Positive electrode material for lithium secondary battery, positive electrode containing this, and lithium secondary battery

Abstract

Positive electrode material comprising a first positive electrode active material, represented by formula 1 below, and a second positive electrode active material, represented by formula 2 below, wherein the first positive electrode active material and the second positive electrode active material are present in a weight ratio of 10:90 to 90:10, the positive electrode material has a bimodal particle size distribution, which includes large diameter particles and small diameter particles, wherein the first positive electrode active material forms the small-diameter particles and the second positive electrode active material forms the large-diameter particles, or wherein the first positive electrode active material forms the large-diameter particles and the second positive electrode active material forms the small-diameter particles, and the difference in mean particle diameter (D 50 ) between the large-diameter particles and the small-diameter particles is 3 µm or more: Li a [Ni b Co c M 1 d M a e ]O2 [Formula 1] where in Formula 1 M 1 Mn is and M a a doping element that is substituted at a transition metal site (Ni, Co and / or Mn), and 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c<0.2, 0.01≤d<0.2 and 0≤e≤0.02. Li x [Ni y Co z Mn w M 2 v M b u ]O2 [Formula 2] where in Formula 2 M 2 Al is and M b a doping element that is substituted at a transition metal site (Ni, Co and / or Mn), and 0.9≤x≤1.2, 0.8≤y<1, 0.01≤z<0.2, 0.01≤w<0.2, 0.01≤v<0.2 and 0≤u≤0.02.

Description

TECHNICAL FIELD Reference to related applications

[0001] This application claims priority over the first application 10-2017-0155957, which was filed with the Korean Intellectual Property Office on November 21, 2017, the disclosure of which is hereby incorporated in its entirety by reference. Technical field

[0002] The present invention relates to a positive electrode material for a lithium secondary battery, a positive electrode containing this material, and a lithium secondary battery. STATE OF THE ART

[0003] With technological advancements and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has also risen rapidly. Among these secondary batteries, lithium-ion batteries with high energy density and voltage, long lifespan, and low self-discharge rate have been commercialized and are widely used.

[0004] A lithium transition metal composite oxide is used as a positive electrode material for lithium secondary batteries. Among these lithium transition metal composite oxides, a lithium cobalt composite metal oxide such as LiCoO2 has been primarily used, exhibiting high operating voltage and excellent capacity properties. However, LiCoO2 has very poor thermal properties due to the destabilization of its crystal structure by de-lithiation and is expensive. Therefore, the use of LiCoO2 as a large-scale energy source for electric vehicles or similar applications is limited.

[0005] Lithium-manganese composite metal oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), and lithium-nickel composite metal oxides (LiNiO2, etc.) have been developed as replacements for LiCoO2. Among these materials, research and development has been actively focused on a lithium-nickel composite metal oxide with a high reversible capacity of approximately 200 mAh / g, enabling the straightforward production of high-capacity batteries. However, compared to LiCoO2, LiNiO2 exhibits lower thermal stability. Furthermore, LiNiO2 suffers from the problem that an internal short circuit, caused by external pressure or similar factors while charged, can decompose the positive electrode active material itself, leading to battery rupture and ignition.Therefore, as a method to improve the thermal stability of LiNiO2 while maintaining its excellent reversible capacity, a lithium nickel cobalt manganese oxide was developed by replacing some of the Ni in LiNiO2 with Mn and Co.

[0006] However, lithium nickel cobalt manganese oxide exhibits a low rolling density of the particles. In particular, when the nickel content is increased to improve the capacitance properties, the rolling density of the particles decreases even further, thus reducing the energy density. When an electrode is heavily rolled to increase the rolling density, problems have arisen, such as current collector breakage and cracking of the positive electrode material.

[0007] Furthermore, in lithium nickel cobalt manganese oxide with a high Ni content, the structural stability at high temperatures is reduced, so that the electrochemical performance, such as the lifetime at high temperatures, deteriorates.

[0008] Therefore, there was a need to develop a positive active material that possesses excellent energy density and capacity properties as well as a long service life at high temperatures. REVELATION OF THE INVENTIONAL PROBLEM

[0009] One aspect of the present invention relates to a high-capacity positive electrode material that possesses excellent high-temperature lifetime properties.

[0010] Another aspect of the present invention relates to a positive electrode comprising the positive electrode material, as well as a lithium secondary battery. TECHNICAL SOLUTION

[0011] According to one aspect of the present invention, a positive electrode material is provided comprising a first positive electrode active material, represented by formula 1, and a second positive electrode active material, represented by formula 2, wherein the positive electrode material has a bimodal particle size distribution comprising large-diameter particles and small-diameter particles, and the difference in mean particle diameter (D) 50 ) between the large-diameter particles and the small-diameter particles is 3 µm or more. Li a [Ni b Co c M 1 d M a e ]O2 [Formula 1]

[0012] In Formula 1, M 1 Mn, Al, Zr or Mg, and M ais one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c<0.2, 0.01≤d<0.2 and 0≤e≤0.02. Li x [Ni y Co z Mn w M 2 v M b u ] O2 [Formula 2]

[0013] In Formula 2, M 2 Al, Mg, Zr or Ti, and M b is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and 0.9≤x≤1.2, 0.8≤y<1, 0.01≤z<0.2, 0.01≤w<0.2, 0.01≤v<0.2 and 0≤u≤0.02.

[0014] At this point, the mean particle diameter (D) can be determined. 50 ) the large-diameter particles are 10 µm to 20 µm, and the mean particle diameter (D 50The diameter of the small-diameter particles can range from 1 µm to 7 µm.

[0015] According to a further aspect of the present invention, a positive electrode is provided comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode material according to the invention.

[0016] According to another aspect of the present invention, a lithium secondary battery is provided comprising the positive electrode according to the invention, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte. BENEFICIAL EFFECTS

[0017] A positive electrode material according to the invention uses a lithium composite transition metal oxide with a nickel content of 80% or more, giving it excellent capacity properties, and has a bimodal particle size distribution, giving it high rolling density and energy density.

[0018] Furthermore, in the positive electrode material according to the invention, two types of lithium composite transition metal oxides with different compositions are mixed and used, giving it excellent properties with regard to lifetime at high temperatures compared to a case in which a lithium nickel cobalt manganese oxide with a single composition is used. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 is a graph showing the high-temperature cycle properties of the lithium secondary batteries produced in Examples 1 and 2, as well as in the comparison example 1. BEST WAY TO IMPLEMENT THE INVENTION

[0019] The present invention will be described in more detail below.

[0020] It is understood that the words or terms used in the description and claims must not be interpreted as having the meanings defined in common dictionaries. It is further understood that the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant field and the technical idea of ​​the invention, based on the principle that an inventor can define the meaning of words or terms in such a way as to best explain the invention.

[0021] In the present description, a mean particle diameter (D) can be used. 50) can be defined as a particle diameter at 50% of a particle diameter distribution and can be measured using a laser diffraction method. Specifically, target particles are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000) to be irradiated with ultrasonic waves at approximately 28 kHz and a power of 60 W. The mean particle diameter (D) can then be determined. 50 ) at 50% in a number-based particle distribution according to the particle diameters in the measuring device.

[0022] Furthermore, unless otherwise stated, % in this description means weight %.

[0023] The inventors have repeatedly conducted research to develop a positive electrode material characterized by excellent capacity properties, energy density, and lifetime at high temperatures. As a result, the inventors have determined that the objectives described above can be achieved by using a positive electrode material containing two types of positive electrode active materials with a specific composition and exhibiting a bimodal particle size distribution comprising large-diameter particles and small-diameter particles with a difference in mean particle diameters of 3 µm or more, and have thus perfected the present invention. Positive electrode material

[0024] First, a positive electrode material according to the invention is described.

[0025] The positive electrode material according to the invention comprises a first positive electrode active material and a second positive electrode active material with different compositions and has a bimodal particle size distribution comprising large-diameter particles and small-diameter particles. At this point, the difference in the mean particle diameter (D) can be 50 ) between the large-diameter particles and the small-diameter particles is 3 µm or more, preferably 3 µm to 15 µm, more preferably 3 µm to 10 µm.

[0026] The first positive electrode active material is a lithium composite transition metal oxide with a nickel content of 80 mol% or more, specifically a lithium composite transition metal oxide represented by the following [Formula 1]. Li a [Ni b Co c M 1 d M a e ] O2 [Formula 1]

[0027] In Formula 1, M 1 Mn, Al, Zr or Mg, and M a is a doping element that is placed at a transition metal site (Ni, Co and / or M) 1 ) is substituted, and it can be one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0028] a represents the molar ratio of lithium and can satisfy the relationship 0.9≤a≤1.2, preferably 1.1≤a≤1.2.

[0029] b represents the molar ratio of nickel in the total transition metals and can satisfy the relationship 0.8≤b<1, preferably 0.8≤b≤0.98.

[0030] c represents the molar ratio of cobalt in the total transition metals and can satisfy the relationship 0.01≤c<0.2, preferably 0.01≤c≤0.15.

[0031] d represents the molar ratio of M 1in all transition metals and can satisfy the relationship 0.01≤d<0.2, preferably 0.01≤d≤0.15.

[0032] e represents the molar ratio of the doping element M a in all transition metals and can satisfy the relationship 0≤e≤0.02, preferably 0≤e≤0.01.

[0033] In particular, the first positive electrode active material Li a [Ni b Co c Mn d ]O2, Li a [Ni b Co c Al d ]O2, Li a [Ni b Co c Zr d ]O2, Li a [Ni b Co c Mg a ]O2, Li a [Ni b Co c Mn d Al e ]O2, Li a [Ni b Co c Mn d Zr e ]O2, Li a [Ni b Co c Mn d Mg e ]O2, Li a [Ni b Co c Al d Zr e O2 or Li a [Nib Co c Al d Mg e ]O2 (where a, b, c, d and e have the same meanings as in formula 1) and the like, but is not limited to that.

[0034] The second positive electrode active material is a lithium composite transition metal oxide with a nickel content of 80 mol% or more, specifically a lithium composite transition metal oxide represented by the following [Formula 2]. Li x [Ni y Co z Mn w M 2 v M b u ]O2 [Formula 2]

[0035] In Formula 2, M 2 Al, Mg, Zr or Ti, and M b is a doping element that is placed at a transition metal site (Ni, Co and / or M) 2 ) is substituted, and can be one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0036] x represents the molar ratio of lithium and can satisfy the relationship 0.9≤x≤1.2, preferably 1.1≤x≤1.2.

[0037] y represents the molar ratio of nickel and can satisfy the relationship 0.8≤y<1, preferably 0.8≤y≤0.98.

[0038] z represents the molar ratio of cobalt and can satisfy the relationship 0.01≤z<0.2, preferably 0.01≤z≤0.15.

[0039] w represents the molar ratio of manganese and can satisfy the relationship 0.01≤w< 0.2, preferably 0.01≤w≤0.1.

[0040] v represents the molar ratio of M 2 and can satisfy the relationship 0.01≤v<0.2, preferably 0.01≤v≤0.1.

[0041] u represents the molar ratio of the doping element M b in all transition metals and can satisfy the relationship 0≤u≤0.02, preferably 0≤u≤0.01.

[0042] In particular, the second positive electrode active material Li x [Ni yCo z Mn w Al v ]O2, Li x [Ni y Co z Mn w Mg v ]O2, Li x [Ni y Co z Mn w Zr v ]O2, Li x [Ni y Co z Mn w Ti v ]O2, Li x [Ni y Co z Mn w Al v Mg u ]O2, Li x [Ni y Co z Mn w Al v Zr u O2, or Li x [Ni y Co z Mn w Al v Ti u ]O2 (where x, y, z, w, v and u are the same as defined in Formula 2) and the like, but is not limited to that.

[0043] If necessary, the first positive electrode active material and / or the second positive electrode active material may further comprise a coating layer on their surface. In this case, the coating layer may contain at least one coating element selected from the group consisting of one or more elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. When the coating layer is configured as described above, contact between the positive electrode active material and an electrolyte is prevented, thereby suppressing the occurrence of a side reaction. Therefore, when the coating layer is used in a battery, the battery's lifetime characteristics can be improved, and the filling density of the positive electrode active material can be increased.

[0044] If, as described above, a coating element is additionally included, the content of the coating element in the coating layer can be 100 ppm to 10,000 ppm, preferably 200 ppm to 5,000 ppm, based on the total weight of the positive electrode active material.

[0045] The coating layer can be formed on the entire surface or on a portion of the surface of the positive electrode active material. If the coating layer is formed on a portion of the surface of the positive electrode active material, it can specifically cover an area of ​​5% to less than 100%, preferably 20% to less than 100%, of the total surface area of ​​the positive electrode active material.

[0046] Meanwhile, the first and second positive electrode active materials can be configured such that the content of transition metal elements in an active material particle is constant regardless of its position, or that the content of one or more metal elements can vary depending on its position within the particle. For example, the positive electrode active material can exhibit a concentration gradient in which the concentration of at least one of the elements Ni, Mn, Co, M 1 or M 2 gradually changes. The “gradually changing concentration gradient” can mean that the concentration of each of the components exists in a concentration distribution that changes continuously in steps across the entire area or a specific area of ​​the particle.

[0047] Since both the first and second positive electrode active materials contain nickel in an amount of 80 mol% or more, excellent capacity properties can be achieved. Furthermore, the inventors' research has shown that mixing a positive electrode active material of [Formula 1] and a positive electrode active material of [Formula 2] and using them as described above results in an improvement in lifetime properties at high temperatures.

[0048] The positive electrode material of the present invention can contain the first positive electrode active material and the second positive electrode active material in a weight ratio of 10:90 to 90:10, preferably 20:80 to 80:20, and more preferably 30:70 to 70:30. A high electrode density can be achieved if the mixing ratio of the first positive electrode active material and the second positive electrode active material meets the aforementioned range.

[0049] The positive electrode material of the present invention has a bimodal particle size distribution, comprising large-diameter particles and small-diameter particles with different mean particle diameters (D). 50). If the positive electrode material has a bimodal particle size distribution as described above, the voids between the large-diameter particles are filled with the small-diameter particles during roll pressing, so that a high roll pressing density and energy density can be achieved.

[0050] At this point, the difference in the mean particle diameter (D) can be determined. 50 ) between the large-diameter and small-diameter particles is 3 µm or more, preferably 3 µm to 5 µm, more preferably 3 µm to 10 µm. If the difference in mean particle diameter (D 50) between large diameter particles and small diameter particles, the above-mentioned range is fulfilled, the small diameter particles are well filled between the large diameter particles, resulting in an excellent effect for improving the rolling press density and energy density.

[0051] In particular, the mean particle diameter (D 50 ) of the large-diameter particles 10 µm to 20 µm, preferably 11 µm to 18 µm, more preferably 12 µm to 18 µm. Furthermore, the mean particle diameter (D) can be 50 ) the particles with a small diameter of 1 µm to 7 µm, preferably 2 µm to 7 µm, more preferably 3 µm to 6 µm.

[0052] The type of active material from which the small diameter particles and the large diameter particles are made is not particularly restricted, and the active material can be the first positive electrode active material and / or the second positive electrode active material.

[0053] According to one embodiment, the positive electrode material of the present invention can be such that the first positive electrode active material forms particles with a large diameter and the second positive electrode active material forms particles with a small diameter.

[0054] According to a further embodiment, the positive electrode material of the present invention can be such that the first positive electrode active material forms particles with a small diameter and the second positive electrode active material forms particles with a large diameter.

[0055] According to a further embodiment, the positive electrode material of the present invention can be such that at least one of the first positive electrode active material or the second positive electrode active material has a bimodal particle diameter distribution that includes both the large diameter particles and the small diameter particles. Positive electrode

[0056] Next, a positive electrode according to the invention will be described.

[0057] The positive electrode according to the invention comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. At this stage, the positive electrode active material layer comprises the positive electrode material according to the invention and optionally a conductive material and / or a binder.

[0058] At this stage, the positive electrode material is the same as described above and can be present in an amount of 80 to 99 wt%, specifically 85 to 98.5 wt%, based on the total weight of the positive electrode active material layer. Excellent capacitance characteristics can be observed when the positive electrode material is present in the aforementioned range.

[0059] The positive electrode current collector is not particularly limited in its applications, as long as it is conductive without causing a chemical change in a battery. For example, stainless steel, aluminum, nickel, titanium, burnt carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, and the like can be used. Furthermore, the positive electrode current collector can typically have a thickness of 3 µm to 500 µm, and microscopic irregularities can be formed on its surface to improve the adhesion of the positive electrode material. For example, the positive electrode current collector can be used in various forms such as a foil, sheet, film, mesh, porous body, foam, or non-woven fabric.

[0060] The conductive material is used to impart conductivity to an electrode, and any conductive material can be used without special restriction, provided it exhibits electronic conductivity without causing a chemical change in the battery being formed. Specific examples include graphite, such as natural or synthetic graphite; a carbon-based material such as carbon black, acetylene carbon black, ketjen carbon black, sewer carbon black, furnace carbon black, lamp carbon black, thermal carbon black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, any one of which, or a mixture of two or more, may be used. The conductive material may be present in an amount of 0.1 to 15 wt%, based on the total weight of the positive electrode active material layer.

[0061] The binder serves to improve the bonding between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder may include polyvinylidene fluoride (PVDF), a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene propylene diene monomer (EPDM), a sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of these or a mixture of two or more may be used. The binder may be present in an amount of 0.1 to 15% by weight, based on the total weight of the positive electrode active material layer.

[0062] The positive electrode according to the invention can be produced according to a typical method for producing a positive electrode, with the exception that the positive electrode material according to the invention is used as the active material of the positive electrode. In particular, the positive electrode can be produced by applying a positive electrode mixture, which is produced by dissolving or dispersing a positive electrode material, a binder and / or a conductive material in a solvent, to a positive electrode current collector and subsequently drying and roll-forming it.

[0063] The solvent can be any solvent commonly used in the industry. Examples of solvents include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and any of these, or a mixture of two or more, can be used. The amount of solvent used is not particularly limited, as long as it can be adjusted to achieve a suitable viscosity for the positive electrode compound, taking into account the deposit thickness, the yield in preparation, the processability, and other factors of the positive electrode material.

[0064] Alternatively, the positive electrode can be produced in another process by casting the positive electrode mixture material onto a separate support and then laminating a film peeled from the support onto a positive electrode current collector. Lithium secondary battery

[0065] Next, a lithium secondary battery according to the invention will be described.

[0066] The lithium secondary battery according to the invention comprises a positive electrode, a negative electrode, a separator arranged between the positive and negative electrodes, and an electrolyte. The positive electrode is the same as the positive electrode according to the invention described above. Therefore, a detailed description of the positive electrode is omitted below, and only the other components are described.

[0067] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0068] The negative electrode current collector is not subject to any particular limitations as long as it exhibits high conductivity without causing any chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or similar materials, an aluminum-cadmium alloy, and the like can be used. Furthermore, the negative electrode current collector can typically have a thickness of 3 µm to 500 µm, and, as with the positive electrode current collector, microscopic irregularities can be formed on the surface of the negative electrode current collector to improve the adhesion of a negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0069] The negative electrode active material layer contains, in addition to the negative electrode active material, a selective binder and a conductive material.

[0070] Various negative electrode active materials commonly used in engineering can be employed without particular restrictions. Specific examples of negative electrode active materials include carbon-containing materials such as synthetic graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; lithium-alloyable metal compounds such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides, which can be lithium-doped or undoped, such as SiO₂. β(0<β<2), SnO2, ein Vanadiumoxid und ein Lithiumvanadiumoxid; oder ein Kompositwerkstoff, der die Metallverbindung und das kohlenstoffhaltige Material enthält, wie ein Si-C-Kompositwerkstoff oder ein Sn-C-Kompositwerkstoff, umfassen, und jedes davon oder eine Mischung aus zwei oder mehr davon kann verwendet werden. Außerdem kann eine dünne Lithiummetallschicht als Negativelektroden-Aktivmaterial verwendet werden. Darüber hinaus können sowohl niedrigkristalliner Kohlenstoff als auch hochkristalliner Kohlenstoff als Kohlenstoffmaterial verwendet werden.Typical examples of low-crystalline carbon can include soft carbon and hard carbon, and typical examples of high-crystalline carbon can include irregular, planar, flaky, spheroidal or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, meso-carbon microspheres, mesophase pitch and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0071] The negative electrode active material can be present in an amount of 80 wt.% to 99 wt.%, based on the total weight of the negative electrode active material layer.

[0072] The binder is a component that facilitates the bond between a conductive material, an active material, and a current collector, and is typically added in an amount of 0.1 wt% to 10 wt%, based on the total weight of a negative electrode active material layer. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene propylene diene monomer (EPDM), a sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, various copolymers thereof, and the like.

[0073] The conductive material is a component for further improving the conductivity of a negative electrode active material and may be added in an amount of 10 wt.% or less, preferably 5 wt.% or less, based on the total weight of a negative electrode active material layer. The conductive material is not particularly limited as long as it exhibits conductivity without causing a chemical change in the battery. For example, graphite, such as natural or synthetic graphite; carbon black, such as acetylene carbon black, ketjen carbon black, sewer carbon black, furnace carbon black, lamp carbon black, and thermal carbon black; conductive fibers, such as carbon fibers and metal fibers; metal powders, such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives and the like, may be used.

[0074] The negative electrode active material layer can be produced by applying a negative electrode mixture, prepared by dissolving or dispersing a negative electrode active material and selectively a binder and a conductive material in a solvent, to a negative electrode current collector and then drying it. Alternatively, the negative electrode active material layer can be produced by casting the negative electrode mixture onto a separate substrate and then laminating a film removed from the substrate onto a negative electrode current collector.

[0075] In a lithium secondary battery, the separator serves to separate the negative and positive electrodes and provide a pathway for lithium ions. Any separator can be used without particular restrictions, as long as it is typically used as a separator in a lithium secondary battery. In particular, a separator with high moisture retention capacity for an electrolyte and low resistance to electrolyte ion movement is preferred. A porous polymer film, such as one made from a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminated structure with two or more layers thereof, can be used as a separator.Furthermore, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, and the like. Additionally, a coated separator with a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can optionally be used in a single-layer or multi-layer structure.

[0076] The electrolyte used in the present invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, all of which can be used in a lithium secondary battery. However, the embodiment of the inventive concept is not limited to these.

[0077] In particular, the electrolyte may contain an organic solvent and a lithium salt.

[0078] Any organic solvent can be used without special restrictions, as long as it can serve as a medium through which ions involved in an electrochemical reaction of a battery can move.In particular, the following can be used as organic solvents: an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and 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 (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol-based solvent such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms and may contain an aromatic ring with a double bond or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes.Among these solvents, a carbonate-based solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and a linear carbonate-based compound with low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate), which can increase the charge / discharge performance of a battery, is even more desirable. In this case, the electrolyte performance can be excellent if the cyclic carbonate and the linear carbonate are mixed in a volume ratio of approximately 1:1 to approximately 1:9.

[0079] Any lithium salt can be used without special restrictions, as long as it is typically used in an electrolyte for a lithium secondary battery. For example, Li +as a positive ion of the lithium salt, and at least one negative ion of it can be selected from the group consisting of F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , PF4C2O4 - , PF2C4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3) 4PF2 - , (CF3) 5PF - , (CF3) 6P - , CF3SO3 - , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -In particular, the lithium salt may comprise a single material or a mixture of two or more materials selected from the group consisting of LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO 2, LiAsF6, LiSbF6, LiAlCl4, LiAlO4, and LiCH3SO3, and in addition to these, any electrolyte salt commonly used in an electrolyte for a lithium secondary battery can be used without restriction, such as an imide salt represented by LiBETI (lithium bisperfluoroethanesulfonimide, LiN(SO2C2F5)2), LiFSI (lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), and LiTFSI (lithium bis(trifluoromethane)sulfonimide, LiN(SO2CF3)2). In particular, the electrolyte salt can comprise a single material or a mixture of two or more materials selected from the group consisting of LiPF6, LiBF4, LiCH3CO2, LiCF3CO2, LiCH3SO3, LiFSI, LiTFSI, and LiN(C2F5SO2)2.

[0080] The lithium salt concentration can be varied within a typically available range. In particular, the lithium salt concentration can be in an electrolyte ranging from 0.8 M to 3 M, especially from 0.1 M to 2.5 M.

[0081] To improve battery lifespan, reduce capacity loss, and enhance discharge capacity, various additives can be used in the electrolyte in addition to the electrolyte components mentioned above. These additives may include, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate; or pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glymes, hexaphosphoric triamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. The additives listed above can be used alone or in combination. The additive may be present in amounts ranging from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0082] The lithium secondary battery described above according to the present invention can be used effectively in portable devices such as mobile phones, notebooks and digital cameras, as well as in electric cars such as hybrid electric vehicles (HEVs).

[0083] Accordingly, according to a further embodiment of the present invention, a battery module containing the lithium secondary battery as a unit cell and a battery pack containing this are provided.

[0084] The battery module or battery pack can be used as a power source for at least one medium to large device, such as a power tool, electric cars including electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), or an energy storage system.

[0085] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape or the like.

[0086] The lithium secondary battery according to the invention can be used in a battery cell that serves as a power source for a small device, and can preferably also be used as a unit cell for a medium-sized and large battery module comprising several battery cells. MODE FOR IMPLEMENTING THE INVENTION

[0087] The present invention is described in more detail below with reference to embodiments. However, the embodiments according to the invention can be modified to various other forms, and the scope of the present invention should not be considered limited to the embodiments described below. The embodiments of the present invention serve to describe the present invention in more detail to those skilled in the art. Example 1

[0088] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 5 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 15 µm were mixed in a weight ratio of 30:70 to produce the positive electrode material A.

[0089] The positive electrode material A, prepared as described above, a conductive carbon black material, and a PVdF binder were mixed in a weight ratio of 96:2:2, and then the mixture was blended in an NMP solvent to produce a positive electrode composite. The positive electrode composite was applied to 12 µm thick aluminum foil, dried, and then roll-pressed to produce a positive electrode.

[0090] Meanwhile, a graphite negative electrode active material, a conductive carbon material (SuperC65), and a PVdF binder were mixed in a weight ratio of 95.6:0.75:3.65, and then the mixture was added to an NMP solvent to produce a negative electrode composite. The negative electrode composite was applied to a 20 µm thick copper foil, dried, and then rolled to produce a negative electrode.

[0091] The positive and negative electrodes, prepared as described above, were laminated together with a polyethylene separator to form an electrode assembly, which was then inserted into a battery casing. An electrolyte, prepared by dissolving 1 M LiPF6 in 0.5 parts by weight of vinylene carbonate (VC) and 1.0 part by weight of 1,3-propanesultone (PS), based on 100 parts by weight of a mixed solvent of ethylene carbonate, propyl propionate, and diethyl carbonate mixed in a 3:1:6 ratio, was then injected into the battery casing to create a lithium secondary battery. Example 2

[0092] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 15 µm and LiNi 0,83 CO 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50) of 5 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material B.

[0093] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material B described above was used. Example 3

[0094] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 10 µm and LiNi 0,83 CO 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 5 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material C.

[0095] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material C described above was used. Example 4

[0096] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 13 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 5 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material D.

[0097] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material D described above was used. Example 5

[0098] LiNi 0,85 Co 0,1 Mn 0,05 O2 with a medium particle diameter (D 50 ) of 15 µm and LiNi 0,83 Co 0,11 Mn 0,05 Mg 0,01 O2 with a medium particle diameter (D 50) of 5 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material E.

[0099] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material E described above was used. Comparative example 1

[0100] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 15 µm and LiNi 0,83 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 5 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material F.

[0101] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material F described above was used. Comparative example 2

[0102] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 6 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 8 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material G.

[0103] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, positive electrode material G as described above was used. Comparative example 3

[0104] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 15 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50) of 15 µm were mixed in a weight ratio of 70:30 to produce the positive electrode material H.

[0105] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material H described above was used. Comparative example 4

[0106] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 5 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 5 µm were mixed in a weight ratio of 30:70 to produce the positive electrode material I.

[0107] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material I described above was used. Comparative example 5

[0108] LiNi 0,6 Co 0,2 Mn 0,2 O2 with a medium particle diameter (D 50 ) of 5 µm and LiNi 0,83 Co 0,11 Mn 0,04 Al 0,02 O2 with a medium particle diameter (D 50 ) of 15 µm were mixed in a weight ratio of 30:70 to produce the positive electrode material J.

[0109] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material J described above was used. Comparative example 6

[0110] LiNi 0,8 Co 0,1 Mn 0,1 O2 with a medium particle diameter (D 50 ) of 5 µm and LiNi 0,6 Co 0,2 Mn 0,2 O2 with a medium particle diameter (D 50) of 15 µm were mixed in a weight ratio of 30:70 to produce the positive electrode material K.

[0111] A lithium secondary battery was manufactured in the same way as in Example 1, except that instead of positive electrode material A, the positive electrode material K described above was used. Experimental Example 1

[0112] The lithium secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 6 were charged / discharged at 45 °C in the range of 2.5 V to 4.2 V under conditions of 0.3 C / 0.3 C to measure the capacity retention rate (%) and the resistance increase rate (%) at the 100th and 200th cycles. The measurement results are shown in Table 1. Furthermore, [the text abruptly ends here, so the translation stops as well.] Fig. a diagram showing the cycle characteristics of the lithium secondary batteries produced in examples 1 and 2 as well as in comparison example 1. [Table 1] 100th cycle 200th cycle Capacity maintenance rate (%) Resistance increase (%) Capacity maintenance rate (%) Resistance increase (%) Example 1 92,5 9,6 88,5 18, 8 Example 2 92,4 14,0 88, 6 23,7 Example 3 90,8 19,8 85,9 30,5 Example 4 91,2 16,9 86,4 27,4 Example 5 90,3 21,4 85,2 34,2 See example 1 90,4 23,2 84,8 37,4 See example 2. 87, 1 29,2 80, 0 44,3 See example 3 86,9 29,8 79,4 44,9 See example 4 85,4 30,7 78,7 46,1 See example 5 88, 1 27,7 82,2 39,7 See example 6 88,2 27,3 82,4 40, 8

[0113] As shown in Table 1 and Fig. As shown in Figure 1, the secondary batteries of Examples 1 to 5, which use a positive electrode material containing two types of positive electrode active materials that satisfy the composition of the present invention, exhibit a bimodal distribution with a difference in the mean particle diameter (D). 50 ) between large-diameter particles and small-diameter particles of 3 µm or more, exhibits better high-temperature cycle properties than the secondary batteries of comparison examples 1-6. In particular, it can be seen that with an increasing number of cycles, the difference in capacity properties and resistance rate increases.

[0114] This utility model is a branch of EP application No. 18 881 779.5. The entire subject matter of that application is hereby incorporated by reference. The subject matter defined by the original claims of EP application No. 18 881 779.5 is referred to below as preferred embodiments. <1> until <12> Revealed again: <1> Positive electrode material comprising a first positive electrode active material, represented by formula 1 below, and a second positive electrode active material, represented by formula 2 below, wherein the positive electrode material has a bimodal particle size distribution, comprising large-diameter particles and small-diameter particles, and the difference in mean particle diameter (D 50 ) between the large-diameter particles and the small-diameter particles is 3 µm or more: Li a [Ni b Coc M 1 d M a e ]O2 [Formula 1] where in Formula 1 M 1 Mn, Al, Zr or Mg is and M a one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c<0.2, 0.01≤d<0.2 and 0≤e≤0.02. Li x [Ni y Co z Mn w M 2 v M b u ]O2 [Formula 2] where in Formula 2 M 2 Al, Mg, Zr or Ti is and M b one or more elements are selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and 0.9≤x≤1.2, 0.8≤y<1, 0.01≤z<0.2, 0.01≤w<0.2, 0.01≤v<0.2 and 0≤u≤0.02. <2> Positive electrode material according to <1> , where the mean particle diameter (D 50) the particle with a large diameter is 10 µm to 20 µm. <3> Positive electrode material according to <1> , where the mean particle diameter (D 50 ) the particle with a small diameter of 1 µm to 7 µm. <4> Positive electrode material according to <1> , wherein the first positive electrode active material forms the small diameter particles and the second positive electrode active material forms the large diameter particles. <5> Positive electrode material according to <1> , wherein the first positive electrode active material formed the large diameter particles and the second positive electrode active material is the small diameter particles. <6> Positive electrode material according to claim <1> , wherein at least one of the first positive electrode active material or the second positive electrode active material has a bimodal particle size distribution comprising the large diameter particles and the small diameter particles. <7> Positive electrode material according to <1> , wherein the first positive electrode active material and the second positive electrode active material are present in a weight ratio of 10:90 to 90:10. <8> Positive electrode material according to <1> , wherein at least one of the first positive electrode active material or the second positive electrode active material comprises a coating layer containing at least one coating element selected from the group consisting of one or more elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si and S. <9> Positive electrode material according to <1> , where in Formula 1 M 1 Mn is and in Formula 2 M 2 Al is. <10> Positive electrode material according to <1> , where the difference is in the mean particle diameter (D 50 ) between the large diameter particles and the small diameter particles is 3 µm to 15 µm. <11> Positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer is the positive electrode material according to any of <1> until <10> includes. 12. Lithium secondary battery, including: the positive electrode according to <11> ; a negative electrode; a separator arranged between the positive electrode and the negative electrode; and an electrolyte. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] EP 18 881 779

[0114]

Claims

[1] Positive electrode material comprising a first positive electrode active material, represented by formula 1 below, and a second positive electrode active material, represented by formula 2 below, wherein the first positive electrode active material and the second positive electrode active material are present in a weight ratio of 10:90 to 90:10, the positive electrode material has a bimodal particle size distribution, which includes large diameter particles and small diameter particles, wherein the first positive electrode active material forms the small-diameter particles and the second positive electrode active material forms the large-diameter particles, or wherein the first positive electrode active material forms the large-diameter particles and the second positive electrode active material forms the small-diameter particles, and the difference in mean particle diameter (D 50 ) between the large-diameter particles and the small-diameter particles is 3 µm or more: Li a [Ni b Co c M 1 d M a e ]O2 [Formula 1] where in Formula 1 M 1 Mn is and M a a doping element that is substituted at a transition metal site (Ni, Co and / or Mn), and 0.9≤a≤1.2, 0.8≤b<1, 0.01≤c<0.2, 0.01≤d<0.2 and 0≤e≤0.

02. Li x [Ni y Co z Mn w M 2 v M b u ]O2 [Formula 2] where in Formula 2 M 2 Al is and M b a doping element that is substituted at a transition metal site (Ni, Co and / or Mn), and 0.9≤x≤1.2, 0.8≤y<1, 0.01≤z<0.2, 0.01≤w<0.2, 0.01≤v<0.2 and 0≤u≤0.

02. [2] Positive electrode material according to claim 1, wherein the mean particle diameter (D 50 ) the particle with a large diameter is 10 µm to 20 µm. [3] Positive electrode material according to claim 1, wherein the mean particle diameter (D 50 ) the particle with a small diameter of 1 µm to 7 µm. [4] Positive electrode material according to claim 1, wherein at least one of the first positive electrode active material or the second positive electrode active material comprises a coating layer. [5] Positive electrode material according to claim 1, wherein the difference in mean particle diameter (D 50 ) between the large diameter particles and the small diameter particles is 3 µm to 15 µm. [6] Positive electrode comprising a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 5. [7] Lithium secondary battery, comprising: the positive electrode according to claim 6; a negative electrode; a separator arranged between the positive electrode and the negative electrode; and an electrolyte.

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