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

Abstract

The present invention relates to a positive electrode active material, and a positive electrode and a lithium secondary battery comprising the same, in which the present invention relates to a positive electrode active material comprising a lithium-rich manganese-based oxide having a composition represented by Chemical Formula 1 as described in the specification, thus, the performance of a lithium secondary battery including the same can be improved.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0008740, filed on January 20, 2023, the disclosure of which is incorporated herein by reference. Technical Field

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

[0004] Lithium secondary batteries are composed of four main components, such as a positive electrode, a negative electrode, a separator, and an electrolyte. Among them, the positive electrode active material contained in the positive electrode is a material that plays an important role in determining the capacity, output, and life of the battery. In order to make lithium secondary batteries have high energy density, high output, and long life, improving the performance of the positive electrode active material is crucial. As a result, a lot of research has been carried out recently to develop high-performance positive electrode active materials.

[0005] Lithium-rich oxide (Li-rich layered oxide) as a positive electrode active material is a mixed phase in which Li2MnO3 phase and LiMO2 (M = nickel (Ni), manganese (Mn), cobalt (Co)) phase are mixed, wherein it has a high operating voltage (>3.5V vs. Li / Li + ) provides a very high capacity of 250 mAh / g. As a result, lithium-rich oxides have attracted attention as low-cost, high-capacity positive electrode active materials.

[0006] However, lithium-rich oxides have problems stemming from their structural characteristics of a two-phase mixture. Specifically, when batteries containing lithium-rich oxides operate at high voltages, irreversible capacity loss occurs during the initial formation process, reducing efficiency. Furthermore, during charge and discharge cycles, the layered structure transforms from a spinel structure to a rock salt structure, leading to voltage decay and the generation of O2 gas.

[0007] Therefore, there is a need to obtain a technology to improve the performance and stability of lithium-rich oxides.

[0008] [Prior art literature]

[0009] [Patent Document]

[0010] (Patent Document 1) China Patent Application Publication No. 109921007 Summary of the Invention

[0011] Technical issues

[0012] One aspect of the present invention is to improve the performance and stability of lithium-rich manganese oxides, thereby improving the performance of batteries containing such lithium-rich manganese oxides.

[0013] In addition, the present invention aims to provide a positive electrode and a lithium secondary battery containing the above positive electrode active material.

[0014] Technical solution

[0015] To solve the above problems, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0016] (1) The present invention provides a positive electrode active material, which contains a lithium-rich manganese oxide having a composition represented by Chemical Formula 1.

[0017] [Chemical Formula 1]

[0018] Li 1+a1 Mn x1 Ni y1 M z1 O 2+b1

[0019] In Chemical Formula 1,

[0020] 0.100 ≤ a1 ≤ 0.400, 0 ≤ b1 < 1.0, 0.50 ≤ x1 < 1.0, 0 < y1 < 0.50, 0.001 ≤ z1 ≤ 0.01, 1.50 ≤ x1 / y1, and

[0021] M is a metal with an oxidation number of +5 or +6.

[0022] (2) The present invention provides the positive electrode active material of (1) above, wherein x1 is 0.55 or more.

[0023] (3) The present invention provides the positive electrode active material of (1) or (2) above, wherein z1 is in the range of 0.002 to 0.009.

[0024] (4) The present invention provides the positive electrode active material of any one of (1) to (3) above, wherein x1 / y1 is 1.80 or more.

[0025] (5) The present invention provides the positive electrode active material of any one of (1) to (4) above, wherein the lithium-rich manganese oxide does not contain cobalt (Co-free).

[0026] (6) The present invention provides the positive electrode active material of any one of (1) to (5) above, wherein M is at least one selected from Mo, Nb, Ti, V, W, Ta, and Ru.

[0027] (7) The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the average particle diameter (D 50 ) of the lithium-rich manganese-based oxide is 1 μm to 15 μm.

[0028] (8) The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein, when the chemical formula 1 is represented as the chemical formula 2, the ratio of x:(1 - x) is in the range of 1:9 to 5:5.

[0029] [Chemical formula 2]

[0030] xLi2MnO3·(1 - x)Li(Ni x2 Mn y2 M z2 )O2

[0031] In the chemical formula 2,

[0032] 0.100 ≤ x ≤ 0.400, 0 < x2 ≤ 0.55, 0.10 ≤ y2 < 1.0, 0 < z2 ≤ 0.015, x2 + y2 + z2 = 1, and

[0033] M is a metal with an oxidation number of +5 or +6.

[0034] (9) The present invention provides a positive electrode comprising the positive electrode active material according to any one of (1) to (8) above.

[0035] (10) The present invention provides a lithium secondary battery comprising the positive electrode of (9) above.

[0036] Advantageous effects

[0037] Since the positive electrode active material of the present invention comprises a lithium-rich manganese-based oxide having the composition represented by the chemical formula 1 described in this specification, the performance of a lithium secondary battery containing the same, such as charge / discharge capacity, initial efficiency, and discharge capacity retention rate, can be improved. Description of the drawings

[0038] Figure 1 is a scanning electron microscope (SEM) image of the positive electrode active material prepared in Example 1.

[0039] Figure 2 is the X-ray diffraction (XRD) data of the respective positive electrode active materials prepared in Examples 1, 4, 5, and 8.

[0040] Figure 3 is the XRD data of the respective positive electrode active materials prepared in Example 5 and Comparative Example 5. Detailed description of the invention

[0041] Hereinafter, the present invention will be described in more detail to allow a clearer understanding of the present invention.

[0042] It should be understood that the words or terms used in the specification and claims should not be construed as limited to the meanings defined in a commonly used dictionary. It should be further understood that, based on the principle that the inventor can appropriately define the meanings of the words or terms to best explain the present invention, the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant technical field and the technical gist of the present invention.

[0043] In this specification, the expression "average particle diameter (D 50 )" represents the particle diameter at 50% of the volume cumulative distribution according to the particle diameter. After dispersing the powder to be measured in a dispersion medium, the dispersion medium is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in the diffraction pattern caused by the particle diameter when the particles pass through the laser beam, and D 50 can be measured by using the measuring device to calculate the particle diameter at 50% of the volume cumulative distribution according to the particle diameter.

[0044] positive electrode active material

[0045] The positive electrode active material according to the present invention is characterized in that the positive electrode active material contains a lithium-rich manganese-based oxide having a composition represented by the following Chemical Formula 1.

[0046] [Chemical Formula 1]

[0047] Li 1+a1 Mn x1 Ni y1 M z1 O 2+b1

[0048] In Chemical Formula 1,

[0049] 0.100 ≤ a1 ≤ 0.400, 0 ≤ b1 < 1.0, 0.50 ≤ x1 < 1.0, 0 < y1 < 0.50, 0.001 ≤ z1 ≤ 0.01, 1.50 ≤ x1 / y1, and

[0050] M is a metal with an oxidation number of +5 or +6.

[0051] The inventors of the present invention found that when the lithium-rich manganese-based oxide among the lithium-rich oxides has a composition represented by Chemical Formula 1, the charge / discharge capacity, initial efficiency, and discharge capacity retention rate of the battery containing the above positive electrode active material can be improved, thus completing the present invention.

[0052] Because the lithium-rich manganese oxide containing lithium, nickel, and manganese is doped with at least one doping element with an oxidation number of +5 or +6, and the manganese content is 50 mol% or greater based on the total amount of metals other than lithium, and the molar ratio of manganese to nickel is greater than 1.5, the stability of the lithium-rich manganese oxide itself is improved, resulting in improved battery performance. Specifically, as the amount of lithium that can be added increases, the amount of lithium that can be intercalated and deintercalated during the formation process increases. This not only increases the charge / discharge capacity of the positive electrode, but also helps improve the structural stability during the intercalation and deintercalation of the doping element, thereby increasing lithium ion conductivity during cycling.

[0053] In a case where the lithium-rich manganese oxide is not doped with at least one doping element having an oxidation number of +5 or +6, or the amount of manganese is less than 50 mol % based on the total amount of metals other than lithium, or the molar ratio of manganese to nickel is less than 1.5, when a battery containing the lithium-rich oxide is operated at a high voltage, there is a problem of irreversible capacity loss occurring in the first formation process, thereby reducing efficiency, or there is a problem of voltage decay and generation of O2 gas while the layered structure transforms into a rock salt structure via a spinel structure during the charge and discharge cycle.

[0054] According to the present invention, a1 is within the range of 0.100 to 0.400. Specifically, a1 can be greater than 0.100, 0.105, 0.110, 0.115, 0.120, 0.125, or 0.128, and less than 0.135, 0.140, 0.150, 0.200, 0.250, 0.300, 0.350, or 0.400. In this case, due to the excessive presence of lithium, the battery can be formed and operated at a high operating voltage.

[0055] According to the present invention, b1 is in the range of 0 to less than 1.0. Specifically, b1 can be 0 or more, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90 or less, or less than 1.0.

[0056] According to the present invention, x1 is the ratio of the number of moles of manganese contained in the lithium-rich manganese oxide to the total number of moles of metals other than lithium, wherein x1 is in the range of 0.50 to less than 1.0. Specifically, x1 can be 0.50, 0.51, 0.52, 0.53, 0.54, or 0.55 or greater, and 0.60, 0.65, 0.70, 0.80, or 0.90 or less, or less than 1.0. Because the lithium-rich manganese oxide according to the present invention contains a large amount of manganese, more lithium can be added, and accordingly, more lithium can be intercalated and deintercalated, thereby increasing the charge / discharge capacity.

[0057] According to the present invention, y1 is the ratio of the number of moles of nickel contained in the lithium-rich manganese oxide to the total number of moles of metals other than lithium, wherein y1 is greater than 0 and less than 0.5. Specifically, y1 can be greater than 0, 0.10, 0.20, or 0.30 or greater, and 0.35, 0.40 or less, or less than 0.50. The lithium-rich manganese oxide according to the present invention contains nickel, but the nickel content is such that the nickel content satisfies the above range. In this case, the initial efficiency and discharge capacity retention of the battery can be further improved.

[0058] According to the present invention, z1 is the ratio of the number of moles of M (metal with an oxidation number of +5 or +6) contained in the lithium-rich manganese oxide to the total number of moles of metals other than lithium, wherein z1 is in the range of 0.001 to 0.01. z1 can be 0.0010, 0.0015, 0.0020, 0.0021, 0.0022 or greater, and 0.0090, 0.0095, 0.010 or less. In this case, the charge / discharge capacity, initial efficiency, and discharge capacity retention of the battery can be further improved.

[0059] According to the present invention, z1 may more specifically be in the range of 0.0020 to 0.0090. In this case, stability may be increased during structural changes that may occur during lithium insertion and extraction.

[0060] According to the present invention, x1 / y1 is the ratio of the number of moles of manganese to the number of moles of nickel contained in the lithium-rich manganese oxide, wherein x1 / y1 is greater than 1.50. x1 / y1 can be greater than 1.50, 1.60, 1.70, or 1.80, and less than 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, or 3.10. In this case, due to the large amount of manganese, more lithium can be added, and accordingly, more lithium can be intercalated and deintercalated, thereby increasing the charge / discharge capacity.

[0061] According to the present invention, x1 / y1 may be more specifically 1.80 or greater. In this case, since the amount of manganese is large, more lithium can be added, and accordingly, more lithium can be intercalated and deintercalated, thereby increasing the charge / discharge capacity.

[0062] According to the present invention, the lithium-rich manganese oxide may be cobalt-free (Co-free). That is, the lithium-rich manganese oxide may not contain expensive cobalt. In the case where the lithium-rich manganese oxide does not contain cobalt, it is advantageous in terms of economic factors.

[0063] According to the present invention, M may be at least one selected from molybdenum (Mo), niobium (Nb), titanium (Ti), vanadium (V), tungsten (W), tantalum (Ta), and ruthenium (Ru). In this case, due to the high oxidation number and the large number of oxidation numbers of ions participating in the oxidation / reduction reaction, the structure of the lithium-rich manganese-based oxide can be stabilized.

[0064] In the case where M is Mo, the structural stability is further improved during the insertion / extraction process, and due to the relatively long bond length of Mo-O, there is an advantage of increased lithium-ion conductivity during cycling. In addition, in the case where M is Nb, it helps to accelerate the diffusion of lithium ions and contributes to the structural stabilization through strong Nb-O bonds. For reference, since the Ni 2+ ions are reduced and the Ni 3+ ions are increased, thus reducing the Li + / Ni 2+ mixing, this contributes to the structural stabilization.

[0065] According to the present invention, the average particle size (D 50 ) of the lithium-rich manganese-based oxide may be 1.00 μm to 15.0 μm. The average particle size (D 50 ) of the lithium-rich manganese-based oxide may specifically be 1.00 μm, 2.00 μm, 3.00 μm, 4.00 μm, 5.00 μm, 6.00 μm or more, 7.00 μm, 8.00 μm, 9.00 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm or less. In this case, since an electrode having excellent tap density can be prepared, there is an advantage of ensuring processability.

[0066] According to the present invention, in the case where Chemical Formula 1 is represented as Chemical Formula 2 below, the ratio of x:(1-x) may be 1:9 to 5:5, specifically, 1:9, 2:8 or more, 4:6, 5:5 or less. In this case, the charge / discharge capacity, initial efficiency, and discharge capacity retention rate of the battery including the positive electrode active material can be further improved.

[0067] [Chemical Formula 2]

[0068] xLi2MnO3·(1-x)Li(Ni x2 Mn y2 M z2 )O2

[0069] In Chemical Formula 2,

[0070] 0.100 ≤ x ≤ 0.400, 0 < x2 ≤ 0.55, 0.10 ≤ y2 < 1.0, 0 < z2 ≤ 0.015, x2 + y2 + z2 = 1, and

[0071] M is a metal having an oxidation number of +5 or +6.

[0072] According to the present invention, the lithium-rich manganese oxide is in the form of spherical secondary particles formed by the agglomeration of tens to hundreds of primary particles. The primary particles may have an intermediate shape between rods and needles with a high aspect ratio, with a length measured by scanning electron microscope (SEM) images ranging from several tens to 200 nm. In this case, there is an advantage of improved reactivity due to the active electron movement caused by the increase in specific surface area.

[0073] The Brunauer-Emmett-Teller (BET) specific surface area of the positive electrode active material according to the present invention may be 0.5 m 2 / g to 3.0m 2 / g. That is, the BET specific surface area of the positive electrode active material according to the present invention can be significantly greater than that of the previously known NCM (A) type positive electrode active material. In this case, since electron movement becomes active during battery operation, the kinetics are improved and the rate performance can be improved. The BET specific surface area can be analyzed using gas adsorption and can be analyzed by measuring the adsorption degree of gas molecules according to pressure changes at extremely low temperatures (77K).

[0074] The positive electrode active material according to the present invention may comprise a core-shell structure. In this case, the core and shell may have the same composition and may differ only in shape. The porosity of the core may be higher than that of the shell. In this case, the charge / discharge capacity may also be excellent due to the stable dynamics exhibited while having a high tap density.

[0075] positive electrode

[0076] The present invention provides a positive electrode including a positive electrode active material.

[0077] The positive electrode may include 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 may include the positive electrode active material described above.

[0078] The positive electrode current collector may include a metal with high conductivity, and is not particularly limited, as long as it is non-reactive within the voltage range of the battery and the positive electrode active material layer is easy to adhere to it. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may generally have a thickness of 3µm to 500µm, and fine concavo-convex surfaces may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0079] In addition to the positive electrode active material, the positive electrode active material layer may optionally contain a conductive material and a binder as needed. In this case, the content of the positive electrode active material may be 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive electrode active material layer. Excellent capacity characteristics can be obtained within this range.

[0080] The conductive material is used to provide conductivity to the electrode, wherein any conductive material can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive material can be: graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one thereof or a mixture of two or more thereof can be used. The content of the conductive material may be 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0081] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the collector. Specific examples of the binder can be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and a polymer in which its hydrogen is replaced by lithium (Li), sodium (Na) or calcium (Ca), or a plurality of copolymers thereof, and any one thereof or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the binder can be 0.1 wt % to 15 wt %.

[0082] The positive electrode can be prepared according to a typical method for preparing a positive electrode, except that the above-mentioned positive electrode active material is used. Specifically, a positive electrode slurry prepared by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent is applied to a positive electrode current collector, and then the coated positive electrode current collector is dried and rolled to prepare the positive electrode; or the positive electrode can be prepared by casting the positive electrode slurry on a separate support and then laminating a film separated from the support on the positive electrode current collector.

[0083] The solvent may be a commonly used solvent in the art and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water, and any one thereof or a mixture of two or more thereof may be used. Considering the coating thickness and manufacturing yield of the slurry, if the solvent can dissolve or disperse the positive electrode active material, the conductive material, the binder and the dispersant, and can have a viscosity that can provide excellent thickness uniformity during subsequent coating for positive electrode preparation, the amount of the solvent used may be sufficient.

[0084] lithium secondary batteries

[0085] The present invention provides a lithium secondary battery including a positive electrode.

[0086] A lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Furthermore, the lithium secondary battery may optionally 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.

[0087] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0088] The negative electrode current collector is not particularly limited, as long as it has high conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can generally have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in a variety of forms, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0089] The negative electrode active material layer may optionally contain a binder and a conductive material in addition to the negative electrode active material.

[0090] Compounds that can reversibly intercalate and deintercalate lithium can be used as negative electrode active materials. Specific examples of negative electrode active materials can include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi)metallic materials that can be alloyed with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; (semi)metallic oxides that can be doped or undoped with lithium, such as SiO β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite comprising a (semi)metallic material and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon can be soft carbon and hard carbon, and typical examples of high-crystalline carbon can be irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-type carbon fibers, mesophase carbon microbeads, mesophase pitch, and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch. The content of the negative electrode active material can be 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0091] The binder of the negative electrode active material layer is a component that assists in bonding the conductive material, the active material, and the current collector. The binder is generally added in an amount of 0.1 to 10% by weight based on the total weight of the negative electrode active material layer. Examples of the binder may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0092] The conductive material of the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material. The conductive material may be added in an amount of 10% by weight or less, preferably 5% by weight 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 has conductivity and does not cause adverse chemical changes in the battery. For example, the following conductive materials may be used: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal 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 oxide; or polyphenylene derivatives.

[0093] The negative electrode can be prepared by coating a negative electrode slurry prepared by dissolving or dispersing an optional binder and a conductive material and a negative electrode active material in a solvent on a negative electrode collector and drying the coated negative electrode collector; or by casting the negative electrode slurry on a separate support and then laminating a film separated from the support on the negative electrode collector.

[0094] The separator separates the negative electrode and the positive electrode and provides a mobile channel for lithium ions, wherein any separator can be used as the separator without particular limitation, as long as it is generally used in a lithium secondary battery, in particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to electrolyte ion transfer can be used. Specifically, a porous polymer film can be used, for example, a porous polymer film prepared by a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure with more than two layers thereof. In addition, a typical porous non-woven fabric can be used, for example, a non-woven fabric formed by high melting point glass fiber or polyethylene terephthalate fiber. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material can be used, and a separator with a single layer or multilayer structure can be optionally used.

[0095] The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the preparation of a lithium secondary battery, but the present invention is not limited thereto. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0096] Any organic solvent can be used as the organic solvent 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 migrate. Specifically, as the organic solvent, there 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; or 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; nitrile such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group, and may contain a double bond, an aromatic ring or an ether bond); amide such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and more preferably a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charge / discharge performance of the battery.

[0097] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt may be at least one selected from the following substances: - 、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 - As the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. The lithium salt can be used in a concentration range of 0.1M to 2.0M. If the concentration of the lithium salt is within the above range, since the electrolyte can have appropriate conductivity and viscosity, excellent electrolyte performance can be obtained, and lithium ions can be efficiently moved.

[0098] In order to improve the life characteristics of the battery, suppress the decline in battery capacity, and improve the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, the electrolyte may further include at least one additive, for example, a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (condensed) glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum chloride. In this case, the content of the additive may be 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0099] Since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent charge / discharge capacity, initial efficiency, and discharge capacity retention rate, the lithium secondary battery is suitable for use in portable devices such as mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0100] The shape of the lithium secondary battery of the present invention is not particularly limited, and a cylindrical type using a can, a prismatic type, a pouch type, or a coin type can be used.

[0101] The lithium secondary battery according to the present invention can be used not only in a battery cell as a power source for small devices but also as a unit cell in a medium or large battery module including a plurality of battery cells.

[0102] Thus, a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0103] The battery module or battery pack can be used as a power source for at least one of the following medium to large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0104] Preferred embodiments

[0105] Below, the embodiment of the present invention will be described in detail in a manner that allows those skilled in the art to easily implement the present invention. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0106] Example

[0107] Example 1

[0108] The composite transition metal hydroxide precursor Mn was mixed using a mixer (SHINIL ELECTRONICS, 353NK). 0.65 Ni 0.35 After mixing (OH)2 and the doping material MoO3 so that the molar ratio of (Mn + Ni): Mo is 1:0.0025, the lithium raw material LiOH is further added so that the molar ratio of (Mn + Ni): Li is 1:1.34, and the mixture is mixed using an acoustic mixer (Resodyn, LabRAM 2) to prepare a mixture. The mixture is sintered at 480°C for 3 hours and 30 minutes and then sintered at 900°C for 9 hours to prepare a positive electrode active material (lithium-rich manganese oxide). Figure 1 The SEM image of the positive electrode active material is shown in FIG.

[0109] For reference, when the temperature was increased from room temperature to 480°C and from 480°C to 900°C, the heating rate was 2°C / min.

[0110] Example 2

[0111] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and the doping material MoO3 are mixed so that the molar ratio of (Mn+Ni):Mo is 1:0.005.

[0112] Example 3

[0113] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and the doping material MoO3 are mixed so that the molar ratio of (Mn+Ni):Mo is 1:0.0075.

[0114] Example 4

[0115] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and the doping material MoO3 are mixed so that the molar ratio of (Mn+Ni):Mo is 1:0.01.

[0116] Example 5

[0117] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.0025.

[0118] Example 6

[0119] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.005.

[0120] Example 7

[0121] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.0075.

[0122] Example 8

[0123] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.01.

[0124] Comparative Example 1

[0125] A positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, no doping raw material was added.

[0126] Comparative Example 2

[0127] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and the doping material MoO3 are mixed so that the molar ratio of (Mn+Ni):Mo is 1:0.0005.

[0128] Comparative Example 3

[0129] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and the doping material MoO3 are mixed so that the molar ratio of (Mn+Ni):Mo is 1:0.015.

[0130] Comparative Example 4

[0131] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35(OH)2 and the doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.0005.

[0132] Comparative Example 5

[0133] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Nb2O5 was used instead of MoO3 as the doping material, and the composite transition metal hydroxide precursor Mn 0.65 Ni 0.35 (OH)2 and doping material Nb2O5 are mixed so that the molar ratio of (Mn+Ni):Nb is 1:0.015.

[0134] Comparative Example 6

[0135] The positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, Ni 0.65 Mn 0.35 (OH)2 replaces Mn 0.65 Ni 0.35 (OH)2 as a precursor of complex transition metal hydroxide.

[0136] Experimental example

[0137] Experimental Example 1: XRD analysis

[0138] After X-ray diffraction (XRD) measurements were performed on each of the positive electrode active materials prepared in Examples 1, 4, 5 and 8, the XRD data were as follows: Figure 2 In addition, after XRD measurement of each positive electrode active material prepared in Example 5 and Comparative Example 5, the XRD data are as follows Figure 3 As shown in .

[0139] In this case, 2 g to 3 g of positive electrode active material particles were collected from each positive electrode active material powder and X-ray diffraction analysis was performed using Cu-Kα radiation (wavelength 1.54 Å) at a scanning speed of 0.2° / s and an accelerating voltage of 40 kV / 40 mA in the 2θ range of 15° to 80°.

[0140] refer to Figure 2 and Figure 3, it can be confirmed that the positive electrode active material prepared according to the present invention is a lithium-rich oxide containing both Li2MnO3 phase and LiM'O2 phase (M' includes Ni, Mn and M, wherein M is the same as defined in Chemical Formula 1). In addition, since separate (006) / (012) peaks and (018) / (110) peaks are clearly observed, it can be confirmed that a lithium-rich oxide having a layered structure is formed. In addition, since there are no impurity peaks due to doping, it can be considered that sintering is well performed during the preparation of the positive electrode active material. On the contrary, for Comparative Example 5 with excessive doping, it can be confirmed that Li3NbO4 peaks are generated (see red arrows near 20° to 25° and 40° to 45°). That is, for Comparative Example 5, it is expected that Nb is not doped into the active material, but exists as agglomerates.

[0141] For reference, the peak with the largest intensity at 17° to 18° is the peak of the Li(NiMn)O2 orthorhombic (R3-m) phase, the small peak at 20° to 23° is the peak corresponding to the Li2MnO3 phase, the peak at 37.5° to 39° is a mixture of peaks corresponding to (006) and (012) of the (R3-m) phase, (002) and (131-) of the Li2MnO3 phase, and the (C2 / m) phase, and the peak at 63° to 67° is a mixture of peaks corresponding to (018), (110), (133-), and (331-) of the Li2MnO3 phase. In this case, the minus sign (-) in the brackets indicates an overline.

[0142] Experimental Example 2: ICP Analysis

[0143] After taking 0.1g of each positive electrode active material prepared in Examples 1 to 8 and Comparative Examples 1 to 6, 1ml of hydrochloric acid was added and heated to dissolve the positive electrode active material. Thereafter, in order to promote the reaction, a small amount of hydrogen peroxide was added to completely dissolve the positive electrode active material to prepare a solution. Subsequently, the analysis sample was prepared by diluting the solution with deionized water so that the total volume of the solution became 10ml. The weight ratio of the constituent elements present in the analysis sample was measured using an inductively coupled plasma (ICP) instrument, and the composition of the positive electrode active material, Li / Me molar ratio (Me=Mn+Ni), Mn / Ni molar ratio, and the weight (ppm) of the doping element are shown in Table 1 below.

[0144]

[0145] Experimental Example 3: Average particle size (D 50 )analyze

[0146] Samples of each positive electrode active material prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were prepared, and the average particle diameter (D 50), and are shown in Table 2 below.

[0147] Experimental Example 4: BET specific surface area analysis

[0148] The specific surface area was measured by the Brunauer-Emmett-Teller (BET) method using a BELSORP-mini II manufactured by Bell Japan. The BET specific surface area was calculated from the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K) and is shown in Table 2 below.

[0149] Specifically, samples of each positive electrode active material prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were prepared and pretreated by placing 3 g of each sample into three tubes and keeping them in a vacuum at 200 ° C for more than 2 hours. Thereafter, the sample was cooled to room temperature, weighed, and placed in a BET measuring instrument. Then, liquid nitrogen was filled so that the sample could be fully immersed in liquid nitrogen, and then measured. Each BET specific surface area value in Table 2 below is a value obtained by averaging the three samples.

[0150]

[0151] Experimental Example 5: Preparation and Capacity Characteristics Evaluation of Coin-Type Half-Cells

[0152] The positive electrode active materials prepared in Examples 1 to 8 and Comparative Examples 1 to 6, a conductive material (Super P), and a binder (polyvinylidene fluoride (PVDF)) were mixed in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 92.5:3.0:4.5 to prepare positive electrode slurries. One surface of an aluminum current collector was coated with the prepared positive electrode slurry, dried at 130°C, and then rolled to prepare each positive electrode.

[0153] A lithium metal electrode was used as the negative electrode, and an electrode assembly was prepared by placing a porous polyethylene separator between the positive and negative electrodes. A coin-type half-cell was prepared by placing the electrode assembly in a battery case and then injecting an electrolyte (in which 1M LiPF6 was dissolved in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) was mixed at a volume ratio of 3:4:3).

[0154] Coin-type half cells containing each of the positive electrode active materials prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were charged to 4.65 V at a constant current of 0.1 C at 45° C. and then discharged to 2.0 V at 0.1 C to perform a formation process, and the charge and discharge capacities in this case were measured.

[0155] Subsequently, the coin-type half-cell was charged to 4.4 V at a constant current of 0.1 C at 25° C. and then discharged to 2.5 V at 0.1 C, thereby measuring the initial charge and discharge capacities.

[0156] Subsequently, a cycle in which the coin-type half cell was charged to 4.4 V at a constant current of 0.33 C at 25° C. and then discharged to 2.5 V at 0.33 C was set as one cycle, and charging and discharging were repeated for a total of 50 cycles, the charge and discharge capacities were measured, and then the capacity retention rate relative to the initial charge and discharge capacities was measured.

[0157] The charge and discharge capacities and capacity retention rates measured at each stage are shown in Table 3 below.

[0158]

[0159] refer to Figure 1 , it can be confirmed that the positive electrode active material prepared in Example 1 is in the form of spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. In addition, referring to Table 3, it can be confirmed that the batteries containing the positive electrode active materials of Examples 1 to 8 not only have excellent charge and discharge capacities, but also have significantly improved initial efficiency and capacity retention compared to batteries containing the positive electrode active materials of Comparative Examples.

[0160] Therefore, it can be understood that in the case where the lithium-rich manganese-based oxide has the composition represented by Chemical Formula 1 in the present invention, the charge / discharge capacity, initial efficiency, and discharge capacity retention rate of a battery including the positive active material can be improved.

Claims

1. A positive electrode active material, the positive electrode active material comprising a lithium-rich manganese-based oxide having a composition represented by Chemical Formula 1: [Chemical Formula 1] Li 1+a1 Mr x1 Ni y1 M z1 O 2+b1 in, In Chemical Formula 1, 0.100 ≤ a1 ≤ 0.400, 0 ≤ b1 < 1.0, 0.50 ≤ x1 < 1.0, 0 < y1 < 0.50, 0.001 ≤ z1 ≤ 0.01, 1.50 ≤ x1 / y1, and M is a metal with an oxidation number of +5 or +6.

2. The positive electrode active material according to claim 1, wherein x1 is 0.55 or more.

3. The positive electrode active material according to claim 1, wherein z1 is in the range of 0.002 to 0.

009.

4. The positive electrode active material according to claim 1, wherein x1 / y1 is 1.80 or more.

5. The positive electrode active material according to claim 1, wherein the lithium-rich manganese-based oxide does not contain cobalt (Co-free).

6. The positive electrode active material according to claim 1, wherein M is at least one selected from Mo, Nb, Ti, V, W, Ta, and Ru.

7. The positive electrode active material according to claim 1, wherein the average particle size (D 50 ) is 1μm to 15μm.

8. The positive electrode active material according to claim 1, wherein In the case where Chemical Formula 1 is represented as Chemical Formula 2, the ratio of x:(1-x) is in the range of 1:9 to 5:5, [Chemical Formula 2] xLi2MnO3·(1-x)Li(Ni x2 Mn y2 M z2 )O2 wherein, in Chemical Formula 2, 0.100 ≤ x ≤ 0.400, 0 < x2 ≤ 0.55, 0.10 ≤ y2 < 1.0, 0 < z2 ≤ 0.015, x2 + y2 + z2 = 1, and M is a metal with an oxidation number of +5 or +6.

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

10. A lithium secondary battery, the lithium secondary battery comprising the positive electrode according to claim 9.

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