Negative electrode for lithium secondary battery, manufacturing method thereof, and lithium secondary battery

Abstract

A negative electrode for a lithium secondary battery according to an embodiment of the present disclosure comprises: a negative electrode current collector; and a negative electrode mixture layer on at least one surface of the negative electrode current collector, the negative electrode mixture layer containing a carbon-based active material, a silicon-based active material, a first binder, and a second binder, wherein each of the first binder and the second binder is a copolymer containing an acrylic acid-derived structural unit represented by chemical formula 1, the content ratio of the acrylic acid-derived structural unit in the first binder is 0 mol% (excusive) to 50 mol% (inclusive) and the content ratio of the acrylic acid-derived structural unit in the second binder is 60 mol% (inclusive) to 100 mol% (exclusive). [Chemical formula 1]

Description

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

[0001] The present disclosure relates to a negative electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery.

[0002] Recently, research on electric vehicles (EVs) that can replace fossil fuel-based vehicles, one of the main causes of air pollution, is actively being conducted, and lithium secondary batteries with high discharge voltage and output stability are mainly used as the power source for these EVs.

[0003] In order to improve the performance of these lithium secondary batteries, it is necessary to develop a technology that can suppress electrode expansion and maintain excellent battery life performance even with repeated use.

[0004] According to one aspect of the present disclosure, volume expansion of a silicon-based active material included in a negative electrode can be suppressed.

[0005] According to another aspect of the present disclosure, a cathode having a reduced degree of swelling even when used repeatedly can be provided.

[0006] According to another aspect of the present disclosure, the adhesion between the electrode current collector and the electrode composite layer can be improved.

[0007] According to another aspect of the present disclosure, the resistance characteristics of the electrode can be improved.

[0008] According to one embodiment of the present disclosure, a negative electrode for a lithium secondary battery comprises: a negative electrode current collector; and a negative electrode mixture layer on at least one surface of the negative electrode current collector, wherein the negative electrode mixture layer comprises a carbon-based active material, a silicon-based active material, a first binder, and a second binder, wherein the first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder is greater than 60 mol% and less than 100 mol%.

[0009] [Chemical Formula 1]

[0010]

[0011] In some embodiments, the copolymer may further include at least one of a vinyl alcohol-derived structural unit represented by the following chemical formula 2 and an acrylamide-derived structural unit represented by the following chemical formula 3.

[0012] [Chemical Formula 2]

[0013]

[0014] [Chemical Formula 3]

[0015]

[0016] In some implementations, the weight ratio of the first binder and the second binder in the negative electrode composite layer may be 3:7 to 7:3.

[0017] In some implementations, the content of the first binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0018] In some implementations, the content of the second binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0019] In some embodiments, the negative electrode composite layer may further include a conductive material, and the content of the conductive material in the negative electrode composite layer may be 0.1 to 5 wt%.

[0020] In some embodiments, the negative electrode composite layer may further include a rubber-based binder, and the content of the rubber-based binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0021] A method for manufacturing an anode for a lithium secondary battery according to one embodiment of the present disclosure includes the steps of: preparing a first anode slurry by mixing a carbon-based active material, a silicon-based active material, and a first binder; preparing a second anode slurry by adding a second binder to the first anode slurry; and forming a anode mixture layer on at least one surface of a cathode current collector with the second anode slurry, wherein the first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder is greater than 60 mol% and less than 100 mol%.

[0022] [Chemical Formula 1]

[0023]

[0024] In some embodiments, the first cathode slurry may further include a conductive material.

[0025] In some embodiments, the method for manufacturing the negative electrode for a lithium secondary battery may further include a step of adding a rubber-based binder to the second negative electrode slurry before forming the negative electrode mixture layer.

[0026] A lithium secondary battery according to one embodiment of the present disclosure includes a negative electrode for a lithium secondary battery according to any one of the above-described embodiments.

[0027] According to one embodiment of the present disclosure, volume expansion of a silicon-based active material in a negative electrode due to battery charging / discharging can be suppressed.

[0028] According to another embodiment of the present disclosure, the mechanical properties of the negative electrode can be strengthened to alleviate physical damage to the negative electrode due to battery use.

[0029] According to another embodiment of the present disclosure, the adhesion between the electrode current collector and the electrode composite layer can be improved.

[0030] According to another embodiment of the present disclosure, the content of binder included in the electrode mixture layer can be reduced.

[0031] Hereinafter, the technology disclosed in this specification and its implementation examples will be described in detail. However, the embodiments of the technology may be modified in various other forms, and the scope is not limited to the implementation examples described below. Furthermore, the technology disclosed in this specification may be applied not only by being limited to the configurations of the implementation examples described below, but also by selectively combining all or some of the implementation examples to enable various modifications.

[0032] To realize high-energy-density secondary batteries, research is being conducted on the application of silicon-based active materials, which have a relatively high discharge capacity compared to carbon-based active materials such as graphite, as anodes. However, silicon-based active materials exhibit a relatively high volume expansion rate compared to carbon-based active materials, and anodes and cells containing silicon-based active materials can experience swelling during battery charge / discharge. This presents challenges in module design and mass production of secondary batteries using silicon-based active materials.

[0033] Meanwhile, a method exists to increase the binder content within the negative electrode to suppress cell volume expansion while increasing the content of silicon-based active material. However, this method can cause a decrease in the cell's energy density and increase in resistance.

[0034] According to one embodiment of the present disclosure, a negative electrode comprises a first binder and a second binder copolymerized with polymers having structural units with different stiffness and softness, each having a different composition, thereby suppressing volume expansion of a silicon-based active material included in the negative electrode. Hereinafter, embodiments of the present disclosure will be described in detail.

[0035] Cathode for lithium secondary batteries

[0036] According to one embodiment, a negative electrode for a lithium secondary battery includes: a negative electrode current collector; and a negative electrode mixture layer on at least one surface of the negative electrode current collector, wherein the negative electrode mixture layer includes a carbon-based active material, a silicon-based active material, a first binder, and a second binder. The first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder is greater than 60 mol% and less than 100 mol%.

[0037] [Chemical Formula 1]

[0038]

[0039] The components of the negative electrode current collector are not particularly limited. For example, the electrode current collector may be a plate or foil made of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and alloys thereof. The thickness of the negative electrode current collector is not particularly limited. For example, the thickness of the negative electrode current collector may be 0.1 to 50 μm.

[0040] The above carbon-based active material is not particularly limited. For example, the carbon-based active material may be a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, or carbon fiber. The crystalline carbon may be, for example, graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, mesocarbon microbeads (MCMB), or mesophase pitch-based carbon fiber (MPCF). The amorphous carbon may be, for example, hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), or mesophase pitch-based carbon fiber (MPCF).

[0041] The content of the carbon-based active material in the negative electrode composite layer is not particularly limited. For example, the content of the carbon-based active material in the negative electrode composite layer may be 70 to 90 wt%.

[0042] The above silicon-based active material is not particularly limited as long as it contains silicon, and may be an active material capable of alloying with lithium (Li). For example, the silicon-based active material may be silicon (Si), silicon oxide (SiOx; 0 <x<2), 금속 도핑된 실리콘 산화물(SiOx; 0<x<2), 탄소 코팅된 실리콘 산화물(SiOx; 0<x<2), 실리콘-탄소 복합체(Si-C) 및 실리콘 합금으로 이루어진 군으로부터 선택된 1종 이상일 수 있다.

[0043] The content of the silicon-based active material in the above-described negative electrode composite layer is not particularly limited. For example, the content of the silicon-based active material in the above-described negative electrode composite layer may be 1 to 20 wt%.

[0044] The first binder can directly mitigate the physical expansion / contraction of the active material due to battery charging / discharging, and can be present on the surface of the negative electrode active material. In some embodiments, the first binder can be added together with the active material during the preparation of the negative electrode slurry and mixed through a kneading process. In this case, the first binder can contribute to the formation of chemical bonds, such as hydrogen bonds, as well as physical bonds between the negative electrode active material and the binder.

[0045] The above second binder is a so-called 'free binder' that can fill the space between active materials within the electrode. The second binder can strengthen the mechanical properties of the electrode and alleviate physical damage such as electrode cracks that occur in the negative electrode due to volume expansion / contraction of the active material.

[0046] The above-described negative electrode for a lithium secondary battery can effectively alleviate swelling of the negative electrode and cell due to the silicon-based active material included in the negative electrode, including the first binder and the second binder having the above-described characteristics, and improve the life characteristics of the battery.

[0047] The first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the chemical formula 1, wherein the content ratio of the acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder is greater than 60 mol% and less than 100 mol%.

[0048] The content ratio of the above acrylic acid-derived structural unit in the first binder may be 10 mol% or more, 20 mol% or more, or 30 mol% or more, and may be 40 mol% or less.

[0049] The content ratio of the above acrylic acid-derived structural unit in the second binder may be 70 mol% or more or 80 mol% or more, and may be less than 90 mol%.

[0050] In some embodiments, the copolymer may further include at least one of a vinyl alcohol-derived structural unit represented by the following chemical formula 2 and an acrylamide-derived structural unit represented by the following chemical formula 3.

[0051] [Chemical Formula 2]

[0052]

[0053] [Chemical Formula 3]

[0054]

[0055] When the above copolymer further includes a structural unit of the type described above together with an acrylic acid-derived structural unit, the volume expansion of the silicon-based active material in the negative electrode can be further alleviated.

[0056] The above copolymer may be poly(acrylamide-co-acrylic acid) represented by the following chemical formula 4 or poly(vinyl alcohol-co-acrylic acid) represented by the following chemical formula 5.

[0057] [Chemical Formula 4]

[0058]

[0059] When the first binder is poly(acrylamide-co-acrylic acid) represented by the chemical formula 4, the values ​​of m and n in the chemical formula 4 may be values ​​that satisfy a content ratio of acrylic acid-derived structural units of more than 0 mol% and less than or equal to 5 mol%.

[0060] When the second binder is poly(acrylamide-co-acrylic acid) represented by the chemical formula 4, the values ​​of m and n in the chemical formula 4 may be values ​​that satisfy a content ratio of acrylic acid-derived structural units of 60 mol% or more and less than 100 mol%.

[0061] [Chemical Formula 5]

[0062]

[0063] When the first binder is poly(vinyl alcohol-co-acrylic acid) represented by the chemical formula 5, the values ​​of m and n in the chemical formula 5 may be values ​​that satisfy a content ratio of acrylic acid-derived structural units of more than 0 mol% and less than or equal to 5 mol%.

[0064] When the second binder is poly(vinyl alcohol-co-acrylic acid) represented by the chemical formula 5, the values ​​of m and n in the chemical formula 5 may be values ​​that satisfy a content ratio of acrylic acid-derived structural units of 60 mol% or more and less than 100 mol%.

[0065] In some embodiments, the weight ratio of the first binder and the second binder in the negative electrode mixture layer may be 3:7 to 7:3. For example, the weight ratio of the first binder and the second binder in the negative electrode mixture layer may be 4:6 to 6:4. When the weight ratio of the first binder and the second binder is within the above-described range, the addition of either the first binder or the second binder in an excessive amount can be prevented, thereby alleviating the relative deterioration of the properties of each of the first binder and the second binder.

[0066] In some embodiments, the content of the first binder in the negative electrode mixture layer may be 0.1 to 5 wt%. For example, the content of the first binder in the negative electrode mixture layer may be 0.5 wt% or more or 0.7 wt% or more, and 3 wt% or less or 1.3 wt% or less.

[0067] In some embodiments, the content of the second binder in the negative electrode composite layer may be 0.1 to 5 wt%. For example, the content of the second binder in the negative electrode composite layer may be 0.5 wt% or more or 0.7 wt% or more, and 3 wt% or less or 1.3 wt% or less.

[0068] When the contents of the first binder and the second binder are within the above-described range, the binder contents can be adjusted relatively low to prevent the energy density of the negative electrode from decreasing or the resistance from increasing.

[0069] In some embodiments, the negative electrode for a lithium secondary battery may further include a conductive material, and the content of the conductive material in the negative electrode mixture layer may be 0.1 to 5 wt%. For example, the content of the conductive material in the negative electrode mixture layer may be 0.3 wt% or more and 1 wt% or less.

[0070] The type of the above-mentioned conductive material is not particularly limited. For example, the conductive material may be at least one selected from a particulate carbon material and a fibrous carbon material. The particulate carbon material may be carbon black such as Super-P or Super-C, acetylene black, or Ketjen black. The fibrous carbon material may be carbon fiber, carbon nanotube (CNT), or vapor-grown carbon fiber (VGCF).

[0071] In some embodiments, the negative electrode for a lithium secondary battery may further include a rubber-based binder, and the content of the rubber-based binder in the negative electrode mixture layer may be 0.1 to 5 wt%. For example, the content of the rubber-based binder in the negative electrode mixture layer may be 0.5 wt% or more and 1.2 wt% or less.

[0072] The type of the above rubber-based binder is not particularly limited. For example, the above rubber-based binder may be at least one selected from styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butadiene rubber, isoprene rubber, and silane-based rubber.

[0073] In some embodiments, the negative electrode for a lithium secondary battery may have an electrode adhesion of 0.35 N / mm or more. For example, the negative electrode for a lithium secondary battery may have an electrode adhesion of 0.36 N / mm or more, 0.40 N / mm or more, 0.41 N / mm or more, or 0.42 N / mm or more, and may be 5 N / mm or less, 1 N / mm or less, or 0.7 N / mm or less.

[0074] The above negative electrode for a lithium secondary battery can be manufactured by a manufacturing method according to any one of the embodiments described below.

[0075] Method for manufacturing a negative electrode for a lithium secondary battery

[0076] According to one embodiment, a method for manufacturing an anode for a lithium secondary battery includes the steps of: preparing a first anode slurry by mixing a carbon-based active material, a silicon-based active material, and a first binder; preparing a second anode slurry by adding a second binder to the first anode slurry; and forming a anode mixture layer on at least one surface of a cathode current collector with the second anode slurry. The first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder is greater than 60 mol% and less than 100 mol%.

[0077] The above method for manufacturing a negative electrode for a lithium secondary battery can improve the life characteristics of the battery by applying different injection times of the first binder and the second binder when manufacturing a negative electrode slurry through mixing, thereby alleviating the degree of swelling of the final manufactured negative electrode and cell according to battery charge / discharge.

[0078] The step of preparing the first negative electrode slurry is a step of mixing the negative electrode active material and the first binder, and the mixing of the carbon-based active material, the silicon-based active material, and the first binder may be performed by a kneading process. In some embodiments, the first binder may be kneaded together with the negative electrode active material and may be present on the surface of the negative electrode active material. In this case, the first binder may contribute to forming a physical bond between the negative electrode active material and the binder as well as a chemical bond such as a hydrogen bond. A detailed description of the first binder is omitted because it overlaps with the above-described content.

[0079] In some embodiments, the first cathode slurry may further include a conductive agent. In this case, the first cathode slurry may be prepared by mixing a carbon-based active material, a silicon-based active material, a first binder, and a conductive agent. A detailed description of the conductive agent is omitted as it overlaps with the above-described content.

[0080] The first cathode slurry may further include a solvent. The solvent is not particularly limited. For example, the solvent may be water. The amount of solvent added may be appropriately adjusted considering the target solids content, viscosity value, etc. of the slurry.

[0081] The step of preparing the second negative electrode slurry is a step of adding a second binder to the first negative electrode slurry. The second binder is added after the first binder to fill the space between the active materials in the negative electrode and enhance the mechanical properties of the negative electrode. A detailed description of the second binder overlaps with the above-described content and is therefore omitted.

[0082] In some embodiments, the second binder may be added to the first cathode slurry together with a solvent. The solvent may be a separate solvent from the solvent that may be added during the preparation of the first cathode slurry, and may be additionally added for mixing the first cathode slurry and the second binder. The solvent is not particularly limited. For example, the solvent may be water. The amount of the solvent added may be appropriately adjusted in consideration of the target solids content, viscosity value, etc. of the slurry.

[0083] In some embodiments, the method for manufacturing the negative electrode for a lithium secondary battery may further include a step of adding a rubber-based binder to the second negative electrode slurry before forming the negative electrode mixture layer. In this case, the rubber-based binder may be added to the second negative electrode slurry together with a solvent. The solvent may be a separate solvent from the solvent that may be added during the preparation of the first negative electrode slurry or during the addition of the second binder, and may be additionally added for mixing the second negative electrode slurry and the rubber-based binder. The solvent is not particularly limited. For example, the solvent may be water. The amount of the solvent added may be appropriately adjusted in consideration of the target solid content, viscosity value, etc. of the slurry. A detailed description of the rubber-based binder is omitted because it overlaps with the above-described content.

[0084] The method for forming a negative electrode mixture layer on at least one surface of a negative electrode current collector using the final manufactured negative electrode slurry is not particularly limited. For example, the negative electrode mixture layer may be formed by applying the slurry to at least one surface of the negative electrode current collector by a method such as bar coating, casting, or spraying, and drying the applied slurry at 80 to 120°C.

[0085] lithium secondary battery

[0086] According to one embodiment, a lithium secondary battery includes an anode for a lithium secondary battery according to any one of the embodiments described above. In some embodiments, the lithium secondary battery may include a unit cell comprising the anode for a lithium secondary battery described above, a cathode, and a separator. The separator may be disposed between the anode and the cathode described above within the unit cell.

[0087] The positive electrode may include a positive electrode current collector; and a positive electrode composite layer on at least one surface of the positive electrode current collector.

[0088] The components of the positive electrode current collector are not particularly limited. For example, the electrode current collector may be a plate or foil made of one or more of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and alloys thereof. The thickness of the positive electrode current collector is not particularly limited. For example, the thickness of the electrode current collector may be 0.1 to 50 μm.

[0089] The positive electrode active material layer may include a positive electrode active material. The positive electrode active material is not particularly limited and may include a compound capable of reversibly intercalating and deintercalating lithium ions. For example, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0090] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1.

[0091] [Chemical Formula 1]

[0092] Li x Ni a Mb O 2+z

[0093] In the above chemical formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0094] The chemical structure represented by the above chemical formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. The above chemical formula 1 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0095] In some embodiments, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. The auxiliary elements may be incorporated into the layered / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0096] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may also function as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, such as Al.

[0097] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1-1.

[0098] [Chemical Formula 1-1]

[0099] Li x Ni a M1 b1 M2 b2 O 2+z

[0100] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1 may be satisfied.

[0101] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0102] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0103] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0104] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0105] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0106] In some embodiments, the positive electrode active material may include a Mn-rich active material, a Li-rich layered oxide (LLO) / over lithiated oxide (OLO) active material, or a Co-less active material having a chemical structure or crystal structure represented by chemical formula 2.

[0107] [Chemical Formula 2]

[0108] p[Li2MnO3]·(1-p)[Li q JO2]

[0109] In chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0110] The above-mentioned positive electrode composite layer may further include a binder. The binder is not particularly limited. For example, the binder may include one or two or more kinds of polyvinylidene fluoride, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0111] The above-described positive electrode composite layer may further include a conductive material. The conductive material is not particularly limited. For example, the conductive material may include one or more types of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotubes (CNT); metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0112] The above separator is not particularly limited. For example, the separator may include a porous polymer film manufactured from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. In addition, the separator may include a nonwoven fabric formed from high-melting-point glass fibers, polyethylene terephthalate fibers, or the like.

[0113] In some embodiments, the lithium secondary battery can be manufactured by housing the above-described unit cell in a pouch, which is a battery case, and then injecting an electrolyte.

[0114] The above electrolyte may include an organic solvent and a lithium salt. The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move, and examples thereof include carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents, which may be used singly or in combination of two or more. When two or more types are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance.

[0115] The above lithium salt is dissolved in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Any known material can be used as the lithium salt at a concentration appropriate for the purpose. The electrolyte may further include a known solvent and known additives, as needed, to improve charge / discharge characteristics, flame retardancy, and the like.

[0116] In some embodiments, the unit cell may not include a separator between the positive and negative electrodes and may include a solid electrolyte. The solid electrolyte is not particularly limited, and may be, for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte.

[0117] Example

[0118] 1. Cathode and secondary battery manufacturing

[0119] 1) Cathode manufacturing

[0120] Carbon-based active material (artificial graphite), silicon-based active material (SiOx; 0 <x<2), 제1바인더, 도전재 및 용매를 니딩(Kneading) 처리로 혼합하여 제1음극 슬러리를 제조하였다. 이후, 제2바인더 및 용매를 첨가 후 혼합하여 제2음극 슬러리를 제조하고, 상기 제2음극 슬러리에 고무계 바인더 및 용매를 첨가 후 혼합하여 최종 음극 슬러리를 제조하였다. 이 때, 상기 도전재로 탄소나노튜브(CNT)를 사용하고, 용매로 물을 사용하고, 고무계 바인더로 스티렌-부타디엔 고무(SBR)를 사용하였다.

[0121] In addition, binders A to H containing acrylic acid-derived structural units, vinyl alcohol-derived structural units, acrylamide-derived structural units, carboxymethyl cellulose (CMC), or a combination thereof were used as the first binder or the second binder (see Table 2 below). The types of binders used as the first binder and the second binder in the examples and comparative examples are as shown in Table 3 below.

[0122] Afterwards, the final cathode slurry was deposited on the copper foil (Cu-foil), which is the cathode current collector, at a density of 8.6 mg / cm. 2 After applying with a loading weight (LW), the mixture was dried at 100℃ for 24 hours to form a negative electrode mixture layer on one side of the negative electrode current collector. The negative electrode with the negative electrode mixture layer formed on both sides of the negative electrode current collector as described above was rolled to have a thickness of 60 μm and a density of 1.70 g / cc to manufacture the final negative electrode. The specific composition of the final negative electrode mixture layer is as shown in Table 1 below.

[0123] Negative electrode composite layer composition (wt%) Negative electrode active material (artificial graphite) 86.8 SiO x 10.0 First binder 1.0 Second binder 1.0 Rubber binder (SBR) 0.7 Conductive material (CNT) 0.5

[0124] Structural unit ratio (mol%)Acrylic acid vinyl alcoholacrylamidecarboxymethylcellulose(CMC)Binder A3070--Binder B30-70-Binder C4060--Binder D5050--Binder E6040--Binder F8020--Binder G100---Binder H---100

[0125] 2) Secondary battery manufacturing

[0126] NCM-based active material (Li[Ni)), a lithium-transition metal composite oxide, on aluminum foil (Al-foil) 0.8 Co 0.1 Mn 0.1 ]O2) was applied and dried to manufacture a cathode. A secondary battery cell manufactured by interposing a polyolefin separator between the cathode and anode manufactured as described above was placed in a lithium secondary battery pouch, and then an electrolyte solution in which 1 M LiPF6 was dissolved in a solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) was injected into the lithium secondary battery pouch, followed by sealing to manufacture a pouch-type lithium secondary battery. The manufactured pouch-type lithium secondary battery was applied as a secondary battery sample of the examples and comparative examples.

[0127] 2. Evaluation of cathode and secondary batteries

[0128] 1) Electrode adhesion

[0129] The electrode adhesion of the negative electrode manufactured as described above was measured using the SAICAS (Surface and Interfacial Cutting Analysis System) equipment. Specifically, the electrode adhesion was measured in constant speed mode by cutting to 25 μm, which is the center thickness of the negative electrode mixture layer, using the SAICAS equipment. At this time, the electrode cutting speed in constant speed mode was set to 0.5 μm / sec in the vertical direction and 5.0 μm / sec in the horizontal direction, the cutting time was measured to be 220 sec or more, and an average value of 200 μm or more was used from the stabilization point. The final results of measuring the electrode adhesion as the horizontal force (Fh) in N / mm are shown in Table 3 below.

[0130] 2) Resistance characteristics

[0131] The secondary battery sample was discharged to SOC 50 compared to the initial discharge capacity of the secondary battery sample at 25℃, and after a rest period of 1 hour, the secondary battery sample was discharged for 10 seconds at a 1C current, and the resistance value was measured according to Equation 1 below. The results are shown in Table 3 below.

[0132] [Formula 1]

[0133] R = (V0- V1) / I

[0134] In the above equation 1, R is the resistance value of the secondary battery, V0 is the voltage of the secondary battery measured after a rest period of 1 hour after adjusting the SOC to 50 at 25°C, V1 is the voltage of the secondary battery measured after discharging for 10 seconds with a 1C current, and I is the 1C current value.

[0135] 3) Swelling evaluation

[0136] (1) Evaluation after full charge (SOC 100)

[0137] After charging the secondary battery sample to SOC 100 at 25°C, the swelling degree of the negative electrode was evaluated according to Equation 2 below, and the results are shown in Table 3 below.

[0138] [Formula 2]

[0139] S1= 100 X (D2 - D1) / D1

[0140] In the above equation 2, S1 is the swelling ratio (%) of the negative electrode after one full charge, D1 is the rolling thickness during the manufacture of the negative electrode, and D2 is the thickness of the negative electrode after the secondary battery sample is fully charged once.

[0141] (2) Evaluation after 500 cycles

[0142] The process of charging the secondary battery sample to SOC 100 at 25°C and discharging to SOC 0 was repeated 500 times, and the swelling degree of the negative electrode was evaluated according to Equation 3 below. The results are shown in Table 3 below.

[0143] [Formula 3]

[0144] S2 = 100 X (D3 - D2) / D2

[0145] In the above equation 3, S2 is the swelling ratio (%) of the negative electrode after 500 full charges, D2 is the thickness of the negative electrode after the secondary battery sample is fully charged once, and D3 is the thickness of the negative electrode after the secondary battery sample is fully charged 500 times.

[0146] 4) Life evaluation

[0147] The secondary battery samples were evaluated for life characteristics in the range of DOD94 (SOC 4-98) at 25℃. The batteries were charged at 0.3C under constant current / constant voltage (CC / CV) conditions to a voltage corresponding to SOC 98, then cut off at 0.05C. After that, the batteries were discharged at 0.3C under constant current (CC) conditions to a voltage corresponding to SOC 4, and the discharge capacity was measured. This was repeated for 500 cycles, and the discharge capacity retention rate was measured as a % compared to the initial discharge capacity, and the capacity retention rate during the room temperature life characteristic evaluation was measured, and the results are shown in Table 3 below.

[0148] Input Binder Electrode Adhesion Resistance Swelling (%) Lifespan Binder 1 Binder 2 SAICAS (N / mm) DC-IR (mOhm) Electrode Fully charged (SOC 100) Cycle (500 cyc) 500 cycle retention (%) Comparative Example 1 Binder A Binder H 0.368 1.120 37.02 2.58 1.4 Comparative Example 2 Binder A Binder A 0.386 1.150 35.019 28 4.9 Comparative Example 3 Binder A Binder D 0.40 11.127 34.816 88 6.6 Comparative Example 4 Binder E Binder E 0.418 1.090 31.817 48 6.2 Comparative Example 5 Binder G Binder E0.4301.07730.220.183.3 Example 1 Binder A Binder E0.4061.04034.215.489.1 Example 2 Binder Binder E0.3620.98936.016.486.7 Example 3 Binder A Binder F0.4221.03233.615.290.8 Example 4 Binder C Binder E0.4111.12732.515.188.2 Example 5 Binder D Binder E0.4151.09832.215.487.8

[0149] Referring to Tables 1 to 3 above, Comparative Example 1, which used Binder H containing 100 mol% of carboxymethyl cellulose (CMC) as the second binder, was found to be unsuitable due to relatively low electrode adhesion, relatively high battery resistance and negative electrode swelling, and poor life performance. In addition, Comparative Examples 2 and 4, which used only one type of binder, were found to be unsuitable due to relatively high negative electrode swelling after 500 cycles and poor life performance. Meanwhile, Comparative Example 3, which used Binder D having a polyacrylic acid (PAA) structural unit content ratio of less than 60 mol% (50 mol%) as the second binder, was found to be unsuitable due to high battery resistance and negative electrode swelling. In addition, in the case of Comparative Example 5, which used binder G with a content ratio of polyacrylic acid (PAA) structural units exceeding 50 mol% (100 mol%) as the first binder, the life performance was found to be very poor and thus unsuitable.

[0150] On the other hand, Examples 1 to 5, which include binders A, B, C, or D having a content ratio of polyacrylic acid (PAA) structural units of more than 0 mol% and less than 50 mol% as a first binder and binders E or F having a content ratio of polyacrylic acid (PAA) structural units of more than 60 mol% and less than 100 mol% as a second binder, showed relatively high electrode adhesion of the negative electrode, low volume expansion rate, and excellent low resistance characteristics and life characteristics of the battery overall.

[0151] While the embodiments of the present disclosure have been described in detail above, they are merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Therefore, the true scope of technical protection of the present disclosure should be determined by the technical spirit of the appended claims.

[0152] The present disclosure may also relate to the following aspects:

[0153] Aspect 1) A negative electrode for a lithium secondary battery comprises: a negative electrode current collector; and a negative electrode mixture layer on at least one surface of the negative electrode current collector, wherein the negative electrode mixture layer comprises a carbon-based active material, a silicon-based active material, a first binder, and a second binder, wherein the first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder may be greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder may be greater than 60 mol% and less than 100 mol%.

[0154] [Chemical Formula 1]

[0155]

[0156] Aspect 2) In aspect 1, the copolymer may further include at least one of a vinyl alcohol-derived structural unit represented by the following chemical formula 2 and an acrylamide-derived structural unit represented by the following chemical formula 3.

[0157] [Chemical Formula 2]

[0158]

[0159] [Chemical Formula 3]

[0160]

[0161] Side 3) In side 1 or 2, the weight ratio of the first binder and the second binder in the negative electrode composite layer may be 3:7 to 7:3.

[0162] Side 4) In any one of Sides 1 to 3, the content of the first binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0163] Side 5) In any one of Sides 1 to 4, the content of the second binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0164] Side 6) In any one of Sides 1 to 5, the negative electrode mixture layer may further include a conductive material, and the content of the conductive material in the negative electrode mixture layer may be 0.1 to 5 wt%.

[0165] Side 7) In any one of Sides 1 to 6, the negative electrode composite layer may further include a rubber-based binder, and the content of the rubber-based binder in the negative electrode composite layer may be 0.1 to 5 wt%.

[0166] Aspect 8) A method for manufacturing an anode for a lithium secondary battery comprises the steps of: preparing a first anode slurry by mixing a carbon-based active material, a silicon-based active material, and a first binder; preparing a second anode slurry by adding a second binder to the first anode slurry; and forming a anode mixture layer on at least one surface of a cathode current collector with the second anode slurry, wherein the first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, and the content ratio of the acrylic acid-derived structural unit in the first binder may be greater than 0 mol% and less than 50 mol%, and the content ratio of the acrylic acid-derived structural unit in the second binder may be greater than 60 mol% and less than 100 mol%.

[0167] [Chemical Formula 1]

[0168]

[0169] Side 9) In side 8, the first cathode slurry may further include a conductive material.

[0170] Aspect 10) In aspect 8 or 9, the method for manufacturing the negative electrode for a lithium secondary battery may further include a step of adding a rubber-based binder to the second negative electrode slurry before forming the negative electrode mixture layer.

[0171] Aspect 11) A lithium secondary battery may include a negative electrode for a lithium secondary battery according to any one of aspects 1 to 7.

[0172] As described above, the features of the present invention can be applied in whole or in part to a negative electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery.

Claims

1. As a negative electrode for lithium secondary batteries, The above negative electrode for a lithium secondary battery comprises a negative electrode current collector; and a negative electrode composite layer on at least one surface of the negative electrode current collector, The above negative electrode composite layer includes a carbon-based active material, a silicon-based active material, a first binder, and a second binder, The first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, The content ratio of the above acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than or equal to 50 mol%, The content ratio of the above acrylic acid-derived structural unit in the second binder is 60 mol% or more and less than 100 mol%, Cathode for lithium secondary batteries. [Chemical Formula 1] 2. In paragraph 1, The above copolymer further comprises at least one of a vinyl alcohol derived structural unit represented by the following chemical formula 2 and an acrylamide derived structural unit represented by the following chemical formula 3. Cathode for lithium secondary batteries. [Chemical formula 2] [Chemical Formula 3] 3. In paragraph 1, The weight ratio of the first binder and the second binder in the above negative electrode composite layer is 3:7 to 7:

3. Cathode for lithium secondary batteries.

4. In paragraph 1, The content of the first binder in the above negative electrode composite layer is 0.1 to 5 wt%, Cathode for lithium secondary batteries.

5. In paragraph 1, The content of the second binder in the above negative electrode composite layer is 0.1 to 5 wt%, Cathode for lithium secondary batteries.

6. In paragraph 1, The above cathode composite layer further includes a conductive material, The content of the conductive material in the above cathode composite layer is 0.1 to 5 wt%. Cathode for lithium secondary batteries.

7. In paragraph 1, The above negative electrode composite layer further includes a rubber-based binder, The content of the rubber-based binder in the above negative electrode composite layer is 0.1 to 5 wt%, Cathode for lithium secondary batteries.

8. A method for manufacturing a negative electrode for a lithium secondary battery, The above method for manufacturing a negative electrode for a lithium secondary battery is as follows: A step of preparing a first negative electrode slurry by mixing a carbon-based active material, a silicon-based active material, and a first binder; A step of preparing a second cathode slurry by adding a second binder to the first cathode slurry; and Comprising a step of forming a negative electrode mixture layer on at least one surface of a negative electrode current collector using the second negative electrode slurry, The first binder and the second binder are each a copolymer including an acrylic acid-derived structural unit represented by the following chemical formula 1, The content ratio of the above acrylic acid-derived structural unit in the first binder is greater than 0 mol% and less than or equal to 50 mol%, The content ratio of the above acrylic acid-derived structural unit in the second binder is 60 mol% or more and less than 100 mol%, A method for manufacturing a negative electrode for a lithium secondary battery. [Chemical Formula 1] 9. In paragraph 8, The above first cathode slurry further includes a conductive material, A method for manufacturing a negative electrode for a lithium secondary battery.

10. In paragraph 8, A step of adding a rubber-based binder to the second cathode slurry before forming the cathode composite layer is further included. A method for manufacturing a negative electrode for a lithium secondary battery.

11. A lithium secondary battery comprising a negative electrode according to any one of claims 1 to 7. Lithium secondary battery.

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