercaptan were used.

[0078] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 90% by weight methyl methacrylate and 10% by weight n-butyl acrylate monomers, which constitute the outer surface of the composite particles. w ): 182,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 101.4°C).

[0079] Manufacturing Example 3: An acrylic polymer polymerized with 80% by weight of methyl methacrylate and 20% by weight of n-butyl acrylate monomer was used. The preparation was carried out in the same manner as in Preparation Example 1, except that a mixed monomer of 122.4 g of methyl methacrylate and 30.6 g of n-butyl acrylate, along with 0.21 g of the chain transfer agent n-octyl mercaptan, was used.

[0080] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 80% by weight of methyl methacrylate and 20% by weight of n-butyl acrylate monomer, which constitute the outer surface of the composite particles. w ): 193,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (same as in Production Example 1, which constitutes the interior of the composite particles) with (79.4°C).

[0081] Production Example 4: An acrylic polymer polymerized with 70% by weight of methyl methacrylate and 30% by weight of n-butyl acrylate monomer was used. The preparation was carried out in the same manner as in Preparation Example 1, except that a mixed monomer of 107.1 g of methyl methacrylate and 45.9 g of n-butyl acrylate and 0.37 g of the chain transfer agent n-octyl mercaptan were used.

[0082] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 70% by weight of methyl methacrylate and 30% by weight of n-butyl acrylate monomers, which constitute the outer surface of the composite particles. w ): 128,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 54.4°C).

[0083] Manufacturing Example 5: An acrylic polymer polymerized with 50% by weight of methyl methacrylate and 50% by weight of methacrylic acid monomer is used. The preparation was carried out in the same manner as in Production Example 1, except that a mixed monomer of 76.5 g of methyl methacrylate and 76.5 g of methacrylic acid, and 0.21 g of the chain transfer agent n-octyl mercaptan were used.

[0084] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 50% by weight methyl methacrylate and 50% by weight methacrylic acid monomer, which constitute the outer surface of the composite particles. w ): 188,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 140.4°C).

[0085] Manufacturing Example 6: An acrylic polymer polymerized with 70% by weight of methyl methacrylate and 30% by weight of methacrylic acid monomer is used. The preparation was carried out in the same manner as in Production Example 1, except that a mixed monomer of 107.1 g of methyl methacrylate and 45.9 g of methacrylic acid, and 0.21 g of the chain transfer agent n-octyl mercaptan were used.

[0086] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 70% by weight methyl methacrylate and 30% by weight methacrylic acid monomer, which constitute the outer surface of the composite particles. w ): 203,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 131.2°C).

[0087] Manufacturing Example 7: An acrylic polymer polymerized with 90% by weight of methyl methacrylate and 10% by weight of methacrylic acid monomer is used. The preparation was carried out in the same manner as in Production Example 1, except that a mixed monomer of 137.1 g of methyl methacrylate and 15.3 g of methacrylic acid, and 0.21 g of the chain transfer agent n-octyl mercaptan were used.

[0088] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 90% by weight methyl methacrylate and 10% by weight methacrylic acid monomer, which constitute the outer surface of the composite particles. w ): 211,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 122.4°C).

[0089] Manufacturing Example 8: An acrylic polymer polymerized with 45% by weight of methyl methacrylate, 25% by weight of n-butyl acrylate, and 30% by weight of methacrylic acid monomer is used. The preparation was carried out in the same manner as in Preparation Example 1, except that a mixed monomer of 68.85 g of methyl methacrylate, 38.25 g of n-butyl acrylate, and 45.9 g of methacrylic acid, along with 0.28 g of the chain transfer agent n-octyl mercaptan, was used.

[0090] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 45% by weight methyl methacrylate, 25% by weight n-butyl acrylate, and 30% by weight methacrylic acid monomer, which constitute the outer surface of the composite particles. w ): 168,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 80:20) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (81.6°C).

[0091] Manufacturing Example 9: Production of composite particles with a weight ratio of polytetrafluoroethylene to acrylic polymer of 90:10 The same method as in Production Example 1 was used, except that 1147.5 g of an aqueous polytetrafluoroethylene dispersion and 1807.7 g of distilled water were used, and a mixed monomer of 61.2 g of methyl methacrylate and 15.3 g of n-butyl acrylate was applied, along with 0.38 g of the initiator ammonium persulfate and 0.11 g of the chain transfer agent n-octyl mercaptan.

[0092] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 80% by weight of methyl methacrylate and 20% by weight of n-butyl acrylate monomer, which constitute the outer surface of the composite particles. w ): 185,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 90:10) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (at 80.1°C).

[0093] Manufacturing Example 10: Production of composite particles with a weight ratio of polytetrafluoroethylene to acrylic polymer of 70:30 The same method as in Production Example 1 was used, except that 892.5 g of an aqueous polytetrafluoroethylene dispersion and 1879.1 g of distilled water were used, and a mixed monomer of 183.6 g of methyl methacrylate and 45.9 g of n-butyl acrylate was applied, along with 1.15 g of the initiator ammonium persulfate and 0.32 g of the chain transfer agent n-octyl mercaptan.

[0094] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 80% by weight of methyl methacrylate and 20% by weight of n-butyl acrylate monomer, which constitute the outer surface of the composite particles. w ): 183,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 70:30) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with 79.9°C.

[0095] Manufacturing Example 11: Production of composite particles with a weight ratio of 50:50 between polytetrafluoroethylene and acrylic polymer. The preparation was carried out in the same manner as in Production Example 1, except that 637.5 g of an aqueous polytetrafluoroethylene dispersion and 1950.5 g of distilled water were used, and a mixed monomer of 306.0 g of methyl methacrylate and 76.5 g of n-butyl acrylate was applied, along with 1.91 g of the initiator ammonium persulfate and 0.54 g of the chain transfer agent n-octyl mercaptan.

[0096] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 80% by weight of methyl methacrylate and 20% by weight of n-butyl acrylate monomer, which constitute the outer surface of the composite particles. w ): 180,000 g / mol, glass transition temperature (T g Composite particles (average particle diameter: 0.3 μm, weight ratio of polytetrafluoroethylene to acrylic polymer: 50:50) were produced by coating the same polytetrafluoroethylene (the same material as in Production Example 1, which constitutes the interior of the composite particles) with (80.5°C).

[0097] Manufacturing Example 12: Production of composite particles in which the weight ratio of polytetrafluoroethylene (standard specific gravity (SSG): 2.31) and acrylic polymer is 80:20. The product was manufactured using the same method as in Manufacturing Example 1, except that a polytetrafluoroethylene aqueous dispersion (Chemours product) with an average particle diameter of 0.22 μm, a solid content concentration of 60%, and a standard specific gravity (SSG) of 2.31 after sintering was used.

[0098] Using the aforementioned method, an acrylic polymer (weight-average molecular weight (M) is polymerized with 100% by weight methyl methacrylate monomer, which is the substance that constitutes the exterior of the composite particles. w ): 505,000 g / mol, glass transition temperature (T gComposite particles with an average diameter of 0.3 μm were produced by coating polytetrafluoroethylene, the substance constituting the interior of the composite particles, with (121.0°C). In the produced composite particles, the weight ratio of polytetrafluoroethylene to acrylic polymer was 80:20.

[0099] Example (Electrode using composite particles) Example 1: Using the composite particles from Manufacturing Example 1 A mixture consisting of 95.5% by weight of NCM particle powder (product: GL80, manufacturer: LG Chem) with an average particle size of 10 μm as the positive electrode active material, 1.5% by weight of conductive material (product: Li-250, manufacturer: Denka), and 3.0% by weight of the composite particles from Production Example 1 as a binder was prepared. The prepared electrode active material, conductive material, and binder were mixed in a Lab Blender (manufacturer: Waring) and mixed at 10,000 RPM for 30 seconds, repeated 10 times, to prepare a mixture for dry electrodes. The mixture was then subjected to high-shear mixing for 5 minutes at 100°C and 100 RPM while applying a shear force through a Twin Screw Kneader (manufacturer: Irie Shokai) to promote fiber formation under heating conditions. Next, a 200 μm thick freestanding film was produced using a two-roll mill (manufacturer: Inoue) at 100°C from the manufactured dough-like secondary mixture.

[0100] Example 2: Using the composite particles from Manufacturing Example 2 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 2 were used as the binder.

[0101] Example 3: Using the composite particles from Manufacturing Example 3 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 3 were used as the binder.

[0102] Example 4: Using the composite particles from Manufacturing Example 4 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 4 were used as the binder.

[0103] Example 5: Using the composite particles from Manufacturing Example 5 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 5 were used as the binder.

[0104] Example 6: Using the composite particles from Manufacturing Example 6 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 6 were used as the binder.

[0105] Example 7: Using the composite particles from Manufacturing Example 7 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 7 were used as the binder.

[0106] Example 8: Using the composite particles from Manufacturing Example 8 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 8 were used as the binder.

[0107] Example 9: Composite particles from Production Example 3 were used (binder content: 1.5% by weight) The electrode was manufactured in the same manner as in Example 1, except that the electrode active material was adjusted to 95.5% by weight, the conductive material to 1.5% by weight, and the binder to 1.5% by weight.

[0108] Example 10: Using the composite particles from Manufacturing Example 9 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 9 were used as the binder.

[0109] Example 11: Using the composite particles from Manufacturing Example 10 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 10 were used as the binder.

[0110] Comparative Example 1: Using the composite particles from Manufacturing Example 11 The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 11 were used as the binder.

[0111] Comparative Example 2: Using polytetrafluoroethylene particles The electrodes were manufactured in the same manner as in Example 1, except that the composite particles from Manufacturing Example 12 were used as the binder.

[0112] Comparative Example 3: Using polytetrafluoroethylene particles (binder content: 1.5% by weight) The electrode was manufactured in the same manner as in Comparative Example 2, except that the electrode active material was adjusted to 97.0% by weight, the conductive material to 1.5% by weight, and the binder to 1.5% by weight.

[0113] Comparative Example 4: Using polytetrafluoroethylene particles (mixed at room temperature) Except for the fact that the prepared electrode active material, conductive material, and binder were mixed at room temperature, Comparative Example 2 The electrodes were manufactured using the same method.

[0114] Experimental examples (evaluation of electrodes) Experimental Example 1: Evaluation of thickness deviation and tensile strength of freestanding film-shaped electrodes Freestanding film electrodes manufactured according to Examples 1-10 and Comparative Examples 1-5 were sampled with a width of 20 mm, a length of 20 mm, and a thickness of 200 μm, and the thickness deviation and tensile strength of the samples were measured. The thickness deviation was measured using an electrode thickness measuring device (product: Millimar, manufacturer: Mahr), and the tensile strength was measured using a UTM-equipped device (manufacturer: LLOYD). The tensile strength was measured as the maximum force applied until the film did not break under conditions of an angle of 180 degrees and a speed of 50 mm / min. The results for the thickness deviation and tensile strength are shown in Table 1 below.

[0115] [Table 1]

[0116] According to Table 1, the electrodes from Examples 1 to 11 exhibited small thickness deviations and a tensile strength of 2,400 gf / cm². 2The above confirms that the physical properties are at a good level. On the other hand, the electrodes from Comparative Examples 1-4 had a tensile strength of 2,200 gf / cm². 2 The following findings confirmed that the physical properties were at an insufficient level. Furthermore, polytetrafluoroethylene, which has a high standard specific gravity (SSG) of 2.31, showed significantly large thickness deviations in the electrodes used in Comparative Examples 2-4.

[0117] Experimental Example 2: Performance evaluation of a battery with applied electrodes Freestanding films with a thickness of 200 μm were manufactured according to Examples 1-10 and Comparative Examples 1-5. The freestanding films were then placed on one surface of a 20 μm thick primer-coated aluminum foil (manufacturer: Dongwon Systems) current collector and bonded through a lamination roll maintained at 120°C to produce a positive electrode. A half-cell was manufactured using lithium metal as the counter electrode and an electrolyte containing 1 M LiPF6 in a solvent with a volume ratio of EC:DMC:DEC (1:2:1).

[0118] The manufactured coin-type half-cells were subjected to 100 charge-discharge cycles at 25°C under voltage ranges of 3 to 4.3V and current conditions of 0.33C-rate. The discharge capacity retention rate for each discharge cycle was then calculated, and the results are shown in Table 2 below.

[0119] [Table 2]

[0120] According to Table 2 above, the electrodes of Examples 1 to 11 showed an improved effect compared to the electrodes of Comparative Examples 1 to 4, which had a capacity retention rate of 95% or more after 100 discharge cycles, compared to the electrodes of Comparative Examples 1 to 4, which had a capacity retention rate of less than 95%.

[0121] Any simple modifications or changes to the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended claims.

Claims

1. It contains composite particles of a polytetrafluoroethylene structure coated with an acrylic polymer, The aforementioned acrylic polymer is a monomer copolymer containing methyl methacrylate and n-butyl acrylate. The acrylic polymer is characterized by having a weight-average molecular weight of 10,000 g / mol to 193,000 g / mol, and is used as a binder for lithium secondary batteries.

2. The binder for lithium secondary batteries according to claim 1, characterized in that the average diameter of the composite particles is 0.01 μm to 2 μm.

3. The binder for lithium secondary batteries according to claim 1, characterized in that the acrylic polymer has a glass transition temperature of 60°C to 150°C.

4. The binder for lithium secondary batteries according to claim 1, characterized in that the acrylic polymer has a weight-average molecular weight of 10,000 g / mol to 185,000 g / mol.

5. The binder for lithium secondary batteries according to claim 1, characterized in that the acrylic polymer is a monomer copolymer containing 40% to 90% by weight of methyl methacrylate based on the total weight of the monomers.

6. The binder for lithium secondary batteries according to claim 1, characterized in that the acrylic polymer is coated on polytetrafluoroethylene at an amount of 5% to 40% by weight, based on the total weight of the composite particles.

7. The binder for lithium secondary batteries according to claim 5, characterized in that the n-butyl acrylate contains 10 to 60 parts by weight based on 100 parts by weight of methyl methacrylate.

8. Composite particles comprising a polytetrafluoroethylene structure coated with an acrylic polymer, The aforementioned acrylic polymer is a monomer copolymer containing methyl methacrylate and n-butyl acrylate. A binder for lithium secondary batteries, characterized in that the monomer further comprises acrylic acid or methacrylic acid.

9. The binder for lithium secondary batteries according to claim 8, characterized in that the acrylic acid or methacrylic acid is present in an amount of 0.1% to 40% by weight based on the total weight of the monomers.

10. The binder for lithium secondary batteries according to claim 1, characterized in that the polytetrafluoroethylene has a standard specific gravity (SSG) of 2.3 or less.

11. An electrode for a lithium secondary battery, manufactured by mixing the binder, electrode active material, and conductive material described in any one of claims 1 to 10, and then pressurizing the mixture.

12. The electrode for a lithium secondary battery according to claim 11, characterized in that the binder is contained in the electrode in an amount of 0.1% to 10% by weight, based on the total weight of the binder, electrode active material, and conductive material.

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