Anode for lithium secondary battery, manufacturing method therefor and lithium secondary battery comprising same

Abstract

The present invention relates to an anode for a lithium secondary battery, a manufacturing method therefor and a lithium secondary battery comprising same, the anode comprising: a metal current collector; a coating layer which is formed on at least one surface of the metal current collector and which includes a first binder and a first conductive material; and an anode active material layer which is formed on the coating layer and which includes an anode active material, a second conductive material and a second binder.

Description

Anode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery comprising the same

[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] The present invention relates to an anode for a lithium secondary battery, which has improved peeling resistance and adhesiveness, thereby improving the lifespan characteristics of the anode and the lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

[0003] With the increasing technological development and demand for mobile devices and electric vehicles, the demand for lithium secondary batteries as an energy source is rapidly increasing. Among these lithium secondary batteries, those with high energy density and voltage, long cycle life, and low discharge rates are being commercialized and widely used.

[0004] In general, a lithium secondary battery is structured to have an electrode assembly in which a porous separator is interposed between a positive electrode and a negative electrode, each of which has an active material applied to a metal current collector, and an electrolyte containing a lithium salt is impregnated therein. Each electrode is manufactured by applying a slurry composition in which an active material, a binder, and a conductive agent are dispersed in a solvent to a metal current collector, and pressing and drying the slurry composition.

[0005] Therefore, the lifespan characteristics of lithium secondary batteries can be primarily determined by how long the electrochemical properties of the electrode, particularly the active material layer, are maintained. However, in the case of existing lithium secondary batteries, there have been many cases where the active material layer peels off from the metal current collector in the negative electrode over time, resulting in a decline in the lifespan characteristics of the lithium secondary battery.

[0006] This appears to be because, since the active material layer of the negative electrode mainly contains a graphite-based negative electrode active material with properties different from those of metal, it is difficult to secure sufficient adhesion, closeness, and peeling resistance with the metal current collector. Due to the poor adhesion of the active material layer of the negative electrode, there was a disadvantage in that the active material layer was easily peeled off from the metal current collector when the lithium secondary battery was in use, and since the peeled active material layer could no longer function as an active region of the lithium secondary battery, the charge / discharge cycle characteristics of the lithium secondary battery rapidly deteriorated.

[0007] Due to these problems, there is a continuous demand for the development of technologies that can improve the lifespan characteristics of lithium secondary batteries by further improving the adhesiveness of the active material layer included in the negative electrode.

[0008] Accordingly, the present invention provides an anode for a lithium secondary battery and a method for manufacturing the same, which can improve the peeling resistance and adhesiveness of a negative electrode active material layer, thereby improving the life characteristics of the anode and a lithium secondary battery.

[0009] The present invention also provides a lithium secondary battery exhibiting improved life characteristics, including the negative electrode for the lithium secondary battery.

[0010] The present invention provides an anode 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; wherein the first conductive material includes multi-walled carbon nanotubes, the coating layer includes 400 parts by weight or more and 2000 parts by weight or less of the first binder based on 100 parts by weight of the multi-walled carbon nanotubes, and a ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer is 0.005 or more and 0.2 or less.

[0011] The present invention also provides a method for manufacturing an anode for a lithium secondary battery, comprising: a step of applying a slurry composition for forming a coating layer, which comprises a first binder, a first conductive agent, and a solvent, onto a metal current collector and drying the same to form a coating layer; a step of applying a negative electrode slurry composition, which comprises a negative electrode active material, a second binder, a second conductive agent, and a solvent, onto the coating layer; and a step of rolling the negative electrode slurry composition; wherein the first conductive agent comprises multi-walled carbon nanotubes, and the slurry composition for forming a coating layer comprises 400 parts by weight or more and 2000 parts by weight or less of the first binder per 100 parts by weight of the multi-walled carbon nanotubes.

[0012] In addition, the present invention provides a lithium secondary battery including the negative electrode for the lithium secondary battery.

[0013] According to the present invention, a negative electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same can be provided, which can improve peeling resistance and adhesiveness, thereby improving the life characteristics of the negative electrode and the lithium secondary battery.

[0014] In such a negative electrode for a lithium secondary battery, even when the lithium secondary battery is used for a long period of time, the phenomenon of the active material layer being peeled off from the metal current collector can be significantly reduced, and as a result, the excellent charge / discharge cycle characteristics of the lithium secondary battery can be maintained for a long period of time.

[0015] Accordingly, a lithium secondary battery including the negative electrode for the lithium secondary battery exhibits greatly improved life characteristics, and can be very preferably used as a power supply means for mobile devices and electric vehicles.

[0016] Hereinafter, a negative electrode for a lithium secondary battery and a method for manufacturing the same according to one embodiment of the invention, and a lithium secondary battery including the same will be described in more detail.

[0017] Unless otherwise specified throughout this specification, the terms “include” or “comprising” refer to the inclusion of a component (or component) without limitation, and cannot be construed as excluding the addition of other components (or components).

[0018] In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

[0019] Furthermore, unless the steps constituting the manufacturing method described herein are explicitly stated to be sequential or consecutive, or there is another special order, the order of one step constituting a manufacturing method from another step is not limited to the order described in the specification. Accordingly, the order of the steps constituting the manufacturing method may be varied within a range readily understandable to those skilled in the art, and in such cases, any subsequent changes apparent to those skilled in the art are within the scope of the present invention.

[0020] According to one embodiment of the invention, a negative electrode for a lithium secondary battery is provided, 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 active material layer formed on the coating layer and including a negative active material, a second conductive material, and a second binder; wherein the first conductive material includes multi-walled carbon nanotubes, and the coating layer includes 400 parts by weight or more and 2000 parts by weight or less of the first binder based on 100 parts by weight of the multi-walled carbon nanotubes.

[0021] The inventors of the present invention continued research to improve the adhesion and peeling resistance of the active material layer of the negative electrode to the metal current collector.

[0022] As a result of these continuous studies, the inventors of the present invention have confirmed that by forming a coating layer on the metal current collector, which includes a first binder and a first conductive agent, wherein the first conductive agent includes multi-walled carbon nanotubes, and includes 400 parts by weight or more and 2000 parts by weight or less of the first binder with respect to 100 parts by weight of the multi-walled carbon nanotubes, the peeling resistance is greatly improved because the multi-walled carbon nanotubes have their own strength, unlike the nano-sized particles used in the related art, and the coating layer implements excellent adhesiveness with the negative electrode active material layer, thereby greatly improving the adhesiveness of the negative electrode active material layer.

[0023] Specifically, the coating layer formed between the metal current collector and the negative electrode active material layer includes multi-walled carbon nanotubes as the first conductive material, and includes 400 parts by weight or more and 2000 parts by weight or less of the first binder based on 100 parts by weight of the multi-walled carbon nanotubes, so that, unlike conventionally used nano-sized particles, the multi-walled carbon nanotubes have their own strength, and thus the peeling resistance is greatly improved. At the same time, the first binder can implement excellent adhesiveness without a side reaction with the electrode, thereby greatly improving the adhesiveness of the negative electrode active material layer.

[0024] Thus, according to an embodiment of the invention, by including a coating layer between a metal current collector and a negative electrode active material layer, an anode for a lithium secondary battery can be manufactured and provided in which the peeling resistance and adhesiveness of the negative electrode active material layer are significantly improved. In such a lithium secondary battery anode, even when the lithium secondary battery is used for a long period of time, the phenomenon of the negative electrode active material layer peeling 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.

[0025] Hereinafter, the negative electrode for a lithium secondary battery according to this embodiment will be described in more detail.

[0026] An anode for a lithium secondary battery of one embodiment basically includes a metal current collector, a coating layer formed on the metal current collector, and an active material layer formed on the coating layer.

[0027] Specifically, the negative electrode for a lithium secondary battery of the above embodiment may include 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.

[0028] Since the negative electrode for a lithium secondary battery of the above embodiment includes the coating layer, the coating layer can have excellent adhesion to the negative electrode active material layer, thereby greatly improving the adhesion and peeling resistance of the negative electrode active material layer.

[0029] The above coating layer may include a first binder and a first conductive material.

[0030] As the first binder, various polymer binders such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), or other various copolymers can be used. Among these, styrene butadiene rubber (SBR) can be preferably used in consideration of excellent adhesiveness to the metal current collector and excellent dispersibility for the negative electrode active material and conductive material.

[0031] The first conductive material may include multi-walled carbon nanotubes.

[0032] Since the coating layer includes multi-walled carbon nanotubes as the first conductive material, peeling resistance can be significantly improved as it includes multi-walled carbon nanotubes that have their own strength, unlike conventionally used nano-sized particles.

[0033] Specifically, the coating layer may contain 400 parts by weight or more and 2000 parts by weight or less of the first binder relative to 100 parts by weight of the multi-walled carbon nanotubes.

[0034] More specifically, the first binder may be included in an amount of 400 parts by weight or more, 450 parts by weight or more, or 500 parts by weight or more, and 2000 parts by weight or less, 1500 parts by weight or less, or 1000 parts by weight or less, with respect to 100 parts by weight of the multi-walled carbon nanotube, and may be included in an amount of 400 parts by weight or more but 2000 parts by weight or less, 400 parts by weight or more but 1500 parts by weight or less, 400 parts by weight or more but 1000 parts by weight or less, 450 parts by weight or more but 2000 parts by weight or less, 450 parts by weight or more but 1500 parts by weight or less, 450 parts by weight or more but 1000 parts by weight or less, 500 parts by weight or more but 2000 parts by weight or less, 500 parts by weight or more but 1500 parts by weight or less, or 500 parts by weight or more but 1000 parts by weight or less.

[0035] Since the coating layer contains the first binder in an amount of 400 parts by weight or more and 2000 parts by weight or less based on 100 parts by weight of the multi-walled carbon nanotubes, the peeling resistance is greatly improved by including the multi-walled carbon nanotubes which have their own strength, unlike the nano-sized particles used in the related art, and at the same time, the first binder can implement excellent adhesive strength without a side reaction with the electrode, thereby greatly improving the adhesive strength of the negative electrode active material layer.

[0036] If the coating layer contains less than 400 parts by weight of the first binder relative to 100 parts by weight of the multi-walled carbon nanotubes, the adhesive strength may be reduced due to the inclusion of an excessively small amount of the first binder that implements adhesive strength, and if the coating layer contains more than 2000 parts by weight of the first binder, the interfacial resistance may be increased due to the inclusion of an excessively small amount of the conductive agent.

[0037] The multi-walled carbon nanotubes included in the coating layer have a specific surface area of ​​100 m 2 / g or more than 400 m 2 / g can be less.

[0038] More specifically, the multi-walled carbon nanotubes have a specific surface area of ​​100 m 2 / g or more, 150 m 2 / g or more, 200 m 2 / g or more, 300 m 2 / g or more, 350 m 2 / g or more or 380 m 2 / g or more, 400 m 2 / g or less, or 390 m 2 / g can be less than 100 m 2 / g or more than 400 m 2 / g or less, 150 m 2 / g or more than 400 m 2 / g or less, 200 m 2 / g or more than 400 m 2 / g or less, 300 m 2 / g or more than 400 m 2 / g or less, 350 m 2 / g or more than 400 m 2 / g or less, 380 m 2 / g or more than 400 m 2 / g or less, 100 m 2 / g or more than 390 m 2 / g or less, 200 m 2 / g or more than 390 m 2 / g or less, 300 m 2 / g or more than 390 m2 / g or less, 350 m 2 / g or more than 390 m 2 / g or less or 380 m 2 / g or more than 390 m 2 / g can be less.

[0039] The specific surface area of ​​the above multi-walled carbon nanotubes is 100 m 2 / g or more than 400 m 2 As / g is less than or equal to, the dispersibility of the challenge material can be secured.

[0040] The specific surface area of ​​the above multi-walled carbon nanotubes is 100 m 2 / g or less, the entanglement of the multi-walled carbon nanotubes may be excessive, which may reduce the dispersibility of the conductive material, and the specific surface area of ​​the multi-walled carbon nanotubes may be less than 400 m 2 / If it exceeds 1g, manufacturing can be difficult.

[0041] In addition, the multi-walled carbon nanotubes included in the coating layer may have a diameter of 1 nm or more and 40 nm or less and a length of 10 μm or more and 30 μm or less.

[0042] Specifically, the multi-walled carbon nanotubes included in the coating layer may have a diameter of 1 nm or more, 3 nm or more, 5 nm or more, or 10 nm or more, and 40 nm or less, 30 nm or less, 20 nm or less, or 15 nm or less, and may be 1 nm or more and 40 nm or less, 3 nm or more and 40 nm or less, 5 nm or more and 40 nm or less, 10 nm or more and 40 nm or less, 1 nm or more and 30 nm or less, 3 nm or more and 30 nm or less, 5 nm or more and 30 nm or less, 10 nm or more and 30 nm or less, 1 nm or more and 20 nm or less, 3 nm or more and 20 nm or less, 5 nm or more and 20 nm or less, 10 nm or more and 20 nm or less, 1 nm or more and 15 nm or less, 3 nm or more and 15 nm or less, 5 nm or more and 15 nm or less, or 10 nm or more and 15 nm or less.

[0043] Specifically, the multi-walled carbon nanotubes included in the coating layer have a length of 10 µm or more or 15 µm or more and 30 µm or less or 20 µm or less, and may be 10 µm or more and 30 µm or less, 15 µm or more and 30 µm or less, 10 µm or more and 20 µm or less or 15 µm or more and 20 µm or less.

[0044] In addition, the multi-walled carbon nanotubes included in the coating layer have a bulk density of 20 kg / m 3 More than 200 kg / m 3 It could be as follows:

[0045] Specifically, the multi-walled carbon nanotubes included in the coating layer have a bulk density of 20 kg / m 3 Above 50 kg / m 3 Above, 60 kg / m 3 or more than 75 kg / m 3 Above, 200 kg / m 3 Less than or equal to 160 kg / m 3 Below 20 kg / m 3 More than 200 kg / m 3Below 20 kg / m 3 More than 160 kg / m 3 Below 50 kg / m 3 More than 200 kg / m 3 Below 50 kg / m 3 More than 160 kg / m 3 Below 60 kg / m 3 More than 200 kg / m 3 Below 60 kg / m 3 More than 160 kg / m 3 Below 75 kg / m 3 More than 200 kg / m 3 Less than or equal to 75 kg / m 3 More than 160 kg / m 3 It could be as follows:

[0046] The bulk density of the multi-walled carbon nanotubes included in the coating layer is 20 kg / m 3 More than 200 kg / m 3 By satisfying the following, it is not only easy to control multi-walled carbon nanotubes, but also excellent electrical properties can be realized even when using small quantities.

[0047] The bulk density of the multi-walled carbon nanotubes included in the coating layer is 20 kg / m 3 More than 200 kg / m 3 If the following conditions are not satisfied, it may be difficult to control multi-walled carbon nanotubes.

[0048] The above coating layer may further include an additional conductive material in addition to the multi-walled carbon nanotube as the first conductive material.

[0049] The first conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, a carbon black-based conductive material such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; a conductive fiber such as carbon fiber or metal fiber; a metal powder such as fluorocarbon, aluminum, or nickel powder; a conductive whisker such as zinc oxide or potassium titanate; a conductive metal oxide such as titanium oxide; a conductive material such as a polyphenylene derivative, etc. can be used.

[0050] The above first conductive material may include at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black.

[0051] For example, the coating layer may include multi-walled carbon nanotubes and carbon black as the first conductive material.

[0052] The above coating layer may contain the multi-walled carbon nanotubes in an amount of 40 wt% or more and 100 wt% or less based on the total weight of the first conductive material.

[0053] Specifically, the multi-walled carbon nanotubes may be included in an amount of 40 wt% or more or 50 wt% or more, 100 wt% or less or 80 wt% or less, and 40 wt% or more but 100 wt% or less, 40 wt% or more but 80 wt% or less, 50 wt% or more but 100 wt% or less, or 50 wt% or more but 80 wt% or less, based on the total weight of the first conductive material.

[0054] As the coating layer contains the multi-walled carbon nanotubes in an amount of 40 wt% or more and 100 wt% or less based on the total weight of the first conductive material, the multi-walled carbon nanotubes in the form of fibers are combined with the first binder, thereby providing an electrochemically superior negative electrode for a lithium secondary battery by exhibiting excellent scratch resistance and simultaneously low interfacial resistance with excellent adhesive strength.

[0055] If the coating layer contains less than 40 wt% of the multi-walled carbon nanotubes based on the total weight of the first conductive material, a problem of poor scratch resistance may occur.

[0056] The above coating layer may have a thickness of 0.1 ㎛ or more and 5.0 ㎛ or less.

[0057] Specifically, the coating layer is 0.1 ㎛ or more, 0.5 ㎛ or more, or 1.0 ㎛ or more, 5.0 ㎛ or less, 4.0 ㎛ or less, 3.0 ㎛ or less, 2.0 ㎛ or less, or 1.5 ㎛ or less, 0.1 ㎛ or more and 5.0 ㎛ or less, 0.1 ㎛ or more and 4.0 ㎛ or less, 0.1 ㎛ or more and 3.0 ㎛ or less, 0.1 ㎛ or more and 2.0 ㎛ or less, 0.1 ㎛ or more and 1.5 ㎛ or less, 0.5 ㎛ or more and 5.0 ㎛ or less, 0.5 ㎛ or more and 4.0 ㎛ or less, 0.5 ㎛ or more and 3.0 ㎛ or less, 0.5 ㎛ or more and 2.0 ㎛ or less, 0.5 ㎛ or more and 1.5 ㎛ or less, 1.0 ㎛ or more and 5.0 ㎛ or less, 1.0 ㎛ or more It may have a thickness of 4.0 ㎛ or less, 1.0 ㎛ or more and 3.0 ㎛ or less, 1.0 ㎛ or more and 2.0 ㎛ or less, or 1.0 ㎛ or more and 1.5 ㎛ or less.

[0058] Since the above coating layer has a thickness of 0.1 ㎛ or more and 5.0 ㎛ or less, excellent adhesion, scratch resistance, and a small interface resistance value can be achieved simultaneously.

[0059] When the coating layer has a thickness of less than 0.1 ㎛, sufficient adhesive strength may not be achieved between the coating layer and the negative electrode active material layer or scratch resistance may be reduced, and when the coating layer has a thickness of more than 5.0 ㎛, interface resistance may become excessively large.

[0060] As the above metal current collector, any metal current collector that has been used as an electrode current collector for lithium secondary batteries, etc., for example, a metal current collector that is conductive and does not cause chemical changes in the battery can be used without particular limitations. A specific example of such a metal current collector may include a current collector comprising one or more metals selected from the group consisting of copper, stainless steel, aluminum, nickel, and titanium. Among these metal current collectors, a copper current collector can be used in consideration of the excellent conductivity of the negative electrode for a lithium secondary battery and excellent adhesion to the active material layer.

[0061] The thickness of the above metal collector is not particularly limited, but may have a thickness of 3 ㎛ or more and 500 ㎛ or less, which is commonly applied.

[0062] Specifically, the thickness of the metal current collector may be 3 ㎛ or more, 5 ㎛ or more, or 7 ㎛ or more, 500 ㎛ or less, 300 ㎛ or less, 100 ㎛ or less, or 50 ㎛ or less, 3 ㎛ or more and 500 ㎛ or less, 3 ㎛ or more and 300 ㎛ or less, 3 ㎛ or more and 100 ㎛ or less, 3 ㎛ or more and 50 ㎛ or less, 5 ㎛ or more and 500 ㎛ or less, 5 ㎛ or more and 300 ㎛ or less, 5 ㎛ or more and 100 ㎛ or less, 5 ㎛ or more and 50 ㎛ or less, 7 ㎛ or more and 500 ㎛ or less, 7 ㎛ or more and 300 ㎛ or less, 7 ㎛ or more and 100 ㎛ or less, or 7 ㎛ or more and 50 ㎛ or less.

[0063] The above negative electrode active material layer may include, for example, a negative electrode active material including a graphite-based active material, a second binder, and a second conductive material.

[0064] Among these, specific examples of the negative electrode active material include at least one graphite-based active material selected from the group consisting of natural graphite, artificial graphite, fibrous artificial graphite, graphitized black, and graphitized nanofibers, and in addition to the graphite-based active material, additional active materials such as silicon-based active materials may be further included.

[0065] In addition, various polymer binders such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), or other various copolymers may be used as the second binder. Among these, a polyvinylidene fluoride-based polymer or copolymer may be preferably used in consideration of excellent adhesiveness to the metal current collector and excellent dispersibility for the negative electrode active material and conductive material.

[0066] In addition, the second conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, a carbon black-based conductive material such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; a conductive fiber such as carbon fiber or metal fiber; a metal powder such as fluorocarbon, aluminum, or nickel powder; a conductive whisker such as zinc oxide or potassium titanate; a conductive metal oxide such as titanium oxide; a conductive material such as a polyphenylene derivative, etc. can be used.

[0067] The second conductive material may include at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black.

[0068] However, when a graphite-based active material is mainly used as the negative electrode active material, a carbon black-based conductive material may be appropriately used as the second conductive material, taking into consideration its excellent dispersibility and electrical properties.

[0069] That is, the first binder and the second binder may each independently include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, and styrene butadiene rubber (SBR).

[0070] The above negative active material layer may have a thickness of 100 ㎛ or more and 200 ㎛ or less.

[0071] Specifically, the negative active material layer may have a thickness of 100 ㎛ or more and 200 ㎛ or less, 100 ㎛ or more and 150 ㎛ or less, or 100 ㎛ or more and 130 ㎛ or less.

[0072] When the negative electrode active material layer has a thickness of less than 100 ㎛, sufficient adhesive strength may not be achieved between the coating layer and the negative electrode active material layer or scratch resistance may be reduced, and when the negative electrode active material layer has a thickness of more than 200 ㎛, interfacial resistance may become excessively large.

[0073] In the negative electrode for a lithium secondary battery of the above embodiment, the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer may be 0.005 or more and 0.2 or less.

[0074] Specifically, the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer may be 0.005 or more, 0.007 or more, or 0.008 or more, and 0.2 or less, 0.02 or less, or 0.015 or less, 0.005 or more and 0.2 or less, 0.007 or more and 0.2 or less, 0.008 or more and 0.2 or less, 0.005 or more and 0.02 or less, 0.007 or more and 0.02 or less, 0.008 or more and 0.02 or less, 0.005 or more and 0.015 or less, 0.007 or more and 0.015 or less, or 0.008 or more and 0.015 or less.

[0075] If the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer is less than 0.005, the coating layer may be too thin, so that sufficient adhesive force may not be achieved between the coating layer and the negative electrode active material layer, or scratch resistance may be reduced. If the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer is more than 0.2, the coating layer may become too thick, so that the interface resistance may become excessively large.

[0076] Meanwhile, the negative electrode active material layer may include 80 wt% to 98 wt%, or 85 wt% to 98 wt%, or 90 wt% to 97 wt% of the negative electrode active material, 0.5 wt% to 15 wt%, or 0.7 wt% to 10 wt%, or 1 wt% to 5 wt% of the second binder, and 0.1 wt% to 10 wt%, or 0.2 wt% to 5 wt%, or 0.3 wt% to 2 wt% of the second conductive agent, based on the total weight of the negative electrode active material layer.

[0077] As the negative electrode active material layer includes the negative electrode active material, the second binder, and the second conductive agent in the above content range, the adhesiveness of the negative electrode active material layer can be further improved, while uniform dispersion of the negative electrode active material and the conductive agent can be achieved, and excellent electrochemical characteristics of the negative electrode for a lithium secondary battery can be achieved.

[0078] The above negative active material layer may be attached to the coating layer with an adhesive strength of 30 gf / 20mm or more and 50 gf / 20mm or less.

[0079] The adhesion of the negative electrode active material layer to the coating layer can be realized when the coating layer and the negative electrode active material layer satisfy the composition and thickness described above.

[0080] Specifically, the negative active material layer may be attached to the coating layer with an adhesive strength of 30 gf / 20mm or more and 50 gf / 20mm or less, 35 gf / 20mm or more and 50 gf / 20mm or less, or 40 gf / 20mm or more and 50 gf / 20mm or less. Since the negative active material layer is attached to the coating layer with an adhesive strength of 30 gf / 20mm or more and 50 gf / 20mm or less, excellent electrochemical characteristics can be maintained for a long period of time, and excellent long-term life characteristics of the lithium secondary battery can be ensured.

[0081] According to another embodiment of the invention, a method for manufacturing an anode for a lithium secondary battery is provided, including: a step of forming a coating layer by applying a slurry composition comprising a first binder, a first conductive agent, and a solvent onto a metal current collector and drying the same; a step of applying a negative electrode slurry composition comprising a negative electrode active material, a second binder, a second conductive agent, and a solvent onto the coating layer; and a step of rolling the negative electrode slurry composition, wherein the first conductive agent comprises multi-walled carbon nanotubes, and the slurry composition for forming a coating layer comprises 400 parts by weight or more and 2000 parts by weight or less of the first binder based on 100 parts by weight of the multi-walled carbon nanotubes.

[0082] The types of the negative active material, the first conductive material, the second conductive material, the first binder, and the second binder have already been described above, and the content ranges of these are also the same as those described above for the content ranges of each component included in the finally formed active material layer, so further description thereof will be omitted.

[0083] As the solvent, a general solvent such as N-methylpyrrolidone, acetone, water, etc. can be used, and the slurry composition can be formed by mixing and stirring such solvent so that the solid content concentration is 30 to 70 wt% or 40 to 60 wt%.

[0084] After forming the slurry composition for forming the coating layer, the slurry composition for forming the coating layer can be applied to the negative electrode current collector using a general coating method. This coating method is not particularly limited, and for example, a coating method using a slot die can be applied, or other methods such as Meyer bar coating, gravure coating, immersion coating, or spray coating can all be applied without particular limitation.

[0085] In addition, after forming the cathode slurry composition, the cathode slurry composition can be applied onto the coating layer using a general coating method. This coating method is not particularly limited, and for example, a coating method using a slot die can be applied, or other methods such as Meyer bar coating, gravure coating, immersion coating, or spray coating can all be applied without particular limitations.

[0086] After this coating process, a rolling process is performed on the cathode slurry composition using a rolling device such as roll pressing, for example.

[0087] After the above-described rolling process is performed, an additional step of drying the slurry composition to remove the solvent may be performed, and this drying process may be performed by a general method, for example, using infrared drying equipment.

[0088] The negative electrode for a lithium secondary battery manufactured by the above-described method can exhibit excellent adhesiveness and peeling resistance of the active material layer, and as a result, a lithium secondary battery including the negative electrode can exhibit greatly improved life characteristics.

[0089] Meanwhile, according to another embodiment of the invention, a lithium secondary battery comprising the anode for the lithium secondary battery described above is provided. Such a lithium secondary battery can be manufactured and provided by injecting a lithium salt-containing electrolyte into an electrode assembly comprising a cathode, the anode as described above, and a separator interposed therebetween.

[0090] The positive electrode can be manufactured by mixing a positive electrode active material, a conductive material, a binder, and a solvent to prepare a slurry composition, and then directly coating the slurry composition on a metal current collector, or by casting the slurry composition on a separate support and laminating a positive electrode active material film peeled from the support onto a metal current collector.

[0091] Active materials used in the anode include LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi. 1-x-y-z Co x M1 y M2 z O2 (M1 and M2 are independently any one selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are independently atomic fractions of oxide composition elements, 0≤x<0.5, 0≤y<0.5, 0≤z<0.5, 0 <x+y+z≤ 1임)로 이루어진 군으로부터 선택된 어느 하나의 활물질 입자 또는 이들 중 2종 이상의 혼합물을 포함할 수 있다.

[0092] Meanwhile, the conductive material, binder and solvent may be the same as those used in manufacturing the cathode.

[0093] The above separator may be a conventional porous polymer film used as a conventional separator, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, used alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0094] The above electrolyte may include a lithium salt and an organic solvent for dissolving the same.

[0095] The above lithium salt can be used without limitation as long as it is one commonly used in electrolytes for lithium secondary batteries, and for example, the anion of the above lithium salt is 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 - One type selected from the group consisting of can be used.

[0096] As the organic solvent included in the above electrolyte, any commonly used one can be used without limitation, and representative examples thereof include at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran.

[0097] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts in the electrolyte. When these cyclic carbonates are mixed with low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0098] Optionally, the electrolyte may further include additives such as overcharge inhibitors included in conventional electrolytes.

[0099] The above lithium secondary battery can be manufactured by forming an electrode assembly by placing a separator between the positive electrode and the negative electrode, placing the electrode assembly in, for example, a pouch, a cylindrical battery case, or a square battery case, and then injecting an electrolyte. Alternatively, the lithium secondary battery can be completed by stacking the electrode assembly, impregnating it with an electrolyte, and placing the resulting product in a battery case and sealing it.

[0100] The above lithium secondary battery may be of a stack type, a wound type, a stack and folding type, or a cable type.

[0101] The lithium secondary battery described above can be used not only as a battery cell used as a power source for small devices, but can also be preferably used as a unit battery in a medium- to large-sized battery module comprising a plurality of battery cells. Preferable examples of the medium- to large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, and in particular, it can be usefully used in areas requiring high output, such as hybrid electric vehicles and batteries for storing renewable energy.

[0102] Below, preferred embodiments are presented to aid understanding of the invention. However, the following examples are intended only to illustrate the invention and are not intended to limit the invention to these embodiments.

[0103] Example 1

[0104] (1) Cathode manufacturing

[0105] Multi-walled carbon nanotubes (Product name: BT1004M (LG Chemical), BET: 180 m) 2 / g, BD(Bulk Density): 130 kg / m 3 , average diameter: 13 nm) as the first conductive agent was dispersed in polyvinylpyrrolidone at 2.4 wt%, and then an aqueous binder SBR (M37, ADB22, first binder) was added in an amount 5 times the weight of the first conductive agent to prepare an aqueous slurry for forming a coating layer with a solid content of 17%.

[0106] A copper current collector (8 ㎛ thick, 260 mm wide) was used as a negative current collector, and the above-mentioned aqueous slurry composition was applied to one surface thereof at 15 mg / cm using a micro gravure coater. 2 The coating layer (thickness after coating: 1.1 ㎛) was formed on the negative electrode collector by applying the loading amount and drying at 100°C for 2 minutes.

[0107] A negative electrode slurry composition was prepared by adding carbon and silicon powders as negative active materials, carbon black as a second conductive agent, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders (second binders) in amounts of 95.5 wt%, 1 wt%, 2.5 wt%, and 1 wt%, respectively, to N-methyl-2 pyrrolidone (NMP) as a solvent.

[0108] On the negative electrode current collector on which the coating layer is formed, the negative electrode slurry composition is applied at 15 mg / cm on the coating layer. 2It was coated with a loading amount of (230 ㎛ thickness after coating).

[0109] In this way, for the slurry composition applied on the copper current collector, a rolling process was performed using a pressing device at 60°C, and then mid-infrared drying was performed at 100°C for 10 hours at an evaporation rate of 605 g / min, thereby manufacturing the negative electrode of Example 1 in which a negative electrode active material layer was formed on the coating layer.

[0110] (2) Anode manufacturing

[0111] A cathode slurry was prepared by adding 97.5 wt% of a lithium nickel cobalt manganese compound as a cathode active material, 1 wt% of carbon black as a conductive agent, and 1.5 wt% of PVDF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. The cathode slurry was applied to and dried on a 10 ㎛ thick aluminum (Al) thin film as a cathode current collector to prepare a cathode, and then roll pressing was performed to prepare a cathode.

[0112] (3) Battery manufacturing

[0113] An electrode assembly was manufactured by interposing a separator between the negative electrode and the positive electrode and stacking them using a stacking method. This was stamped into a coating shape, and an electrolyte (propylene carbonate (PC): ethyl methyl carbonate (EMC): ethylene carbonate (EC) = 3:4:3 (volume ratio), lithium hexafluorophosphate (LiPF6) 1 mol) was injected into the assembled battery to manufacture a lithium secondary battery.

[0114] Example 2

[0115] A negative electrode was manufactured in the same manner as in Example 1, except that when manufacturing an aqueous slurry for forming a negative electrode coating layer during the manufacture of the negative electrode, the aqueous binder SBR (M37, ADB22) was added in an amount 10 times the weight of the first conductive material, and a coating layer was formed on the negative electrode current collector so that the thickness after coating was 1.0 ㎛. A positive electrode and a battery were manufactured in the same manner as in Example 1.

[0116] Example 3

[0117] When manufacturing a cathode, a multi-walled carbon nanotube (product name: BT1004M (LG Chemical), BET: 180 m) is used as the first conductive material in the production of an aqueous slurry for forming a cathode coating layer. 2 / g, BD(Bulk Density): 130 kg / m 3 , average diameter: 6 nm) instead of using multi-walled carbon nanotubes (product name: BT2001M, BET: 380 m 2 / g, BD(Bulk Density): 75 kg / m 3 , average diameter: 6 nm) and Denka carbon black (solid content 20 wt%, Li-250, BET: 60 m 2 / g, DBP: 200 ml / 100g) were mixed in a weight ratio of 1:1 and used, and a coating layer was formed on the negative electrode current collector so that the thickness after coating was 1.0 ㎛, and a negative electrode was manufactured in the same manner as in Example 1, and a positive electrode and a battery were manufactured in the same manner as in Example 1.

[0118] Comparative Example 1

[0119] When manufacturing a cathode, a multi-walled carbon nanotube (product name: BT1004M (LG Chemical), BET: 180 m) is used as the first conductive material in the production of an aqueous slurry for forming a cathode coating layer. 2 / g, BD(Bulk Density): 130 kg / m 3 , average diameter: 6 nm) instead of using Denka carbon black (solid content 20 wt%, Li-250, BET: 60 m 2 / g, DBP: 200 ml / 100g) and forming a coating layer on the negative electrode current collector so that the thickness after coating was 1.0 ㎛, and a negative electrode was manufactured in the same manner as in Example 1, and a positive electrode and a battery were manufactured in the same manner as in Example 1.

[0120] Comparative Example 2

[0121] A negative electrode was manufactured in the same manner as in Example 1, except that when manufacturing an aqueous slurry for forming a negative electrode coating layer, an aqueous binder SBR (M37, ADB22, first binder) was added in an amount 1 times the weight of the first conductive material, and a coating layer was formed on the negative electrode current collector so that the thickness after coating was 1.0 ㎛. A positive electrode and a battery were manufactured in the same manner as in Example 1.

[0122] Comparative Example 3

[0123] A negative electrode was manufactured in the same manner as in Example 1, except that when manufacturing an aqueous slurry for forming a negative electrode coating layer, an aqueous binder SBR (M37, ADB22, first binder) was added in an amount 0.5 times the weight of the first conductive material, and a coating layer was formed on the negative electrode current collector so that the thickness after coating was 1.0 ㎛. A positive electrode and a battery were manufactured in the same manner as in Example 1.

[0124] Comparative Example 4

[0125] A negative electrode was manufactured in the same manner as in Example 1, except that a coating layer was formed on the negative electrode current collector so that the thickness after coating was 0.2 ㎛ during the manufacture of the negative electrode, and a positive electrode and a battery were manufactured in the same manner as in Example 1.

[0126] Comparative Example 5

[0127] A negative electrode was manufactured in the same manner as in Example 1, except that a coating layer was formed on the negative electrode current collector so that the thickness after coating was 32.0 μm during the manufacture of the negative electrode, and a positive electrode and a battery were manufactured in the same manner as in Example 1.

[0128] Comparative Example 6

[0129] A negative electrode was manufactured in the same manner as in Example 1, except that when manufacturing an aqueous slurry for forming a negative electrode coating layer, an aqueous binder SBR (M37, ADB22, first binder) was added in an amount three times the weight of the first conductive material, and a coating layer was formed on the negative electrode current collector so that the thickness after coating was 1.0 ㎛. A positive electrode and a battery were manufactured in the same manner as in Example 1.

[0130] Test Example 1: Adhesion

[0131] In the negative electrodes of the above-mentioned manufactured examples and comparative examples, the adhesive strength between the negative electrode active material layer and the coating layer was measured by the following method.

[0132] First, each negative electrode sample was cut to a predetermined size (50 mm x 50 mm) and fixed on a slide glass, and then the 180° adhesion between the negative electrode active material layer and the coating layer was measured. The adhesion was measured three times for each sample and the average value was calculated.

[0133] Test Example 2: Peel strength

[0134] In the above-mentioned manufactured examples and comparative examples, the peel strength was measured for the laminate of the negative electrode current collector on which the coating layer was formed.

[0135] The negative electrode current collector on which the coating layer was formed was punched to a predetermined size (60 mm x 60 mm), and the average peel strength was measured after horizontal cutting for 5 minutes.

[0136] Test Example 3: Interface Resistance

[0137] In the cathodes of the above-mentioned manufactured examples and comparative examples, the interface resistance was measured by the following method.

[0138] First, each cathode sample was punched to a predetermined size (50 mm x 50 mm) using a puncher. After inputting the thickness of the punched electrode, the thickness of the copper foil, and the resistivity of the current collector using an MP tester (HIOKI), the interface resistance was measured by placing the punched electrode high above the tip with the built-in probe and lowering the bar.

[0139] Test Example 4: Scratch Resistance

[0140] In the above-mentioned manufactured examples and comparative examples, the scratch resistance of the laminate of the negative electrode current collector on which the coating layer was formed was measured.

[0141] The negative electrode current collector having the coating layer formed was punched out to a predetermined size (60 mm x 60 mm), polyethylene terephthalate was attached to the other side of the negative electrode current collector, and the surface of the coating layer was rubbed back and forth three times at a speed of 27 with a ball of a rubbing tester, and the area of ​​the negative electrode current collector exposed at this time was measured.

[0142] The results are shown in Table 1 below.

[0143]

[0144] Referring to Table 1 above, it was confirmed that in the case of the example, excellent scratch resistance and high adhesive strength could be achieved, and the interface resistance was also very small.

[0145] On the other hand, in Comparative Examples 1 to 3 and 6, which do not use multi-walled carbon nanotubes or use multi-walled carbon nanotubes but are outside the content range of the examples of the present invention, it was confirmed that the adhesive strength was poor, the scratch resistance was poor, or the interface resistance was large compared to the examples.

[0146] In addition, in Comparative Examples 4 and 5, where multi-walled carbon nanotubes were used in the same content as in the examples of the present invention, but the ratio of the thickness of the coating layer to the thickness of the negative electrode active material layer was outside the range of the examples of the present invention, it was confirmed that the adhesive strength was very low or the interface resistance was very large.

[0147] That is, the negative electrode for a lithium secondary battery of the present invention has improved peeling resistance and adhesiveness, so that the life characteristics of the negative electrode and the lithium secondary battery are excellent, and a lithium secondary battery using the negative electrode can maintain excellent charge / discharge cycle characteristics for a long period of time.

Claims

1. Metal current collector; A coating layer formed on at least one surface of the above metal collector and including a first binder and a first conductive material; and A negative electrode active material layer formed on the above coating layer and including a negative electrode active material, a second conductive material, and a second binder; The first challenge material comprises a multi-walled carbon nanotube, The coating layer contains the first binder in an amount of 400 parts by weight or more and 2000 parts by weight or less based on 100 parts by weight of the multi-walled carbon nanotubes, A negative electrode for a lithium secondary battery, wherein the ratio of the thickness of the coating layer to the thickness of the negative active material layer is 0.005 or more and 0.2 or less.

2. In paragraph 1, The above multi-walled carbon nanotubes have a surface area of ​​100 m 2 / g over 400 m 2 / g or less, negative electrode for lithium secondary batteries.

3. In paragraph 1, The above multi-walled carbon nanotubes have a diameter of 1 nm or more and 40 nm or less, A negative electrode for a lithium secondary battery, having a length of 10 ㎛ or more and 30 ㎛ or less.

4. In paragraph 1, The above multi-walled carbon nanotubes have a bulk density of 20 kg / m 3 More than 200 kg / m 3 Below, a negative electrode for a lithium secondary battery.

5. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the negative electrode active material comprises at least one graphite-based active material selected from the group consisting of natural graphite, artificial graphite, fibrous artificial graphite, graphitized black, and graphitized nanofibers.

6. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the second challenge material comprises at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black.

7. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first binder and the second binder each independently include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, and styrene butadiene rubber (SBR).

8. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the coating layer contains the multi-walled carbon nanotubes in an amount of 40 wt% to 100 wt% based on the total weight of the first conductive material.

9. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the coating layer has a thickness of 0.1 ㎛ or more and 5.0 ㎛ or less.

10. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the negative active material layer has a thickness of 100 ㎛ or more and 200 ㎛ or less.

11. In paragraph 1, The above metal current collector is an anode for a lithium secondary battery, comprising at least one metal selected from the group consisting of copper, stainless steel, aluminum, nickel, and titanium.

12. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the negative active material layer is attached to the coating layer with an adhesive strength of 30 gf / 20mm or more and 50 gf / 20mm or less.

13. A step of applying a slurry composition for forming a coating layer, which includes a first binder, a first conductive agent, and a solvent, onto a metal current collector and drying it to form a coating layer; A step of applying a negative electrode slurry composition including a negative electrode active material, a second binder, a second conductive agent, and a solvent onto the coating layer; and A step of rolling the above cathode slurry composition; The first challenge material comprises a multi-walled carbon nanotube, A method for manufacturing an anode for a lithium secondary battery, wherein the slurry composition for forming the coating layer contains 400 parts by weight or more and 2000 parts by weight or less of the first binder with respect to 100 parts by weight of the multi-walled carbon nanotubes.

14. In paragraph 13, A step of rolling the above cathode slurry composition; After that, A method for manufacturing a negative electrode for a lithium secondary battery, further comprising the step of drying the negative electrode slurry composition to remove the solvent.

15. Cathode for lithium secondary battery; A negative electrode for a lithium secondary battery according to claim 1; and A lithium secondary battery comprising a separator interposed between the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery.

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