Positive electrodee and lithium secondary battery comprising the same

Abstract

The cathode according to the present invention may comprise a lithium nickel-based transition metal oxide in at least one form among a single particle consisting of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and may comprise a cathode active material having a D50 of 4.5 μm to 6.7 μm and a crystal strain of 320 x 10⁻⁶ or less.

Description

Technology Field

[0001] The present invention relates to a positive electrode and a lithium secondary battery including the same, and more specifically to a negative electrode using a silicon-based negative electrode active material, an available high-capacity low-efficiency positive electrode, and a lithium secondary battery including the same. Background Technology

[0003] Recently, interest in energy storage technology has been steadily increasing, and as application fields expand to include energy for mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts in the research and development of electrochemical devices are becoming increasingly concrete.

[0004] Among electrochemical devices, there is growing interest in the development of rechargeable secondary batteries, and in particular, lithium secondary batteries developed in the early 1990s are gaining attention for their advantages of high operating voltage and significantly higher energy density.

[0005] With the recent increase in demand for high-energy-density secondary batteries, such as those for electric vehicles, active development is underway for high-voltage secondary batteries that operate at high voltages. Furthermore, research is being conducted to apply silicon-based anode active materials with superior capacity to achieve higher capacities.

[0006] Automotive lithium-ion batteries developed to date primarily utilize lithium-nickel-based oxides as the cathode active material; however, the application of lithium-nickel-based oxides leads to problems such as structural collapse of the cathode active material, transition metal leaching, and gas generation at high voltages. Furthermore, when silicon-based anode active materials are used, the efficiency imbalance between the two electrodes prevents lithium ions from rapidly penetrating into the anode, resulting in irreversible precipitation on the anode surface. This causes adverse reactions with the electrolyte, as well as issues such as gas generation and reduced lifespan at room temperature. The problem to be solved

[0008] The present invention is intended to solve the above-mentioned problems, and D of a specific range 50 The present invention aims to provide a positive electrode having low initial efficiency and a lithium secondary battery including the same, which includes a single-particle positive electrode active material having a crystal strain and is balanced with a negative electrode using a silicon-based negative electrode active material. means of solving the problem

[0010] In one aspect, the present invention comprises a lithium nickel-based transition metal oxide in at least one form among a single particle consisting of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and D 50 The particle size is 4.5 µm to 6.7 µm, and the crystal strain is 320 x 10⁻⁶ -6 A positive electrode containing a positive electrode active material is provided.

[0011] The above positive active material is D 50 This can be 5.5㎛ to 6.5㎛.

[0012] The above positive active material has a crystal strain of 220 x 10 -6 Up to 320 x 10 -6 It could be.

[0013] The above positive active material may have a cation mixing ratio of 0.7 at% to 1.2 at%.

[0014] The above positive active material may have an average grain size of 160 nm or more.

[0015] The above lithium nickel-based transition metal oxide may have a molar ratio of Ni of 80 mol% or more among the total transition metals.

[0016] The above lithium nickel-based transition metal oxide may be represented by the following chemical formula 1.

[0017] [Chemical Formula 1]

[0018] Li 1+x Ni a Co b M 1 c M2 d O2

[0019] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≤x≤0.50, 0.80≤a<1.00, 0 <b<0.20, 0<c<0.20, 및 0≤d≤0.20일 수 있다.

[0020] The above anode may have an initial charging capacity of 242 mAh / g or more.

[0021] The above anode may have an initial efficiency of 87% to 89%.

[0023] In another aspect, a lithium secondary battery comprising the anode; the cathode; and the electrolyte is provided.

[0024] The above cathode may include a silicon-based cathode active material, a carbon-based cathode active material, or a combination thereof.

[0025] The above cathode may include a silicon-based cathode active material and a carbon-based cathode active material.

[0026] The above lithium secondary battery may have a capacity retention rate of 88.8% or more after charging and discharging for 50 cycles, with one cycle consisting of charging to 4.25V at 0.5C CCCV at 45℃ and discharging to 3.0V at 1.0C CC. Effects of the invention

[0028] The positive electrode and lithium secondary battery according to the present invention are, in a specific range D 50 By including a single-particle positive electrode active material having a crystal strain, the initial efficiency is lowered to balance with the negative electrode using a silicon-based negative electrode active material, and the lithium precipitation phenomenon on the negative electrode surface is controlled, thereby enabling improved room temperature lifespan characteristics.

[0029] In addition, the positive electrode and lithium secondary battery according to the present invention can achieve a high capacity retention rate and improved high-temperature life characteristics by controlling the lithium precipitation phenomenon caused by differences in rate characteristics. Brief explanation of the drawing

[0031] Figure 1 is a graph showing the initial charge capacity according to the crystal strain of the positive active material. Specific details for implementing the invention

[0032] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0033] In the present invention, a “single particle” is a particle consisting of one single nodule. In the present invention, a “pseudo-single particle” refers to a composite particle formed of 30 or fewer nodules.

[0034] In the present invention, “nodule” refers to a particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not apparent when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM). The average grain size of the nodule may be measured as the arithmetic mean of the grain sizes of each nodule measured using a scanning electron microscope (SEM).

[0035] In the present invention, "secondary particle" refers to a particle formed by the aggregation of tens to hundreds of multiple primary particles. More specifically, the secondary particle is an aggregate of 40 or more primary particles.

[0036] The expression “particle” used in the present invention may include any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0037] In the present invention, "D 50 " refers to the particle size at the 50% standard of the volume cumulative particle size distribution of the positive active material. The above D 50 It can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of about 28 kHz at an output of 60 W, obtained a volume cumulative particle size distribution graph, and then measured by determining the particle size corresponding to 50% of the volume cumulative amount.

[0038] In the present invention, the "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at a liquid nitrogen temperature (77K) using BEL SORP-mino II from BEL Japan.

[0039] In the present invention, “crystallization degree,” “cation mixing ratio,” and “average grain size” can be measured by analyzing XRD data obtained by X-ray diffraction analysis of the cathode active material powder using the Rietveld refinement method. At this time, the X-ray diffraction analysis was performed by placing the sample into a groove of a general powder holder, smoothing the surface of the sample using a slide glass, and filling the sample so that its height matched the edge of the holder, and then measuring using an X-ray diffraction analyzer (Bruker D8 Endeavor) (FDS 0.5°, 2θ=15° ~ 90°, Step size=0.02°, total scan time: 20 min). Based on the measured data, Rietveld refinement was performed considering the potential (charge) at each site (metals at transition metal sites +3, Ni at Li sites +2) and cation mixing. Specifically, when analyzing crystal strain, cation mixing ratio, and average grain size, instrumental broadening was considered using the Fundamental Parameter Approach (FPA) built into the Bruker TOPAS program, and all peaks of the measurement range were used during fitting. The peak shape was fitted using only the Lorentzian contribution as the First Principle (FP) among the peak types available in TOPAS.

[0041] The present invention will be described in more detail below.

[0043] anode

[0044] The anode according to the present invention comprises an anode active material. Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector, wherein the anode active material layer comprises an anode active material.

[0045] The positive active material is explained in detail below.

[0046] The positive electrode active material according to the present invention comprises a lithium nickel-based transition metal oxide in at least one form among a single particle consisting of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules.

[0047] Lithium nickel-based oxides in the form of single particles and / or similar-single particles have higher particle strength compared to conventional lithium nickel-based oxides in the form of secondary particles in which tens to hundreds of primary particles are aggregated, so there is less particle breakage during rolling.

[0048] In addition, in the case of the lithium nickel-based oxide in the form of a single particle or a quasi-single particle according to the present invention, since the number of sub-components (i.e., nodules) constituting the particle is small, there is less change due to volume expansion and contraction of the primary particles during charging and discharging, and accordingly, the occurrence of cracks inside the particle is significantly reduced.

[0049] In particular, the inventors of the present invention D 50 The particle size is 4.5 µm to 6.7 µm, and the crystal strain is 320 x 10⁻⁶ -6 It was discovered that when a positive electrode active material of the following value is applied, the initial efficiency satisfies 87% to 89%, and the lithium precipitation phenomenon is suppressed in a battery composed of a negative electrode with silicon oxide applied, and the energy density can be improved.

[0050] The positive active material according to the present invention is D 50 This may be 4.5㎛ to 6.7㎛, 4.5㎛ to 6.5㎛, or 4.6㎛ to 6.0㎛. D 50 If this is less than 4.5㎛, the room temperature lifespan characteristics deteriorate, and if it exceeds 6.7㎛, the lithium mobility in the cathode active material decreases, resulting in high resistance and reduced energy density.

[0051] The positive electrode active material according to the present invention has a crystal strain of 320 x 10 -6 Below, preferably 220 x 10 -6 Up to 320 x 10 -6 , more preferably 230 x 10 -6 Up to 310 x 10 -6 It can be. Crystal strain is 320 x 10 -6 In the case of exceeding a certain range, the initial efficiency of the anode becomes below a certain range, and a difference in rate characteristics with the anode with silicon oxide applied occurs, resulting in a lithium plating phenomenon where lithium is deposited on the surface of the anode and a decrease in energy density.

[0052] Meanwhile, the positive electrode active material according to the present invention may have a cation mixing ratio of 0.7 at% to 1.2 at%, preferably 0.7 at% to 1.1 at%. If the cation mixing ratio is less than 0.7 at%, a problem may arise in which the initial efficiency becomes excessively high due to the high structural completeness, and if it exceeds 1.2 at%, a problem arises in which the initial efficiency falls below the target level and the initial resistance increases due to the low structural completeness.

[0053] Meanwhile, the positive electrode active material according to the present invention may have an average grain size of 160 nm or more, preferably 160 nm to 220 nm, and more preferably 180 nm to 220 nm. When the average grain size is less than 160 nm, there is a problem in that the initial efficiency falls below the target due to the low structural completeness and the initial resistance increases.

[0054] Meanwhile, the positive electrode active material according to the present invention may include a lithium nickel-based transition metal oxide in which the molar ratio of Ni among the total transition metals is 80 mol% or more.

[0055] Meanwhile, the positive electrode active material according to the present invention may include a lithium nickel-based oxide having a composition as shown in Chemical Formula 1 below.

[0056] [Chemical Formula 1]

[0057] Li 1+x Ni a Co b M 1 c M 2 d O2

[0058] In the above chemical formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≤x≤0.50, 0.80≤a<1.00, 0 <b<0.20, 0<c<0.20, 및 0≤d≤0.20일 수 있다.

[0059] The above 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0≤x≤0.50, 0≤x≤0.30, or 0≤x≤0.20.

[0060] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.80≤a<1.00, 0.83≤a<1.00, or 0.86≤a<1.00.

[0061] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b<0.20, 0<b<0.17, 또는 0<b<0.15일 수 있다.

[0062] The above c is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of, 0 <c<0.20, 0<c<0.17, 또는 0<c<0.15일 수 있다.

[0063] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements, which can be 0≤d≤0.20, 0≤d≤0.17, or 0≤d≤0.15.

[0065] Next, each step of the method for manufacturing the positive electrode active material is explained in detail.

[0066] First, the positive active material precursor and the lithium raw material are mixed and then calcined.

[0067] At this time, the above-mentioned positive active material precursor may be a commercially available precursor such as a nickel-cobalt-manganese-based hydroxide, or may be manufactured according to a precursor manufacturing method known in the relevant technical field, such as the co-precipitation method.

[0068] For example, nickel (Ni), cobalt (Co), and M 1 After preparing a transition metal-containing solution containing a cation, an ammonium cation-containing complex-forming agent and a basic aqueous solution are added to the transition metal-containing solution to carry out a co-precipitation reaction, thereby producing a positive electrode active material precursor.

[0069] The above transition metal-containing solution includes a nickel-containing raw material, a cobalt-containing raw material, M 1 It may include a contained raw material, and the above M 1 The contained raw material may be a manganese-containing raw material and / or an aluminum-containing raw material.

[0070] Nickel-containing raw materials may be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and specifically, may be Ni(OH)2, NiO, NiOOH, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, nickel fatty acid salts, nickel halides, or combinations thereof, but are not limited thereto.

[0071] The cobalt-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4, Co(SO4)2ㆍ7H2O or a combination thereof, but is not limited thereto.

[0072] The manganese-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically, manganese oxides such as Mn2O3, MnO2, Mn3O4, etc.; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, manganese fatty acid; manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0073] Aluminum-containing raw materials may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides or combinations thereof.

[0074] The transition metal-containing solution is a nickel-containing raw material, a cobalt-containing raw material, and M 1 It is prepared by adding a containing raw material to a solvent, specifically water, or a mixed solvent of an organic solvent that can be uniformly mixed with water (e.g., alcohol, etc.), or an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material and M 1 It may be manufactured by mixing the contained raw materials.

[0075] The ammonium cation-containing complex-forming agent may be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof, but is not limited thereto. Meanwhile, the ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent.

[0076] Basic compounds may be hydroxides of alkali metals or alkaline earth metals such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Basic compounds may also be used in the form of aqueous solutions, in which case water or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, alcohols, etc.) may be used as the solvent.

[0077] Basic compounds are added to adjust the pH of the reaction solution, and can be added in an amount such that the pH of the metal solution becomes 8 to 12.

[0078] The co-precipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon at a temperature range of 35°C to 80°C.

[0079] Nickel-cobalt-M by the above process 1 Hydroxide cathode active material precursor particles are generated and precipitated in the reaction solution. Nickel-containing raw material, cobalt-containing raw material and M 1 By controlling the concentration of the contained raw materials, a positive active material precursor can be manufactured in which the nickel (Ni) content of the total metal content is 60 mol% or more. The positive active material precursor can be manufactured by separating the precipitated positive active material precursor particles according to a conventional method and drying them.

[0080] Meanwhile, the positive active material precursor prepared as described above is D 50This can be 4.3㎛ to 8.0㎛, preferably 5.0㎛ to 7.5㎛, more preferably 5.5㎛ to 7.0㎛. D of the precursor 50 In cases where this is less than 4.3㎛, D of the positive active material 50 It is highly likely to be smaller than this optimal range, and if it exceeds 8.0㎛, the specific surface area (BET) decreases, which reduces reactivity when mixed with lithium raw materials and may lower the structural completeness of the cathode active material.

[0081] Meanwhile, the above-mentioned positive active material precursor has a specific surface area of ​​1 m² 2 / g to 15m 2 / g, preferably 2m 2 / g to 15m 2 It can be / g. In the present invention, D 50 Using a precursor with a lower specific surface area (BET) can be more advantageous for improving the structural completeness of the cathode active material.

[0082] Afterwards, the positive electrode active material precursor and the lithium raw material can be mixed.

[0083] The above lithium raw material may include lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the above lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and any one or more of these may be used.

[0084] The cathode active material precursor and the lithium raw material may be mixed in a molar ratio of 1:1, 1:1.05, 1:1.10, 1:1.15, or 1:1.20, but are not limited thereto. When the mixing ratio of the metal in the lithium raw material and the cathode active material precursor satisfies the above range, the layered crystal structure of the cathode active material is well developed, and a cathode material with excellent capacity characteristics and structural stability can be manufactured.

[0085] Afterward, the above mixture may be subjected to primary calcination. The primary calcination may be carried out under an air or oxygen atmosphere. The primary calcination is performed under conditions that grow the grains of the positive electrode active material to satisfy the particle size range of the present invention.

[0086] The first firing can be performed at a temperature of 700°C to 1000°C, 800°C to 900°C, or 825°C to 875°C.

[0087] The first firing can be performed for 1 to 15 hours, preferably 6 to 15 hours, and more preferably 10 to 15 hours. In this specification, an oxygen atmosphere refers to an atmosphere containing a sufficient amount of oxygen for firing, including an atmospheric atmosphere. In particular, it is preferable to perform the firing in an atmosphere where the oxygen partial pressure is higher than that of an atmospheric atmosphere.

[0088] It is desirable to perform a grinding process after the above-mentioned calcination to control the particle size distribution to a desired level. At this time, the grinding can be performed using general grinding methods known in the art, such as a ball mill or a jet mill. By performing such a grinding process, the particle size of the cathode active material can be controlled more appropriately.

[0089] Afterwards, the first fired product can be fired a second time. The second firing can be performed at a temperature of 500°C to 1000°C, 600°C to 900°C, or 700°C to 800°C.

[0090] The second firing can be performed for 6 to 18 hours, preferably 8 to 16 hours, and more preferably 10 to 14 hours.

[0091] Meanwhile, M 2 In the case of manufacturing a lithium complex transition metal oxide containing metal, M during the co-precipitation reaction or the calcination step 2 Metal-containing raw materials can be additionally mixed. At this time, the above M 2 Metal-containing raw materials are M 2 It may be metal acetates, carbonates, nitrates, sulfates, halides, sulfides, or oxides.

[0093] As the positive active material has been described above, a detailed explanation is omitted, and only the remaining components are described in detail below.

[0094] The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0095] The above positive active material layer may, together with the positive active material, optionally include a conductive material and a binder as needed.

[0096] At this time, the positive active material may be included in an amount of 80% to 99% by weight, preferably 90% to 98% by weight, based on the total weight of the positive active material layer.

[0097] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.01% to 10% by weight, preferably 0.1% to 9% by weight, and more preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0098] The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0099] The above-described anode can be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it can be manufactured by applying an anode slurry composition, prepared by dissolving or dispersing the above-described anode active material and, if necessary, optionally a binder, a conductive material, and a dispersant in a solvent, onto an anode current collector, and then drying and rolling.

[0100] The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for anode manufacturing thereafter.

[0101] In addition, the anode may also be manufactured by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0102] Meanwhile, the anode according to the present invention may have an initial charge capacity of 242 mAh / g or more, preferably 242 mAh / g to 244 mAh / g.

[0103] Meanwhile, the anode according to the present invention may have an initial efficiency of 87% to 89%, preferably 88% to 89%. When the initial efficiency of the anode according to the present invention satisfies the above range, the lithium precipitation phenomenon is suppressed in a battery composed of a negative electrode to which a silicon-based negative electrode active material is applied, and accordingly, the energy density can be improved.

[0105] lithium secondary battery

[0106] Next, a lithium secondary battery according to the present invention will be described.

[0107] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0108] Additionally, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0109] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0110] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0111] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0112] The above negative electrode active material layer can be disposed on one or both sides of the positive electrode current collector.

[0113] The above negative electrode active material may include a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof.

[0114] The above silicon-based negative electrode active materials include Si and SiOx (0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님) 또는 이들의 조합일 수 있다.

[0115] As the above-mentioned carbon-based negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples may include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon. Furthermore, both low-crystallinity and high-crystallinity carbons may be used as carbonaceous materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0116] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight, preferably 82% to 99% by weight, and more preferably 84% to 99% by weight, based on the total weight of the negative electrode active material layer.

[0117] When a cathode containing the above-described cathode active material is combined with a cathode having an initial efficiency of 87% to 89% as described above, the phenomenon of lithium precipitation on the surface of the cathode is suppressed, thereby enabling the realization of high energy density.

[0118] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically 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 such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0119] The above conductive material is a component for further improving the conductivity of the negative electrode active material and may be included in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0120] The above-mentioned cathode active material layer may be manufactured by applying a cathode slurry composition, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the cathode slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0121] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0122] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0123] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0124] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based 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-based solvents such as ethyl alcohol and isopropyl alcohol; 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 a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0125] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, as the anion of the above lithium salt, 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 - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc. may be used. It is preferable to use the lithium salt within a concentration range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0126] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10.0 weight% based on the total weight of the electrolyte.

[0127] As described above, the lithium secondary battery including the positive electrode according to the present invention has a high charging capacity and thus can achieve high energy density, making it useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0128] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0129] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0130] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0132] Examples and Comparative Examples

[0133] Example 1

[0134] D with a molar ratio of Ni : Co : Mn of 90 : 6 : 4 50 This 4.3㎛ lithium nickel-based transition metal hydroxide precursor and lithium raw material LiOH were mixed such that the molar ratio of transition metal (Ni+Co+Mn) : Li was 1:1, and then first calcined at 850℃ for 4 hours.

[0135] Subsequently, the above first calcined product is secondarily calcined at 790°C for 10 hours to obtain the cathode active material powder LiNi 0.90 Co 0.06 Mn 0.04 O2 was manufactured.

[0136] Example 2

[0137] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 6.06 μm, the first calcination was performed at 850°C for 4 hours, and the second calcination was performed at 790°C for 10 hours.

[0138] Example 3

[0139] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 5.9 μm, the first calcination was performed at 830°C for 12 hours, and the second calcination was performed at 780°C for 12 hours.

[0140] Example 4

[0141] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 5.9 μm, the first calcination was performed at 810°C for 12 hours, and the second calcination was performed at 750°C for 8 hours.

[0142] Example 5

[0143] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 5.5 μm, the first calcination was performed at 810°C for 12 hours, and the second calcination was performed at 750°C for 8 hours.

[0144] Example 6

[0145] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 6.06 μm, the first calcination was performed at 850°C for 4 hours, and the second calcination was performed at 820°C for 9.7 hours.

[0146] Example 7

[0147] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 5.9 μm, the first calcination was performed at 820°C for 7 hours, and the second calcination was performed at 750°C for 8 hours.

[0149] Comparative Example 1

[0150] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 3.5 μm, the first calcination was performed at 830°C for 6 hours, and the second calcination was performed at 780°C for 9 hours.

[0151] Comparative Example 2

[0152] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 9.0 μm, the first calcination was performed at 830°C for 6 hours, and the second calcination was performed at 780°C for 9 hours.

[0153] Comparative Example 3

[0154] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 9.0 μm, the first calcination was performed at 800°C for 6 hours, and the second calcination was performed at 780°C for 9 hours.

[0155] Comparative Example 4

[0156] D of the above lithium nickel-based transition metal hydroxide precursor 50 A positive electrode active material was prepared in the same manner as in Example 1, except that the thickness was 6.06 μm, the first calcination was performed at 850°C for 4 hours, and the second calcination was performed at 790°C for 9.7 hours.

[0158] D of the positive active material of the above-described Examples 1 to 7 and Comparative Examples 1 to 4 50 Crystal strain, cation mixing ratio, and average grain size were measured. The measurement results are shown in [Table 1] below. A graph of the initial charge capacity according to the crystal strain of the cathode active material is shown in Figure 1.

[0160] D 50 can be defined as the particle size at the 50% reference of the volume-cumulative particle size distribution of the positive electrode active material and can be measured using the laser diffraction method. For example, D of the positive electrode active material 50The measurement method involves dispersing particles of the positive electrode active material in a dispersion medium, introducing them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating them with ultrasound at approximately 28 kHz at an output of 60 W, and then D corresponding to 50% of the volume accumulated in the measuring device 50 It can produce.

[0161] Crystal strain, cation mixing ratio, and average grain size can be measured by analyzing XRD data obtained from X-ray diffraction (XRD) analysis by Cu Kα X-rays using the Rietveld refinement method. At this time, the X-ray diffraction analysis was performed by placing the sample into a groove of a general powder holder, smoothing the surface of the sample using a slide glass, and filling the sample so that its height matched the edge of the holder, and then measuring it using an X-ray diffraction analyzer (Bruker D8 Endeavor) (FDS 0.5°, 2θ=15° ~ 90°, Step size=0.02°, total scan time: 20 min). Based on the measured data, Rietveld refinement was performed considering the potential (charge) at each site (metals at transition metal sites +3, Ni at Li sites +2) and cation mixing. Specifically, when analyzing crystal strain, cation mixing ratio, and average grain size, instrumental broadening was considered using the Fundamental Parameter Approach (FPA) built into the Bruker TOPAS program, and all peaks of the measurement range were used during fitting. The peak shape was fitted using only the Lorentzian contribution as the First Principle (FP) among the peak types available in TOPAS.

[0162] D 50 (㎛) Crystal strain (x 10 -6 ) Cation mixing ratio (at%) Average grain size (nm) Example 1 4.67 219 0.7 216 Example 2 4.69 289 1.1 166 Example 3 5.61 296 0.5 259 Example 4 5.64 287 0.3 209 Example 5 5.10 238 0.7 217 Example 6 5.18 308 1.2 185 Example 7 5.61 258 0.7 211 Comparative Example 1 3.96 268 0.7 193 Comparative Example 2 6.89 504 1.1 142 Comparative Example 3 6.80 376 0.9 167 Comparative Example 4 5.01 336 0.7 163

[0163] Experimental Example 1: Evaluation of Initial Charge Capacity and Initial Efficiency

[0164] For lithium secondary battery coin half cells prepared as follows using the positive active materials of Examples 1 to 7 and Comparative Examples 1 to 4 described above, the initial charge capacity and initial efficiency were evaluated after charging to 4.25V at 0.1C in CC-CV mode at 25℃ and discharging to 3.0V at 1.0C. The measurement results are shown in [Table 2] below.

[0165] Specifically, the lithium secondary battery coin half cell was manufactured as follows.

[0166] The positive active material, carbon black conductive material, and PVDF binder prepared in Examples 1 to 7 and Comparative Examples 1 to 4, respectively, were mixed in N-methylpyrrolidone in a weight ratio of 97.0:1.5:1.5 to prepare a pre-dispersion solution having a solid content of 11.2 wt%. Subsequently, the pre-dispersion solution and N-methylpyrrolidone (NMP) were mixed in a weight ratio of 3:1 to prepare a positive slurry. The positive slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0167] The cathode used lithium metal.

[0168] An electrode assembly was manufactured by interposing a separator between the anode and the cathode manufactured as described in the above-described manufacturing example, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a coin half cell. The electrolyte was prepared by dissolving 1M concentration of LiPF6 in a mixed organic solvent mixed in a volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1, and adding 5 wt% of vinylene carbonate (VC).

[0170] Experimental Example 2: Evaluation of High-Temperature Life Characteristics

[0171] For the coin half cell fabricated in Experimental Example 1, the high-temperature life characteristics were evaluated by performing 50 cycles of charge and discharge, with one cycle consisting of charging to 4.25V at 0.5C in CC-CV mode at 45℃ and discharging to 3.0V at 1.0C, and then measuring the capacity retention rate (%). The measurement results are shown in [Table 2] below.

[0172] Initial charge capacity (mAh / g) Initial efficiency (%) High-temperature capacity retention rate (%) Example 1 244.7 88.8 89.53 Example 2 244.3 88.0 89.64 Example 3 244.8 88.2 88.30 Example 4 244.9 88.3 87.71 Example 5 246.6 88.1 89.74 Example 6 243.9 88.3 89.86 Example 7 244.4 88.1 89.90 Comparative Example 1 244.0 90.5 88.68 Comparative Example 2 237.3 85.9 86.92 Comparative Example 3 241.6 86.5 91.13 Comparative Example 4 242.9 89.3 88.77

[0173] Referring to [Table 2] above, it can be seen that the capacity retention rate of the anode containing the anode active material of Examples 1 to 7 and Comparative Examples 1 to 4 is equivalent, but the initial efficiency of the anode containing the anode active material of Examples 1 to 7 is 87% to 89%.

[0174] In other words, when the positive electrode active material according to the present invention is applied, it can be seen that an initial efficiency of a specific range is achieved, and at the same time, the lithium precipitation phenomenon caused by the difference in rate characteristics with the negative electrode using a silicon-based negative electrode active material is controlled, resulting in a high capacity retention rate and improved high-temperature life characteristics.

Claims

Claim 1 It comprises a lithium nickel-based transition metal oxide in at least one form among a single particle consisting of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and D 50 The particle size is 4.5 µm to 6.7 µm, and the crystal strain is 320 x 10⁻⁶ -6 A positive electrode comprising a positive electrode active material of the following magnitude. Claim 2 In claim 1, the positive active material is D 50 This anode is 5.5㎛ to 6.5㎛ in diameter. Claim 3 In claim 1, the positive active material has a crystal strain of 220 x 10 -6 Up to 320 x 10 -6 Phosphorus anode. Claim 4 The positive electrode active material of claim 1 is a positive electrode having a cation mixing ratio of 0.7 at% to 1.2 at%. Claim 5 In claim 1, the positive active material is a positive electrode having an average grain size of 160 nm or more. Claim 6 The anode according to claim 1, wherein the lithium nickel-based transition metal oxide has a molar ratio of Ni of 80 mol% or more among the total transition metals. Claim 7 The anode of claim 1, wherein the lithium nickel-based transition metal oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li 1+x Ni a Co b M 1 c M 2 d In the above chemical formula 1, O2, M 1 is Mn, Al, or a combination thereof, and M 2 is one or more selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 0≤x≤0.50, 0.80≤a<1.00, 0 <b<0.20, 0<c<0.20, 및 0≤d≤0.20임. Claim 8 In claim 1, the anode is an anode having an initial charge capacity of 242 mAh / g or more. Claim 9 In claim 1, the anode is an anode having an initial efficiency of 87% to 89%. Claim 10 A lithium secondary battery comprising the positive electrode; the negative electrode; and the electrolyte of claim 9. Claim 11 A lithium secondary battery according to claim 10, wherein the negative electrode comprises a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof. Claim 12 A lithium secondary battery according to claim 10, wherein the negative electrode comprises a silicon-based negative electrode active material and a carbon-based negative electrode active material. Claim 13 A lithium secondary battery according to claim 10, wherein the lithium secondary battery has a capacity retention rate of 88.8% or more after charging and discharging for 50 cycles, with one cycle comprising charging to 4.25V at 0.5C CCCV at 45℃ and discharging to 3.0V at 1.0C CC.

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