Positive electrode active material and method for manufacturing the same

Abstract

The present invention relates to a positive electrode active material and a method for producing the same, comprising a lithium transition metal oxide in which the nickel content among the total metals other than lithium is 70 mol% or more, and the EELS analysis result on the particle surface satisfies Equation 1.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2023-0123472 dated September 15, 2023, and Korean Patent Application No. 10-2024-0123371 dated September 10, 2024, and all content disclosed in the documents of the said Korean patent applications is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the positive electrode active material, and a lithium secondary battery containing the positive electrode. [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 attracting attention as a power source for portable devices due to their light weight and high energy density. Consequently, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] In a lithium secondary battery, an organic electrolyte or polymer electrolyte is filled between a positive electrode and a negative electrode, both made of an active material that allows for the insertion and deintercalation of lithium ions. Electrical energy is generated by oxidation and reduction reactions that occur when lithium ions are inserted into and deintercalated at the positive and negative electrodes.

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Furthermore, to maintain the excellent reversible capacity of LiNiO2 and improve its low thermal stability, lithium composite metal oxides (hereinafter simply referred to as "NCM-based lithium composite transition metal oxides") have been developed in which some of the nickel (Ni) is replaced with cobalt (Co) and manganese (Mn). However, conventionally developed NCM-based lithium composite transition metal oxides have not had sufficient capacity characteristics and have had limitations in their application.

[0006] To address these issues, recent research has focused on increasing the nickel content in NCM-based lithium-composite transition metal oxides. However, high-nickel (High-Ni) cathode active materials, due to the high reactivity of nickel, generate large amounts of gas during the charge-discharge process. This leads to significant lattice structure instability due to cation mixing and oxygen desorption, resulting in an increased amount of lithium impurities remaining on the surface.

[0007] As the lithium impurity content increases, it can cause gelation and swelling of the cathode slurry; therefore, high-nickel cathode active materials are typically subjected to a water washing process during manufacturing. While such a water washing process is advantageous in reducing gas generation by removing lithium by-products from the surface, it can cause surface damage to the cathode active material particles, which may be detrimental in terms of lifespan and storage. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention is intended to solve the problems described above, and provides a method capable of effectively removing lithium by-products remaining on the surface without damaging the particle structure when producing a positive electrode active material containing high nickel content, and a positive electrode active material produced using the same that exhibits excellent resistance and lifespan characteristics. [Means for Solving the Problem]

[0009] [1] The present invention provides a positive electrode active material comprising a lithium transition metal oxide having a nickel content of 70 mol% or more among all metals other than lithium, wherein an EELS analysis result of the particle surface satisfies the following formula 1. [Formula 1] 0.85≦I(854eV) / I(855.5eV)<1 In the above formula 1, I(854eV) is the peak intensity shown near 854eV, I(855.5eV) is the peak intensity shown near 855.5eV.

[0010] [2] The present invention provides the positive electrode active material according to [1] above, wherein a molar ratio of lithium to all metal elements other than lithium in the lithium transition metal oxide is 1.01 to 1.09.

[0011] [3] The present invention provides the positive electrode active material according to [1] or [2] above, wherein the lithium transition metal oxide is represented by the following chemical formula 1. [Chemical Formula 1] Li a Ni b Co c Mn d Q e O 2+f In the above chemical formula 1, a, b, c, d, e and f are respectively 1.03≦a≦1.09, 0.7≦b<1.0, 0<c<0.3, 0<d<0.3, 0≦e≦0.1, b+c+d+e=1, and -0.1≦f≦1.0, Q is one or more elements selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0012] [4] In the present invention, in at least one of the above [1] to [3], the D of the positive electrode active material 50 We provide a positive electrode active material with a diameter of 8 μm to 15 μm.

[0013] [5] The present invention provides a method for producing a positive electrode active material according to at least one of the above [1] to [4], comprising the steps of: mixing a precursor containing 70 mol% or more nickel with respect to the total number of moles of transition metals and a lithium source, and firing the mixture to produce a calcined body; and washing the calcined body with 30 to 70 parts by weight of an aqueous washing solution per 100 parts by weight of the calcined body to produce a lithium transition metal oxide.

[0014] [6] The present invention provides a method for producing a positive electrode active material, wherein the step of producing the calcined body in [5] is to mix the precursor and the lithium source such that the molar ratio of lithium in the lithium source to the total metal elements of the precursor, Li / M, is 1.01 to 1.09.

[0015] [7] The present invention provides a method for producing a positive electrode active material, wherein the washing step for producing the lithium transition metal oxide in [5] or [6] is carried out by placing the calcined body in water and stirring it at a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes at a temperature of 15°C to 25°C.

[0016] [8] The present invention provides a method for producing a positive electrode active material, wherein in at least one of the above [5] to [7], the firing step for producing the fired body is carried out at 700°C to 900°C.

[0017] [9] The present invention provides a positive electrode comprising at least one positive electrode active material from among [1] to [4] above.

[0018]

[10] The present invention provides a lithium secondary battery comprising the positive electrode described in [9] above, 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]

[0019] The present invention provides optimal water washing conditions for manufacturing high-nickel cathode active materials, which require a water washing process, that minimize damage to the particle surface and effectively remove lithium by-products remaining on the particle surface.

[0020] Furthermore, the present invention provides a positive electrode active material that has high capacity, low initial resistance, a long lifespan, and low gas generation due to the inclusion of a high nickel content, as well as a method for producing the same. [Brief explanation of the drawing]

[0021] [Figure 1] This figure shows the EELS spectra of the surface of the positive electrode active material produced in Example 1 and Comparative Examples 1 and 2 of the present invention. [Modes for carrying out the invention]

[0022] The present invention will be described in more detail below to aid in understanding the present invention.

[0023] In this invention, "EELS analysis results" refers to the EELS spectrum obtained by electron energy-loss spectroscopy (EELS). The EELS spectrum can be obtained using HR-TEM equipment, with the horizontal axis representing the energy loss region and the vertical axis representing the peak intensity.

[0024] In Formula 1 of the present invention, "around 854 eV" means the region of 854 ± 2.0 eV, and "around 855.5 eV" means the region of 855.5 ± 2.0 eV.

[0025] In this invention, "particle surface" means a region within a distance of 100 nm from the surface of the particle toward the center.

[0026] 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.

[0027] Method for manufacturing positive electrode active material First, the method for producing a positive electrode active material according to the present invention will be described.

[0028] High-nickel (High Ni) cathode active materials, in which the nickel content of the total metals other than lithium is 70 mol% or more, have the advantage of enabling high capacity, but they have the disadvantage of undergoing many changes in the lattice constant, i.e., changes in the volume within the unit cell. Such volume changes can cause cracks to form within the active material particles, and these cracks can cause voids within the active material, which can lead to a decrease in battery performance.

[0029] Furthermore, due to the high nickel content, a significant amount of cation mixing occurs between lithium ions and nickel ions, resulting in a large amount of lithium by-products on the surface of the positive electrode active material particles. These lithium by-products not only cause gelation of the positive electrode slurry and swelling of the battery, but also trigger side reactions with the electrolyte, accelerating its decomposition and potentially shortening the battery's lifespan.

[0030] Therefore, unlike conventional cathode active materials with a nickel content of less than 70 mol%, high-nickel cathode active materials with a nickel content of 70 mol% or more require a water washing step to remove lithium by-products from the particle surface during the manufacturing process. However, if the water washing step is not properly controlled and leads to over-washing, it can result in surface degradation, where not only lithium by-products on the surface but also lithium forming the structure within the particles is lost. When the surface degrades in this way, resistance increases, and the lifespan and storage characteristics may deteriorate.

[0031] Conversely, if washing is not performed properly and lithium by-products are not sufficiently removed, the remaining residual lithium by-products can act as resistors, either increasing the initial resistance or accelerating the decomposition reaction of the electrolyte, leading to increased gas generation.

[0032] Therefore, the inventors have manufactured a high-nickel cathode active material by including the steps described later, so that lithium by-products can be removed without surface degradation by a properly adjusted water washing process. Furthermore, they have confirmed that this prevents the excessive formation of lithium by-products on the surface, improves the surface stability of the cathode active material particles, and improves the lifespan and storage characteristics of batteries containing the cathode active material.

[0033] The following describes each step included in the method for producing a positive electrode active material according to the present invention.

[0034] a) Steps for manufacturing a fired body A method for producing a positive electrode active material according to one embodiment of the present invention includes the step of mixing a precursor containing 70 mol% or more nickel relative to the total number of moles of transition metals with a lithium source, and then firing the mixture to produce a fired body.

[0035] Here, the precursor can be produced as a transition metal precursor, for example, a commercially available nickel-cobalt-manganese hydroxide, or by a method for producing precursors that is well known in the art.

[0036] Specifically, the precursor may be a transition metal hydroxide containing nickel, cobalt and manganese, and containing nickel in an amount of 70 mol% or more based on the total mole number of the entire transition metal. When the nickel content in the precursor satisfies the above range, high capacity characteristics can be achieved.

[0037] Specifically, the precursor may be represented by the following Chemical Formula 1-1.

[0038] [Chemical Formula 1-1] Ni b1 Co c1 Mn d1 Q e1 (OH)₂

[0039] In Chemical Formula 1-1, b1, c1, d1 and e1 each satisfy 0.7≦b1<1.0, 0<c1<0.3, 0<d1<0.3, 0≦e1≦0.1, and b1+c1+d1+e1=1, Q is one or more selected from the group consisting of Al, Mg, V, Ti and Zr.

[0040] In one embodiment of the present invention, b1, c1, d1 and e1 in Chemical Formula 1-1 may each satisfy 0.7≦b1<1.0, 0<c1≦0.15, 0<d1≦0.25 and 0≦e1≦0.05, more preferably may satisfy 0.7≦b1<1.0, 0<c1≦0.1, 0<d1≦0.2 and 0≦e1≦0.03.

[0041] The precursor can be produced, for example, by charging an aqueous transition metal solution, an ammonium cation complex forming agent and a basic compound into a reactor, and performing a coprecipitation reaction while stirring.

[0042] The aqueous transition metal solution can be produced by dissolving a transition metal-containing raw material in a solvent such as water, for example, can be produced by dissolving a nickel-containing raw material, a cobalt-containing raw material and a manganese-containing raw material in water. Further, if necessary, the aqueous transition metal solution may further contain the Q metal-containing raw material.

[0043] On the other hand, the transition metal-containing raw material may be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the transition metal.

[0044] Specifically, the nickel-containing raw material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0045] The cobalt-containing raw material may be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0046] The manganese-containing raw material may be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, or combinations thereof.

[0047] The Q metal-containing raw material may be an aluminum-containing raw material, such as Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halides, or combinations thereof. However, in the case of Al, it may not be added to the transition metal aqueous solution but added together with the lithium source in the calcination step described later. Other examples include acetates, carbonates, nitrates, sulfates, halides, sulfides, or oxides of the Q metal.

[0048] The amount of each transition metal-containing raw material to be added can be determined by considering the molar ratio of the transition metal in the cathode active material that is ultimately to be produced.

[0049] 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 (NH4)2CO3, 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 can be homogeneously mixed with water (specifically, an alcohol, etc.).

[0050] The basic compound may 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.).

[0051] As described above, when an aqueous transition metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reactor and stirred, the transition metal in the aqueous transition metal solution coprecipitates, and precursor particles in the form of transition metal hydroxide are generated.

[0052] Here, the transition metal aqueous 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.

[0053] After the precursor particles are formed by the method described above, the particles are separated from the reaction solution to obtain the transition metal precursor. For example, the reaction solution can be filtered to separate the transition metal precursor, and then the separated transition metal precursor can be washed with water and dried to obtain the transition metal precursor. Here, if necessary, steps such as grinding and / or classification may be performed.

[0054] The transition metal precursor obtained in this way is mixed with a lithium source and then calcined to produce a lithium transition metal oxide. If necessary, a Q metal-containing raw material can be mixed in and then calcined.

[0055] Suitable lithium sources include lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof.

[0056] On the other hand, in one embodiment of the present invention, the step of producing the calcined body may involve mixing the precursor and the lithium source such that the Li / M ratio, which is the molar ratio of lithium in the lithium source to the total metal elements in the precursor, is 1.01 to 1.09, preferably 1.01 to 1.06, and more preferably 1.02 to 1.05. A Li / M of 1.01 or higher is preferable because it results in a higher degree of structural completeness. However, if excess lithium by-products remain on the surface, they may act as resistors, potentially increasing the amount of gas generated by residual lithium; therefore, a Li / M ratio of 1.09 or lower is preferable.

[0057] In one embodiment of the present invention, the firing step in producing the fired body can be carried out in an oxygen atmosphere at 700°C to 900°C, preferably 800°C to 900°C, for 8 to 12 hours. It is preferable that the firing temperature and firing time are within the above range in that sufficient reaction is achieved to ensure structural stability and optimal electrochemical properties.

[0058] b) Steps for producing lithium transition metal oxides A method for producing a positive electrode active material according to one embodiment of the present invention includes the step of washing the calcined body with 30 to 70 parts by weight of a washing solution per 100 parts by weight of the calcined body to produce a lithium transition metal oxide.

[0059] In the present invention, the washing effect is optimized in terms of surface properties and residual lithium content by adjusting the content of the washing solution to 35 to 60 parts by weight, preferably 40 to 50 parts by weight, based on 100 parts by weight of the calcined body during the washing process. Specifically, if the content of the washing solution is less than 30 parts by weight per 100 parts by weight of the calcined body, an excessive amount of residual lithium by-products remains on the surface of the particles, which can cause problems such as increased side reactions due to the excessive lithium by-products and gelation of the slurry. If it exceeds 70 parts by weight, the surface is damaged by excessive washing.

[0060] The washing solution may be water or a mixture of water and an additive, and preferably water. As the washing solution additive, LiOH, which can replenish lithium ions lost during the washing process, and / or NaOH, which can produce a flux effect, can be used, but are not limited to these.

[0061] In one embodiment of the present invention, the water washing step in the production of the lithium transition metal oxide can be carried out by placing the calcined body in water and stirring it at a temperature of 15°C to 25°C at a speed of 1,500 rpm to 2,500 rpm for 1 to 20 minutes.

[0062] Specifically, the washing can be carried out by stirring the calcined body with water using a magnetic bar in a stirrer, the temperature during stirring may be 15°C to 25°C, preferably 15°C to 20°C, and the stirring speed may be 1,500 rpm to 2,500 rpm, preferably 1,500 rpm to 2,000 rpm.

[0063] After the aforementioned washing, a drying step can be carried out at a temperature of 130°C to 150°C for 12 to 24 hours, but is not limited to this.

[0064] positive electrode active material Next, the positive electrode active material according to the present invention will be described. The positive electrode active material according to the present invention can be manufactured by the manufacturing method of the present invention described above, and the description of each component can be made by referring to the description of the manufacturing method described above.

[0065] The positive electrode active material according to the present invention contains a lithium transition metal oxide in which the nickel content among the total metals other than lithium is 70 mol% or more, and the EELS analysis result on the particle surface of the positive electrode active material satisfies the following formula 1.

[0066] [Formula 1] 0.85 ≤ I(854eV) / I(855.5eV) < 1

[0067] In the above formula 1, I(854eV) is the peak intensity shown around 854eV. I(855.5eV) is the peak intensity shown around 855.5eV.

[0068] The EELS analysis results showed that Ni 2+ In this case, at around 854eV, Ni 3+ In this case, it is shown at around 855.5 eV, so by comparing the intensity of each peak, Ni 2+ and Ni 3+ The content of can be compared. That is, formula 1 above is expressed as having Ni on the surface of the particles of the positive electrode active material according to the present invention. 3+ Ni 2+ This means that there are even more of them compared to [the previous number].

[0069] On the other hand, the more severe the surface deterioration due to washing, the more the NiO phase is formed as the structure changes from a layered structure to a rock salt structure, therefore Ni 2+As the oxidation state of Ni increases, the oxidation state of Ni is shown to be low, and as described above, the positive electrode active material according to the present invention has the effect of reducing surface damage due to water washing, resulting in less degradation, and the value of I(854eV) / I(855.5eV) can be shown to be less than 1, as shown in Formula 1 above. However, if the value of I(854eV) / I(855.5eV) is less than 0.85, the lithium compound remaining on the surface of the particles not only acts as a resistor but also accelerates battery degradation through side reactions with the electrolyte, which is disadvantageous in terms of resistance and life characteristics.

[0070] Specifically, the value of I(854eV) / I(855.5eV) may be 0.88 or greater, more specifically 0.90 or greater, and may be 0.99 or less, or 0.95 or less.

[0071] In one embodiment of the present invention, the molar ratio of lithium to the total metal elements other than lithium in the lithium transition metal oxide may be 1.01 to 1.09, preferably 1.01 to 1.06, and more preferably 1.02 to 1.05.

[0072] In one embodiment of the present invention, the lithium transition metal oxide may contain nickel, cobalt, and manganese, and may contain 70 mol% or more nickel relative to the total number of moles of the transition metals. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0073] Specifically, the lithium transition metal oxide can be represented by the following chemical formula 1.

[0074] [Chemical formula 1] Li a Ni b Co c Mn d Q e O 2+f

[0075] In the above chemical formula 1, a, b, c, d, e and f respectively satisfy 1.01≦a≦1.09, 0.7≦b<1.0, 0<c<0.3, 0<d<0.3, 0≦e≦0.1, b+c+d+e=1, and -0.1≦f≦1.0, Q is at least one element selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0076] Preferably, a in Chemical Formula 1 may be 1.01 to 1.06, more preferably 1.02 to 1.05.

[0077] In an embodiment of the present invention, b, c, d and e in Chemical Formula 1 may respectively satisfy 0.7≦b<1.0, 0<c≦0.15, 0<d≦0.25 and 0≦e≦0.05, more preferably 0.7≦b<1.0, 0<c≦0.1, 0<d≦0.2 and 0≦e≦0.03.

[0078] In an embodiment of the present invention, the positive electrode active material is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and D 50 may be 8 μm to 15 μm, preferably 9 μm to 15 μm, more preferably 9 μm to 12 μm. D 50 of 8 μm or more is preferred in terms of increasing the rolling density; however, if the particle size is too large, the particles may penetrate the current collector foil during rolling and lead to electrode breakage, so it is preferred that the particle size does not exceed 15 μm.

[0079] positive electrode Next, the positive electrode according to the present invention will be described.

[0080] The positive electrode according to the present invention includes the mixed positive electrode material described above. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector and containing the mixed positive electrode material.

[0081] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0082] Furthermore, the positive electrode active material layer may include a conductive material and a binder along with the positive electrode active material described above.

[0083] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples 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; 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; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The conductive material can usually be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0084] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene 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, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0085] The positive electrode can be manufactured by a conventional positive electrode manufacturing method. For example, it can be manufactured by mixing a positive electrode active material, a binder, and / or a conductive material in a solvent to produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0086] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0087] Alternatively, the positive electrode can be manufactured by casting the positive electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0088] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described.

[0089] The lithium secondary battery of the present invention comprises 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 lithium secondary battery may further optionally include a battery container housing the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0090] The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector and containing a negative electrode active material.

[0091] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. 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 bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0092] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0093] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can 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 alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metal 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 one or more mixtures of these can be used.

[0094] Furthermore, a metallic lithium thin film can also be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical low-crystallinity carbons include soft carbon and hard carbon, while typical high-crystallinity carbons include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. Preferably, the negative electrode active material may be graphite, SiO₂, or a mixture thereof.

[0095] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in a battery that does not cause chemical changes and has electronic conductivity. Specific examples 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; 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; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material can usually be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0096] The binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene 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, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the negative electrode active material layer.

[0097] The negative electrode active material layer can also be manufactured, for example, by applying a negative electrode slurry containing a negative electrode active material and selectively a binder and conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto another support, peeling it off this support, and then laminating the resulting film onto the negative electrode current collector.

[0098] 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.

[0099] On the other hand, examples of 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.

[0100] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0101] The organic solvent can be used without particular limitations as long as it serves 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), 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 C2-C20 linear, branched, or cyclic hydrocarbon group, which 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.

[0102] 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 lithium salt can be 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 lithium salt is preferably used in a concentration range of 0.1M to 5.0M, more preferably 0.1M to 3.0M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0103] In addition to the components of the electrolyte, the electrolyte may further contain additives to improve the battery's lifespan, suppress the decrease in battery capacity, and improve the battery's discharge capacity. For example, the additives may include, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either alone or in combination.

[0104] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it 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).

[0105] 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.

[0106] 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.

[0107] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by persons with ordinary skill in the art to which the present invention pertains.

[0108] [Examples and Comparative Examples: Manufacturing of Cathode Materials] Example 1. Ni 0.7 Co 0.1 Mn 0.2 A (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.03, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce a calcined body. Next, 70g of the produced calcined body was placed in a beaker filled with 30g of water and placed on a stirrer, and washed with water by stirring at 2,000 rpm for 10 minutes at 15°C. After washing with water, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn 0.2 A lithium transition metal oxide having the composition ]O2 was manufactured. The manufactured lithium transition metal oxide was used as a positive electrode active material, and its D 50 It was 10 μm.

[0109] Comparative Example 1. Ni 0.7 Co 0.1 Mn 0.2A (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.10, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce a calcined body. Next, 70g of the produced calcined body was placed in a beaker filled with 30g of water and placed on a stirrer, and washed with water by stirring at 2,000 rpm for 5 minutes at 15°C. After washing with water, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.10 [Ni 0.7 Co 0.1 Mn 0.2 A lithium transition metal oxide having the composition ]O2 was manufactured. The manufactured lithium transition metal oxide was used as a positive electrode active material, and its D 50 It was 10 μm.

[0110] Comparative Example 2. Ni 0.7 Co 0.1 Mn 0.2 A (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.03, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce a calcined body. Next, 50g of the produced calcined body was placed in a beaker filled with 50g of water and placed on a stirrer, and washed with water by stirring at 2,000 rpm for 10 minutes at 15°C. After washing with water, it was dried by vacuum drying at 130°C for 24 hours, and Li 1.03 [Ni 0.7 Co 0.1 Mn 0.2 A lithium transition metal oxide having the composition ]O2 was manufactured. The manufactured lithium transition metal oxide was used as a positive electrode active material, and its D 50 It was 10 μm.

[0111] [Experimental Example: EELS Analysis and Performance Evaluation] Experimental Example 1. EELS Analysis For each of the positive electrode active materials produced in the above examples and comparative examples, spectra were obtained by analyzing the particles from the surface down to 100 nm using a TEM-equipped instrument (FEI Ttitan G2 80-200 ChemiSTEM) in EELS mode, and the results are shown in Figure 1. After confirming the peak intensities at 854 eV and 855.5 eV in these spectra, I(854 eV) / I(855.5 eV) was calculated and is shown in Table 1 below.

[0112] Experimental Example 2. Evaluation of Resistance and Lifespan (1) Manufacturing of half cells The positive electrode active material, conductive material (carbon black), and binder (PVDF) produced in the above examples and comparative examples were mixed in N-methylpyrrolidone in a weight ratio of 96:2:2 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 100°C, and then rolled to produce a positive electrode.

[0113] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the lithium metal negative electrode. This assembly was then placed inside a battery case, and an electrolyte solution was injected into the case to produce a half cell. The electrolyte solution was prepared by dissolving 1M LiPF6 in a mixed organic solvent consisting of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 3:4:3.

[0114] (2) Measurement of initial resistance After performing an activation process on each of the manufactured half-cells, the initial resistance was obtained by measuring the voltage drop while applying a discharge pulse (2.5C) for 10 seconds at 25°C under constant current-constant voltage conditions, using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd.). The voltage drop was measured after the pulse was applied at 2.5C for 10 seconds. The results are shown in Table 1 below.

[0115] (3) Measurement of lifespan For each of the manufactured half-cells, charging was performed at 45°C at a 1C rate under constant current-constant voltage conditions up to 4.3V (0.05C cutoff), and then discharging at a 1C rate down to 3.0V under constant current (CC). This constituted one cycle, and after repeating the same charge / discharge 100 times, the capacity retention rate was measured using the following formula. The measurement results are shown in Table 1 below.

[0116] -Capacity retention rate (%) = (Discharge capacity after 100 cycles / Discharge capacity after 1 cycle) × 100

[0117] (4) Measurement of gas Each of the manufactured half-cells was charged in CCCV mode at a rate of 0.1C until it reached 4.3V (termination current 1 / 20C). After charging, the cell was disassembled to obtain two charged positive electrodes and two polyethylene separators. These positive electrodes and separators were then alternately stacked on the bottom plate of a coin cell, an electrolyte was injected, and the coin cell was reassembled. Subsequently, the amount of gas generated after storage at 70°C for four weeks was measured using GC-MS (gas chromatograph-mass spectrometer).

[0118] [Table 1]

[0119] By referring to the results in Table 1, it can be confirmed that using a positive electrode active material that satisfies Formula 1 is effective in lowering initial resistance, improving lifespan, and reducing gas generation.

[0120] On the other hand, in Comparative Example 1, an excessive amount of lithium source was added, and although a large amount of lithium remained on the surface, the water washing process was performed for a shorter time compared to Example 1, resulting in less surface damage and Ni 2+ Ni 3+Because it is less than the other value, it can be confirmed that the value of I(854eV) / I(855.5eV) is less than 0.85. As a result, it can be confirmed that the lithium compound remaining on the surface of the particles not only acts as a resistor but also causes side reactions with the electrolyte, leading to a deterioration in initial resistance and lifetime characteristics, and a significant increase in gas generation.

[0121] On the other hand, in Comparative Example 2, in which the calcined body was washed with 100 parts by weight of a washing solution per 100 parts by weight during the manufacturing process, excessive washing caused severe surface damage, resulting in a lower Ni oxidation state that could not satisfy Equation 1. As a result, it can be confirmed that the performance in terms of initial resistance, lifetime characteristics, and gas generation amount was lower compared to Example 1.

Claims

1. It contains a lithium transition metal oxide in which nickel content is 70 mol% or more of the total metals other than lithium, The EELS analysis results for the particle surface satisfy the following equation 1, [Formula 1] 0.85≦I(854eV) / I(855.5eV)<1 In the above formula 1, I (854 eV) is the peak intensity shown around 854 eV. I (855.5 eV) is the peak intensity of the positive electrode active material, exhibited around 855.5 eV.

2. The positive electrode active material according to claim 1, wherein the molar ratio of lithium to the total metal elements other than lithium in the lithium transition metal oxide is 1.01 to 1.

09.

3. The aforementioned lithium transition metal oxide is represented by the following chemical formula 1, [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ Q ｅ O ２＋ｆ In the aforementioned chemical formula 1, a, b, c, d, e, and f are such that 1.03 ≤ a ≤ 1.09, 0.7 ≤ b < 1.0, 0 < c < 0.3, 0 < d < 0.3, 0 ≤ e ≤ 0.1, b + c + d + e = 1, and -0.1 ≤ f ≤ 1.0, respectively. The positive electrode active material according to claim 1, wherein Q is one or more selected from the group consisting of Al, Mg, V, Ti, Zr, W, Cu, Fe, Cr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

4. D of the positive electrode active material ５０ The positive electrode active material according to claim 1, wherein the diameter is 8 μm to 15 μm.

5. A step of mixing a precursor containing 70 mol% or more nickel relative to the total number of moles of transition metals with a lithium source, and then firing the mixture to produce a calcined body, A method for producing a positive electrode active material according to claim 1, comprising the step of washing the calcined body with 30 to 70 parts by weight of a washing solution per 100 parts by weight of the calcined body to produce a lithium transition metal oxide.

6. The method for producing a positive electrode active material according to claim 5, wherein the step of producing the calcined body is to mix the precursor and the lithium source such that the molar ratio of lithium in the lithium source to the total metal elements in the precursor, Li / M, is 1.01 to 1.

09.

7. The method for producing a positive electrode active material according to claim 5, wherein the washing in the step of producing the lithium transition metal oxide is carried out by placing the calcined body in water and stirring it at a temperature of 15°C to 25°C at a speed of 1,500 rpm to 2,500 rpm for 1 minute to 20 minutes.

8. The method for producing a positive electrode active material according to claim 5, wherein the firing in the step of producing the aforementioned fired body is carried out at 700°C to 900°C.

9. A positive electrode comprising the positive electrode active material described in claim 1.

10. A lithium secondary battery comprising a positive electrode according to claim 9, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

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