Negative electrode and lithium secondary battery comprising the same

Abstract

The negative electrode of an example embodiment of the present invention includes: a negative electrode current collector; and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes: a first region provided on the negative electrode current collector and containing niobium oxide as a negative electrode active material; and a second region provided on the first region and containing a carbon-based material as a negative electrode active material.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0136593, filed on October 8, 2024, the disclosure of which is incorporated herein by reference.

[0002] This invention relates to a negative electrode and a lithium secondary battery. Background Technology

[0003] Recently, with technological advancements and increasing demand for mobile devices, the demand for batteries as energy sources has grown rapidly. As HEV, PHEV, and EV vehicles gain attention as the future of automobiles, extensive research is underway on batteries capable of meeting diverse requirements.

[0004] In particular, research on lithium-ion rechargeable batteries with high energy density and excellent lifespan and cycle characteristics is actively underway. Traditional lithium-ion rechargeable batteries mainly use carbon-based compounds as anode active materials, which can reversibly insert and extract lithium ions while maintaining structural and electrical properties. However, recently, with the increasing demand for developing batteries with high energy density, in addition to carbon-based compounds, transition metals (Group IV and Group V) that react with lithium chemistry, such as silicon and tin, or their alloys or oxides, have been extensively studied.

[0005] To achieve batteries with high energy density and high power output, research is underway on high-load electrodes and resistance improvements. In high-load electrodes, as the movement path of lithium ions becomes longer, ion diffusion is delayed, which increases resistance and reduces battery output. Therefore, there is a need to develop techniques to improve the resistance characteristics of high-load electrodes and increase battery output. Summary of the Invention

[0006] [Technical Issues]

[0007] The technical problem sought to be solved by the present invention is to provide a high-load negative electrode with improved resistance characteristics and enhanced battery output characteristics.

[0008] The problems to be solved by the present invention are not limited to those described above, and those skilled in the art will clearly understand, based on this specification and the accompanying drawings, any problems not mentioned.

[0009] [Technical Solution]

[0010] A negative electrode according to an exemplary embodiment of the present invention comprises: a negative electrode current collector; and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises: a first region disposed on the negative electrode current collector and containing niobium oxide as a negative electrode active material; and a second region disposed on the first region and containing a carbon-based material as a negative electrode active material.

[0011] In an exemplary embodiment, the thickness of the first region is 15% or less of the thickness of the negative electrode active material layer.

[0012] In an exemplary embodiment, the niobium oxide is a compound represented by the following Chemical Formula 1: [Chemical Formula 1] M x Nb y O z In Chemical Formula 1, M comprises one or more selected from the group consisting of W, Mo, Zn, Ni, Sr and Cu, and 0≤x ≤10, 1≤y ≤20 and 1.5≤z ≤70.

[0013] In an exemplary embodiment, the loading amount of the negative electrode active material layer is 200 mg / 25 cm 2 or more.

[0014] In an exemplary embodiment, the niobium oxide is one or a mixture of two or more selected from the group consisting of NbO, NbO₂, Nb₂O₃ and Nb₂O₅.

[0015] In an exemplary embodiment, the thickness of the first region is 15 μm or less.

[0016] In an exemplary embodiment, the thickness of the first region is from 3 μm to 13 μm.

[0017] In an exemplary embodiment, the carbon-based material is one or a mixture of two or more selected from the group consisting of natural graphite, artificial graphite, hard carbon obtained by pyrolysis of phenolic resin or furan resin, coke, needle coke, and soft carbon obtained by carbonization of pitch.

[0018] In an exemplary embodiment, each of the first region and the second region comprises a binder, and the binder content in the first region is greater than the binder content in the second region.

[0019] In an exemplary embodiment, the second region further comprises one or a mixture of two or more selected from the group consisting of Si, SiO x (0<x<2), Si-C composites and Si metal alloys as a negative electrode active material.

[0020] An exemplary embodiment of the lithium secondary battery of the present invention includes: a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the negative electrode is the negative electrode described above.

[0021] [Beneficial Effects]

[0022] According to an exemplary embodiment of the present invention, a high-load negative electrode with excellent output and resistance characteristics is provided, which enables a high-energy-density battery. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view showing the negative electrode of an exemplary embodiment. Detailed Implementation

[0024] A more detailed description of the invention is provided below to aid in understanding it.

[0025] The terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings, but should be interpreted based on the inventor's ability to appropriately define the concepts of the terms in order to describe the invention in the best possible way, according to the technical concepts of the invention.

[0026] The terminology used in this specification is for describing exemplary embodiments only and is not intended to limit the scope of the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0027] In this specification, terms such as “comprising,” “equipped with,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof implemented, and should not be construed as excluding the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0028] In this specification, the term "combination thereof" as contained in the Markush form of the description means a mixture or combination of one or more of the groups of components selected from the group of components described in the Markush form of the description, meaning that it includes one or more of the groups of components selected from the group of components described in the Markush form of the description.

[0029] In this specification, the description of "A and / or B" means "A or B or both".

[0030] negative electrode

[0031] Figure 1 This is a schematic cross-sectional view showing the negative electrode of an exemplary embodiment.

[0032] Reference Figure 1In an exemplary embodiment, the negative electrode 100 includes a negative electrode current collector 110 and a negative electrode active material layer 120, wherein the negative electrode active material layer 120 includes a first region 121 and a second region 122. The first region 121 is disposed on the negative electrode current collector 110 and includes niobium oxide as the negative electrode active material. The second region 122 is disposed on the first region 121 and includes a carbon-based material as the negative electrode active material.

[0033] The carbon-based material contained in the second region 122 is a conventional negative electrode active material with excellent structural stability, and therefore the volume change due to repeated charging and discharging is not significant. In this invention, in order to improve the resistance and output characteristics in the high-load negative electrode, the negative electrode active material layer 120 is configured as a bilayer structure including a first region 121 and a second region 122, and contains niobium oxide, which has excellent output characteristics, as the negative electrode active material in the first region 121 near the negative electrode current collector 110. Since niobium oxide can exist in a lithium-containing state within the charge and discharge voltage range of the carbon-based material contained in the second region, it can improve the output characteristics of the battery. In addition, because the first region 121 contains niobium oxide at a certain distance from the negative electrode surface, the movement path of lithium ions is improved, thereby further improving the output characteristics of the secondary battery. Furthermore, compared with titanium materials, niobium oxide has excellent fast charging performance and lifetime characteristics, therefore niobium oxide is selected as the negative electrode active material of the first region 121.

[0034] The thickness of the first region 121 can be less than 15% of the thickness of the negative electrode active material layer 120. Since the first region 121 is used to improve the movement path of lithium ions, the predetermined thickness range is sufficient. Because the niobium oxide included as the negative electrode active material in the first region 121 has a relatively small capacity compared to carbon-based negative electrode active materials, it is not preferable to exceed this thickness range for achieving high energy density in the secondary battery. The thickness of the first region 121 can be less than 15% of the thickness of the negative electrode active material layer 120, specifically 3% to 15%, and more specifically 6% to 12%.

[0035] The thickness of the negative electrode active material layer 120 can be 70 to 200 μm, specifically 80 to 170 μm, and more specifically 90 to 150 μm. Additionally, the thickness of the first region 121 can be less than 15 μm, specifically 3 to 13 μm, and more specifically 6 to 12 μm.

[0036] The loading of the negative electrode active material layer 120 can be 200 mg / 25 cm. 2 That's all. Specifically, the loading of the negative electrode active material layer 120 can be: 200 mg / 25 cm³. 2 Above; 200 mg / 25cm2 Up to 900 mg / 25cm 2 250 mg / 25cm 2 Up to 900 mg / 25cm 2 300 mg / 25cm 2 Up to 900 mg / 25cm 2 200 mg / 25cm 2 Up to 800 mg / 25cm 2 250 mg / 25cm 2 Up to 800 mg / 25cm 2 250 mg / 25cm 2 Up to 750 mg / 25cm 2 250 mg / 25cm 2 Up to 700 mg / 25 cm 2 300 mg / 25cm 2 Up to 600 mg / 25cm 2 Or 250 mg / 25cm 2 Up to 500 mg / 25cm 2 The loading amount is based on the loading amount of the negative electrode active material layer disposed on one surface of the current collector. When the loading amount of the negative electrode active material layer 120 is within this range, high output performance can be achieved together with the energy density of the negative electrode, so it can be easily applied not only to devices requiring high output (e.g., electric vehicles) but also to devices requiring high energy density (e.g., ESS).

[0037] The first region 121 includes niobium oxide as the negative electrode active material.

[0038] Niobium oxide can be a compound represented by the following chemical formula 1.

[0039] [Chemical Formula 1]

[0040] M x Nb y O z

[0041] In chemical formula 1, M includes one or more selected from W, Mo, Zn, Ni, Sr, and Cu, and 0≤x≤10, 1≤y≤20 and 1.5≤z≤70.

[0042] In this invention, niobium oxide is a compound represented by the above-mentioned chemical formula 1, meaning an oxide containing niobium (Nb) as the main metallic component. Specifically, niobium oxide can be a mixture of one or more compounds selected from NbO, NbO2, Nb2O3, and Nb2O5.

[0043] After initial charging, niobium oxide can maintain the lithium-ion intercalation state within the charge / discharge voltage range of the carbon-based anode active material. Therefore, niobium oxide can easily release lithium ions to the anode current collector, thereby shortening the lithium-ion migration path of the anode.

[0044] Furthermore, the niobium oxide may be doped with one or more elements selected from tungsten (W), molybdenum (Mo), zinc (Zn), nickel (Ni), strontium (Sr), and copper (Cu). In this case, based on the mole fraction of niobium (Nb), the doping amount of the element can be greater than 0 mol% and at most 50 mol%. Specifically, based on the mole fraction of niobium (Nb), the doping amount of the element can be greater than 0 mol% and at most 40 mol%, greater than 0 mol% and at most 30 mol%, greater than 0 mol% and at most 20 mol%, greater than 0 mol% and at most 10 mol%, 1 mol% to 9 mol%, 1 mol% to 20 mol%, 5 mol% to 15 mol%, 10 mol% to 30 mol%, 20 mol% to 40 mol%, or 5 mol% to 35 mol%. In one embodiment, the niobium oxide may comprise Nb₂O₅ doped with 5 mol% to 10 mol% of tungsten (W) based on the mole fraction of niobium (Nb).

[0045] By employing elemental doping, niobium oxides can expand their lattice structure, thereby enhancing lithium-ion diffusion performance. Furthermore, when the niobium oxide is Nb₂O₅, the diffusion rate of tetravalent niobium ions (Nb₂O₅) can be increased. 4+ The ratio of oxygen vacancies to oxygen vacancies results in excellent conductivity and high-rate charge / discharge performance.

[0046] Niobium oxides can have a predetermined average particle size (D 50 Specifically, the average particle size (D) of niobium oxide 50 The average particle size (D) can range from 0.5 μm to 100 μm. For example, the average particle size of niobium oxide is... 50 The micrometer size can be 1 μm to 90 μm; 5 μm to 70 μm; 5 μm to 50 μm; 5 μm to 30 μm; 5 μm to 20 μm; 5 μm to 10 μm; 10 μm to 30 μm; 10 μm to 50 μm; 15 μm to 45 μm; 50 μm to 100 μm; 60 μm to 90 μm; 40 μm to 70 μm; 1 μm to 9 μm; or 0.5 μm to 0.9 μm.

[0047] When the average particle size of niobium oxide exceeds the above-mentioned upper limit, the average particle size of niobium oxide (D) is increased. 50 By adjusting the parameters to the aforementioned range, the present invention can prevent the output performance of the negative electrode from decreasing due to a reduction in specific surface area. Furthermore, it can prevent a decrease in lithium-ion diffusion capacity in the first region 121 due to the average particle size of niobium oxide being smaller than the aforementioned lower limit.

[0048] Furthermore, niobium oxides can have a structure coated with a carbon layer. Compared to the case without a carbon layer coating, niobium oxides coated with a carbon layer can achieve a higher reversible capacity.

[0049] At this point, a carbon layer of predetermined thickness can be formed on the surface of the niobium oxide. Specifically, the thickness of the carbon layer can be 1 nm to 20 nm, and more specifically 1 nm to 15 nm; 1 nm to 10 nm; 5 nm to 20 nm; 10 nm to 20 nm; 5 nm to 15 nm; or 7 nm to 13 nm.

[0050] The second region 122 includes carbon-based materials as negative electrode active materials.

[0051] Carbon-based materials have been used as conventional anode active materials, and compared with niobium oxide contained in the first region 121, they have the advantage of being conducive to achieving high energy density.

[0052] There are no particular restrictions on carbon-based materials, as long as they can insert and extract lithium ions, and they can be crystalline carbon compounds, amorphous carbon compounds, or mixtures thereof.

[0053] Representative examples of crystalline carbon compounds include graphite. This type of graphitic crystalline carbon includes, for example, artificial graphite in the form of potato-shaped or mesophase carbon microspheres (MCMB), or natural graphite that has undergone surface treatment to smooth its edges. Amorphous carbon compounds are materials in which carbon atoms have an amorphous crystalline structure, and examples include hard carbon obtained by the pyrolysis of phenolic or furan resins, coke, needle coke, or soft carbon obtained by the carbonization of pitch.

[0054] According to a preferred embodiment, the carbon-based material can be natural or artificial graphite, which has excellent density and electrical conductivity, resulting in large capacity, high energy density, and good output and rate characteristics.

[0055] For high densification of the negative electrode active material layer, carbon-based materials can meet the predetermined range of average particle size and tap density.

[0056] Specifically, the average particle size (D) of carbon-based materials 50) may be 0.5 μm to 20 μm. Specifically, the average particle size of the carbon-based material (D 50 ) may be 0.5 μm to 15 μm; 0.5 μm to 10 μm; 5 μm to 20 μm; 10 μm to 20 μm; 12 μm to 18 μm; 2 μm to 7 μm; 0.5 μm to 5 μm; or 1 μm to 3 μm.

[0057] Advantageously, the particle size of the carbon-based material is made as small as possible to maximize disorder in the expansion direction of each particle, thereby preventing particle expansion caused by lithium ion charging. However, if the particle diameter of the carbon-based material is less than 0.5 μm, a large amount of binder may be required due to the increase in the number of particles per unit volume. On the other hand, if the maximum particle size exceeds 20 μm, expansion becomes severe, and when charging and discharging are repeated, the bonding between particles and between particles and the current collector deteriorates, which can significantly reduce cycle characteristics.

[0058] In addition, the tap density of the carbon-based material may be 0.7 g / cc to 1.5 g / cc. Specifically, the tap density of the carbon-based anode active material may be: 0.7 g / cc to 1.4 g / cc; 0.7 g / cc to 1.3 g / cc; 0.8 g / cc to 1.3 g / cc; 0.92 g / cc to 1.2 g / cc; or 0.95 g / cc to 1.15 g / cc.

[0059] The tap density of the carbon-based material refers to the density obtained by uniformly tapping or vibrating particles to fill the voids between the particles, which is the mass per unit volume of the carbon-based material composed of particles. The tap density of the carbon-based material not only directly affects the energy density of the anode, but also is highly correlated with the electrolyte impregnation performance of the anode. The present invention can prevent the decrease in capacity per unit volume caused by the relatively reduced content of the anode active material per unit volume of the anode by maintaining the tap density of the carbon-based material at or above the lower limit of the above range. In addition, the present invention can prevent the phenomenon of peeling from the current collector due to insufficient rolling of the anode active material layer during anode manufacturing by maintaining the tap density of the carbon-based material at or below the upper limit of the above range, while preventing the deterioration of the electrolyte impregnation performance and high-rate charge-discharge performance of the anode active material layer.

[0060] In addition to the carbon-based material, the second region 122 may further include SiO x (0<x <2), one or a mixture of two or more selected from the group consisting of Si-C composites and Si metal alloys as anode active materials. When a silicon-based material is included, it is advantageous for realizing a high energy density battery.

[0061] In addition to the aforementioned negative electrode active material, the negative electrode active material layer 120 may also include an adhesive and a conductive material.

[0062] The adhesive provides bonding between the negative electrode active material and the conductive material, and also provides bonding between the negative electrode active material layer and the negative electrode current collector. The adhesive can be one or more selected from the group consisting of: vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0063] Based on the total weight of the negative electrode active material layer 120, the content of the binder can be from 0.5% to 10% by weight, from 1% to 6% by weight, or from 2% to 6% by weight.

[0064] In an exemplary embodiment, the first region and the second region each include an adhesive, and the adhesive content in the first region may be greater than the adhesive content in the second region. Here, the adhesive content in the first region refers to the weight percentage of the adhesive contained in the first region relative to the total weight of the first region. Similarly, the adhesive content in the second region refers to the weight percentage of the adhesive contained in the second region relative to the total weight of the second region. When the adhesive content in the first region is greater than the adhesive content in the second region, the adhesion between the negative electrode current collector and the negative electrode active material layer is further improved, thereby enabling the realization of a battery with excellent capacity characteristics.

[0065] Conductive materials are not particularly limited, as long as they are conductive without causing chemical changes in the battery, and examples include: graphite, such as natural or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; conductive tubes, such as carbon nanotubes; fluorocarbon powders; metal powders, such as aluminum or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives.

[0066] Based on the total weight of the negative electrode active material layer 120, the content of conductive material can be from 0.5% to 10% by weight, from 1% to 6% by weight, or from 2% to 6% by weight.

[0067] The negative electrode current collector 110 is a highly conductive metal onto which the slurry of the negative electrode active material can easily adhere, and any metal that does not react within the voltage range of the battery can be used. Specifically, it can be: copper, stainless steel, aluminum, nickel, titanium, sintered carbon; stainless steel surface-treated with carbon, nickel, titanium, or silver; aluminum-cadmium alloy; non-conductive polymer surface-treated with conductive materials; or conductive polymer. Furthermore, fine irregularities can be formed on the surface to enhance the adhesion of the negative electrode active material, and it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0068] The negative electrode 100 can be prepared, for example, by adding a negative electrode mixture containing negative electrode active material to a predetermined solvent to prepare a negative electrode slurry, then coating it onto a current collector such as a metal foil, and drying and rolling it.

[0069] Lithium secondary batteries

[0070] Next, the lithium secondary battery of the present invention will be described.

[0071] The lithium secondary battery of the present invention may include: a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0072] The lithium secondary battery of the present invention can be manufactured according to conventional methods known in the art. For example, it can be manufactured by placing a separator between the positive and negative electrodes and injecting an electrolyte.

[0073] In an exemplary embodiment of the present invention, the negative electrode is as described above.

[0074] For example, the negative electrode includes: a negative electrode current collector 110; and a negative electrode active material layer 120 disposed on the negative electrode current collector 110; wherein the negative electrode active material layer 120 includes: a first region 121 disposed on the negative electrode current collector 110 and containing niobium oxide as a negative electrode active material; and a second region 122 disposed on the first region 121 and containing carbon-based material as a negative electrode active material, wherein the thickness of the first region 121 is less than 15% of the thickness of the negative electrode active material layer 120.

[0075] According to an exemplary embodiment of the present invention, niobium oxide is contained in a first region 121 away from the negative electrode surface, thus improving the movement path of lithium ions in a high-load electrode, thereby producing excellent resistance characteristics. Furthermore, niobium oxide can improve the output characteristics of the battery. Moreover, by controlling the thickness of the first region 121 containing niobium oxide within a predetermined range, the energy density of the battery is excellent.

[0076] Since the negative electrode has already been described in detail above, further redundant descriptions have been omitted.

[0077] 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.

[0078] 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. Examples include stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness from 3 μm to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0079] There are no particular limitations on the positive electrode active material, and compounds known in the art capable of reversibly inserting and deintercalating lithium can be used without restriction. Specifically, the positive electrode active material may include: layered compounds, such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium manganese oxide, such as Li... 1+x Mn 2-x O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, such as LiV3O8, LiV3O4, V2O5 or Cu2V2O; LiNi 1-x M x Nickel-site lithium nickel oxides represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); LiMn 2-x M x Lithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); and LiNi x Mn 2-x Lithium manganese composite oxides with a spinel structure represented by O4; LiMn2O4 in which Li is partially replaced by alkaline earth metal ions; disulfides; lithium iron phosphate represented by LiFePO4; disulfides; or Fe2(MoO4)3, but not limited thereto.

[0080] However, since the batteries using the present invention require improved energy density, the positive electrode active material can be a lithium transition metal oxide with a high Ni content, represented by the following chemical formula 2.

[0081] [Chemical Formula 2]

[0082] Li1+x Ni a Co b Mn c M 1-(a+b+c) O 2-y A y

[0083] In the above formula, M is selected from at least one of the following groups: Cu, Ti, Mg, Al, Pt, and Zr. A is a halogen that substitutes for oxygen, and 0≤x ≤0.5, 0.8≤a ≤1, 0≤b ≤0.2, 0≤c ≤0.2, 0.9≤a+b+c ≤1 and 0≤y ≤0.001.

[0084] More specifically, a can be 0.88 ≤ a < 1.

[0085] Furthermore, lithium transition metal oxides represented by chemical formula 2 can be mixed with other active materials.

[0086] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder.

[0087] The positive electrode conductive material is used to provide conductivity to the electrode and can be made of materials such as carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxides, and organic conductive materials. Currently commercially available conductive materials include acetylene black series (from Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (from Armak Company), Vulcan XC-72 (from Cabot Company), and Super P (from MMM). Carbon nanotubes, carbon nanofibers, and carbon black are preferred as conductive materials in this invention, with carbon nanotubes being the most preferred. The conductive network of carbon nanotubes can mitigate the migration of binders during the drying process of the positive electrode slurry, making it the most preferred conductive material included in the positive electrode of this invention.

[0088] The BET specific surface area of ​​carbon nanotubes can be: 100 m² 2 / g to 1000 m 2 / g, 150 m 2 / g to 800 m 2 / g, 150m 2 / g to 500 m 2 / g, 150 m 2 / g to 300 m 2 / g or 150 m 2 / g to 200 m 2 / g.

[0089] The positive electrode active material layer may contain 0.1 wt% to 30 wt%, specifically 0.1 wt% to 10 wt%, and more specifically 0.5 wt% to 5 wt% of positive electrode conductive material.

[0090] As a positive electrode binder, commonly used binder polymers can be used without limitation. Examples include: polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and various types of binder polymers.

[0091] The positive electrode active material layer may contain 0.1% to 30% by weight, specifically 0.1% to 10% by weight and more specifically 0.5% to 5% by weight of a positive electrode binder.

[0092] As the separator, any porous substrate commonly used as a separator in lithium secondary batteries can be used. For example, polyolefin porous membranes or nonwoven fabrics can be used, but are not particularly limited thereto. In particular, it is preferred to have low resistance to the movement of electrolyte ions and excellent electrolyte retention capacity.

[0093] Examples of polyolefin porous membranes include membranes formed from polyolefin polymers, such as polyethylene (e.g., high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutene, polypentene, etc., either alone or in mixtures.

[0094] As nonwoven fabrics, in addition to polyolefin-based nonwoven fabrics, for example, nonwoven fabrics formed alone or as mixtures thereof can be used, such as those made from polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyvinyl naphthalene, etc. The structure of the nonwoven fabric can be spunbond nonwoven fabric or meltblown nonwoven fabric composed of long fibers.

[0095] There is no particular limitation on the thickness of the porous substrate, but it can be from 5 μm to 50 μm. There is also no particular limitation on the pore size and porosity present in the porous substrate, but they can be from 0.01 μm to 50 μm and 10% to 95%, respectively.

[0096] Meanwhile, in order to improve the mechanical strength of the diaphragm made of porous substrate and suppress short circuits between the positive and negative electrodes, a porous coating comprising inorganic particles and binder polymer can be further included on at least one surface of the porous substrate.

[0097] Meanwhile, in lithium secondary batteries, the electrolyte can include organic solvents and lithium salts commonly used as electrolytes, and there are no particular limitations.

[0098] As organic solvents, any solvent that can serve as a medium through which ions participating in the electrochemical reactions of the battery can move can be used without particular limitation. Specifically, the following substances can be used as organic solvents: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene or fluorobenzene; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC).

[0099] Among them, carbonate solvents are preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can enhance the charge and discharge performance of the battery is even more preferred.

[0100] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, lithium salts can be: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Lithium salts are preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0101] In addition to the electrolyte components mentioned above, the electrolyte may also include one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Examples include: pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additives can be from 0.1% by weight to 5% by weight, based on the total weight of the electrolyte.

[0102] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly by placing a separator between the positive and negative electrodes, placing the electrode assembly in a cylindrical or prismatic battery case, and then injecting an electrolyte. Alternatively, after stacking the electrode assembly, it can be manufactured by impregnating the electrode assembly with an electrolyte and sealing the result in a battery case.

[0103] When manufacturing the lithium secondary battery of the present invention, the electrode assembly can be dried to remove one or more organic solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate used in the manufacture of the positive electrode. If an electrolyte having the same composition as the organic solvent used in the manufacture of the positive electrode is used as the electrolyte, the step of drying the electrode assembly can be omitted.

[0104] Unlike the lithium secondary battery described above, another embodiment of the present invention may use an all-solid-state battery.

[0105] The battery casing can be any battery casing commonly used in the art, and there are no restrictions on its external shape depending on the intended use of the battery. For example, it can be cylindrical, prismatic, pouch-shaped, or coin-shaped, similar to a can.

[0106] The lithium secondary battery of the present invention can stably exhibit excellent resistance characteristics, discharge capacity, output characteristics and capacity retention, and is therefore suitable for use in portable devices such as mobile phones, laptops, digital cameras, energy storage systems (ESS) and electric vehicles such as hybrid electric vehicles (HEVs).

[0107] The invention will be described in more detail below by way of examples. However, the following examples are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0108] Example 1: Preparation of the negative electrode

[0109] (Preparation of the first negative electrode slurry)

[0110] Water was injected into a homogeneous mixer, and niobium oxide (average particle size (D)) was added and mixed as the negative electrode active material. 50 A first negative electrode slurry was prepared by adding carbon black (20±5 μm) as a conductive material and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a weight ratio of 1:1 as a binder. At this point, the weight ratio of the negative electrode active material, conductive material, and binder was 90:5:5.

[0111] (Preparation of the second negative electrode slurry)

[0112] Water is injected into a homogeneous mixer, and artificial graphite as the negative electrode active material, carbon black as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a weight ratio of 1:1 as a binder are added and mixed to prepare a second negative electrode slurry. At this point, the weight ratio of the negative electrode active material, the conductive material, and the binder is 94:3:3.

[0113] (Preparation of the negative electrode)

[0114] On one surface of a copper foil (average thickness: 12 μm) serving as the negative electrode current collector, first and second negative electrode slurries are simultaneously coated, such that the first negative electrode slurry is stacked on the negative electrode current collector and the second negative electrode slurry is stacked on the first negative electrode slurry.

[0115] Then, it was dried in a vacuum oven at 130°C and rolled to prepare the negative electrode. At this time, the loading of the rolled negative electrode active material layer was approximately 330±20 mg / 25cm. 2 Furthermore, the thickness of the first region formed by the first negative electrode slurry is 10 μm, which is 10% of the thickness of the negative electrode active material layer.

[0116] Examples 2 to 6: Preparation of the negative electrode

[0117] The negative electrode was prepared in the same manner as in Example 1, except that the type of niobium oxide contained in the first negative electrode slurry or the thickness of the first region was changed, as shown in Table 1.

[0118] [Table 1]

[0119] Comparative example: Preparation of the negative electrode

[0120] The negative electrode slurry was prepared using the same composition and method as the second negative electrode slurry in Example 1.

[0121] A negative electrode slurry was coated onto a copper foil (average thickness: 12 μm) serving as the negative electrode current collector, dried in a vacuum oven at 130°C, and then rolled to prepare the negative electrode. At this point, the loading of the rolled negative electrode active material layer was approximately 330 ± 20 mg / 25 cm². 2 .

[0122] Experimental Example 1: Evaluation of Discharge Resistance Characteristics

[0123] (Preparation of the positive electrode)

[0124] LiNi will be used as the positive electrode active material 0.8 Co 0.1 Mn 0.1O2, carbon black as a conductive material, and PVdF (polyvinylidene fluoride) as a binder are mixed and stirred in N-methylpyrrolidone solvent at a weight ratio of 90:5:5 to prepare a positive electrode slurry.

[0125] The positive electrode slurry was coated on both sides of the aluminum current collector with a thickness of 20 μm, and then dried and rolled to prepare the positive electrode.

[0126] (Assembly of lithium secondary batteries)

[0127] Electrode assemblies were fabricated by alternately stacking two single-sided positive electrodes, one double-sided positive electrode, and a separator from Example 1. The electrode assemblies were then inserted into a battery casing, and an electrolyte was injected to fabricate a complete cell. The electrolyte used was an organic solvent in which 1M LiPF6 was dissolved in a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3.

[0128] Each full cell was manufactured using the negative electrodes of Examples 2 to 6 and the Comparative Examples in the same manner as described above.

[0129] (Preparation of lithium secondary batteries)

[0130] For each full cell manufactured using the negative electrodes of Examples 1 to 6 and the Comparative Examples, after pre-aging at room temperature (22±2°C) for 2 days, they were activated by charging at 0.1C until reaching 30% state of charge (SOC). Then, each activated lithium secondary battery was aged at room temperature (22±2°C) and 60°C for 1 day each, and the gas formed in the bag was vented to prepare experimental lithium secondary batteries.

[0131] (Evaluation of discharge resistance)

[0132] At room temperature (22±2°C), each of the prepared lithium secondary batteries manufactured in the Examples and Comparative Examples was charged to 10% of its state of charge (SOC). Then, each lithium secondary battery was discharged at 2.5C for 10 seconds, and the voltage drop was recorded. The DC internal resistance (DCIR) of each lithium secondary battery was calculated from the recorded results using R=V / I.

[0133] In addition, each of the prepared lithium secondary batteries manufactured in the Examples and Comparative Examples was charged to 50% of its state of charge (SOC) at room temperature (22±2°C). Then, each lithium secondary battery was discharged at 2.5C for 10 seconds, and the voltage drop was recorded. The DC internal resistance (DCIR) of each lithium secondary battery was calculated from the recorded results using R=V / I.

[0134] At this point, charging and discharging are performed under the following conditions, and the calculated resistance values ​​are shown in Table 2 below: [Charging] 0.33C CC / CV, 4.2V and 0.05C cutoff. [Discharge] 0.33C CC, 2.5V cutoff Experiment Example 2: Output Characteristic Evaluation Lithium secondary batteries were prepared using the negative electrodes of Examples 1 to 6 and the Comparative Examples in the same manner as in Experimental Example 1.

[0135] At room temperature (22±2°C), each of the prepared lithium secondary batteries manufactured in the examples and comparative examples was charged to 4.2V at a constant current of 0.33C, and then charged at a constant voltage of 4.2V until the current value reached 0.05C. Afterward, each lithium secondary battery was aged for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, while measuring the discharge capacity.

[0136] Subsequently, after charging in the same manner as described above, the discharge capacity was measured while discharging at a constant current of 2C up to 2.5V. The ratio of the discharge capacity measured at a constant current of 2C to that measured at a constant current of 0.33C was calculated to evaluate the output characteristics. The results are shown in Table 2.

[0137] Experimental Example 3: Measurement of Energy Density per Unit Volume

[0138] The volumetric energy density of each lithium secondary battery manufactured using the negative electrodes of Examples 1 to 6 and the Comparative Examples was measured, and the results are shown in Table 2.

[0139] [Table 2]

[0140] Compared with lithium secondary batteries manufactured using the negative electrode of the comparative example, lithium secondary batteries manufactured using the negative electrodes of Examples 1 to 6 exhibit superior resistance and output characteristics.

[0141] Compared to the lithium secondary battery manufactured using the negative electrode of Example 6, the lithium secondary batteries manufactured using the negative electrodes of Examples 1 to 5 exhibit better volumetric energy density. Since the negative electrode of Example 6 has the thickest first region containing niobium oxide, it is evaluated that the energy density is reduced due to the relatively lower content of carbon-based material. Meanwhile, compared to the lithium secondary battery manufactured using the negative electrode of Example 5, the lithium secondary battery manufactured using the negative electrode of Example 6 does not show a significant improvement in resistance and output characteristics. Therefore, in this invention, it is evaluated that the first region is preferably 15% or less of the thickness of the negative electrode active material layer.

[0142] The present invention has been described in more detail above with reference to the accompanying drawings and embodiments. However, it should be understood that the configurations described in the drawings or embodiments are merely one embodiment of the present invention and do not represent all the technical ideas of the present invention, and various equivalents and modifications that can replace them may exist at the time of filing this application.

[0143] [Explanation of reference numerals in the attached figures]

[0144] 100: Negative electrode

[0145] 110: Negative electrode current collector

[0146] 120: Negative electrode active material layer

[0147] 121: Area 1

[0148] 122: Second Area

Claims

1. A negative electrode comprising: Negative electrode current collector; and A layer of negative electrode active material is disposed on the negative electrode current collector, wherein... The negative electrode active material layer includes: A first region, wherein the first region is disposed on the negative electrode current collector and contains niobium oxide as the negative electrode active material; and The second region is disposed on the first region and contains a carbon-based material as the negative electrode active material.

2. The negative electrode as described in claim 1, wherein, The thickness of the first region is less than 15% of the thickness of the negative electrode active material layer.

3. The negative electrode as described in claim 1, wherein, The niobium oxide is a compound represented by the following chemical formula 1: [Chemical Formula 1] M x Nb y O z In chemical formula 1, M includes one or more selected from W, Mo, Zn, Ni, Sr, and Cu, and 0≤x≤10, 1≤y≤20 and 1.5≤z≤70.

4. The negative electrode as described in claim 1, wherein, The loading of the negative electrode active material layer is 200 mg / 25cm. 2 above.

5. The negative electrode as described in claim 1, wherein, The niobium oxide is selected from one or more of NbO, NbO2, Nb2O3 and Nb2O5.

6. The negative electrode as described in claim 1, wherein, The thickness of the first region is less than 15 μm.

7. The negative electrode as described in claim 1, wherein, The thickness of the first region is 3 μm to 13 μm.

8. The negative electrode as described in claim 1, wherein, The carbon-based material is selected from one or more of the following: natural graphite, artificial graphite, hard carbon obtained by pyrolysis of phenolic resin or furan resin, coke, needle coke, or soft carbon obtained by carbonization of pitch.

9. The negative electrode as described in claim 1, wherein, The first region and the second region each include an adhesive, and The adhesive content in the first region is greater than the adhesive content in the second region.

10. The negative electrode as claimed in claim 1, wherein, The second region further comprises SiO with 0<x<2 selected from Si x , a mixture of one or more selected from the group consisting of Si-C composites and Si metal alloys as a negative electrode active material.

11. A lithium secondary battery, comprising: Positive electrode; negative electrode; membrane; and electrolyte, among which, The negative electrode is the negative electrode according to any one of claims 1 to 10.

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