Electrode composition for lithium secondary battery, electrode slurry, electrode, and lithium secondary battery

Abstract

This application relates to an electrode composition for a lithium secondary battery, an electrode slurry containing the same, an electrode, and a lithium secondary battery, which include an electrode active material, a conductive material, and a binder, wherein the binder is a copolymer of a (meth)acrylamide monomer, a (meth)acrylic acid monomer, an acrylonitrile monomer, and a metal-substituted (meth)acrylic acid monomer and satisfies specific formulas (I) to (III). According to this application, the problem of volume expansion can be solved when charging and discharging are repeated.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0184423 filed with the Korean Intellectual Property Office on December 26, 2022, and Korean Patent Application No. 10-2023-0175688 filed with the Korean Intellectual Property Office on December 6, 2023, and all of its contents are included herein.

[0002] This specification relates to an electrode composition for a lithium secondary battery, an electrode slurry, an electrode, and a lithium secondary battery.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the field most actively studied is the field of power generation and power storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage area is showing a trend of increasing more and more.

[0005] On the other hand, with the development of technologies related to mobile devices and the increase in demand, the demand for secondary batteries has been rapidly increasing. Therefore, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharge rate have been commonly used and widely used. Thus, in order to manufacture an electrode with high energy density per unit volume as an electrode for a high-capacity lithium secondary battery, active research is being conducted.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. In particular, the negative electrode may include a negative electrode active material, and silicon-based particles having a large charge and discharge capacity can be used as the negative electrode active material.

[0007] In particular, recently, with the demand for secondary batteries having high-energy electrodes, as an anode active material, Si / C or SiO having a capacity more than 10 times greater than that of graphite-based materials x (0 < x < 2) and other silicon-based compounds are used together to increase the capacity, and research on this method is being actively conducted. However, in the case of silicon-based compounds, compared with conventional graphite-based materials, during the repeated charge and discharge process, the volume expands due to the generation of hydrogen gas, blocking the conduction path, and therefore, there is a problem of degrading battery characteristics.

[0008] In order to solve the volume expansion during the repeated charge and discharge process described above, research on the composition of the binder has also been conducted, and as a result, research on binder polymers having strong stress has been carried out. In particular, attempts have been made to change the composition and content of the binder polymer.

[0009] In addition, in order to ensure the conductivity of the anode, the secondary battery further includes a conductive material. Conventionally, carbon black etc. have been mainly used, but in order to improve the capacity of the secondary battery, single-walled carbon nanotubes (SWCNT) with a thin and long shape are used.

[0010] To solve the above problems, various solutions are being discussed. As one of the solutions, it is necessary to explore a solution that can easily adjust the physical properties of the binder by changing the type and / or content of the components constituting the binder so that the binder has strong stress.

Summary of the Invention

Problems to be Solved by the Invention

[0011] The inventors of the present invention have found that by including a (meth)acrylamide monomer in a predetermined content range as a main component of the binder, the glass transition temperature (Tg) value of the binder can be easily adjusted, and thereby, the electrode slurry, electrode, and lithium secondary battery including the binder in the future can ensure high strength, excellent binding property and flexibility, and high electrode density, and solve the above problems.

[0012] Furthermore, the inventors of the present invention have attempted to improve the performance through various aspects, such as including a silicon-based active material as the electrode active material to improve the capacity, using single-walled carbon nanotubes as the conductive material to further improve the capacity of the secondary battery, using a water-based binder with high dispersibility as the binder to improve the compatibility of the single-walled carbon nanotubes, and adjusting the pH of the binder within a predetermined range to prevent swelling during repeated charging and discharging processes of the electrode, thereby completing the present invention.

[0013] Accordingly, the present application aims to provide an electrode composition for a lithium secondary battery, an electrode slurry, an electrode, and a lithium secondary battery including the above technical features.

Means for Solving the Problems

[0014] One embodiment of the present specification is an electrode composition for a lithium secondary battery including an electrode active material, a conductive material, and a binder, wherein the binder is a copolymer of a (meth)acrylamide monomer, a (meth)acrylic acid monomer, a (meth)acrylonitrile monomer, and a metal-substituted (meth)acrylic acid monomer, and satisfies the following formulas (I) to (III). 1 ≦ [AM] / ([AA-H] + [AA-M]) ≦ 10 - Formula (I) 0.01 ≦ [AA-H] / ([AA-H] + [AA-M]) ≦ 0.5 - Formula (II) 2 ≦ ([AM] + [AA-H] + [AA-M]) / [AN] ≦ 10000 - Formula (III) In the above formulas (I) to (III), Based on 100 parts by weight of the binder, [AM] is the part by weight of the (meth)acrylamide monomer, [AA-H] is the part by weight of the (meth)acrylic acid monomer, [AA-M] is the part by weight of the metal (M)-substituted (meth)acrylic acid monomer, [AN] is the part by weight of the (meth)acrylonitrile monomer.

[0015] In addition, one embodiment of the present specification provides an electrode slurry for a lithium secondary battery, which includes the electrode composition for a lithium secondary battery and a solvent.

[0016] In addition, one embodiment of the present specification provides an electrode for a lithium secondary battery, which includes an electrode active material layer containing the electrode slurry for a lithium secondary battery on one or both surfaces of the electrode current collector layer.

[0017] Finally, one embodiment of the present specification provides a lithium secondary battery, which includes a first electrode, a second electrode, a separator provided between the first electrode and the second electrode, and an electrolyte, wherein either one of the first electrode and the second electrode is the electrode for a lithium secondary battery.

Advantages of the Invention

[0018] The electrode composition for a lithium secondary battery according to the present application includes an electrode active material having a large charge and discharge capacity, and can prevent the problem of volume expansion due to repeated charge and discharge, has excellent phase stability, and further improves the battery life.

Modes for Carrying Out the Invention

[0019] Before describing the present invention, first, some terms are defined.

[0020] In the present specification, when a certain part "includes" a certain component, this means that, unless otherwise specified, it does not exclude other components, but may further include other components.

[0021] In the present specification, "p~q" means "p or more and q or less".

[0022] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in the polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0023] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless explicitly stated as "homopolymer".

[0024] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the polystyrene equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as the standard substance. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0025] Hereinafter, a detailed description will be given so that a person having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0026] <Electrode composition for lithium secondary battery> One embodiment of this specification is an electrode composition for a lithium secondary battery, comprising an electrode active material, a conductive material, and a binder, wherein the binder is a copolymer of a (meth)acrylamide monomer, a (meth)acrylic acid monomer, a (meth)acrylonitrile monomer, and a metal-substituted (meth)acrylic acid monomer, and satisfies the following formulas (I) to (III), and provides an electrode composition for a lithium secondary battery. 1 ≦ [AM] / ([AA-H] + [AA-M]) ≦ 10 - Formula (I) 0.01 ≦ [AA-H] / ([AA-H] + [AA-M]) ≦ 0.5 - Formula (II) 2 ≦ ([AM] + [AA-H] + [AA-M]) / [AN] ≦ 10,000 - Formula (III) In the above formulas (I) to (III), Based on 100 parts by weight of the binder, [AM] is the part by weight of the (meth) acrylamide monomer, [AA-H] is the part by weight of the (meth) acrylic acid monomer, [AA-M] is the part by weight of the metal (M) - substituted (meth) acrylic acid monomer, [AN] is the part by weight of the (meth) acrylonitrile monomer.

[0027] According to the above embodiment, when the binder is according to the above formulas (I) to (III), the shrinkage and expansion due to charge / discharge of the battery can be suppressed, and the life performance can be improved.

[0028] According to an embodiment of the present invention, the metal (M) may be Li, Na, Ca, or a combination thereof.

[0029] In an embodiment of the present specification, based on 100 parts by weight of the binder, the content of the (meth) acrylamide monomer may be 40 parts by weight or more and 80 parts by weight or less.

[0030] The electrode composition for a lithium secondary battery according to the above embodiment, by including the content of (meth) acrylamide within the above range, the shrinkage and expansion due to charge / discharge of the battery can be further suppressed, and the life performance can be further improved.

[0031] In an embodiment of the present specification, the glass transition temperature (Tg) of the binder may be 125 °C or more and 150 °C or less.

[0032] The electrode composition for a lithium secondary battery according to the above embodiment, by controlling Tg within the above range, the shrinkage and expansion due to charge / discharge of the battery can be further suppressed, and the life performance can be further improved.

[0033] As used herein, the term "(meth)acrylic" may include methacrylic or acrylic.

[0034] As used herein, based on 100 parts by weight of the binder, the content of the (meth)acrylamide may be about 40 parts by weight or more, about 45 parts by weight or more, or about 50 parts by weight or more, or may be about 80 parts by weight or less, about 75 parts by weight or less, or about 70 parts by weight or less.

[0035] As used herein, for the production of the copolymer, a polymerization initiator is used. As an example of the polymerization initiator, ammonium persulfate may be used, but is not limited thereto.

[0036] As used herein, the binder containing a plurality of compounds having a specific ratio (expressed in parts by weight or weight ratio) can mean including each compound (e.g., (meth)acrylamide, (meth)acrylic acid, (meth)acrylonitrile, and metal-substituted (meth)acrylic acid) as a monomer of the binder polymer.

[0037] In one embodiment of the present specification, the electrode active material may be 60 parts by weight or more based on 100 parts by weight of the electrode composition for a lithium secondary battery.

[0038] In one embodiment of the present specification, the electrode active material may be included in an amount of about 60 parts by weight or more, preferably about 65 parts by weight or more, more preferably about 70 parts by weight or more, or may be included in an amount of about 95 parts by weight or less, preferably about 90 parts by weight or less, based on 100 parts by weight of the electrode composition for a lithium secondary battery.

[0039] In one embodiment of the present specification, the electrode active material may include one or more selected from the group consisting of a silicon-based active material and a carbon-based active material.

[0040] In this specification, the silicon-based active material has a capacity more than 10 times higher than that of the carbon-based active material. Thus, when the silicon-based active material is applied to an electrode, particularly a negative electrode, an electrode with a high level of energy density can be realized even with a thinner thickness than when the carbon-based active material is included alone.

[0041] In another embodiment of this specification, when the electrode active material is composed of a silicon-based active material and a carbon-based active material, the composition ratio between the silicon-based active material and the carbon-based active material can be in the range of 2:98 to 30:70.

[0042] The electrode active material according to the above embodiment can additionally provide the effect of having a carbon-based active material as the main component, with less volume expansion of the electrode during charge and discharge and excellent conductive connectivity within the electrode.

[0043] In one embodiment of this specification, the silicon-based active material may include one or more of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys.

[0044] In this specification, the electrode active material includes silicon particles, which may exist in, for example, crystalline or amorphous forms. Specifically, the silicon particles may preferably be spherical particles, but are not limited thereto.

[0045] In one embodiment of this specification, the electrode composition for the lithium secondary battery is a negative electrode composition. Thus, the silicon-based active material, the conductive material, and the binder may all be for the negative electrode composition.

[0046] Even when using a silicon-based active material with a significantly high capacity within the above range, the negative electrode composition can include it within the above range using a specific conductive material and binder that can control the volume expansion rate during the charge / discharge process without degrading the performance of the negative electrode, and has the characteristic of excellent output characteristics during charging and discharging.

[0047] In this specification, the SiO x In the case of SiO2 where x is 2, it is not included. This SiO2 does not react with lithium ions and cannot store lithium. Therefore, x is preferably within the range of the above-described embodiments.

[0048] In this specification, the silicon-based active material may be Si / C or Si composed of a composite of Si and C.

[0049] In this specification, two or more of the above-described silicon-based active materials may be mixed and used.

[0050] In this specification, in some cases, in addition to the above-described silicon-based active material, a carbon-based active material may be further included.

[0051] Generally, it is known that the silicon-based active material has a capacity 10 times or more higher than that of the carbon-based active material. Thus, when applying the silicon-based active material to an electrode, particularly a negative electrode, it is expected that an electrode with a high level of energy density can be realized even with a thin thickness.

[0052] In one embodiment of this specification, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be included in an amount of 70 parts by weight or more.

[0053] In another embodiment of this specification, the silicon-based active material, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, or may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0054] In yet another embodiment, the average particle size (D50) of the silicon-based active material may be 3 μm to 10 μm.

[0055] In this specification, "Dn" means the particle size distribution and represents the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the particle size distribution may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern due to the particle size is measured to calculate the particle size distribution.

[0056] In one embodiment of the present invention, the carbon-based active material may include one or more selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0057] Conventionally, it has been common to use only a carbon-based active material as the negative electrode active material. However, recently, as the demand for high-capacity batteries has increased, in order to increase the capacity, attempts have been increasing to use a silicon-based compound or to mix a silicon-based active material with the carbon-based active material for use.

[0058] In another embodiment, the conductive material may be 0.3 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the electrode composition for a lithium secondary battery.

[0059] In another embodiment, the conductive material may be contained in an amount of 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, more preferably 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the electrode composition.

[0060] In another embodiment, the conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0061] In yet another embodiment, the conductive material may be a mixture of a dot-shaped conductive material and a linear conductive material.

[0062] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, and means a dot-shaped or spherical conductive material having conductivity without inducing a chemical change. Specifically, the dot-shaped conductive material may 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, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may contain carbon black in terms of realizing high conductivity and excellent dispersibility.

[0063] In this specification, the planar conductive material can play a role of increasing the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk-type conductive material. Examples of the planar conductive material may include at least any one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0064] In this specification, the linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube units. Specifically, here, the "bundle type" refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in parallel or twisted with substantially the same orientation along the longitudinal axis of the carbon nanotube unit, unless otherwise specified. The carbon nanotube unit has a cylindrical shape with a nanosize diameter and an sp2 bonding structure for the graphite plane (graphite sheet). At this time, depending on the angle and structure by which the graphite plane is wound, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotube can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotube, and can smoothly form a conductive network in the negative electrode, improving the conductivity of the negative electrode.

[0065] In another embodiment, the conductive material may be a negative electrode conductive material.

[0066] In this specification, the negative electrode conductive material is applied to the negative electrode and has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material, it plays a role of controlling the contact points between silicon-based active materials with a very large volume expansion of the electrode during charging and discharging, and the positive electrode conductive material plays a role of imparting partial conductivity while providing a buffering action as a buffer during rolling. Therefore, the negative electrode conductive material and the positive electrode conductive material have completely different configurations and roles.

[0067] In one embodiment of the present invention, the binder may be 3 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the electrode composition for the lithium secondary battery.

[0068] In another embodiment, the binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or 3 parts by weight or more, preferably 5 parts by weight or more, based on 100 parts by weight of the electrode composition for a lithium secondary battery.

[0069] In another embodiment, the binder may be a negative electrode binder.

[0070] According to the embodiment, when a Si-based compound is used for the negative electrode as compared with a conventional carbon-based negative electrode, it has a feature of excellent bonding strength with a conductive material and a binder.

[0071] In one embodiment of the present invention, the binder may be an aqueous binder.

[0072] In one embodiment of the present invention, the binder may be a copolymer further including at least one selected from the group consisting of a (meth)acrylic acid monomer, a (meth)acrylonitrile monomer, and a metal-substituted (meth)acrylic acid monomer.

[0073] According to one embodiment of the present invention, the pH of the binder may be 4.5 or more and 7.5 or less. For example, the pH of the binder may be 4.5 or more, 4.6 or more, or 4.7 or more, or 7.5 or less, 7.4 or less, or 7.3 or less.

[0074] In this specification, the hydrogen ion concentration (pH) is measured using a Methler seven compact pH meter.

[0075] In another embodiment, the weight average molecular weight of the binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0076] <Electrode slurry for a lithium secondary battery> In one embodiment of the present invention, there is provided an electrode composition for a lithium secondary battery and an electrode slurry containing a solvent.

[0077] In still another embodiment of the present invention, the solvent includes those known in the art. For example, it may be distilled water or NMP.

[0078] The electrode slurry of the present invention is a negative electrode slurry, and thus the electrode composition may be for the negative electrode slurry.

[0079] In some cases, in addition to appropriately adjusting the average particle diameter (D50) of the silicon-based active material, by appropriately adjusting the specific surface area of the particles, if the viscosity of the electrode slurry is controlled within an appropriate range, the dispersion of the components in the slurry (e.g., conductive material, binder, silicon-based active material, etc.) can be improved. As a result, the contact area between the components can be improved, the conductive network can be sustained, the capacity retention rate can be increased, and the non-uniformity phenomenon of the current density during charge / discharge can also be prevented.

[0080] Also, in some cases, the viscosity of the electrode slurry can be adjusted to be 5000 Cps to 6000 Cps. Thereby, when the electrode slurry is coated on one or both sides of the electrode current collector layer in the future, it has excellent coating properties and storage properties.

[0081] <Electrode for lithium secondary battery> Still another embodiment of the present invention provides an electrode for a lithium secondary battery, including an electrode current collector layer and an electrode active material layer coated with the electrode slurry on one or both sides of the electrode current collector layer.

[0082] In still another embodiment of the present invention, the electrode is a negative electrode, and thus the electrode current collector layer, the electrode slurry, and the electrode active material layer are all for the negative electrode.

[0083] In this specification, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Also, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0084] In one 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 layer 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.

[0085] However, the thickness may vary diversely depending on the type and use of the negative electrode used, and is not limited thereto.

[0086] <Lithium secondary battery> One embodiment of the present invention is a lithium secondary battery including a first electrode, a second electrode, a separator provided between the first electrode and the second electrode, and an electrolyte, wherein either one of the first electrode or the second electrode is an electrode for the lithium secondary battery.

[0087] The lithium secondary battery according to the above embodiment may particularly include the electrode for the lithium secondary battery described above.

[0088] Specifically, the first electrode may be a negative electrode and the second electrode may be a positive electrode, or the first electrode may be a positive electrode and the second electrode may be a negative electrode.

[0089] The secondary battery according to an embodiment of the present specification may particularly include the negative electrode for a 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, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0090] 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 the positive electrode active material.

[0091] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0092] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where 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) represented by Ni-site type lithium nickel oxide; chemical formula LiMn2-c3 M c3 O2 (where 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 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn), or lithium manganese composite oxides represented by, but not limited to, LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions. The positive electrode may be Li metal (Li-metal).

[0093] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0094] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be constructed, it can be used without particular limitation as long as it has electron conductivity without causing chemical changes. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more thereof may be used.

[0095] Further, the positive electrode binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0096] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a secondary battery can be used without particular limitation. In particular, those with low resistance to the ion migration of the electrolyte and excellent moisture retention ability of the electrolyte solution are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, a coated separator containing a ceramic component or a polymer substance to ensure heat resistance or mechanical strength may be used, and it may be selectively used in a single-layer or multilayer structure.

[0097] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0098] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0099] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0100] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and can preferably be used because they can well dissociate lithium salts. By mixing linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate with such cyclic carbonates in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so it can be more preferably used.

[0101] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0102] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0103] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0104] <Method for manufacturing a lithium secondary battery> In still another embodiment of the present invention, a step of mixing a composition for a lithium secondary battery and a solvent to produce an electrode slurry for a lithium secondary battery; a step of applying the electrode slurry for a lithium secondary battery to one or both surfaces of an electrode current collector layer; and a step of drying the electrode current collector layer coated with the electrode slurry for a lithium secondary battery, wherein the composition for a lithium secondary battery, the solvent, the electrode current collector layer, and the application are as described above.

[0105] In this specification, known methods such as air drying are employed for drying.

[0106] In this specification, steps such as rolling applied after the above steps are as known in the art.

Examples

[0107] Hereinafter, in order to assist in the understanding of the present invention, preferred examples are presented. However, the following examples are merely illustrative of the present description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the scope of the technical idea, and such variations and modifications naturally belong to the scope of the claims.

[0108] Production Example. Production of Binder <Production Examples 1 to 3 and Comparative Production Examples 1 to 3> Into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, as described in Table 1 below, each monomer (i.e., (meth)acrylamide (AM: (meth)acryl amide, using a 50% aqueous solution), (meth)acrylic acid (AA-H: (meth)acrylic acid, using an 80% aqueous solution), (meth)acrylonitrile (AN: (meth)acrylonitrile), and metal (M)-substituted (meth)acrylic acid (AA-M: Metal substituted (meth)acrylic acid)) was mixed at the following contents (based on weight ratio), and after adding ammonium persulfate as a polymerization initiator, the reaction was carried out at 75 ° C for 8 hours to produce an aqueous polymer solution.

[0109] Thereafter, an aqueous solution of 0.1 mol / L NaOH was added dropwise to the aqueous polymer solution to produce an aqueous binder having a desired pH (see Table 2).

[0110] [Table 1]

[0111] However, formula (I): [AM] / ([AA-H] + [AA-M]) Formula (II): [AA-H] / ([AA-H] + [AA-M]) Formula (III): ([AM] + [AA-H] + [AA-M]) / [AN] In the above formulas (I) to (III), based on 100 parts by weight of the binder, [AM] is the part by weight of the (meth)acrylamide monomer, [AA-H] is the part by weight of the (meth)acrylic acid monomer, [AA-M] is the part by weight of the metal (M)-substituted (meth)acrylic acid monomer, and [AN] means the part by weight of the (meth)acrylonitrile monomer.

[0112] Example. Production of Electrode Slurry Example 1. Si with D50 = 5.2 μm was used as the negative electrode active material, and three types of carbon black (Super C65, Timcal), artificial graphite (SFG6L, Timcal), and SWCNT were used as the conductive materials. The aqueous binder of Production Example 1 was mixed at a ratio of negative electrode active material:carbon black:artificial graphite:SWCNT:aqueous binder = 82:3:6.3:0.7:12 (based on weight ratio) to prepare an electrode composition.

[0113] Water was added as a solvent to produce an electrode slurry. Here, the water content was adjusted in consideration of coatability, viscosity, and solid content. The viscosity of the obtained electrode slurry was adjusted to be 5000 Cps to 6000 Cps.

[0114] Examples 2 and 3. An electrode slurry was produced in the same manner as in Example 1, except that the aqueous binders of Production Examples 2 and 3 were used respectively.

[0115] Example 4. An electrode slurry was produced in the same manner as in Example 1, except that artificial graphite (QCG-N2, Shanshan Co., Ltd.): SiO (E82, Daito Electronics Co., Ltd.) was used at a ratio of 9:1 as the negative electrode active material.

[0116] Example 5. An electrode slurry was produced in the same manner as in Example 1, except that artificial graphite: SiC (SD5100A, Sila nano Co., Ltd.) was used at a ratio of 9:1 as the negative electrode active material.

[0117] Comparative Examples 1 to 3. An electrode slurry was produced in the same manner as in Example 1, except that the aqueous binders of Comparative Production Examples 1 to 3 were used respectively.

[0118] Comparative Example 4. An electrode slurry was produced in the same manner as in Comparative Example 1, except that artificial graphite: SiO was used at a ratio of 9:1 as the negative electrode active material.

[0119] Comparative Example 5. An electrode slurry was produced in the same manner as in Comparative Example 1, except that artificial graphite: SiC was used at a ratio of 9:1 as the negative electrode active material.

[0120] Experimental Example. Experimental Example 1. Measurement of glass transition temperature (Tg) of binder The glass transition temperatures (Tg) of the binders obtained in Production Examples 1 to 3 and Comparative Production Examples 1 to 3 were measured by heating at intervals of 5°C from -50°C to 180°C by the DSC measurement method. The results are as shown in Table 2 below.

[0121] Experimental Example 2. Measurement of binder pH Using the seven compact pH meter of Methler, the pH of the binders obtained in Production Examples 1 to 3 and Comparative Production Examples 1 to 3 was measured respectively. The results are as described in Table 2 below.

[0122]

Table 2

[0123] According to Table 2 above, based on 100 parts by weight of the binder, in Production Examples 1 to 3 where the content of the (meth)acrylamide monomer is 40 parts by weight or more and 80 parts by weight or less, the glass transition temperature of the binder belongs to the range of 125°C or more and 150°C or less. However, in Comparative Production Examples 1 to 3 where the content of the (meth)acrylamide monomer is less than 40 parts by weight or exceeds 80 parts by weight, the glass transition temperature is less than 120°C or exceeds 150°C.

[0124] Experimental Example 3. Manufacture of battery and evaluation of battery characteristics The electrode slurries of Examples 1 to 5 and Comparative Examples 1 to 5 were respectively coated on a copper foil with a thickness of 15 μm and dried to form an electrode active material layer with a thickness of 48 μm on one side of the copper foil, and then punched into a circular shape with a diameter of 14Φ (mm) to manufacture a test electrode (negative electrode). A metal lithium foil with a thickness of 0.3 mm was used as the positive electrode, a porous polyethylene sheet with a thickness of 0.1 mm was used as the separator, and as the electrolyte, a solution in which LiPF6 was dissolved at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 was used.

[0125] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to manufacture an evaluation coin cell with a thickness of 2 mm and a diameter of 32 mm. The coin cell was charged at a constant current of 0.05C until the voltage reached 0.01V, and discharged at a constant current of 0.05C until the voltage reached 1.5V to obtain the discharge capacity and initial efficiency. Then, the cycle characteristics were carried out at a constant current of 0.2C in the same voltage range as above to perform a capacity retention rate test, and the results are shown in Table 3 below.

[0126]

Table 3

[0127] As shown in Table 3 above, for the electrode slurries of Examples 1 to 5, a binder having a (meth)acrylamide monomer content of 40 parts by weight or more and 80 parts by weight or less (each having a glass transition temperature of 125°C or more and 150°C or less) was used based on 100 parts by weight of the binder, and the batteries manufactured therefrom had a capacity retention rate of 79% or more. In contrast, for the electrode slurries of Comparative Examples 1 to 5, a binder having a (meth)acrylamide monomer content of less than 40 parts by weight or exceeding 80 parts by weight (each not satisfying the range of a glass transition temperature of 125°C or more and 150°C or less) was used based on 100 parts by weight of the binder, and the batteries manufactured therefrom had a capacity retention rate of less than 70%.

Claims

1. An electrode composition for a lithium secondary battery comprising an electrode active material, a conductive material, and a binder, wherein the binder is a copolymer of a (meth)acrylamide monomer, a (meth)acrylic acid monomer, a (meth)acrylonitrile monomer, and a metal-substituted (meth)acrylic acid monomer, and satisfies the following formulas (I) to (III): An electrode composition for a lithium secondary battery: 1 ≤ [AM] / ([AA-H] + [AA-M]) ≤ 10 - Formula (I) 0.01 ≤ [AA-H] / ([AA-H] + [AA-M]) ≤ 0.5 - Formula (II) 2 ≤ ([AM] + [AA-H] + [AA-M]) / [AN] ≤ 10000 - Formula (III) In the above formulas (I) to (III), Based on 100 parts by weight of the binder, [AM] is the part by weight of the (meth)acrylamide monomer, [AA-H] is the part by weight of the (meth)acrylic acid monomer, [AA-M] is the part by weight of the metal (M)-substituted (meth)acrylic acid monomer, [AN] is the part by weight of the (meth)acrylonitrile monomer.

2. The electrode composition for a lithium secondary battery according to claim 1, wherein the content of the (meth)acrylamide monomer is 40 parts by weight or more and 80 parts by weight or less based on 100 parts by weight of the binder.

3. The electrode composition for a lithium secondary battery according to claim 1, wherein the glass transition temperature (Tg) of the binder is 125°C or higher and 150°C or lower.

4. The electrode composition for a lithium secondary battery according to claim 1, wherein the electrode active material is 60 parts by weight or more based on 100 parts by weight of the electrode composition for a lithium secondary battery.

5. The electrode composition for a lithium secondary battery according to claim 1, wherein the electrode active material contains one or more selected from the group consisting of silicon-based active materials and carbon-based active materials.

6. The silicon-based active material is SiO ｘ (x=0), SiO ｘ 6. The electrode composition for a lithium secondary battery according to claim 5, comprising one or more of (0<x<2), SiC, and a Si alloy.

7. The electrode composition for a lithium secondary battery according to claim 5, wherein the carbon-based active material contains one or more selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

8. The electrode composition for a lithium secondary battery according to claim 1, wherein the conductive material contains one or more selected from the group consisting of dot-shaped conductive materials, planar conductive materials, and linear conductive materials.

9. The electrode composition for a lithium secondary battery according to claim 1, wherein the binder is an aqueous binder.

10. The electrode composition for a lithium secondary battery according to claim 1, wherein the pH of the binder is 4.5 or more and 7.5 or less.

11. An electrode slurry for a lithium secondary battery, comprising the electrode composition for a lithium secondary battery according to any one of claims 1 to 10 and a solvent.

12. An electrode current collector layer; and An electrode active material layer including the electrode slurry for a lithium secondary battery according to claim 11 on one or both surfaces of the electrode current collector layer; An electrode for a lithium secondary battery, comprising:

13. A lithium secondary battery including a first electrode, a second electrode, a separator provided between the first electrode and the second electrode, and an electrolyte, wherein either one of the first electrode and the second electrode is the electrode for a lithium secondary battery according to claim 12.

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