Negative electrode for lithium secondary battery, method for manufacturing same, and lithium secondary battery including same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same, the negative electrode for a lithium secondary battery comprising: a metal current collector; a coating layer formed on at least one surface of the metal current collector and including a first binder and a first conductive material; and a negative electrode active material layer formed on the coating layer and including a negative electrode active material, a second conductive material, and a second binder.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0107173, filed with the Korean Intellectual Property Office on August 16, 2023, the entire contents of which are incorporated herein by reference.

[0002] This invention relates to a negative electrode for lithium secondary batteries, a method for producing the same, and a lithium secondary battery including the same, wherein the negative electrode for lithium secondary batteries has improved peel resistance and adhesion of the negative electrode active material layer, which can improve the life characteristics of the negative electrode and the lithium secondary battery. Background Technology

[0003] Technological advancements and the increasing demand for mobile devices and electric vehicles have led to a rapid increase in the demand for lithium-ion batteries as an energy source. Among these lithium-ion batteries, those with high energy density and voltage, long cycle life, and low discharge rate have been commercialized and are widely used.

[0004] Typically, lithium-ion secondary batteries have a structure in which an electrode assembly is impregnated with an electrolyte containing a lithium salt. The electrode assembly includes a positive electrode containing active material applied to a metal current collector, a negative electrode containing active material applied to a metal current collector, and a porous separator between the positive and negative electrodes. Each electrode is manufactured by applying a slurry composition in which active material, binder, and conductive material are dispersed in a solvent onto the metal current collector, followed by pressing and drying.

[0005] Therefore, the lifespan characteristics of lithium-ion batteries can be primarily determined by how long the electrochemical properties of the electrodes, especially the active material layer, are maintained. However, in the case of conventional lithium-ion batteries, there are many instances where the active material layer peels off from the metal current collector in the negative electrode over time, leading to a deterioration in the battery's lifespan characteristics.

[0006] This appears to be because the active material layer of the negative electrode contains graphite-based negative electrode active material as its main component, which has properties different from those of metals. Therefore, it is difficult to ensure sufficient adhesion, tight adhesion, and anti-peeling properties of the active material layer to the metal current collector. Due to this poor adhesion of the active material layer, a drawback is that the active material layer easily peels off from the metal current collector as the lithium-ion battery is used for an extended period. Furthermore, the peeled active material layer can no longer be used as an active region in the lithium-ion battery, thus causing a rapid deterioration in the charge / discharge cycle characteristics of the lithium-ion battery.

[0007] Because of these issues, there is a continued need to develop technologies that can improve the lifespan characteristics of lithium secondary batteries by further improving the adhesion of the active material layers included in the negative electrode. Summary of the Invention

[0008] Technical issues

[0009] Therefore, the present invention aims to provide a negative electrode for lithium secondary batteries and a method for producing the same, wherein the negative electrode for lithium secondary batteries has improved peel resistance and adhesion of the negative electrode active material layer, which can improve the life characteristics of the negative electrode and the lithium secondary battery.

[0010] The present invention also aims to provide a lithium secondary battery that exhibits improved lifespan characteristics by including the negative electrode for the lithium secondary battery.

[0011] Technical solution

[0012] The present invention provides a negative electrode for a lithium secondary battery, comprising: a metal current collector; a coating formed on at least one surface of the metal current collector and comprising a first binder and a first conductive material; and a negative electrode active material layer formed on the coating and comprising a negative electrode active material, a second conductive material, and a second binder, wherein the first conductive material comprises multi-walled carbon nanotubes based on 100 parts by weight of the multi-walled carbon nanotubes, the coating comprises the first binder in an amount of 400 parts by weight to 2,000 parts by weight, and the thickness of the coating is in the ratio of the thickness of the negative electrode active material layer to 0.005 to 0.2.

[0013] The present invention also provides a method for producing a negative electrode for a lithium secondary battery, comprising the steps of: applying a slurry composition for forming a coating, comprising a first binder, a first conductive material and a solvent, to a metal current collector, and then drying to form a coating; applying a negative electrode slurry composition comprising a negative electrode active material, a second binder, a second conductive material and a solvent to the coating; and pressing the negative electrode slurry composition, wherein the first conductive material comprises multi-walled carbon nanotubes, and the slurry composition for forming the coating comprises the first binder in an amount of 400 parts by weight to 2,000 parts by weight based on 100 parts by weight of multi-walled carbon nanotubes.

[0014] The present invention also provides a lithium secondary battery including the negative electrode for the lithium secondary battery.

[0015] Beneficial effects

[0016] According to the present invention, a negative electrode for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same can be provided, wherein the negative electrode for the lithium secondary battery has improved peel resistance and adhesion of the negative electrode active material layer, which can improve the life characteristics of the negative electrode and the lithium secondary battery.

[0017] With such a negative electrode for lithium secondary batteries, even when lithium secondary batteries are used for a long time, the phenomenon of the active material layer peeling off from the metal current collector can be significantly reduced, and as a result, the excellent charge / discharge cycle characteristics of lithium secondary batteries can be maintained for a long time.

[0018] Therefore, lithium secondary batteries including the negative electrode for lithium secondary batteries can exhibit significantly improved lifespan characteristics and can thus be very advantageously used as power supply devices for mobile devices and electric vehicles. Detailed Implementation

[0019] The following describes in more detail a negative electrode for a lithium secondary battery according to an embodiment of the present invention, a method for producing the same, and a lithium secondary battery comprising the same.

[0020] Throughout this specification, unless otherwise stated, the terms “comprising” or “including” mean to include any constituent element (or constituent component) without limitation and are not construed as excluding the addition of other constituent elements (or constituent components).

[0021] In this invention, terms such as first, second, etc. are used to describe various components, and these terms are used only for the purpose of distinguishing one component from another.

[0022] Furthermore, unless the steps included in the production method described in this specification are specified as sequential or consecutive, or otherwise stated, one step and another included in the production method should not be construed as being limited to the order described in the specification. Therefore, the order of steps included in the production method can be varied to a degree readily understood by those skilled in the art, and in such cases, incidental modifications that are obvious to those skilled in the art fall within the scope of this invention.

[0023] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery is provided, comprising: a metal current collector; a coating formed on at least one surface of the metal current collector and comprising a first binder and a first conductive material; and a negative electrode active material layer formed on the coating and comprising a negative electrode active material, a second conductive material and a second binder, wherein the first conductive material comprises multi-walled carbon nanotubes, and the coating comprises the first binder in an amount of 400 parts by weight to 2,000 parts by weight based on 100 parts by weight of multi-walled carbon nanotubes.

[0024] The inventors of this invention continued their research to improve the adhesion and peel resistance of the active material layer of the negative electrode to the metal current collector.

[0025] As a result of these ongoing studies, the inventors of this invention have discovered that when a coating comprising a first binder and a first conductive material (wherein the first conductive material comprises multi-walled carbon nanotubes, and the coating comprises the first binder in an amount of 400 to 2,000 parts by weight based on 100 parts by weight of the multi-walled carbon nanotubes) is formed on a metal current collector, unlike conventionally used nano-sized particles, the peel resistance of the negative electrode active material layer can be significantly improved due to the inclusion of multi-walled carbon nanotubes with their own strength in the coating, and the coating can significantly improve the adhesion of the negative electrode active material layer by exhibiting excellent adhesion to the negative electrode active material layer.

[0026] Specifically, since the coating formed between the metal current collector and the negative electrode active material layer contains a first conductive material containing multi-walled carbon nanotubes, and contains a first binder in an amount of 400 to 2,000 parts by weight based on 100 parts by weight of multi-walled carbon nanotubes, the peel resistance of the coating can be significantly improved due to the inclusion of multi-walled carbon nanotubes with their own strength, unlike conventionally used nano-sized particles. At the same time, the first binder can significantly improve the adhesion of the negative electrode active material layer by exhibiting excellent adhesion without side reactions with the electrode.

[0027] Therefore, according to one embodiment of the present invention, by including a coating between the metal current collector and the negative electrode active material layer, a negative electrode for lithium secondary batteries with significantly improved peel resistance and adhesion of the negative electrode active material layer can be produced and provided. In the case of such a negative electrode for lithium secondary batteries, even when the lithium secondary battery is used for a long time, the phenomenon of the negative electrode active material layer peeling off from the metal current collector can be significantly reduced, and as a result, the life characteristics of the lithium secondary battery can be significantly improved.

[0028] The negative electrode for a lithium secondary battery according to one embodiment will be described in more detail below.

[0029] According to one embodiment, the negative electrode for a lithium secondary battery basically comprises a metal current collector, a coating formed on the metal current collector, and an active material layer formed on the coating.

[0030] Specifically, the negative electrode for a lithium secondary battery according to this embodiment may include: a metal current collector; a coating formed on at least one surface of the metal current collector and comprising a first binder and a first conductive material; and a negative electrode active material layer formed on the coating and comprising a negative electrode active material, a second conductive material, and a second binder.

[0031] Since the negative electrode for a lithium secondary battery according to one embodiment includes a coating, the coating can significantly improve the adhesion and peel resistance of the negative electrode active material layer by exhibiting excellent adhesion to the negative electrode active material layer.

[0032] The coating may include a first adhesive and a first conductive material.

[0033] Various polymeric binders can be used as the primary binder, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-copolymer-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), or other copolymers. Among these, styrene-butadiene rubber (SBR) is preferred due to its excellent adhesion to metal current collectors and its excellent dispersibility in negative electrode active materials and conductive materials.

[0034] The first conductive material may contain multi-walled carbon nanotubes.

[0035] Because the coating contains multi-walled carbon nanotubes as the primary conductive material, peel resistance can be significantly improved compared to conventionally used nano-sized particles, due to the inclusion of multi-walled carbon nanotubes with their own strength.

[0036] Specifically, based on 100 parts by weight of multi-walled carbon nanotubes, the coating may contain a first binder in an amount of 400 parts by weight to 2,000 parts by weight.

[0037] More specifically, based on 100 parts by weight of multi-walled carbon nanotubes, the coating may contain the first binder in the following amounts: 400 parts by weight or more, 450 parts by weight or more, or 500 parts by weight or more, and 2,000 parts by weight or less, 1,500 parts by weight or less, or 1,000 parts by weight or less, 400 parts by weight to 2,000 parts by weight, 400 parts by weight to 1,500 parts by weight, 400 parts by weight to 1,000 parts by weight, 450 parts by weight to 2,000 parts by weight, 450 parts by weight to 1,500 parts by weight, 450 parts by weight to 1,000 parts by weight, 500 parts by weight to 2,000 parts by weight, 500 parts by weight to 1,500 parts by weight, or 500 parts by weight to 1,000 parts by weight.

[0038] Since the coating contains a first binder in an amount of 400 to 2,000 parts by weight, based on 100 parts by weight of multi-walled carbon nanotubes, unlike conventionally used nano-sized particles, the peel resistance can be significantly improved due to the inclusion of multi-walled carbon nanotubes with their own strength in the coating. At the same time, the first binder can significantly improve the adhesion of the negative electrode active material layer by exhibiting excellent adhesion without side-reacting with the electrode.

[0039] If the coating contains less than 400 parts by weight of the first binder based on 100 parts by weight of multi-walled carbon nanotubes, its adhesion may be reduced due to the coating containing too little of the first binder that exhibits adhesion, while if the coating contains more than 2,000 parts by weight of the first binder, the interfacial resistance may be increased due to the coating containing too little of the conductive material.

[0040] The coating contains multi-walled carbon nanotubes with a specific surface area of ​​up to 100 m². 2 / g to 400 m 2 / g.

[0041] More specifically, the coating contains multi-walled carbon nanotubes with a specific surface area of ​​up to 100 m². 2 / g or larger, 150m 2 / g or greater, 200 m 2 / g or greater, 300 m 2 / g or greater, 350 m 2 / g or greater, or 380 m 2 / g or greater, and 400 m 2 / g or less, or 390 m 2 / g or less, 100 m 2 / g to 400 m 2 / g, 150 m 2 / g to 400 m 2 / g、200 m 2 / g to 400 m 2 / g、300 m 2 / g to 400 m 2 / g、350 m 2 / g to 400 m 2 / g、380 m 2 / g to 400 m 2 / g、100 m 2 / g to 390 m 2 / g、200 m 2 / g to 390 m 2 / g、300 m 2 / g to 390 m2 / g、350 m 2 / g to 390 m 2 / g, or 380 m 2 / g to 390 m 2 / g.

[0042] Because the specific surface area of ​​multi-walled carbon nanotubes is 100 m² 2 / g to 400 m 2 / g, thus ensuring the dispersion of conductive materials.

[0043] If the specific surface area of ​​multi-walled carbon nanotubes is less than 100 m² 2 If the specific surface area of ​​the multi-walled carbon nanotubes is greater than 400 m² / g, the entanglement of the multi-walled carbon nanotubes may be excessive, which could reduce the dispersibility of the conductive material. 2 If the output is less than / g, production may be difficult.

[0044] Furthermore, the multi-walled carbon nanotubes contained in the coating can have a diameter of 1 nm to 40 nm and a length of 10 μm to 30 μm.

[0045] Specifically, the multi-walled carbon nanotubes contained in the coating can have a diameter of 1 nm or greater, 3 nm or greater, 5 nm or greater, or 10 nm or greater, and 40 nm or less, 30 nm or less, 20 nm or less, or 15 nm or less, 1 nm to 40 nm, 3 nm to 40 nm, 5 nm to 40 nm, 10 nm to 40 nm, 1 nm to 30 nm, 3 nm to 30 nm, 5 nm to 30 nm, 10 nm to 30 nm, 1 nm to 20 nm, 3 nm to 20 nm, 5 nm to 20 nm, 10 nm to 20 nm, 1 nm to 15 nm, 3 nm to 15 nm, 5 nm to 15 nm, or 10 nm to 15 nm.

[0046] Specifically, the multi-walled carbon nanotubes contained in the coating can have a length of 10 μm or greater, or 15 μm or greater, and 30 μm or less, or 20 μm or less, 10 μm to 30 μm, 15 μm to 30 μm, 10 μm to 20 μm, or 15 μm to 20 μm.

[0047] Furthermore, the packing density of the multi-walled carbon nanotubes contained in the coating can be 20 kg / m³. 3 Up to 200 kg / m 3 .

[0048] Specifically, the packing density of the multi-walled carbon nanotubes contained in the coating can be 20 kg / m³.3 Or larger, 50 kg / m 3 Or larger, 60 kg / m 3 Or larger, or 75 kg / m 3 Or larger, and 200 kg / m 3 Or smaller, or 160 kg / m 3 or smaller, 20 kg / m 3 Up to 200 kg / m 3 20 kg / m 3 Up to 160 kg / m 3 50 kg / m 3 Up to 200 kg / m 3 50 kg / m 3 Up to 160kg / m 3 60 kg / m 3 Up to 200 kg / m 3 60 kg / m 3 Up to 160 kg / m 3 75 kg / m 3 Up to 200 kg / m 3 Or 75 kg / m 3 Up to 160 kg / m 3 .

[0049] Because the packing density of the multi-walled carbon nanotubes contained in the coating meets the requirement of 20 kg / m³ 3 Up to 200 kg / m 3 The range is such that multi-walled carbon nanotubes can be easily controlled, and multi-walled carbon nanotubes can exhibit excellent electrical properties even when used in small quantities.

[0050] If the packing density of the multi-walled carbon nanotubes contained in the coating does not meet 20 kg / m³ 3 Up to 200 kg / m 3 If the range is too wide, it may be difficult to control multi-walled carbon nanotubes.

[0051] In addition to multi-walled carbon nanotubes, which serve as the primary conductive material, the coating may also contain other conductive materials.

[0052] There are no particular limitations on the first conductive material, as long as it is conductive and will not cause chemical changes in the battery. Examples of first conductive materials that can be used include carbon black-based conductive materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0053] The first conductive material may include at least one selected from carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black.

[0054] For example, the coating may contain multi-walled carbon nanotubes and carbon black as the first conductive material.

[0055] Based on the total weight of the first conductive material, the coating may contain multi-walled carbon nanotubes in an amount ranging from 40% to 100% by weight.

[0056] Specifically, based on the total weight of the first conductive material, the coating may contain multi-walled carbon nanotubes in amounts of 40% or more, 50% or more, and 100% or less, or 80% or less, 40% to 100% of weight, 40% to 80% of weight, 50% to 100% of weight, or 50% to 80% of weight.

[0057] Since the coating contains multi-walled carbon nanotubes in an amount of 40% to 100% by weight based on the total weight of the first conductive material, when multi-walled carbon nanotubes in fibrous form are combined with the first binder, they can have excellent scratch resistance and exhibit excellent adhesion and low interfacial resistance, thus providing an excellent negative electrode for lithium secondary batteries in terms of electrochemistry.

[0058] If the coating contains multi-walled carbon nanotubes in an amount of less than 40% by weight based on the total weight of the first conductive material, the coating may have poor scratch resistance.

[0059] The coating thickness can range from 0.1 μm to 5.0 μm.

[0060] Specifically, the coating thickness can be 0.1 μm or greater, 0.5 μm or greater, or 1.0 μm or greater, and 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, 2.0 μm or less, 1.5 μm or less, 0.1 μm to 5.0 μm, 0.1 μm to 4.0 μm, 0.1 μm to 3.0 μm, 0.1 μm to 2.0 μm, 0.1 μm to 1.5 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, 0.5 μm to 1.5 μm, 1.0 μm to 5.0 μm, 1.0 μm to 4.0 μm, 1.0 μm to 3.0 μm, 1.0 μm to 2.0 μm, or 1.0 μm. μm to 1.5 μm.

[0061] Because the coating thickness ranges from 0.1 μm to 5.0 μm, it can simultaneously exhibit excellent adhesion and scratch resistance as well as low interfacial resistance.

[0062] If the coating thickness is less than 0.1 μm, sufficient adhesion between the coating and the negative electrode active material layer may not be achieved, or scratch resistance may be reduced. If the coating thickness is greater than 5.0 μm, the interfacial resistance may increase excessively.

[0063] As a metal current collector, any metal current collector used as an electrode current collector for lithium secondary batteries, etc., can be used without particular limitation. For example, a metal current collector that is conductive without causing chemical changes in the battery. Specific examples of such metal current collectors include current collectors containing at least one metal selected from copper, stainless steel, aluminum, nickel, and titanium. Among these metal current collectors, copper current collectors can be used, considering their excellent conductivity as a negative electrode for lithium secondary batteries and their excellent adhesion to the active material layer.

[0064] Although there are no particular limitations on the thickness of the metal current collector, the thickness of the metal current collector can range from 3 μm to 500 μm, which is commonly used.

[0065] Specifically, the thickness of the metal current collector can be 3 μm or greater, 5 μm or greater, or 7 μm or greater, and 500 μm or less, 300 μm or less, 100 μm or less, or 50 μm or less, 3 μm to 500 μm, 3 μm to 300 μm, 3 μm to 100 μm, 3 μm to 50 μm, 5 μm to 500 μm, 5 μm to 300 μm, 5 μm to 100 μm, 5 μm to 50 μm, 7 μm to 500 μm, 7 μm to 300 μm, 7 μm to 100 μm, or 7 μm to 50 μm.

[0066] The negative electrode active material layer may include, for example, a negative electrode active material containing a graphite-based active material, a second binder, and a second conductive material.

[0067] Specific examples of negative electrode active materials may include at least one graphite-based active material selected from natural graphite, artificial graphite, fibrous artificial graphite, graphitized carbon black, and graphitized nanofibers, and in addition to graphite-based active materials, specific examples of negative electrode active materials may also include other active materials, such as silicon-based active materials.

[0068] Furthermore, various polymeric binders can be used as the second binder, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-copolymer-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), or other various copolymers. Among these, polyvinylidene fluoride polymers or copolymers are preferred due to their excellent adhesion to metal current collectors and their excellent dispersibility in negative electrode active materials and conductive materials.

[0069] Furthermore, there are no particular limitations on the second conductive material, as long as it is conductive and does not cause chemical changes in the battery. Examples of usable second conductive materials include carbon black-based conductive materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, and thermally cracked black; conductive fibers, such as carbon fibers or metal fibers; metal powders, such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0070] The second conductive material may include at least one selected from carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black.

[0071] However, when graphite-based active materials are mainly used as negative electrode active materials, carbon black-based conductive materials can be appropriately used as secondary conductive materials, considering their excellent dispersibility and electrical properties in the negative electrode active materials.

[0072] That is, the first adhesive and the second adhesive may each independently contain at least one of the following: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-copolymer-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid and styrene-butadiene rubber (SBR).

[0073] The thickness of the negative electrode active material layer can be from 100 μm to 200 μm.

[0074] Specifically, the thickness of the negative electrode active material layer can be 100 μm to 200 μm, 100 μm to 150 μm, or 100 μm to 130 μm.

[0075] If the thickness of the negative electrode active material layer is less than 100 μm, sufficient adhesion between the coating and the negative electrode active material layer may not be achieved, or scratch resistance may be reduced. If the thickness of the negative electrode active material layer is greater than 200 μm, the interface resistance may increase excessively.

[0076] In a lithium secondary battery anode according to one embodiment, the ratio of the coating thickness to the thickness of the anode active material layer can be from 0.005 to 0.2.

[0077] Specifically, the ratio of the coating thickness to the thickness of the negative electrode active material layer can be 0.005 or greater, 0.007 or greater, or 0.008 or greater, and 0.2 or less, 0.02 or less, or 0.015 or less, 0.005 to 0.2, 0.007 to 0.2, 0.008 to 0.2, 0.005 to 0.02, 0.007 to 0.02, 0.008 to 0.02, 0.005 to 0.015, 0.007 to 0.015, or 0.008 to 0.015.

[0078] If the ratio of the coating thickness to the thickness of the negative electrode active material layer is less than 0.005, the coating is too thin and may therefore fail to achieve sufficient adhesion between the coating and the negative electrode active material layer, or may reduce scratch resistance. If the ratio of the coating thickness to the thickness of the negative electrode active material layer is greater than 0.2, the coating becomes too thick and the interfacial resistance may increase excessively.

[0079] Meanwhile, the negative electrode active material layer may include: a negative electrode active material in an amount of 80% to 98% by weight, or 85% to 98% by weight, or 90% to 97% by weight, based on the total weight of the negative electrode active material layer; a second binder in an amount of 0.5% to 15% by weight, or 0.7% to 10% by weight, or 1% to 5% by weight, based on the total weight of the negative electrode active material layer; and a second conductive material in an amount of 0.1% to 10% by weight, or 0.2% to 5% by weight, or 0.3% to 2% by weight, based on the total weight of the negative electrode active material layer.

[0080] Since the negative electrode active material layer contains negative electrode active material, second binder and second conductive material in the amounts within the above range, the adhesion of the negative electrode active material layer can be further improved, and at the same time, the uniform dispersion of negative electrode active material and conductive material can be achieved, and excellent electrochemical characteristics of negative electrode for lithium secondary batteries can be achieved.

[0081] The negative electrode active material layer can be adhered to the coating with an adhesion force of 30 gf / 20 mm to 50 gf / 20 mm.

[0082] When the coating and the negative electrode active material layer meet the above composition and thickness, the adhesion of the negative electrode active material layer to the coating can be achieved.

[0083] Specifically, the negative electrode active material layer can be attached to the coating with an adhesion force of 30 gf / 20 mm to 50 gf / 20 mm, 35 gf / 20 mm to 50 gf / 20 mm, or 40 gf / 20 mm to 50 gf / 20 mm. Because the negative electrode active material layer is attached to the coating with an adhesion force of 30 gf / 20 mm to 50 gf / 20 mm, it can maintain excellent electrochemical characteristics for a long time and ensure excellent long-term lifespan characteristics of the lithium secondary battery.

[0084] According to another embodiment of the present invention, a method for producing a negative electrode for a lithium secondary battery is provided, comprising the steps of: applying a slurry composition for forming a coating, comprising a first binder, a first conductive material and a solvent, to a metal current collector, and then drying to form a coating; applying a negative electrode slurry composition comprising a negative electrode active material, a second binder, a second conductive material and a solvent to the coating; and pressing the negative electrode slurry composition, wherein the first conductive material comprises multi-walled carbon nanotubes, and the slurry composition for forming the coating comprises the first binder in an amount of 400 parts by weight to 2,000 parts by weight based on 100 parts by weight of multi-walled carbon nanotubes.

[0085] The types of the negative electrode active material, the first conductive material, the second conductive material, the first binder and the second binder are as described above, and the content ranges of these components are also as described above with respect to the content ranges of the components contained in the final active material layer, and therefore further descriptions will be omitted.

[0086] As a solvent, common solvents such as N-methylpyrrolidone, acetone, water, etc. can be used, and a slurry composition can be formed by mixing and stirring the components in such a solvent to achieve a solid content concentration of 30% to 70% by weight or 40% to 60% by weight.

[0087] After forming the slurry composition for forming the coating, the slurry composition for forming the coating can be applied to the negative electrode current collector using a general coating method. There are no particular limitations on the coating method; for example, a coating method using a slit mold can be applied, or any other method can be applied without particular limitation, such as Mayer bar coating, gravure coating, dip coating, or spray coating.

[0088] Furthermore, after forming the negative electrode slurry composition, the negative electrode slurry composition can be applied to the coating using a general coating method. There are no particular limitations to this coating method; for example, a slit-die coating method can be used, or any other method can be used without particular limitation, such as Mayer bar coating, gravure coating, dip coating, or spray coating.

[0089] After the coating process, the negative electrode slurry composition is pressed using a pressing device, such as a roller press.

[0090] After the pressing process described above, an additional step of drying the slurry composition to remove the solvent can be performed. This drying process can be carried out using a general method, such as an infrared drying device.

[0091] The negative electrode for lithium secondary batteries produced by the above method exhibits excellent adhesion and anti-peel properties of the active material layer, and as a result, the lithium secondary battery containing it exhibits significantly improved lifespan characteristics.

[0092] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery including the above-described negative electrode for a lithium secondary battery is provided. Such a lithium secondary battery can be manufactured and supplied by injecting a lithium salt-containing electrolyte into an electrode assembly including a positive electrode, the above-described negative electrode, and a separator therebetween.

[0093] The positive electrode can be produced by mixing positive electrode active material, conductive material, binder and solvent to prepare a slurry composition, and then directly coating the slurry composition onto the metal current collector. Alternatively, the positive electrode can be produced by casting the slurry composition onto a separate support and laminating a film of positive electrode active material peeled off from the support onto the metal current collector.

[0094] The active material used for the positive electrode can include materials selected from LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and Active material particles consisting of any one or a mixture of two or more of the elements M1 and M2, each independently selected from Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, and x, y, and z each independently representing the atomic fraction of the constituent elements of the oxide, and satisfying the following conditions: , , and .

[0095] Meanwhile, conductive materials, binders, and solvents can be used in the same way as those used in the production of negative electrodes.

[0096] The separator can be a conventional porous polymer membrane commonly used as a separator. For example, the porous polymer membrane can be a porous polymer membrane made of polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene-butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer). These porous polymer membranes can be used alone or in the form of a laminate. Additionally, insulating films with high ion permeability and mechanical strength can be used. The separator may include a safety-reinforced separator (SRS) comprising a thin ceramic material coating formed on the surface of the separator. Furthermore, conventional porous nonwoven fabrics can be used, such as, but not limited to, nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0097] The electrolyte may contain lithium salt and an organic solvent for dissolving the lithium salt.

[0098] As a lithium salt, any lithium salt can be used without restriction, as long as it is conventionally used in electrolytes for lithium secondary batteries. For example, the anion of the lithium salt can be selected from any of the following: F - Cl - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - .

[0099] As an organic solvent contained in the electrolyte, any organic solvent can be used without restriction, as long as it is conventionally used. Typically, the organic solvent can be selected from at least one of the following: propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0100] In particular, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and can be preferred because they can readily dissociate lithium salts in the electrolyte due to their high dielectric constant. When such cyclic carbonates are used after being mixed with linear carbonates (e.g., dimethyl carbonate or diethyl carbonate) having low viscosity and low dielectric constant in an appropriate ratio, an electrolyte with higher conductivity can be prepared, and therefore such mixtures can be used more preferably.

[0101] Optionally, the electrolyte may also contain additives included in conventional electrolytes, such as overcharge protection agents.

[0102] Lithium-ion batteries can be manufactured by inserting a separator between the positive and negative electrodes to form an electrode assembly, placing the electrode assembly in, for example, a bag, a cylindrical battery case, or a prismatic battery case, and then injecting electrolyte into it. Alternatively, lithium-ion batteries can be manufactured by stacking electrode assemblies, impregnating the stack with electrolyte, placing the resulting product in a battery case, and then sealing it.

[0103] Lithium secondary batteries can be stacked, wound, stacked and folded, or cable-type.

[0104] The aforementioned lithium secondary batteries can be used as battery cells for powering small devices, and are preferably used as cell batteries for medium or large battery modules comprising a plurality of battery cells. Preferred examples of medium or large devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. In particular, lithium secondary batteries can be used as batteries for hybrid electric vehicles requiring high output, as well as novel renewable energy storage batteries.

[0105] Invention Embodiments

[0106] Preferred embodiments will be presented below to aid in understanding the invention. However, the following embodiments are intended to illustrate the invention only, and the invention is not limited to these embodiments.

[0107] Example 1

[0108] (1) Production of negative electrode

[0109] Multi-walled carbon nanotubes (product name: BT1004M (LG Chem), BET: 180m) will be used as the primary conductive material. 2 / g, Bulk density (BD): 130 kg / m³ 3 The average diameter (13 nm) was dispersed in polyvinylpyrrolidone at a rate of 2.4% by weight, and then an aqueous binder SBR (M37, ADB22) as the first binder was added thereto at a rate of five times the weight of the first conductive material, thereby preparing an aqueous slurry with a solid content of 17% for forming the coating.

[0110] A copper current collector (8 μm thick and 260 mm wide) was used as the negative electrode current collector. The aqueous slurry composition was applied using a microgravure coating machine at a concentration of 15 mg / cm². 2 The loading amount is applied to one surface of the copper current collector and dried at 100°C for 2 minutes to form a coating on the negative current collector (1.1 μm thick after coating).

[0111] A negative electrode slurry composition was prepared by adding silicon carbide-based powder as the negative electrode active material, carbon black as the second conductive material, and styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders (second binders) to N-methyl-2-pyrrolidone (NMP) as a solvent in amounts of 95.5% by weight, 1% by weight, 2.5% by weight, and 1% by weight, respectively.

[0112] The negative electrode slurry composition was prepared at 15 mg / cm 2 The load is applied to the coating formed on the negative electrode current collector (230 μm thick after application).

[0113] The slurry composition applied to the copper current collector as described above was subjected to a pressing process at 60°C using a pressing device, and then subjected to mid-infrared drying at 100°C at an evaporation rate of 605 g / min for 10 hours, thereby producing the negative electrode of Example 1, which includes a negative electrode active material layer formed on the coating.

[0114] (2) Production of the positive electrode

[0115] A positive electrode slurry was prepared by adding 97.5 wt% of a lithium-nickel-cobalt-manganese compound as the positive electrode active material, 1 wt% of carbon black as the conductive material, and 1.5 wt% of PVDF as the binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode slurry was applied to a 10 μm thick aluminum (Al) film as the positive electrode current collector and dried to produce a positive electrode, which was then rolled to produce the positive electrode.

[0116] (3) Battery production

[0117] Electrode assemblies are fabricated by inserting separators between the negative and positive electrodes and stacking them using a stacking method. The electrode assemblies are then stamped into a coin shape, and an electrolyte (propylene carbonate (PC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) = 3:4:3 (volume ratio), 1 mole of lithium hexafluorophosphate (LiPF6)) is injected into the assembled battery to produce a lithium secondary battery.

[0118] Example 2

[0119] The negative electrode was produced in the same manner as in Example 1, except that when preparing the aqueous slurry for forming the negative electrode coating, an aqueous binder SBR (M37, ADB22) was added in an amount 10 times the weight of the first conductive material, and a coating was formed on the negative electrode current collector, resulting in a coating thickness of 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0120] Example 3

[0121] The negative electrode was produced in the same manner as in Example 1, except that multi-walled carbon nanotubes (product name: BT2001M, BET: 380 m) were used in the preparation of the aqueous slurry for forming the negative electrode coating. 2 / g, Bulk density (BD): 75 kg / m³ 3 Average diameter: 6 nm) and Denka carbon black (solids content: 20 wt%, Li-250, BET: 60 m) 2 A 1:1 (weight / weight) mixture of multi-walled carbon nanotubes (product name: BT1004M (LGChem), BET: 180 m) was used instead of DBP: 200 ml / 100 g. 2 / g, Bulk density (BD): 130 kg / m³ 3 An average diameter of 6 nm was used as the first conductive material, and a coating was formed on the negative electrode current collector, resulting in a coating thickness of 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0122] Comparative Example 1

[0123] The negative electrode was produced in the same manner as in Example 1, except that only Denka black (solids content: 20% by weight, Li-250, BET: 60 m) was used in the preparation of the aqueous slurry for forming the negative electrode coating. 2 / g, DBP: 200 ml / 100g) can be used instead of multi-walled carbon nanotubes (product name: BT1004M (LG Chem), BET: 180 m 2 / g, Bulk density (BD): 130 kg / m³ 3 An average diameter of 6 nm was used as the first conductive material, and a coating was formed on the negative electrode current collector, resulting in a coating thickness of 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0124] Comparative Example 2

[0125] The negative electrode was produced in the same manner as in Example 1, except that when preparing the aqueous slurry for forming the negative electrode coating, an aqueous binder SBR (M37, ADB22) as the first binder was added in an amount equal to the weight of the first conductive material, and a coating was formed on the negative electrode current collector, such that the thickness after coating was 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0126] Comparative Example 3

[0127] The negative electrode was produced in the same manner as in Example 1, except that when preparing the aqueous slurry for forming the negative electrode coating, an aqueous binder SBR (M37, ADB22) as the first binder was added in an amount of 0.5 times the weight of the first conductive material, and a coating was formed on the negative electrode current collector, resulting in a coating thickness of 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0128] Comparative Example 4

[0129] The negative electrode was produced in the same manner as in Example 1, except that a coating was formed on the negative electrode current collector, resulting in a coating thickness of 0.2 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0130] Comparative Example 5

[0131] The negative electrode was produced in the same manner as in Example 1, except that a coating was formed on the negative electrode current collector, resulting in a coating thickness of 32.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0132] Comparative Example 6

[0133] The negative electrode was produced in the same manner as in Example 1, except that when preparing the aqueous slurry for forming the negative electrode coating, an aqueous binder SBR (M37, ADB22) as the first binder was added in an amount three times the weight of the first conductive material, and a coating was formed on the negative electrode current collector, resulting in a coating thickness of 1.0 μm. Furthermore, the positive electrode and the battery were produced in the same manner as in Example 1.

[0134] Test Example 1: Adhesive Force

[0135] In the negative electrodes produced in the examples and comparative examples, the adhesion between the negative electrode active material layer and the coating was measured in the following manner.

[0136] First, each negative electrode sample was cut to a predetermined size (50 mm × 50 mm) and fixed onto a glass slide. Then, the adhesion force between the negative electrode active material layer and the coating was measured at a 180° angle. The adhesion force was measured three times for each sample, and the average value was calculated.

[0137] Test Example 2: Peel Strength

[0138] In the negative electrodes produced in the examples and comparative examples, the peel strength of the laminate including the negative electrode current collector on which the coating is formed was measured.

[0139] The coated negative electrode current collector was stamped to a predetermined size (60 mm × 60 mm), and the average peel strength was measured after horizontal cutting for 5 minutes.

[0140] Test Example 3: Interface Resistance

[0141] In the negative electrode produced in the examples and comparative examples, the interface resistance was measured in the following manner.

[0142] First, each negative electrode sample was stamped to a predetermined size (50 mm × 50 mm) using a stamping machine. Using an MP tester (HIOKI), the thickness of the stamped electrode, the thickness of the copper foil, and the resistivity of the current collector were input. Then, the stamped electrode was placed under a tip with a built-in probe, the rod was lowered, and the interfacial resistance was measured.

[0143] Test Example 4: Scratch Resistance

[0144] In the negative electrodes produced in the examples and comparative examples, the scratch resistance of the laminate including the negative electrode current collector on which a coating is formed was measured.

[0145] The negative electrode current collector with the coating formed on it is stamped to a predetermined size (60 mm × 60 mm). Polyethylene terephthalate is attached to the other surface of the negative electrode current collector, and the surface of the coating is rubbed back and forth three times with the tip of a tribometer at a speed of 27. At this time, the area of ​​the exposed negative electrode current collector is measured.

[0146] The results are shown in Table 1 below.

[0147] [Table 1]

[0148]

[0149] Referring to Table 1 above, it can be determined that, in the case of the embodiments, excellent scratch resistance and high adhesion can be achieved, and the interfacial resistance is also very low.

[0150] On the other hand, it can be determined that, compared with the embodiments, in Comparative Examples 1 to 3 and 6, where multi-walled carbon nanotubes are not used or are used in amounts outside the content range used in the embodiments of the present invention, the adhesion is poor, the scratch resistance is poor, or the interfacial resistance is high.

[0151] Furthermore, it can be determined that in Comparative Examples 4 and 5, in which multi-walled carbon nanotubes are used in the same amount as in the embodiments of the present invention, but the ratio of coating thickness to negative electrode active material layer thickness is outside the range used in the embodiments of the present invention, the adhesion is very low or the interfacial resistance is very high.

[0152] That is, the negative electrode for lithium secondary batteries according to the present invention has improved peel resistance and adhesion of the negative electrode active material layer, which can improve the life characteristics of the negative electrode and the lithium secondary battery, and the lithium secondary battery including the negative electrode can maintain excellent charge / discharge cycle characteristics for a long time.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Metal current collector; A coating formed on at least one surface of the metal current collector and comprising a first binder and a first conductive material; as well as A negative electrode active material layer is formed on the coating and comprises a negative electrode active material, a second conductive material, and a second binder. The first conductive material comprises multi-walled carbon nanotubes. Based on 100 parts by weight of the multi-walled carbon nanotubes, the coating comprises the first binder in an amount of 400 parts by weight to 2,000 parts by weight, and The ratio of the thickness of the coating to the thickness of the negative electrode active material layer is 0.005 to 0.

2.

2. The negative electrode according to claim 1, wherein the specific surface area of ​​the multi-walled carbon nanotubes is 100 m². 2 / g to 400m 2 / g.

3. The negative electrode according to claim 1, wherein the multi-walled carbon nanotubes have a diameter of 1 nm to 40 nm and a length of 10 μm to 30 μm.

4. The negative electrode according to claim 1, wherein the packing density of the multi-walled carbon nanotubes is 20 kg / m³. 3 Up to 200kg / m 3 .

5. The negative electrode according to claim 1, wherein the negative electrode active material comprises at least one graphite-based active material selected from natural graphite, artificial graphite, fibrous artificial graphite, graphitized carbon black, and graphitized nanofibers.

6. The negative electrode according to claim 1, wherein the second conductive material comprises at least one selected from carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, and thermal cracking black.

7. The negative electrode according to claim 1, wherein the first binder and the second binder each independently comprise at least one selected from: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-copolymer-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, and styrene-butadiene rubber (SBR).

8. The negative electrode according to claim 1, wherein the coating comprises the multi-walled carbon nanotubes in an amount of 40% to 100% by weight, based on the total weight of the first conductive material.

9. The negative electrode according to claim 1, wherein the thickness of the coating is from 0.1 μm to 5.0 μm.

10. The negative electrode according to claim 1, wherein the thickness of the negative electrode active material layer is 100 μm to 200 μm.

11. The negative electrode according to claim 1, wherein the metal current collector comprises at least one metal selected from copper, stainless steel, aluminum, nickel and titanium.

12. The negative electrode according to claim 1, wherein the negative electrode active material layer is attached to the coating with an adhesive force of 30 gf / 20 mm to 50 gf / 20 mm.

13. A method for producing a negative electrode for lithium secondary batteries, comprising the following steps: A slurry composition for forming a coating, comprising a first binder, a first conductive material, and a solvent, is applied to a metal current collector and then dried to form a coating. A negative electrode slurry composition comprising a negative electrode active material, a second binder, a second conductive material, and a solvent is applied to the coating. as well as Press the negative electrode slurry composition. The first conductive material comprises multi-walled carbon nanotubes, and Based on 100 parts by weight of the multi-walled carbon nanotubes, the slurry composition for forming the coating contains the first binder in an amount of 400 to 2,000 parts by weight.

14. The method of claim 13, further comprising, after the step of pressing the negative electrode slurry composition, drying the negative electrode slurry composition to remove the solvent.

15. A lithium secondary battery, comprising: Positive electrode for lithium secondary batteries; The negative electrode for a lithium secondary battery according to claim 1; and A separator located between the positive electrode and the negative electrode.

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