Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a cathode active material that includes a lithium-excess manganese-based transition metal oxide and has a compactness (P) of 42 to 50. The cathode active material can provide a cathode that can have an optimal density after electrode coating and rolling by optimizing the ratio between the lattice parameter of the unit cell and the rolling density under weak pressure to maximize the interparticle compactness.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183709 filed December 23, 2022 and Korean Patent Application No. 10-2023-0187698 filed December 20, 2023, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for a lithium secondary battery, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] A lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high cost and unstable supply of cobalt, the raw material, make it difficult to commercially apply to large-capacity batteries. Lithium nickel oxide has poor structural stability and is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but poor capacity characteristics. To address the issues of lithium transition metal oxides containing only Ni, Co, or Mn, lithium nickel-based transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxides containing Ni, Co, and Mn are widely used in the field of electric vehicle batteries.

[0005] Recently, there has been an increasing demand for high-power, high-capacity batteries, such as those used in electric vehicles, and as a result, the nickel content in the positive electrode active material has been gradually increasing. When the nickel content in the positive electrode active material increases, the initial capacity characteristics improve, but the nickel content is highly reactive during electrode rolling or charge / discharge processes. +4 The large amount of ions generated causes the structure of the positive electrode active material to collapse, which increases surface side reactions, increases the rate of deterioration of the positive electrode active material, and reduces the lifespan characteristics and safety of the battery.

[0006] Meanwhile, research and development is being conducted on lithium-excess manganese-based active materials as a replacement for high-nickel-content cathode active materials, which are expensive and have poor durability due to structural stability issues. Lithium-excess manganese-based active materials have a high theoretical capacity, but to achieve this, they require a driving voltage of 4.4V or more, which hinders battery life and high-temperature storage characteristics, making them difficult to commercialize.

[0007] Another method for achieving high theoretical capacity is to increase the rolling density. Increasing the rolling density increases the amount of active material per unit volume, which allows for higher capacity. However, excessively high rolling density can lead to particle cracking, while excessively low rolling density can result in low energy density. These issues are difficult to control, and instead, the porosity within the secondary particles must be minimized to increase interparticle density. However, this density can only be measured indirectly and is difficult to quantitatively analyze, making it impossible to determine the characteristics of an active material that maximizes energy density and is free of particle cracking. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above problems by providing a cathode active material capable of optimizing interparticle compactness through the unit cell volume derived by analyzing the crystalline characteristics of cathode active material particles and the rolling density at a low pressure.

[0009] Another object of the present invention is to provide a positive electrode and a lithium secondary battery that contain the positive electrode active material, thereby maximizing energy density by optimizing rolling density, eliminating particle cracking, and significantly reducing the occurrence of side reactions, thereby improving life characteristics and providing excellent capacity characteristics. [Means for solving the problem]

[0010] In order to solve the above problems, one aspect of the present invention provides a positive electrode active material that includes a lithium-excess manganese-based transition metal oxide and has a compactness (P) of 42 to 50 calculated by the following formula 1:

[0011] [Formula 1]

number

[0012] In the above formula 1, V unit-cell is the volume of the unit cell (Å 3 ) and is derived by the following formula 2 (numerical formula 2), and d 400 is the rolling density (g / cm) when rolling at 400 kgf. 3 ) and

[0013] [Formula 2]

number

[0014] In the above formula 2, a and c are crystal lattice parameters (Å) derived from XRD measurement of the positive electrode active material.

[0015] In order to solve the above problems, in another aspect of the present invention, there is provided a positive electrode including the positive electrode active material according to the present invention.

[0016] In order to solve the above problems, in another aspect of the present invention, there is provided a lithium secondary battery including the positive electrode according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that correspond to the technical ideas of the present invention based on the principle that an inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0018] As used herein, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and are understood not to preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] In the present invention, a "single particle" refers to a particle consisting of one single nodule. In the present invention, a "nodule" refers to a particle unit that may be a single crystal lacking crystalline grain boundaries, or a polycrystalline particle that appears to have no grain boundaries when observed at 5,000x to 20,000x magnification using a scanning electron microscope (SEM). In the present invention, a "quasi-single particle" refers to a particle that is a complex formed from 30 or fewer nodules.

[0020] In the present invention, "secondary particles" refer to particles formed by agglomeration of several tens to several hundreds of primary particles. More specifically, secondary particles are agglomerations of 50 or more primary particles.

[0021] The term "particle" as used herein may include any one or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle.

[0022] In this invention, "D 50" means the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder. 50 can be measured using a laser diffraction method. For example, after dispersing a positive electrode active material powder in a dispersion medium, the dispersion is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac's MT3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0023] The present invention will now be described in more detail.

[0024] positive electrode active material The positive electrode active material according to the present invention is characterized in that it contains a lithium-excess manganese-based transition metal oxide and has a compactness (P) of 42 to 50 calculated by the following formula 1 (mathematical formula 3).

[0025] [Formula 1]

number

[0026] In the above formula 1, V unit-cell is the volume of the unit cell (Å 3 ) and is derived by the following equation 2 (Equation 4), and d 400 is the rolling density (g / cm) when rolling at 400 kgf. 3 )

[0027] [Formula 2]

number

[0028] In the above formula 2, a and c are the lattice parameters (Å) of the unit cell in the crystal structure derived from XRD measurement of the positive electrode active material.

[0029] According to one embodiment of the present invention, the positive electrode active material includes a lithium-excess manganese-based transition metal oxide having a compactness of 42 to 50. The compactness may represent the degree to which particles can be packed together without cracking, i.e., the degree to which particles can be well packed without being damaged. Preferably, the compactness may be 43 or more, or 44 or more, and 49 or less, or 48 or less. A compactness of less than 42 indicates a smaller unit cell volume compared to a given rolling density. The unit cell volume depends on the lattice parameter, which can vary depending on factors such as sintering process conditions, the molar ratio of transition metals, the molar ratio of lithium to transition metals, doping, coating, etc. It can be seen that a small lattice parameter due to a specific factor results in relatively poor lithium ion mobility.

[0030] Meanwhile, when the compactness of the lithium-excess manganese-based transition metal oxide according to one embodiment of the present invention is greater than 50, this means that the rolling density relative to the unit cell volume is low due to an imbalance in the ratio between the unit cell volume and the rolling density, and although there may be various reasons for this, it may mean that the secondary particles have structure and particle size characteristics that prevent good packing due to issues with the voids, shape, particle size, etc. In this case, even when rolling at an appropriate pressure, good packing does not occur, resulting in low energy density and low capacity, or particle cracking, which can shorten the lifespan.

[0031] Such particle compactness has the advantage that the energy density can be maximized even before the actual rolling process by determining the rolling density under weak pressure, i.e., a value similar to the true density of the actual particles, and specifying the ratio of this to the volume of the unit cell present in the crystal structure, thereby providing an active material with high capacity characteristics.

[0032] The lattice parameters a and c refer to either side of a unit cell in a crystal structure. A cathode active material according to one embodiment of the present invention typically has a layered structure (R-3m) and a rock-salt monoclinic structure (C2 / m). In such structures, the sides along the x and y axes are represented by a, and the sides along the z axis are represented by c. In the case of Formula 2 according to one embodiment of the present invention, the lattice parameters were applied assuming that the crystal structure of the cathode active material is entirely layered. The a may be 2.83 to 2.90, and the c may be 14.21 to 14.31. Specifically, the a may be 2.85 to 2.88, and the c may be 14.23 to 14.29.

[0033] According to one embodiment of the present invention, d in Formula 1 400 is the density of the lithium-excess manganese-based transition metal oxide when rolled at 400 kgf, which may be close to the true density of the actual particles. 400 is 2.00g / cm 3 ~2.40g / cm 3 and preferably 2.03 g / cm 3 More than 2.05g / cm 3 More than 2.07g / cm 3 More than 2.10g / cm 3 or more, or 2.12 g / cm 3 It may be equal to or greater than 2.37 g / cm 3 Below 2.35g / cm 3 Below, 2.33g / cm 3 Below 2.30g / cm 3 The following may be possible: 400 When the volume of the unit cell is within the above range, the ratio of the volume of the unit cell can be appropriately adjusted. Even if the volume of the unit cell is derived from a lattice parameter that is determined to some extent, the lattice parameter itself can change relatively widely. 400 The limited range of d may be meaningful. 400 The density range can be a basic condition for optimizing the energy density depending on whether the volume of the unit cell is filled or not.

[0034] According to one embodiment of the present invention, the rolling density of the lithium-excess manganese-based transition metal oxide is 2.30 g / cm 3 At this time, the pressure during rolling may be 2000 kgf. The rolling density may be 2.35 g / cm 3 More than 2.37g / cm 3 More than 2.40g / cm 3 More than 2.42g / cm 3 or more, or 2.43 g / cm 3 In this range, the energy density of the positive electrode can be maximized.

[0035] The positive electrode active material according to the present invention may include a lithium-excess manganese-based transition metal oxide, specifically, a lithium-excess manganese-based transition metal oxide having a composition represented by the following Chemical Formula 1:

[0036] [Chemical formula 1] Li 1+a [Mn 1-b-c-d Ni b M1 c M2 d ]O 2-e A e

[0037] In the formula 1, M1 and M2 each independently include at least one selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, Ta, Y, and Zr; A includes at least one selected from the group consisting of N, P, S, F, and Cl; a, b, and c each independently represent an atomic fraction of an element, and are within the range of 0.1≦a≦0.6, 0≦b≦0.5, 0≦c≦0.5, 0≦d≦0.05, 0 <b+c+d≦0.5、および0≦e≦0.05である。

[0038] In Formula 1, M1 includes Co, Al, or a combination thereof, preferably Co or a combination of Co and Al. M2 includes at least one element selected from the group consisting of Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, Ta, Y, and Zr, preferably at least one element selected from the group consisting of W, Zr, Y, Mg, and Ti, and more preferably W, Zr, Y, Ti, or a combination thereof. The M2 element is not essential, but when present in an appropriate amount, it can promote particle growth during firing and improve the stability of the crystal structure. Furthermore, A is an anion substituted for the oxygen site and can include N, P, S, F, or Cl.

[0039] The 1+a indicates the molar ratio of lithium in the lithium-excess manganese-based transition metal oxide, and may be 0.1≦a≦0.6, 0.1≦a≦0.5, or 0.2≦a≦0.5.

[0040] The b represents the molar ratio of nickel to all metals excluding lithium in the lithium-excess manganese-based transition metal oxide, and may be 0≦b≦0.50, 0.05≦b≦0.50, 0.10≦b≦0.50, or 0.10≦b≦0.45.

[0041] The c represents the molar ratio of the M1 element in all metals excluding lithium in the lithium-excess manganese-based transition metal oxide, and may be 0≦c≦0.50, 0.05≦c≦0.50, 0.10≦c≦0.50, or 0.10≦c≦0.45.

[0042] The d represents the molar ratio of the M2 element in all metals excluding lithium in the lithium-excess manganese-based transition metal oxide, and may be 0≦d≦0.05, 0≦d≦0.02, or 0≦d≦0.01.

[0043] In addition, the total molar ratio of the metal remaining after removing manganese from the total metal excluding lithium in the lithium-excess manganese-based transition metal oxide, nickel, M1, and M2 metals, that is, b + c + d, can be 0 < b + c + d ≤ 0.5, 0.05 ≤ b + c + d ≤ 0.50, 0.10 ≤ b + c + d ≤ 0.50, or 0.10 ≤ b + c + d ≤ 0.45. Therefore, the molar ratio of Mn can always be 0.5 or more.

[0044] On the other hand, the lithium-excess manganese-based transition metal oxide can further include a coating layer containing at least one coating element 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 on the particle surface.

[0045] When a coating layer exists on the particle surface of the lithium-excess manganese-based transition metal oxide, the contact between the electrolyte and the lithium-excess manganese-based transition metal oxide is suppressed by the coating layer, and thus the effect of reducing the elution of transition metals and gas generation due to side reactions with the electrolyte can be obtained.

[0046] Method for manufacturing a positive electrode active material Next, the method for manufacturing the positive electrode active material powder of the present invention will be described.

[0047] The method for manufacturing the positive electrode active material powder according to the present invention includes (S1) a step of introducing a transition metal-containing solution containing cations of nickel (Ni), manganese (Mn), and M1, a basic aqueous solution, and an ammonium solution, and subjecting them to a coprecipitation reaction to produce a positive electrode active material precursor, and (S2) a step of mixing and heat-treating the positive electrode active material precursor and a lithium raw material to produce a positive electrode active material powder.

[0048] The produced positive electrode active material includes a lithium-excess manganese-based transition metal oxide in the form of at least one of secondary particles formed by agglomerations of tens to hundreds of primary particles, single particles consisting of one nodule that can be formed through the coarsening of crystal grains, and similar single particles that are a complex of 30 or less nodules, or a mixture of these two forms.

[0049] Each step of the method for producing the positive electrode active material powder will be specifically described below.

[0050] First, a transition metal-containing solution containing nickel (Ni), manganese (Mn), and M1 cations is prepared. For example, the transition metal-containing solution may contain a nickel-containing source material, a manganese-containing source material, and an M1-containing source material, and the M1-containing source material may be a cobalt-containing source material and / or an aluminum-containing source material.

[0051] Thereafter, a complexing agent containing ammonium cations and a basic aqueous solution are added to the transition metal solution to cause a coprecipitation reaction, thereby producing a positive electrode active material precursor.

[0052] The nickel-containing source material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, such as, but not limited to, Ni(OH)2, NiO, NiOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, a fatty acid nickel salt, a nickel halide, or a combination thereof.

[0053] The manganese-containing source material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically may be, but is not limited to, manganese oxides such as MnO, MnO, MnO, etc.; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0054] The cobalt-containing source material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, such as, but not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0055] The aluminum-containing source material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halide, or combinations thereof.

[0056] The transition metal-containing solution may be prepared by adding a nickel-containing raw material, a manganese-containing raw material, and an M1-containing raw material to a solvent, specifically water or a mixed solvent of an organic solvent (e.g., alcohol) that can be uniformly mixed with water, or by mixing an aqueous solution of the nickel-containing raw material, an aqueous solution of the manganese-containing raw material, and an M1-containing raw material.

[0057] The ammonium cation-containing complexing agent may be, but is not limited to, NHOH, (NH)SO, NHNO, NHCl, CHCOONH, NHCO, or a combination thereof. Meanwhile, the ammonium cation-containing complexing agent may be used in the form of an aqueous solution, in which case the solvent used is water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0058] The basic compound may be a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH), a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, in which case the solvent used may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0059] The basic compound is added to adjust the pH of the reaction solution, and can be added in an amount that will bring the pH of the metal solution to 8 to 12.

[0060] The co-precipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon at a temperature range of 35°C to 80°C.

[0061] This allows the production of a positive electrode active material precursor containing nickel, manganese, and M1 cations.

[0062] Through the above process, nickel-manganese-M1 hydroxide cathode active material precursor particles are produced and precipitated in the reaction solution. By adjusting the concentrations of the nickel-containing raw material, manganese-containing raw material, and M1-containing raw material, a cathode active material precursor having a manganese (Mn) content of 50 mol% or more, 55 mol% or more, preferably 60 mol% or more, more preferably 63 mol%, even more preferably 65 mol%, even more preferably 66 mol%, and even more preferably 67 mol% or more of the total metal content can be produced. The precipitated cathode active material precursor particles can be separated and dried using a conventional method to produce the cathode active material precursor.

[0063] Thereafter, the positive electrode active material precursor and the lithium raw material are mixed and heat-treated.

[0064] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium source material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, or a mixture of two or more of these.

[0065] The positive electrode active material precursor and the lithium source material may be mixed in a molar ratio of 1:1 to 1:1.1, for example, about 1:1, about 1:1.02, about 1:1.05, about 1:1.07, or about 1:1.10, but are not limited thereto.

[0066] In the case of a manganese-excessive lithium-rich manganese-based transition metal composite oxide having a manganese (Mn) content of 50 mol % or more, the heat treatment can be carried out in a temperature range of 750°C to 1000°C. For example, the heat treatment can be carried out preferably in a temperature range of 800°C to 975°C, and more preferably in a temperature range of 850°C to 950°C.

[0067] As a result, the produced positive electrode active material may have reduced particle cracking and strain within the crystalline structure during the rolling process or during charge and discharge of a lithium secondary battery including the same, thereby improving initial resistance characteristics.

[0068] The heat treatment may be carried out in an air or oxygen atmosphere for, for example, 4 to 12 hours. Specifically, the heat treatment may be carried out for, for example, 4 hours or more, 6 hours or more, 8 hours or more, or 10 hours or more, or 12 hours or less, 10 hours or less, 8 hours or less, or 6 hours or less.

[0069] Meanwhile, when preparing a lithium-excess manganese-based transition metal oxide containing an M2 metal, an M2 metal-containing raw material can be added during the co-precipitation reaction or calcination step. In this case, the M2 metal-containing raw material can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the M2 metal.

[0070] Meanwhile, if a coating layer is to be formed on the surface of the lithium-excess manganese-based transition metal oxide, the heat treatment may be followed by a further step of mixing the lithium-excess manganese-based transition metal oxide produced through the heat treatment with a coating raw material, followed by further heat treatment. The mixing may be performed as a solid-phase or liquid-phase mixture, and the heat treatment may be performed at an appropriate temperature depending on the coating raw material. For example, the heat treatment in the coating process may be performed at a temperature ranging from 200°C to 700°C, or from 300°C to 600°C, but is not limited thereto.

[0071] In addition, it is preferable not to perform a water washing process after the heat treatment when preparing the cathode active material powder of the present invention. Conventionally, when preparing a lithium composite transition metal oxide, a water washing process has been performed after the heat treatment to reduce the content of lithium by-products. However, research by the present inventors has revealed that performing a water washing process during the preparation of a lithium transition metal oxide can deteriorate the surface properties of the lithium transition metal oxide during the water washing process, resulting in increased resistance. Therefore, it is preferable not to perform water washing when preparing the cathode active material of the present invention, and to consume the residual lithium on the surface of the lithium transition metal oxide during the formation of the coating layer. In this way, when preparing a cathode active material without washing the lithium transition metal oxide with water, an increase in resistance due to surface defects can be suppressed.

[0072] positive electrode The positive electrode according to the present invention includes the positive electrode active material powder according to the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material powder according to the present invention. Since the positive electrode active material powder has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0073] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it easily adheres to the positive electrode active material layer and is non-reactive within the battery voltage range. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector typically has a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0074] The positive electrode active material layer may optionally contain a conductive material and a binder in addition to the positive electrode active material powder, as required.

[0075] In this case, the positive electrode active material powder may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98.5 wt %, based on the total weight of the positive electrode active material layer. When contained in this amount range, excellent capacity characteristics can be exhibited.

[0076] The conductive material is used to impart conductivity to the electrode and can be any material with electronic conductivity that does not undergo chemical changes in the resulting battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, or silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material can be present in an amount of 0.1 to 15 wt % based on the total weight of the positive electrode active material layer.

[0077] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof. These may be used alone or in combination. The binder may be contained in an amount of 0.1 to 15% by weight based on the total weight of the positive electrode active material layer.

[0078] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material powder. Specifically, the positive electrode may be manufactured by dissolving or dispersing the positive electrode active material powder and, optionally, a binder, a conductive material, and a dispersant in a solvent to prepare a positive electrode slurry composition, which is then coated on a positive electrode current collector, followed by drying and rolling.

[0079] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and may be used alone or in combination. The amount of the solvent used is determined in consideration of the coating thickness of the slurry and the production yield, and is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a cathode.

[0080] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling it off from the support, and laminating the resulting film on a positive electrode current collector.

[0081] Electrochemical elements Next, an electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the cathode of the present invention described above. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0082] The lithium secondary battery specifically includes a positive electrode, a negative electrode facing the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is as described above, detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0083] The lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0084] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0085] The negative electrode current collector may be any material that does not induce chemical changes in the battery and has high conductivity, including, for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the current collector may have a fine irregularity on its surface to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0086] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0087] The negative electrode active material is a compound capable of reversibly inserting and extracting lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β(0<β<2) Metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. One or a mixture of two or more of these can be used. Metallic lithium thin film can also be used as the negative electrode active material. Both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0088] The negative electrode active material may be included in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0089] The binder is a component that helps bind the conductive material, active material, and current collector, and is typically added in an amount of 0.1 to 10 wt % based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0090] The conductive material is a component for further improving the conductivity of the 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 the negative electrode active material layer. The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0091] The negative electrode active material layer may be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, on a negative electrode current collector and drying the coating. Alternatively, the negative electrode slurry composition may be cast on a separate support, peeled from the support, and the resulting film may be laminated on the negative electrode current collector.

[0092] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification ability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, a separator coated with a ceramic component or a polymer material to ensure heat resistance or mechanical strength can be used, and it can be used in either a single-layer or multi-layer structure.

[0093] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0094] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0095] The organic solvent may be any solvent capable of acting as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0096] The lithium salt can be used without any particular limitation as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0097] In addition to the constituents of the electrolyte, the electrolyte may further contain one or more additives, such as a haloalkylene carbonate compound (e.g., difluoroethylene carbonate), pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0098] Example Although the present invention may be embodied in many different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0099] Example 1 Ni synthesized by coprecipitation reaction 0.83 Co 0.11 Mn 0.06 The (OH)2 precursor was mixed with LiOH to a Li / Me(Ni+Mn) molar ratio of 1.38, and then fired in an oxygen atmosphere to produce Li 1.38 Ni 0.37 Mn 0.63 A positive electrode active material having an O2 composition was prepared.

[0100] Example 2 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0101] Example 3 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0102] Example 4 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0103] Comparative Example 1 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0104] Comparative Example 2 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0105] Comparative Example 3 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0106] Comparative Example 4 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0107] Comparative Example 5 A positive electrode active material having the same composition as that of Example 1 and having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0108] Experimental Example 1: Measurement of the characteristics of the positive electrode active material 1) Derivation of lattice parameters a and c: These were measured by X-ray diffraction (XRD) using Cu-Kα X-rays (Xrα). Specifically, measurements were performed at 40 kV using a Rikaku XRD instrument with a Cu-Ka target as the reference. The produced particles were placed in a holder and irradiated with X-rays to analyze the resulting diffraction pattern. The lattice parameters were then measured, and the unit cell volume was calculated using Equation 2 above.

[0109] 2) Rolling density when pressed at 400 kgf: The rolling density of the positive electrode active material was measured using a density measuring device (Caver Pellet Press). Specifically, 5 g of the positive electrode active material was divided into small portions and tightly packed into a cylindrical holder with a diameter of 13 mm, and then a pressure of 400 kgf was applied to measure the rolling density.

[0110] [Table 1]

[0111] <Manufacturing lithium secondary batteries> The positive electrode active materials prepared in Examples 1 to 4 and Comparative Examples 1 to 5, carbon black conductive material, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare positive electrode slurries. The positive electrode slurries were applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare positive electrodes.

[0112] Graphite as the negative electrode active material, super C as the conductive material, and SBR / CMC as the binder were mixed in a weight ratio of 95.6:1.0:3.4 to prepare a negative electrode slurry, which was then applied to one side of a copper current collector, dried at 130°C, and rolled to prepare a negative electrode.

[0113] After fabricating the electrode assembly with a separator between the positive and negative electrodes, the assembly was placed inside a battery case, and an electrolyte solution was injected into the case to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving LiPF6 at a concentration of 1M in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 1:2:1, and adding 2 wt% vinylene carbonate (VC).

[0114] Experimental Example 2: Performance measurement of positive electrode active material 1) Rolling density when pressed at 2000 kgf (2 ton): The rolling density of the positive electrode active material was measured using a density measuring device (Caver Pellet Press). Specifically, 5 g of the positive electrode active material was divided into small portions and tightly packed into a cylindrical holder with a diameter of 13 mm. Then, a pressure of 2000 kgf was applied to measure the rolling density. The results are shown in Table 2.

[0115] 2) Capacity characteristics: During activation, electrode loading is 0.35g / 25cm 2 The measurements were performed under the conditions of an upper limit voltage of 4.6 V, a lower limit voltage of 2.0 V, a temperature of 40° C., and a current of 20 mA, and the results are shown in Table 2 below.

[0116] 3) Rate characteristics: In the capacity characteristics, only the current was changed to 0.33 C, and the discharge capacity was measured. The measured value was divided by the discharge capacity in the capacity characteristics to obtain a percentage, which is shown in Table 2 below.

[0117] [Table 2]

[0118] Referring to Table 2, it can be seen that Examples 1 to 4 have excellent rolling density, and the initial discharge capacity is evaluated as higher than that of Comparative Examples 1 to 5, and the rate characteristics are improved. [Industrial Applicability]

[0119] The positive electrode active material for a lithium secondary battery according to the present invention can improve energy density by determining the active material characteristics in which the density between particles is maximized by optimizing the ratio of the volume of a unit cell and the rolling density at a low pressure.

[0120] In addition, the positive electrode for a lithium secondary battery according to the present invention is free from particle cracking, thereby significantly reducing the occurrence of side reactions, and has a high energy density, thereby exhibiting excellent life characteristics and high capacity characteristics.

Claims

1. a lithium-rich manganese-based transition metal oxide; The density (P) calculated by the following formula 1 is 42 to 50, [Equation 1] In the above equation 1, V ｕｎｉｔ－ｃｅｌｌ is the volume of the unit cell (Å ３ ) is derived by the following equation 2, and d ４００ is the rolling density (g / cm) when rolling at 400 kgf. ３ ) and [Equation 2] In the above formula 2, a and c are crystal lattice parameters (Å) derived from an XRD measurement of the positive electrode active material.

2. 2. The positive electrode active material according to claim 1, wherein the compactness (P) is 43 to 49.

3. 2. The positive electrode active material according to claim 1, wherein the compactness (P) is 44 to 48.

4. 2. The positive electrode active material according to claim 1, wherein a is 2.85 Å to 2.88 Å, and c is 14.23 Å ​​to 14.29 Å.

5. The above d ４００ is 2.00 g / cm ３ ~2.40 g / cm ３ The positive electrode active material according to claim 1 ,

6. The lithium-excess manganese-based transition metal oxide is represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ａ [Mn １－ｂ－ｃ－ｄ Ni ｂ M1 ｃ M2 ｄ ]O ２－e A e In the above Chemical Formula 1, M1 and M2 each independently comprise one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, Ta, Y, and Zr; A includes at least one selected from the group consisting of N, P, S, F, and Cl; 2. The positive electrode active material according to claim 1, wherein 0.1≦a≦0.6, 0≦b≦0.5, 0≦c≦0.5, 0≦d≦0.05, 0<b+c+d≦0.5, and 0≦e≦0.

05.

7. The positive electrode active material has a rolling density of 2.42 g / cm when rolled at 2000 kgf. ３ The positive electrode active material according to claim 1 .

8. A positive electrode comprising the positive electrode active material according to claim 1 .

9. A lithium secondary battery comprising the positive electrode according to claim 8, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

10. The lithium secondary battery according to claim 9 , wherein the negative electrode comprises a silicon-based negative electrode active material.

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