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

Abstract

The present invention relates to a positive electrode active material, and a positive electrode, a positive electrode slurry, and a lithium secondary battery, each comprising the positive electrode active material, the positive electrode active material including: a lithium nickel-based oxide including nickel, cobalt, and manganese and having a nickel content of 90 mol % or more among metals excluding lithium; and a metal element M1 doped on the lithium nickel-based oxide, wherein the metal element M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, and has an absolute value of zeta potential of 30 mV or greater as measured at room temperature.

Description

Cathode active material, cathode slurry containing same, cathode and lithium secondary battery

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0105931, filed August 11, 2023, and No. 10-2024-0008351, filed January 18, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a cathode active material, a cathode slurry containing the same, a cathode, and a lithium secondary battery.

[0003] The recent rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity secondary batteries. Lithium secondary batteries, in particular, are attracting attention as power sources for portable electronic devices due to their lightweight characteristics and high energy density. Small lithium secondary batteries used in these devices require high energy density and excellent battery performance under high-temperature and high-voltage conditions. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] Typically, a lithium secondary battery comprises an electrode assembly comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte that encapsulates the electrode assembly. The positive electrode and negative electrode can be manufactured by coating an electrode slurry containing an active material, a binder, and a conductive material dispersed in a solvent onto a current collector.

[0005] At this time, particle aggregation may occur due to van der Waals forces acting between the active materials in the electrode slurry, or between the active materials and the conductive agent and / or binder. This particle aggregation leads to gelation of the slurry, which prevents the electrode active material layer from forming uniformly, which may increase resistance within the electrode and reduce capacity. This ultimately leads to degradation of the battery's lifespan and reduced safety. If the slurry gelation is severe, electrode production may become impossible.

[0006] In particular, when lithium nickel cobalt manganese oxide (hereinafter, NCM oxide) is used as an active material, increasing the nickel content to achieve high capacity may make the battery more susceptible to slurry gelation problems, so it is necessary to develop a technology that can simultaneously solve the capacity improvement and slurry gelation problems.

[0007] The present invention aims to provide a cathode active material with improved dispersibility, a cathode slurry containing the same, a cathode, and a lithium secondary battery.

[0008] The present invention relates to a lithium nickel-based oxide comprising nickel, cobalt and manganese, and having a nickel content of 90 mol% or more among metals other than lithium; and

[0009] A positive electrode active material comprising a metal element M1 doped in the lithium nickel-based oxide, wherein the metal element M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, and an absolute value of zeta potential measured at room temperature is 30 mV or more is provided.

[0010] In addition, the present invention provides a cathode slurry comprising the above-described cathode active material, binder, conductive agent, and solvent.

[0011] In addition, the present invention provides a positive electrode comprising 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.

[0012] In addition, the present invention provides a lithium secondary battery including the above-described positive electrode; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

[0013] The cathode active material according to the present invention has a high nickel content, thus providing excellent capacity, and can reduce the amount of cobalt used, thereby being advantageous in terms of material supply and price.

[0014] In addition, since it includes a metal element with a higher oxidation number than the transition metal contained in the parent material lithium nickel oxide as a doping element, it exhibits a zeta potential of 30 mV or more, so it can form a high repulsive force between particles.

[0015] Accordingly, the problems of surface instability and reduced dispersibility of high-nickel positive electrode active materials can be effectively solved, while the aforementioned positive electrode slurry gelation problem can be prevented, ultimately enabling the implementation of a lithium secondary battery with advantageous capacity and life characteristics.

[0016] Figure 1 is a graph showing the viscosity increase rate of a positive electrode slurry containing a positive electrode active material manufactured in an example and a comparative example.

[0017] Hereinafter, the present invention will be described in detail.

[0018]

[0019] In the present invention, “zeta potential” is an indicator indicating the degree of surface charge of positive electrode active material particles, and can be measured by dissolving the positive electrode active material to be measured in N-methyl-2-pyrrolidone (NMP) diluted to 0.002 wt%, and then using Zetasizer Pro (manufactured by Malvern Panalytical) equipment at 25°C.

[0020] In the present invention, “viscosity” can be measured by submerging the spindle of a B-type viscometer in the slurry to be measured and rotating it at 12 rpm for 3 minutes.

[0021] In the present invention, “primary particle” means a particle unit that has no apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0022] In the present invention, “D 50 “It refers to the particle size corresponding to 50% of the volume accumulation in the volume accumulation particle size distribution of the target powder, and can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S-3500), irradiating it with ultrasonic waves of about 28 kHz with an output of 60 W, obtaining a volume accumulation particle size distribution graph, and finding the particle size at the point where the volume accumulation amount is 50% from the obtained graph.

[0023] Hereinafter, each component of the present invention will be described in more detail.

[0024]

[0025] <Cathode active material>

[0026] The present invention relates to a positive electrode active material, and more particularly, to a positive electrode active material for a lithium secondary battery.

[0027] The cathode active material of the present invention comprises a lithium nickel-based oxide containing nickel, cobalt, and manganese, and having a nickel content of 90 mol% or more among metals other than lithium; and a metal element M1 doped into the lithium nickel-based oxide, wherein the metal element M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo, and Nb, and has an absolute value of zeta potential measured at room temperature of 30 mV or more.

[0028] As mentioned above, increasing the nickel content in lithium nickel-based oxides can secure higher capacity, but it also reduces structural stability. Specifically, high-nickel cathode active materials often contain large amounts of lithium compounds remaining on their surfaces, which can cause side reactions and gas emissions during charge / discharge. Furthermore, alkaline substances such as LiOH among the residual lithium compounds can increase the pH of the cathode active material, which can trigger a crosslinking reaction of the binder within the cathode slurry, leading to gelation. Gelation of the slurry not only increases viscosity, which reduces processability, but also disrupts uniform coating, potentially degrading the performance of the electrode itself.

[0029] Accordingly, the inventors of the present invention have discovered 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 have solved the above problem by providing a cathode active material having a zeta potential of 30 mV or more through doping.

[0030] Specifically, in nickel cobalt manganese oxides with a Ni content of 90 mol% or more, Ni has an oxidation number of +2 to +3. When Al with an oxidation number of +3 is used as a doping element, Ni is substituted with Al with a higher oxidation number than Ni, causing oxygen deficiency. As a result, oxygen vacancy decreases in order to maintain charge neutrality, and the zeta potential takes on a more negative value. As the absolute value of the zeta potential increases, the repulsive force between positive electrode active material particles becomes stronger, which can improve dispersibility, ultimately having the effect of preventing gelation of positive electrode slurry containing high-nickel positive electrode active material. In addition, when Ti(+4), Zr(+4), W(+6), Mo(+5), and Nb(+5) with high oxidation numbers are used as doping elements, the effect is also realized through a mechanism of substitution with Ni or Co atoms.

[0031]

[0032] In one embodiment of the present invention, the absolute value of the zeta potential of the positive electrode active material measured at room temperature may be 35 mV or more, preferably 40 mV or more, and more preferably 45 mV or more. However, considering practical feasibility, it may be 60 mV or less.

[0033] In one embodiment of the present invention, the metal element M1 may be at least one selected from the group consisting of Al, Ti, Zr, W, Mo and Nb, preferably Al, Ti or a combination thereof, and more preferably Al.

[0034] Meanwhile, the metal element M1 may 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 based on the total weight of the positive electrode active material. When the amount of M1 is 3,000 ppm or more, it is easy to control the absolute value of the zeta potential to 30 mV or more through the above mechanism. However, since the capacity decreases as the amount of M1 increases, it is preferably 10,000 ppm or less.

[0035] The content of the metal element M1 included in the above positive electrode active material can be measured by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0036]

[0037] In the case where the nickel content of the above lithium nickel-based oxide is less than 90 mol% among all metals excluding lithium, the cobalt content is relatively high, so a stable structure is already formed, and the effect of doping M1 is minimal.

[0038] In addition, when manganese is not included in the lithium nickel-based oxide, since the oxidation number of nickel is +3, the oxygen deficiency caused by substituting Al with the oxidation number of +3 described above and the increase in the absolute value of the zeta potential are minimal, making it difficult to implement the intended effect of the present invention.

[0039] In one embodiment of the present invention, the lithium nickel-based oxide may have a nickel content of 92 mol% or more, preferably 93 mol% or more, and more preferably 95 mol% to 99 mol% among all metals excluding lithium.

[0040] In one embodiment of the present invention, the lithium nickel-based oxide may have a manganese content of 0.5 mol% or more, preferably 0.8 mol% or more, more preferably 1.0 mol% or more among all metals excluding lithium, but may be 5.0 mol% or less.

[0041] Specifically, the lithium nickel-based oxide may have a composition represented by the following chemical formula 1.

[0042] [Chemical Formula 1]

[0043] Li 1+x (Ni a Co b Mn c M1 d M2 e )O2

[0044] In the above chemical formula 1,

[0045] M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo and Nb,

[0046] M2 is at least one 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,

[0047] 1+x, a, b, c, d and e are the atomic fractions of independent elements, respectively.

[0048] -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, a+b+c+d+e=1이다.

[0049] The above 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may 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.

[0050] The above a represents the molar ratio of nickel among the total metal excluding lithium in the lithium nickel-based oxide, and may be 0.92≤a<1, 0.93≤a<1, or 0.95≤a<1. When the molar ratio of nickel satisfies the above range, a high energy density is exhibited, enabling high capacity implementation.

[0051] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel-based oxide, and is 0. <b≤0.025, 0<b≤0.015, 또는 0<b≤0.01일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0052] The above c represents the molar ratio of manganese among all metals excluding lithium in the lithium nickel oxide, and is 0. <c≤0.050, 0.005≤c≤0.040, 또는 0.010≤c≤0.035일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0053] The above d represents the molar ratio of the M1 element among all metals excluding lithium in the lithium nickel oxide, and the above d is 0. <d≤0.045, 0.020≤d≤0.040, 또는 0.030≤d≤0.040일 수 있다.

[0054] The above e represents the molar ratio of the M2 element among all metals excluding lithium in the lithium nickel oxide, and can be adjusted as needed.

[0055]

[0056] In one embodiment of the present invention, when the positive electrode active material is mixed with a binder and a conductive agent in a solvent to prepare a positive electrode slurry, the viscosity increase rate according to the following equation 1 may be 100% or less.

[0057] [Formula 1]

[0058] Viscosity increase rate = (V1-V0) / V0×100(%)

[0059] In the above equation 1,

[0060] V0 is the viscosity of the cathode slurry measured at room temperature immediately after manufacturing,

[0061] V1 is the viscosity of the cathode slurry measured after storage for 24 hours under conditions of room temperature and relative humidity of 10% or less.

[0062] Specifically, the positive electrode active material may have a viscosity increase rate of 80% or less, preferably 60% or less, and more preferably 40% or less according to the above formula 1. As described above, the positive electrode active material according to the present invention has a zeta potential of 30 mV or more, and thus has excellent dispersibility, and thus can exhibit such a low viscosity increase rate.

[0063] Meanwhile, the positive electrode active material may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the D of the positive electrode active material 50 The size may be from 2.5㎛ to 20㎛, but is not limited thereto.

[0064]

[0065] <Method for manufacturing positive electrode active material>

[0066] Meanwhile, the method for manufacturing the positive electrode active material comprises the steps of: supplying a transition metal-containing solution including a transition metal precursor, an ammonium cation complex forming agent, and a basic compound to a reactor while performing a co-precipitation reaction to form a nickel transition metal precursor having a nickel content of 90 mol% or more;

[0067] It includes a step of mixing and heat-treating a precursor containing the nickel transition metal precursor, a lithium raw material, and a metal element M1 to form a lithium nickel-based oxide doped with the metal element M1. At this time, the heat treatment can be performed 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.

[0068] The positive electrode active material manufactured by the above manufacturing method has an absolute value of zeta potential measured at room temperature of 30 mV or more.

[0069] The step of forming the above nickel transition metal precursor can be prepared, for example, by dissolving each transition metal precursor in a solvent to prepare a transition metal-containing solution, then mixing the transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound, and then performing a coprecipitation reaction. In addition, an oxidizing agent or oxygen gas may be additionally added during the coprecipitation reaction, if necessary.

[0070] Meanwhile, the transition metal precursor may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, etc. of each transition metal.

[0071] Specifically, the nickel precursor may be at least one selected from the group consisting of NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, and nickel sulfide, and the cobalt precursor may be at least one selected from the group consisting of Co(OH)2, Co3O4, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, and Co(SO4)2·7H2O. In addition, the manganese precursor may be at least one selected from the group consisting of Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, and manganese sulfide.

[0072] Meanwhile, the lithium raw material may be an oxide, hydroxide, oxyhydroxide, halide, nitrate, carbonate, acetate, oxalate, citrate, or sulfate containing lithium. More specifically, the lithium raw material may be at least one selected from the group consisting of Li2CO3, LiNO3, LiNO2, LiOH, LiOH H2O, LiH, LiF, LiCl, LiBr, LiI, Li2O, Li2SO4, CH3COOLi, and Li3C6H6O7.

[0073] At this time, the input amount of each transition metal precursor can be determined by considering the molar ratio of the transition metal in the positive electrode active material to be ultimately produced.

[0074] Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, as the solvent, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

[0075] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be introduced into the reactor in the form of a solution in which the compound is dissolved in a solvent. At this time, the solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0076] As described above, when a transition metal-containing solution, an ammonium cation complex forming agent, and a basic compound are introduced into a reactor and stirred, the transition metals in the transition metal-containing solution coprecipitate, generating precursor particles in the form of transition metal hydroxides.

[0077] At this time, the transition metal-containing solution, ammonium cation complex forming agent, and basic compound are added in an amount such that the pH of the reaction solution becomes within the desired range.

[0078] Once precursor particles are formed in the above manner, they are separated from the reaction solution to obtain the precursor. For example, the precursor can be separated from the reaction solution by filtering the reaction solution, and then the separated precursor can be washed and dried to obtain the precursor. Processes such as grinding and / or classification may also be performed as needed.

[0079]

[0080] A nickel transition metal precursor manufactured in this manner and a precursor including a lithium raw material and a metal element M1 are mixed and heat-treated to manufacture a lithium nickel-based oxide.

[0081] As the lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used.

[0082] Meanwhile, the lithium raw material and the nickel transition metal precursor may be mixed so that the molar ratio of Li: 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-based oxide is well developed, so that a positive electrode active material with excellent capacity characteristics and structural stability can be manufactured.

[0083] In addition, the precursor containing the metal element M1 comprises the metal element M1. It may contain oxides, hydroxides, oxyhydroxides, halides, nitrates, carbonates, acetates, oxalates, citrates or sulfates.

[0084] When additionally doping with metal element M2, the type and amount of the metal element M2 can be controlled by considering the type and content of the metal element M2 included in the positive electrode active material described above.

[0085]

[0086] <Polar slurry>

[0087] Next, the cathode slurry according to the present invention will be described.

[0088] The positive electrode slurry according to the present invention comprises the positive electrode active material, binder, conductive material and solvent of the present invention described above.

[0089] In one embodiment of the present invention, the positive electrode slurry may have a solid content of 70 wt% or more and a viscosity of 3,500 cP or less based on the total weight of the positive electrode slurry. That is, by including the positive electrode active material, a certain solid content can be secured 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 terms of suppressing binder migration and increasing electrode productivity, but it is preferably 80 wt% or less to prevent the viscosity from becoming excessively high. However, in the case of a dry electrode, the solid content may be 100 wt%.

[0090] Meanwhile, the viscosity of the positive electrode slurry may be 3,500 cP or less, preferably 3,000 cP or less, and more preferably 2,500 cP or less, taking into account ease of slurry transport and coating processability. However, considering slurry sedimentation and phase stability, the viscosity is preferably 500 cP or more.

[0091] In one embodiment of the present invention, the binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof, and preferably polyvinylidene fluoride.

[0092] The binder may be included in an amount of 0.5 wt% to 3.0 wt%, preferably 1.0 wt% to 2.5 wt%, and more preferably 1.5 wt% to 2.5 wt%, based on the total weight of the solid content in the positive electrode slurry. When the binder content is within the above range, sufficient adhesion to the current collector and bonding between particles can be secured, thereby improving the durability of the positive electrode while maintaining a low initial resistance.

[0093] The conductive material may be at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; carbon-based materials such as 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, and preferably carbon nanotubes or carbon black, and most preferably carbon nanotubes.

[0094] The conductive agent may be included in an amount of 0.1 wt% to 2.5 wt%, preferably 0.3 wt% to 2.0 wt%, and more preferably 0.5 wt% to 2.0 wt%, based on the total weight of the solid content in the positive electrode slurry. When the content of the conductive agent is within the above range, it is preferable in that the dead volume can be reduced while maintaining conductivity between active materials.

[0095] In addition, the above cathode slurry may optionally further include a dispersant, and the dispersant may be hydrogenated nitrile butadiene rubber (HNBR).

[0096] Meanwhile, the solvent of the positive electrode slurry may be a solvent generally used in the relevant technical field, and examples thereof include N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, dimethyl formamide (DMF), acetone, water, or a mixture of two or more thereof. The solvent may be used in an amount adjusted to have the viscosity of the positive electrode slurry described above.

[0097]

[0098] Bipolar

[0099] In addition, 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. In addition, the positive electrode according to the present invention includes a positive electrode active material layer formed by coating the positive electrode slurry described above on at least one surface of the positive electrode current collector.

[0100] Since the positive electrode active material and positive electrode slurry have been described above, a detailed description will be omitted, and only the remaining components will be described in detail below.

[0101] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0102] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode material is used. Specifically, the positive electrode can be manufactured by applying the positive electrode slurry onto a positive electrode current collector, followed by drying and rolling, or by casting the positive electrode slurry onto a separate support, then peeling the support, and laminating the resulting film onto a positive electrode current collector.

[0103]

[0104] lithium secondary battery

[0105] Next, a lithium secondary battery according to the present invention will be described.

[0106] The lithium secondary battery specifically includes a positive electrode, a negative electrode including a negative electrode active material, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description is omitted, and only the remaining components are specifically described below.

[0107] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0108] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0109] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0110] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0111] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0 <β< 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and a mixture of one or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0112] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0113] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include 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 fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0114] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode composite 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, or by casting the negative electrode composite on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0115] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0116] In addition, examples of the electrolyte 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.

[0117] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0118] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 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; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0119] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above 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 - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 4.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0120] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0121]

[0122] As described above, a lithium secondary battery including a cathode material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and lifespan characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0123] 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.

[0124] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0125] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0126] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0127] Examples of the above medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0128]

[0129] Hereinafter, the present invention will be described in more detail through specific examples.

[0130] [Example: Preparation of positive electrode active material]

[0131] Example 1.

[0132] After adding 4 L of distilled water to a co-precipitation reactor (capacity 20 L), the temperature was maintained at 50°C, and 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4, CoSO4, and MnSO4 such that the molar ratio of Ni:Co:Mn was 97.0:0.5:2.5, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0133] 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 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 a composition of O2 was manufactured.

[0134]

[0135] Example 2.

[0136] A precursor was prepared by 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 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 a composition of O2 was manufactured.

[0137]

[0138] Example 3.

[0139] A precursor was prepared by 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 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 a composition of O2 was manufactured.

[0140]

[0141] Example 4.

[0142] After adding 4 L of distilled water to a co-precipitation reactor (capacity 20 L), the temperature was maintained at 50°C, and 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4, CoSO4, and MnSO4 such that the molar ratio of Ni:Co:Mn was 96.0:3.0:1.0, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0143] The precursors, LiOH and TiO2 synthesized by the coprecipitation reaction were mixed so that the molar ratio of Li:(Ni+Co+Mn):Ti was 1:0.988:0.012, and 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 a composition of O2 was manufactured.

[0144]

[0145] Example 5.

[0146] A precursor was prepared by 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 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 a composition of O2 was manufactured.

[0147]

[0148] Comparative Example 1.

[0149] A precursor was prepared by 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 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 a composition of O2 was manufactured.

[0150]

[0151] Comparative Example 2.

[0152] After adding 4 L of distilled water to a co-precipitation reactor (capacity 20 L), the temperature was maintained at 50°C, and 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4 and CoSO4 in a molar ratio of Ni:Co of 97.0:3.0, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0153] The precursors, LiOH and Al(OH)3 synthesized by the coprecipitation reaction were mixed so that the molar ratio of Li:(Ni+Co):Al was 1:0.968:0.032, and 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 a composition of O2 was manufactured.

[0154]

[0155] Comparative Example 3.

[0156] After adding 4 L of distilled water to a co-precipitation reactor (capacity 20 L), the temperature was maintained at 50°C, and 100 mL of an ammonia aqueous solution with a concentration of 28 wt% was added. Then, a transition metal solution mixed with NiSO4, CoSO4, and MnSO4 such that the molar ratio of Ni:Co:Mn was 83.0:11.0:6.0, an ammonia aqueous solution, and a sodium hydroxide solution were added to the co-precipitation reactor, and a co-precipitation reaction was performed to form a precursor. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0157] 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 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 a composition of O2 was manufactured.

[0158]

[0159] Comparative Example 4.

[0160] A precursor was prepared by the same process as in Example 4 above. The synthesized precursor and LiOH were mixed so that the molar ratio of Li:(Ni+Co+Mn) was 1:1, and 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 a composition of O2 was manufactured.

[0161]

[0162] [Experimental Example]

[0163] Experimental Example 1. Confirmation of doping content

[0164] For the positive electrode active materials manufactured in the above examples and comparative examples, the Al content based on the total weight of each positive electrode active material was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer) and is shown in Table 1 below.

[0165]

[0166] Experimental Example 2. Zeta Potential Measurement

[0167] The results of measuring the zeta potential of the positive electrode active materials manufactured in the above examples and comparative examples are shown in Table 1 below. The zeta potential was measured by dissolving each positive electrode active material in NMP at 0.002 wt% dilution at 25°C using a Zetasizer Pro (manufactured by Malvern Panalytical).

[0168]

[0169] Experimental Example 3. Measurement of viscosity increase rate

[0170] Each of the positive electrode active materials manufactured in the above examples and comparative examples, PVDF as a binder, and acetylene black as a conductive material were mixed in a weight ratio of 96.5:2.0:1.5 in N-methylpyrrolidone (NMP) to manufacture a positive electrode slurry having a solid content of 70 wt%.

[0171] The viscosity of the positive electrode slurry was measured immediately after manufacturing under conditions of 25℃ and relative humidity of 10% or less, and is shown in Table 1 below. Afterwards, the viscosity was stored under the same conditions, and the viscosity increase rate after 3 hours and 24 hours compared to the viscosity immediately after manufacturing was measured, and is shown in Figure 1. At this time, the viscosity was measured using a B-type viscometer (DV2T EXTRA Touch screen viscometer, BROOKFIELD AMETEK Co.), and the spindle of the viscometer was immersed in each positive electrode slurry and rotated at 12 rpm for 3 minutes.

[0172] Ni / Co / Mn input molar ratioExperimental example 1Experimental example 2Experimental example 3Content of doping element (ppm)Zeta potential (mV)Viscosity (cP)Example 197.0 / 0.5 / 2.59,000-48.02,510Example 297.0 / 0.5 / 2.56,000-42.82,715Example 397.0 / 0.5 / 2.53,000-33.63,180Example 496.0 / 3.0 / 1.06,000-46.22,910Example 596.0 / 3.0 / 1.03,000-38.43,100Comparative example 197.0 / 0.5 / 2.50-23.13,850Comparative example 297.0 / 3.0 / 09,000-12.05,170 Comparative example 383.0 / 11.0 / 6.09,000-8.75,910 Comparative example 496.0 / 3.0 / 1.00-28.03,880

[0173] Through the above Table 1, it can be confirmed that when the positive electrode active materials of Examples 1 to 5 having an absolute value of zeta potential of 30 mV or more were used, the slurry viscosity was as low as 3,200 cP or less, but when the positive electrode active materials of Comparative Examples 1 to 4 having an absolute value of zeta potential of less than 30 mV were used, the slurry viscosity was as high as 3,800 cP or more.

[0174]

[0175] Experimental Example 4. Capacity and Life Evaluation

[0176] (1) Battery manufacturing

[0177] A positive electrode slurry containing each of the positive electrode active materials manufactured in the above examples and comparative examples was manufactured in the same manner as in Experimental Example 3.

[0178] The manufactured cathode slurry was loaded with 16 mg / cm 2 The anode was manufactured by applying the coating to both sides of a 15㎛ thick aluminum current collector, drying at 130℃, and then rolling between two rolling rolls.

[0179] A mixture of natural graphite and artificial graphite as negative active materials in a weight ratio of 50:50, SBR and CMC as binders, and SuperC as a conductive material were mixed in a weight ratio of 95.6:1.1:2.3:1.0 in water as a solvent to prepare a negative electrode slurry having a solid content of 60 wt%. The negative electrode slurry had a loading capacity of 4.63 mAh / cm 2 The negative electrode was manufactured by applying the coating to both sides of a 10㎛ thick copper current collector, drying at 130℃, and then rolling between two rolling rolls.

[0180] An electrode assembly was manufactured by interposing a 15 μm thick porous polyethylene separator between the manufactured positive and negative electrodes, and then inserted into a pouch-type battery case and an electrolyte was injected to manufacture a secondary battery. At this time, a solution of 1 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:2 was used as the electrolyte.

[0181]

[0182] (2) Measurement of initial capacity and capacity retention rate

[0183] For each battery manufactured above, an activation (formation) process was performed, and then the batteries were charged at 25°C at a 0.2C rate to 4.25 V under CC-CV conditions using a PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.) and CC discharged to 2.5 V at a 0.2C rate to measure the initial discharge capacity.

[0184] The charge / discharge above was considered as one cycle, and the same charge / discharge was repeated 30 times, after which the capacity retention rate was measured using the following formula. The measurement results are shown in Table 2 below.

[0185] - Capacity retention rate (%) = (discharge capacity after 30 cycles / initial discharge capacity) × 100

[0186] Experimental Example 4 Initial Discharge Capacity (mAh / g) Capacity Retention Rate (%) Example 1 216.4 9 6.8 Example 2 219.3 9 4.0 Example 3 224.2 9 1.3 Comparative Example 1 228.1 8.7

[0187]

[0188] Through the above Table 2, it can be confirmed that in Examples 1 to 3 using a positive electrode active material containing Al as a doping element and having an absolute value of zeta potential of 30 mV or more according to an embodiment of the present invention, the initial viscosity and viscosity increase rate of the slurry are lower, and the initial capacity and capacity retention rate are greatly improved compared to Comparative Example 1 using a positive electrode active material having an absolute value of zeta potential of less than 30 mV.

[0189] Meanwhile, 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 significantly high capacity retention rate of 94% or more.

Claims

1. Lithium nickel oxide containing nickel, cobalt and manganese, and having a nickel content of 90 mol% or more among metals excluding lithium; and As a cathode active material comprising a metal element M1 doped into the above lithium nickel-based oxide, The above metal element M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo and Nb, A cathode active material having an absolute value of zeta potential of 30 mV or more measured at room temperature.

2. In claim 1, A cathode active material, wherein the metal element M1 is contained in an amount of 3,000 ppm to 10,000 ppm based on the total weight of the cathode active material.

3. In claim 1, A cathode active material, wherein the metal element M1 is Al, Ti or a combination thereof.

4. In claim 1, A cathode active material having an absolute value of zeta potential measured at room temperature of 35 mV or more and 60 mV or less.

5. In claim 1, The above lithium nickel-based oxide is a cathode active material having a composition of the following chemical formula 1: [Chemical Formula 1] Li 1+x (Ni a Co b Mr c M1 d M2 e )O 2 In the above chemical formula 1, M1 is at least one selected from the group consisting of Al, Ti, Zr, W, Mo and Nb, M2 is at least one 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, respectively. -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, a+b+c+d+e=1이다.

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

7. In claim 1, The above lithium nickel-based oxide is a cathode active material having a nickel content of 95 mol% to 99 mol% among metals other than lithium.

8. In claim 1, The above lithium nickel-based oxide is a cathode active material having a manganese content of 0.5 mol% or more among metals other than lithium.

9. A cathode slurry comprising a cathode active material, a binder, a conductive agent, and a solvent according to claim 1.

10. In claim 9, A cathode slurry having a solid content of 70 wt% or more based on the total weight of the cathode slurry and a viscosity of 3,500 cP or less at room temperature.

11. Anode current collector; and Including a positive electrode active material layer provided on at least one surface of the positive electrode current collector, A positive electrode, wherein the positive electrode active material layer comprises the positive electrode active material according to claim 1.

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

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