Positive electrode and lithium secondary battery including same

Abstract

The positive electrode according to the present invention may comprise: a lithium nickel-based transition metal oxide having at least one form of a single particle composed of one single node and a pseudo-single particle which is a composite of at most 30 nodes; and a positive electrode active material having a D50 of 4.5 [mu] m to 6.7 [mu] m and a crystal strain of at most 320 * 10 <-6 >.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2022-0181144, filed with the Korean Intellectual Property Office on December 21, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a positive electrode and a lithium secondary battery including the positive electrode, and more particularly, to a negative electrode applying a silicon-based negative electrode active material, an available high-capacity and low-efficiency positive electrode, and a lithium secondary battery including the negative electrode and the positive electrode. Background Art

[0003] Recently, interest in energy storage technology has been increasing, and as the application fields of energy storage technology have expanded to energy in mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts to research and develop electrochemical devices are becoming more specific.

[0004] Among electrochemical devices capable of charge and discharge, there has been increasing interest in the development of secondary batteries. In particular, lithium secondary batteries developed in the early 1990s have received attention due to their high operating voltage and significantly high energy density.

[0005] Recently, as the demand for secondary batteries with high energy density (such as batteries for electric vehicles) has increased, the development of high-voltage secondary batteries operating at high voltages has been actively carried out. In addition, research is being conducted on applying a silicon-based negative electrode active material with excellent capacity to achieve higher capacity.

[0006] The lithium secondary batteries of electric vehicles developed so far mainly use lithium nickel-based oxides as the positive electrode active material. However, when applying lithium nickel-based oxides, limitations such as structural collapse of the positive electrode active material, elution of transition metals, and gas generation occur. In addition, when a silicon-based negative electrode active material is used, there are the following limitations: Since the efficiency of the two electrodes is unbalanced, lithium ions cannot be quickly inserted into the interior of the negative electrode, so an irreversible process of lithium ion precipitation on the surface of the negative electrode occurs, causing a side reaction with the electrolyte solution, generating gas, and deteriorating the room temperature life characteristics. Summary of the Invention

[0007] Technical Problem

[0008] To solve the above limitations, an aspect of the present invention provides a positive electrode and a lithium secondary battery including the positive electrode, the positive electrode having a low initial efficiency to balance with a negative electrode applying a silicon-based negative electrode active material by including a single particle positive electrode active material having a specific range of D 50 and crystal strain.

[0009] Technical Solution

[0010] According to one aspect of the present invention, a positive electrode is provided, which includes: a lithium nickel-based transition metal oxide having at least one of a pseudo-single particle and a single particle composed of a single nodule, the pseudo-single particle being a complex of 30 or fewer nodules; and a positive electrode active material having a D of 4.5 μm to 6.7 μm 50 and 320×10 -6 or less crystal strain.

[0011] The positive electrode active material may have a D of 5.5 μm to 6.5 μm 50 .

[0012] The positive electrode active material may have a strain of 220×10 -6 to 320×10 -6 .

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

[0014] The positive electrode active material may have an average particle size of at least 160 nm.

[0015] In the lithium nickel-based transition metal oxide, the molar ratio of Ni among all transition metals may be 80 mol% or more.

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

[0017] [Formula 1]

[0018] Li 1+x Ni a Co b M 1 c M 2 d O2

[0019] In the above Formula 1, M 1 may be Mn, Al, or a combination thereof, M 2 may be at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, 0 ≤ x ≤ 0.50, 0.80 ≤ a < 1.00, 0 < b < 0.20, 0 < c < 0.20, and 0 ≤ d ≤ 0.20.

[0020] The positive electrode may have an initial charge capacity of at least 242 mAh / g.

[0021] The positive electrode may have an initial efficiency of 87% to 89%.

[0022] According to another aspect of the present invention, there is provided a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte.

[0023] The negative electrode may include a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof.

[0024] The negative electrode may include a silicon-based negative electrode active material and a carbon-based negative electrode active material.

[0025] Taking one cycle as charging at 0.5C until 4.25V in CCCV mode at 45°C and then discharging at 1.0CCC to 3.0V, after performing 50 charge-discharge cycles, the lithium secondary battery may have a capacity retention rate of more than 88.8%.

[0026] Advantageous Effects

[0027] Since each of the positive electrode and the lithium secondary battery according to the present invention includes a positive electrode active material having a single particle with D within a specific range 50 and crystal strain, the initial efficiency can be reduced to balance with the negative electrode using a silicon-based negative electrode active material, and the lithium precipitation phenomenon on the surface of the negative electrode can be controlled, thereby improving the room temperature life characteristics.

[0028] In addition, the lithium precipitation phenomenon caused by the difference in rate performance can be controlled in the positive electrode and the lithium secondary battery according to the present invention, thereby improving the capacity retention rate and the high temperature life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a graph showing the initial charge capacity according to the crystal strain of the positive electrode active material. DETAILED DESCRIPTION

[0030] It will be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary, and it will be further understood that, based on the fact that the inventor can appropriately define the meanings of the words or terms to best explain the principles of the present invention, the words or terms should be construed as having meanings consistent with their meanings in the context of the relevant art and the technical concept of the present invention.

[0031] According to the present invention, a "single particle" is a particle composed of one single nodule. According to the present invention, a "pseudo single particle" refers to a composite particle formed by 30 or fewer nodules.

[0032] According to the present invention, a "nodule" refers to the main body of a particle unit that constitutes a single particle and a pseudo-single particle, and when observed using a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times, the "nodule" can be a single crystal without grain boundaries or a polycrystal without distinct grain boundaries. The average diameter of the nodules can be measured as the arithmetic mean of the diameters of the corresponding nodules measured using a scanning electron microscope (SEM).

[0033] According to the present invention, a "secondary particle" refers to a particle formed by coalescing dozens to hundreds of primary particles, and more specifically, an aggregate of at least 40 primary particles.

[0034] 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.

[0035] According to the present invention, "D 50 " refers to the particle diameter at 50% of the volume cumulative particle size distribution of the positive electrode active material. The D 50 can be measured using a laser diffraction method. For example, the D 50 .

[0036] According to the present invention, the "specific surface area" is measured by the BET method, and specifically, it can be calculated using BELSORP-mino II from BEL Japan, Inc. based on the nitrogen adsorption amount at liquid nitrogen temperature (77K).

[0037] According to the present invention, "crystal strain", "cation mixing ratio", and "average particle size" can be measured by analyzing XRD data obtained from X-ray diffraction analysis of the positive electrode active material powder in the Rietveld refinement method. In this case, after placing the sample powder in the groove of the holder for general powder and using a glass slide to make the surface of the sample powder flat while filling the sample to a height of the sample powder equal to the edge of the holder, an X-ray diffractometer (Bruker D8 endeavor) is used to measure the X-ray diffraction analysis (FDS is 0.5°, 2θ = 15° to 90°, step size = 0.02°, and the total scanning time is 20 minutes). Rietveld refinement is performed on the measured data considering the charge at each site (metal +3 at the transition metal site and Ni +2 at the Li site) and cation mixing. Specifically, during the analysis of crystal strain, cation mixing ratio, and average particle size, the instrumental broadening is considered using the fundamental parameter method (FPA) constructed in the Bruker TOPAS program, and all peaks in the measurement range are used during fitting. The peak shape is FP (First principle) among the peak types available in TOPAS, and only the Lorentzian contribution is used to fit the peak shape.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] Positive electrode

[0040] The positive electrode according to the present invention includes a positive electrode active material. Specifically, the positive electrode includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0041] Hereinafter, the positive electrode active material will be described in detail.

[0042] The positive electrode active material according to the present invention includes a lithium nickel-based transition metal oxide having at least one of a single particle composed of a single nodule and a pseudo-single particle that is a complex of 30 or fewer nodules.

[0043] The lithium nickel-based oxide having a single particle and / or pseudo-single particle form has higher particle strength than the lithium nickel-based oxide having a form of secondary particles in which dozens to hundreds of primary particles coalesce, and thus there is less particle breakage during rolling.

[0044] In addition, since the lithium nickel-based oxide in the form of single particles or pseudo-single particles according to the present invention has a small amount of sub-components (i.e., nodules) constituting the particles, the changes caused by the volume expansion and contraction of the primary particles during charging and discharging are small, and thus the generation of cracks inside the particles is also significantly reduced.

[0045] Specifically, the inventors of the present invention found that when applying a positive electrode active material with a D 50 ranging from 4.5 μm to 6.7 μm and a crystal strain of 320×10 -6 or less, the initial efficiency satisfies 87% to 89%, and thus the lithium precipitation phenomenon can be suppressed in a negative electrode using silicon oxide and a battery constituted by using the negative electrode, and the energy density can be improved.

[0046] The positive electrode active material according to the present invention may have a D 50 ranging from 4.5 μm to 6.7 μm, preferably from 4.5 μm to 6.5 μm, and more preferably from 4.6 μm to 6.0 μm. There are the following limitations: when D 50 is less than 4.5 μm, the room temperature life characteristics deteriorate, and when D 50 is greater than 6.7 μm, the lithium mobility in the positive electrode active material decreases, resulting in an increase in resistance and a decrease in energy density.

[0047] The positive electrode active material according to the present invention has a crystal strain of 320×10 -6 or less, preferably from 220×10 -6 to 320×10 -6 , and more preferably from 230×10 -6 to 310×10 -6 . There are the following limitations: when the crystal strain is greater than 320×10 -6 , the initial efficiency of the positive electrode is equal to or less than a specific range, resulting in a difference in the rate performance with a negative electrode using silicon oxide, and thus a lithium plating phenomenon in which lithium precipitates on the surface of the negative electrode occurs, and the energy density decreases.

[0048] In addition, the positive electrode active material according to the present invention may have a cation mixing ratio of 0.7 at% to 1.2 at%, and preferably 0.7 at% to 1.1 at%. There may be such limitations: when the cation mixing ratio is less than 0.7 at%, the initial efficiency becomes too high due to high structural integrity, and there is such a limitation: when the cation mixing ratio is greater than 1.2 at%, the initial efficiency becomes lower than the target value due to low structural integrity, and the initial resistance increases.

[0049] In addition, the positive electrode active material according to the present invention may have an average particle diameter of 160 nm or more, preferably 160 nm to 220 nm, and more preferably 180 nm to 220 nm. There is such a limitation: when the average particle diameter is less than 160 nm, due to low structural integrity, the initial efficiency becomes lower than the target value, and the initial resistance increases.

[0050] In addition, the positive electrode active material according to the present invention may include a lithium nickel-based transition metal oxide, wherein in the lithium nickel-based transition metal oxide, the molar ratio of Ni among all transition metals is 80 mol% or more.

[0051] In addition, the positive electrode active material according to the present invention may include a lithium nickel-based oxide having the composition of Formula 1 below.

[0052] [Chemical Formula 1]

[0053] Li 1+x Ni a Co b M 1 c M 2 d O2

[0054] In the above Chemical Formula 1, M 1 may be Mn, Al, or a combination thereof, and M 2 may be one or more selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, 0 ≤ x ≤ 0.50, 0.80 ≤ a < 1.00, 0 < b < 0.20, 0 < c < 0.20, and 0 ≤ d ≤ 0.20.

[0055] Among them, 1 + x represents the molar ratio of lithium in the lithium nickel-based oxide, and 0 ≤ x ≤ 0.50, preferably 0 ≤ x ≤ 0.30, and more preferably 0 ≤ x ≤ 0.20.

[0056] a represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide, and 0.80 ≤ a < 1.00, preferably 0.83 ≤ a < 1.00, and more preferably 0.86 ≤ a < 1.00.

[0057] b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide, and 0 < b < 0.20, preferably 0 < b < 0.17, and more preferably 0 < b < 0.15.

[0058] c represents the molar ratio of M 1 among all metals other than lithium in the lithium nickel-based oxide, and 0 < c < 0.20, preferably 0 < c < 0.17, and more preferably 0 < c < 0.15.

[0059] d represents the molar ratio of element M among all metals other than lithium in the lithium nickel-based oxide, and 0 ≤ d ≤ 0.20, preferably 0 ≤ d ≤ 0.17, and more preferably 0 ≤ d ≤ 0.15. 2

[0060] Hereinafter, each step of the method for preparing the positive electrode active material will be specifically described.

[0061] First, after mixing the positive electrode active material precursor and the lithium raw material, a primary firing is performed.

[0062] In this case, a precursor such as a commercially available nickel-cobalt-manganese-based hydroxide is purchased and used as the positive electrode active material precursor, or the positive electrode active material precursor can be prepared according to a method known in the art for preparing precursors (e.g., coprecipitation).

[0063] For example, the positive electrode active material precursor can be prepared by adding an ammonium cation complex former and an aqueous alkaline solution to a transition metal-containing solution containing cations of M 1 , nickel (Ni), and cobalt (Co) to perform a coprecipitation reaction.

[0064] The transition metal-containing solution may include a nickel raw material, a cobalt raw material, and an M 1 raw material, and the M 1 raw material may be a manganese raw material and / or an aluminum raw material.

[0065] The nickel raw material may be, for example, an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, etc. containing nickel, and specifically may be Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0066] The cobalt raw material may be, for example, an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, etc. containing cobalt, and specifically may be Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof, but is not limited thereto.

[0067] ​The manganese-containing raw material can, for example, be an acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide of manganese, or a combination thereof, and specifically can be: manganese oxides such as Mn2O3, MnO2 or Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese salts of dicarboxylic acids, manganese citrate, manganese salts of fatty acids, manganese hydroxide, manganese chloride or a combination thereof, but not limited thereto.

[0068] The aluminum-containing raw material can, for example, be Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halide or a combination thereof.

[0069] The solution containing transition metals can be prepared by adding a nickel-containing raw material, a cobalt-containing raw material and an M 1 raw material to a solvent (specifically, a mixed solvent of water or an organic solvent that can be uniformly mixed with water (such as alcohol, etc.)), or can be prepared by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material and an aqueous solution of an M 1 raw material.

[0070] The ammonium cation complex former can, for example, be NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof, but not limited thereto. In addition, the ammonium cation complex former can be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.) can be used as the solvent.

[0071] The basic compound can be a hydroxide of an alkali metal or an alkaline earth metal, such as NaOH, KOH or Ca(OH)2, its hydrate or a combination thereof. The basic compound can also be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that can be mixed with water (specifically, alcohol, etc.) can be used as the solvent.

[0072] A basic compound can be added to adjust the pH of the reaction solution, and can be added in an amount such that the pH of the metal solution is 8 to 12.

[0073] The coprecipitation reaction can be carried out in a nitrogen atmosphere or an inert atmosphere such as argon in the temperature range of 35 °C to 80 °C.

[0074] Nickel-cobalt-M 1 Precursor particles of the positive electrode active material of nickel-cobalt-M 1The concentration of the raw materials is used to prepare a precursor of a positive electrode active material with a nickel (Ni) content of at least 60 mol% of the total metal content. The precursor of the positive electrode active material can be prepared by separating and drying the precipitated precursor particles of the positive electrode active material in a typical method.

[0075] In addition, the precursor of the positive electrode active material prepared as described above may have a D of 4.3 μm to 8.0 μm, preferably 5.0 μm to 7.5 μm, and more preferably 5.5 μm to 7.0 μm. 50 . When the D of the precursor 50 is less than 4.3 μm, the D of the positive electrode active material 50 is more likely to be less than the appropriate range, and when D 50 is greater than 8.0 μm, due to the decrease in the specific surface area (BET), the reactivity during mixing with the lithium raw material may decrease, thereby possibly reducing the structural integrity of the positive electrode active material.

[0076] In addition, the precursor of the positive electrode active material may have a specific surface area of 1 m 2 / g to 15 m 2 / g, preferably 2 m 2 / g to 15 m 2 / g. According to the present invention, using a precursor with a specific surface area (BET) smaller than D 50 may be more advantageous in improving the structural integrity of the positive electrode active material.

[0077] Thereafter, the precursor of the positive electrode active material and the lithium raw material can be mixed.

[0078] Sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, hydroxyoxides, etc. containing lithium can be used as the lithium raw material, but as long as it is soluble in water, and there is no special limitation on the lithium raw material. Specifically, the lithium raw material can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7, etc., and any one or a mixture of at least two of them can be used.

[0079] The precursor of the positive electrode active material and the lithium raw material can be mixed in a molar ratio of 1:1, 1:1.05, 1:1.10, 1:15, or 1:1.20, but the molar ratio is not limited thereto. When the ratio of the mixed metal in the lithium raw material to the precursor of the positive electrode active material satisfies the above range, the layered crystal structure of the positive electrode active material develops well, so that a positive electrode material with excellent capacity characteristics and structural stability can be prepared.

[0080] Thereafter, the mixture can be fired for the first time. The first firing can be carried out in an air or oxygen atmosphere. The first firing is carried out under conditions that cause the grains of the positive electrode active material to grow to meet the particle size range of the present invention.

[0081] The first firing can be carried out in a temperature range of 700 °C to 1000 °C, preferably 800 °C to 900 °C, and more preferably 825 °C to 875 °C.

[0082] The first firing can be carried out for 1 hour to 15 hours, preferably 6 hours to 15 hours, and more preferably 10 hours to 15 hours. In the present disclosure, the oxygen atmosphere refers not only to the atmospheric atmosphere but also to an atmosphere containing sufficient oxygen for firing. In particular, it is preferably carried out in an atmosphere having a higher oxygen partial pressure than the atmospheric atmosphere.

[0083] After firing, a grinding process is preferably carried out to be controlled to have a desired particle size distribution. In this case, the grinding can be carried out by conventional grinding known in the art (e.g., ball milling, jet milling, etc.). When the above grinding process is carried out, the particle size of the positive electrode active material can be more appropriately controlled.

[0084] Thereafter, the material fired for the first time can be fired for the second time. The second firing can be carried out at a temperature of 500 °C to 1000 °C, preferably 600 °C to 900 °C, and more preferably 700 °C to 800 °C.

[0085] The second firing can be carried out for 6 hours to 18 hours, preferably 8 hours to 16 hours, and more preferably 10 hours to 14 hours.

[0086] In addition, when preparing a lithium composite transition metal oxide containing M 2 metal, a raw material containing M 2 metal is additionally mixed during the coprecipitation process or the firing step. In this case, the raw material containing M 2 metal can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, oxide, etc. of M 2 metal.

[0087] Since the positive electrode active material has been described in detail, its detailed description is omitted, and hereinafter, only the remaining parts of the configuration will be specifically described.

[0088] The positive electrode current collector may include a metal having high electrical conductivity, and is not particularly limited as long as it can be easily joined to the positive electrode active material layer without being reactive within the voltage range of the battery. For example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. can be used as the positive electrode current collector. In addition, the positive electrode current collector generally may have a thickness of 3 μm to 500 μm, and may have high adhesion to the positive electrode active material by forming fine irregularities on its surface. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0089] The positive electrode active material layer, together with the positive electrode active material, may selectively include a conductive material and a binder as needed.

[0090] In this case, the positive electrode active material may be included in an amount of 80% by weight to 99% by weight, and preferably 90% by weight to 99% by weight, based on the total weight of the positive electrode active material layer.

[0091] The conductive material is used to impart electrical conductivity to the electrode and can be used without particular limitation as long as it has electronic conductivity in the constructed battery without causing chemical changes. Graphites such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal carbon black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive polymers such as polyphenylene derivatives, etc. can be specific examples, and one of them can be used alone or a mixture of at least two of them can be used. The conductive material may be included in an amount of 0.01% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, and more preferably 0.1% by weight to 5% by weight, based on the total weight of the positive electrode active material layer.

[0092] The binder is used to attach between the positive electrode active material particles and improve the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is replaced by Li, Na or Ca, various copolymers thereof, etc., and one of them can be used alone or a mixture of at least two of them can be used. Relative to the total weight of the positive electrode active material layer, the binder can be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%.

[0093] The positive electrode can be manufactured by a typical method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by coating a positive electrode slurry composition prepared by dissolving and dispersing the positive electrode active material, and optionally a binder, a conductive material, and a dispersant in a solvent on a positive electrode current collector, and then drying and rolling.

[0094] The solvent can be a solvent commonly used in the art. Dimethyl sulfoxide (DMSO), isopropyl alcohol, N - methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc. can be solvents, and one of them can be used alone, or a mixture of at least two of them can be used. Considering the coating thickness of the slurry and the manufacturing yield, as long as the solvent has a viscosity that can show excellent thickness uniformity when it is coated to manufacture the positive electrode after dissolving and dispersing the positive electrode active material, the conductive material, the binder, and the dispersant, its amount is sufficient.

[0095] In addition, the positive electrode can be manufactured by other methods: casting the positive electrode slurry composition on a separate support, and laminating the film obtained by peeling from the support on the positive electrode current collector.

[0096] In addition, the positive electrode according to the present invention can have an initial charge capacity of at least 242 mAh / g, and preferably 242 mAh / g to 244 mAh / g.

[0097] In addition, the positive electrode according to the present invention can have an initial efficiency of 87% to 89%, and preferably 88% to 89%. When the initial efficiency of the positive electrode according to the present invention satisfies the above range, the lithium precipitation phenomenon can be suppressed in the negative electrode using the silicon - based negative electrode active material and the constituted battery, thereby improving the energy density.

[0098] Lithium secondary battery

[0099] Next, a lithium secondary battery according to the present invention will be described.

[0100] The lithium secondary battery specifically includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as that described above, its detailed description is omitted, and hereinafter, only the remaining configurations will be specifically described.

[0101] In addition, the lithium secondary battery may selectively further include a battery case for accommodating an electrode assembly composed of a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery case.

[0102] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0103] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes to the battery. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel treated with carbon, nickel, titanium, silver, etc. on the surface, aluminum-cadmium alloy, etc. can be used as the negative electrode current collector. In addition, the negative electrode current collector usually may have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, the adhesion of the negative electrode active material can be strengthened by forming fine irregularities on the surface of the current collector. For example, the negative electrode current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric.

[0104] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0105] The negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector.

[0106] The negative electrode active material may include a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof.

[0107] The silicon-based negative electrode active material may be Si, SiO x (0 < x < 2), an Si-Q alloy (Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and Q is not Si), or a combination thereof.

[0108] The carbon-based negative electrode active material can be a compound capable of reversibly inserting and extracting lithium. Carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon can be specific examples thereof. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbonaceous materials. Soft carbon and hard carbon are representatives of low-crystalline carbon, and amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microspheres, mesophase pitch, and carbon subjected to high-temperature heat treatment such as coke derived from petroleum or coal tar pitch are representatives of high-crystalline carbon.

[0109] Relative to the total weight of the negative electrode active material layer, the negative electrode active material can 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.

[0110] When the negative electrode containing the negative electrode active material is combined with the positive electrode having the above initial efficiency of 87% to 89%, the lithium precipitation phenomenon can be suppressed on the surface of the negative electrode, thereby achieving a high energy density.

[0111] The binder is a component that helps the adhesion between the conductive material, the active material, and the current collector, and is generally added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of the binder can be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluorine-containing elastomers, and various copolymers thereof.

[0112] The conductive material is a component for further improving the conductivity of the negative electrode active material, and can 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 relative to the total weight of the negative electrode active material layer. As long as it has conductivity and does not cause chemical changes in the battery, the conductive material is not particularly limited. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal carbon black; conductive fibers such as carbon fiber or metal fiber; carbon fluoride; metal powders 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, etc. can be used as the conductive material.

[0113] The negative electrode active material layer can be manufactured by coating a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent on a negative electrode current collector and drying, or can be manufactured by laminating a film obtained by casting a negative electrode slurry composition on a separate support and then peeling it off from the support on the negative electrode current collector.

[0114] In addition, in a lithium secondary battery, a separator separates the negative electrode and the positive electrode and provides a movement path for lithium ions. As long as it is used as a separator in a typical lithium secondary battery, it can be used as a separator without special limitations, and in particular, it is preferably a separator having a low resistance to ion movement in an electrolyte and having excellent electrolyte wetting ability. Specifically, for example, a porous polymer film prepared from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a stacked structure of at least two layers thereof can be used. In addition, a typical porous nonwoven fabric, for example, a nonwoven fabric made of polyethylene terephthalate fibers, glass fibers having a high melting point, etc. can be used. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and the separator can be selectively used as a single-layer or multi-layer structure.

[0115] In addition, the electrolyte used in the present invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used to manufacture a lithium secondary battery, but is not limited thereto.

[0116] Specifically, the electrolyte can include an organic solvent and a lithium salt.

[0117] As long as it is used as a medium for ions involved in an electrochemical reaction capable of moving a battery, organic solvents can be used without particular limitation. Specifically, ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene or fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol-based solvents such as ethanol or isopropyl alcohol; nitriles such as R-CN (R is a hydrocarbon group having a linear, branched, or cyclic structure with 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; sulfolane, etc. can be used as organic solvents. Among them, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate-based compound having a high ionic conductivity and a high dielectric constant to improve the charge-discharge performance of the battery (for example, ethylene carbonate or propylene carbonate) and a linear carbonate-based compound having a low viscosity (for example, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferred.

[0118] As long as it is a compound capable of providing lithium ions used in a lithium secondary battery, lithium salts can be used without particular limitation. Specifically, the anion of the lithium salt can be selected from F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N -At least one of the group consisting of, etc., and LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used as the lithium salt. A lithium salt with a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M is preferably used. Since when the concentration of the lithium salt is included within the above range, the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

[0119] In addition to the above electrolyte components, for example, at least one additive can also be included in the above electrolyte, such as a compound based on a halogenated alkylene carbonate, such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol dimethyl ether, triamide hexanoate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidinone, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc., to improve the life characteristics of the battery, inhibit the reduction of the battery capacity, increase the discharge capacity of the battery, etc. In this case, the additive can be included in an amount of 0.1 wt% to 10.0 wt% based on the total weight of the electrolyte.

[0120] As described above, the lithium secondary battery including the positive electrode according to the present invention has a high charging capacity to achieve a high energy density, and thus can be used in portable devices such as mobile phones, laptop computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

[0121] Therefore, according to another embodiment of the present invention, there is provided a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module.

[0122] The battery module and the battery pack can be used as a medium to large-sized device power source for at least any one of power tools, electric vehicles including electric vehicles (HV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV), and systems for storing electric power.

[0123] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0124] Examples and comparative examples

[0125] Example 1

[0126] Mix a lithium nickel-based transition metal hydroxide precursor with a molar ratio of Ni:Co:Mn of 90:6:4 and D 50 of 4.3 μm and a lithium raw material LiOH so that the molar ratio of transition metal (Ni + Co + Mn):Li is 1:1, and then initially fire the mixture at 850 °C for 4 hours.

[0127] After that, secondarily fire the initially fired product at 790 °C for 10 hours to prepare a positive electrode active material powder of LiNi 0.90 Co 0.06 Mn 0.04 O2.

[0128] Example 2

[0129] Prepare the positive electrode active material using the same method as in Example 1 above, except that the D 50 of the lithium nickel-based transition metal hydroxide precursor is 6.06 μm, the first firing is carried out at 850 °C for 4 hours, and the second firing is carried out at 790 °C for 10 hours.

[0130] Example 3

[0131] Prepare the positive electrode active material using the same method as in Example 1 above, except that the D 50 of the lithium nickel-based transition metal hydroxide precursor is 5.9 μm, the first firing is carried out at 830 °C for 12 hours, and the second firing is carried out at 780 °C for 12 hours.

[0132] Example 4

[0133] Prepare the positive electrode active material using the same method as in Example 1 above, except that the D 50 of the lithium nickel-based transition metal hydroxide precursor is 5.9 μm, the first firing is carried out at 810 °C for 12 hours, and the second firing is carried out at 750 °C for 8 hours.

[0134] Example 5

[0135] Prepare the positive electrode active material using the same method as in Example 1 above, except that the D 50 of the lithium nickel-based transition metal hydroxide precursor is 5.5 μm, the first firing is carried out at 810 °C for 12 hours, and the second firing is carried out at 750 °C for 8 hours.

[0136] Example 6

[0137] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 6.06 μm, the first firing was carried out at 850 °C for 4 hours, and the second firing was carried out at 820 °C for 9.7 hours.

[0138] Example 7

[0139] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 5.9 μm, the first firing was carried out at 820 °C for 7 hours, and the second firing was carried out at 750 °C for 8 hours.

[0140] Comparative example 1

[0141] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 3.5 μm, the first firing was carried out at 830 °C for 6 hours, and the second firing was carried out at 780 °C for 9 hours.

[0142] Comparative example 2

[0143] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 9.0 μm, the first firing was carried out at 830 °C for 6 hours, and the second firing was carried out at 780 °C for 9 hours.

[0144] Comparative example 3

[0145] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 9.0 μm, the first firing was carried out at 800 °C for 6 hours, and the second firing was carried out at 780 °C for 9 hours.

[0146] Comparative example 4

[0147] The positive electrode active material was prepared by the same method as in Example 1 above, except that the D of the lithium nickel-based transition metal hydroxide precursor 50 was 6.06 μm, the first firing was carried out at 850 °C for 4 hours, and the second firing was carried out at 790 °C for 9.7 hours.

[0148] According to the D of the positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 described above 50, the crystal strain and the average particle size were measured. The measurement results are shown in [Table 1] below. In Figure 1 A graph of the initial charge capacity according to the crystal strain of the positive electrode active material is shown.

[0149] D 50 can be defined as the particle size corresponding to 50% of the volume cumulative particle size distribution of the positive electrode active material, and can be measured using a laser diffraction method. For example, the D of the positive electrode active material 50 can be measured as follows: After dispersing the positive electrode active material particles in a dispersant, the particle size corresponding to 50% of the volume cumulative amount in the measuring device is obtained, introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves with a frequency of about 28 kHz are irradiated at an output power of 60 W.

[0150] The crystal strain, cation mixing ratio, and average particle size can be measured by analyzing the XRD data obtained by X-ray diffraction analysis using Cu K α X-rays in the Rietveld refinement method. In this case, after placing the sample powder in the groove of the holder for general powder and using a glass slide to fill the groove so that the surface of the sample powder is flat while the height of the sample powder is equal to the edge of the holder, an X-ray diffractometer (Bruker D8 Endeavor) is used to measure the X-ray diffraction analysis (FDS is 0.5°, 2θ = 15° to 90°, step size = 0.02°, total scan time is 20 minutes). Rietveld refinement is performed on the measured data considering the charge at each site (metal +3 at the transition metal site and Ni+2 at the Li site) and cation mixing. Specifically, during the analysis of the crystal strain, cation mixing ratio, and average particle size, the instrumental broadening is considered using the fundamental parameter method (FPA) constructed in the Bruker TOPAS program, and all peaks in the measurement range are used during fitting. The peak shape is FP (First principle) among the peak types available in TOPAS, and only the Lorentzian contribution is used to fit the peak shape.

[0151] [Table 1]

[0152]

[0153] Experimental example 1: Evaluation of initial charge capacity and initial efficiency

[0154] The lithium secondary battery button half-cells fabricated using the cathode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 above were charged at 0.1C to 4.25V in a CC-CV mode at 25°C and discharged at 1.0C to 3.0V to evaluate the initial charge capacity and initial efficiency. The measurement results are shown in [Table 2] below.

[0155] Specifically, the lithium secondary battery button half-cells were fabricated as follows.

[0156] A linear dispersion with a solid content of 11.2 wt% was fabricated by mixing the cathode active materials, carbon black conductive material, and PVDF binder with a weight ratio of 97.0:1.5:1.5 prepared in Examples 1 to 7 and Comparative Examples 1 to 4 above in N-methylpyrrolidone. Thereafter, a cathode paste was prepared by mixing the linear dispersion and N-methylpyrrolidone (NMP) at a weight ratio of 3:1. The cathode was fabricated by coating the cathode paste on one surface of an aluminum current collector, drying at 130°C, and rolling.

[0157] Lithium metal was used as the anode.

[0158] The button half-cells were fabricated by inserting a separator between the cathode and anode fabricated similarly to the above manufacturing examples, placing the electrode assembly in a battery case, and injecting an electrolyte into the case. The electrolyte was fabricated by dissolving 1M LiPF6 in a mixed organic solvent and adding 5 wt% vinylene carbonate (VC), in which ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1.

[0159] Experimental example 2: Evaluation of high-temperature life characteristics

[0160] The high-temperature life characteristics were evaluated by measuring the capacity retention rate (%) of the button half-cells fabricated in Experimental Example 1 after performing 50 charge-discharge cycles, where each cycle included charging at 0.5C to 4.25V at 45°C in a CC-CV mode, followed by discharging at 1.0C to 3.0V. The measurement results are shown in [Table 2] below.

[0161]

Table 2

[0162]

[0163] Referring to the above [Table 2], it can be confirmed that the capacity retention rates of the positive electrodes including the positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 4 are equal, but the initial efficiency of the positive electrodes including the positive electrode active materials of the above Examples 1 to 7 is 87% to 89%. That is to say, it can be seen that when applying the positive electrode active material according to the present invention, it is possible to achieve an initial efficiency within a specific range, and at the same time, it is possible to control the lithium precipitation phenomenon caused by the difference in rate performance from the negative electrode using a silicon-based negative electrode active material, thereby improving the capacity retention rate and the high-temperature life characteristics.

Claims

1. A positive electrode, the positive electrode comprising: A lithium nickel-based transition metal oxide having at least one of a pseudo-single particle and a single particle composed of a single nodule, the pseudo-single particle being a complex of 30 or fewer nodules; and A positive electrode active material having a D of 4.5 μm to 6.7 μm 50 and 320×10 -6 or less crystal strain.

2. The positive electrode according to claim 1, wherein, The positive electrode active material has a D of 5.5 μm to 6.5 μm 50 .

3. The positive electrode according to claim 1, wherein, The positive electrode active material has a crystal strain of 220×10 -6 to 320×10 -6 .

4. The positive electrode according to claim 1, wherein, The positive electrode active material has a cation mixing ratio of 0.7 at% to 1.2 at%.

5. The positive electrode according to claim 1, wherein, The positive electrode active material has an average particle size of more than 160 nm.

6. The positive electrode according to claim 1, wherein, In the lithium nickel-based transition metal oxide, the molar ratio of Ni among all transition metals is 80 mol% or more.

7. The positive electrode according to 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 O2 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, 0 ≤ x ≤ 0.50, 0.80 ≤ a < 1.00, 0 < b < 0.20, 0 < c < 0.20, and 0 ≤ d ≤ 0.

20.

8. The positive electrode according to claim 1, wherein, The positive electrode has an initial charge capacity of at least 242 mAh / g.

9. The positive electrode according to claim 1, wherein, The positive electrode has an initial efficiency of 87% to 89%.

10. A lithium secondary battery, the lithium secondary battery comprising: The positive electrode according to claim 9 above; A negative electrode; And An electrolyte.

11. The lithium secondary battery according to claim 10, wherein, The negative electrode includes a silicon-based negative electrode active material, a carbon-based negative electrode active material, or a combination thereof.

12. The lithium secondary battery according to claim 10, wherein, The negative electrode includes a silicon-based negative electrode active material and a carbon-based negative electrode active material.

13. The lithium secondary battery according to claim 10, wherein, Taking charging at 0.5C until 4.25V in the CCCV mode at 45°C and then discharging at 1.0CCC to 3.0V as one cycle, after performing 50 cycles of charge and discharge, the lithium secondary battery has a capacity retention rate of more than 88.8%.

Images