Cathode active material and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode active material capable of reducing the amount of gas generated during an activation process or the like of a lithium secondary battery and further improving the energy density and discharge capacity characteristics of the lithium secondary battery, and a lithium secondary battery comprising the same. The positive electrode active material includes: a first phase containing lithium manganese oxide having a rock salt structure in a mixed state; and a second phase containing a lithium metal oxide having a layered structure. In the positive electrode active material, a content of manganese may account for about 50 mol% or more of a total content of a metal other than lithium contained in the positive electrode active material, and may further include niobium (Nb) additionally doped on the positive electrode active material in an amount of about 2,000 ppm to 9,500 ppm based on a total amount of the positive electrode active material.

Description

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Korean Patent Application No. 10-2023-0119293, filed with the Korean Intellectual Property Office on September 7, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to a positive electrode active material and a lithium secondary battery including the same, which can reduce the amount of gas generated during the activation process of the lithium secondary battery and exhibit improved energy density and discharge capacity characteristics. Background Technology

[0004] Recently, as the application of lithium secondary batteries has rapidly expanded not only to power electronic devices such as power, electronics, communications and computers, but also to power storage supply for large equipment such as automobiles and power storage devices, the demand for secondary batteries with high capacity, high output and high stability is increasing.

[0005] Lithium-ion rechargeable batteries typically consist of a positive electrode containing positive active materials, a negative electrode containing negative active materials, an electrolyte serving as a medium for transferring lithium ions, and a separator. Research has been steadily progressing to reduce the manufacturing costs of these components and to improve the energy density and capacity of lithium-ion rechargeable batteries. Summary of the Invention

[0006] This disclosure provides a manganese oxide-based positive electrode active material that has high energy density, reduces gas generation during the activation process of lithium secondary batteries, and exhibits improved discharge capacity characteristics.

[0007] This disclosure also provides a positive electrode and a lithium secondary battery comprising the aforementioned positive electrode active material, thereby exhibiting reduced gas generation and improved energy density and discharge capacity characteristics.

[0008] Technical solution

[0009] This disclosure provides a positive electrode active material comprising a first phase containing lithium manganese oxide having a rock salt structure and a second phase containing lithium metal oxide of Formula 1 having a layered structure in a mixed state. In the positive electrode active material, the manganese content accounts for more than 50 mol% of the total content of metals other than lithium contained in the positive electrode active material, and further comprises additional niobium (Nb) doped onto the positive electrode active material in an amount of about 2,000 ppm to 9,500 ppm based on the total amount of the positive electrode active material. [Formula 1] Li[Ni1-b-c Mn b M c O2 In Equation 1, b is greater than or equal to 0.4 and less than 1, c is between 0 and 0.2, and M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr, and Zr.

[0010] This disclosure also provides a positive electrode for a lithium secondary battery. The positive electrode includes: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material, a binder, and a conductive material.

[0011] In addition, this disclosure provides a lithium secondary battery comprising the aforementioned positive electrode, negative electrode and electrolyte.

[0012] When stored for two weeks at 100% SOC (State of Charge) and 60°C, lithium secondary batteries exhibit a reduction in gas production of less than 2.9 mL.

[0013] Technical effect

[0014] The positive electrode active material disclosed herein is a manganese-rich oxide-based oxide and does not contain cobalt in its structure, wherein a predetermined amount of niobium (Nb) is included as a dopant on the positive electrode active material.

[0015] As experimental results from the inventors, it was confirmed that the positive electrode active material exhibits a relatively high energy density characteristic of manganese-rich oxides, while also showing reduced gas generation under the activation conditions of a lithium secondary battery. Furthermore, it was confirmed that coating with a predetermined amount of niobium (Nb) can improve the discharge capacity characteristics of the lithium secondary battery, particularly its discharge capacity characteristics at high temperatures. Attached Figure Description

[0016] Figure 1 This is a graph showing the comparative evaluation results of the gas generation of lithium secondary batteries manufactured using the positive electrode active materials of Comparative Example 1 and Example 2. Detailed Implementation

[0017] The terms or words used in this specification and claims should not be construed as having their usual or dictionary meaning, but should be interpreted as having meanings and concepts consistent with the technical ideas of this disclosure, based on the principle that the inventor can appropriately define the concepts of the terms in order to best interpret his / her own invention.

[0018] In this specification, it should be understood that terms such as “comprising,” “equipped with,” or “having” are intended to specify the presence of the implemented features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] Given the inherent manufacturing and material tolerances, the terms “approximately,” “roughly,” and “substantially” used in this specification are used to indicate a range or approximation of a numerical or degree value.

[0020] As positive electrode active materials for lithium-ion secondary batteries, lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, or lithium nickel cobalt manganese composite oxides are mainly used. To reduce the manufacturing cost of positive electrode active materials and improve energy density and capacity, lithium-excess manganese-rich oxides have attracted considerable attention. Lithium-excess manganese-rich oxides can achieve relatively low manufacturing costs because the content of relatively inexpensive and abundant manganese (Mn) is increased, while the content of cobalt (Co) is reduced.

[0021] Lithium-rich manganese oxides can exist in the positive electrode of a lithium secondary battery in a mixed state of a lithium manganese oxide phase with a rock salt structure (Li₂MnO₃) and a lithium metal oxide phase with a layered structure (LiMO₂; M: at least one metal element including manganese). Here, due to the presence of the rock salt structure phase, the molar ratio of lithium content can be greater than that of metals such as manganese per unit mole. Therefore, the positive electrode active material of this disclosure can have a higher energy density than conventional positive electrode active materials.

[0022] Meanwhile, the initial activation process of lithium-ion secondary batteries containing excessive lithium and manganese-rich oxides may generate a large amount of gas. This can lead to problems such as reduced battery capacity and decreased cell stability.

[0023] One embodiment of this disclosure provides a lithium-rich manganese oxide-based positive electrode active material that can reduce the amount of gas generated during the activation process of a secondary battery and improve energy density and capacity characteristics.

[0024] The positive electrode active material of the present disclosure, as well as the positive electrode and lithium secondary battery including the present disclosure, will be described below.

[0025] According to embodiments of this disclosure, a positive electrode active material is provided, comprising: a first phase containing lithium manganese oxide having a rock salt structure in a mixed state and a second phase containing lithium metal oxide of Formula 1 having a layered structure. In the positive electrode active material, manganese accounts for more than 50 mol% of the total content of metals other than lithium. This also includes additional niobium (Nb) doping on the positive electrode active material, in amounts ranging from approximately 2,000 ppm to 9,500 ppm based on the total amount of the positive electrode active material: [Formula 1] Li[Ni 1-b-c Mn b M c O2 In Formula 1, b is greater than or equal to about 0.4 and less than 1, c is from about 0 to 0.2, and M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr and Zr.

[0026] The positive electrode active material of the embodiments of this disclosure corresponds to a manganese-rich oxide or a complex thereof, wherein the manganese content accounts for about 50 mol% or more, about 50 mol% to 95 mol%, or about 50 mol% to 90 mol% of the total metal content excluding lithium. This positive electrode active material of the embodiments of this disclosure includes a first phase containing a lithium manganese oxide (e.g., Li₂MnO₃) having a rock salt structure and a lithium metal oxide (e.g., Li[Ni₂]O₃) having a layered structure. 1-b-c Mn b M c The first and second phases (O2) can exist in the cathode active material in a mixed or combined state. Here, since the first phase has a higher molar ratio of lithium than metals such as manganese, the cathode active material of this embodiment can contain a relatively large amount of lithium, and therefore can have a higher energy density than existing cathode active materials.

[0027] Furthermore, the positive electrode active material of this embodiment can be a so-called "cobalt-free" positive electrode active material that does not contain cobalt in the entire structure including the first phase and the second phase. According to this "cobalt-free" form, when using the positive electrode active material of one embodiment, since the energy density can be increased while reducing the manufacturing cost of the positive electrode active material, the manufacturing cost per unit of energy can be relatively reduced.

[0028] However, in one embodiment of the positive electrode active material, although the energy density can be improved due to the aforementioned characteristics (e.g., excess lithium and rich manganese), lithium ions may be deintercalated from the transition metal oxide layer during activation, and the structure of the positive electrode may change. Furthermore, oxygen free radicals are generated / deintercalated through redox reactions, and gases such as CO, CO2, or O2 are generated through electrolyte side reactions and electrolyte decomposition. This gas generation can lead to capacity reduction due to gas retention, and also negatively impacts cell stability.

[0029] Meanwhile, in one embodiment of the positive electrode active material, niobium (Nb) is included in a predetermined amount, for example, based on the total amount of the positive electrode active material, the amount is about 2,000 ppm to 9,500 ppm, about 3,500 ppm to 8,000 ppm, or about 4,500 ppm to 5,500 ppm. Therefore, the energy density and discharge capacity characteristics of the lithium secondary battery can be improved, especially the discharge capacity characteristics at high temperatures, and the amount of gas generated can be reduced. It is predicted that this is because when niobium (Nb) is doped into the positive electrode active material, the crystal structure of the positive electrode active material can be further stabilized, and lithium ions can move more smoothly.

[0030] Meanwhile, when the doping concentration is too low, for example less than about 2,000 ppm, the improvement in energy density and discharge capacity or the reduction in gas generation may not be substantially observed. Furthermore, when the doping concentration is too high, for example greater than about 9,500 ppm, a decrease in discharge capacity was confirmed, thus the effect of niobium (Nb) doping cannot be observed.

[0031] Meanwhile, in one embodiment, the positive electrode active material substantially comprises nickel and manganese, such that the total molar ratio of nickel to manganese is 1:1 to 1:5, or 1:1 to 1:4. Furthermore, in Formula 1, b corresponding to the molar ratio of manganese can satisfy a range of about 0.4 or more and less than 1, about 0.45 to 0.95, or about 0.5 to 0.9.

[0032] When this range is met, thus containing manganese in a relatively large molar ratio, the cathode active material of one embodiment can maintain the structural stability of the overall cathode active material, including the first phase and the second phase, while exhibiting relatively high energy density and capacity characteristics.

[0033] In Equation 1, M can define additional doping elements other than niobium (Nb), and c can define the molar ratio of the additional doping elements M. There are no particular restrictions on the type of additional doping elements, and c can satisfy a range of approximately 0 to 0.2, or approximately 0 to 0.1. When the content of additional doping elements is too high, it can adversely affect the capacity characteristics of the active material, and furthermore, the amount of gas generated can increase due to, for example, the increase in oxygen redox reactions.

[0034] Meanwhile, one embodiment of the cathode active material can exhibit high energy density and capacity characteristics by including an excess of lithium based on the total molar number of metals other than lithium, including nickel (Ni), manganese (Mn), and metallic M. For example, in the cathode active material, the ratio of the total molar number of lithium to the total molar number of metals other than lithium can be greater than about 1 and less than 1.5, about 1.1 to 1.4, or about 1.2 to 1.4. In this way, by including an excess of lithium, excellent energy density and capacity characteristics can be exhibited. However, when the molar ratio of lithium becomes too large, the ratio of the first phase with a rock salt structure may increase excessively, thereby reducing the structural stability of the cathode active material and accelerating the degradation rate.

[0035] Furthermore, in one embodiment, the positive electrode active material may comprise a first phase having a rock salt structure and a second phase having a layered structure in a molar ratio of approximately 1:9 to 5:5, or approximately 2:8 to 4:6. Due to the content ratio of the first phase to the second phase, the positive electrode active material can exhibit overall structural stability, while also possessing excellent energy density and capacity characteristics by including an excess of lithium.

[0036] One embodiment of the positive electrode active material exhibiting the above-described overall characteristics may, in one instance, comprise a lithium metal oxide composite of Formula 2, wherein, based on the total amount of the positive electrode active material, the content of niobium (Nb) additionally doped onto such lithium metal oxide composite may be from approximately 3,500 ppm to 8,000 ppm: [Equation 2] X{Li2MnO3} (1-X){Li[Ni 1-b-c Mn b M c O2} In Equation 2, X is about 0.1 to 0.5, b is about 0.45 to 0.95, c is about 0 to 0.2, and M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr, and Zr.

[0037] Furthermore, if necessary, the positive electrode active material may also include a coating formed on the lithium metal oxide composite. When the positive electrode active material includes a coating, contact with the electrolyte is suppressed, thereby reducing side reactions and further reducing gas generation.

[0038] The coating may contain a coating element M1, and the coating element M1 may be at least one selected from the group consisting of Al, B, Co, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr, and Zr, or, for example, Al, Co, W, or combinations thereof. This coating element may exist in the coating in the form of an oxide, such as M1Oz (1≤z≤4).

[0039] Furthermore, the coating can be formed to cover approximately 10% to 100%, approximately 30% to 100%, or approximately 50% to 100% of the total surface area of ​​the positive electrode active material (e.g., lithium metal oxide composite particles), thereby further improving the lifetime characteristics of the positive electrode active material.

[0040] Meanwhile, in order to prepare the above-mentioned positive electrode active material, a precursor can be prepared by mixing and firing metal precursors such as nickel, manganese and M, and then a niobium precursor can be additionally mixed with lithium raw material and fired.

[0041] In this manufacturing method, lithium raw materials can be, for example, lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O) etc.), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3) etc.) and chlorides (e.g., lithium chloride (LiCl) etc.), and one of these can be used alone or a mixture of two or more can be used.

[0042] Furthermore, metal precursors such as nickel, manganese, M, or niobium (Nb) can be in the form of hydroxides, oxides, or carbonates. When using precursors in the form of carbonates, positive electrode active materials with relatively high specific surface areas can be prepared.

[0043] The metal precursors and lithium feedstock can be mixed according to the molar ratios of the elements defined in Formula 2, etc., and then the various firing steps can be performed. The firing steps can be carried out at a temperature of about 600°C to 1,000°C or about 700°C to 950°C, and the firing time can be about 5 h to 30 h or about 5 h to 20 h. In addition, the firing atmosphere can be an air atmosphere or an oxygen atmosphere, for example, an atmosphere containing about 20 vol% to 100 vol% oxygen.

[0044] Meanwhile, since the positive electrode active material of one embodiment can be manufactured, for example, according to the general manufacturing process and conditions of positive electrode active materials in the form of lithium metal oxide, its additional description will be omitted.

[0045] Meanwhile, according to another embodiment of this disclosure, a positive electrode for a lithium secondary battery is provided. The positive electrode includes: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material, binder, and conductive material of the above embodiment.

[0046] In another embodiment of the positive electrode, the positive electrode current collector is not particularly limited, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, and silver, as well as aluminum-cadmium alloys can be used. Furthermore, the positive electrode current collector can typically have a thickness of about 3 μm to 500 μm and can take various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0047] Furthermore, examples of conductive materials in the positive electrode active material layer may include: spherical or flake graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, single-walled carbon nanotubes, and multi-walled carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and in these, one or a mixture of two or more may be used alone. Based on the total weight of the positive electrode active material layer, the content of conductive material may be from about 0.1% to 20% by weight, from about 1% to 20% by weight, or from about 1% to 10% by weight.

[0048] Furthermore, examples of adhesives may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and in these, one may be used alone or a mixture of two or more may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from about 0.1% to 20% by weight, from about 1% to 20% by weight, or from about 1% to 10% by weight.

[0049] In addition, in the positive electrode active material layer, the content of the positive electrode active material in one embodiment can be from about 80% to 99% by weight based on the total weight.

[0050] In addition to the positive electrode active material of this embodiment, the positive electrode of another embodiment can be manufactured according to the general manufacturing process of positive electrodes, for example, by preparing a slurry composition by mixing the above-mentioned components in a solvent, and then coating, drying and rolling it onto a positive electrode current collector.

[0051] Meanwhile, according to another embodiment of this disclosure, a lithium secondary battery is provided, which includes a positive electrode, a negative electrode, and an electrolyte. Because it incorporates the positive electrode active material of the above embodiment, this lithium secondary battery can exhibit reduced gas generation during activation processes and other procedures, and can have improved discharge capacity characteristics, etc.

[0052] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0053] There are no particular restrictions on the negative electrode current collector, as long as it has relatively high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, and silver, as well as aluminum-cadmium alloys can be used. In addition, the thickness and shape of the negative electrode current collector can be the same as or correspond to the thickness and shape of the positive electrode current collector.

[0054] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0055] For the negative electrode active material, compounds capable of reversibly inserting and deintercalating lithium can be used. Examples include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic materials that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides that can be doped or dedoped with lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; and composites containing metallic and carbonaceous materials, such as Si-C composites or Sn-C composites, thus allowing the use of any one or a mixture of two or more of these. Furthermore, a thin film of metallic lithium can also be used for the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from approximately 80% by weight to 99% by weight.

[0056] Meanwhile, in the negative electrode active material layer, the types and content ranges of binders and conductive materials can be the same as or substantially the same as those described in the positive electrode active material layer, so their additional descriptions will be omitted.

[0057] Furthermore, the negative electrode active material layer and the negative electrode can be manufactured by mixing the components of the aforementioned negative electrode active material, binder, and conductive material in a solvent to prepare a slurry composition, which is then coated, dried, and rolled onto the negative electrode current collector. In another example of manufacturing, a negative electrode mixture comprising the negative electrode active material, binder, and conductive material can be cast onto a separate support, and then a film layer obtained by peeling it off from the support can be pressed onto the negative electrode current collector.

[0058] Meanwhile, for the electrolyte of lithium secondary batteries, organic liquid electrolytes, inorganic liquid electrolytes, polymer solid electrolytes, gel polymer electrolytes, inorganic solid electrolytes or molten inorganic electrolytes that can be used to manufacture secondary batteries can be used.

[0059] As an example, an electrolyte can be a liquid electrolyte containing an organic solvent and a lithium salt.

[0060] Organic solvents can be used without any particular restrictions, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. For example, organic solvents that can be used include: 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), methyl ethyl carbonate (MEC), 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 straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfolane.

[0061] Carbonate solvents may be used appropriately, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with relatively high ionic conductivity and relatively high dielectric constant and low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charging / discharging performance of the battery may be used.

[0062] Lithium salts can be used without any particular restrictions, as long as they are compounds that can provide lithium ions used in lithium-ion secondary batteries. For example, 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 (CF3CF2SO2)2N - At least one of the group consisting of. For example, for lithium salts, 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.

[0063] Furthermore, the concentration of lithium salts used in liquid electrolytes can fall within the range of approximately 0.1 M to 4.0 M. When the concentration of lithium salts falls within this range, the electrolyte exhibits excellent electrolyte performance due to its suitable conductivity and viscosity, and lithium ions can move efficiently.

[0064] In addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity. These additives may include, for example, alkyl halogenated carbonate compounds such as ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. Here, based on the total weight of the electrolyte, the content of the additives may be from about 0.1% by weight to 5% by weight.

[0065] Furthermore, the aforementioned lithium secondary battery may further include a separator that separates the negative electrode from the positive electrode and provides a channel for lithium ion movement. For this separator, a porous polymer membrane with relatively low resistance to ion movement of the electrolyte and excellent electrolyte retention, or a stacked structure of two or more layers thereof, can be used. For example, the porous polymer membrane can be made using polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer). Alternatively, conventional porous nonwoven fabrics, such as nonwoven fabrics made of relatively high-melting-point glass fibers and polyethylene terephthalate fibers, can also be used.

[0066] In addition, coated diaphragms containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0067] There are no particular restrictions on the shape of lithium secondary batteries, but they can be cylindrical, prismatic, pouch-shaped, or coin-shaped, similar to those used in cans.

[0068] The aforementioned lithium secondary battery exhibits excellent energy density and discharge capacity characteristics, as well as reduced gas generation, due to the inclusion of a positive electrode active material according to one embodiment. For example, when the lithium secondary battery is stored at 100% SOC (State of Charge) and 60°C for two weeks, it exhibits a relatively small gas generation of less than approximately 0.29 mL or less than 0.25 mL.

[0069] Therefore, lithium secondary batteries can be used in portable devices such as mobile phones, laptops and digital cameras, as well as in electric vehicles (EVs) such as hybrid electric vehicles (HEVs).

[0070] Therefore, lithium secondary batteries can be used as battery cells for powering small devices, and also as unit cells in medium and large battery modules, each containing multiple battery cells.

[0071] Examples of medium to large-sized equipment may include, but are not limited to, electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (HEVs), and energy storage systems.

[0072] Embodiments of this disclosure will be described in detail below to enable those skilled in the art to readily implement this disclosure. However, this disclosure may be implemented in various forms and is not limited to the embodiments described herein.

[0073] Comparative Example 1: 0.3 {Li2MnO3} 0.7{Li[Ni 0.5 Mn 0.5 Preparation of O2

[0074] Ni 0.35 Mn 0.65 (OH)₂ and lithium hydroxide (LiOH) were added to a Henschel mixer (700 L) to make the molar ratio of Li:transition metal (Ni+Mn) 1.3:1, and mixed at 300 rpm for 20 minutes. The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and calcined at 850 °C for 10 hours in an oxygen atmosphere to prepare the positive electrode active material of Comparative Example 1.

[0075] Example 1: 0.3 Li₂MnO₃ doped with Nb (2,500 ppm) 0.7{Li[Ni 0.5 Mn 0.5 Preparation of O2

[0076] Ni 0.35 Mn 0.65 Lithium hydroxide (LiOH)₂ and lithium hydroxide (LiOH) were added to a Henschel mixer (700 L) to achieve a Li:transition metal (Ni+Mn) molar ratio of 1.3:1, and mixed at 300 rpm for 20 minutes. During this mixing process, niobium oxide (NbO) was additionally mixed, resulting in a niobium (Nb) content of 2,500 ppm based on the final cathode active material.

[0077] The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and calcined at 850 °C for 10 hours in an oxygen atmosphere to prepare the positive electrode active material of Example 1.

[0078] Example 2: 0.3% Li₂MnO₃ doped with Nb (5,000 ppm) 0.7{Li[Ni 0.5 Mn 0.5 Preparation of O2

[0079] Ni 0.35 Mn 0.65 Lithium hydroxide (LiOH)₂ and lithium hydroxide (LiOH) were added to a Henschel mixer (700 L) to achieve a Li:transition metal (Ni+Mn) molar ratio of 1.3:1, and mixed at 300 rpm for 20 minutes. During this mixing process, niobium oxide (NbO) was additionally mixed, resulting in a niobium (Nb) content of 5,000 ppm based on the final cathode active material.

[0080] The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and calcined at 850 °C for 10 hours in an oxygen atmosphere to prepare the positive electrode active material of Example 2.

[0081] Example 3: 0.3% Li₂MnO₃ doped with Nb (9,000 ppm) 0.7{Li[Ni 0.5 Mn 0.5 Preparation of O2

[0082] Ni 0.35 Mn 0.65 Lithium hydroxide (LiOH)₂ and lithium hydroxide (LiOH) were added to a Henschel mixer (700 L) to achieve a Li:transition metal (Ni+Mn) molar ratio of 1.3:1, and mixed at 300 rpm for 20 minutes. During this mixing process, niobium oxide (NbO) was additionally mixed, resulting in a niobium (Nb) content of 9,000 ppm based on the final cathode active material.

[0083] The mixed powder was placed in an alumina crucible with dimensions of 330 mm × 330 mm and calcined at 850 °C for 10 hours in an oxygen atmosphere to prepare the positive electrode active material of Example 3.

[0084] Manufacturing example: Manufacturing of lithium secondary batteries

[0085] The positive electrode active material, single-walled carbon nanotubes, and PVDF binder of the examples or comparative examples were mixed in N-methylpyrrolidone at a weight ratio of 96.0:1.0:3.0 to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum current collector, dried, and rolled to prepare a positive electrode.

[0086] A negative electrode slurry was prepared by mixing graphite anode active material, single-walled carbon nanotubes, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 96.2:0.8:2:1. The negative electrode slurry was then coated onto a copper current collector sheet, dried, and rolled to manufacture the negative electrode.

[0087] At the same time, positive and negative electrodes are manufactured so that by adjusting the load, the ratio of the discharge capacity of the negative electrode to the discharge capacity of the positive electrode (N / P ratio) becomes 115%.

[0088] An electrode assembly is manufactured by inserting a polyethylene separator between the positive and negative electrodes as described above. The electrode assembly is then inserted into a battery casing and an electrolyte is injected. An activation process is then performed at 45°C, followed by charging to 4.6 V at a constant current of 0.1 C, and then discharging to 2.0 V at a constant current of 0.1 C, thereby manufacturing a lithium-ion secondary battery.

[0089] Experimental Example 1: Evaluation of Gas Production

[0090] The amount of gas generated was evaluated when lithium secondary batteries manufactured using the positive electrode active materials of Example 2 and Comparative Example 1 were stored for two weeks at 100% SOC (State of Charge) and 60°C. The amount of gas generated was measured and evaluated using gas chromatography, and the evaluation results are shown below. Figure 1 middle.

[0091] refer to Figure 1 It was confirmed that the amount of gas generated by the lithium secondary battery manufactured using Example 2 was reduced by about 14% compared to the battery manufactured using Comparative Example 1.

[0092] Experimental Example 2: Evaluation of Electrochemical Properties

[0093] Lithium-ion secondary batteries manufactured using the positive electrode active materials of the Examples or Comparative Examples were subjected to charge / discharge tests at 25°C and within a voltage range of 4.4 V to 2.5 V at c-rates of 0.1 C and 0.33 C. Based on the results of these charge / discharge tests, the discharge capacity, average voltage, and energy density were evaluated, and the evaluation results are listed in Tables 1 and 2 below. Table 1 shows the results of a comparative evaluation of the average voltage and energy density of the batteries of Example 2 and Comparative Example 1, and Table 2 shows the results of a comparative evaluation of the discharge capacity of the batteries of Examples 1 to 3.

[0094] Here, in order to calculate the energy density, the value obtained by multiplying the discharge capacity by the average voltage is divided by the unit volume of the secondary battery, and the average voltage is calculated as the integral value of the capacity-voltage curve divided by the capacity.

[0095] [Table 1]

[0096] [Table 2]

[0097] Referring to Table 1 above, it was confirmed that the battery manufactured by Example 2 exhibited a relatively higher energy density compared to Comparative Example 1, and that the difference in energy density was significant at higher discharge rates. For example, a higher energy density per unit weight means that relatively high energy can be generated even with a relatively small amount of active material, thus allowing for the manufacture of lighter batteries in practical applications.

[0098] Furthermore, referring to Table 2 above, it was confirmed that the batteries manufactured using the positive electrode active materials of the examples exhibited relatively high discharge capacity. In particular, it was confirmed that the discharge capacity was maximized in Example 2, which was doped with 5,000 ppm niobium (Nb). Additionally, the de-rating value is expressed as a percentage of the ratio of 0.33 C capacity to 0.1 C capacity. Here, C is the C-rate value, representing the charge / discharge rate of the battery. When the C-rate is 0.1 C, the battery takes 10 hours to charge / discharge, and when the C-rate is 0.33 C, the battery takes approximately 3 hours to charge / discharge. This means that as the C-rate value increases, a faster charge / discharge rate can be achieved, and it is advantageous even when using the battery in situations requiring a large instantaneous current. This means that as the percentage of discharge capacity expressed as 0.33 C / discharge capacity expressed as 0.1 C approaches 100%, a higher charging / discharging rate is possible. This means that when 5,000 ppm niobium (Nb) is added, high-speed charging / discharging is possible.

[0099] Table 1 confirms the improved energy density, and Table 2 confirms the increased derating rate achieved by adding 5,000 ppm. Based on this, it can be found that when niobium (Nb) is added at appropriate levels, lightweight batteries with improved energy density can be manufactured, and high-speed charging / discharging is possible. These conditions are believed to be more advantageous for use as batteries in electric vehicles.

[0100] Although embodiments of this disclosure have been described above with reference to them, those skilled in the art will understand that various modifications and alterations can be made to this disclosure without departing from the spirit and scope of the disclosure as set forth in the patent claims described below. Therefore, the technical scope of this disclosure is not limited to what is described in the detailed description of the specification, but should be determined by the patent claims.

Claims

1. A positive electrode active material, comprising: The first and second phases are in a mixed state. The first phase contains lithium manganese oxides with a rock salt structure; and The second phase contains lithium metal oxide of Formula 1 with a layered structure. In the positive electrode active material, the manganese content accounts for more than 50 mol% of the total content of metals other than lithium contained in the positive electrode active material, and It also includes additional niobium (Nb) doped onto the positive electrode active material, with the amount of niobium (Nb) ranging from 2000 ppm to 9500 ppm based on the total amount of the positive electrode active material. [Formula 1] Li[Ni 1-b-c Mr b M c ]O2 Wherein, b is greater than or equal to 0.4 and less than 1, c is between 0 and 0.2, and M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr and Zr.

2. The positive electrode active material according to claim 1, wherein, The first phase contains lithium manganese oxide represented by Li2MnO3.

3. The positive electrode active material according to claim 1, wherein, The first phase and the second phase are contained in a molar ratio of 1:9 to 5:

5.

4. The positive electrode active material according to claim 1, wherein, Based on the total number of moles of nickel (Ni), manganese (Mn), and metallic M contained in the positive electrode active material, the ratio of the total number of moles of lithium contained in the positive electrode active material is greater than 1 and less than 1.

5.

5. The positive electrode active material according to claim 1, wherein, The total molar ratio of nickel (Ni):manganese (Mn) contained in the positive electrode active material is 1:1 to 1:

5.

6. The positive electrode active material according to claim 1, further comprising a lithium metal oxide composite of formula 2 below, in, Based on the total amount of the positive electrode active material, the niobium (Nb) content is between 3500 ppm and 8000 ppm. [Equation 2] X{Li2MnO3} (1-X){Li[Ni 1-b-c Mn b M c ]O2} Wherein, X is 0.1 to 0.5, b is 0.45 to 0.95, c is 0 to 0.2, and M is at least one selected from the group consisting of Al, B, W, Mg, V, Ti, Zn, Ga, In, Ru, Sn, Sr and Zr.

7. A positive electrode for a lithium secondary battery, the positive electrode comprising: Positive current collector; as well as A positive electrode active material layer, the positive electrode active material layer being formed on the positive electrode current collector and comprising the positive electrode active material, binder and conductive material as described in any one of claims 1 to 6.

8. A lithium secondary battery comprising the positive electrode, negative electrode, and electrolyte as described in claim 7.

9. The lithium secondary battery according to claim 8, wherein, After two weeks of storage at 100% SOC (State of Charge) and 60°C, the amount of gas produced was less than 2.9 mL.

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