Positive electrode active material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material comprising a lithium-rich manganese-based transition metal oxide, in which a density (P) obtained by mathematical formula 1 below is 42 to 50, in which the positive electrode active material optimizes a ratio of a lattice parameter of a unit cell to a calendering density at a low pressure so as to maximize a density between particles, thus, a positive electrode capable of having an optimized density after electrode coating and calendering is provided. [Mathematical formula 1] # imgabs 0 # in Mathematical formula 1, V unit cells are the volume (3) of unit cells obtained by the following Mathematical formula 2, d400 is the rolling density (g / cm3) when rolled at 400 kgf, and [Mathematical formula 2] # imgabs 1 # in Mathematical formula 2, a and c are lattice parameters () obtained from XRD measurement of the positive electrode active material.

Description

Technical Field

[0001] Cross-reference to Related Applications

[0002] This application claims the priority benefits of Korean Patent Application No. 10-2022-0183709, filed with the Korean Intellectual Property Office on December 23, 2022, and Korean Patent Application No. 10-2023-0187698, filed with the Korean Intellectual Property Office on December 20, 2023. The disclosures of these Korean patent applications are incorporated herein by reference in their entirety.

[0003] The present invention relates to a positive electrode active material for a secondary battery, a positive electrode including the same, and a lithium secondary battery. Background Art

[0004] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0005] As positive electrode active materials for lithium secondary batteries, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), lithium iron phosphate compound (LiFePO4), etc. have been used. Among them, lithium cobalt oxide has the advantages of a high working voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high and its supply is unstable, which makes it difficult to be commercially applied to large-capacity batteries. The structural stability of lithium nickel oxide is poor, which makes it difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but has a problem of deteriorating capacity characteristics. Therefore, in order to compensate for the problems of lithium transition metal oxides containing only Ni, Co, or Mn, lithium nickel-based transition metal oxides containing two or more types of transition metals have been developed. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0006] Recently, the demand for high-output and high-capacity batteries such as batteries for electric vehicles has been increasing day by day. Therefore, the nickel content in the positive electrode active material tends to gradually increase. When the nickel content in the positive electrode active material increases, the initial capacity characteristics are improved, but the problem is that a large amount of highly reactive Ni 4+ ions are generated during electrode calendering or during charge and discharge, which leads to the structural collapse of the positive electrode active material, an increase in surface side reactions, an increase in the deterioration rate of the positive electrode active material, a decrease in life characteristics, and a decrease in battery safety.

[0007] On the other hand, research and development are being carried out on lithium-rich manganese-based active materials as substitutes for cathode active materials with a high nickel content (which have low durability and high costs due to structural stability problems). Lithium-rich manganese-based active materials have a high theoretical capacity, but to achieve this, a driving voltage of 4.4 V or more must be used. However, the high driving voltage leads to a decrease in battery life and high-temperature storage characteristics, so it is not easily commercialized.

[0008] Another method for achieving a high theoretical capacity is to increase the calendering density. If the calendering density increases, the amount of active material per unit volume increases, which enables a high capacity. However, if the calendering density is too high, there is a problem of particle breakage, and if the calendering density is too low, there is a problem of low energy density. Therefore, it is not easy to adjust the calendering density, and the pores inside the secondary particles must be minimized, and the density between particles must be high. Since this density can only be indirectly confirmed and is difficult to quantitatively analyze, it is impossible to identify the characteristics of the active material that has the maximum energy density without particle breakage. Summary of the Invention

[0009] Technical Problem

[0010] The present invention aims to solve the above problems, and an object of the present invention is to provide a cathode active material that can optimize the density between particles by analyzing the unit cell volume and the calendering density under low pressure obtained from the crystal characteristics of the cathode active material particles.

[0011] Another object of the present invention is to provide a cathode and a lithium secondary battery including the cathode active material, thereby maximizing the energy density while not having particle breakage by optimizing the calendering density, significantly reducing the occurrence of side reactions, improving the life characteristics, and having excellent capacity characteristics.

[0012] Technical Solution

[0013] To achieve the above object, in one aspect of the present invention, there is provided an electrode assembly including a lithium-rich manganese-based transition metal oxide,

[0014] wherein the density (P) obtained by the following Mathematical Formula 1 is 42 to 50.

[0015] [Mathematical Formula 1]

[0016]

[0017] In Mathematical Formula 1,

[0018] V 晶胞 is the volume (Å 3 ) of the unit cell obtained by the following Mathematical Formula 2,

[0019] d 400 is the calendering density (g / cm 3 ) when calendering under 400 kgf,

[0020] [Mathematical formula 2]

[0021]

[0022] In Mathematical formula 2,

[0023] a and c are lattice parameters (Å) obtained from XRD measurement of the positive electrode active material.

[0024] To achieve the above object, in another aspect of the present invention, a positive electrode including the positive electrode active material according to the present invention is provided.

[0025] To achieve the above object, in still another aspect of the present invention, a lithium secondary battery including the positive electrode active material according to the present invention is provided. Detailed Description

[0026] The terms or words used in this specification and claims should not be construed as limited to the ordinary meaning or dictionary meaning, but should be interpreted according to the meaning and concept consistent with the technical gist of the present invention based on the principle that the inventor can appropriately define the terms so as to best describe the inventor's own invention.

[0027] It should be understood that the terms "including", "comprising", "having", etc. used herein specify the presence of the described features, integers, steps, components or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, components or combinations thereof.

[0028] In the present invention, a "single particle" refers to a particle composed of a single nodule. In the present invention, a "nodule" is a single crystal lacking any crystal grain boundary, or may be a polycrystal in which no grain boundary appears when observed with a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times. In the present invention, a "quasi-single particle" refers to a particle that is a composite formed by 30 or fewer nodules.

[0029] In the present invention, a "secondary particle" refers to a particle formed by agglomerating dozens to hundreds of primary particles. More specifically, a secondary particle is an agglomerate of 50 or more primary particles.

[0030] In the present invention, when describing "particles", any one or all of single particles, quasi-single crystals, primary particles, nodules, and secondary particles may be covered.

[0031] In the present invention, "D 50” refers to the particle size corresponding to a cumulative volume of 50% in the particle size distribution of the positive electrode active material. The average particle size D 50 can be measured by the laser diffraction method. For example, the average particle diameter can be measured by the following steps: Disperse the positive electrode active material powder in a dispersion medium, introduce the resulting material into a commercially available laser diffraction particle size analyzer (e.g., MT 3000 of Microtrac), perform ultrasonic irradiation at a frequency of about 28 kHz and an output of 60 W, obtain a cumulative volume particle size distribution graph, and then determine the particle size corresponding to a cumulative volume of 50%.

[0032] The present invention will be described in more detail below.

[0033] Positive Electrode Active Material

[0034] The positive electrode active material according to the present invention contains a lithium-rich manganese-based transition metal oxide, wherein the apparent density (P) obtained by the following Mathematical Formula 1 is 42 to 50.

[0035] [Mathematical Formula 1]

[0036]

[0037] In Mathematical Formula 1,

[0038] V 晶胞 is the volume of the unit cell (Å 3 ) obtained by the following Mathematical Formula 2,

[0039] d 400 is the calendering density (g / cm 3 ) when calendering under 400 kgf,

[0040] [Mathematical Formula 2]

[0041]

[0042] In Mathematical Formula 2,

[0043] a and c are lattice parameters (Å) obtained from the XRD measurement of the positive electrode active material.

[0044] According to an embodiment of the present invention, the positive electrode active material includes a lithium-rich manganese-based transition metal oxide having a tap density of 42 to 50. The tap density can represent the degree of tightness with which particles are packed together without breaking, that is, the degree of denseness of packed particles without damaging the particles. Preferably, the tap density can be 43 or more or 44 or more, and 49 or less or 48 or less. If the tap density is less than 42, it means that the volume of the unit cell is small relative to the same calendering density. It can be seen that the volume of the unit cell can depend on the lattice parameters, and the lattice parameters can vary depending on factors such as the conditions of the sintering process, the molar ratio of transition metals, the molar ratio of lithium to transition metals, doping, coating, etc. The lattice parameters become smaller due to certain factors, and the mobility of lithium ions is relatively poor.

[0045] On the other hand, when the tap density of the lithium-rich manganese-based transition metal oxide according to an embodiment of the present invention is greater than 50, there may be several reasons. Among them, due to the imbalance between the unit cell volume and the calendering density, the calendering density is small relative to the unit cell volume, but this may mean that due to problems such as voids, shape, and particle size within the secondary particles, the structural and particle size characteristics prevent them from packing well. In this case, even when calendered under appropriate pressure, the packing may not proceed properly, which may lead to problems such as low capacity due to low energy density or shortened life due to particle breakage.

[0046] The tap density of such particles gives the calendering density at low pressure (i.e., a value similar to the true density of the actual particles), defining the ratio of this calendering density to the volume of the unit cell present in the crystal structure, thereby providing the advantage of maximizing the energy density even before the actual calendering process and providing an active material with high capacity characteristics.

[0047] The lattice parameters a and c mean the lattice parameters of any side of the unit cell in the crystal structure. The positive electrode active material according to an embodiment of the present invention generally has a layered structure (R-3m) and a rock salt monoclinic structure (C2 / m). In such a structure, the sides existing on the x-axis and y-axis can be represented by a, and the side existing on the z-axis can be represented by c. In the case of Mathematical Formula 2 according to an embodiment of the present invention, assuming that the crystal structure of the positive electrode active material is entirely layered, the lattice parameters are applied. a can be 2.83 to 2.90, and c can be 14.21 to 14.31.

[0048] According to an embodiment of the present invention, d in Mathematical Formula 1 400 is the density of the lithium-rich manganese-based transition metal oxide when calendered at 400 kgf, which may be close to the true density of the actual particles. d 400 can be 2.00 g / cm 3 to 2.40 g / cm 3 and preferably 2.03 g / cm3 2.05 g / cm or more 3 2.07 g / cm or more 3 2.10 g / cm or more 3 or 2.12 g / cm or more 3 or more, preferably 2.37 g / cm 3 2.35 g / cm or less 3 2.33 g / cm or less 3 2.30 g / cm or less 3 or less. When d 400 is within the above range, the ratio to the unit cell volume can be adjusted appropriately. Even though the volume of the unit cell is obtained from lattice parameters determined to a certain extent, considering that the lattice parameters themselves can vary over a relatively wide range, the limited d 400 range may be meaningful. That is, the d 400 density range can be a basic condition for optimizing the energy density according to whether the volume of the unit cell is satisfied.

[0049] According to one embodiment of the present invention, the calendering density of the lithium-rich manganese-based transition metal oxide can be 2.30 g / cm 3 or more. At this time, the pressure during calendering can be 2000 kgf. The calendering density can be 2.35 g / cm 3 or more, 2.37 g / cm 3 or more, 2.40 g / cm 3 or more, 2.42 g / cm 3 or more or 2.43 g / cm 3 or more. The advantage of this range is that it can maximize the energy density of the positive electrode.

[0050] The positive electrode active material according to the present invention may include a lithium-rich manganese-based transition metal oxide. Specifically, the positive electrode active material may include a lithium-rich manganese-based transition metal oxide having the composition shown in Chemical Formula 1 below.

[0051] [Chemical Formula 1]

[0052] Li 1+a [Mn 1-b-c-d Ni b M1 c M2 d O 2-e A e

[0053] In Chemical Formula 1,

[0054] M1 and M2 each independently contain at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, Ta, Y, and Zr,

[0055] A contains at least one selected from N, P, S, F, and Cl, and

[0056] 0.1 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.05, 0 < b + c + d ≤ 0.5, 0 ≤ e ≤ 0.05.

[0057] In Chemical Formula 1, M1 contains Co, Al, or a combination thereof. Preferably, M1 can be Co or a combination of Co and Al. M2 contains at least one selected from Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, Ta, Y, and Zr. Preferably, it can contain at least one selected from W, Zr, Y, Mg, and Ti. More preferably, it can contain W, Zr, Y, Ti, or a combination thereof. The M2 element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting particle growth or improving the stability of the crystal structure during sintering. In addition, A is an anion substituted at the oxygen site and can contain N, P, S, F, or Cl.

[0058] 1 + a represents the molar ratio of lithium in the lithium-rich manganese-based transition metal oxide and can be 0.1 ≤ a ≤ 0.6, 0.1 ≤ a ≤ 0.5, or 0.2 ≤ a ≤ 0.5.

[0059] b represents the molar ratio of nickel to all metals except lithium in the lithium-rich manganese-based transition metal oxide and can be 0 ≤ b ≤ 0.50, 0.05 ≤ b ≤ 0.50, 0.10 ≤ b ≤ 0.50, or 0.10 ≤ b ≤ 0.45.

[0060] c represents the molar ratio of the M1 element among all metals except lithium in the lithium-rich manganese-based transition metal oxide and can be 0 ≤ c ≤ 0.50, 0.05 ≤ c ≤ 0.50, 0.10 ≤ c ≤ 0.50, or 0.10 ≤ c ≤ 0.45.

[0061] d represents the molar ratio of the M2 element among all metals except lithium in the lithium-rich manganese-based transition metal oxide and can be 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02, or 0 ≤ d ≤ 0.01.

[0062] In addition, the sum of the molar ratios of the remaining metals other than manganese among all the metals other than lithium in the lithium-rich manganese-based transition metal oxide (nickel and M1 and M2 metals), i.e., (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.

[0063] On the other hand, the lithium-rich manganese-based transition metal oxide may also include a coating on the particle surface, and the coating contains at least one coating element selected from Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0064] If there is a coating on the surface of the lithium-rich manganese-based transition metal oxide particles, the contact between the electrolyte and the lithium-rich manganese-based transition metal oxide is inhibited by the coating, which makes it possible to obtain the effect of reducing the transition metal dissolution or gas generation due to the side reaction with the electrolyte solution.

[0065] Method for Preparing Positive Electrode Active Material

[0066] Next, a method for preparing the positive electrode active material powder of the present invention will be described.

[0067] The method for preparing the positive electrode active material powder according to the present invention includes:

[0068] (S1) Adding a transition metal-containing solution containing cations of nickel (Ni), manganese (Mn), and M1, an alkaline aqueous solution, and an ammonium solution, and performing a coprecipitation reaction to prepare a positive electrode active material precursor; and

[0069] (S2) Mixing the positive electrode active material precursor with a lithium raw material and performing heat treatment on them to prepare a positive electrode active material powder.

[0070] In addition, the prepared positive electrode active material contains a lithium-rich manganese-based transition metal oxide, which has at least one of the forms of secondary particles formed by agglomeration of dozens to hundreds of primary particles, or single particles composed of one small block that can be formed by coarsening of crystal grains and quasi-single particles that are composites of 30 or fewer small blocks, or a mixed form of these two forms.

[0071] Next, each step of the method for preparing the positive electrode active material powder will be described in detail.

[0072] First, a transition metal-containing solution containing cations of nickel (Ni), manganese (Mn), and M1 is prepared. For example, the transition metal-containing solution may include a nickel-containing raw material, a manganese-containing raw material, and an M1-containing raw material. The M1-containing raw material may be a cobalt-containing raw material and / or an aluminum-containing raw material.

[0073] Subsequently, a precursor of the positive electrode active material can be prepared by adding a complexing agent containing ammonium cations and an alkaline aqueous solution to the transition metal solution and causing a coprecipitation reaction.

[0074] The nickel-containing raw material may include, for example, nickel acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, etc. Specifically, it may include Ni(OH)2, NiO, NiOOH, NiCO3•2Ni(OH)2•4H2O, NiC2O2•2H2O, Ni(NO3)2•6H2O, NiSO4, NiSO4•6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0075] The manganese-containing raw material may include, for example, manganese acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may include manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0076] The cobalt-containing raw material may include cobalt acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide. Specifically, it may include Co(OH)2, CoOOH, Co(OCOCH3)2•4H2O, Co(NO3)2•6H2O, CoSO4, Co(SO4)2•7H2O, or a combination thereof, but is not limited thereto.

[0077] The aluminum-containing raw material may include, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide, or a combination thereof.

[0078] The transition metal-containing solution can be prepared by adding the nickel-containing raw material, the manganese-containing raw material, and the M1-containing raw material to a solvent (specifically water, or a mixed solvent of water and an organic solvent (such as alcohol, etc.) that is mixed with water to form a homogeneous mixture), or by mixing an aqueous solution of the nickel-containing raw material, an aqueous solution of the manganese-containing raw material, and the M1-containing raw material.

[0079] The complexing agent containing ammonium cations may include, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, (NH4)2CO3, or a combination thereof, but is not limited thereto. On the other hand, the complexing agent containing ammonium cations can be used in the form of an aqueous solution, and in this case, the solvent may include water or a mixture of water and an organic solvent (specifically, alcohols, etc.) that mixes with water to form a homogeneous mixture.

[0080] The basic compound may include hydroxides or hydrates of alkali metals or alkaline earth metals such as NaOH, KOH, or Ca(OH)2, or a combination thereof. The basic compound can also be used in the form of an aqueous solution, and in this case, the solvent may include water or a mixture of water and an organic solvent (specifically, alcohols, etc.) that mixes with water to form a homogeneous mixture.

[0081] A basic compound can be added to adjust the pH of the reaction solution, and the addition amount can make the pH of the metal solution 8 to 12.

[0082] The coprecipitation reaction can be carried out in an inert atmosphere of nitrogen or argon within a temperature range of 35 °C to 80 °C.

[0083] Therefore, a precursor of a positive electrode active material containing cations of nickel, manganese, and M1 can be prepared.

[0084] Precursor particles of the positive electrode active material of nickel manganese M1 hydroxide are manufactured by the above process and precipitated in the reaction solution. A positive electrode active material precursor with a manganese (Mn) content of 50 mol% or more, 55 mol% or more, preferably 60 mol% or more, more preferably 63 mol% or more, more preferably 65 mol% or more, still more preferably 66 mol% or more, and further more preferably 67 mol% or more in the total metal content can be prepared by adjusting the concentrations of the nickel-containing raw material, the manganese-containing raw material, and the M1-containing raw material. The precipitated positive electrode active material precursor particles are separated and dried by a conventional method to prepare the positive electrode active material precursor.

[0085] Subsequently, the positive electrode active material precursor is mixed with a lithium raw material and heat-treated.

[0086] The lithium raw material may include (but is not particularly limited) any material that is soluble in water and may include, for example, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specifically, the lithium raw material may include Li2CO3, LiNO3, LiNO2, LiOH, LiOH•H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, etc. Any one or a mixture of two or more of these materials can be used.

[0087] The precursor of the positive electrode active material and the lithium raw material can be mixed in a molar ratio of 1:1 to 1:1.1. The precursor of the positive electrode active material and the lithium raw material can be mixed in a molar ratio of, for example, about 1:1, about 1:1.02, about 1:1.05, about 1:1.07, or about 1:1.10, but not limited thereto.

[0088] In the case of a lithium-rich manganese-based transition metal complex oxide with 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. The heat treatment can preferably be carried out, for example, in a temperature range of 800 °C to 975 °C, more preferably in a temperature range of 850 °C to 950 °C.

[0089] The positive electrode active material prepared thereby can reduce particle breakage and stress within the crystal structure during the calendering process or charge and discharge of a lithium secondary battery containing the positive electrode active material, and can improve the initial resistance characteristics.

[0090] The heat treatment can be carried out in an air or oxygen atmosphere for, for example, 4 to 12 hours. Specifically, the heat treatment can be carried out for, for example, 4 hours or more, 6 hours or more, 8 hours or more, or 10 hours or more and 12 hours or less, 10 hours or less, 8 hours or less, and 6 hours or less.

[0091] On the other hand, when attempting to prepare a lithium-rich manganese-based transition metal oxide containing M2 metal, the M2 metal-containing raw material can also be mixed during the coprecipitation reaction or in the sintering step. At this time, the M2 metal-containing raw material can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of M2 metal.

[0092] On the other hand, when attempting to form a coating on the surface of the lithium-rich manganese-based transition metal oxide, after the heat treatment, the following steps can also be carried out: mixing the lithium-rich manganese-based transition metal oxide prepared by the heat treatment with the coating raw material, and then heat-treating the mixture. At this time, the mixing can include solid-phase mixing or liquid-phase mixing, depending on the coating raw material, and the heat treatment can be carried out at an appropriate temperature. For example, the heat treatment of the coating process can be carried out in a temperature range of 200 °C to 700 °C, or 300 °C to 600 °C, but not limited thereto.

[0093] In addition, when preparing the positive electrode active material powder of the present invention, it is preferably not to perform a washing process after heat treatment. Generally, when preparing a lithium composite transition metal oxide, a washing process is usually performed after heat treatment to reduce the content of lithium by-products. However, according to the research conducted by the present inventors, when a washing process is performed during the manufacture of a lithium transition metal oxide, the surface characteristics of the lithium transition metal oxide deteriorate and the resistance increases during the water washing process. Therefore, when preparing the positive electrode active material of the present invention, it is preferably not to perform water washing, but to consume the lithium remaining on the surface of the lithium transition metal oxide during the coating formation process. When the positive electrode active material is prepared in this way without washing the lithium transition metal oxide, an increase in resistance due to surface defects can be suppressed.

[0094] Positive Electrode

[0095] According to the present invention, a positive electrode containing the positive electrode active material powder of the present invention is provided. Specifically, the positive electrode includes 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 contains the positive electrode active material powder according to the present invention. Since the positive electrode active material powder has been described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0096] The positive electrode current collector can contain a metal with high conductivity, and the positive electrode active material layer can easily adhere thereto, but there is no particular limitation as long as it is non-reactive within the voltage range of the battery. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. can be used. The thickness of the positive electrode current collector can generally be 3 to 500 μm, and the positive electrode current collector can have fine irregularities on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, and non-woven fabric structure.

[0097] On the basis of containing the positive electrode active material powder, the positive electrode active material layer can optionally contain a conductive material and a binder as needed.

[0098] At this time, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material powder can be 80 to 99% by weight, more specifically 85 to 98.5% by weight. When the contained positive electrode active material powder is within the above content range, excellent capacity characteristics can be exhibited.

[0099] The conductive material is used to impart conductivity to the electrode, and the conductive material can be used without particular limitation as long as it has electron conductivity and does not cause chemical changes in the battery to be constructed. Specific examples thereof include graphite, such as natural graphite and artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them can be used alone or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be 0.1 to 15% by weight.

[0100] The binder is used to improve the adhesion between the positive electrode active materials and the adhesion force between the positive electrode active material and the current collector. Specific examples thereof may 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 monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is replaced by Li, Na, or Ca, or various copolymers thereof, and any one of them can be used alone or a mixture of two or more of them can be used. Based on the total weight of the positive electrode active material layer, the content of the binder can be 0.1 to 15% by weight.

[0101] In addition to using the above positive electrode active material powder for the positive electrode, the positive electrode can be manufactured according to a typical positive electrode manufacturing method. Specifically, the positive electrode can be prepared by the following steps: dissolving or dispersing the above 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, coating the slurry composition on a positive electrode current collector, and then drying and rolling.

[0102] A solvent commonly used in the art can be used as the solvent, and examples thereof may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N - methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, etc., and any one of them can be used alone or a mixture of two or more of them can be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, the conductive material, the binder, and the dispersant in consideration of the coating thickness of the slurry and the manufacturing yield, and has a viscosity that can exhibit excellent thickness uniformity when subsequently applied to the manufacture of the positive electrode.

[0103] Alternatively, the positive electrode can be manufactured by the following steps: casting a positive electrode paste on a separate support, and then laminating the film obtained by peeling off the support on the positive electrode current collector.

[0104] Electrochemical Device

[0105] Next, the electrochemical device according to the present invention will be described. The electrochemical device according to the present invention includes the above positive electrode. The electrochemical device can specifically be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0106] The lithium secondary battery specifically includes: a positive electrode; a negative electrode arranged to face the positive electrode; a separator arranged between the positive electrode and the negative electrode; and an electrolyte, and the positive electrode is the same as the above positive electrode. Therefore, its detailed description will be omitted, and only the remaining structures will be described in detail below.

[0107] In addition, the lithium secondary battery may optionally further include: a battery container for storing the electrode assembly of the positive electrode, the negative electrode, and the separator; and a sealing member for sealing the battery container.

[0108] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0109] There is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause any chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface, or an aluminum cadmium alloy can be used. In addition, the conventional thickness of the negative electrode current collector can be 3 μm to 500 μm, and similar to the positive electrode current collector, the negative electrode current collector can form fine irregularities on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric structure.

[0110] In addition to the negative electrode active material, the negative electrode active material layer may optionally further include a binder and a conductive material.

[0111] As the negative electrode active material, a compound capable of reversibly inserting and extracting lithium can be used. Specific examples thereof may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; (semi) metallic materials capable of forming an alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; (semi) metal oxides capable of doping and dedoping lithium, such as SiO β(0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; composites containing (semi) metallic materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one of them can be used alone or a mixture of two or more of them can be used. In addition, a thin film of metallic lithium can be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon. Typical examples of high-crystalline carbon include natural graphite or artificial graphite in irregular, plate-like, flaky, spherical, or fibrous forms, condensated graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, high-temperature sintered carbon such as coke derived from mesophase pitch and petroleum or coal tar pitch.

[0112] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% by weight to 99% by weight.

[0113] The binder is a component that helps the bonding between the conductive material, the active material, and the current collector. Based on the total weight of the negative electrode active material layer, the addition amount of the binder is usually 0.1% by weight to 10% by weight. Examples of such binders can include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, or various copolymers thereof.

[0114] The conductive material is a component that further improves the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the conductive material can be 10% by weight or less, preferably 5% by weight or less. There is no particular limitation on such a conductive material as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite and artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxides; or polyphenylene derivatives.

[0115] The negative electrode active material layer can be prepared by coating a negative electrode paste composition prepared by dissolving or dispersing the negative electrode active material and optionally the binder and the conductive material in a solvent onto the negative electrode current collector and drying it, or by casting the negative electrode paste composition onto a separate support and then laminating the film obtained by peeling from the support onto the negative electrode current collector.

[0116] On the other hand, in a lithium secondary battery, a separator is used to separate the negative electrode and the positive electrode and provide a path for the movement of lithium ions. Any separator can be used without particular limitation as long as it is commonly used as a separator in a lithium secondary battery. In particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to the movement of electrolyte ions is preferred. Specifically, a porous polymer film can be used, such as a porous polymer film made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, typical porous non-woven fabrics can be used, such as non-woven fabrics formed of high melting point glass fibers, polyethylene terephthalate fibers, etc. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0117] In addition, the electrolyte used in the present invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten-type inorganic electrolyte, etc. All of these electrolytes can be used to manufacture a lithium secondary battery, but are not limited thereto.

[0118] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0119] Any organic solvent can be used without particular limitation as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, the following can be used: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate having a high ionic conductivity and a high dielectric constant (e.g., ethylene carbonate or propylene carbonate) and a linear carbonate compound having a low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate), which can improve the charge / discharge performance of the battery.

[0120] Any lithium salt can be used without particular limitation as long as it can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt can be selected from 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 at least one of (CF3CF2SO2)2N - Among them, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. The lithium salt can be used in a concentration range of 0.1 M to 2.0 M. When the concentration of the contained lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0121] In the electrolyte, in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, one or more additives can also be included. For example, haloalkyl carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (poly)ethylene glycol dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidone, N,N-substituted imidazoline, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride, etc. At this time, based on the total weight of the electrolyte, the content of the additive can be 0.1 to 5 parts by weight.

[0122] Examples

[0123] The embodiments of the present invention have been described in detail above, enabling those skilled in the art to which the present invention pertains to easily implement the embodiments. However, the present invention can be modified in various different ways and is not limited to the embodiments described herein.

[0124] Example 1

[0125] The Ni 0.83 Co 0.11 Mn 0.06 (OH)2 precursor synthesized by coprecipitation reaction was mixed with LiOH such that the Li / Me (Ni + Mn) molar ratio was 1.38 and sintered in an oxygen atmosphere to prepare a positive electrode active material having a composition of Li 1.38 Ni 0.37 Mn 0.63 O2.

[0126] Example 2

[0127] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0128] Example 3

[0129] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0130] Example 4

[0131] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0132] Comparative Example 1

[0133] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0134] Comparative Example 2

[0135] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0136] Comparative Example 3

[0137] A positive electrode active material having the same composition as in Example 1 but having the unit cell volume and rolling density at 400 kgf shown in Table 1 below was prepared.

[0138] Comparative Example 4

[0139] A positive electrode active material having the same composition as that of Example 1 but having the unit cell volume shown in Table 1 below and the rolling density at 400 kgf was prepared.

[0140] Comparative Example 5

[0141] A positive electrode active material having the same composition as that of Example 1 but having the unit cell volume shown in Table 1 below and the rolling density at 400 kgf was prepared.

[0142] Experimental Example 1: Measurement of Characteristics of Positive Electrode Active Material

[0143] 1) Obtaining the lattice parameters a and c: Measurement was performed by X-ray diffraction (XRD) using Cu-Kα X-rays (Xrα). Specifically, measurement was performed based on a Cu-Kα target at 40 kV using an XRD apparatus manufactured by Rikaku Corporation. The prepared particles were placed in a holder, irradiated with X-rays, and the obtained diffraction lattice was analyzed to measure the lattice parameters, and the unit lattice volume was obtained according to Mathematical formula 2.

[0144] 2) Rolling density when rolled at 400 kgf: The rolling density of the positive electrode active material was measured using a density measuring instrument (Caver Pellet Press). Specifically, 5 g of the positive electrode active material was divided into several portions, stacked in a cylindrical holder with a diameter of 13 mm without any gaps, and then a pressure of 400 kgf was applied to measure the rolling density.

[0145]

[0146] <Manufacture of Lithium Secondary Battery>

[0147] The positive electrode active materials, carbon black conductive materials, and PVDF binders prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were mixed in a weight ratio of 95:2:3 in N-methylpyrrolidone to prepare a positive electrode paste. The positive electrode paste was coated on one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode.

[0148] 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 paste, which was then coated on one surface of a copper current collector, dried at 130°C, and then rolled to manufacture a negative electrode.

[0149] A separator is inserted between the positive electrode and the negative electrode to prepare an electrode assembly, which is then placed inside a battery case. Then, an electrolyte is injected into the case to manufacture a lithium secondary battery. The electrolyte is prepared by the following steps: dissolving LiPF6 with a concentration of 1 M in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate with a volume ratio of 1:2:1, and adding 2 wt% of vinylene carbonate (VC).

[0150] Experimental Example 2: Performance Measurement of Positive Electrode Active Material

[0151] 1) Calendering density when calendering under 2000 kgf (2 tons): The calendering density of the positive electrode active material is measured using a density measuring instrument (Caver PelletPress). Specifically, 5 g of the positive electrode active material is divided into several portions and stacked in a cylindrical holder with a diameter of 13 mm without any gaps. The calendering density is measured by applying a pressure of 2000 kgf, and the results are listed in Table 2.

[0152] 2) Capacity characteristics: During activation, measurements are carried out under the conditions of an electrode load of 0.35 g / 25 cm 2 , 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. The results are listed in Table 2 below.

[0153] 3) Rate characteristics: In the above capacity characteristics, the discharge capacity is measured by only changing the current to 0.33 C, and the ratio (%) obtained by dividing the measured value by the discharge capacity in the capacity characteristics is listed in Table 2 below.

[0154]

[0155] Referring to Table 2, it is confirmed that in the cases of Examples 1 to 4, their calendering densities are excellent, the initial discharge capacity is evaluated to be higher than that of Comparative Examples 1 to 5, and the rate characteristics are improved.

[0156] Industrial applicability

[0157] The positive electrode active material for a lithium secondary battery according to the present invention identifies the active material characteristics, in which by optimizing the ratio of the unit cell volume to the calendering density under low pressure, the density between particles is maximized, thereby improving the energy density.

[0158] In addition, the positive electrode for a lithium secondary battery according to the present invention has no particle breakage, significantly reduces the occurrence of side reactions, has a high energy density, has excellent life characteristics, and can exhibit high capacity characteristics.

Claims

1. A positive electrode active material, the positive electrode active material comprising a lithium-rich manganese-based transition metal oxide, wherein the apparent density (P) obtained by the following Mathematical Formula 1 is 42 to 50, [Mathematical Formula 1] In Mathematical Formula 1, V 晶胞 is the volume (Å 3 ) of the unit cell obtained by the following Mathematical Formula 2 d 400 is the calendering density (g / cm 3 ) when calendering at 400 kgf [Mathematical Formula 2] In Mathematical Formula 2, a and c are lattice parameters (Å) obtained from the XRD measurement of the positive electrode active material.

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

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

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

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

6. The positive electrode active material according to claim 1, wherein: the lithium-rich 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-d A d In Chemical Formula 1, M1 and M2 each independently contain at least one selected from Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr, and Zr, A contains at least one selected from N, P, S, F, and Cl, and 0.1 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.05, 0 < b + c + d ≤ 0.5, 0 ≤ e ≤ 0.

05.

7. The positive electrode active material according to claim 1, wherein: The calendering density of the positive electrode active material when calendered under a pressure of 2000 kgf is 2.42 g / cm 3 or more.

8. A positive electrode, the positive electrode comprising the positive electrode active material according to any one of claims 1 to 7.

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

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

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