Negative electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a negative electrode for a lithium secondary battery capable of maintaining an excellent expansion reduction effect and an electric network, and exhibiting excellent life characteristics.SOLUTION: The negative electrode for a lithium secondary battery includes a Si-based negative electrode active material, a binder, a linear carbon conductive material, a dispersant, and an additive having at least one multifunctionalhydroxylgroup and capable of being adsorbed onto a surface of the dispersant, wherein the binder is a copolymer including an acrylic group and a cyano group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0002] Recently, the demand for high-energy-density, high-capacity secondary batteries has increased dramatically with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles. To address this demand, active research and development efforts are being conducted to improve the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a cathode and an anode, each containing an active material capable of intercalating and deintercalating lithium ions, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are intercalated and deintercalated at the cathode and anode. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment is to provide a negative electrode for a lithium secondary battery that can have an excellent expansion reduction effect, maintain an electrical network, and exhibit excellent life characteristics.

[0005] Another embodiment provides a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0006] One embodiment provides a negative electrode for a lithium secondary battery, comprising: a Si-based negative electrode active material; a binder; a linear carbon conductive material; a dispersant; and an additive having one or more multifunctional hydroxyl groups and capable of adsorbing to a surface of the dispersant, wherein the binder is a copolymer containing an acrylic group and a cyano group.

[0007] Another embodiment provides a lithium secondary battery comprising: the negative electrode; a positive electrode; and a non-aqueous electrolyte.

[0008] Other specific details of the embodiments of the present invention are included in the following detailed description. [Effects of the Invention]

[0009] The negative electrode for a lithium secondary battery according to an embodiment may exhibit excellent initial efficiency and electrochemical properties. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is given by way of example only, and the present invention is not limited thereto, but is defined only by the scope of the claims that follow.

[0012] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between.

[0013] Unless otherwise specified herein, the singular can also include the plural, and unless otherwise specified, "A or B" can mean "including A, including B, or including A and B."

[0014] As used herein, "combinations thereof" can mean mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0015] Unless otherwise defined herein, particle size refers to the average particle size. Furthermore, particle size refers to the average particle size (D50), which refers to the diameter of particles with a cumulative volume of 50% in a particle size distribution. The average particle size (D50) can be measured by methods well known to those skilled in the art, such as using a particle size analyzer or a transmission electron microscope or scanning electron microscope. Alternatively, the average particle size (D50) can be measured using a measuring device that uses dynamic light scattering, and the data can be analyzed to count the number of particles in each particle size range, followed by calculation to obtain the average particle size (D50). Alternatively, the average particle size (D50) can be measured using a laser diffraction method. When measuring by the laser diffraction method, more specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac's MT3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0016] In one embodiment, the average particle size can be measured by various methods as described above, for example, by a particle size analyzer.

[0017] In one embodiment, the thickness can be measured using a cross-sectional SEM or TEM image, but is not limited thereto, and can be measured using any method known in the art for measuring thickness. The thickness can be an average thickness.

[0018] In one embodiment, the weight average molecular weight (Mw) can be measured by gel permeation chromatography.

[0019] As used herein, soft carbon refers to a graphitizable carbon material that can be graphitized by heat treatment at a high temperature, for example, 2800°C, and hard carbon refers to a non-graphitizable carbon material that is not graphitized or is substantially not graphitized by heat treatment. Soft carbon and hard carbon are terms widely known in the art.

[0020] In one embodiment, crystalline carbon and amorphous carbon can be classified by X-ray diffraction analysis. Crystalline carbon includes natural graphite and artificial graphite. Natural graphite refers to naturally occurring graphite obtained by separation from minerals, and has a d002 of 3.350 Å to 3.360 Å in X-ray diffraction analysis. Artificial graphite refers to graphite produced by graphitization, and has a d002 of 3.355 Å to 3.365 Å in X-ray diffraction analysis. Amorphous carbon has a d002 of 3.34 Å or less in X-ray diffraction analysis. X-ray diffraction analysis (XRD) can be performed using an X-ray diffraction analyzer, such as an X'Pert (manufactured by Malvern Panalytical), with CuKα radiation as the target radiation. The monochromator can be removed to improve peak intensity resolution. The measurement conditions can be 2θ=10° to 80°, scan speed (° / s)=0.044 to 0.089, and step size (° / step)=0.013 to 0.039.

[0021] According to one embodiment, a negative electrode for a lithium secondary battery includes a Si-based negative electrode active material, a binder, a linear carbon conductive material, a dispersant, and an additive having one or more multifunctional hydroxyl groups and capable of adsorbing to the surface of the dispersant. The binder is a copolymer containing an acrylic group and a cyano group. The multifunctional hydroxyl groups can be one or more OH functional groups.

[0022] In one embodiment, the binder copolymer includes a first monomer, a second monomer, and a third monomer, and may be, for example, an acrylic copolymer or an acrylic terpolymer.

[0023] The binder may be an expansion-reducing binder that can suppress the volumetric expansion of the Si-based active material during charge and discharge. Because the binder can suppress the volumetric expansion of the Si-based active material, it is possible to prevent the Si-based active material from shrinking and expanding, which can cause separation between the active material or between the active material and the current collector, resulting in a decrease in charge capacity and discharge capacity.

[0024] The first monomer includes an acryloyl group (CH2CHCO-), and examples thereof include (meth)acrylic acid, a metal salt of (meth)acrylic acid, an ammonium salt of (meth)acrylic acid, an amine salt of (meth)acrylic acid, or a combination thereof.

[0025] As used herein, "(meth)" means that a methyl group may or may not be included. For example, (meth)acrylate means acrylate or methacrylate.

[0026] In the metal salt of (meth)acrylic acid, the metal can be an alkali metal or alkaline earth metal. For example, it can be lithium, sodium, potassium, calcium, or magnesium. Examples of the metal salt of (meth)acrylic acid include sodium acrylate, lithium acrylate, potassium acrylate, calcium acrylate, magnesium acrylate, sodium methacrylate, lithium methacrylate, potassium methacrylate, calcium methacrylate, magnesium methacrylate, or a combination thereof.

[0027] The ammonium salt of (meth)acrylic acid may be an ammonia-neutralized product, a monoethanolamine-neutralized product, a diethanolamine-neutralized product, a hydroxylamine-neutralized product of (meth)acrylic acid, or a combination thereof.

[0028] When a metal salt of (meth)acrylic acid, which is partially substituted with a metal ion, is used as the first monomer and used as the negative electrode binder, the battery resistance can be reduced and the water solubility of the binder can be increased, thereby improving processability.

[0029] In one embodiment, the metal salt of (meth)acrylic acid may have some hydrogen atoms substituted with a metal, or may have all hydrogen atoms substituted with a metal. For example, the degree of substitution of the metal salt of (meth)acrylic acid may be 20 mol% to 100 mol%. This means that when the total acrylic acid is 100 mol%, 20 mol% to 100 mol% of the acrylic acid is substituted with a metal. + is metal + This means that it has been replaced by

[0030] The degree of substitution of the (meth)acrylic acid metal salt can be confirmed using various physicochemical analyses known in the art, for example, ICP spectroscopy (Inductively Coupled Plasma Spectroscopy).

[0031] In another embodiment, the degree of substitution of the metal (meth)acrylate can be determined from the mixing ratio of the metal (meth)acrylate and (meth)acrylic acid as the first monomer. For example, a degree of substitution of the metal (meth)acrylate of 20 mol % to 100 mol % can be obtained by mixing the metal (meth)acrylate and (meth)acrylic acid as the first monomer in a ratio of 20:80 wt % to 100:0 wt %.

[0032] The second monomer contains a cyano group, and an example is acrylonitrile.

[0033] The third monomer can include an acrylate group, for example, a (meth)acrylate including a sulfonate group or a sulfonic acid group or a (meth)acrylate including an ethylene glycol group. In one embodiment, the third monomer can be a (meth)acrylate including a sulfonate group or a sulfonic acid group.

[0034] The (meth)acrylate containing a sulfonic acid group can be 2-acrylamido-2-methyl-1-propanesulfonic acid, and the (meth)acrylate containing an ethylene glycol group can be a polyethylene glycol methacrylate monomer.

[0035] In one embodiment of the binder, the mixing ratio of the first monomer, the second monomer, and the third monomer may be 1:1.48:0.03 to 1:0.58:0.08 by weight, 1:1.12:0.12 to 1:0.7:0.09 by weight, or 1:0.96:0.1 to 1:0.67:0.05 by weight. When the weight ratio of the first monomer, the second monomer, and the third monomer is within the above range, volume expansion of the Si-based active material can be effectively suppressed, and adhesion of the negative electrode active material to the current collector can be further improved. The content of the first monomer may be 40% to 60% by weight, or 50% to 55% by weight, based on 100% by weight of the total of the first monomer, the second monomer, and the third monomer. When the content of the first monomer is within the above range, the copolymer becomes more soluble in water, which can further improve the dispersibility of the negative electrode active material and the storage stability of the negative electrode active material layer composition, and can effectively suppress the occurrence of cracks during the negative electrode manufacturing process.

[0036] The content of the second monomer may be 35% by weight to 59% by weight, or 40% by weight to 50% by weight, relative to 100% by weight of the total of the first monomer, second monomer, and third monomer. When the content of the second monomer is within the above range, the adhesion of the negative electrode active material layer to the current collector can be further improved, and the dispersibility of the negative electrode active material and the storage stability of the negative electrode active material layer composition can be further improved.

[0037] The content of the third monomer may be 1% by weight to 5% by weight, or 2% by weight to 3% by weight, relative to 100% by weight of the total of the first monomer, the second monomer, and the third monomer.

[0038] When the content of the third monomer is within the above range, the occurrence of cracks during the production of the negative electrode can be more effectively suppressed.

[0039] Furthermore, when the contents of the first monomer, the second monomer, and the third monomer are within the above ranges, the resulting copolymer can have appropriate water solubility, the processability of the negative electrode manufacturing process using this copolymer can be ensured, and the expansion of the negative electrode can be suppressed and the resistance can be effectively reduced.

[0040] In one embodiment, the binder may be a copolymer including a first monomer, a second monomer, and a third monomer, for example, a copolymer obtained by polymerizing a first monomer, a second monomer, and a third monomer. The first monomer, the second monomer, and the third monomer may also be referred to as repeat units. For example, the copolymer may include a first repeat unit derived from the first monomer, a second repeat unit derived from the second monomer, and a third repeat unit derived from the third monomer.

[0041] The binder can be produced by mixing the first, second, and third monomers in appropriate content ranges, adding an initiator and a solvent to the mixture, and copolymerizing the mixture. Any compound capable of inducing a copolymerization reaction can be used as the initiator, such as benzoyl peroxide or azobisisobutyronitrile.

[0042] The binder content may be 0.5 wt % to 3 wt %, 1 wt % to 2 wt %, or 1.2 wt % to 1.5 wt %, based on 100 wt % of the negative electrode active material layer. When the binder content is within the above range, there may be an advantage in that expansion of the negative electrode is significantly reduced.

[0043] In one embodiment, the linear carbon conductive material can effectively form an electrical network between the active materials, thereby effectively suppressing degradation of the electrical network that occurs when the active materials are separated due to volume expansion of the Si-based active material.

[0044] Such an effect can be obtained from a linear carbon conductive material, which can maintain better conductivity between active materials than a spherical, e.g., particulate, carbon conductive material, and therefore can exhibit a better lifespan.

[0045] In one embodiment, the linear carbon conductive material may be a carbon nanotube, a carbon nanofiber, or a combination thereof. The carbon nanotube may be a single-walled carbon nanotube, a multi-walled carbon nanotube, or a combination thereof. In another embodiment, the linear carbon conductive material may be a carbon nanotube, or in another embodiment, a single-walled carbon nanotube.

[0046] The average diameter of the carbon nanotubes may be 1 nm to 5 nm, or may be 1 nm to 2 nm. When the average diameter of the carbon nanotubes is within the above range, a small amount can impart conductivity to a large volume (area).

[0047] The average length of the carbon nanotubes may be 10 μm or less, and may be 0.1 μm to 10 μm. When the average length of the carbon nanotubes is within the above range, the electrolyte impregnation of the negative electrode and the ion mobility in the battery can be further improved while exhibiting appropriate conductivity.

[0048] In one embodiment, the average diameter and average length may be the average values ​​of the diameters and lengths of 20 carbon nanotubes. Furthermore, the minor axis of a carbon nanotube corresponds to the diameter, and the major axis corresponds to the length. The length and diameter of such carbon nanotubes can be measured using a SEM.

[0049] The content of the linear carbon conductive material may be 0.005 wt % to 0.2 wt %, 0.01 wt % to 0.1 wt %, or 0.03 wt % to 0.08 wt %, based on 100 wt % of the negative electrode active material layer. When the content of the linear carbon conductive material is within this range, the electrical conductivity of the negative electrode can be maximized and a long life can be maintained.

[0050] In one embodiment, the dispersant may function to ensure that the binder and the linear carbon conductive material are well dispersed within the negative electrode active material layer.

[0051] The dispersing agent can be, but is not limited to, polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkyl polyimine, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, polyethylenimine, or combinations thereof.

[0052] In one embodiment, the weight-average molecular weight (Mw) of the dispersant may be 30,000 Dalton or more, 30,000 Dalton to 100,000 Dalton, or 30,000 Dalton to 50,000 Dalton. When the weight-average molecular weight (Mw) of the dispersant is within this range, the dispersibility of the Si-based negative electrode active material and the linear carbon conductive material may be further improved, and the active material, binder, and conductive material dispersion may be mixed to maintain stable dispersion in a slurry.

[0053] The content of the dispersant may be 0.009 wt % to 0.35 wt %, 0.02 wt % to 0.15 wt %, or 0.05 wt % to 0.13 wt %, based on 100 wt % of the negative electrode active material layer. When the content of the dispersant is within this range, there may be an advantage in that the dispersibility of the carbon nanotubes is maintained.

[0054] In one embodiment, the additive is a compound having one or more multifunctional hydroxyl groups and capable of adsorbing to the surface of the dispersant. Because such an additive can be adsorbed to the surface of the dispersant, it can prevent the dispersant from coming into direct contact with materials such as the active material and binder, thereby preventing the problem of the dispersant being adsorbed to materials such as the active material and binder, which would result in a decrease in dispersibility. Therefore, the dispersant can effectively improve dispersibility.

[0055] In an embodiment of the negative electrode, an additive having physical properties capable of being adsorbed onto the surface of the dispersant is used together with the dispersant, thereby effectively preventing aggregation of the dispersant with the Si-based negative electrode active material and the linear carbon conductive material.

[0056] The use of the additive together with the dispersant effectively suppresses aggregation of the Si-based negative electrode active material and the linear carbon conductive material, and in particular, more effectively suppresses aggregation, which can occur severely when an aqueous solvent is used during negative electrode fabrication. As a result, the Si-based negative electrode active material and the linear carbon conductive material can be well dispersed within the negative electrode active material layer, resulting in improved expansion reduction and a long lifespan.

[0057] In one embodiment, the additive may be a polyphenolic compound, a polysaccharide-based compound, or a combination thereof. The polyphenolic compound may be tannin, pyrogallol, or a combination thereof, and the polysaccharide-based compound may be lignin, hyaluronic acid, or a combination thereof.

[0058] The content of the additive may be 0.003 wt % to 0.14 wt %, 0.01 wt % to 0.07 wt %, or 0.02 wt % to 0.06 wt % relative to 100 wt % of the negative electrode active material layer. When the content of the additive is within this range, the dispersant surface can be substantially completely surrounded, thereby sufficiently preventing the problem of the dispersant being adsorbed onto substances such as the active material and binder.

[0059] In one embodiment, the negative electrode active material may be a Si-based negative electrode active material. Si-based negative electrode active materials can exhibit improved current density and high capacity, but can also experience significant volume expansion during charge and discharge. In one embodiment, the negative electrode active material layer includes an expansion-reducing binder, which effectively suppresses volume expansion of the Si-based negative electrode active material. The linear carbon conductive material can be used to adequately maintain an electrical network. The Si-based negative electrode active material and the linear carbon conductive material can be uniformly dispersed in the negative electrode active material layer by using both a dispersant and an additive.

[0060] The Si-based negative electrode active material may be a silicon-carbon composite. The carbon may be amorphous carbon or may include amorphous and crystalline carbon. The crystalline carbon may be natural graphite, artificial graphite, or a combination thereof. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof.

[0061] The silicon-carbon composite may be in the form of silicon particles coated with amorphous carbon. For example, the silicon-carbon composite may include silicon particles and an amorphous carbon coating layer located on the surface of the silicon particles. Alternatively, the silicon composite may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, e.g., the primary silicon particles may be coated with amorphous carbon. For example, the secondary particles may be dispersed in an amorphous carbon matrix. The primary silicon particles may be nanosilicon particles. The average particle size of the nanosilicon particles may be 10 nm to 900 nm, 10 nm to 800 nm, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 200 nm. When the average particle size of the nanosilicon particles is within the above range, excessive volume expansion that occurs during charging and discharging can be suppressed, and conductive path disconnection due to particle crushing during charging and discharging can be prevented. In one embodiment, the particle size of the silicon secondary particles does not need to be particularly limited.

[0062] The amorphous carbon can be soft carbon, hard carbon, mesophase pitch charcoal, calcined coke, carbon fiber, or a combination thereof.

[0063] The thickness of the amorphous carbon coating layer can be appropriately adjusted, for example, about 2 nm to 800 nm, 5 nm to 600 nm, 10 nm to 400 nm, or 20 nm to 200 nm. The thickness of the amorphous carbon coating layer can be measured using an SEM or TEM image of a cross section of the silicon-carbon composite, but is not limited thereto, and can be measured by any method known in the art that can measure the thickness of an amorphous carbon coating layer.

[0064] The average particle size of the silicon-carbon composite can be appropriately adjusted and can be, for example, 30 μm or less, for example, 1 μm to 30 μm, 2 μm to 25 μm, 3 μm to 20 μm, or 5 μm to 15 μm.

[0065] The content of silicon particles may be 30% to 70% by weight, or 40% to 65% by weight, based on 100% by weight of the silicon-carbon composite. The content of amorphous carbon may be 30% to 70% by weight, or 35% to 60% by weight, based on 100% by weight of the entire silicon-carbon composite. When the contents of silicon particles and amorphous carbon satisfy the above ranges, a higher capacity can be achieved.

[0066] In the silicon-carbon composite, the carbon can include amorphous carbon and crystalline carbon. In one embodiment, the silicon-carbon composite can include a core including silicon particles and crystalline carbon, and an amorphous carbon coating layer disposed on the surface of the core. For example, the silicon-carbon composite can include a core including silicon primary particles and secondary particles formed by granulating crystalline carbon, and an amorphous carbon coating layer disposed on the core. The amorphous carbon can also be disposed between the silicon primary particles or between the crystalline carbon, so that the amorphous carbon is filled between the silicon primary particles or the crystalline carbon.

[0067] The crystalline carbon may be amorphous, plate-like, flake-like, spherical or fibrous natural graphite, artificial graphite or a combination thereof.

[0068] The content of crystalline carbon may be 10 to 70% by weight, for example 20 to 60% by weight, based on 100% by weight of the total of silicon particles, amorphous carbon, and crystalline carbon. When crystalline carbon is contained in the above content range, the conductivity can be further improved.

[0069] In an embodiment, the negative electrode may further include a carbon-based negative electrode active material in addition to the silicon-based negative electrode active material. When both the silicon-based negative electrode active material and the carbon-based negative electrode active material are used, the weight ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be 1:99 to 50:50. More specifically, the weight ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be 5:95 to 20:80.

[0070] The content of the negative electrode active material in the negative electrode active material layer may be 90% by weight to 99% by weight, or 95% by weight to 98% by weight, relative to 100% by weight of the negative electrode active material layer.

[0071] The negative electrode active material layer may further include an adhesive binder commonly used in negative electrodes. The adhesive binder may be a water-based binder. When the negative electrode active material layer further includes an adhesive binder, the content of the adhesive binder may be appropriately adjusted, for example, 0.1 wt % to 3 wt % or 0.2 wt % to 2 wt % relative to 100 wt % of the total negative electrode active material layer.

[0072] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0073] The negative electrode according to one embodiment includes a current collector that supports the negative electrode active material.

[0074] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal coated polymer substrate, and combinations thereof.

[0075] <Lithium secondary battery> Another embodiment provides a lithium secondary battery including a negative electrode, a positive electrode, and an electrolyte.

[0076] [Positive electrode] The positive electrode may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer includes a positive electrode active material, and may further include a binder and / or a conductive material.

[0077] As an example, the positive electrode may further include an additive that can act as a sacrificial positive electrode.

[0078] The content of the positive electrode active material may be 90% by weight to 99.5% by weight relative to 100% by weight of the positive electrode active material layer, and the contents of the binder and conductive material may be 0.5% by weight to 5% by weight each relative to 100% by weight of the positive electrode active material layer.

[0079] The positive electrode active material may be a compound capable of reversibly inserting and extracting lithium (lithiated insertion compound). Specifically, one or more of composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0080] The composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0081] As an example, a compound represented by any one of the following chemical formulas can be used: Li a A1-b X b About 2-c D c (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05);Li a Mn 2-b X b About 4-c D c (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.05);Li a Ni 1-b-c Co b X c About 2-α D α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.5、0<α<2);Li a Ni 1-b-c Mn b X c About 2-α D α (0.90≦a≦1.8、0≦b≦0.5、0≦c≦0.5、0<α<2);Li a Ni b Co c L 1 d G e O2(0.90≦a≦1.8、0≦b≦0.9、0≦c≦0.5、0≦d≦0.5、0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8、0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8、0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8、0.001≦b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8、0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8、0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4(0.90≦a≦1.8) In the formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0082] For example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more but 99 mol% or less relative to 100 mol% of metals excluding lithium in a lithium transition metal composite oxide. The high-nickel positive electrode active material can realize high capacity and therefore can be applied to high-capacity, high-density lithium secondary batteries.

[0083] The binder serves to effectively adhere the positive electrode active material particles to each other and to effectively adhere the positive electrode active material to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0084] The conductive material is used to impart conductivity to the electrode, and any electron-conductive material that does not undergo chemical change in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0085] The current collector may be made of Al, but is not limited to this.

[0086] [Electrolyte] The electrolyte solution includes a non-aqueous organic solvent and a lithium salt.

[0087] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate.

[0088] The non-aqueous organic solvent can be a carbonate, ester, ether, ketone, or alcohol solvent, an aprotic solvent, or a combination thereof.

[0089] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0090] Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0091] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0092] The non-aqueous organic solvents can be used alone or in combination of two or more kinds.

[0093] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0094] The electrolyte may further include vinyl ethyl carbonate, vinylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, or combinations thereof as additives.

[0095] Lithium salts are substances dissolved in organic solvents and act as a source of lithium ions in the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0096] [Separator] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0097] The separator can include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0098] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0099] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0100] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0101] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are stacked.

[0102] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams illustrating a lithium secondary battery according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 1. Also, as shown in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0103] The lithium secondary battery according to an embodiment of the present invention may be applied to automobiles, mobile phones, and / or various types of electrical devices, but the present invention is not limited thereto.

[0104] Examples and comparative examples of the present invention will be described below. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0105] Example 1 Acrylic acid (AA) as a first monomer, acrylonitrile (AN) as a second monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a third monomer were added to a reactor in amounts of 55 wt %, 40 wt %, and 5 wt %, respectively, and benzoyl peroxide initiator and water were added to the reactor to carry out a copolymerization reaction.

[0106] Sodium hydroxide was added to the resulting copolymerization reaction product and stirred to produce an aqueous binder solution (solids content 6 wt%) containing an expansion-reducing binder, which is a copolymer of the first, second, and third monomers. The amount of sodium hydroxide used was adjusted so that 60 mol% of the first monomer was substituted with sodium ions, resulting in a copolymer binder containing sodium polyacrylate in which 60 mol% of the acrylic groups contained in the first monomer were substituted with sodium ions. The degree of sodium ion substitution of the first monomer was measured by ICP spectroscopy and was found to be 60 mol%.

[0107] A silicon-carbon composite negative electrode active material (average particle size (D50): 10 μm), the obtained binder aqueous solution (solid content: 6 wt%), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt%, 1.4 wt% (binder content in the binder aqueous solution: 1.4 wt%), 0.07 wt%, 0.15 wt%, and 0.05 wt%.

[0108] The silicon-carbon composite used contained granules, which were secondary particles formed by granulating artificial graphite and silicon nanoparticles, with a soft carbon coating layer formed on the surface of the granules. The artificial graphite content was 40 wt% of the total weight of the silicon-carbon composite, the silicon nanoparticle content was 40 wt%, and the soft carbon content was 20 wt%.

[0109] The negative electrode active material layer slurry was applied to a copper current collector, dried, and rolled to prepare a negative electrode having a negative electrode active material layer formed on the current collector.

[0110] LiNi 0.8 Co 0.1 Mn 0.1A positive electrode active material layer slurry was prepared by mixing 96 wt% of O2 positive electrode active material, 2 wt% of Ketjen Black, and 2 wt% of polyvinylidene fluoride in N-methylpyrrolidone solvent. The resulting positive electrode active material layer slurry was coated onto an aluminum foil current collector, dried, and rolled to prepare a positive electrode.

[0111] A full cell was fabricated using the prepared anode, cathode, and electrolyte. The electrolyte was 1.5 M LiPF6 dissolved in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio: 20:10:70).

[0112] Example 2 A negative electrode was fabricated in the same manner as in Example 1, except that acrylic acid (AA) as the first monomer, acrylonitrile (AN) as the second monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as the third monomer were used in amounts of 50 wt%, 45 wt%, and 5 wt%, respectively, and tannin was used as an additive.

[0113] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0114] Example 3 A negative electrode and a full cell were produced in the same manner as in Example 2, except that pyrogallol was used as the additive instead of tannin.

[0115] Example 4 A negative electrode and a full cell were manufactured in the same manner as in Example 2, except that lignin was used as the additive instead of tannin.

[0116] Example 5 A negative electrode and a full cell were manufactured in the same manner as in Example 2, except that hyaluronic acid was used as the additive instead of tannin.

[0117] Example 6 Acrylic acid (AA) as a first monomer, acrylonitrile (AN) as a second monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a third monomer were added in amounts of 45 wt %, 50 wt %, and 5 wt %, respectively, and benzoyl peroxide as an initiator and water were added to a reactor to carry out a copolymerization reaction.

[0118] Sodium hydroxide was added to the resulting copolymerization reaction product and stirred to produce an aqueous binder solution containing an expansion-reducing binder, which is a copolymer of the first, second, and third monomers. The amount of sodium hydroxide used was adjusted so that 60 mol% of the first monomer was substituted with sodium ions, resulting in a copolymer binder containing sodium polyacrylate in which 60 mol% of the acrylic groups contained in the acrylamide first monomer were substituted with sodium ions. The degree of sodium ion substitution of the acrylamide first monomer was measured by ICP spectroscopy and was found to be 60 mol%.

[0119] The negative electrode active material of Example 1, the obtained binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, 0.15 wt %, and 0.05 wt %.

[0120] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0121] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0122] Example 7 Acrylic acid (AA) as a first monomer, acrylonitrile (AN) as a second monomer, and polyethylene glycol methacrylate (PEGMA) as a third monomer were added to a reactor in amounts of 50 wt %, 45 wt %, and 5 wt %, respectively, and benzoyl peroxide initiator and water were added to the reactor to carry out a copolymerization reaction.

[0123] Sodium hydroxide was added to the resulting copolymerization reaction product and stirred to produce an aqueous binder solution containing an expansion-reducing binder, which is a copolymer of the first, second, and third monomers. The amount of sodium hydroxide used was adjusted so that 60 mol% of the first monomer was substituted with sodium ions, resulting in a copolymer binder containing sodium polyacrylate in which 60 mol% of the acrylic groups contained in the acrylic acid first monomer were substituted with sodium ions. The degree of sodium ion substitution of the acrylic acid first monomer was measured by ICP spectroscopy and was found to be 60 mol%.

[0124] The negative electrode active material of Example 1, the obtained binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, 0.15 wt %, and 0.05 wt %.

[0125] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0126] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0127] (Comparative Example 1) Carboxymethyl cellulose (CMC) was added to water to prepare a binder aqueous solution with a solid content of 1 wt %.

[0128] A negative electrode active material layer slurry was prepared by mixing the silicon-carbon composite negative electrode active material, the binder aqueous solution (solid content: 1 wt%), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and hyaluronic acid additive in amounts of 98.33 wt%, 1.4 wt% (binder content in the binder aqueous solution: 1.4 wt%), 0.07 wt%, 0.15 wt%, and 0.05 wt%.

[0129] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0130] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0131] (Comparative Example 2) Acrylic acid (AA) as a first monomer and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a third monomer were added to a reactor in amounts of 95% by weight and 5% by weight, respectively, and then benzoyl peroxide as an initiator and water were added to the reactor to carry out a copolymerization reaction.

[0132] Sodium hydroxide was added to the resulting copolymerization reaction product and stirred to produce an aqueous binder solution containing an expansion-reducing binder, which is a copolymer of the first and third monomers. The amount of sodium hydroxide used was adjusted so that 60 mol% of the first monomer was substituted with sodium ions, resulting in a copolymer binder containing sodium polyacrylate in which 60 mol% of the acrylic groups contained in the acrylic acid first monomer were substituted with sodium ions. The degree of sodium ion substitution of the acrylic acid first monomer was measured by ICP spectroscopy and was found to be 60 mol%.

[0133] The negative electrode active material of Example 1, the obtained binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, 0.15 wt %, and 0.05 wt %.

[0134] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0135] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0136] (Comparative Example 3) Acrylonitrile (AN) as a second monomer and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as a third monomer were added to a reactor in amounts of 95% by weight and 5% by weight, respectively, and benzoyl peroxide as an initiator and water were added to the reactor to carry out a copolymerization reaction to produce an aqueous binder solution.

[0137] The negative electrode active material of Example 1, the obtained binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, 0.15 wt %, and 0.05 wt %.

[0138] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0139] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0140] Comparative Example 4 Acrylic acid (AA) as a first monomer and acrylonitrile (AN) as a second monomer were added to a reactor in amounts of 60% by weight and 40% by weight, respectively, and benzoyl peroxide as an initiator and water were added to the reactor to carry out a copolymerization reaction.

[0141] Sodium hydroxide was added to the resulting copolymerization reaction product and stirred to produce an aqueous binder solution (solid content: 6 wt%) containing an expansion-reducing binder, which is a copolymer of the first and second monomers. The amount of sodium hydroxide used was adjusted so that 60 mol% of the first monomer was substituted with sodium ions, resulting in a copolymer binder containing sodium polyacrylate in which 60 mol% of the acrylic groups contained in the acrylic acid first monomer were substituted with sodium ions. The degree of sodium ion substitution of the acrylic acid first monomer was measured by ICP spectroscopy and was found to be 60 mol%.

[0142] The negative electrode active material of Example 1, the obtained binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa), and lignin additive were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, 0.15 wt %, and 0.05 wt %.

[0143] The obtained negative electrode active material layer slurry was applied to a copper current collector, dried and rolled to produce a negative electrode in which a negative electrode active material layer was formed on the current collector.

[0144] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0145] (Comparative Example 5) A negative electrode was fabricated in the same manner as in Example 1, except that the silicon-carbon composite negative electrode active material used in Example 1, the binder aqueous solution (solid content: 6 wt %) of Example 1, and carbon black (CB) conductive material were mixed to prepare a negative electrode active material layer slurry in amounts of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), and 0.27 wt %.

[0146] A full cell was manufactured in the same manner as in Example 1, except that the manufactured negative electrode was used.

[0147] (Comparative Example 6) A negative electrode was fabricated in the same manner as in Example 1, except that the silicon-carbon composite negative electrode active material, binder aqueous solution (solid content: 6 wt %), single-walled carbon nanotubes (SWCNTs, average diameter: 1 nm to 2 nm, average length: <10 μm), and polyvinylpyrrolidone dispersant (PVP, Mw: 30 KDa) used in Example 1 were mixed to prepare negative electrode active material layer slurries at concentrations of 98.33 wt %, 1.4 wt % (binder content in the binder aqueous solution: 1.4 wt %), 0.07 wt %, and 0.02 wt %, respectively.

[0148] The binder compositions, conductive materials, dispersants and additives of Examples 1 to 7 and Comparative Examples 1 to 6 are summarized in Table 1 below.

[0149] [Table 1]

[0150] Experimental Example 1) Evaluation of the average particle size (D50) of negative electrode active material The binder, conductive material (single-walled carbon nanotubes), dispersant, and additive used in Examples 1 to 7 and Comparative Examples 1 to 6 were added to an aqueous solvent to prepare a dispersion. The average particle size (D50) of the single-walled carbon nanotubes in this dispersion was measured using a particle size analyzer (product name: PSA Series, manufacturer: Anton Paar). The increase rate of the average particle size (D50, B) of the single-walled carbon nanotubes in the measured dispersion relative to the average particle size (D50, A) of the single-walled carbon nanotubes used in manufacturing the negative electrode was calculated using the following formula 1. The results are shown in Table 2 below. [Formula 1] Growth rate = [(BA) / A]*100

[0151] Experimental Example 2) Evaluation of carbon nanotube (CNT) aggregation The aggregation of carbon nanotubes in the negative electrodes produced in Examples 1 to 7 and Comparative Examples 1 to 6 was measured using an SEM. The results are shown in Table 2 below. In Table 2 below, X means that no aggregation was observed, and O means that aggregation was observed. Furthermore, since carbon black conductive material was used in Comparative Example 5, this experiment was not performed.

[0152] Experimental Example 3) Evaluation of negative electrode expansion rate The full cells prepared in Examples 1 to 7 and Comparative Examples 1 to 6 were charged and discharged 100 times under the conditions of 0.5C constant current-constant voltage (CC-CV) 4.2V, 0.05C cutoff charge, and 0.5C constant current (CC) 2.5V cutoff discharge. The thickness of the negative electrode before and after charge and discharge was measured, and the negative electrode expansion rate was calculated using the following equation 2. [Formula 2] Expansion rate (%) = {(negative electrode thickness after charge / discharge - negative electrode thickness before charge / discharge) / negative electrode thickness before charge / discharge} * 100

[0153] Experimental example 4) Evaluation of lifespan maintenance rate The full cells prepared in Examples 1 to 7 and Comparative Examples 1 to 6 were charged and discharged 100 times under the conditions of 0.5C constant current-constant voltage (CC-CV) at 4.2 V, 0.05C cutoff charge, and 0.5C constant current (CC) at 2.5 V cutoff discharge. The ratio of the 100th charge capacity to the single charge capacity was calculated. The results are shown in Table 2 below as capacity retention.

[0154] [Table 2]

[0155] As shown in Table 2, the D50 increase rates of Examples 1 to 7 were 3% to 8%, which was much lower than that of Comparative Example 2, and no CNT aggregation occurred in the negative electrode. In addition, a low negative electrode expansion rate and an excellent capacity retention rate were observed.

[0156] In the case of Comparative Example 1, in which a CMC binder was used, the D50 increase rate was low and no aggregation occurred within the CNT negative electrode, but the negative electrode showed a very high expansion rate and a low capacity retention rate.

[0157] In the case of Comparative Example 2, in which an expansion-reducing binder not containing the second monomer was used, the negative electrode expansion rate was somewhat low, but the D50 increase rate was very high, and CNT aggregation occurred in the negative electrode, resulting in a low lifespan maintenance rate.

[0158] In the case of Comparative Example 3, in which a copolymer binder containing no first monomer was used, the binder was insoluble, and subsequent experiments could not be carried out.

[0159] In addition, in the case of Comparative Example 4, in which a copolymer binder containing no third monomer was used, high battery resistance characteristics were observed due to the absence of the third monomer, and therefore, a somewhat low lifespan was observed.

[0160] Although the same expansion-reducing binder as in Example 4 was used, Comparative Example 5, which used a carbon black conductive material, showed a low negative electrode expansion rate but also a low lifespan maintenance rate.

[0161] In addition, in Comparative Example 6, which used the same expansion-reducing binder as in Example 1 but did not use any additives, the D50 increase rate was very high, and CNT aggregation occurred in the negative electrode, resulting in a low lifespan maintenance rate.

[0162] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is to be understood that these modifications also fall within the scope of the present invention. [Explanation of symbols]

[0163] 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab 100 Lithium secondary battery

Claims

1. a negative electrode active material layer including a Si-based negative electrode active material, a binder, a linear carbon conductive material, a dispersant, and an additive having one or more multifunctional hydroxyl groups and capable of adsorbing to a surface of the dispersant; The negative electrode for a lithium secondary battery, wherein the binder is a copolymer containing an acrylic group and a cyano group.

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the additive is a polyphenol-based compound, a polysaccharide-based compound, or a combination thereof.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the additive is tannin, gallol, lignin, hyaluronic acid, or a combination thereof.

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the weight average molecular weight (Mw) of the dispersant is 30,000 Daltons or more.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the binder is an expansion-reducing binder.

6. the copolymer comprises a first monomer, a second monomer, and a third monomer; the first monomer comprises an acryloyl group; the second monomer comprises a cyano group; The negative electrode for a lithium secondary battery according to claim 1 , wherein the third monomer contains an acrylate group.

7. 7. The negative electrode for a lithium secondary battery according to claim 6, wherein the content of the first monomer is 40% by weight to 60% by weight with respect to 100% by weight of the copolymer.

8. 7. The negative electrode for a lithium secondary battery according to claim 6, wherein the first monomer is (meth)acrylic acid, a metal salt of (meth)acrylic acid, an ammonium salt of (meth)acrylic acid, an amine salt of (meth)acrylic acid, or a combination thereof.

9. 9. The negative electrode for a lithium secondary battery according to claim 8, wherein the metal in the metal salt of (meth)acrylic acid is an alkali metal or an alkaline earth metal.

10. 9. The negative electrode for a lithium secondary battery according to claim 8, wherein the metal salt of (meth)acrylic acid has a degree of metal ion substitution of 20 mol % to 100 mol %.

11. The negative electrode for a lithium secondary battery according to claim 6 , wherein the second monomer is acrylonitrile.

12. The negative electrode for a lithium secondary battery according to claim 6 , wherein the third monomer is a (meth)acrylate containing a sulfonic acid group or an ethylene glycol group.

13. 13. The negative electrode for a lithium secondary battery according to claim 12, wherein the third monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid or polyethylene glycol methacrylate monomer.

14. 14. The negative electrode for a lithium secondary battery according to claim 13, wherein the third monomer is 2-acrylamido-2-methyl-1-propanesulfonic acid.

15. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the linear carbon conductive material is a carbon nanotube, a carbon nanofiber, or a combination thereof.

16. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the linear carbon conductive material is 0.005 wt % to 0.2 wt % relative to 100 wt % of the negative electrode active material layer.

17. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the binder is 0.5% by weight to 3% by weight relative to 100% by weight of the negative electrode active material layer.

18. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the dispersant is 0.009% by weight to 0.35% by weight relative to 100% by weight of the negative electrode active material layer.

19. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of the additive is 0.003% by weight to 0.14% by weight relative to 100% by weight of the negative electrode active material layer.

20. The negative electrode according to any one of claims 1 to 19; a positive electrode; and non-aqueous electrolyte A lithium secondary battery comprising:

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