Negative electrode and lithium secondary battery comprising same

Abstract

A negative electrode according to exemplary embodiments 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 area disposed on the negative electrode current collector and including niobium oxide as a negative electrode active material, and a carbon-based material which is a negative electrode active material and is disposed on the first area.

Description

Negative electrode and lithium secondary battery including the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0136593 filed on October 8, 2024.

[0002] The present invention relates to a negative electrode and a lithium secondary battery.

[0003]

[0004] Recently, as technology development and demand for mobile devices have increased, the demand for batteries as an energy source has been rapidly increasing. As HEVs, PHEVs, and EVs are gaining attention as future vehicles, various studies are being conducted on batteries that can meet these diverse demands.

[0005] In particular, active research is being conducted on lithium secondary batteries that possess high energy density and excellent lifespan and cycle characteristics. Conventional lithium secondary batteries have primarily utilized carbon-based compounds as negative electrode active materials, which allow for reversible lithium ion insertion and extraction while maintaining structural and electrical properties. However, with the recent increase in demand for the development of high-energy-density batteries, much research is being conducted on transition metals (Group IV and V) such as silicon and tin, which chemically react with lithium, as well as their alloys and oxides, in addition to the aforementioned carbon-based compounds.

[0006] To realize batteries with high energy density and high output, research is being conducted on high-loading electrodes and resistance improvements. In high-loading electrodes, as the lithium ion migration path lengthens, ion diffusion slows down, leading to increased resistance and a decrease in battery output. Therefore, there is a need to develop technologies that can improve the resistance characteristics of high-loading electrodes and increase battery output.

[0007]

[0008] The problem that the technical concept of the present invention aims to solve is to provide a high-loading negative electrode in which resistance characteristics are improved and battery output characteristics are enhanced.

[0009] The problems to be solved by the present invention are not limited to those described above, and problems not mentioned will be clearly understood by those skilled in the art to which the present invention belongs from this specification and the attached drawings.

[0010]

[0011] A cathode according to exemplary embodiments of the present invention comprises: a cathode current collector; and a cathode active material layer disposed on the cathode current collector; wherein the cathode active material layer comprises: a first region disposed on the cathode current collector and comprising niobium oxide as a cathode active material; and a carbon-based material disposed on the first region and comprising a cathode active material.

[0012] In exemplary embodiments, the thickness of the first region is 15% or less of the thickness of the negative electrode active material layer.

[0013] In exemplary embodiments, the niobium oxide is a compound represented by the following chemical formula 1.

[0014] [Chemical Formula 1]

[0015] M x Nb y O z

[0016] In the above chemical formula 1,

[0017] M includes one or more of Wo, Mo, Zn, Ni, Sr, and Cu, and

[0018] 0≤x≤10, 1≤y≤20 and 1.5≤z≤70.

[0019] In exemplary embodiments, the loading amount of the negative electrode active material layer is 200 mg / 25 cm 2 That is all.

[0020] In exemplary embodiments, the niobium oxide is one or more of NbO, NbO2, Nb2O3, and Nb2O5.

[0021] In exemplary embodiments, the thickness of the first region is 15 μm or less.

[0022] In exemplary embodiments, the thickness of the first region is in the range of 3 to 13 μm.

[0023] In exemplary embodiments, the carbon-based material is one or more mixtures selected from natural graphite, artificial graphite, hard carbon obtained by pyrolyzing phenolic resin or furan resin, and soft carbon obtained by carbonizing coke, needle coke, or pitch.

[0024] In exemplary embodiments, the first region and the second region each include a binder, and the content of the binder included in the first region is greater than the content of the binder included in the second region.

[0025] In exemplary embodiments, the second region is additionally Si, SiO as a negative electrode active material. x (0 <x<2), Si-C 복합체 및 Si 금속 합금으로 이루어진 군으로부터 선택된 1종 또는 2종 이상의 혼합물을 더 포함한다.

[0026] A lithium secondary battery according to exemplary embodiments comprises a positive electrode; a negative electrode; a separator; and an electrolyte, wherein the negative electrode is the negative electrode described above.

[0027]

[0028] According to exemplary embodiments of the present invention, a high-loading cathode is provided that has excellent output characteristics and resistance characteristics and enables the realization of a high-energy density battery.

[0029]

[0030] FIG. 1 is a cross-sectional view schematically showing a cathode according to exemplary embodiments.

[0031]

[0032] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0033] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0034] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0035] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0036] In this specification, the term “combination(s) thereof” included in the surface of the Markush type means one or more mixtures or combinations selected from the group consisting of components described in the representation of the Markush type, and means including one or more selected from the group consisting of said components.

[0037] In this specification, the description “A and / or B” means “A or B or both.”

[0038]

[0039] cathode

[0040] FIG. 1 is a cross-sectional view schematically showing a cathode according to exemplary embodiments.

[0041] Referring to FIG. 1, a cathode (100) according to exemplary embodiments comprises a cathode current collector (110); and a cathode active material layer (120), wherein the cathode active material layer (120) comprises a first region (121) and a second region (122). The first region (121) is disposed on the cathode current collector (110) and comprises niobium oxide as the cathode active material. The second region (122) is disposed on the first region (121) and comprises a carbon-based material as the cathode active material.

[0042] The carbon-based material included in the second region (122) is a traditional negative electrode active material with excellent structural stability, so there is no significant change in volume due to repeated charging and discharging. In the present invention, to improve resistance and output characteristics in a negative electrode with a high loading amount, the negative electrode active material layer (120) is configured as a double-layer structure including a first region (121) and a second region (122), and the first region (121), which is close to the negative electrode current collector (110), includes niobium oxide, which has excellent output characteristics as a negative electrode active material. Since niobium oxide can exist in a state containing lithium within the charge-discharge voltage range of the carbon-based material, which is the active material included in the second region, the output characteristics of the battery can be improved. Furthermore, as the first region (121), which is far from the surface of the negative electrode, includes niobium oxide, the movement path of lithium ions is improved, and the output characteristics of the secondary battery can be further improved. In addition, niobium oxide has superior rapid charging performance and lifespan characteristics compared to titanium material, so niobium oxide was selected as the negative electrode active material of the first region (121).

[0043] The thickness of the first region (121) may be 15% or less of the thickness of the negative electrode active material layer (120). Since the first region (121) serves to improve the movement path of lithium ions, a predetermined thickness range is sufficient. Since niobium oxide, which is the negative electrode active material included in the first region (121), does not have a large capacity compared to a negative electrode active material of a carbon-based material, if the thickness of the first region exceeds the above range, it is undesirable in terms of realizing high energy density of the secondary battery. The thickness of the first region (121) may be 15% or less of the thickness of the negative electrode active material layer (120), specifically in the range of 3 to 15%, and more specifically in the range of 6 to 12%.

[0044] The thickness of the above-mentioned negative electrode active material layer (120) may be in the range of 70 to 200 μm, more specifically 80 to 170 μm, and more specifically 90 to 150 μm. In addition, the thickness of the above-mentioned first region (121) may be in the range of 15 μm or less, more specifically 3 to 13 μm, and more specifically 6 to 12 μm.

[0045] The loading amount of the above negative electrode active material layer (120) may be 200 mg / 25 cm² or more. Specifically, the loading amount of the negative electrode active material layer (120) is 200 mg / 25 cm² or more; 200 mg / 25 cm² to 900 mg / 25 cm²; 250 mg / 25 cm² to 900 mg / 25 cm²; 300 mg / 25 cm² to 900 mg / 25 cm²; 200 mg / 25 cm² to 800 mg / 25 cm²; 250 mg / 25 cm² to 800 mg / 25 cm²; 250 mg / 25 cm² to 750 mg / 25 cm²; 250 mg / 25 cm² to 700 mg / 25 cm²; The loading amount may be in the range of 300 mg / 25㎠ to 600 mg / 25㎠; or 250 mg / 25㎠ to 500 mg / 25㎠. The above loading amount is based on the loading amount of the negative active material layer disposed on one side of the current collector. When the loading amount of the negative active material layer (120) is in the above range, high output performance can be achieved along with the energy density of the negative electrode, so it can be easily applied to devices requiring high output, such as electric vehicles, as well as devices requiring high energy density, such as ESS.

[0046] The first region (121) above includes niobium oxide as a negative electrode active material.

[0047] The above niobium oxide may be a compound represented by the following chemical formula 1.

[0048] [Chemical Formula 1]

[0049] M x Nb y O z

[0050] In the above chemical formula 1,

[0051] M includes one or more of Wo, Mo, Zn, Ni, Sr, and Cu, and

[0052] 0≤x≤10, 1≤y≤20 and 1.5≤z≤70.

[0053] In the present invention, the niobium oxide is a compound represented by the chemical formula 1, and refers to an oxide containing niobium (Nb) as a major metal component. Specifically, the niobium oxide may be one or more compounds selected from the group consisting of NbO, NbO2, Nb2O3, and Nb2O5.

[0054] Niobium oxide can maintain a state in which lithium ions are inserted within the charge-discharge voltage range of the carbon-based anode active material after initial charging. Therefore, since niobium oxide can easily release lithium ions toward the anode current collector, it can shorten the lithium ion migration path of the anode.

[0055] Additionally, 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, the elements may be doped in an amount greater than 0 mol% and less than or equal to 50 mol% with respect to the mole fraction of niobium (Nb). Specifically, the elements may be doped in an amount greater than 0 mol% and less than or equal to 40 mol%, greater than 0 mol% and less than or equal to 30 mol%, greater than 0 mol% and less than or equal to 20 mol%, greater than 0 mol% and less than or equal to 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% with respect to the mole fraction of niobium (Nb). In one embodiment, the niobium oxide may comprise Nb2O5 doped with tungsten (W) at a molar percentage of 5 to 10 mol% relative to the molar fraction of niobium (Nb).

[0056] The above niobium oxide can expand the crystal lattice of the niobium oxide by having a form doped with the above element, thereby enhancing the diffusion performance of lithium ions. In addition, when the niobium oxide is Nb2O5, tetravalent niobium ions (Nb 4+Since the content ratio and oxygen deficiency of ) can be improved, the electrical conductivity is excellent and the high-speed charge / discharge performance is excellent.

[0057] The above niobium oxide has a predetermined average particle size (D 50 ) may have. Specifically, the niobium oxide has an average particle size (D) of 0.5㎛ to 100㎛. 50 ) may have an average particle size (D 50 Can have ).

[0058] The present invention relates to the average particle size (D) of niobium oxide. 50 By controlling the above-described range, it is possible to prevent the average particle size of the niobium oxide from exceeding the above-described upper limit, thereby reducing the specific surface area and consequently lowering the output performance of the cathode. Additionally, it is possible to prevent the lithium ion diffusion ability in the first region (121) from decreasing because the average particle size of the niobium oxide is smaller than the above-described lower limit.

[0059] In addition, the niobium oxide may have a structure coated with a carbon layer. The niobium oxide coated with a carbon layer can achieve a high reversible capacity compared to the case where the carbon layer is not coated.

[0060] At this time, the carbon layer may be provided on the surface of the niobium oxide with a predetermined thickness. Specifically, the carbon layer may have a thickness of 1 nm to 20 nm, and more specifically, may have a thickness of 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.

[0061] The second region (122) includes a carbon-based material as a negative electrode active material.

[0062] The above carbon-based material has been used as a traditional cathode active material and has advantages in achieving high energy density compared to niobium oxide included in the first region (121).

[0063] The above carbon-based material is not particularly limited as long as it is capable of absorbing and extracting lithium ions, and may be a crystalline carbon-based compound, an amorphous carbon-based compound, or a mixture thereof.

[0064] Representative examples of the above-mentioned crystalline carbon compounds include graphite, and examples of such graphite-based crystalline carbon include artificial graphite in the shape of a potato or MCMB (MesoCarbon MicroBead), or natural graphite that has undergone surface treatment to smooth the edge. In addition, the above-mentioned amorphous carbon compounds are materials in which carbon atoms have an amorphous crystal structure, and examples include hard carbon obtained by thermally decomposing phenolic resin or furan resin, and soft carbon obtained by carbonizing coke, needle coke, or pitch.

[0065] According to preferred embodiments, the carbon-based material may be natural or artificial graphite, which has good output characteristics and rate characteristics due to its high energy density and excellent density and conductivity, and has a large capacity and high energy density.

[0066] The above carbon-based material can satisfy a predetermined range for average particle size and tap density to increase the density of the cathode active material layer.

[0067] Specifically, the carbon-based material has an average particle size (D) of 0.5㎛ to 20㎛. 50) can be represented. Specifically, the carbon-based material may have an average particle size (D) of 0.5㎛ to 15㎛; 0.5㎛ to 10㎛; 5㎛ to 20㎛; 10㎛ to 20㎛; 12㎛ to 18㎛; 2㎛ to 7㎛; 0.5㎛ to 5㎛; or 1㎛ to 3㎛. 50 It can represent ).

[0068] The average particle size of the carbon-based material may be more advantageous when made smaller to maximize the disorder in the expansion direction for each particle, thereby preventing particle expansion caused by lithium ion charging. However, if the particle size 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 as charging and discharging are repeated, the bonding between particles and the bonding between particles and the current collector decrease, which may significantly reduce cycle characteristics.

[0069] In addition, the carbon-based material may have a tap density of 0.7 g / cc to 1.5 g / cc. Specifically, the carbon-based negative electrode active material may have a tap density of 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.

[0070] The tap density of the carbon-based material described above refers to the density of the carbon-based material composed of particles, specifically the mass per unit volume, in which the voids between particles are filled by applying constant tapping or vibration. This tap density of the carbon-based material not only directly affects the energy density of the cathode but also has a high correlation with the electrolyte impregnation properties of the cathode. By maintaining the tap density of the carbon-based material above the lower limit of the aforementioned range, the present invention can prevent a relative decrease in the content of the cathode active material per unit volume, thereby preventing a reduction in capacity per unit volume. Furthermore, by maintaining the tap density of the carbon-based material below the upper limit of the aforementioned range, the present invention can prevent the phenomenon of delamination from the current collector caused by the failure of the rolling of the cathode active material layer during cathode manufacturing, while simultaneously preventing a decline in the electrolyte impregnation properties and high-speed charge / discharge performance of the cathode active material layer.

[0071] The second region (122) above is a negative electrode active material, in addition to the carbon-based material, Si, SiO x (0 <x<2), Si-C 복합체 및 Si 금속 합금으로 이루어진 군으로부터 선택된 1종 또는 2종 이상의 혼합물을 더 포함할 수 있다. 상기 규소계 재료를 포함하는 경우, 고에너지 밀도 전지 규현에 유리하다.

[0072] The above negative electrode active material layer (120) may further include a binder and a conductive material in addition to the negative electrode active material described above.

[0073] The binder above provides adhesion between the negative electrode active material and the conductive material, and further provides adhesion between the negative electrode active material layer and the negative electrode current collector. The binder above may be one or more selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluororubber.

[0074] The content of the binder may be in the range of 0.5% to 10%, 1% to 6%, or 2% to 6% with respect to the total weight of the negative electrode active material layer (120).

[0075] In exemplary embodiments, the first region and the second region each include a binder, and the content of the binder included in the first region may be greater than the content of the binder included in the second region. Here, the content of the binder included in the first region refers to the weight percentage of the binder included in the first region relative to the total weight of the first region. And the content of the binder included in the second region refers to the weight percentage of the binder included in the second region relative to the total weight of the second region. When the content of the binder included in the first region is greater than the content of the binder included 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.

[0076] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0077] The content of the conductive material may be in the range of 0.5% to 10%, 1% to 6%, or 2% to 6% with respect to the total weight of the negative electrode active material layer (120).

[0078] The above negative electrode current collector (110) is a metal that has high conductivity and allows the slurry of the negative electrode active material to adhere easily. Any metal that is non-reactive within the voltage range of the battery can be used. Specifically, copper, stainless steel, aluminum, nickel, titanium, calcined carbon; stainless steel surface-treated with carbon, nickel, titanium, or silver; aluminum-cadmium alloy; non-conductive polymer surface-treated with a conductive material; or conductive polymer can be used. Additionally, fine irregularities can be formed on the surface to strengthen the bonding strength of the negative electrode active material, and it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0079] The above cathode (100) can be manufactured, for example, by adding a cathode mixture containing a cathode active material to a predetermined solvent to prepare a cathode slurry, then applying it onto a current collector such as a metal foil, and drying and rolling it.

[0080]

[0081] lithium secondary battery

[0082] Next, a lithium secondary battery according to the present invention will be described.

[0083] A lithium secondary battery according to one embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0084] 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 a positive electrode and a negative electrode and introducing an electrolyte.

[0085] In exemplary embodiments of the present invention, the cathode is as described above.

[0086] For example, the above cathode comprises a cathode current collector (110); and a cathode active material layer (120) disposed on the cathode current collector (110); wherein the cathode active material layer (120) comprises a first region (121) disposed on the cathode current collector (110) and comprising niobium oxide as a cathode active material; and a second region (122) disposed on the first region (121) and comprising a carbon-based material as a cathode active material, and the thickness of the first region (121) is 15% or less of the thickness of the cathode active material layer (120).

[0087] According to exemplary embodiments of the present invention, niobium oxide is included in a first region (121) far from the surface of the cathode, thereby improving the movement path of lithium ions in the high-loading electrode, and as a result, excellent resistance characteristics. In addition, niobium oxide can improve the output characteristics of the battery. Furthermore, by controlling the thickness of the first region (121) containing niobium oxide to a predetermined range, the energy density of the battery is excellent.

[0088] As the above-mentioned cathode has been explained in detail above, further redundant explanation is omitted.

[0089] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material.

[0090] In the above-mentioned positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0091] The above-mentioned cathode active material is not particularly limited, and any compound known in the art capable of reversible intercalation and deintercalation of lithium may be used without limitation. Specifically, the above-mentioned cathode active material is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); LiV3O8, LiV3O4, V2O5, Cu2V2O Vanadium oxide of the like; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 ~ 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiNi x Mn 2-x It may include, but is not limited to, a spinel-structured lithium manganese complex oxide represented by O4; LiMn2O4 in which part of the Li of the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; a lithium iron phosphate represented by LiFePO4; a disulfide compound; Fe2(MoO4)3, etc.

[0092] However, for the battery to which the present invention is applied, improvement in energy density is important, and therefore, the positive electrode active material may be a lithium transition metal oxide with a high Ni content represented by the following chemical formula 2.

[0093] [Chemical Formula 2]

[0094] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O 2-y A y

[0095] In the above formula,

[0096] M is at least one selected from the group consisting of Cu, Ti, Mg, Al, Pt, and Zr, and

[0097] A is an oxygen-substituted halogen, and

[0098] 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.

[0099] More specifically, the above a may be 0.88≤a<1.

[0100] In addition, a mixture of the lithium transition metal oxide represented by the above chemical formula 2 and other active materials may also be used.

[0101] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0102] The above-mentioned anode conductive material is used to impart conductivity to the electrode and may include carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc. Currently commercially available conductive materials include acetylene black series (products from Chevron Chemical Company or Gulf Oil Company, etc.), Ketjen Black EC series (product from Armak Company), Vulcan XC-72 (product from Cabot Company), and Super P (product from MMM). Among these, carbon nanotubes, carbon nanofibers, and carbon black are preferred as the conductive material of the present invention, and carbon nanotubes are most preferred. The conductive network of carbon nanotubes is most desirable as a conductive material included in the anode of the present invention because it can alleviate the lifting phenomenon of the binder during the drying process of the anode slurry.

[0103] The BET specific surface area of ​​the carbon nanotube may be 100 m² / g to 1000 m² / g, 150 m² / g to 800 m² / g, 150 m² / g to 500 m² / g, 150 m² / g to 300 m² / g, or 150 m² / g to 200 m² / g.

[0104] The above-mentioned positive conductive material may be included in the positive active material layer in an amount of 0.1 to 30 weight%, more specifically 0.1 to 10 weight%, and more specifically 0.5 to 5 weight%.

[0105] The above-mentioned anode binder can be any commonly used binder polymer without limitation. For example, various types of binder polymers such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) can be used.

[0106] The above anode binder may be included in the anode active material layer in an amount of 0.1 to 30 weight%, more specifically 0.1 to 10 weight%, and more specifically 0.5 to 5 weight%.

[0107] The above separator can be any porous substrate commonly used as a separator in lithium secondary batteries, and for example, a polyolefin-based porous membrane or nonwoven fabric may be used, but is not particularly limited thereto. In particular, it is desirable that it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity.

[0108] Examples of the above-mentioned polyolefin-based porous membranes include membranes formed from polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, either individually or as a mixture thereof.

[0109] In addition to polyolefin-based nonwoven fabrics, the above nonwoven fabric may be formed from polymers such as polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either individually or in a mixture thereof. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a melt-blown nonwoven fabric composed of long fibers.

[0110] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and porosity present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0111] Meanwhile, to improve the mechanical strength of the separator composed of the above porous substrate and to suppress short circuits between the anode and the cathode, a porous coating layer comprising inorganic particles and a binder polymer may be further included on at least one surface of the above porous substrate.

[0112] Meanwhile, in the above lithium secondary battery, the electrolyte may include an organic solvent and a lithium salt commonly used in electrolytes, and is not particularly limited.

[0113] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) may be used.

[0114] Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0115] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may 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. It is preferable that the lithium salt be included in the electrolyte at a concentration of approximately 0.6 mol% to 2 mol%.

[0116] In addition to the above electrolyte components, the above electrolyte may further include one or more additives, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0117] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly by placing a separator between a positive electrode and a negative electrode, placing the electrode assembly into a cylindrical battery case or a prismatic battery case, and then injecting an electrolyte. Alternatively, the electrode assembly may be manufactured by stacking the electrode assemblies, impregnating them with an electrolyte, placing the resulting product into a battery case, and sealing it.

[0118] When manufacturing the lithium secondary battery of the present invention, the electrode assembly may be dried to remove one or more organic solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethylmethyl carbonate, ethylene carbonate, and dimethyl carbonate used in the manufacture of the anode. If an electrolyte having the same components as the organic solvent used in the manufacture of the anode is used as the electrolyte, the process of drying the electrode assembly may be omitted.

[0119] Unlike the lithium secondary battery described above, the lithium secondary battery according to another embodiment of the present invention may be a solid-state battery.

[0120] The above battery case may be adopted from those commonly used in the field, and there are no restrictions on the external shape according to the application of the battery; for example, it may be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0121] Since the lithium secondary battery according to the present invention stably exhibits excellent resistance characteristics, discharge capacity, output characteristics, and capacity retention rate, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, energy storage systems (ESS), and electric vehicles such as hybrid electric vehicles (HEV).

[0122]

[0123] The present invention will be explained in more detail below through examples. However, the following examples are intended to illustrate the present invention and do not limit the scope of the present invention.

[0124]

[0125] Example 1: Preparation of a cathode

[0126] (Preparation of the first cathode slurry)

[0127] Water is injected into a homo mixer, and niobium oxide (average particle size (D)) is used as the negative electrode active material. 50 A first cathode slurry was prepared by adding and mixing carbon black as a conductive material (20±5㎛), and carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) as binders in a 1:1 weight ratio. At this time, the weight ratio of the cathode active material, conductive material, and binder was 90:5:5.

[0128] (Preparation of the second cathode slurry)

[0129] A second cathode slurry was prepared by injecting water into a homo mixer, adding artificial graphite as the cathode active material, carbon black as the conductive material, and carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) mixed in a 1:1 weight ratio as binders, and mixing. At this time, the weight ratio of the cathode active material, conductive material, and binder was 94:3:3.

[0130] (Manufacturing of the cathode)

[0131] The first and second cathode slurries were simultaneously coated on one side of a copper foil (average thickness: 12 μm) as a cathode current collector, such that the first cathode slurry was laminated on the cathode current collector and the second cathode slurry was laminated on the first cathode slurry.

[0132] Subsequently, the cathode was manufactured by drying in a vacuum oven at 130°C and then rolling. At this time, the loading amount of the rolled cathode active material layer was approximately 330±20 mg / 25㎠, and the thickness of the first region formed from the first cathode slurry was 10㎛, which was 10% of the thickness of the cathode active material layer.

[0133]

[0134] Examples 2 to 6: Preparation of the cathode

[0135] A cathode was prepared in the same manner as in Example 1, except that the type of niobium oxide included in the first cathode slurry or the thickness of the first region was changed as shown in Table 1.

[0136] Type of Niobium Oxide Thickness of the First Region (㎛) Ratio of the thickness of the first region (%) based on the thickness of the cathode active material layer Example 1 Nb2O5 1010 Example 2 Nb2O5 88 Example 3 10 mol% W-doped Nb2O5 1010 Example 4 NbO1010 Example 5 Nb2O5 1515 Example 6 Nb2O5 2525

[0137]

[0138] Comparative Example: Preparation of cathode

[0139] A cathode slurry was prepared using the same composition and method as the second cathode slurry of Example 1 above.

[0140] A cathode was manufactured by coating the above cathode slurry onto a copper foil (average thickness: 12 μm) as a cathode current collector, drying it in a vacuum oven at 130°C, and then rolling it. At this time, the loading amount of the rolled cathode active material layer was approximately 330 ± 20 mg / 25 cm².

[0141]

[0142] Experimental Example 1: Evaluation of Discharge Resistance Characteristics

[0143] (Manufacturing of the anode)

[0144] LiNi as a positive electrode active material 0.8 Co 0.1 Mn 0.1 An anode slurry was prepared by mixing and stirring O2, carbon black as a conductive material, and PVdF (polyvinylidene fluoride) as a binder in an N-methylpyrrolidone solvent in a weight ratio of 90:5:5.

[0145] The anode was manufactured by coating the above anode slurry on both sides of an aluminum current collector with a thickness of 20 μm, and then drying and rolling it.

[0146] (Assembly of lithium secondary batteries)

[0147] An electrode assembly was manufactured by alternately stacking two single-sided anodes of Example 1, one double-sided anode, and a separator. The electrode assembly was inserted into a battery case, and an electrolyte was injected to manufacture a full cell. At this time, the electrolyte used was an electrolyte in which 1M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3.

[0148] Each full cell was prepared using the cathode of Examples 2 to 6 and Comparative Example in the same manner as above.

[0149] (Manufacturing of lithium secondary batteries)

[0150] For each full-cell prepared using each cathode of Examples 1 to 6 and Comparative Example, the cells were pre-aged at room temperature (22±2℃) for 2 days, and then activated by charging at 0.1C until the state of charge (SOC) reached 30%. Then, each activated lithium secondary battery was aged at room temperature (22±2℃) and 60℃ for 1 day each, and the gas formed inside the pouch was discharged to prepare an experimental lithium secondary battery.

[0151] (Discharge Resistance Evaluation)

[0152] In each prepared example and comparative example, the lithium secondary battery prepared was charged to a state of charge (SOC) of 10% at room temperature (22±2℃). Then, the voltage drop occurring while discharging each lithium secondary battery at 2.5C for 10 seconds was recorded, and the DC resistance (DCIR) of each lithium secondary battery was calculated from the recorded result using R=V / I.

[0153] In addition, the lithium secondary batteries prepared in each prepared example and comparative example were charged to a state of charge (SOC) of 50% at room temperature (22±2℃). Then, the voltage drop occurring while discharging each lithium secondary battery at 2.5C for 10 seconds was recorded, and the DC resistance (DCIR) of each lithium secondary battery was calculated from the recorded results using R=V / I.

[0154] At this time, the above charging and discharging were performed under the following conditions, and the calculated resistance values ​​are shown in Table 2 below:

[0155] [Charging] 0.33C CC / CV, 4.2V and 0.05C cut-off

[0156] [Discharge] 0.33C CC, 2.5V cut-off

[0157]

[0158] Experimental Example 2: Evaluation of Output Characteristics

[0159] Lithium secondary batteries were prepared using each negative electrode of Examples 1 to 6 and Comparative Example in the same manner as Experimental Example 1 above.

[0160] Each lithium secondary battery prepared in the prepared examples and comparative examples was charged to 4.2V at a constant current of 0.33C at room temperature (22±2℃), and then charged until the current value became 0.05C at a constant voltage of 4.2V. After that, each lithium secondary battery was aged for 10 minutes, and the discharge capacity was measured while discharging until it reached 2.5V at a constant current of 0.33C.

[0161] Next, charging was performed in the same manner as above, and the discharge capacity was measured while discharging at a constant current of 2C until it reached 2.5V. The output characteristics were evaluated by calculating the ratio of the discharge capacity measured at a constant current of 2C to the discharge capacity measured at a constant current of 0.33C. The results are shown in Table 2.

[0162]

[0163] Experimental Example 3: Measurement of Energy Density Per Volume

[0164] The energy density per unit volume of lithium secondary batteries manufactured using each negative electrode of Examples 1 to 6 and Comparative Examples was measured, and the results are shown in Table 2.

[0165]

[0166] Discharge Resistance @ SOC 50(Ω) Discharge Resistance @ SOC 10(Ω) 2C Capacity vs. 0.33C Capacity (%) Energy Density per Volume (Wh / L) Example 1 0.58 1.049 2.3457 Example 2 0.60 1.079 1.64458 Example 3 0.57 1.029 3.0458 Example 4 0.59 1.069 1.95458 Example 5 0.57 1.039 3.3453 Example 6 0.55 1.019 3.5431 Comparative Example 0.62 1.149 0.67460

[0167]

[0168] The lithium secondary battery manufactured using the cathode according to Examples 1 to 6 was found to have superior resistance characteristics and output characteristics compared to the lithium secondary battery manufactured using the cathode according to the Comparative Example.

[0169] It was found that the lithium secondary battery manufactured using the cathode according to Examples 1 to 5 exhibited a much superior energy density per unit volume compared to the lithium secondary battery manufactured using the cathode according to Example 6. It is evaluated that the energy density decreased as a result of the relatively reduced content of carbon-based materials, because the thickness of the first region containing niobium oxide in the cathode according to Example 6 is the thickest. Meanwhile, it was found that the lithium secondary battery manufactured using the cathode according to Example 6 did not show a significant improvement in resistance characteristics and output characteristics compared to the lithium secondary battery manufactured using the cathode according to Example 5. Therefore, in the present invention, it is evaluated that the first region is preferably 15% or less of the thickness of the cathode active material layer.

[0170]

[0171] The present invention has been described in more detail above through drawings and embodiments. However, the configurations described in the drawings or embodiments described in this specification are merely one embodiment of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0172]

[0173] [Explanation of the symbol]

[0174] 100: Cathode

[0175] 110: Cathode current collector

[0176] 120: Cathode active material layer

[0177] 121: First Zone

[0178] 122: Second Zone

Claims

1. Cathode current collector; and A negative electrode active material layer disposed on the above negative electrode current collector; comprising, The above cathode active material layer is, A first region disposed on the above-mentioned negative electrode current collector, comprising niobium oxide as a negative electrode active material; and A cathode disposed on the first region, comprising a second region including a carbon-based material as a cathode active material.

2. In Claim 1, A cathode, wherein the thickness of the first region is 15% or less of the thickness of the cathode active material layer.

3. In Claim 1, The above niobium oxide is a cathode, which is a compound represented by the following chemical formula 1. [Chemical Formula 1] M x Nb y O z In the above chemical formula 1, M includes one or more of Wo, Mo, Zn, Ni, Sr, and Cu, and 0≤x≤10, 1≤y≤20 and 1.5≤z≤70.

4. In Claim 1, The loading amount of the above cathode active material layer is 200 mg / 25 cm 2 Lee Sang-in, cathode.

5. In Claim 1, The above niobium oxide is a cathode that is one or more of NbO, NbO2, Nb2O3, and Nb2O5.

6. In Claim 1, A cathode having a thickness of 15㎛ or less in the first region.

7. In Claim 1, A cathode having a thickness of the first region in the range of 3 to 13 μm.

8. In Claim 1, The above carbon-based material is a cathode that is one or more mixtures selected from natural graphite, artificial graphite, hard carbon obtained by pyrolyzing phenolic resin or furan resin, and soft carbon obtained by carbonizing coke, needle coke, or pitch.

9. In Claim 1, The first region and the second region each include a binder, and A cathode in which the content of the binder contained in the first region is greater than the content of the binder contained in the second region.

10. In Claim 1, The second region above additionally includes Si and SiO as negative electrode active materials. x (0 <x<2), Si-C 복합체 및 Si 금속 합금으로 이루어진 군으로부터 선택된 1종 또는 2종 이상의 혼합물을 더 포함하는, 음극.

11. A positive electrode; a negative electrode; a separator; and an electrolyte, comprising The above-mentioned cathode is a lithium secondary battery that is a cathode according to any one of claims 1 to 10.

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