Positive electrode active material, positive electrode slurry containing the same, positive electrode, and lithium secondary battery

Abstract

The present invention provides a positive electrode active material comprising a lithium nickel-based oxide containing nickel, cobalt, and manganese, wherein the nickel content among the metals other than lithium is 90 mol% or more, and a metallic element M1 doped into the lithium nickel-based oxide, wherein the metallic element M1 is one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, and the absolute value of the zeta potential measured at room temperature is 30 mV or more, a positive electrode containing the positive electrode active material, a positive electrode slurry, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2023-0105931 dated August 11, 2023, and Korean Patent Application No. 10-2024-0008351 dated January 18, 2024, and all content disclosed in the documents of the said Korean patent applications is incorporated herein by reference.

[0002] This invention relates to a positive electrode active material, a positive electrode slurry containing the same, a positive electrode, and a lithium secondary battery. [Background technology]

[0003] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for rechargeable batteries that are small, lightweight, and relatively high-capacity has been rapidly increasing. In particular, lithium-ion batteries are lightweight and have high energy density, making them a popular power source for portable electronic devices. Small lithium-ion batteries used in such portable electronic devices are required to have high energy density and excellent battery performance under high temperature and high voltage conditions. Therefore, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] Generally, a lithium secondary battery includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, and an electrolyte impregnating the electrode assembly. The positive and negative electrodes can be manufactured by coating a current collector with an electrode slurry in which an active material, a binder, and a conductive material are dispersed in a solvent.

[0005] Here, in the electrode slurry, aggregation of particles may occur due to the van der Waals force acting between the active materials or between the active material and the conductive material and / or binder. Such aggregation of particles leads to gelation of the slurry, whereby the electrode active material layer cannot be formed uniformly, the internal resistance of the electrode increases, and the capacity may decrease. This ultimately causes deterioration of the battery life and reduction of stability. In severe cases of slurry gelation, it may even become impossible to fabricate the electrode from the beginning.

[0006] In particular, when using lithium nickel cobalt manganese oxide (hereinafter referred to as NCM oxide) as the active material, increasing the nickel content for high capacity realization may make it more vulnerable to such slurry gelation problems, and it is necessary to develop a technology that can simultaneously solve the problems of capacity improvement and slurry gelation.

Summary of the Invention

Problems to be Solved by the Invention

[0011] Furthermore, the present invention provides a lithium secondary battery comprising the above-described positive electrode, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0012] The positive electrode active material according to the present invention has excellent capacity due to its high nickel content, which in turn reduces the amount of cobalt used, making it advantageous in terms of material supply and demand and price.

[0013] Furthermore, by including metallic elements with higher oxidation states than the transition metals contained in the lithium nickel oxide base material as doping elements, it is possible to increase the repulsive force between particles by exhibiting a zeta potential of 30 mV or higher.

[0014] This effectively solves the problems of surface instability and reduced dispersibility inherent in high-nickel cathode active materials, prevents the aforementioned problem of cathode slurry gelation, and ultimately enables the realization of lithium secondary batteries with advantageous capacity and lifespan characteristics. [Brief explanation of the drawing]

[0015] [Figure 1] This graph shows the viscosity increase rate of the positive electrode slurry containing the positive electrode active material produced in the examples and comparative examples. [Modes for carrying out the invention]

[0016] The present invention will be described in detail below.

[0017] In this invention, "Zeta potential" is an index indicating the degree of surface charge possessed by positive electrode active material particles. The positive electrode active material to be measured can be diluted and dissolved in N-methyl-2-pyrrolidone (NMP) at 0.002% by weight, and then measured at 25°C using a Zetasizer Pro (Malvern Panalytical) instrument.

[0018] In this invention, "viscosity" can be measured by immersing the spindle of a type B viscometer in the slurry to be measured and rotating it at 12 rpm for 3 minutes.

[0019] In this invention, "primary particle" refers to a particle unit that, when observed using a scanning electron microscope at a field of view of 5,000x to 20,000x, does not appear to have a grain boundary.

[0020] In the present invention, "D 50 "50% of the volume cumulative particle size distribution of the powder being measured" refers to the particle size corresponding to 50% of the volume cumulative particle size distribution, and can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S-3500), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph is obtained. The particle size at the point where the volume cumulative amount is 50% in the obtained graph can then be determined to measure it.

[0021] The various components of the present invention will be described in more detail below.

[0022] <Cathode active material> This invention relates to a positive electrode active material, specifically a positive electrode active material for lithium secondary batteries.

[0023] The positive electrode active material of the present invention comprises a lithium nickel-based oxide containing nickel, cobalt, and manganese, wherein the nickel content among the metals other than lithium is 90 mol% or more, and a metal element M1 doped into the lithium nickel-based oxide, wherein the metal element M1 is one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, and the positive electrode active material has an absolute value of 30 mV or more of zeta potential measured at room temperature.

[0024] As mentioned above, while increasing the nickel content in lithium nickel oxides can ensure high capacity, it also leads to a decrease in structural stability. Specifically, high-nickel cathode active materials have a large amount of lithium compounds remaining on the surface, which can cause side reactions during the charge-discharge process and generate gas. Furthermore, basic substances such as LiOH among the residual lithium compounds raise the pH of the cathode active material, which can cause cross-linking reactions of the binder in the cathode slurry, leading to slurry gelation. When the slurry gels, not only does the viscosity increase and processability decrease, but uniform coating is not achieved, potentially degrading the performance of the electrode itself.

[0025] Therefore, the inventors have resolved the above-mentioned problems by clarifying the correlation between doping elements and zeta potential in an ultra-high nickel cathode active material having a nickel content of 90 mol% or more, and by providing a cathode active material in which the zeta potential is 30 mV or more due to doping.

[0026] Specifically, in nickel-cobalt-manganese oxides with a Ni content of 90 mol% or more, Ni has an oxidation state of +2 to +3. However, when Al, which has an oxidation state of +3, is used as a doping element, Ni is replaced by Al, which has a higher oxidation state than Ni, resulting in oxygen deficiency. As a result, oxygen vacancies decrease in order to maintain charge neutrality, and the zeta potential becomes an even larger negative value. Thus, an increase in the absolute value of the zeta potential strengthens the repulsive force between positive electrode active material particles, improving dispersibility and ultimately preventing gelation of positive electrode slurries containing high-nickel positive electrode active materials. Similarly, when Ti (+4), Zr (+4), W (+6), Mo (+5), and Nb (+5), which have high oxidation states, are used as doping elements, the same effect is achieved through a mechanism of substitution with Ni or Co atoms.

[0027] In one embodiment of the present invention, the positive electrode active material may have an absolute value of zeta potential of 35 mV or more, preferably 40 mV or more, and more preferably 45 mV or more, as measured at room temperature. However, considering practical feasibility, it may be 60 mV or less.

[0028] In one embodiment of the present invention, the metal element M1 can be one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, preferably Al, Ti, or a combination thereof, and more preferably Al.

[0029] On the other hand, the metal element M1 can be included in an amount of 3,000 ppm to 10,000 ppm, preferably 6,000 ppm to 10,000 ppm, and more preferably 8,000 ppm to 10,000 ppm, relative to the total weight of the positive electrode active material. When the M1 content is 3,000 ppm or more, it is easy to adjust the absolute value of the zeta potential to 30 mV or more by the mechanism described above. However, since the capacity decreases as the M1 content increases, it is preferable that it be 10,000 ppm or less.

[0030] The content of the metallic element M1 in the positive electrode active material can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0031] When the nickel content of the aforementioned lithium nickel oxide is less than 90 mol% of all metals other than lithium, a stable structure is already formed due to the relatively high cobalt content, and the effect of doping with M1 is minimal.

[0032] Furthermore, if the lithium nickel oxide does not contain manganese, the oxidation state of nickel is +3, and the effect of substituting Al, which also has an oxidation state of +3, on oxygen deficiency and the increase in the absolute value of the zeta potential is minimal, making it difficult to achieve the effects intended in this invention.

[0033] In one embodiment of the present invention, the lithium nickel oxide may have a nickel content of 92 mol% or more, preferably 93 mol% or more, and more preferably 95 mol% to 99 mol% of all metals other than lithium.

[0034] In one embodiment of the present invention, the lithium nickel oxide may have a manganese content of 0.5 mol% or more, preferably 0.8 mol% or more, and more preferably 1.0 mol% or more, among all metals other than lithium, but may be 5.0 mol% or less.

[0035] Specifically, the lithium nickel oxide may have the composition of the following chemical formula 1.

[0036] [Chemical formula 1] Li 1+x (Ni a Co b Mn c M1 d M2e )O2

[0037] In the chemical formula 1, M1 is one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, M2 is one or more selected from the group consisting of Cu, Fe, V, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Mg, and B, 1 + x, a, b, c, d, and e are atomic fractions of independent elements, -0.2 ≤ x ≤ 0.2, 0.90 ≤ a < 1, 0 < b < 0.1, 0 < c < 0.1, 0 < d ≤ 0.05, 0 ≤ e ≤ 0.05, and a + b + c + d + e = 1.

[0038] The 1 + x represents the molar ratio of lithium in the lithium nickel-based oxide, and it can be -0.1 ≤ x ≤ 0.2 or 0 ≤ x ≤ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0039] The a represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide, and it can be 0.92 ≤ a < 1, 0.93 ≤ a < 1, or 0.95 ≤ a < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and enables the realization of a high capacity.

[0040] The b represents the cobalt molar ratio among all metals other than lithium in the lithium nickel-based oxide, and it can be 0 < b ≤ 0.025, 0 < b ≤ 0.015, or 0 < b ≤ 0.01. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0041] c represents the molar ratio of manganese among all metals other than lithium in the lithium nickel-based oxide, and can be 0 < c ≤ 0.050, 0.005 ≤ c ≤ 0.040, or 0.010 ≤ c ≤ 0.035. When the molar ratio of manganese satisfies the above range, the structural stability of the positive electrode active material is excellent.

[0042] d represents the molar ratio of the M1 element among all metals other than lithium in the lithium nickel-based oxide, and d can be 0 < d ≤ 0.045, 0.020 ≤ d ≤ 0.040, or 0.030 ≤ d ≤ 0.040.

[0043] e represents the molar ratio of the M2 element among all metals other than lithium in the lithium nickel-based oxide, and can be adjusted as needed.

[0044] In one embodiment of the present invention, when the positive electrode active material is mixed with a binder and a conductive material in a solvent to produce a positive electrode slurry, the viscosity increase rate according to the following formula 1 can be 100% or less.

[0045] [Formula 1] Viscosity increase rate = (V1 - V0) / V0 × 100 (%)

[0046] In the above formula 1, V0 is the viscosity of the positive electrode slurry measured at room temperature immediately after production, V1 is the viscosity of the positive electrode slurry measured after storage for 24 hours under the conditions of room temperature and a relative humidity of 10% or less.

[0047] Specifically, the viscosity increase rate of the positive electrode active material according to the above formula 1 can be 80% or less, preferably 60% or less, and more preferably 40% or less. As described above, since the positive electrode active material according to the present invention has a zeta potential of 30 mV or more, it has excellent dispersibility, and thus can exhibit a low viscosity increase rate.

[0048] On the other hand, the positive electrode active material can be in the form of secondary particles in which a large number of primary particles are aggregated, and the D of the positive electrode active material50 The particle size can be between 2.5 μm and 20 μm, but is not limited to this range.

[0049] <Method for manufacturing positive electrode active material> On the other hand, the method for producing the positive electrode active material includes the steps of supplying a transition metal-containing solution containing a transition metal precursor, an ammonium cation complex-forming agent, and a basic compound to a reactor and causing a coprecipitation reaction to form a nickel transition metal precursor having a nickel content of 90 mol% or more, The process includes the steps of mixing the nickel transition metal precursor, the lithium raw material, and the precursor containing the metal element M1, and heat-treating the mixture to form a lithium nickel oxide doped with the metal element M1. Here, the heat treatment can be carried out at 600°C to 900°C, preferably 650°C to 850°C, and more preferably 700°C to 800°C for 15 to 24 hours.

[0050] The positive electrode active material produced by the above manufacturing method has an absolute value of 30 mV or higher for its zeta potential, as measured at room temperature.

[0051] The step of forming the nickel transition metal precursor can be carried out, for example, by dissolving each transition metal precursor in a solvent to produce a transition metal-containing solution, then mixing the transition metal-containing solution, an ammonium cation complex-forming agent, and a basic compound, and finally performing a coprecipitation reaction. Furthermore, if necessary, an oxidizing agent or oxygen gas may be added during the coprecipitation reaction.

[0052] On the other hand, the transition metal precursor can be an acetate, carbonate, nitrate, sulfate, halide, or sulfide of each transition metal.

[0053] Specifically, the nickel precursor can be one or more selected from the group consisting of NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, and nickel sulfide. The cobalt precursor can be one or more selected from the group consisting of Co(OH)2, Co3SO4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, and Co(SO4)2·7H2O. The manganese precursor can be one or more selected from the group consisting of Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, and manganese sulfide.

[0054] On the other hand, the lithium raw material can be an oxide, hydroxide, oxyhydroxide, halide salt, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing lithium. More specifically, the lithium raw material can be one or more selected from the group consisting of Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, Li2O, Li2SO4, CH3COOLi, and Li3C6H5O7.

[0055] Here, the amount of each transition metal precursor added can be determined by considering the molar ratio of the transition metal in the cathode active material that is ultimately to be produced.

[0056] On the other hand, the ammonium cation complex-forming agent may contain at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and the compound may be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent may be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0057] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and the compound can be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent can be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0058] As described above, when a transition metal-containing solution, an ammonium cation complex-forming agent, and a basic compound are added to a reactor and stirred, the transition metal in the transition metal-containing solution co-precipitates, generating precursor particles in the form of transition metal hydroxides.

[0059] Here, the transition metal-containing solution, the ammonium cation complex-forming agent, and the basic compound are added in amounts such that the pH of the reaction solution falls within the desired range.

[0060] Once the precursor particles are formed by the method described above, they are separated from the reaction solution to obtain the precursor. For example, the reaction solution can be filtered to separate the precursor, and then the separated precursor can be washed with water and dried to obtain the precursor. Here, if necessary, steps such as grinding and / or classification may be performed.

[0061] The nickel transition metal precursor produced in this manner is mixed with a lithium raw material and a precursor containing the metal element M1, and then heat-treated to produce a lithium nickel oxide.

[0062] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0063] On the other hand, the lithium raw material and the nickel transition metal precursor can be mixed such that the molar ratio of Li to total metal in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium raw material and the metal in the precursor satisfies the above range, the layered crystal structure of the lithium nickel oxide develops well, and a positive electrode active material with excellent capacitance characteristics and structural stability can be produced.

[0064] Furthermore, the precursor containing the metal element M1 may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing the metal element M1.

[0065] When doping with additional metal element M2, the type and amount of metal element M2 added can be adjusted considering the type and content of metal element M2 contained in the positive electrode active material described above.

[0066] <Positive electrode slurry> Next, the positive electrode slurry according to the present invention will be described.

[0067] The positive electrode slurry according to the present invention comprises the positive electrode active material, binder, conductive material, and solvent described above.

[0068] In one embodiment of the present invention, the positive electrode slurry may have a solid content of 70% by weight or more and a viscosity of 3,500 cP or less relative to the total weight of the positive electrode slurry. That is, by including the positive electrode active material, it is possible to ensure a solid content above a predetermined level without excessively increasing the viscosity, thereby ensuring both the capacity and processability of the positive electrode. A higher solid content in the slurry is preferable in that it suppresses binder migration and improves electrode productivity, but it is preferable that the solid content be 80% by weight or less to prevent the viscosity from becoming too high. However, in the case of a dry electrode, the solid content may be 100% by weight.

[0069] On the other hand, the viscosity of the positive electrode slurry can be 3,500 cP or less, preferably 3,000 cP or less, and more preferably 2,500 cP or less, taking into consideration the ease of slurry transfer and coating processability. However, considering slurry precipitation and phase stability, it is preferable that the viscosity be 500 cP or more.

[0070] In one embodiment of the present invention, the binder can be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and is preferably polyvinylidene fluoride.

[0071] The binder can be included in the positive electrode slurry in an amount of 0.5% to 3.0% by weight, preferably 1.0% to 2.5% by weight, and more preferably 1.5% to 2.5% by weight, relative to the total weight of the solid content. When the binder content is within this range, sufficient adhesion to the current collector and interparticle bonding can be ensured, improving the durability of the positive electrode and maintaining a low initial resistance.

[0072] The conductive material can be one or more selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, carbon fibers, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. Preferably, it can be carbon nanotubes or carbon black, and most preferably, carbon nanotubes.

[0073] The conductive material can be included in the positive electrode slurry in an amount of 0.1% to 2.5% by weight, preferably 0.3% to 2.0% by weight, and more preferably 0.5% to 2.0% by weight, relative to the total weight of the solids. When the content of the conductive material is within the above range, it is preferable in that it is possible to maintain conductivity between the active materials and reduce dead volume.

[0074] In addition, the positive electrode slurry may further selectively contain a dispersant, which may be hydrogenated nitrile butadiene rubber (HNBR).

[0075] On the other hand, the solvent for the positive electrode slurry can be a solvent commonly used in the art, such as N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethylformamide (DMF), acetone, water, or a mixture of two or more of these. The solvent can be used in an amount that gives the positive electrode slurry the viscosity described above.

[0076] <Positive electrode> Furthermore, the positive electrode according to the present invention includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material described above. Furthermore, the positive electrode according to the present invention includes a positive electrode active material layer formed by coating at least one surface of the positive electrode current collector with the positive electrode slurry described above.

[0077] Since the positive electrode active material and positive electrode slurry have been described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0078] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on its surface to enhance adhesion to the positive electrode active material. It can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0079] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except for using the positive electrode material described above. Specifically, it can be manufactured by applying the positive electrode slurry onto a positive electrode current collector, then drying and rolling it, or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0080] Lithium-ion rechargeable battery Next, the lithium secondary battery according to the present invention will be described.

[0081] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode is as described above, and specific description thereof is omitted. Hereinafter, only the remaining configurations will be specifically described.

[0082] Further, the lithium secondary battery can selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0083] In the lithium secondary battery, the negative electrode can include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0084] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Further, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven bodies, etc.

[0085] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0086] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; SiO βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. The negative electrode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0087] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually 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 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.

[0088] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, 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, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0089] The negative electrode active material layer can be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode composite material onto another support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0090] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0091] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0092] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0093] The organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0094] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is 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 - The lithium salt can be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 4.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0095] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride. Here, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0096] As described above, lithium secondary batteries containing the positive electrode material according to the present invention exhibit excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making them useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0097] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0098] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0099] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-shaped, or coin-shaped, using a can.

[0100] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0101] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0102] The present invention will be described in more detail below with reference to specific examples.

[0103] [Example: Production of positive electrode active material] Example 1. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution prepared by mixing NiSO4, CoSO4, and MnSO4 in a Ni:Co:Mn molar ratio of 97.0:0.5:2.5, an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0104] The precursors synthesized by the coprecipitation reaction, LIOH and Al(OH)3, were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.968:0.032, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.939 Co 0.005 Mn 0.024 Al 0.032 A positive electrode active material having the composition of ]O2 was manufactured.

[0105] Example 2. The precursor was prepared using the same process as in Example 1. The synthesized precursor, LiOH, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.978:0.022, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.949 Co 0.005 Mn 0.024 Al 0.022 A positive electrode active material having the composition of ]O2 was manufactured.

[0106] Example 3. The precursor was prepared using the same process as in Example 1. The synthesized precursor, LiOH, and Al(OH)3 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.989:0.011, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.960 Co 0.005 Mn 0.024 Al 0.011 A positive electrode active material having the composition of ]O2 was manufactured.

[0107] Example 4. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution prepared by mixing NiSO4, CoSO4, and MnSO4 in a Ni:Co:Mn molar ratio of 96.0:3.0:1.0, an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0108] The precursors synthesized by the coprecipitation reaction, LiOH and TiO2, were mixed so that the molar ratio of Li:(Ni+Co+Mn):Ti was 1:0.988:0.012, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.948 Co 0.030 Mn 0.010 Ti 0.012 A positive electrode active material having the composition of ]O2 was manufactured.

[0109] Example 5. The precursor was prepared using the same process as in Example 4. The synthesized precursor, LiOH, and TiO2 were mixed so that the molar ratio of Li:(Ni+Co+Mn):Ti was 1:0.994:0.006, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.954 Co 0.030 Mn 0.010 Ti 0.006 A positive electrode active material having the composition of ]O2 was manufactured.

[0110] Comparative Example 1. A precursor was prepared using the same process as in Example 1. The synthesized precursor and LiOH were mixed so that the molar ratio of Li:(Ni+Co+Mn) was 1:1, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.970 Co 0.005 Mn 0.025 A positive electrode active material having the composition of ]O2 was manufactured.

[0111] Comparative Example 2. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution (NiSO4 and CoSO4 mixed in a Ni:Co molar ratio of 97.0:3.0), an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0112] The precursors synthesized by the coprecipitation reaction, LiOH and Al(OH)3, were mixed in a molar ratio of Li:(Ni+Co):Al of 1:0.968:0.032, and then heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.939 Co 0.029 Al 0.032 A positive electrode active material having the composition of ]O2 was manufactured.

[0113] Comparative Example 3. Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and then 100 ml of a 28 wt% aqueous ammonia solution was added while maintaining the temperature at 50°C. Next, a transition metal solution prepared by mixing NiSO4, CoSO4, and MnSO4 in a Ni:Co:Mn molar ratio of 83.0:11.0:6.0, an aqueous ammonia solution, and a sodium hydroxide solution were added to the coprecipitation reactor to form a precursor. The precursor particles were separated and washed, and then dried in an oven at 130°C to produce the precursor.

[0114] The precursors synthesized by the coprecipitation reaction, LiOH and Al(OH)3, were mixed so that the molar ratio of Li:(Ni+Co+Mn):Al was 1:0.968:0.032, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.803 Co 0.106 Mn 0.058 Al 0.032 A positive electrode active material having the composition of ]O2 was manufactured.

[0115] Comparative Example 4. The precursor was prepared using the same process as in Example 4. The synthesized precursor and LiOH were mixed so that the molar ratio of Li:(Ni+Co+Mn) was 1:1, and the mixture was heat-treated at 720°C for 20 hours under an oxygen atmosphere to obtain Li[Ni 0.960 Co 0.030 Mn 0.010 A positive electrode active material having the composition of ]O2 was manufactured.

[0116] [Example of experiment] Experimental Example 1: Confirmation of Doping Content The Al content relative to the total weight of each positive electrode active material produced in the above examples and comparative examples was measured using an inductively coupled plasma atomic emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer) and is shown in Table 1 below.

[0117] Experimental Example 2. Measurement of Zeta Potential The zeta potentials of the positive electrode active materials produced in the above examples and comparative examples are shown in Table 1 below. The zeta potentials were measured at 25°C using a Zetasizer Pro (Malvern Panalytical) instrument after diluting each positive electrode active material to 0.002% by weight and dissolving it in NMP.

[0118] Experimental Example 3. Measurement of Viscosity Increase Rate The positive electrode active materials produced in the above examples and comparative examples, PVDF as a binder, and acetylene black as a conductive material were mixed in N-methylpyrrolidone (NMP) in a weight ratio of 96.5:2.0:1.5 to produce a positive electrode slurry with a solid content of 70% by weight.

[0119] The viscosity of the positive electrode slurry was measured immediately after manufacturing under conditions of 25°C and relative humidity of 10% or less, and is recorded in Table 1 below. Next, while stored under the same conditions, the viscosity increase rate after 3 hours and 24 hours was measured relative to the viscosity immediately after manufacturing, and is shown in Figure 1. Here, viscosity was measured using a B-type viscometer (DV2T EXTRA Touch screen viscometer, manufactured by BROOKFIELD AMETEK), with the viscometer spindle immersed in each positive electrode slurry and rotated at 12 rpm for 3 minutes.

[0120] [Table 1]

[0121] As shown in Table 1 above, when using the positive electrode active materials of Examples 1 to 5, in which the absolute value of the zeta potential is 30 mV or more, the slurry viscosity is low, at 3,200 cP or less. However, when using the positive electrode active materials of Comparative Examples 1 to 4, in which the absolute value of the zeta potential is less than 30 mV, the slurry viscosity is high, at 3,800 cP or more.

[0122] Experimental Example 4. Evaluation of Capacity and Lifespan (1) Battery manufacturing A cathode slurry containing the respective cathode active materials produced in the above examples and comparative examples was prepared using the same method as in Experimental Example 3.

[0123] The manufactured positive electrode slurry was loaded at a rate of 16 mg / cm³. 2 The material was adjusted, coated onto both sides of a 15 μm thick aluminum current collector, dried at 130°C, and then rolled between two rolling mills to produce the positive electrode.

[0124] A negative electrode slurry was prepared by mixing a mixture of natural graphite and artificial graphite in a 50:50 weight ratio as the negative electrode active material, SBR and CMC as binders, and SuperC as a conductive material in a weight ratio of 95.6:1.1:2.3:1.0 with water as the solvent, resulting in a solid content of 60% by weight. The negative electrode slurry was then loaded at a rate of 4.63 mAh / cm³. 2 The material was adjusted, coated onto both sides of a 10 μm thick copper current collector, dried at 130°C, and then rolled between two rolling mills to produce the negative electrode.

[0125] An electrode assembly was manufactured by interposing a 15 μm thick porous polyethylene separator between the manufactured positive and negative electrodes. This assembly was then inserted into a pouch-type battery case, and an electrolyte was injected to produce a secondary battery. As the electrolyte, a solution of 1 M LiPF6 dissolved in an organic solvent, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2, was used.

[0126] (2) Measurement of initial capacity and capacity retention rate After performing an activation process on each of the batteries manufactured as described above, they were charged to 4.25V at 25°C at a rate of 0.2C using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.) under CC-CV (constant current-constant voltage) conditions, and then discharged to 2.5V at a rate of 0.2C using CC discharge, and the initial discharge capacity was measured.

[0127] The above charge / discharge cycle was considered one cycle, and after repeating the same charge / discharge 30 times, the capacity retention rate was measured using the following formula. The measurement results are shown in Table 2 below.

[0128] - Capacity retention rate (%) = (Discharge capacity after 30 cycles / Initial discharge capacity) × 100

[0129] [Table 2]

[0130] As shown in Table 2 above, in Examples 1 to 3, which use a positive electrode active material containing Al as a doping element and having an absolute value of 30 mV or more according to one embodiment of the present invention, the initial viscosity and viscosity increase rate of the slurry are lower, and the initial volume and volume retention rate are significantly improved compared to Comparative Example 1, which uses a positive electrode active material with an absolute value of less than 30 mV.

[0131] On the other hand, among the examples, it can be confirmed that Examples 1 and 2, in which the absolute value of the zeta potential is 40 mV or more, have a remarkably high capacity retention rate of 94% or more.

Claims

1. A lithium nickel oxide containing nickel, cobalt, and manganese, with a nickel content of 90 mol% or more among the metals other than lithium, A positive electrode active material comprising a metal element M1 doped into the lithium nickel oxide, The aforementioned metal element M1 is one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb. A positive electrode active material whose zeta potential, measured at room temperature, has an absolute value of 30 mV or higher.

2. The positive electrode active material according to claim 1, wherein the metal element M1 is contained in an amount of 3,000 ppm to 10,000 ppm relative to the total weight of the positive electrode active material.

3. The positive electrode active material according to claim 1, wherein the metal element M1 is Al, Ti, or a combination thereof.

4. The positive electrode active material according to claim 1, wherein the absolute value of the zeta potential measured at room temperature is 35 mV or more and 60 mV or less.

5. The lithium nickel oxide has the composition of the following chemical formula 1, [Chemical formula 1] Li １＋ｘ (N ａ Co ｂ Mn ｃ M1 ｄ M2 ｅ )O ２ In the aforementioned chemical formula 1, M1 is one or more selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb. M2 is one or more elements selected from the group consisting of Cu, Fe, V, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Mg, and B. 1 + x, a, b, c, d, and e are the atomic fractions of independent elements. The positive electrode active material according to claim 1, wherein -0.2 ≤ x ≤ 0.2, 0.90 ≤ a < 1, 0 < b < 0.1, 0 < c < 0.1, 0 < d ≤ 0.05, 0 ≤ e ≤ 0.05, and a + b + c + d + e = 1.

6. When the positive electrode active material is mixed with a binder and a conductive material in a solvent to produce a positive electrode slurry, the viscosity increase rate according to the following formula 1 is 100% or less. [Formula 1] Viscosity increase rate = (V １ -V ０ ) / V ０ ×100 (%) In the above formula 1, V ０ This is the viscosity of the positive electrode slurry measured at room temperature immediately after manufacturing. V １ The positive electrode active material according to claim 1, wherein is the viscosity of the positive electrode slurry measured after storage for 24 hours under conditions of room temperature and relative humidity of 10% or less.

7. The positive electrode active material according to claim 1, wherein the lithium nickel oxide has a nickel content of 95 mol% to 99 mol% among metals other than lithium.

8. The positive electrode active material according to claim 1, wherein the lithium nickel oxide has a manganese content of 0.5 mol% or more among the metals other than lithium.

9. A positive electrode slurry comprising the positive electrode active material, binder, conductive material, and solvent according to claim 1.

10. The positive electrode slurry according to claim 9, wherein the solid content relative to the total weight of the positive electrode slurry is 70% by weight or more, and the viscosity at room temperature is 3,500 cP or less.

11. Positive electrode current collector and The positive electrode current collector includes a positive electrode active material layer provided on at least one surface of the positive electrode current collector, The positive electrode comprises the positive electrode active material layer described in claim 1.

12. The positive electrode according to claim 11, A negative electrode containing a negative electrode active material, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

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