To improve the high temperature life characteristic optimized positive electrode and secondary battery comprising it

Abstract

A positive electrode in which a positive electrode mixture containing a positive electrode active material is formed on a positive electrode current collector, wherein the positive electrode active material includes a lithium transition metal oxide powder represented by the following chemical formula 1, Li a Ni x Co y M z O 2-w A w (1) wherein M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, A is an oxygen-substituted halogen and 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4 and 0≤w≤0.001, wherein the lithium transition metal oxide powder is composed of: large particles in which secondary particles are formed by aggregation of primary particles and an average particle diameter (D50) of the secondary particles is 7 µm to 17 µm, and small particles in which individual particles are formed and which have an average particle diameter (D50) of 2 µm to 7 µm, wherein a mixing ratio of the large particles and the small particles is 5:5 to 9:1 by weight, and where an electrode density of the positive electrode is 3.2 g / cm 3 up to 3.45 g / cm 3 amounts.

Description

[0001] This application claims the benefit of Korean Patent Application No. 10-2019-0170943, filed on December 19, 2019, and Korean Patent Application No. 10-2020-0131094, filed on October 12, 2020, with the Intellectual Property Office of the Republic of Korea, each of which is incorporated herein in its entirety.

[0002] The present disclosure relates to a positive electrode optimized for improving high-temperature life characteristics and a secondary battery comprising the same. [STATE OF THE ART]

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative energy or clean energy is also increasing, and as a part of this, the areas of power generation and power storage using electrochemistry are areas that are being most actively studied.

[0004] At present, a secondary battery is a representative example of an electrochemical device that utilizes such electrochemical energy, and its application range tends to expand gradually.

[0005] With increasing technological development and the demand for mobile devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as a power source has also been rapidly increasing recently. Among such secondary batteries, numerous studies have been conducted on a lithium secondary battery that features high energy density and high operating potential, long cycle life, and low self-discharge rate, and is now marketed and widely used.

[0006] As interest in environmental issues grows, research is also being frequently conducted on electric vehicles, hybrid electric vehicles, and other technologies that can replace fossil fuel-powered vehicles such as gasoline or diesel vehicles, which are one of the main causes of air pollution. Although nickel-metal hydride secondary batteries are primarily used as the power source for electric vehicles and hybrid electric vehicles, active research is currently being conducted on the use of lithium secondary batteries with high energy density and discharge voltage, with some projects in the commercialization phase.

[0007] Currently, lithium-containing cobalt oxide (LiCoO2) is primarily used as the positive electrode material for lithium secondary batteries. In addition, the use of lithium-containing manganese oxides such as LiMnO2 with a layered crystal structure and LiMn2O4 with a spinel crystal structure, as well as lithium-containing nickel oxide (LiNiO2), is also being considered.

[0008] Among the above-mentioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent cycle life characteristics and excellent charge and discharge efficiency. However, due to its poor structural stability and poor price competitiveness due to resource constraints on cobalt used as a raw material, LiCoO2 faces limitations in its mass use as an energy source in fields such as electric vehicles.

[0009] LiNiO2-based positive electrode active materials have relatively low prices and battery characteristics with high discharge capacity, but are problematic in that a rapid phase transition can occur in a crystal structure due to the volume change during charge / discharge cycles, and the stability can decrease sharply when exposed to air and moisture.

[0010] In addition, lithium manganese oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent stability and relatively low price, but have problems such as low capacity, poor cycling characteristics and poor high-temperature properties.

[0011] Therefore, a ternary or quaternary lithium transition metal oxide containing three or more transition metals has recently been developed by substituting a part of LiNiO2 with Co, Mn, Al or the like.

[0012] The ternary or quaternary lithium transition metal oxide is generally used by forming a secondary particle with primary particles.

[0013] However, the lithium transition metal oxide present in the form of secondary particles leads to particle cracking during the electrode rolling process, which increases the specific surface area of ​​the active material, thus exacerbating the deterioration of storage and lifetime performance at high temperatures. Such particle cracking of such secondary particles is more pronounced in small particles with an average particle diameter (D50) of approximately 5 µm.

[0014] Therefore, there is a high demand for the development of a positive electrode capable of minimizing particle cracking during rolling of a positive electrode including the lithium transition metal oxide as the active material and improving the high-temperature lifetime characteristics. [DETAILED DESCRIPTION OF THE INVENTION][Technical Problem]

[0015] The present disclosure is intended to optimize the composition, mixing conditions, and rolling conditions of the positive electrode active material to minimize particle cracking in the positive electrode active material, thereby improving the high-temperature cycle life characteristics of a secondary battery containing the same. [Technical solution]

[0016] Terms and words used in the present specification and claims should not be construed as being limited to ordinary or dictionary terms, and the present disclosure should be interpreted with meanings and concepts consistent with the technical idea of ​​the present disclosure based on the principle that the inventors can appropriately define concepts of the terms to adequately describe their own disclosure in the best way.

[0017] A positive electrode active material, a manufacturing method thereof, and a secondary battery including the same according to an embodiment of the present invention will now be described.

[0018] According to one embodiment of the present disclosure, there is provided a positive electrode in which a positive electrode mixture containing a positive electrode active material is formed on a positive electrode current collector, wherein the positive electrode active material includes a lithium transition metal oxide powder represented by the following chemical formula 1, Li a Ni x Co y M z O 2-w A w (1) wherein M is at least one selected from the group consisting of Mn, Ti, Mg, Al, Zr and Ni, A is an oxygen-substituted halogen and 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4 and 0≤w≤0.001, wherein the lithium transition metal oxide powder is composed of: large particles in which secondary particles are formed by aggregation of primary particles and an average particle diameter (D50) of the secondary particles is 7 µm to 17 µm, and small particles in which individual particles are formed and which have an average particle diameter (D50) of 2 µm to 7 µm, wherein a mixing ratio of the large particles and the small particles is 5:5 to 9:1 by weight, and wherein the positive electrode mixture has a porosity of 22% to 35%.

[0019] In particular, the average particle size (D50) of the large particles can be 9 µm to 11 µm, and the average particle size (D50) of the small particles can be 4 µm to 6 µm.

[0020] Furthermore, the mixing ratio of the large particles and the small particles can be in particular 6:4 to 8:2, based on weight.

[0021] Furthermore, the porosity of the positive electrode mixture can be in particular 24% to 30%.

[0022] In addition, an electrode density of the positive electrode of 3.0 g / cm 3 up to 3.6 g / cm 3 and in particular, an electrode density of the positive electrode may be 3.2 g / cm 3 up to 3.45 g / cm 3 be.

[0023] Meanwhile, in the lithium transition metal oxide powder of chemical formula 1 contained in the positive electrode active material, M Mn b Al C , where 0≤b≤1 and 0≤c≤1.

[0024] The positive electrode mixture may further include a binder and a conductive material, wherein the binder is contained in an amount of 1 to 5 wt% based on the total weight of the positive electrode mixture and the conductive material is contained in an amount of 0.5 to 5 wt% based on the total weight of the positive electrode mixture.

[0025] According to another embodiment of the present disclosure, there is provided a secondary battery having a structure in which an electrode assembly in a state impregnated with an electrolyte is incorporated into a battery case, the electrode assembly including: the positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. [BENEFICIAL EFFECTS]

[0026] The positive electrode according to the present disclosure includes a positive electrode active material obtained by forming single particles with small particles of lithium transition metal oxide powder, and the porosity of the positive electrode mixture is adjusted in an optimal range according to the mixing ratio of the large particles and the small particles and the rolling conditions, thereby improving the high-temperature life characteristics of the secondary battery incorporating the same. [DETAILED DESCRIPTION OF THE EMBODIMENTS]

[0027] A positive electrode and a secondary battery according to the present disclosure will be described in more detail below.

[0028] According to one embodiment of the present disclosure, there is provided a positive electrode in which a positive electrode mixture containing a positive electrode active material is formed on a positive electrode current collector, wherein the positive electrode active material includes a lithium transition metal oxide powder represented by the following chemical formula 1, Li a Ni x Co y M z O 2-w A w (1) wherein M is at least one selected from the group consisting of Mn, Ti, Mg, Al, Zr and Ni, A is an oxygen-substituted halogen and 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4 and 0≤w≤0.001, wherein the lithium transition metal oxide powder is composed of: large particles in which secondary particles are formed by aggregation of primary particles and an average particle diameter (D50) of the secondary particles is 7 µm to 17 µm, and small particles in which individual particles are formed and which have an average particle diameter (D50) of 2 µm to 7 µm, wherein a mixing ratio of the large particles and the small particles is 5:5 to 9:1 by weight, and wherein the positive electrode mixture has a porosity of 22% to 35%.

[0029] As described above, the lithium transition metal oxide represented by Chemical Formula 1 is generally used as a positive electrode active material in a secondary particle state.

[0030] Furthermore, large particles with an average particle diameter (D50) of about 11 µm and small particles with an average particle diameter (D50) of about 5 µm are mixed and used, but in the electrode rolling process, there is a problem that the lithium transition metal oxide powder cracks in the form of secondary particles.

[0031] In particular, particle cracking mostly occurred in the small particles and partial particle cracking occurred in the large particles.

[0032] Therefore, the inventors found that, to solve the above-mentioned problems, particle cracking can be reduced by forming individual particles with small particles in the lithium transition metal oxide powder. However, when large particles in the form of secondary particles and small particles in the form of individual particles are mixed, the cracking of the large particles in the form of secondary particles is increased compared to the conventional case where the large particles in the form of secondary particles and the small particles are mixed, depending on the mixing conditions and rolling conditions of the large particles and the small particles, so the fatigue life deterioration may be more severe.Thus, the inventors have found the optimal mixing ratio of large and small particles, the porosity according to rolling, and the optimized electrode density at which the cracking of large particles in the form of secondary particles does not increase compared to the existing configuration, and completed the present disclosure.

[0033] Therefore, in the positive electrode according to the present disclosure, the lithium transition metal oxide powder of Chemical Formula 1 included as the positive electrode active material was composed of a mixture of large particles in the form of secondary particles and small particles in the form of single particles.

[0034] Most lithium transition metal oxide particles in the form of single particles have an average particle diameter (D50) of about 5 μm. Small particles in the form of single particles are easy to produce. However, the heat treatment temperature and time required to produce large particles in the form of single particles are too high, making production difficult. As the particle size of the single particles increases, the charge / discharge efficiency and C-rate characteristics decrease rapidly. Therefore, it is preferable to use large particles in the form of secondary particles.

[0035] In the present disclosure, the shape of secondary particles refers to a state in which several tens to several hundred primary particles are aggregated, and the shape of single particles refers to a form in which primary particles are singly present or aggregated with less than 10 particles.

[0036] The diameter of the major axis of the primary particles, which form the large particles in the form of secondary particles, can be, for example, 100 nm to 1,000 nm, and the diameter of the major axis of the primary particles, which form the small particles in the form of individual particles, can be 500 nm to 7,000 nm.

[0037] The average particle diameter (D50) of the large particles in the form of secondary particles formed by aggregation of several tens to several hundred of such primary particles may be 7 µm to 17 µm as defined above, and may in particular be 9 µm to 11 µm.

[0038] Furthermore, the average particle diameter (D50) of the small particles in the form of individual particles in which primary particles are present individually or aggregated with less than 10 particles as defined above may be 2 µm to 7 µm, and in particular may be 4 µm to 6 µm.

[0039] When the average particle diameter (D50) of large particles and the average particle diameter (D50) of small particles are outside the above range, and the average particle diameter of large particles is too large, the low efficiency and low C-rate characteristics of small particles in the form of individual particles will be weighted, resulting in a decrease in capacity and a decrease in performance. If the average particle diameter of large particles is too small, the electrode rollability will deteriorate, and the particle cracking of large particles during rolling will be increased due to the small particles in the form of individual particles, resulting in a decrease in high-temperature service life.However, if the average particle size of the small particles in the form of single particles is too small, the manufacturing becomes difficult due to the deterioration of processability, and if the average particle size is too large, the charge / discharge efficiency and C-rate characteristics deteriorate, which is undesirable.

[0040] Here, the average particle diameter (D50) refers to the diameter at a point where the cumulative distribution of the volume of particles corresponding to the particle size is 50%. The average particle diameter (D50) can be measured using a laser diffraction method. Specifically, the powder to be measured, after being dispersed in a dispersion medium, is introduced into a commercially available laser diffraction particle sizer (for example, Microtrac S3500) to measure the difference in the diffraction pattern corresponding to the particle size when the particles pass through a laser beam, thereby calculating the particle size distribution. D50 can be measured by calculating the particle diameters at points where the cumulative distribution of the volume of particles corresponding to the particle size in the measuring instrument is 50%.

[0041] However, according to the present disclosure, when small particles in the form of single particles and large particles in the form of secondary particles are mixed as described above, particle cracking of large particles in the form of secondary particles is more likely to increase depending on the mixing conditions and the porosity and electrode density conditions corresponding to rolling. Therefore, it is very important to adjust the mixing ratio of large particles to small particles and the porosity according to rolling.

[0042] First, the mixing of the large particles and the small particles can be achieved by preparing each of these particles separately. The mixing ratio to achieve the effect of the present disclosure can be, in particular, 5:5 to 9:1, and more specifically, 6:4 to 8:2, and even more specifically, 7:3.

[0043] If the content of small particles is too high outside the above range, the particle cracking of the large particles during electrode rolling will be aggravated by the small particles with stronger particle strength, and the high-temperature durability may deteriorate. If the content of small particles is too low, the filling rate will be low due to the small particles, and the electrode density will decrease, which is undesirable.

[0044] Second, in order to achieve the effect of the present disclosure, the porosity of the positive electrode mixture may be 22% to 35%, particularly 24% to 30%, and more specifically 25% to 28%, according to the adjustment of the rolling conditions.

[0045] Here, the porosity is calculated as follows using the ratio of the electrode density to the true density of the total solid content of the positive electrode mixture. (True density − electrode density) / true density×100

[0046] If the porosity is too small outside the above range, it means the rolling strength is high. Therefore, there is a problem that the particle cracking of the large particles in the form of secondary particles increases. If the porosity is too large, the rolling strength is low, but the electrode density decreases accordingly, which is undesirable in terms of energy density. There is a problem that the power decreases due to the loss of the conductive path between the particles.

[0047] Based on the optimization of the porosity according to the mixing ratio of the large particle and the small particle and the rolling conditions, the electrode density can be set in the most preferable range for achieving the effects of the present disclosure, and the electrode density in the preferable range of the positive electrode according to the present disclosure can be 3.0 g / cm 3 up to 3.6 g / cm 3 and in particular 3.3 g / cm 3 up to 3.45 g / cm 3 be.

[0048] The electrode density can be calculated as the weight per unit volume excluding the electrode current collector.

[0049] If the electrode density is too small outside the above range, the energy per unit volume decreases, which is undesirable. If the electrode density is too large, the problem is that particle cracking of the secondary particles increases and the high-temperature durability properties are more likely to deteriorate.

[0050] Meanwhile, the positive electrode active material may include a lithium transition metal oxide powder represented by Chemical Formula 1. Specifically, M in Chemical Formula 1 may be Mn b Al Cwhere 0≤b≤1 and 0≤c≤1. In other words, the lithium transition metal oxide powder contained as the positive electrode active material specifically has a transition metal in its composition and may include one or more selected from the group consisting of Li-Ni-Co-Mn oxide containing Ni, Co, and Mn, Li-Ni-Co-Al oxide containing Ni, Co, and Al, and Li-Ni-Co-Mn-Al oxide containing Ni, Co, Mn, and Al.

[0051] The inclusion of the lithium transition metal oxide powder represented by Chemical Formula 1 may independently mean the inclusion of a lithium transition metal oxide having a composition selected from the range of Chemical Formula 1, but when it is within the range of Chemical Formula 1, it may be in the form of a mixture of lithium transition metal oxide powders having different compositions.

[0052] Furthermore, the positive electrode active material may further include compounds known as conventional positive electrode active materials such as LiNiO2, LiMnO2, LiMn2O4, LiCo 1-d Mn d O2, LiNi 1-d Mn d O2(0.2 <d<1), Li(Ni a Co b Mn c )O4 (0 <a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn 2-e Ni e O4, LiMn 2-e Co e O (0 <e<2), LiCoPO4 oder LiFePO4 zusätzlich zu dem durch die chemische Formel 1 dargestellten Lithium-Übergangsmetalloxid einschließen, und es versteht sich von selbst, dass eines allein oder eine Mischung von zwei oder mehr von diesen ferner in einer kleiner Menge enthalten sein kann.

[0053] However, the lithium transition metal oxide represented by Chemical Formula 1 may be contained in an amount of at least 60 wt% or more based on the total weight of the positive electrode active material.

[0054] The positive electrode mixture may further include a binder and a conductive material in addition to the positive electrode active material, and may further optionally include a filler.

[0055] The conductive material is used to impart conductivity to the electrode, and in the battery to be configured, the conductive material can be used without particular restriction as long as it does not cause chemical changes and has electronic conductivity. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs); graphite such as natural graphite and artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative. Any one or a mixture of two or more of these can be used. The conductive material can be used in an amount of 0.1 to 30 wt.-%, in particular 0.3 to 10 wt.% and more precisely 0.5 to 5 wt.%, based on the total weight of the positive electrode mixture.

[0056] The binder plays a role in improving the adhesion between the positive electrode active material particles and the bonding strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. One or a mixture of two or more of these can be used. The binder may be present in an amount of 1 to 30 wt%, in particular 1 to 10 wt% and more precisely 1 to 5 wt%, based on the total weight of the positive electrode mixture.

[0057] Furthermore, a filler is optionally used as a component to inhibit the expansion of the positive electrode. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the corresponding secondary battery. Examples of the filler include olefin-based polymers such as polyethylene and polypropylene, and fibrous materials such as glass fiber and carbon fiber. In this case, the filler is added in an amount of 0.1 to 3 wt% based on the total weight of the positive electrode mixture.

[0058] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can have a thickness of 3 μm to 500 μm and can have fine irregularities formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. It can be used in various forms, such as films, plates, foils, meshes, porous bodies, foams, and nonwovens.

[0059] According to another embodiment of the present disclosure, there is further provided a secondary battery having a structure in which an electrode assembly in a state impregnated with an electrolyte solution is installed in a battery case, the electrode assembly including: the positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode.

[0060] In particular, the secondary battery may be a lithium secondary battery.

[0061] The negative electrode may also be prepared in a form in which a negative electrode mixture including a negative electrode active material is coated on a negative electrode current collector, and the negative electrode mixture may further include a conductive material and a binder as described above, together with the negative electrode active material and optionally a filler.

[0062] As the active material for the negative electrode, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic substances suitable for alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides suitable for doping or dedoping such as SiO x(0<x<2), SnO2, Vanadiumoxid und Lithiumvanadiumoxid oder ein Komposit, das die obige metallische Substanz und das kohlenstoffhaltige Material einschließt wie ein Si-C-Komposit oder ein Sn-C-Komposit oder dergleichen einschließen, und es kann irgendeines oder eine Mischung von zwei oder mehr von diesen verwendet werden. Außerdem kann ein Dünnfilm aus metallischem Lithium als das Anodenaktivmaterial verwendet werden. Ferner kann sowohl niedrigkristalliner Kohlenstoff als auch hochkristalliner Kohlenstoff als Kohlenstoffmaterial verwendet werden. Typische Beispiele für den niedrigkristallinen Kohlenstoff können Weichkohlenstoff und Hartkohlenstoff sein.Typical examples of highly crystalline carbon may include amorphous, planar, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesocarbon microspheres, mesophase pitches, and high-temperature calcined carbon such as cokes derived from petroleum and coal tar pitch.

[0063] The current collector for the negative electrode is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloys, and the like can be used. In addition, the anode current collector can generally have a thickness of 3 μm to 500 μm and, like the cathode current collector, can have fine irregularities formed on a surface to increase the bonding strength of the anode active material. For example, it can be used in various forms such as films, plates, foils, meshes, porous bodies, foams, and nonwovens.

[0064] The separator separates the negative electrode and the positive electrode and provides a passage for the migration of lithium ions. Any separator can be used without particular limitation as long as it is generally used as a separator in a lithium secondary battery. In particular, a separator that has excellent moisture retention capacity for an electrolyte while also having low resistance to electrolyte migration is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure comprising two or more layers thereof, can be used.In addition, a conventional porous nonwoven fabric, such as a high-melting-point glass fiber nonwoven fabric, polyethylene terephthalate fiber, or the like, can also be used. To ensure heat resistance and thermal strength, a coated separator containing a ceramic component or a polymer material can also be used, and a single-layer or multi-layer structure can optionally be used.

[0065] In addition, the electrolyte used in the present disclosure may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a polymer solid electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte, an inorganic molten electrolyte, or the like used in the manufacture of a lithium secondary battery.

[0066] In particular, the electrolyte may include an organic solvent and a lithium salt.

[0067] As the organic solvent, any solvent can be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate.Specifically, as the organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone, an ether-based solvent such as dibutyl ether or tetrahydrofuran, a ketone-based solvent such as cyclohexanone, an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene, a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MED), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC), an alcohol-based solvent such as ethyl alcohol or isopropyl alcohol, nitriles such as R-CN (wherein R is a straight, branched or cyclic C2-C20 hydrocarbon group and may include an aromatic ring having a double bond or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane or sulfolane are used.Among them, the carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, which can enhance the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) can be particularly preferably used. In this case, if the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the electrolyte can achieve excellent performance.

[0068] The lithium salt can be used without particular limitation as long as it is a compound suitable for providing lithium ions used in a lithium secondary battery. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, or the like, can be used as the lithium salt. It is preferable to use the lithium salt in a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance can be achieved, and lithium ions can migrate effectively.

[0069] To improve the battery life characteristics, suppress a reduction in battery capacity, and improve the battery discharge capacity, one or more additives such as a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidones, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride may be added to the electrolyte solution in addition to the above electrolyte components. In this case, the additive may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte solution.

[0070] The above-described secondary battery according to the present embodiment can be used as a power source for devices in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0071] Embodiments of the present disclosure are described in more detail below so that those skilled in the art can easily implement them. The present disclosure may be modified in various ways and is not limited to the embodiments described herein. <Herstellungsbeispiel 1> (Large particles in the form of secondary particles)

[0072] In a 5 L batch reactor set at 60°C, nickel sulfate, cobalt sulfate, and manganese sulfate were mixed in water at a molar ratio of 70:10:20 to prepare a metal salt solution with a concentration of 2 M. The container containing the metal salt was connected to extend into the reactor. A 4 M NaOH solution and a 7% aqueous NH4OH solution were prepared and connected to each reactor. Three liters of deionized water were added to a coprecipitation reactor (capacity of 5 L). Nitrogen gas was purged into the reactor at a rate of 2 liters / minute to remove oxygen dissolved in the water, and the reactor interior was placed in a non-oxidizing atmosphere. Then, 100 ml of 4 M NaOH was added and then maintained to reach a pH of 12.0 at a stirring speed of 1,200 rpm at a temperature of 60°C.Then, the metal salt solution was added at a rate of 180 ml / h, an aqueous NaOH solution at a rate of 180 ml / h, and an NH4OH solution at a rate of 10 ml / h and subjected to a co-precipitation reaction for 10 hours to obtain a nickel-cobalt-manganese mixed oxyhydroxide of Ni. 0,7 Co 0,1 Mn 0,2 (OH)2 (average particle diameter (D50): 11 µm).

[0073] The particles of the resulting nickel-cobalt-manganese-based metal mixed hydroxide were mixed with lithium hydroxide as lithium starting material at a molar ratio of 1:1.07 and then heat-treated at 860°C for 15 hours in air to obtain Ni 0,7 Co 0,1 Mn 0,2 (OH)2 powder consisting of large particles (average particle diameter (D50): 11 µm).

[0074] Upon SEM observation, the large particle powder for a positive electrode was in the form of secondary particles obtained by aggregation of several tens or more primary particles, and their shape was spherical or elliptical. <Herstellungsbeispiel 2> (Small particles in the form of individual particles)

[0075] A nickel-cobalt-manganese mixed oxyhydroxide of Ni 0,7 Co 0,1 Mn 0,2 (OH)2 (average particle diameter (D50): 4.5 µm) was synthesized in the same manner as in Preparation Example 1, except that the co-precipitation reaction time in Preparation Example 1 was reduced to 3 hours.

[0076] The particles of the resulting nickel-cobalt-manganese-based metal mixed hydroxide were mixed with lithium hydroxide as lithium starting material at a molar ratio of 1:1 and then heat-treated at 950°C for 15 hours in air to remove Ni 0,7 Co0,1 Mn 0,2 To obtain O2 powder from small particles (average particle diameter (D50): 5 µm).

[0077] When observed by SEM, the small particle powder for a positive electrode had a shape in which primary particles were present singly or aggregated with less than 10 particles, and their shape was spherical or ellipsoidal. <Herstellungsbeispiel 3> (Small particles in the form of secondary particles)

[0078] A nickel-cobalt-manganese mixed oxyhydroxide of Ni 0,7 Co 0,1 Mn 0,2 (OH)2 (average particle diameter (D50): 4.5 µm) was synthesized in the same manner as in Preparation Example 1, except that the co-precipitation reaction time in Preparation Example 1 was reduced to 3 hours.

[0079] The particles of the resulting nickel-cobalt-manganese-based mixed metal hydroxide were mixed with lithium hydroxide as the lithium starting material at a molar ratio of 1:1.7 and then heat-treated at 840°C for 15 hours in air to obtain LiNi 0,7 Co 0,1 Mn 0,2 To obtain O2 powder from small particles (average particle diameter (D50): 4.5 µm).

[0080] Upon SEM observation, the small particle powder for a positive electrode had a shape in which secondary particles were formed by aggregation of 10 or more such primary particles, and their shape was spherical or ellipsoidal. <Beispiel 1>

[0081] The large-particle positive electrode powder prepared in Preparation Example 1 and the small-particle positive electrode powder prepared in Preparation Example 2 were mixed in a weight ratio of 7:3 and used as a positive electrode active material. PVdF was used as a binder, and carbon black was used as a conductive material. Positive electrode active material: binder: conductive material were well mixed with NMP in a weight ratio of 96:2:2 to prepare a slurry (viscosity: 5,000 mPa s). The slurry was then coated on a 20 μm-thick Al current collector, dried at 130°C, and then rolled at a pressure of 1.7 tons / cm to prepare a 74.5 μm-thick positive electrode. <Beispiel 2>

[0082] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the large particle positive electrode powder prepared in Preparation Example 1 and the small particle positive electrode powder prepared in Preparation Example 2 were mixed in a weight ratio of 5:5 and used as a positive electrode active material. <Beispiel 3>

[0083] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the large particle positive electrode powder prepared in Preparation Example 1 and the small particle positive electrode powder prepared in Preparation Example 2 were mixed in a weight ratio of 8:2 and used as a positive electrode active material. <Beispiel 4>

[0084] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the rolling pressure was 2.1 tons / cm and the electrode thickness was 73.1 µm. <Beispiel 5>

[0085] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the rolling pressure was 1.1 tons / cm and the electrode thickness was 76.8 µm. <Beispiel 6>

[0086] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the rolling pressure was 0.7 ton / cm and the electrode thickness was 78.4 µm. <Vergleichsbeispiel 1>

[0087] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the large particle powder for a positive electrode prepared in Preparation Example 1 and the small particle powder for a positive electrode prepared in Preparation Example 3 were mixed in a weight ratio of 7:3. <Vergleichsbeispiel 2>

[0088] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the large particle positive electrode powder prepared in Preparation Example 1 and the small particle positive electrode powder prepared in Preparation Example 2 were mixed in a weight ratio of 4:6 and used as a positive electrode active material. <Vergleichsbeispiel 3>

[0089] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the rolling pressure was 2.5 tons / cm and the electrode thickness was 71.8 µm. <Vergleichsbeispiel 4>

[0090] A positive electrode was prepared in the same manner as in Example 1, except that in Example 1, the rolling pressure was 0.2 ton / cm and the electrode thickness was 82.8 µm. <Experimentelles Beispiel 1>

[0091] In the positive electrodes prepared in Examples 1 to 6 and Comparative Examples 1 to 4, the porosity and electrode density of the positive electrode mixture were obtained as follows, and the results are shown in Table 1 below.

[0092] * Porosity was calculated as follows using the ratio of the electrode density to the true density of the total solid content of the positive electrode mixture. (True density − electrode density) / true density×100

[0093] * The electrode density was calculated as the weight per unit volume excluding the electrode current collector. [Table 1] Porosity (%) Electrode density (g / cm 3 ) Example 1 25 3,36 Example 2 25 3,36 Example 3 25 3,36 Example 4 23 3,45 Example 5 28 3,21 Example 6 30 3,15 Comparison example 1 25 3,36 Comparison example 2 25 3,36 Comparison example 3 21 3,55 Comparison example 4 36 2,86 <Experimentelles Beispiel 2>

[0094] The positive electrodes prepared in Examples 1 to 6 and Comparative Examples 1 to 4 and lithium metal as the negative electrode were used, and an electrolyte solution containing 1 M LiPF6 in a solvent of EC:DMC:DEC = 1:2:1 was used to prepare a half-button cell.

[0095] The manufactured half-button cell was charged at 25°C with a constant current (CC) of 0.1 C until it reached 4.25 V, and then charged at a constant voltage (CV) of 4.25 V. The first charge was performed until the charging current reached 0.05 mAh. Afterward, it was allowed to stand for 20 minutes and then discharged at a constant current of 0.1 C until it reached 3.0 V. The discharge capacity at the first cycle was measured.

[0096] It was charged at 0.5 C to 4.25 V under constant current / constant voltage (CC / CV) conditions at 45 °C until 0.05 mAh was reached, and then discharged at 1 C to 3.0 V under constant current (CC) conditions. This was set as 1 cycle and repeated for up to 50 cycles. The value calculated by (capacity after 50 cycles / capacity after 1 cycle) × 100 was defined as the high-temperature life retention rate (%), and the results are shown in Table 2 below. [Table 2] Capacity retention rate (%) at 45°C Example 1 93 Example 2 89 Example 3 92 Example 4 89 Example 5 94 Example 6 92 Comparison example 1 88 Comparison example 2 86 Comparison example 3 85 Comparison example 4 85

[0097] Referring to Table 2 together with Table 1, it can be confirmed that when a positive electrode satisfying the conditions of the present disclosure is used, particle cracking is small and thus the high-temperature life characteristics are excellent.

[0098] This utility model is branched off from EP application No. 20 901 464.6. The entire subject matter of that application is incorporated herein by reference. The subject matter defined by the original claims of EP application No. 20 901 464.6 is disclosed again below in preferred embodiments [1] to

[11] : [1] Positive electrode in which a positive electrode mixture containing a positive electrode active material is formed on a positive electrode current collector, wherein the positive electrode active material includes a lithium transition metal oxide powder represented by the following chemical formula 1, Li a Ni x Co y M z O 2-w A w (1) wherein M is at least one selected from the group consisting of Mn, Ti, Mg, Al, Zr and Ni, A is an oxygen-substituted halogen and 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4 and 0≤w≤0.001, wherein the lithium transition metal oxide powder is composed of: large particles in which secondary particles are formed by aggregation of primary particles and a average particle diameter (D50) of the secondary particles is 7 µm to 17 µm, and small particles in which individual particles are formed and which have an average particle diameter (D50) of 2 µm to 7 µm, wherein a mixing ratio of the large particles and the small particles is 5:5 to 9:1 by weight, and wherein the positive electrode mixture has a porosity of 22% to 35%. [2] Positive electrode according to embodiment [1], wherein the average particle size (D50) of the large particles is 9 µm to 11 µm. [3] The positive electrode according to embodiment [1], wherein the average particle size (D50) of the small particles is 4 µm to 6 µm. [4] The positive electrode according to embodiment [1], wherein the mixing ratio of the large particles and the small particles is 6:4 to 8:2 by weight. [5] Positive electrode according to embodiment [1], wherein a porosity of the positive electrode mixture is 24% to 30%. [6] The positive electrode according to embodiment [1], wherein an electrode density of the positive electrode is 3.0 g / cm 3 up to 3.6 g / cm 3 amounts. [7] Positive electrode according to embodiment [6], wherein an electrode density of the positive electrode is 3.2 g / cm 3 up to 3.45 g / cm 3 amounts. [8] Positive electrode according to embodiment [1], wherein M Mn b Al C where 0≤b≤1 and 0≤c≤1. [9] The positive electrode according to embodiment [1], wherein the positive electrode mixture further comprises a binder and a conductive material.

[10] The positive electrode according to embodiment [9], wherein the binder is contained in an amount of 1 to 5 wt% based on the weight of the positive electrode mixture and the conductive material is contained in an amount of 0.5 to 5 wt% based on the total weight of the positive electrode mixture.

[11] A secondary battery having a structure in which an electrode assembly in a state impregnated with an electrolyte solution is incorporated in a battery case, the electrode assembly comprising: the positive electrode according to embodiment [1], a negative electrode and a separator arranged between the positive electrode and the negative electrode. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] KR 10-2019-0170943

[0001] KR 10-2020-0131094

[0001] EP 20 901 464.6

[0098]

Claims

[1] Positive electrode in which a positive electrode mixture containing a positive electrode active material is formed on a positive electrode current collector, wherein the positive electrode active material includes a lithium transition metal oxide powder represented by the following chemical formula 1, Li a Ni x Co y M z O 2-w A w (1) wherein M is at least one selected from the group consisting of Mn, Ti, Mg, Al, and Zr, A is an oxygen-substituted halogen and 1.00≤a≤1.05, 0.1≤x≤0.8, 0.1≤y≤0.8, 0.01≤z≤0.4 and 0≤w≤0.001, wherein the lithium transition metal oxide powder is composed of: large particles in which secondary particles are formed by aggregation of primary particles and an average particle diameter (D50) of the secondary particles is 7 µm to 17 µm, and small particles in which individual particles are formed and which have an average particle diameter (D50) of 2 µm to 7 µm, wherein a mixing ratio of the large particles and the small particles is 5:5 to 9:1 by weight, and where an electrode density of the positive electrode is 3.2 g / cm 3 up to 3.45 g / cm 3 amounts. [2] The positive electrode according to claim 1, wherein the average particle size (D50) of the large particles is 9 µm to 11 µm. [3] The positive electrode according to claim 1 or 2, wherein the average particle size (D50) of the small particles is 4 µm to 6 µm. [4] The positive electrode according to any one of claims 1 to 3, wherein the mixing ratio of the large particles and the small particles is 6:4 to 8:2 by weight. [5] The positive electrode according to any one of claims 1 to 4, wherein a porosity of the positive electrode mixture is 22% to 35%. [6] Positive electrode according to any one of claims 1 to 5, wherein M Mn b Al C where 0≤b≤1 and 0≤c≤1. [7] The positive electrode according to any one of claims 1 to 6, wherein the positive electrode mixture further comprises a binder and a conductive material. [8] The positive electrode according to claim 7, wherein the binder is contained in an amount of 1 to 5 wt% based on the weight of the positive electrode mixture and the conductive material is contained in an amount of 0.5 to 5 wt% based on the total weight of the positive electrode mixture. [9] A secondary battery having a structure in which an electrode assembly in a state impregnated with an electrolyte solution is incorporated in a battery case, the electrode assembly comprising: the positive electrode according to any one of claims 1 to 8, a negative electrode and a separator arranged between the positive electrode and the negative electrode.