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

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2021-0180142, filed with the Korean Intellectual Property Office on December 15, 2021, the entire contents of which are incorporated herein by reference.

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

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

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

[0005] With technological advancements and increasing demand for mobile devices, the need for secondary batteries as an energy source has surged. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. Furthermore, methods for manufacturing high-density electrodes with even higher energy density per unit volume, used as electrodes in such high-capacity lithium-ion batteries, are being actively researched.

[0006] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode comprises a negative electrode active material that inserts and extracts lithium ions from the positive electrode, and silicon-based particles with high discharge capacity can be used as negative electrode active materials.

[0007] In particular, in response to the increasing demand for high-density energy batteries in recent years, there is active research into methods to increase capacity by using silicon-based compounds, such as Si / C and SiOx, which have a capacity 10 times higher than graphite-based materials, as negative electrode active materials. However, compared to commonly used graphite, silicon-based compounds, while possessing large capacity as high-capacity materials, undergo rapid volume expansion during charging, thereby disrupting the conductive path and degrading battery characteristics.

[0008] Therefore, to address the problems arising when using silicon-based compounds as anode active materials, the following measures have been discussed: measures for controlling the driving potential; measures for suppressing self-volume expansion, such as methods for additionally coating a thin film on the active material layer and methods for controlling the particle size of the silicon-based compound; or various measures to prevent the breakage of the conductive path. However, the above measures may actually further degrade the battery performance, thus limiting their application and restricting the commercialization of batteries with anodes containing high silicon-based compounds.

[0009] In particular, research is underway on binder compositions based on volume expansion, and studies are being conducted on using binder polymers with high stress to suppress the volume expansion of negative electrode active materials that undergo large volume changes during charging / discharging. However, these binder polymers alone have limitations in suppressing the increase in electrode thickness caused by the shrinkage and expansion of the negative electrode active material and the resulting performance degradation of lithium secondary batteries.

[0010] In addition, studies have been conducted to address the aforementioned issues by introducing crosslinking agents into the binder polymer. However, this method has a drawback: due to viscosity changes and phase stability issues associated with long-term battery storage, it is difficult to apply these studies to practical processes.

[0011] Therefore, it is necessary to study a negative electrode binder that can minimize the change in negative electrode thickness and thereby improve capacity retention, even when using negative electrode active materials that have undergone large volume expansion.

[0012] <List of References>

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

[0014] Technical issues

[0015] As a result of research on anode compositions that can suppress volume expansion and contraction of active materials during charging / discharging, minimize thickness changes caused by electrode expansion, and achieve excellent lifetime performance, it was found that when graphene oxide under specific conditions is used with a binder, volume changes of the electrode can be suppressed and capacity retention can be improved.

[0016] Therefore, this 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.

[0017] Technical solution

[0018] An exemplary embodiment of this specification provides a negative electrode composition comprising a negative electrode binder containing graphene oxide and one or more water-soluble macromolecular polymers; a negative electrode active material; and a negative electrode conductive material, wherein the graphene oxide has a lateral size of 0.3 μm or greater and 20 μm or less, and wherein the graphene oxide has a carbon (C) / oxygen (O) ratio of 0.5 or greater and 3.5 or less.

[0019] Another exemplary embodiment of the present invention provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer comprising a negative electrode composition according to the present application formed on one or both surfaces of the negative electrode current collector layer.

[0020] Another exemplary embodiment of the present invention provides a lithium secondary battery, 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 exemplary embodiment of the present invention has the following main characteristics: it contains graphene oxide in the negative electrode binder having a particle size (lateral size) of 0.3 μm or larger and 20 μm or smaller and a carbon (C) / oxygen (O) ratio of 0.5 or larger and 3.5 or smaller.

[0023] Therefore, even when using negative electrode active materials (especially silicon-based active materials) that undergo large volume expansion during charging / discharging, volume expansion and contraction can be suppressed, and thickness changes due to electrode swelling can be minimized, resulting in lithium secondary batteries with excellent lifespan performance.

[0024] That is, the negative electrode composition according to an exemplary embodiment of the present invention contains a silicon-based active material with high theoretical capacity as the negative electrode active material to improve capacity characteristics, and solves the problem of volume expansion during charging / discharging as a silicon-based active material by using a negative electrode binder containing specific graphene oxide according to the present application. Attached Figure Description

[0025] Figure 1 A laminated structure for a negative electrode of a lithium secondary battery according to an exemplary embodiment of this application is shown.

[0026] Figure 2 A laminated structure of a lithium secondary battery according to an exemplary embodiment of this application is shown.

[0027] <Figure Labels>

[0028] 10: Negative electrode current collector layer

[0029] 20: Negative electrode active material layer

[0030] 30: Partition

[0031] 40: Positive electrode active material layer

[0032] 50: Positive current collector layer

[0033] 100: Anode used in lithium secondary batteries

[0034] 200: Used as the positive electrode in lithium secondary batteries Detailed Implementation

[0035] Before describing the present invention, some terms will be defined.

[0036] When a part "includes", "contains", or "has" a component element in this specification, unless otherwise specifically described, this does not mean that another component element is excluded, but rather that another component element may be further included.

[0037] In this specification, "p to q" means the range of "p or greater and q or less".

[0038] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen adsorbed using Bel Japan's Belsorp-Mino II at liquid nitrogen temperature (77K). That is, in this application, BET specific surface area can refer to the specific surface area measured by the above method.

[0039] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point in the cumulative distribution of the number of particles according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative distribution of the number of particles according to particle size, D90 is the particle size at the 90% point in the cumulative distribution of the number of particles according to particle size, and D10 is the particle size at the 10% point in the cumulative distribution of the number of particles according to particle size. The particle size distribution can be measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S 3500) that measures the difference in diffraction patterns according to particle size when a laser beam passes through the particles. The particle size distribution is then calculated.

[0040] In this specification, the description "the polymer includes a monomer as a monomeric unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this specification, when the polymer includes a monomer, it is interpreted in the same way as when the polymer includes a monomer as a monomeric unit.

[0041] In this specification, it should be understood that the term "polymer" is used in a broad sense to include copolymers, unless otherwise explicitly stated as "homogeneous polymer".

[0042] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene conversion molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers with different degrees of polymerization (standard samples) as standard materials for measuring molecular weight. Unless otherwise specified, molecular weight in this specification refers to weight-average molecular weight.

[0043] In the following description, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can readily implement the present invention. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0044] An exemplary embodiment of this specification provides a negative electrode composition comprising: a negative electrode binder comprising graphene oxide and one or more water-soluble macromolecular polymers; a negative electrode active material; and a negative electrode conductive material, wherein the graphene oxide has a particle size (lateral size) of 0.3 μm or larger and 20 μm or smaller, and wherein the graphene oxide has a carbon (C) / oxygen (O) ratio of 0.5 or larger and 3.5 or smaller.

[0045] The negative electrode composition according to an exemplary embodiment of the present invention comprises a silicon-based active material having a high theoretical capacity as the negative electrode active material to improve capacity characteristics, and solves the problem of volume expansion during charging / discharging that is a problem for silicon-based active materials by using a negative electrode binder containing specific graphene oxide according to the present application.

[0046] In an exemplary embodiment of this application, the negative electrode binder may include graphene oxide and one or more water-soluble macromolecular polymers.

[0047] In an exemplary embodiment of this application, graphene oxide may have a lateral size of 0.3 μm or larger and 20 μm or smaller.

[0048] In another exemplary embodiment, the lateral size of the graphene oxide can be 0.3 μm or larger and 20 μm or smaller, preferably 0.5 μm or larger and 15 μm or smaller, more preferably 0.5 μm or larger and 10 μm or smaller, and can be within the range of 1 μm or larger and 10 μm or smaller.

[0049] By using graphene oxide with the aforementioned lateral dimensions, this application can achieve sufficient mechanical strength to function as an adhesive. Specifically, when the lateral dimensions of the graphene oxide are smaller than the lower limit of this range, the electrode connectivity is insufficient, and when the lateral dimensions exceed the upper limit of this range, the electrode itself does not possess sufficient mechanical strength.

[0050] In an exemplary embodiment of this application, the carbon (C) / oxygen (O) ratio of graphene oxide can be 0.5 or greater and 3.5 or less.

[0051] In another exemplary embodiment, the carbon (C) / oxygen (O) ratio of the graphene oxide can be 0.5 or greater and 3.5 or less, preferably 1.0 or greater and 3.0 or less, more preferably 1.5 or greater and 2.5 or less.

[0052] In an exemplary embodiment of this application, the carbon (C) / oxygen (O) ratio of graphene oxide can refer to the ratio of the number of carbon atoms and oxygen atoms contained in the entire graphene oxide.

[0053] Because graphene oxide satisfies the carbon / oxygen ratio requirement, the number of functional groups in the molecule is appropriate, resulting in excellent charge / discharge efficiency and excellent water dispersion stability. Specifically, when this ratio is below the lower limit of the range, the number of functional groups in the graphene oxide molecule increases, leading to a decrease in charge / discharge efficiency. When this ratio exceeds the upper limit of the range, water dispersion stability decreases, making it difficult for graphene oxide to achieve a uniform distribution in the anode composition.

[0054] Therefore, the negative electrode binder according to this application contains graphene oxide under the specific conditions described above, thereby suppressing volume expansion and contraction even when using negative electrode active materials (especially silicon-based active materials) that undergo large volume expansion during charging / discharging, minimizing thickness changes due to electrode swelling, and resulting in lithium secondary batteries with excellent lifespan performance.

[0055] That is, it can be confirmed that when the negative electrode binder contains graphene oxide that satisfies the above two conditions, the effect according to this application occurs.

[0056] In an exemplary embodiment of this application, the negative electrode binder may include one or more water-soluble macromolecular polymers.

[0057] In exemplary embodiments of this application, the water-soluble macromolecular polymer may specifically include one or more of the following groups: carboxymethyl cellulose and its derivatives, water-soluble polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), and polyacrylamide (PAM).

[0058] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein the water-soluble macromolecular polymer is a polymer of one or more monomers selected from the group consisting of: compounds containing (meth)acrylamide groups; unsaturated organic acids or salts of unsaturated organic acids; and α,β-unsaturated nitrile and (meth)acrylate hydroxyalkyl esters.

[0059] In an exemplary embodiment of this application, the negative electrode adhesive polymer may include a compound containing a (meth)acrylamide group.

[0060] In an exemplary embodiment of this application, (meth)acrylamide may include methacrylamide or acrylamide.

[0061] In exemplary embodiments of this application, unsaturated organic acids can be used without limitation, as long as they are organic acids that can be contained in the adhesive; specifically, acrylic acid can be used. In this case, the salt of the unsaturated organic acid can refer to a salt form containing ions in the unsaturated organic acid, which can also be used without limitation.

[0062] In an exemplary embodiment of this application, one or more monomers selected from the group consisting of α,β-unsaturated nitrile and (meth)acrylate hydroxyalkyl esters may be acrylonitrile.

[0063] In an exemplary embodiment of this application, the water-soluble macromolecular polymer may include a polymer resin having at least one carboxyl group.

[0064] In an exemplary embodiment of this application, some or all of the carboxyl groups may have the property of being affected by Li + Na + or K + The structure that is replaced.

[0065] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein the water-soluble macromolecular polymer has a weight-average molecular weight of 100,000 g / mol or greater and 3,000,000 g / mol or less.

[0066] In another exemplary embodiment, the weight-average molecular weight of the water-soluble macromolecular polymer may be in the range of 100,000 g / mol or greater and 3,000,000 g / mol or less, and preferably 200,000 g / mol or greater and 1,500,000 g / mol or less.

[0067] When the weight-average molecular weight of the water-soluble macromolecular polymer meets the above-mentioned range, as mentioned above, it exhibits excellent mechanical strength, and due to the high degree of intermolecular interaction, the electrode bonding force is excellent. Furthermore, when the above range is met, the viscosity of the negative electrode binder can be selected within an appropriate range; therefore, when used to manufacture the negative electrode, the electrode's coatability is excellent.

[0068] In an exemplary embodiment of this application, based on 100 parts by weight of the negative electrode composition, the amount of the water-soluble macromolecular polymer can be 1 part by weight or more and 20 parts by weight or less, preferably 1.5 parts by weight or more and 15 parts by weight or less.

[0069] When water-soluble macromolecular polymers are included in the above range, the negative electrode active material can be effectively dispersed, and high electrode adhesion and high binding force between the active materials in the electrode are obtained to resist the shrinkage and expansion of the negative electrode active material during the charging and discharging of the lithium secondary battery.

[0070] In an exemplary embodiment of this application, the negative electrode adhesive may 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted by Li, Na, or K, and may further include various copolymers thereof.

[0071] The adhesive according to an exemplary embodiment of this application is used to hold the negative electrode active material and the negative electrode conductive material together to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. All common negative electrode adhesives can be used when these functions are satisfied. Specifically, water-based adhesives can be used.

[0072] In an exemplary embodiment of the present application, an anode composition is provided, wherein based on 100 parts by weight of the anode binder, the anode binder comprises graphene oxide in an amount of 0.1 part by weight or more and 30 parts by weight or less.

[0073] In another exemplary embodiment, based on 100 parts by weight of the anode binder, graphene oxide in the anode binder may satisfy the range of 0.1 part by weight or more and 30 parts by weight or less, preferably 0.5 part by weight or more and 20 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less.

[0074] When the anode binder contains graphene oxide in the above-mentioned parts by weight, the anode active material can be effectively dispersed, and high electrode adhesion and high binding force between active materials in the electrode can be obtained to resist the characteristics of contraction and expansion of the anode active material during charging and discharging of a lithium secondary battery.

[0075] In an exemplary embodiment of the present application, an anode composition is provided, wherein based on 100 parts by weight of the anode composition, the anode binder is included in an amount of 1 part by weight or more and 20 parts by weight or less.

[0076] In another exemplary embodiment, based on 100 parts by weight of the anode composition, the anode binder may be included in an amount of 1 part by weight or more and 20 parts by weight or less, preferably 2 parts by weight or more and 15 parts by weight or less, more preferably 3 parts by weight or more and 15 parts by weight or less.

[0077] In an exemplary embodiment of the present application, an anode composition is provided, wherein the anode active material comprises one or more selected from the group consisting of silicon-based active materials and carbon-based active materials.

[0078] In an exemplary embodiment of the present application, the silicon-based active material may comprise one or more selected from the group consisting of SiO x (x=0), SiO x (0<x<2), SiC and Si alloys.

[0079] The active material of the present invention comprises a silicon-based active material. The silicon-based active material may be SiO x , Si / C or Si, SiO x may comprise SiO xa compound represented by (0≤x<2). Since SiO₂ does not react with lithium ions and cannot store lithium, x is preferably within the above range. The silicon-based active material may be Si / C or Si composed of a composite of Si and C. In addition, two or more of the above silicon-based active materials may be mixed and used. The negative electrode active material may further include a carbon-based active material together with the above silicon-based active material. The carbon-based active material can contribute to improving the cycle characteristics or battery life performance of the negative electrode or the secondary battery of the present invention.

[0080] In general, it is known that the capacity of a silicon-based active material is 10 times larger than that of a carbon-based active material. Therefore, when a silicon-based active material is applied to a negative electrode, it is expected that an electrode with a high level of energy density can be achieved even with a small thickness.

[0081] In an exemplary embodiment of the present application, the carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon and soft carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0082] In an exemplary embodiment of the present application, the negative electrode active material may be any material, including at least one of (1) artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, or combinations thereof, (2) silicon-based alloys, (3) a complex comprising or consisting of: i) at least one of artificial graphite, natural graphite, surface-modified graphite, coke, hard carbon, soft carbon, carbon fiber, conductive carbon, or 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.

[0083] In an exemplary embodiment of the present application, a negative electrode composition is provided, wherein the silicon-based active material comprises one or more selected from the group consisting of SiO x (x=0) and SiO x (0<x<2), and based on 100 parts by weight of the silicon-based active material, comprises 70 parts by weight or more of SiO x (x=0).

[0084] In another exemplary embodiment, based on 100 parts by weight of the silicon-based active material, SiOx (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, and 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

[0085] In an exemplary embodiment of this application, the silicon-based active material may use only pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, based on 100 parts by weight of the total silicon-based active material as described above, pure Si particles (SiO₂) not bonded to other particles or elements... x (x=0) is included in the above range.

[0086] Silicon-based active materials have a significantly higher capacity than commonly used graphite-based active materials, leading to increased efforts to apply them. However, silicon-based active materials exhibit high volume expansion during charge / discharge, thus limiting their use to small-scale blends with graphite-based active materials.

[0087] Therefore, the present invention is characterized by using silicon-based active materials as negative electrode active materials to improve capacity performance, while using binders with specific conditions to solve the problems of maintaining the conductive path and the combination of conductive materials, binders and active materials related to volume expansion.

[0088] The average particle size (D50) of the silicon-based active material of the present invention 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 is within the above range, the specific surface area of ​​the particles is within an appropriate range, thereby forming a negative electrode slurry viscosity within an appropriate range. Therefore, the particles constituting the negative electrode slurry are smoothly dispersed. Furthermore, when the size of the silicon-based active material has a value equal to or greater than the lower limit, due to the composite of the conductive material and the binder in the negative electrode slurry, the contact area between the silicon particles and the conductive material is excellent, thereby increasing the possibility of continuity of the conductive network and improving the capacity retention rate. At the same time, when the average particle size meets the above range, excessively large silicon particles are excluded, thereby forming a smooth surface of the negative electrode. Therefore, uneven current density during charging and discharging can be prevented.

[0089] In exemplary embodiments of this application, the silicon-based active material typically has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably from 0.01 to 150.0 m². 2 / g, more preferably 0.1 to 100.0 m 2 / g, with a particularly preferred concentration of 0.2 to 80.0 mg. 2 / g, with an optimal range of 0.2 to 18.0 m 2 / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0090] In exemplary embodiments of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmented. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0091] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein, based on 100 parts by weight of the negative electrode composition, a negative electrode active material is included in an amount of 60 parts by weight or more.

[0092] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein a silicon-based 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 another exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0094] The negative electrode composition according to this application uses specific conductive materials and binders, enabling control of the volume expansion rate during charging and discharging even when using silicon-based active materials with significantly high capacity within the aforementioned range. Therefore, even when the silicon-based active material is within the aforementioned range, the negative electrode composition does not degrade the performance of the negative electrode and exhibits excellent output characteristics during charging and discharging.

[0095] In an exemplary embodiment of this application, the silicon-based active material may have a non-spherical shape and a roundness of, for example, 0.9 or less, such as 0.7 to 0.9, 0.8 to 0.9, and 0.85 to 0.9.

[0096] In this application, the circularity is determined by Equation 1-1, where A is the area and P is the boundary line.

[0097] [Formula 1-1]

[0098] 4πA / P 2

[0099] In related technologies, graphite-based compounds are typically used only as negative electrode active materials. However, in recent years, with the increasing demand for high-capacity batteries, attempts to mix and use silicon-based compounds to increase capacity have increased. However, a limitation of silicon-based compounds is that they expand rapidly in volume during charging / discharging, which damages the conductive paths formed in the negative electrode active material layer, thereby reducing battery performance.

[0100] Therefore, in the exemplary embodiments of this application, when using an adhesive having the above-described properties, a specific negative conductive material may also be included.

[0101] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein the negative electrode conductive material includes one or more of the group consisting of point-type conductive materials, planar conductive materials and linear conductive materials.

[0102] In exemplary embodiments of this application, a dot-type conductive material refers to a conductive material that can be used to improve the conductivity of the negative electrode, forms conductivity without causing a chemical change, and has a circular or dot shape. Specifically, the dot-type 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 cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium dioxide, and polystyrene derivatives. Furthermore, in terms of high conductivity and excellent dispersibility, it preferably includes carbon black.

[0103] In an exemplary embodiment of this application, the point-type conductive material may have a 40 μm 2 / g or greater and 70 m 2 / g or less, preferably 45 m 2 / g or greater and 65 m 2 / g or less, and more preferably 50 m 2 / g or greater and 60 m 2 / g or less of BET specific surface area.

[0104] In exemplary embodiments of this application, the particle size of the dot-type conductive material can be from 10 nm to 100 nm, preferably from 20 nm to 90 nm, and more preferably from 40 nm to 60 nm.

[0105] In an exemplary embodiment of this application, the conductive material may include a planar conductive material.

[0106] Planar conductive materials are conductive materials that improve conductivity by increasing the surface contact between silicon particles in the negative electrode, while simultaneously suppressing the interruption of conductive paths due to volume expansion. Planar conductive materials can be represented as plate-shaped conductive materials or block-shaped conductive materials.

[0107] In exemplary embodiments of this 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 preferably may be plate graphite.

[0108] In exemplary embodiments of this application, the average particle size (D50) of the planar conductive material can be from 2 μm to 7 μm, particularly from 3 μm to 6 μm, and even more particularly from 4 μm to 5 μm. When the above range is met, sufficient particle size results in easy dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersed using the same equipment and time, the dispersion effect is excellent.

[0109] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein the planar conductive material has a D10 of 0.5 μm or larger and 1.5 μm or smaller, a D50 of 4.0 μm or larger and 5.0 μm or smaller, and a D90 of 7.0 μm or larger and 15.0 μm or smaller.

[0110] In an exemplary embodiment of this application, for planar conductive materials, a planar conductive material with a high BET specific surface area or a planar conductive material with a low specific surface area can be used.

[0111] In exemplary embodiments of this application, planar conductive materials, whether having a high specific surface area or a low specific surface area, can be used without limitation. However, in particular, the planar conductive material according to this application can affect electrode performance to some extent through a dispersion effect; therefore, it is particularly preferred to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0112] In an exemplary embodiment of this application, the planar conductive material may have a 1 m 2 / g or greater BET specific surface area.

[0113] In another exemplary embodiment, the planar conductive material may have a 1 m 2 / g or greater and 500 m 2 / g or less, preferably 5 m 2 / g or greater and 300 m 2 / g or less, and more preferably 5 m 2 / g or greater and 250 m 2 / g or less of BET specific surface area.

[0114] In another exemplary embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area can meet 50 m². 2 / g or greater and 500 m 2 / g or less, preferably 80 m 2 / g or greater and 300 m 2 / g or less, and more preferably 100 m 2 / g or greater and 300 m2 / g or a smaller range.

[0115] In another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can meet the requirement of 1 m². 2 / g or greater and 40 m 2 / g or less, preferably 5 m 2 / g or greater and 30 m 2 / g or less, and more preferably 5 m 2 / g or greater and 25 m 2 / g or a smaller range.

[0116] Other conductive materials can include linearly conductive materials, such as carbon nanotubes. Carbon nanotubes can be bundled carbon nanotubes. Bundled carbon nanotubes can comprise multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" as used herein refers to a bundle-like or rope-like secondary shape in which multiple carbon nanotube units are arranged side-by-side or entangled with substantially the same orientation along their longitudinal axes. The carbon nanotube units are cylindrical graphite sheets with nanometer-sized diameters and sp2 bonding structures. In this case, depending on the winding angle and structure of the graphite sheet, they can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, bundled carbon nanotubes can be more uniformly dispersed during anode fabrication and can more readily form a conductive network in the anode to improve its conductivity.

[0117] In an exemplary embodiment of this 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.

[0118] In an exemplary embodiment of this application, the carbon nanotubes may be SWCNTs and / or MWCNTs. When the linearly conductive material is SWCNT, the length of the SWCNT may be 0.5 μm-100 μm, and preferably 1-80 μm.

[0119] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein, based on 100 parts by weight of the negative electrode composition, a negative electrode conductive material is included in an amount of 5 parts by weight or more and 40 parts by weight or less.

[0120] In another exemplary embodiment of this application, based on 100 parts by weight of the negative electrode composition, the negative electrode conductive material is 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, more preferably 5 parts by weight or more and 25 parts by weight or less.

[0121] In an exemplary embodiment of this application, the negative electrode conductive material includes a point-type conductive material and a linear conductive material, and the ratio of the point-type conductive material to the linear conductive material can satisfy 1:0.1 to 1:0.5.

[0122] In an exemplary embodiment of this application, since the negative electrode conductive material includes point-type conductive material and linear conductive material, and satisfies the above composition and ratio respectively, the life characteristics of existing lithium secondary batteries are not significantly affected, and the number of points that are feasible for charging and discharging is increased, thereby resulting in excellent output characteristics at high C-rates.

[0123] The negative electrode conductive material according to this application has a completely different configuration from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to this application is used to maintain contact between the silicon-based active materials whose electrode volume expansion is very large due to charging and discharging, while the positive electrode conductive material is used to impart a certain conductivity and act as a buffer during rolling, and is completely different from the negative electrode conductive material of the present invention in terms of configuration and function.

[0124] Furthermore, the negative electrode conductive material according to this application uses a silicon-based active material and has a completely different configuration from conductive materials using graphite-based active materials. That is, since the conductive material used in the electrode with graphite-based active material has smaller particles than the active material, the conductive material has the property of improving output characteristics and imparting a certain conductivity, and in terms of configuration and function, it is completely different from the negative electrode conductive material used together with silicon-based active materials as in this application.

[0125] In an exemplary embodiment of this application, the plate-shaped conductive material used as the aforementioned negative electrode conductive material has a different structure and function than the carbon-based active material typically used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material can be artificial graphite or natural graphite, and refers to a material processed and used in a spherical or dot-like shape to promote the storage and release of lithium ions.

[0126] On the other hand, the plate-shaped conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be represented as plate-shaped graphite. That is, the plate-shaped conductive material is a material included to maintain a conductive path in the negative electrode active material layer, and means a material used to ensure a conductive path in a planar shape inside the negative electrode active material layer, rather than playing a role in storing and releasing lithium.

[0127] That is, in this application, using plate-shaped graphite as the conductive material means that the graphite is processed into a planar or plate-like shape and used as a material to ensure the conductive path rather than to store or release lithium. In this case, the negative electrode active material included together has high capacity characteristics in terms of storing and releasing lithium, and is used to store and release all lithium ions transferred from the positive electrode.

[0128] On the other hand, in this application, using carbon-based active materials as active materials means processing carbon-based active materials into dots or spheres and using them as materials for storing or releasing lithium.

[0129] In an exemplary embodiment of this application, the negative electrode composition may contain a solvent for forming a negative electrode slurry and form a negative electrode slurry, and the negative electrode slurry may be applied to a negative electrode current collector layer to form a negative electrode.

[0130] In this case, the solid content of the negative electrode slurry can be between 10% and 60%.

[0131] In exemplary embodiments of this application, solvents for forming the negative electrode slurry can be used without limitation, as long as they can dissolve the negative electrode composition; specifically, distilled water or NMP can be used.

[0132] In exemplary embodiments of the present invention, the method of mixing the negative electrode slurry is not particularly limited, and examples include ball mills, sand mills, pigment dispersers, ultrasonic dispersers, homogenizers, planetary mixers, Hobart mixers, etc., and preferably, homogenizers and / or planetary mixers are used for kneading.

[0133] In the exemplary embodiments of this application, there are no particular limitations on the means of applying the negative electrode slurry to the negative electrode current collector layer, and conventionally known coating devices can be used, such as comma coating machines, gravure coating machines, micro-gravure coating machines, die coating machines, doctor blade coating machines, etc.

[0134] Furthermore, a drying process can be performed after applying the negative electrode slurry. There are no particular limitations on the drying method, and the temperature is suitablely between 60 and 200°C, preferably between 100 and 180°C. The atmosphere can be dry air or an inert atmosphere. The thickness of the electrode (cured coating) is not particularly limited, but is suitablely between 5 and 300 μm, preferably between 10 and 250 μm.

[0135] In an exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, comprising: a negative electrode current collector layer; and a negative electrode active material layer comprising the negative electrode composition according to this application formed on one or both surfaces of the negative electrode current collector layer.

[0136] Figure 1A laminated structure for a negative electrode of a lithium secondary battery according to an exemplary embodiment of this application is shown. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Figure 1 It is shown that the negative electrode active material layer is formed on one surface of the negative electrode current collector layer, but the negative electrode active material layer can be formed on both surfaces of the negative electrode current collector layer.

[0137] In exemplary embodiments of this application, the negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. There are no particular limitations on the negative electrode current collector layer, as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper, or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys, etc., can be used. The negative electrode current collector layer may have microscopic irregularities formed on its surface to enhance the coupling force of the negative electrode active material, and can be used in various forms, such as thin films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics. In particular, when the electrode active material is used as the negative electrode, copper foil is preferred as the current collector.

[0138] In an exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or greater and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or greater and 500 μm or less.

[0139] However, the thickness can be modified in various ways depending on the type and purpose of the negative electrode used, and is not limited to this.

[0140] In an exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness variation rate of the negative electrode active material layer satisfies the following equation 1.

[0141] [Equation 1]

[0142] 0% ≤ [(X2-X1) / X1] x 100(%) ≤15%

[0143] In equation 1, X1 is the thickness of the negative electrode active material layer at 0 cycles for the negative electrode used in lithium secondary batteries, and X2 is the thickness of the negative electrode active material layer after 30 cycles for use in lithium secondary batteries.

[0144] Zero cycles can refer to the state in which the negative electrode for a lithium secondary battery is manufactured without undergoing charging / discharging, and more specifically, it can refer to the negative electrode for a lithium secondary battery after manufacturing.

[0145] That is, the negative electrode for lithium secondary batteries according to this application has the following characteristics: since a negative electrode binder containing specific graphene oxide is used as the binder, the volume expansion of the negative electrode active material is prevented even after repeated cycling when using the negative electrode binder, and therefore the thickness change is small.

[0146] In an exemplary embodiment of this application, a lithium secondary battery is provided, comprising: a positive electrode; a negative electrode of the lithium secondary battery according to this application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0147] Figure 2 The laminated structure of a lithium secondary battery according to a specific embodiment of the present invention is shown. Specifically, it can be seen that a negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery includes a positive electrode active material layer 40 on one surface of the positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 of the lithium secondary battery are laminated in a manner in which a separator 30 is inserted.

[0148] A secondary battery according to an exemplary embodiment of the present invention may specifically include the negative electrode described above for a lithium secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator inserted between the positive and negative electrodes, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has already been described above, its detailed description is omitted.

[0149] 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 positive electrode active material.

[0150] In the positive electrode, there are no particular restrictions on the current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive current collector can typically have a thickness of 3 to 500 μm, and its surface can have microscopic irregularities to enhance the adhesion of the positive electrode active material. For example, the positive current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0151] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; lithium manganese oxide, such as Li 1+Cl Mn 2-ClO4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; and 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 ≤ 0.6) represents a Ni-site type lithium nickel oxide; LiMn 2-C3 M C3 Lithium-manganese composite oxides represented by 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 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, etc., where a portion of the Li in the chemical formula is replaced by an alkaline earth metal ion, but not limited to these. The positive electrode can be Li metal.

[0152] In an exemplary embodiment of this application, the positive electrode active material includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co) and manganese (Mn). The lithium composite transition metal compound includes single particles or secondary particles, and the average particle size (D50) of the single particles can be 1 μm or greater.

[0153] For example, the average particle size (D50) of a single particle can be 1 μm or larger and 12 μm or smaller, 1 μm or larger and 8 μm or smaller, 1 μm or larger and 6 μm or smaller, larger than 1 μm and 12 μm or smaller, larger than 1 μm and 8 μm or smaller, or larger than 1 μm and 6 μm or smaller.

[0154] Even when forming individual particles with a small average particle size (D50) of 1 μm or larger and 12 μm or smaller, the particle strength can still be excellent. For example, when the strength is 650 kgf / cm³, the particle strength can be exceptionally high. 2 When pressed by a high-pressure roller, individual particles can have a particle strength of 100 to 300 MPa. Therefore, even when using 650 kgf / cm², the strength of the particles can be significantly increased. 2 The powerful rolling action of the rollers also reduces the increase of microparticles in the electrode caused by particle breakage, thereby improving the battery's lifespan characteristics.

[0155] Individual particles can be manufactured by mixing and sintering transition metal precursors and lithium source materials. Secondary particles can be manufactured using different methods than individual particles, and their composition can be the same as or different from that of individual particles.

[0156] There are no particular restrictions on the method of forming individual particles, but they can usually be formed by over-firing at elevated firing temperatures, or by using additives, such as grain growth promoters that facilitate over-firing, or by changing the starting materials.

[0157] For example, sintering is carried out at a temperature that allows for the formation of individual particles. Therefore, sintering should be performed at a temperature higher than that for secondary particles. For example, when the composition of the precursor is the same, sintering should be performed at a temperature approximately 30°C to 100°C higher than that for secondary particles. The sintering temperature used to form individual particles can vary depending on the metal composition in the precursor. For example, when forming individual particles of a high-nickel (Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or higher, the sintering temperature can be approximately 700°C to 1000°C, preferably approximately 800°C to 950°C. When the sintering temperature meets the above range, a positive electrode active material containing individual particles with excellent electrochemical properties can be manufactured. If the sintering temperature is below 790°C, a positive electrode active material containing lithium composite transition metal compounds in the form of secondary particles can be manufactured, and if the sintering temperature exceeds 950°C, over-sintering occurs and a layered crystal structure cannot be properly formed, potentially degrading the electrochemical properties.

[0158] In this specification, a single particle is a term used to distinguish it from a typical secondary particle resulting from an aggregation of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of a primary particle and a quasi-single particle form as an aggregation of 30 or fewer primary particles.

[0159] Specifically, in this invention, a single particle can be a single particle consisting of a primary particle or a quasi-single particle of an aggregate of 30 or fewer primary particles, and a secondary particle can be an aggregate of hundreds of primary particles.

[0160] In an exemplary embodiment of this application, the lithium composite transition metal compound used as the positive electrode active material further comprises secondary particles, and the average particle size (D50) of a single particle is smaller than the average particle size (D50) of the secondary particles.

[0161] In this invention, a single particle can be a single particle consisting of a primary particle or a quasi-single particle of an aggregate of 30 or fewer primary particles, and a secondary particle can be an aggregate of hundreds of primary particles.

[0162] The aforementioned lithium complex transition metal compounds may further comprise secondary particles. Secondary particles refer to those formed by the aggregation of primary particles and can be distinguished from the concept of a single particle, which includes a primary particle, a single particle, and a quasi-single particle form as an aggregate of 30 or fewer primary particles.

[0163] The secondary particles can have a particle size (D50) of 1 μm to 20 μm, 2 μm to 17 μm, and preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles can be 0.05 m². 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0164] In another exemplary embodiment of this application, the secondary particles are aggregates of the primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of an aggregate of hundreds of primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0165] When the average particle size (D50) of the primary particles meets the above-mentioned range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of aggregates of primary particles forming lithium nickel-based oxide particles increases, thereby reducing the effect of suppressing particle breakage during rolling. Conversely, if the average particle size (D50) of the primary particles is too large, the lithium diffusion path inside the primary particles may be prolonged, thereby increasing resistance and reducing output characteristics.

[0166] According to another exemplary embodiment of this application, the average particle size (D50) of a single particle is smaller than the average particle size (D50) of a secondary particle. As a result, even if a single particle is formed with a small particle size, it can still have excellent particle strength, thus mitigating the increase in microparticles in the electrode due to particle breakage, thereby improving the battery's lifespan characteristics.

[0167] In an exemplary embodiment of this application, the average particle size (D50) of a single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particles.

[0168] For example, the average particle size (D50) of a single particle can be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0169] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of a secondary particle, for example, when the above range is met, even if a single particle is formed with a small particle size, it can still have excellent particle strength. As a result, the increase in microparticles in the electrode due to particle breakage is reduced, thereby improving the battery's lifespan characteristics and energy density.

[0170] According to another exemplary embodiment of this application, based on 100 parts by weight of the positive electrode active material, individual particles are included in an amount of 15 parts by weight to 100 parts by weight. Based on 100 parts by weight of the positive electrode active material, individual particles may be included in an amount of 20 parts by weight to 100 parts by weight or 30 parts by weight to 100 parts by weight.

[0171] For example, based on 100 parts by weight of the positive electrode active material, individual particles may be included in amounts of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more. Based on 100 parts by weight of the positive electrode active material, individual particles may be included in amounts of 100 parts by weight or less.

[0172] When individual particles are contained within the above-mentioned range, they can be combined with the aforementioned negative electrode materials to exhibit excellent battery characteristics. In particular, when individual particles are 15 parts by weight or more, the increase in particulate matter in the electrode due to particle breakage during the rolling process after electrode manufacturing can be mitigated, thereby improving the battery's lifespan characteristics.

[0173] In an exemplary embodiment of this application, the lithium complex transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less based on 100 parts by weight of the positive electrode active material. Based on 100 parts by weight of the positive electrode active material, the secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less. Based on 100 parts by weight of the positive electrode active material, the secondary particles may be 0 parts by weight or more.

[0174] When the above range is met, the above effect is maximized due to the presence of individual particles in the positive electrode active material. In the case of a positive electrode active material containing secondary particles, its composition may be the same as or different from those exemplified in the above-mentioned single-particle positive electrode active materials, and may refer to the aggregate form of individual particles.

[0175] In an exemplary embodiment of this application, the positive electrode active material in the 100 parts by weight of the positive electrode active material layer may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and most preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0176] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the aforementioned positive electrode material.

[0177] In this context, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular restrictions, as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the battery. Specific examples may include graphite, such as natural and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lampblack, thermal cracking black, and carbon fibers; 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, etc., and any one of them or a mixture of two or more of them may be used.

[0178] In addition, positive electrode binders are used to improve the adhesion between particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), vinylidene 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), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more of them may be used.

[0179] The separator is used to isolate the negative and positive electrodes and provide a path for lithium ions to move. Any separator commonly used in secondary batteries can be used as a separator without particular limitation. In particular, separators with high electrolyte retention capacity and low resistance to the movement of electrolyte ions are preferred. Specifically, porous polymer membranes or laminated structures having two or more layers can be used, the porous polymer being made, for example, from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. Furthermore, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, coated separators comprising ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can be selectively used.

[0180] Examples of electrolytes may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0181] Specifically, electrolytes can include non-aqueous organic solvents and metal salts.

[0182] As non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0183] In particular, among carbonate organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, are high-viscosity organic solvents because they have high dielectric constants, which allow them to dissociate lithium salts well, and are therefore preferred. When cyclic carbonates are mixed and used with linear carbonates (such as dimethyl carbonate or diethyl carbonate) having low viscosity and low dielectric constants in appropriate proportions, electrolytes with high conductivity can be prepared, and are therefore preferred.

[0184] Lithium salts can be used as metal salts, and lithium salts are readily soluble in non-aqueous electrolytes. For example, lithium salts selected from 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 - (CF3CF2SO2)2N - It can be used as an anion of lithium salts.

[0185] In addition to the electrolyte components mentioned above, one or more additives may be further included in the electrolyte to improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity. For example, compounds based on haloalkylene carbonates, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, N-glycol dimethyl ether (glyme), triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride.

[0186] The lithium secondary battery according to the present invention can be used in portable devices, such as mobile phones, laptops, and digital cameras, as well as electric vehicles, such as hybrid electric vehicles (HEVs), and is particularly preferred as a component battery in medium and large battery modules. Therefore, the present invention provides a medium and large battery module comprising the above-described lithium secondary battery as a unit cell.

[0187] An exemplary embodiment of the present invention provides a battery module including a secondary battery as a unit cell, and a battery pack including the battery module. Since the battery module and battery pack include a secondary battery with high capacity, high rate capability, and high cycle characteristics, the battery module and battery pack can 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 energy storage systems.

[0188] Forms for implementing the present invention

[0189] Preferred embodiments will be provided below to better understand the invention. It will be apparent to those skilled in the art that the embodiments provided are for illustrative purposes only, and various modifications and changes can be made within the scope and spirit of the invention. Such modifications and changes naturally fall within the scope of the claims included herein.

[0190] <Manufacturing Example>

[0191] <Manufacturing of Water-Soluble Macromolecular Polymers>

[0192] Synthesis example 1

[0193] 45g of PVA (polyvinyl alcohol, Mw=2400) and 500g of water were placed in a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet pipe, and the mixture was heated to 90°C and dissolved. 0.3g of glutaraldehyde (25% aqueous solution) and 30g of water were mixed and added to the solution, and the mixture was kept for 2 hours. Afterward, the reaction mixture was cooled to 50°C, and a solution of 1g of APS (ammonium persulfate) dissolved in 10g of water and a solution of 0.3g of NaHSO3 dissolved in 3g of water were added sequentially, and the mixture was kept for 10 minutes.

[0194] While introducing nitrogen gas, 35g of acrylic acid (AA), 15g of N-hydroxyethylacrylamide (HEAA), and 250g of water were mixed, and the mixture was then added dropwise over 30 minutes and maintained for 2 hours. Next, an aqueous solution of 0.5g NaOH dissolved in 3g of water was gradually added to prepare an aqueous solution of the macromolecular polymer.

[0195] Synthesis example 2

[0196] 1254 g of water, 200 g of acrylamide (50% aqueous solution), 40 g of acrylic acid (AA) (80% aqueous solution), 20 g of 48% sodium hydroxide (48% aqueous solution), and 50 g of acrylonitrile were placed in a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet pipe, and the temperature was raised to 50°C. 2.0 g of 2,2'-azobis-2-amidinylpropane dihydrochloride and 20 g of water were added, the temperature was raised to 80°C, and the reaction was carried out for 3 hours to prepare an aqueous solution of polyacrylamide macropolymer.

[0197] <Manufacturing of Negative Electrode Slurry>

[0198] <Example 1>

[0199] As the negative electrode active material, 1) artificial graphite with a D50 of 15 μm was used, and 2) SiOx (D50 = 1 to 6 μm) was used as silicon, and graphite and silicon were mixed at a graphite:silicon weight ratio of 7:3. As the conductive material, Super-P Black and SWCNT (Super-P:SWCNT weight ratio = 1:0.001) were used, and the active material, conductive material, and binder were mixed at a weight ratio of 85:5:10 to prepare the negative electrode composition. At this time, the water content as a solvent was adjusted considering coatability, viscosity, and solids content. The viscosity of the resulting slurry composition was adjusted to 5,000 to 6,000 cps.

[0200] As a binder, the macromolecular polymer and graphene oxide in Synthesis Example 1 were mixed in a weight ratio of 98:2, in which case the C / O ratio of graphene oxide was 1.5 and its lateral size was 2 μm.

[0201] <Example 2>

[0202] Except that the weight ratio of active material, conductive material and binder in Example 1 is 85:5:10, and the macromolecular polymer and graphene oxide from Synthesis Example 2 are used as binders in a weight ratio of 98:2, with graphene oxide having a C / O ratio of 2.0 and a lateral size of 5 μm, the negative electrode composition is manufactured in the same manner as in Example 1.

[0203] <Example 3>

[0204] Except that the weight ratio of active material, conductive material and binder in Example 1 is 85:5:10, and the macromolecular polymer and graphene oxide from Synthesis Example 1 are used as binder in a weight ratio of 65:35, the C / O ratio of graphene oxide is 2.0 and its lateral size is 5 μm, the negative electrode composition is manufactured in the same manner as in Example 1.

[0205] <Example 4>

[0206] Except that in Example 1, Si (average particle size (D50): 3.5 μm) was used as the silicon-based active material, Super-P black and SWCNT (Super-P:SWCNT weight ratio = 1:0.001) were used as the conductive materials, and the active material, conductive material and binder were mixed in a weight ratio of 85:5:10 to prepare the negative electrode composition, the negative electrode composition was prepared by the same method as in Example 1.

[0207] <Example 5>

[0208] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of graphene oxide was 1.5 and its lateral size was 1 μm.

[0209] <Example 6>

[0210] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of graphene oxide was 1.5 and its lateral size was 10 μm.

[0211] <Example 7>

[0212] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of the graphene oxide was 2.5 and its lateral size was 10 μm.

[0213] <Example 8>

[0214] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of the graphene oxide was 2.5 and its lateral size was 1 μm.

[0215] <Comparative Example 1>

[0216] The negative electrode composition was manufactured in the same manner as in Example 1, except that the weight ratio of active material, conductive material and binder was 85:5:10 in Example 1 and graphene oxide was not used as a binder.

[0217] <Comparative Example 2>

[0218] Except that the weight ratio of active material, conductive material and binder in Example 1 is 85:5:10, and the macromolecular polymer and graphene oxide from Synthesis Example 1 are used as binders in a weight ratio of 95:5, with graphene oxide having a C / O ratio of 4.0 and a lateral size of 2 μm, the negative electrode composition is manufactured in the same manner as in Example 1.

[0219] <Comparative Example 3>

[0220] Except that the weight ratio of active material, conductive material and binder in Example 1 is 85:5:10, and the macromolecular polymer and graphene from Synthesis Example 1 are used as binders in a weight ratio of 98:2, and pure graphene with a lateral size of 40 μm is used, the negative electrode composition is manufactured in the same manner as in Example 1.

[0221] <Comparative Example 4>

[0222] Except that the weight ratio of active material, conductive material and binder in Example 1 is 85:5:10, and the macromolecular polymer and graphene oxide from Synthesis Example 1 are used as binders in a weight ratio of 95:5, with graphene oxide having a C / O ratio of 3.0 and a lateral size of 60 μm, the negative electrode composition is manufactured in the same manner as in Example 1.

[0223] <Comparative Example 5>

[0224] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of graphene oxide was 1.5 and its lateral size was 25 μm.

[0225] <Comparative Example 6>

[0226] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of graphene oxide was 1.5 and its lateral size was 0.1 μm.

[0227] <Comparative Example 7>

[0228] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of the graphene oxide was 2.5 and its lateral size was 25 μm.

[0229] <Comparative Example 8>

[0230] In Example 4, the macromolecular polymer and graphene oxide from Synthesis Example 1 were used as binders in a weight ratio of 98:2. In this case, the C / O ratio of the graphene oxide was 2.5 and its lateral size was 0.1 μm.

[0231] <Battery manufacturing and battery performance evaluation>

[0232] The negative electrode slurry of the examples and comparative examples was coated onto a copper foil with a thickness of 18 μm and dried to form an active material layer with a thickness of 50 μm on one surface of the copper foil. This was then stamped into a circle with a diameter of 14Φ to manufacture the test electrode (negative electrode). A lithium metal 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 a solution obtained by dissolving LiPF6 as a lithium salt in a mixed solvent at a concentration of approximately 1 mol / L was used as the electrolyte. The mixed solvent consisted of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a 1:1 volume ratio.

[0233] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to manufacture a coin battery with a thickness of 2 mm and a diameter of 32 mm for evaluation. The evaluation results are shown in Tables 1 and 2 below.

[0234] [Table 1]

[0235] [Table 2]

[0236] - Initial efficiency (%): The coin cell battery was charged at a constant current of 0.05C to a voltage of 0.01V and discharged at a constant current of 0.05C to a voltage of 1.5V to obtain the discharge capacity and initial efficiency, respectively. The initial efficiency is expressed as the value of (discharge capacity / charge capacity) × 100 (%).

[0237] - Capacity retention (%): The coin cell was charged to 0.01V at a constant current of 0.05C and discharged to 1.5V at a constant current of 0.05C. Subsequently, the cycle characteristics were calculated by performing a capacity retention test at a constant current of 0.2C within the same voltage range as described above for 30 cycles.

[0238] -Thickness Increase Rate (%): The thickness (X1) of the negative electrode active material layer in the manufactured coin cell was measured. The coin cell was charged to a voltage of 0.01V at a constant current of 0.05C and discharged to a voltage of 1.5V at a constant current of 0.05C. Subsequently, the cycle characteristics for 30 cycles were calculated by performing a capacity retention test at a constant current of 0.2C within the same voltage range as described above. Then, the thickness (X2) of the negative electrode active material layer in the coin cell was measured after 30 cycles.

[0239] As can be seen from the results in Tables 1 and 2, it can be confirmed that even when using negative electrode active materials (especially silicon-based active materials) that undergo large volume expansion during charging / discharging, the batteries according to Examples 1 to 8 can suppress volume expansion and contraction, minimize thickness changes due to electrode swelling, and exhibit excellent lifespan performance of lithium secondary batteries.

[0240] Specifically, in Examples 4 to 8, 100% Si was used as the negative electrode active material. Pure Si is typically difficult to apply due to severe volume expansion during charging and discharging. However, it was confirmed that, because of the inclusion of the specific binder according to the invention, the initial efficiency was superior to that of Examples 1 to 3. In terms of material properties, the increase in thickness was also greater than in Examples 1 to 3 because pure Si particles were used. However, with the application of the binder of the invention, the thickness increase rate was within the range of 0 to 15%, in which case driving the negative electrode was not a problem. That is, it was confirmed that the negative electrodes of Examples 4 to 8 could easily control volume expansion while maximizing capacity characteristics.

[0241] Comparative Example 1 is a case in which a specific graphene oxide is not included, Comparative Example 2 is a case in which graphene oxide is used but the C / O ratio exceeds the scope of this application, Comparative Example 3 is a case in which graphene is used instead of graphene oxide (no C / O ratio), and Comparative Example 4 corresponds to a case in which the lateral dimension of graphene oxide exceeds the scope of this invention.

[0242] Furthermore, Comparative Examples 5 to 8 use graphene oxide, where the C / O ratio meets the scope of this application, but the lateral size does not.

[0243] As can be seen from each of Comparative Examples 1 to 8, it can be confirmed that the initial efficiency itself was calculated to be similar to that of the Examples, but since the specific graphene oxide according to this application was not included, the capacity retention rate decreased due to the volume expansion of the silicon-based active material and the increase rate of the thickness of the negative electrode active material layer increased.

[0244] Furthermore, when comparing Examples 1 to 3, based on 100 parts by weight of the negative electrode binder, the graphene oxide contained in Examples 1 and 2 was included in an amount of 0.1 parts by weight or more and 30 parts by weight or less. When comparing Examples 1 and 2 with Example 3, it can be confirmed that the negative electrode of Example 3 has a particularly excellent capacity retention rate and can effectively control the increase in thickness. This is because the negative electrode can effectively disperse the negative electrode active material containing the above-mentioned amount of graphene oxide, and can have high electrode adhesion and high binding force between the active materials in the electrode to resist the shrinkage and expansion of the negative electrode active material during the charging and discharging of the lithium secondary battery.

Claims

1. A negative electrode composition comprising: A negative electrode binder, wherein the negative electrode binder comprises graphene oxide and one or more water-soluble macromolecular polymers; Negative electrode active materials; and Negative electrode conductive material, The graphene oxide described therein has a lateral dimension of 0.3 μm or larger and 20 μm or smaller, and The graphene oxide described therein has a carbon / oxygen ratio of 0.5 or greater and 3.5 or less. The water-soluble macromolecular polymers mentioned herein include one or more selected from the group consisting of: carboxymethyl cellulose and its derivatives, water-soluble polyacrylic acid, polyvinyl alcohol, polyacrylonitrile, and polyacrylamide. The negative electrode active material includes silicon-based active materials.

2. The negative electrode composition according to claim 1, The negative electrode adhesive comprises 100 parts by weight of the graphene oxide in an amount of 0.1 parts by weight or more and 30 parts by weight or less.

3. The negative electrode composition according to claim 1, wherein the negative electrode binder is included in an amount of 1 part or more and 20 parts or less, based on 100 parts by weight of the negative electrode composition.

4. The negative electrode composition according to claim 1, The water-soluble macromolecular polymer described therein has a weight-average molecular weight of 100,000 g / mol or greater and 3,000,000 g / mol or less.

5. The negative electrode composition according to claim 1, In the negative electrode composition, which is based on 100 parts by weight, the amount of the water-soluble macromolecular polymer is 1 part by weight or more and 20 parts by weight or less.

6. The negative electrode composition according to claim 1, The water-soluble macromolecular polymer described therein is a polymer of one or more monomers selected from the group consisting of: compounds containing (meth)acrylamide groups; unsaturated organic acids or salts of unsaturated organic acids; and α,β-unsaturated nitriles and (meth)acrylate hydroxyalkyl esters.

7. The negative electrode composition according to claim 1, The negative electrode conductive material includes one or more of the group consisting of point-type conductive materials, planar conductive materials, and linear conductive materials.

8. The negative electrode composition according to claim 1, The negative electrode active material includes silicon-based active materials and carbon-based active materials.

9. The negative electrode composition according to claim 8, The silicon-based active material includes those selected from Si and SiO. x One or more of the constituent groups, and based on 100 parts by weight of the said silicon-based active material, comprising 70 parts by weight or more of Si, wherein 0 <x<2。 10. The negative electrode composition according to claim 1, The negative electrode composition is based on 100 parts by weight, wherein the negative electrode active material is included in an amount of 60 parts by weight or more.

11. A negative electrode for a lithium secondary battery, comprising: Negative electrode current collector layer; and A layer of negative electrode active material comprising the negative electrode composition according to any one of claims 1 to 10 is formed on one or both surfaces of the negative electrode current collector layer.

12. The negative electrode for a lithium secondary battery according to claim 11, The thickness of the negative electrode current collector layer is 1 μm or greater and 100 μm or less, and The thickness of the negative electrode active material layer is 20 μm or greater and 500 μm or less.

13. The negative electrode for a lithium secondary battery according to claim 11, The thickness variation rate of the negative electrode active material layer satisfies the following equation 1: [Equation 1] 0%≤[(X2-X1) / X1]x 100(%)≤15% In equation 1, X1 is the thickness of the negative electrode active material layer at 0 cycles of the negative electrode used in the lithium secondary battery, and X2 is the thickness of the negative electrode active material layer after 30 cycles of the negative electrode used in the lithium secondary battery.

14. A lithium secondary battery, comprising: positive electrode; The negative electrode for a lithium secondary battery according to claim 11; A partition is disposed between the positive electrode and the negative electrode; and Electrolytes.

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