Negative electrode composition, negative electrode for lithium secondary battery comprising the negative electrode composition, and lithium secondary battery comprising the negative electrode

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery comprising the negative electrode composition, and a lithium secondary battery comprising the negative electrode.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent No. 10-2021-0180143, filed on December 15, 2021, which is hereby incorporated by reference in its entirety.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery comprising the negative electrode composition, and a lithium secondary battery comprising the negative electrode. Background Art

[0003] Due to the rapid increase in the use of fossil fuels, there is an increasing demand for the use of alternative or clean energy, and as part of this, the most active research area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, secondary batteries are perhaps a representative example of electrochemical devices that utilize such electrochemical energy, and their use is gradually expanding.

[0005] With the development of mobile device technology and the increase in demand, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, a method for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries is being actively studied.

[0006] Generally speaking, secondary batteries are composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for intercalating and deintercalating lithium ions extracted from the positive electrode, and silicon-containing particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, in accordance with recent demands for high-density energy batteries, research is being actively conducted on using materials such as Si / C or SiO2 that have a capacity 10 times or more greater than that of graphite-containing materials. x A method for increasing capacity by combining silicon-containing compounds with conventional graphite as negative electrode active materials. However, while silicon-containing compounds, as high-capacity materials, have a high capacity compared to conventionally used graphite, they have a problem of rapid volume expansion during the charging process, which cuts off the conductive path and degrades battery performance.

[0008] Therefore, in order to solve the problem when using silicon-containing compounds as negative electrode active materials, methods for suppressing volume expansion itself have been discussed, such as methods for controlling the driving potential, methods for further coating a thin film on the active material layer, methods for controlling the particle diameter of the silicon-containing compound, and various methods for preventing the conduction path from being cut off. However, with the above methods, since battery performance may be significantly deteriorated, there are limitations on their application, and the commercialization of negative electrode batteries with high silicon-containing compound content remains limited.

[0009] In particular, research has been conducted on the composition of binders based on volume expansion. To suppress the volume expansion caused by the charge and discharge of negative electrode active materials, which experience large volume changes, the use of binder polymers with strong lateral stress resistance is being studied. However, these binder polymers themselves have limitations in suppressing increases in electrode thickness due to the contraction and expansion of negative electrode active materials and the resulting deterioration in lithium secondary battery performance.

[0010] In order to solve the above problems, research has also been conducted on introducing cross-linking agents into the binder polymer. However, this approach is difficult to apply in practical processes because it may cause viscosity changes and phase stability issues in the slurry due to long-term storage of batteries.

[0011] Therefore, even when using a negative electrode active material having a large volume expansion, it is possible to minimize the change in thickness of the negative electrode, and thus it is necessary to develop a negative electrode binder that can improve the capacity retention rate.

[0012] <Prior Art Documents>

[0013] (Patent Document 1) Japanese Patent Unexamined Publication No. 2009-080971 Summary of the Invention

[0014] Technical issues

[0015] As a result of research on binders applied to, for example, silicon-containing negative electrodes, for binders having improved slurry dispersibility and excellent adhesion, it has been found that the above problems can be solved when the negative electrode binder polymer has a specific composition that can have a partially crosslinked structure.

[0016] Therefore, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the negative electrode composition, and a lithium secondary battery including the negative electrode.

[0017] Technical Solution

[0018] An embodiment of the present specification provides a negative electrode composition, the negative electrode composition including a negative electrode binder polymer, a negative electrode active material and a negative electrode conductive material; wherein the negative electrode binder polymer includes: a compound including a (meth)acrylamide group; an unsaturated organic acid or a salt of the unsaturated organic acid; a monomer unit including an α,β-unsaturated nitrile; and a compound including diacrylamide or diacrylate; and the negative electrode composition includes: based on 100 parts by weight of the negative electrode binder polymer, 1 part by weight or more and 30 parts by weight or less of the monomer unit including the α,β-unsaturated nitrile, and 0.1 part by weight or more and 15 parts by weight or less of the compound including diacrylamide or diacrylate.

[0019] In another embodiment, a negative electrode for a lithium secondary battery is provided, including: a negative electrode current collector; and a negative electrode active material layer including the negative electrode composition according to the present application on one surface or both surfaces of the negative electrode current collector.

[0020] Finally, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0021] Beneficial effects

[0022] The negative electrode composition according to an embodiment of the present disclosure is characterized in that the negative electrode composition includes a negative electrode binder polymer, which includes: a compound including a (meth)acrylamide group; an unsaturated organic acid or a salt of the unsaturated organic acid; a monomer unit including an α,β-unsaturated nitrile; and a compound including diacrylamide or diacrylate.

[0023] In particular, the negative electrode composition may include: based on 100 parts by weight of the negative electrode binder polymer, 1 part by weight or more and 30 parts by weight or less of a monomer unit including an α,β-unsaturated nitrile, and 0.1 part by weight or more and 15 parts by weight or less of a compound including a diacrylamide or a diacrylate. Therefore, even when using a negative electrode active material (particularly a silicon-containing active material) that has a large volume expansion due to charge / discharge, it is characterized in that the volume expansion and contraction can be suppressed, and the thickness change due to electrode swelling (swelling) can be minimized, thereby excellent life performance of the lithium secondary battery.

[0024] The negative electrode binder polymer according to the present application may form a partially crosslinked structure by including a specific amount of a compound including diacrylamide or diacrylate, so that the binder polymer is partially crosslinked.

[0025] When a negative electrode binder polymer having the characteristics described above is present, the thickness of the electrode changes little during charge and discharge due to the partially crosslinked structure of the binder itself, and the capacity retention rate is improved during life evaluation. The content of the compound containing diacrylamide or diacrylate can indicate the degree of partial crosslinking of the polymer.

[0026] That is, the present disclosure is characterized in that the negative electrode composition according to the embodiment of the present disclosure improves capacity characteristics by including a silicon-containing active material having a high theoretical capacity as the negative electrode active material, and solves the volume expansion problem caused by charge and discharge, which is a problem of the silicon-containing active material, by using a specific negative electrode binder polymer according to the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a diagram illustrating a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application.

[0028] Figure 2 is a diagram illustrating a laminated structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] Before describing the present disclosure, some terms are first defined.

[0030] In the present specification, if a prescribed part “includes” a prescribed element, it means that another element may be further included rather than excluding other elements unless there is any specific description to the contrary.

[0031] In this specification, “p to q” means a range of “p or more and q or less”.

[0032] In this specification, "specific surface area" is measured by the BET method, and specifically is calculated from the nitrogen adsorption amount at liquid nitrogen temperature (77K) using BEL Japan's BELSORP-mino II. That is, the BET specific surface area in this application may refer to the specific surface area measured by the above measurement method.

[0033] In this specification, "Dn" refers to the particle size distribution, and refers to the particle diameter at the n% point of the cumulative distribution of the number of particles according to the particle diameter. That is, D50 is the particle diameter (average particle diameter) at the 50% point of the cumulative distribution of the number of particles according to the particle diameter, D90 is the particle diameter at the 90% point of the cumulative distribution of the number of particles according to the particle diameter, and D10 is the particle diameter at the 10% point of the cumulative distribution of the number of particles according to the particle diameter. At the same time, the particle size distribution of the particles can be measured using a laser diffraction method. Specifically, after the measuring target powder is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam.

[0034] In this specification, when a polymer is said to include a certain monomer or compound as a monomer or compound unit, it means that the monomer or compound participates in a polymerization reaction and is contained in the polymer as a repeating unit. In this specification, when it is said that a polymer includes a monomer or compound, this is interpreted as the polymer including the monomer or compound as a monomer unit.

[0035] In this specification, the term "polymer" should be understood as being used in a broad sense including copolymers, unless a "homopolymer" is specified.

[0036] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene conversion molecular weights obtained by measuring commercially available monodisperse polystyrene polymers of different degrees of polymerization (standard samples) of molecular weight measurement as standard materials by gel permeation chromatography (GPC). In this specification, unless otherwise specified, molecular weight refers to weight average molecular weight.

[0037] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present disclosure. However, the present disclosure can be embodied in various forms and is not limited to the following description.

[0038] An embodiment of the present specification provides a negative electrode composition, including a negative electrode binder polymer, a negative electrode active material, and a negative electrode conductive material; wherein the negative electrode binder polymer includes: a compound including a (meth)acrylamide group; an unsaturated organic acid or a salt of the unsaturated organic acid; a monomer unit including an α,β-unsaturated nitrile; and a compound including diacrylamide or diacrylate; and the negative electrode composition includes: based on 100 parts by weight of the negative electrode binder polymer, 1 part by weight or more and 30 parts by weight or less of the monomer unit including the α,β-unsaturated nitrile, and 0.1 part by weight or more and 15 parts by weight or less of the compound including diacrylamide or diacrylate.

[0039] The negative electrode binder polymer according to the present application can form a partially crosslinked structure by including a specific amount of a compound containing diacrylamide or diacrylate, so that the binder polymer is partially crosslinked. That is, when the negative electrode binder polymer having the above-described characteristics is included, there is a feature that the thickness of the negative electrode changes little during charge and discharge due to the partially crosslinked structure of the binder itself, and the capacity retention rate is improved when performing life evaluation.

[0040] In an embodiment of the present application, the negative electrode binder polymer may include: a compound including a (meth)acrylamide group; an unsaturated organic acid or a salt thereof; a monomer unit including an α,β-unsaturated nitrile; and a compound including diacrylamide or diacrylate.

[0041] In the embodiment of the present application, the compound including a (meth)acrylamide group may be included in an amount of 30 parts by weight or more and 80 parts by weight or less based on 100 parts by weight of the negative electrode binder polymer.

[0042] In another embodiment, the compound including a (meth)acrylamide group may be included in an amount of 30 parts by weight or more and 80 parts by weight or less, preferably 35 parts by weight or more and 75 parts by weight or less, and more preferably 40 parts by weight or more and 70 parts by weight or less, based on 100 parts by weight of the negative electrode binder polymer.

[0043] In an embodiment of the present application, the unsaturated organic acid or the salt of the unsaturated organic acid may be present in an amount of 5 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 35 parts by weight or less, and more preferably 15 parts by weight or more and 35 parts by weight or less, based on 100 parts by weight of the negative electrode binder polymer.

[0044] In an embodiment of the present application, a negative electrode composition is provided, comprising: based on 100 parts by weight of a negative electrode binder polymer, 1 part by weight or more and 30 parts by weight or less of a monomer unit including an α,β-unsaturated nitrile, and 0.1 parts by weight or more and 15 parts by weight or less of a compound including diacrylamide or diacrylate.

[0045] In another embodiment, the monomer unit including the α,β-unsaturated nitrile may be present in an amount of 1 part by weight or more and 30 parts by weight or less, preferably 3 parts by weight or more and 30 parts by weight or less, and more preferably 5 parts by weight or more and 30 parts by weight or less, based on 100 parts by weight of the negative electrode binder polymer.

[0046] In another embodiment, the compound including diacrylamide or diacrylate may be included in an amount of 0.1 parts by weight or more and 15 parts by weight or less, preferably 0.5 parts by weight or more and 12 parts by weight or less, based on 100 parts by weight of the negative electrode binder polymer.

[0047] The negative electrode binder polymer according to the present application includes the four types of monomer units as described above, and in particular, the negative electrode binder polymer is characterized in that the monomer units are included in the amounts described above. Due to the above content of the monomer units, the negative electrode binder polymer forms a partially cross-linked structure and has improved binding force, so that the thickness of the electrode containing the negative electrode binder polymer during charge and discharge changes is small, and thus, the capacity retention rate is improved when performing life evaluation.

[0048] In the embodiment of the present application, a composition including specific parts by weight based on 100 parts by weight of the negative electrode binder polymer may refer to a weight ratio of each component monomer relative to the total weight of 100 monomer groups of the negative electrode binder polymer and is expressed in parts by weight.

[0049] In an embodiment of the present application, a negative electrode composition is provided, wherein the molar ratio of the compound containing a (meth)acrylamide group to the unsaturated organic acid or the salt of the unsaturated organic acid is 1:0.1 to 1:0.6.

[0050] The molar ratio may refer to a molar ratio based on 100 parts by weight of the negative electrode binder polymer according to the present application, and may specifically refer to a mol % ratio.

[0051] In an embodiment of the present application, the negative electrode binder polymer may include a compound including a (meth)acrylamide group.

[0052] In an embodiment of the present application, the (meth)acrylamide may include: methacrylamide; or acrylamide.

[0053] In the embodiment of the present application, unsaturated organic acid can be used without restriction, as long as it is an organic acid that can be included in the adhesive, but specifically acrylic acid can be used.At this moment, the salt of unsaturated organic acid can refer to the salt form containing ion in unsaturated organic acid, and this also can be used without restriction.The specific but non-restrictive example of unsaturated organic acid includes for example carboxylic acid or its salt.Carboxylic acid can be used with carboxylic acid monomer or salt, such as (methyl) acrylic acid, itaconic acid, fumaric acid, crotonic acid, maleic acid, itaconic acid monomethyl ester, methyl fumarate, monobutyl fumarate, and can use with two or more mixtures in these materials.

[0054] In an embodiment of the present application, the monomer unit including the α,β-unsaturated nitrile may be acrylonitrile.

[0055] In an embodiment of the present application, a negative electrode composition is provided, wherein the compound containing diacrylamide or diacrylate is: alkyl diacrylamide; oxidized alkyl alkyl diacrylamide; or oxidized alkyl diacrylate.

[0056] Specifically, the compound containing bisacrylamide or diacrylate may include: N,N'-methylenebisacrylamide; or ethylene glycol diacrylate.

[0057] The negative electrode binder polymer according to the present application includes four components having specific contents and compositions as described above, and even when using a negative electrode active material (especially a silicon-containing active material) that has a large volume expansion according to charge and discharge, it can suppress volume expansion and contraction and minimize thickness changes due to electrode swelling (Swelling), and thus, the life performance of the lithium secondary battery can be improved.

[0058] The above four components can be polymerized to form a negative electrode binder polymer.

[0059] In an embodiment of the present application, a negative electrode composition is provided, wherein a weight average molecular weight of the negative electrode binder polymer may be 100,000 g / mol or more and 3,000,000 g / mol or less.

[0060] In another embodiment, the negative electrode binder polymer may have a weight average molecular weight of 100,000 g / mol or more and 3,000,000 g / mol or less, preferably 200,000 g / mol or more and 1,500,000 g / mol or less.

[0061] When the negative electrode binder polymer as described above satisfies the above weight average molecular weight range of 100,000 g / mol or more and 3,000,000 g / mol or less, the mechanical strength is excellent and the intermolecular interaction is high, so that the electrode can have excellent binding force. In addition, when the above range is met, the viscosity of the negative electrode binder can be selected within an appropriate range so that when the negative electrode is manufactured using the negative electrode binder, the electrode can have excellent coating performance.

[0062] In an embodiment of the present application, there is provided a negative electrode composition including 1 part by weight or more and 20 parts by weight or less of a negative electrode binder polymer based on 100 parts by weight of the negative electrode composition.

[0063] In another embodiment, the negative electrode binder polymer may be present in an amount of 1 part by weight or more and 20 parts by weight or less, preferably 3 parts by weight or more and 15 parts by weight or less, and more preferably 4 parts by weight or more and 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0064] When the negative electrode binder polymer is present in the range of more than 1 part by weight and less than 20 parts by weight, the negative electrode active material can be effectively dispersed, and it can have the characteristic of having a high bonding force between the electrode adherent and the active material in the electrode with respect to the shrinkage and expansion of the negative electrode active material due to the charge and discharge of the lithium secondary battery.

[0065] In the embodiment of the present application, the Young's modulus of the negative electrode binder polymer may be 10 3 MPa or higher.

[0066] In another embodiment of the present application, the Young's modulus of the negative electrode binder polymer may be 1×10 3 MPa or higher, preferably 2×10 3 MPa or higher, and more preferably 5×10 3 MPa or higher. In another embodiment, the Young's modulus of the negative electrode binder polymer may be 25×10 3 MPa or lower, preferably 22×10 3 MPa or less, and more preferably 20×10 3 MPa or lower.

[0067] In the Young's modulus measurement method, the negative electrode binder polymer is placed in a coating bowl and dried at room temperature for a long period of time to remove moisture. The dried film is then vacuum-dried at 130°C for 10 hours, according to the electrode drying temperature. The dried film is then cut or punched into 6 mm x 100 mm samples for collection. The tensile strength (Young's modulus) is measured using a UTM device.

[0068] The Young's modulus of the negative electrode binder polymer varies depending on the binder measurement method, speed, and measurement state, but is a value measured in a dry room with a dew point of -5°C to 10°C and a temperature of 20°C to 22°C.

[0069] In this application, the dew point is the temperature at which humid air begins to condense, and the partial pressure of water vapor in the air is equal to the saturated vapor pressure of water at that temperature. In other words, when the temperature of a gas containing water vapor drops, the relative humidity can reach 100%, and thus it can refer to the temperature at which dew begins to form.

[0070] The dew point is -5°C to 10°C, and a temperature of about 20°C to 22°C is generally defined as a dry room, in which case the humidity corresponds to a very low level.

[0071] The negative electrode binder polymer can have dispersibility for dispersing the negative electrode active material in a negative electrode slurry containing the negative electrode composition, and adhesion for bonding to the negative electrode current collector and the negative electrode active material layer after drying. Furthermore, the adhesive strength corresponds to a relatively low adhesive strength. In other words, the negative electrode binder polymer according to the present application satisfies the Young's modulus and can be a binder having a planar bonding form.

[0072] The negative electrode binder polymer may have a hydrophilic property and be insoluble in an electrolyte or electrolyte solution commonly used in secondary batteries. When applied to a negative electrode or a lithium secondary battery, this property can impart strong stress or tensile strength to the negative electrode binder polymer, and thus, the volume expansion / contraction problem caused by the charge / discharge of the silicon-based active material can be effectively suppressed.

[0073] In an embodiment of the present application, the negative electrode binder polymer may further include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and a material in which hydrogen is replaced by Li, Na or K, and may further include various copolymers thereof.

[0074] The negative electrode binder polymer according to an embodiment of the present application is used to fix a negative electrode active material and a negative electrode conductive material so as to prevent distortion and structural deformation of the negative electrode structure in volume expansion and relaxation of the silicon-containing active material.

[0075] In an embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode active material includes one or more selected from the group consisting of silicon-containing active materials and carbon-containing active materials.

[0076] In the embodiment of the present application, the negative electrode active material is one or more selected from the group consisting of silicon-based active materials and carbon-based active materials; the silicon-based active material includes one or more selected from the group consisting of SiO x (x=0), SiO x (0<x<2), one or more of the group consisting of SiC and Si alloy.

[0077] In the embodiment of the present application, the negative electrode active material is a silicon-based active material; the silicon-based active material includes a material selected from SiO x (x=0) and SiO x One or more of the group consisting of (0<x<2); and SiO x (x=0) is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

[0078] In an embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode active material is a silicon-based active material; the silicon-based active material includes a material selected from SiO x (x=0) and SiO x One or more of the group consisting of (0<x<2); and SiO x(x=0) is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

[0079] In the embodiment of the present application, the silicon-containing active material may include a material selected from the group consisting of SiO x (x=0), SiO x (0<x<2), one or more of the group consisting of SiC and Si alloy.

[0080] The active material of the present disclosure may include a silicon-containing active material. The silicon-containing active material may be SiO x 、Si / C or Si. SiO x It can include SiO x (0≤x<2) represents a compound. In the case of SiO2, since this material does not react with lithium ions, so that lithium cannot be stored, x is preferably within the above range. The silicon-containing active material may be Si / C or Si composed of a composite of Si and C. In addition, two or more types of silicon-containing active materials may be mixed and used. The negative electrode active material may further include a carbon-containing active material together with the above-mentioned silicon-containing active material. The carbon-containing active material may contribute to the excellent cycle characteristics of the negative electrode or secondary battery of the present disclosure or the improvement of the battery life performance.

[0081] Generally, it is known that the capacity of silicon-containing active materials is more than 10 times higher than that of carbon-containing active materials. Therefore, when silicon-containing active materials are applied to the negative electrode, it is expected to achieve an electrode with a high level of energy density even with a thin thickness.

[0082] In an embodiment of the present application, the carbon-containing active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon, preferably at least one selected from the group consisting of artificial graphite and natural graphite.

[0083] In an embodiment of the present application, the negative electrode active material may be any substance including: (1) artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, and combinations thereof; (2) silicon-containing alloys; (3) composite compounds including or consisting of: i) at least one of artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, and combinations thereof, and ii) a metal selected from the group consisting of Al, Ag, Bi, In, Ge, Mg, Pb, Si, Sn, Ti, and combinations thereof; (4) lithium composite metal oxides; (5) lithium-containing nitrides; (6) silicon-graphene; (7) silicon-carbon nanotubes; (8) silicon oxide; (9) silicon; and (10) combinations thereof.

[0084] In an embodiment of the present application, a negative electrode composition is provided, wherein the silicon-containing active material comprises a material selected from the group consisting of SiO x (x=0) and SiO x One or more of the group consisting of (0<x<2); and SiO x (x=0) is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

[0085] In another embodiment, based on 100 parts by weight of the silicon-based active material, SiO x (x=0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, and more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

[0086] In the embodiment of the present application, only pure silicon (Si) among the silicon-containing active materials may be used as the silicon-containing active material. Using pure silicon (Si) as the silicon-containing active material may refer to including pure silicon particles (SiO2) within the above range that are not combined with other particles or elements when the total amount of the silicon-containing active material is based on 100 parts by weight as described above. x (x=0)).

[0087] When compared with conventionally used graphite-containing active materials, silicon-containing active materials have significantly higher capacity, so attempts to apply them are increasing. However, due to their high volume expansion rate during the charge and discharge process, their use is limited to small amounts when mixed with graphite-containing active materials.

[0088] Therefore, in the case of the present disclosure, it is characterized in that while using a silicon-containing active material as a negative electrode active material to improve capacity performance, a thermally cross-linked negative electrode binder under specific conditions is used in order to solve the problem of maintaining a conductive path due to volume expansion as described above and maintain the combination of the conductive material, the binder and the active material.

[0089] At the same time, the average particle size (D50) of the silicon-containing active material of the present disclosure can be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size (D50) is included in the above range of 5 μm to 10 μm, the specific surface area of ​​the particles is included in a suitable range, so that the viscosity of the negative electrode slurry is formed in a suitable range. Therefore, it is conducive to the dispersion of the particles constituting the negative electrode slurry. In addition, since the size of the silicon-containing active material has a value greater than or equal to the lower limit range, since the conductive material and the binder in the negative electrode slurry form a composite material, the contact area between the silicon-containing active material particles and the conductive material is excellent, and the possibility of continued formation of the conductive network is increased, thereby increasing the capacity retention rate. On the other hand, when the average particle size (D50) satisfies the above range, excessively large silicon particles are excluded to form a negative electrode with a smooth surface, thereby preventing the current density from being uneven during charge and discharge.

[0090] In the embodiment of the present application, the silicon-containing active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-containing active material is preferably 0.01 m 2 / g to 150.0m 2 / g, more preferably 0.1m 2 / g to 100.0m 2 / g, particularly preferably 0.2m 2 / g to 80.0m 2 / g, and most preferably 0.2m 2 / g to 18.0m 2 The BET specific surface area is measured using nitrogen according to DIN 66131.

[0091] In embodiments of the present application, the silicon-containing active material may be present in a crystalline or amorphous state, and is preferably non-porous. The silicon particles are preferably spherical or crushed particles. Optionally, but not preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0092] In an embodiment of the present application, the negative electrode active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0093] In an embodiment of the present application, there is provided a negative electrode composition, wherein the silicon-containing active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0094] In another embodiment, the silicon-containing active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0095] The negative electrode composition according to the present application does not deteriorate the performance of the negative electrode even when containing a silicon-containing active material within the above range, and even when a silicon-containing active material having a significantly high capacity is used within the above range, it has excellent output characteristics during charge and discharge by using a specific conductive material and a binder that can maintain a volume expansion rate during charge and discharge processes.

[0096] In an embodiment of the present application, the silicon-containing active material may have a non-spherical shape, and the roundness thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, and for example, 0.85 to 0.9.

[0097] In the present application, circularity is determined by the following formula 1-1, where A is the area and P is the boundary line.

[0098] [Formula 1-1]

[0099] 4πA / P 2

[0100] Traditionally, it has been common to use only graphite-containing compounds as negative electrode active materials. However, with the increasing demand for high-capacity batteries, attempts to increase capacity by mixing and using silicon-containing compounds have also increased. However, silicon-containing compounds have the limitation that they rapidly expand during the charge / discharge process, thereby destroying the conductive paths formed in the negative electrode active material layer and significantly compromising battery performance.

[0101] Therefore, in an embodiment of the present application, the negative electrode composition may use a binder having the above characteristics and simultaneously include a specific negative electrode conductive material.

[0102] In an embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode conductive material includes one or more selected from the group consisting of: a point-shaped conductive material; a planar conductive material; and a linear conductive material.

[0103] In embodiments of the present application, the dot-shaped conductive material is a material that can be used to improve the conductivity of the negative electrode and can form conductivity without causing chemical changes, and refers to a conductive material having a circular or dot-shaped shape. Specifically, the dot-shaped conductive material can be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, carbon fluoride, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and a polyphenylene derivative. In terms of achieving high conductivity and excellent dispersibility, the dot-shaped conductive material can preferably include carbon black.

[0104] In the embodiment of the present application, the BET specific surface area of ​​the point-shaped conductive material can be 40 m 2 / g or above and 70m 2 / g or less, preferably 45m 2 / g or above and 65m 2 / g or less, and more preferably 50m 2 / g or above and 60m 2 / g or less.

[0105] In an embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0106] In an embodiment of the present application, the negative electrode conductive material may include a planar conductive material.

[0107] Planar conductive materials are materials that enhance conductivity by increasing surface contact between silicon particles in the negative electrode, while also preventing volume expansion that could cause the conduction path to be disconnected. Planar conductive materials can be either plate-shaped or bulk-shaped.

[0108] In an embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and is preferably plate graphite.

[0109] In an embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the above range of 2 μm to 7 μm is met, the viscosity of the negative electrode slurry does not increase excessively due to sufficient particle size, and dispersion is easy. Therefore, when the same equipment and time are used for dispersion, the dispersion effect is very good.

[0110] In an embodiment of the present application, a negative electrode composition is provided, wherein the planar conductive material has a D10 of 0.5 μm to 1.5 μm, a D50 of 4.0 μm to 5.0 μm, and a D90 of 7.0 μm to 15.0 μm.

[0111] In an embodiment of the present application, the planar conductive material may include: a high specific surface area planar conductive material having a high BET specific surface area; or a low specific surface area planar conductive material.

[0112] In an embodiment of the present application, the planar conductive material may include without limitation: a high specific surface area planar conductive material; or a low specific surface area planar conductive material, but in particular, since the planar conductive material according to the present application may be affected to a certain extent by dispersion in terms of electrode performance, it is particularly preferred to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0113] In the embodiment of the present application, the BET specific surface area of ​​the planar conductive material can be 1m 2 / g or greater.

[0114] In another embodiment, the BET specific surface area of ​​the planar conductive material can be 1 m 2 / g and above and 500m 2 / g or less, preferably 5m 2 / g and above and 300m 2 / g or less, and more preferably 5m 2 / g and above and 250m 2 / g or less.

[0115] In another embodiment, the planar conductive material can be a high specific surface area planar conductive material and can meet the BET specific surface area range of 50 m 2 / g and above and 500m 2 / g or less, preferably 80m 2 / g and above and 300m 2 / g or less, and more preferably 100m 2 / g and above and 250m 2 / g or less.

[0116] In another embodiment, the planar conductive material can be a low specific surface area planar conductive material and can meet the BET specific surface area range of 1 m 2 / g or above and 40m 2 / g or less, preferably 5m 2 / g or above and 30m 2 / g or less, and more preferably 5m 2 / g or above and 25m 2 / g or less.

[0117] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, in this article, unless otherwise specified, the term "bundle type" refers to a secondary shape in the form of a bundle or rope (melt-blown), in which a plurality of carbon nanotube units are arranged side by side or entangled so that the axes of the carbon nanotube units in the longitudinal direction have substantially the same direction. The carbon nanotube unit has a graphite sheet in the form of a cylinder with a diameter of nanometer size and has an sp2 bond structure. At this time, the carbon nanotube unit can exhibit the properties of a conductor or a semiconductor, depending on the rolling angle and structure of the graphite sheet. Compared with entangled type carbon nanotubes, bundle-type carbon nanotubes can be evenly dispersed during the manufacture of the negative electrode and can smoothly form a conductive network in the negative electrode, thereby enabling the conductivity of the negative electrode to be improved.

[0118] In an embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode conductive material includes a linear conductive material, and the linear conductive material is a carbon nanotube.

[0119] In an embodiment of the present application, the carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) and / or multi-walled carbon nanotubes (MWCNTs). When the linear conductive material is SWCNTs, the length of the SWCNTs may be 0.5 μm to 100 μm, preferably 1 μm to 80 μm.

[0120] In an embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is included in an amount of 5 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0121] In another embodiment, the negative electrode conductive material may be included in an amount of 5 parts by weight or more and 40 parts by weight or less, preferably 5 parts by weight or more and 30 parts by weight or less, and more preferably 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0122] In an embodiment of the present application, the negative electrode conductive material may include a point-shaped conductive material and a line-shaped conductive material, and the ratio of the point-shaped conductive material to the line-shaped conductive material may satisfy 1:0.001 to 1:0.05.

[0123] In an embodiment of the present application, since the negative electrode conductive material can include a point-like conductive material and a linear conductive material, and satisfies each of the composition and proportion, the life characteristics of the existing lithium secondary battery are not significantly affected, and the number of sites capable of charge and discharge is increased, thereby obtaining excellent output characteristics at a high C-rate.

[0124] The negative electrode conductive material according to the present application can have a completely different structure from the conductive material used for the positive electrode. Specifically, the negative electrode conductive material according to the present application can be used to maintain contact points between the silicon-containing active material of the electrode, which experiences significant volume expansion due to charge and discharge. The positive electrode conductive material can serve as a buffer during rolling and impart a certain degree of conductivity, and can have a completely different structure and function from the negative electrode conductive material of the present disclosure.

[0125] In an embodiment of the present application, the thickness change rate of the negative electrode active material layer after curing or drying satisfies the following Formula 1.

[0126] [Formula 1]

[0127] 0%≤[(X2-X1) / X1]×100(%)≤15%

[0128] In formula 1,

[0129] X1 is the thickness of the negative electrode active material layer of the negative electrode for a lithium secondary battery after solidification or drying at 0 cycles; and

[0130] X2 is the thickness of the negative electrode active material layer of the negative electrode for a lithium secondary battery after solidification or drying after 30 cycles.

[0131] 0 cycles may refer to a state where the negative electrode for a lithium secondary battery has been manufactured but has not yet been charged or discharged, and specifically may refer to the negative electrode for a lithium secondary battery after manufacturing.

[0132] In the embodiment of the present application, the negative electrode composition may form a negative electrode slurry by including a solvent for forming a negative electrode slurry, and may form a negative electrode by applying the negative electrode slurry to one side or both sides of a negative electrode collector.

[0133] At this time, the solid content of the negative electrode slurry may meet 10% to 60%.

[0134] In the embodiment of the present application, the solvent for forming the negative electrode slurry may be used without limitation as long as it can disperse the negative electrode composition, but specifically, distilled water or NMP may be used.

[0135] In the embodiment of the present disclosure, the method of mixing the negative electrode slurry is not particularly limited, and a ball mill, a sand mill, a pigment disperser, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, etc. are exemplified, and kneading is preferably performed using a homogenizer and / or a planetary mixer as appropriate.

[0136] In the embodiment of the present application, the method of applying the negative electrode slurry to the negative electrode collector is not particularly limited, and conventionally known coating devices such as a comma coater, a gravure coater, a micro gravure coater, a die coater, a rod coater, etc. can be used.

[0137] In addition, the drying process can be performed after applying the negative electrode slurry. The drying method is not particularly limited. The temperature is preferably 60°C to 200°C, preferably 100°C to 180°C. The atmosphere can be dry air or an inert atmosphere. Although the thickness of the electrode (cured coating) is not particularly limited, it is preferably 5 μm to 300 μm, preferably 10 μm to 250 μm.

[0138] In an embodiment of the present application, a negative electrode for a lithium secondary battery is provided, including: a negative electrode current collector; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one surface or both surfaces of the negative electrode current collector.

[0139] In an embodiment of the present application, the negative electrode active material layer may have an additional negative electrode active material layer on a surface opposite to the surface in contact with the negative electrode current collector. In this case, the additional negative electrode active material layer may include a commonly used negative electrode active material, such as a carbonaceous negative electrode active material or a silicon-containing negative electrode active material.

[0140] Figure 1 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. Specifically, it can be confirmed that the negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 formed on one surface of a negative electrode current collector 10, Figure 1 It is shown that the negative electrode active material layer is formed on one surface thereof, but it may be formed on both surfaces thereof.

[0141] In an embodiment of the present application, the negative electrode current collector generally has a thickness of 1 μm to 100 μm. This negative electrode current collector is not particularly limited as long as it is a current collector with high conductivity and does not cause chemical changes in the relevant battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, a material in which the surface of copper or stainless steel is surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can strengthen the bonding force of the negative electrode active material by forming fine irregularities on its surface, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc. Among them, copper foil is preferred as a current collector when an electrode active material is used in the negative electrode.

[0142] In an embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector is 1 μm to 100 μm, and the thickness of the negative electrode active material layer is 20 μm to 500 μm.

[0143] However, the thickness may be variously modified according to the type and purpose of the negative electrode used, but the present disclosure is not limited thereto.

[0144] In an embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein a thickness variation rate of a negative electrode active material layer satisfies the following Formula 1.

[0145] [Formula 1]

[0146] 0%≤[(X2-X1) / X1]×100(%)≤15%

[0147] In formula 1,

[0148] X1 is the thickness of the negative electrode active material layer of the negative electrode for lithium secondary batteries at 0 cycles; and

[0149] X2 is the thickness of the negative electrode active material layer of the negative electrode for a lithium secondary battery after 30 cycles.

[0150] 0 cycles may refer to a state where the negative electrode for a lithium secondary battery has been manufactured but has not yet been charged or discharged, and specifically may refer to the negative electrode for a lithium secondary battery after manufacturing.

[0151] In addition, the thickness change rate refers to the thickness change rate of the negative electrode active material layer after the negative electrode composition is solidified or dried.

[0152] That is, the negative electrode for a lithium secondary battery according to the present application is characterized in that, by using a specific negative electrode binder polymer, the volume expansion of the negative electrode active material is prevented even after repeated cycles, and thus the thickness change is small.

[0153] In an embodiment of the present application, a lithium secondary battery is provided, including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0154] Figure 2 The figure shows a laminated structure of a lithium secondary battery according to an embodiment of the present application. Specifically, it can be confirmed that the negative electrode 100 for the lithium secondary battery includes a negative electrode active material layer 20 formed on one surface of the negative electrode current collector 10, and it can be confirmed that the positive electrode 200 for the lithium secondary battery includes a positive electrode active material layer 40 formed on one surface of the positive electrode current collector layer 50. The negative electrode 100 for the lithium secondary battery and the positive electrode 200 for the lithium secondary battery are formed into a structure in which they are stacked together with a separator 30 interposed therebetween.

[0155] In particular, the secondary battery according to the embodiment of the present specification may include the negative electrode for the lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, the negative electrode being the same as the negative electrode described above.

[0156] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material.

[0157] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, a material in which the surface of aluminum or stainless steel is surface-treated with carbon, nickel, titanium, silver, or the like, or the like can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and the adhesion strength of the positive electrode active material can be increased by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0158] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include: a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or the like, or a compound substituted by one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium ion battery having the formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; LiNi 1-c2 M c2 Ni-type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3); c3 M c3 The positive electrode may be a lithium manganese composite oxide represented by the formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which Li in the formula is partially replaced by an alkaline earth metal ion; and the like, but the present disclosure is not limited thereto. The positive electrode may be lithium metal.

[0159] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder as well as the positive electrode active material.

[0160] At this time, the positive electrode conductive material is a material used to impart conductivity to the electrode. In the battery to be configured, the positive electrode conductive material can be used without any particular limitation as long as it has electronic conductivity without causing chemical changes. Specific examples of the positive electrode conductive material can include: graphite, such as natural graphite, artificial graphite, etc.; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, etc.; metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide, potassium titanate, etc.; conductive metal oxides, such as titanium oxide, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or the like, which can be used alone or as a mixture of two or more thereof.

[0161] In addition, the positive electrode binder is used to improve the adhesion between the positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile (polyacrylonitrile), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, various copolymers thereof, or the like, and may be used alone or in mixtures of two or more thereof.

[0162] Separator is a separator that separates the negative electrode and the positive electrode and provides a mobile channel for lithium ions. As long as it is commonly used as a separator in a secondary battery, it can be used without any particular restrictions. In particular, it is preferred that the separator has excellent electrolyte moisture-containing capacity and has lower resistance to the ion movement of the electrolyte. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or a two-layer or multilayer laminate structure thereof. In addition, a common porous non-woven fabric can be used, for example, a non-woven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, in order to ensure heat resistance or mechanical strength, a coated separator comprising a ceramic component or a polymer material can be used, and can be used as appropriate with a single layer or multilayer structure.

[0163] Examples of the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used when manufacturing a lithium secondary battery, but the present disclosure is not limited thereto.

[0164] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0165] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, cyclopentane, methylcyclopentane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, etc. can be used.

[0166] In particular, among organic solvents containing carbonates, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and are preferably used because they have high dielectric constants and dissociate lithium salts well. If such cyclic carbonates are mixed and used in appropriate proportions with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, electrolytes with high conductivity can be prepared, and thus they can be more preferably used.

[0167] A lithium salt can be used as the metal salt. The lithium salt is a material that is well soluble in a non-aqueous electrolyte. For example, one or more selected from the group consisting of the following can be used as an anion of the lithium salt: - 、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 - .

[0168] In addition to the electrolyte components, the electrolyte may further include one or more additives, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, increasing the discharge capacity of the battery, etc., for example, compounds containing halogenated olefin carbonates such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ethylene glycol dimethyl ether (glyme), hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N'-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc.

[0169] The lithium secondary battery according to the present disclosure can be used in portable devices such as mobile phones, laptop computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). In particular, it can be preferably used as a battery constituting a medium-to-large battery module. Therefore, the present disclosure also provides a medium-to-large battery module including the lithium secondary battery described above as a unit cell.

[0170] Embodiments of the present disclosure provide a battery module including the secondary battery as a unit cell and a battery pack including the battery module. Because the battery module and the battery pack include secondary batteries with high capacity, high rate performance, and cycle characteristics, they can be used as power sources for medium-to-large devices selected from the group consisting of electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and power storage systems.

[0171] Embodiments of the invention

[0172] In the following, preferred embodiments are proposed to help understand the present disclosure, but these embodiments are only for illustrating the present disclosure. It is obvious to those skilled in the art that various changes and modifications can be made within the scope and technical spirit of the present disclosure. Needless to say, such changes and modifications fall within the scope of the appended claims.

[0173] <Preparation Example>

[0174] <Preparation of Binder Polymer>

[0175] Example 1

[0176] 900 g of water, 65 g of acrylamide, 20 g of acrylic acid, 10 g of acrylonitrile, and 5 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0177] Example 2

[0178] 900 g of water, 60 g of acrylamide, 23 g of acrylic acid, 5 g of acrylonitrile, and 12 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0179] Example 3

[0180] 900 g of water, 65 g of acrylamide, 20 g of acrylic acid, 10 g of acrylonitrile, and 5 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0181] Example 4

[0182] 900 g of water, 65 g of acrylamide, 20 g of acrylic acid, 10 g of acrylonitrile, and 5 g of ethylene glycol diacrylate, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe. The temperature was raised to 90° C. and polymerization was carried out for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0183] Comparative Example 1

[0184] 900 g of water, 50 g of acrylamide, 35 g of acrylic acid, and 15 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0185] Comparative Example 2

[0186] 900 g of water, 50 g of acrylamide, 30 g of acrylic acid, and 20 g of acrylonitrile, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0187] Comparative Example 3

[0188] 900 g of water, 15 g of acrylamide, 20 g of acrylic acid, 60 g of acrylonitrile, and 5 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0189] Comparative Example 4

[0190] 900 g of water, 45 g of acrylamide, 20 g of acrylic acid, 10 g of acrylonitrile, and 25 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0191] Comparative Example 5

[0192] 900 g of water, 45 g of acrylamide, 20 g of acrylic acid, 10 g of acrylonitrile, and 17 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, and the temperature was raised to 90° C. to carry out polymerization for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0193] Comparative Example 6

[0194] 900 g of water, 40 g of acrylamide, 30 g of acrylic acid, 20 g of hydroxyethyl acrylate (HEA), and 5 g of N,N'-methylenebisacrylamide, as well as 0.5 g of ammonium persulfate as a polymerization initiator, were injected into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe. The temperature was raised to 90° C. and polymerization was carried out for 5 hours. Then, the pH of the polymerization reaction product was adjusted to pH 5 with an aqueous NaOH solution to prepare a binder polymer.

[0195] The compositions and contents of Examples 1 to 4 and Comparative Examples 1 to 6 prepared as described above are shown in Table 1.

[0196] [Table 1]

[0197]

[0198] <Preparation of Negative Electrode Slurries of Examples 1, 2, and 4 and Comparative Examples 1 to 6>

[0199] When 1) artificial graphite with d50=15 μm as graphite and 2) SiO x After mixing the negative electrode active material (d50 = 1 to 6 μm, 0.9 ≤ x ≤ 1.5, e.g., x = 1.05) at a weight ratio of 7:3 and the conductive material (1:0.005) with Super-P Black and SWCNTs, the negative electrode active material, the conductive material, and the binder were mixed at a weight ratio of 85:5:10 to prepare a negative electrode composition. The water content as a solvent was adjusted to take into account coating performance, viscosity, and solid content. The viscosity of the resulting slurry composition was adjusted to 5,000 to 6,000 cps.

[0200] At this time, the adhesives prepared in Table 1 above were used as adhesives.

[0201] <Preparation of Negative Electrode Slurry of Example 3>

[0202] A negative electrode composition was prepared using pure Si with an average particle size (D50) of 3.5 μm as the silicon-containing active material, and Super-P black and SWCNT (Super-P:SWCNT weight ratio of 1:0.005) as the conductive material. The active material, conductive material, and binder were mixed at a weight ratio of 85:5:10. The water content of the solvent was adjusted to take into account coating performance, viscosity, and solid content. The viscosity of the resulting slurry composition was adjusted to 5,000 to 6,000 cps.

[0203] At this time, the adhesive of Example 3 prepared in Table 1 above was used as the adhesive.

[0204] <Battery Manufacturing and Battery Performance Evaluation>

[0205] The negative electrode slurries of Examples 1 to 4 and Comparative Examples 1 to 6 were coated on a copper foil having a thickness of 18 μm and dried. An active material layer having a thickness of 50 μm was formed on one surface of the copper foil, and a hole was punched on a circle having a diameter of 14 Φ to produce an electrode (negative electrode) for testing. A metal lithium foil having a thickness of 0.3 mm was used as the positive electrode, a porous polyethylene sheet having a thickness of 0.1 mm was used as the separator, and a solution obtained by dissolving LiPF6 as a lithium salt at a concentration of about 1 mol / L in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 was used as the electrolyte.

[0206] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to produce a coin cell having a thickness of 2 mm and a diameter of 32 mm for evaluation. The evaluation results are shown in Table 2 below.

[0207] [Table 2]

[0208]

[0209] -Initial efficiency (%): The coin cell was charged at a constant current of 0.05C until the voltage became 0.01V, and discharged at a constant current of 0.05C until the voltage became 1.5V, thereby obtaining the discharge capacity and initial efficiency, respectively, and expressed as a value of (discharge capacity / charge capacity)×100(%).

[0210] -Capacity retention rate (%): The coin cell was charged at a constant current of 0.05C until the voltage became 0.01V, discharged at a constant current of 0.05C until the voltage became 1.5V, and then cycled at a constant current of 0.2C within the same voltage range as above to perform a capacity retention test, thereby calculating the capacity retention rate based on 30 cycles.

[0211] -Thickness increase rate (%): The thickness value (X1) of the negative electrode active material layer in the prepared coin battery was measured, and the battery was charged at a constant current of 0.05C until the voltage became 0.01V, discharged at a constant current of 0.05C until the voltage became 1.5V, and then the cycle characteristics were performed at a constant current of 0.2C within the same voltage range as above, thereby measuring the thickness value (X2) of the negative electrode active material layer in the coin battery after 30 cycles.

[0212] The above Examples 1 to 4 correspond to the case of using the negative electrode binder according to the present disclosure. Thus, it can be confirmed that even when using a negative electrode active material (particularly a silicon-containing active material) that has a large volume expansion due to charge / discharge, volume expansion and contraction can be suppressed, and the thickness change due to electrode swelling (swelling) can be minimized, and therefore, the life performance of the lithium secondary battery is excellent.

[0213] Specifically, it was confirmed that in order to partially crosslink the linear polymer, a specific amount of a compound containing diacrylamide or diacrylate was included to form a partially crosslinked structure, resulting in little change in electrode thickness during charge and discharge due to the partially crosslinked structure of the binder itself, and improved capacity retention during life evaluation.

[0214] In particular, in the case of Example 3 above, a negative electrode to which 100% Si is applied is used as the negative electrode active material. In the case of pure silicon, since the volume expansion with charge and discharge is very serious, it is difficult to apply it universally. However, it can be confirmed that due to the inclusion of a specific binder according to the contents of the present disclosure, its initial efficiency is better than the initial efficiencies of the other Examples 1, 2, and 4 above. Although the use of pure Si particles also increases the thickness due to material characteristics compared to other Examples 1 and 2, by applying the binder of the contents of the present disclosure, the thickness increase rate is in the range of 0% to 15%, and in this case, it corresponds to a level that does not cause problems when driving the negative electrode. That is, it can be confirmed that the negative electrode of Example 3 is able to maximize the capacity characteristics while easily controlling the volume expansion.

[0215] Comparative Examples 1 and 2 do not contain monomer units containing α,β-unsaturated nitrile, or compounds containing diacrylamide or diacrylate. In these cases, it was confirmed that the initial efficiency was similar to that of the respective Examples, but the binder was unable to control the volume expansion of the silicon-containing active material and therefore failed to function as a binder.

[0216] Comparative Examples 3 to 5 above contain the four components of the negative electrode binder polymer according to the present disclosure, but their contents vary. In these cases, it was also confirmed that in Comparative Examples 1 and 2, the volume expansion of the silicon-containing active material was not controlled, the conduction path was destroyed, and thus the battery performance was reduced.

[0217] It was observed that Comparative Example 6 included a monomer unit containing a hydroxyalkyl (meth)acrylate. When a monomer unit containing a hydroxyalkyl (meth)acrylate was used, it was confirmed that the initial efficiency was similar to that of each Example, but the binder could not control the volume expansion of the silicon-containing active material, and thus the binder function could not be fully exerted.

Claims

1. A negative electrode composition comprising: Anode binder polymer; negative electrode active material; and negative electrode conductive material; The negative electrode binder polymer is composed of repeating units derived from the following components: (Meth)acrylamide; an unsaturated carboxylic acid selected from (meth)acrylic acid, itaconic acid, fumaric acid, crotonic acid and maleic acid, or a salt thereof; Acrylonitrile; and Diacrylamide or diacrylate; and The negative electrode composition includes: based on 100 parts by weight of the negative electrode binder polymer, 40 parts by weight or more and 80 parts by weight or less of (meth)acrylamide, 15 parts by weight or more and 40 parts by weight or less of the unsaturated carboxylic acid or its salt, 1 part by weight or more and less than 30 parts by weight of acrylonitrile, and 0.1 parts by weight or more and 15 parts by weight or less of the diacrylamide or diacrylate. 2 . The negative electrode composition according to claim 1 , wherein the diacrylamide or diacrylate is at least one selected from alkyldiacrylamide, oxidized alkyldiacrylamide, or oxidized alkyldiacrylate. 3 . The negative electrode composition according to claim 1 , wherein a molar ratio of the (meth)acrylamide to the unsaturated carboxylic acid or the salt thereof is 1:0.1 to 1:0.

6. 4 . The negative electrode composition of claim 1 , wherein the negative electrode binder polymer is present in an amount of 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition. 5 . The negative electrode composition according to claim 1 , wherein the negative electrode binder polymer has a weight average molecular weight of 100,000 g / mol or more and 3,000,000 g / mol or less. 6 . The negative electrode composition according to claim 1 , wherein the negative electrode conductive material comprises at least one selected from the group consisting of a point-like conductive material, a plane-like conductive material, and a line-like conductive material. 7 . The negative electrode composition of claim 1 , wherein the negative electrode active material comprises at least one selected from the group consisting of a silicon-containing active material and a carbon-containing active material.

8. The negative electrode composition according to claim 7, wherein the negative electrode active material comprises the silicon-containing active material, and the silicon-containing active material comprises at least one selected from the group consisting of SiO with x = 0 x and SiO with 0 < x < 2 x , and the SiO with x = 0 x is present in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-containing active material.

9. The negative electrode composition according to claim 1, wherein the negative electrode active material consists of a silicon-containing active material, and the silicon-containing active material includes at least one selected from the group consisting of SiO with x = 0 x and SiO with 0 < x < 2 x , and the SiO with x = 0 x is present in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-containing active material. 10 . The negative electrode composition according to claim 9 , wherein the average particle size D50 of the silicon-containing active material is 5 μm to 10 μm. 11 . The negative electrode composition according to claim 1 , wherein the negative electrode conductive material comprises a dot-shaped conductive material and a linear conductive material, and a ratio of the dot-shaped conductive material to the linear conductive material is 1:0.001 to 1:0.

05. 12 . The negative electrode composition of claim 1 , wherein the negative electrode active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

13. A negative electrode for a lithium secondary battery, comprising: negative electrode current collector; and A negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 12 on at least one surface of the negative electrode current collector. 14 . The negative electrode for a lithium secondary battery according to claim 13 , wherein the thickness of the negative electrode current collector is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

15. The negative electrode for a lithium secondary battery according to claim 13, wherein the thickness variation rate of the negative electrode active material layer satisfies the following formula 1: [Formula 1] 0%≤[(X2-X1) / X1]×100(%)≤15% In formula 1, X1 is the thickness of the negative electrode active material layer of the negative electrode for the lithium secondary battery at 0 cycles; and X2 is the thickness of the negative electrode active material layer of the negative electrode for a lithium secondary battery after 30 cycles.

16. A lithium secondary battery comprising: positive electrode; The negative electrode for a lithium secondary battery according to claim 13; a separator between the positive electrode and the negative electrode; and electrolytes.

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