Mixed cathode material and method for manufacturing the same

Abstract

The present invention comprises a first positive electrode active material containing a first lithium transition metal oxide and a second positive electrode active material containing a second lithium transition metal oxide, wherein the first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more of the total metals other than lithium, and the D of the first positive electrode active material 50 D of the second positive electrode active material 50 More specifically, the present invention relates to a mixed cathode material and a method for manufacturing the same, wherein the EELS analysis results for the particle surfaces of the first cathode active material and the second cathode active material each satisfy 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. 10-2024-0123370 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 mixed cathode material, a method for producing the same, a cathode containing the mixed cathode material, and a lithium secondary battery containing the cathode. [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 aims to solve the above-mentioned problems and to provide a method for effectively removing lithium by-products remaining on the surface without damaging the particle structure when manufacturing a bimodal cathode material with a high nickel content, and a cathode material manufactured using this method that exhibits excellent resistance and lifetime characteristics. [Means for solving the problem]

[0009] [1] The present invention comprises a first positive electrode active material comprising a first lithium transition metal oxide and a second positive electrode active material comprising a second lithium transition metal oxide, wherein the first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more of the total metals other than lithium, and the D of the first positive electrode active material 50 D of the second positive electrode active material 50 The present invention provides a mixed cathode material in which the EELS analysis results for the particle surfaces of the first cathode active material and the second cathode active material each satisfy the following formula 1. [Formula 1] I(854eV) / I(855.5eV)<1 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.

[0010] [2] The present invention provides a mixed cathode material in which, in [1] above, the value of I(854eV) / I(855.5eV) in formula 1 is 0.85 or more.

[0011] [3] The present invention provides a mixed cathode material in which, in [1] or [2] above, the molar ratio of lithium to the total metal elements other than lithium in the first lithium transition metal oxide is 1.01 to 1.09.

[0012] [4] In at least one of [1] to [3] above, the present invention provides a mixed positive electrode material, wherein the molar ratio of lithium to all metal elements other than lithium in the second lithium transition metal oxide is 1.01 to 1.04.

[0013] [5] In at least one of [1] to [4] above, the present invention provides a mixed positive electrode material, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 6:4 to 8:2.

[0014] [6] In at least one of [1] to [5] above, the present invention provides a mixed positive electrode material, wherein the first 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 Chemical Formula 1 above, 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 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.

[0015] [7] In at least one of [1] to [6] above, the present invention provides a mixed positive electrode material, wherein the second lithium transition metal oxide is represented by the following Chemical Formula 2. [Chemical Formula 2] Li g Ni h Co i Mn j Q' k O 2+q In Chemical Formula 2 above, g, h, i, j, k, and q are such that 1.01 ≤ g ≤ 1.04, 0.7 ≤ h < 1.0, and 0 respectively. <i<0.3、0<j<0.3、0≦k≦0.1、h+i+j+k=1、-0.1≦q≦1.0であり、 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.

[0016] [8] The present invention relates to at least one of the above [1] to [7], wherein the D of the first positive electrode active material 50 A mixed cathode material is provided in which the thickness is 8 μm to 15 μm.

[0017] [9] The present invention relates to at least one of the above [1] to [8], wherein the D of the second positive electrode active material 50 A mixed cathode material is provided in which the particle size is 2 μm to 5 μm.

[0018]

[10] The present invention comprises the steps of: producing a first calcined body by mixing a first precursor containing 70 mol% or more nickel with respect to the total number of moles of transition metals and a first lithium source and calcining the mixture; producing a first lithium transition metal oxide by washing the first calcined body with 50 to 70 parts by weight of a washing solution per 100 parts by weight of the first calcined body; producing a second lithium transition metal oxide by mixing a second precursor containing 70 mol% or more nickel with respect to the total number of moles of transition metals and a second lithium source and calcining the mixture; and producing a second lithium transition metal oxide by washing the second calcined body with 60 to 80 parts by weight of a washing solution per 100 parts by weight of the second calcined body, wherein the D 50 The D of the second lithium transition metal oxide 50 The present invention provides a method for manufacturing a mixed cathode material by at least one of the above [1] to [9], which is larger than [1].

[0019]

[11] The present invention provides a method for producing a mixed cathode material, wherein the step of producing the first calcined body in

[10] is to mix the first precursor and the first lithium source such that the molar ratio (Li / M)1 of lithium in the first lithium source to the total metal elements of the first precursor is 1.03 to 1.09.

[0020]

[12] The present invention provides a method for producing a mixed cathode material, wherein, in

[10] or

[11] , the step of producing the second calcined body is to mix the second precursor and the second lithium source such that the molar ratio (Li / M)2 of lithium in the second lithium source to the total metal elements of the second precursor is 1.01 to 1.04.

[0021]

[13] The present invention provides a method for producing a mixed cathode material, further comprising the step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:2 in at least one of the above

[10] to

[12] .

[0022]

[14] The present invention provides a method for producing a mixed cathode material, wherein in at least one of the above

[10] to

[13] , the water washing step for producing the first lithium transition metal oxide is carried out by placing the first 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.

[0023]

[15] The present invention provides a method for producing a mixed cathode material, wherein in at least one of the above

[10] to

[14] , the water washing step for producing the second lithium transition metal oxide is carried out by placing the second 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.

[0024]

[16] The present invention provides a method for manufacturing a mixed cathode material, wherein in at least one of the above

[10] to

[15] , the firing in the step of manufacturing the first fired body is carried out at 700°C to 900°C.

[0025]

[17] The present invention provides a method for manufacturing a mixed cathode material, wherein in at least one of the above

[10] to

[16] , the firing in the step of manufacturing the second fired body is carried out at 700°C to 900°C.

[0026]

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

[0027]

[19] The present invention provides a lithium secondary battery comprising the positive electrode described in

[18] 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]

[0028] The present invention provides a mixed cathode material and a method for manufacturing the same, which, due to its high nickel content, has high capacity and a bimodal configuration, thereby enabling the realization of high energy density.

[0029] Furthermore, when manufacturing high-nickel cathode active materials, which require a water washing process, by providing separate optimal water washing conditions for small particles with relatively large surface areas and large particles with relatively small surface areas, lithium by-products remaining on the surface can be effectively removed without damaging the particles.

[0030] Furthermore, by applying different ratios of the number of moles of lithium to the total number of moles of other metals (hereinafter referred to as the Li / M molar ratio) for small particles with a large surface area that are highly reactive, and for large particles that are not, it is possible to prevent the problem of excessive formation of lithium byproducts after calcination in small particles, and to prevent a decrease in structural stability in large particles.

[0031] As a result, a mixed cathode material with excellent resistance and lifespan characteristics can be provided. [Brief explanation of the drawing]

[0032] [Figure 1]This figure shows the EELS spectra of the surface of the first positive electrode active material produced in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. [Figure 2] This figure shows the EELS spectra of the surface of the second positive electrode active material produced in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention. [Figure 3] This figure shows the EELS spectra of the surface of the first positive electrode active material produced in Comparative Examples 3 and 4 of the present invention. [Figure 4] This figure shows the EELS spectra of the surface of the second positive electrode active material produced in Comparative Examples 3 and 4 of the present invention. [Modes for carrying out the invention]

[0033] The present invention will be described in more detail below to aid in understanding the present invention.

[0034] 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 an HR-TEM instrument, with the horizontal axis representing the energy loss region and the vertical axis representing the peak intensity.

[0035] 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.

[0036] In this invention, "particle surface" means a region within a distance of 100 nm from the surface of the particle toward the center.

[0037] 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.

[0038] Manufacturing method for mixed cathode materials First, the method for producing the mixed cathode material according to the present invention will be described.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Furthermore, in the case of bimodal cathode materials in which large and small particles are mixed, if the washing conditions are adjusted to suit the large particles, lithium by-products on the surface of the small particles are not sufficiently removed, leading to problems such as them acting as resistors or an increase in gas generation. Conversely, if the conditions are adjusted to suit the small particles, the large particles are excessively washed, causing damage to their surface and resulting in increased resistance.

[0043] Therefore, the inventors have manufactured a high-nickel bimodal cathode material by including the steps described later, so that lithium by-products are removed without surface degradation through a water washing process in which both large and small particles are appropriately controlled. This prevents the excessive formation of lithium by-products on the surface, thereby improving the surface stability of the cathode material, and it has been confirmed that the lifespan and storage characteristics of batteries containing the cathode material are improved.

[0044] The following describes each step included in the method for producing the mixed cathode material of the present invention.

[0045] a) Step of manufacturing the first calcined body. A method for producing a mixed cathode material according to one embodiment of the present invention includes the step of mixing a first precursor containing 70 mol% or more nickel with respect to the total number of moles of transition metals and a first lithium source, and then firing the mixture to produce a first calcined body.

[0046] Here, the first precursor may be a transition metal precursor, for example, a commercially available precursor such as a nickel-cobalt-manganese-based hydroxide, or may be one produced by a method for producing a precursor well known in the art.

[0047] Specifically, the first precursor may be a transition metal hydroxide containing nickel, cobalt and manganese, and containing 70 mol% or more of nickel 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.

[0048] Specifically, the first precursor may be represented by the following Chemical Formula 1-1.

[0049] [Chemical Formula 1-1] Ni b1 Co c1 Mn d1 Q e1 (OH)₂

[0050] In Chemical Formula 1-1, b1, c1, d1 and e1 respectively 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.

[0051] In one embodiment of the present invention, b1, c1, d1 and e1 in Chemical Formula 1-1 may respectively satisfy 0.7≦b1<1.0, 0<c1≦0.15, 0<d1≦0.25 and 0≦e1≦0.05, and more preferably may respectively satisfy 0.7≦b1<1.0, 0<c1≦0.1, 0<d1≦0.2 and 0≦e1≦0.03.

[0052] The first precursor and the second precursor described later can be produced, for example, by forming an ammonium cation complex with an aqueous transition metal solution, charging a basic compound into a reactor, and carrying out a coprecipitation reaction while stirring.

[0053] The transition metal aqueous solution can be produced by dissolving a transition metal-containing raw material in a solvent such as water. For example, it can be produced by dissolving nickel-containing raw material, cobalt-containing raw material, and manganese-containing raw material in water. Furthermore, if necessary, the transition metal aqueous solution may further contain the Q and Q' metal-containing raw materials.

[0054] 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.

[0055] 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.

[0056] The cobalt-containing raw material may be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0057] 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.

[0058] The metal-containing raw materials Q and Q' may also be aluminum-containing raw materials, 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 materials may include acetates, carbonates, nitrates, sulfates, halides, sulfides, or oxides of the metals Q and Q'.

[0059] 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.

[0060] 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.).

[0061] 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.).

[0062] 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 hydroxides are generated.

[0063] 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.

[0064] Once 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.

[0065] The transition metal precursor obtained in this way is used as the first precursor and mixed with the first lithium source, then calcined to produce the first lithium transition metal oxide. Here, if necessary, a Q metal-containing raw material can be mixed in and calcined together.

[0066] As the first lithium source, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used, for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0067] On the other hand, in one embodiment of the present invention, the step of producing the first calcined body may involve mixing the first precursor and the first lithium source such that the molar ratio (Li / M)1 of lithium in the first lithium source to the total metal elements in the first precursor is 1.03 to 1.09, preferably 1.03 to 1.06, and more preferably 1.04 to 1.05. A (Li / M)1 of 1.03 or higher is preferable because it results in a higher degree of structural completeness. However, if excess lithium byproducts remain on the surface, they may act as resistors, potentially increasing the amount of gas generated by residual lithium, so a ratio of 1.09 or lower is preferable.

[0068] In one embodiment of the present invention, the firing step for producing the first 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. The firing temperature and time being within the above range is preferable in that it ensures structural stability through sufficient reaction and ensures optimal electrochemical properties.

[0069] b) Steps for producing the first lithium transition metal oxide. A method for producing a mixed cathode material according to one embodiment of the present invention includes the step of washing the first calcined body with 50 to 70 parts by weight of a washing solution per 100 parts by weight of the first calcined body to produce a first lithium transition metal oxide.

[0070] In the present invention, in the water washing process, the content of the washing solution is adjusted to 50 to 70 parts by weight, preferably 60 to 70 parts by weight, based on 100 parts by weight of the first calcined body, thereby achieving an optimal water washing effect in terms of surface properties and residual lithium content. Specifically, if the content of the washing solution relative to 100 parts by weight of the first calcined body is less than 50 parts by weight, 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.

[0071] In one embodiment of the present invention, the water washing step for producing the first lithium transition metal oxide can be carried out by placing the first 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.

[0072] Specifically, the washing can be carried out by stirring the first 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.

[0073] 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.

[0074] c) Step of manufacturing the second fired body. A method for producing a mixed positive electrode material according to one embodiment of the present invention comprises the step of mixing a second precursor containing 70 mol% or more of nickel relative to the total number of moles of transition metals and a second lithium source, followed by firing to produce a second fired body.

[0075] Here, the second precursor can be produced as a transition metal precursor, for example, from a precursor such as a commercially available nickel-cobalt-manganese-based hydroxide, or by a method for producing a precursor well known in the art.

[0076] Specifically, the second precursor may be a transition metal hydroxide containing nickel, cobalt and manganese, and containing 70 mol% or more of nickel relative to the total number of moles of all transition metals. When the nickel content in the precursor satisfies the above range, high capacity characteristics can be achieved.

[0077] Specifically, the second precursor can be represented by the following Chemical Formula 2-1.

[0078] [Chemical Formula 2-1] Ni h1 Co i1 Mn j1 Q’ k1 (OH)2

[0079] In Chemical Formula 2-1 above, h1, i1, j1 and k1 respectively satisfy 0.7≦h1<1.0, 0<i1<0.3, 0<j1<0.3, 0≦k1≦0.1, and h1+i1+j1+k1=1, Q' is at least one selected from the group consisting of Al, Mg, V, Ti and Zr.

[0080] In one embodiment of the present invention, h1, i1, j1 and k1 in Chemical Formula 2-1 may respectively satisfy 0.7≦h1<1.0, 0<i1≦0.15, 0<j1≦0.25 and 0≦k1≦0.05, more preferably 0.7≦h1<1.0, 0<i1≦0.1, 0<j1≦0.2 and 0≦k1≦0.03.

[0081] As the second precursor, a transition metal precursor produced by the method described in the description of the steps for producing the first calcined body above can be used. The second precursor is mixed with a second lithium source and then calcined to produce a second lithium transition metal oxide. Here, if necessary, a Q' metal-containing raw material can be mixed together and calcined.

[0082] As the second lithium source, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0083] On the other hand, in one embodiment of the present invention, the step of producing the second calcined body may involve mixing the second precursor and the second lithium source such that the molar ratio (Li / M)2 of lithium in the second lithium source to the total metal elements in the second precursor is 1.01 to 1.04, preferably 1.02 to 1.04, and more preferably 1.02 to 1.03. A (Li / M)2 of 1.01 or higher is preferable because it results in a higher degree of structural completeness. However, if excess lithium byproducts remain on the surface, they may act as resistors and increase the amount of gas generated by residual lithium; therefore, a ratio of 1.04 or lower is preferable.

[0084] In one embodiment of the present invention, the firing step for producing the second 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. The firing temperature and time being within the above range is preferable in that it ensures structural stability through sufficient reaction and ensures optimal electrochemical properties.

[0085] d) Steps to produce a lithium-2 transition metal oxide. A method for producing a mixed cathode material according to one embodiment of the present invention includes the step of washing the second calcined body with 60 to 80 parts by weight of a washing solution per 100 parts by weight of the second calcined body to produce a second lithium transition metal oxide.

[0086] 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 based on 100 parts by weight of the second calcined body to 60 to 80 parts by weight, preferably 60 to 70 parts by weight, during the washing process. Specifically, if the content of the washing solution based on 100 parts by weight of the second calcined body is less than 60 parts by weight, 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 80 parts by weight, the surface is damaged by excessive washing.

[0087] In one embodiment of the present invention, the water washing step for producing the second lithium transition metal oxide can be carried out by placing the second 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.

[0088] Specifically, the washing can be carried out by stirring the second 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, more preferably 1,500 rpm to 2,000 rpm.

[0089] Next, a vacuum drying step can be performed at a temperature of 130°C to 180°C for 12 to 24 hours, but is not limited to this.

[0090] Furthermore, a method for producing a mixed cathode material according to one embodiment of the present invention may further include a step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:2, preferably 7:3 to 8:2. A higher content of the first lithium transition metal oxide compared to the second lithium transition metal oxide is advantageous for increasing the rolling density.

[0091] On the other hand, the D of the first lithium transition metal oxide 50 The D of the second lithium transition metal oxide is 50 It is larger than the above, and may be 8 μm to 15 μm, preferably 9 μm to 15 μm, and more preferably 9 μm to 12 μm. Also, the D of the second lithium transition metal oxide 50 The particle size may be 2 μm to 5 μm, preferably 3 μm to 5 μm, and more preferably 3 μm to 4 μm.

[0092] On the other hand, in the process of washing the first and second calcined bodies with water, the washing solution may be water or a mixture of water and an additive, preferably water. As the washing solution additive, LiOH, which can replenish the lithium ions lost during the washing process, and / or NaOH, which can provide a flux effect, can be used, but are not limited to these.

[0093] Mixed cathode material Next, the mixed cathode material according to the present invention will be described. The mixed cathode 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.

[0094] The mixed cathode material according to the present invention comprises a first cathode active material containing a first lithium transition metal oxide and a second cathode active material containing a second lithium transition metal oxide, wherein the first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more of the total metals other than lithium, and the D of the first cathode active material 50 D of the second positive electrode active material50 More specifically, the EELS analysis results for the particle surfaces of the first and second cathode active materials satisfy the following equation 1, respectively.

[0095] [Formula 1] I(854eV) / I(855.5eV)≦1

[0096] 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.

[0097] EELS analysis results showed 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, the mixed cathode material satisfying formula 1 has Ni on the surface of the particles, specifically on the surface of the particles of the first cathode active material and the second cathode active material. 3+ Ni 2+ There are more of them compared to [the other group].

[0098] 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. 2+ As the oxidation state of Ni increases, the oxidation state of Ni remains low, and as described above, the mixed cathode material according to the present invention has the effect of reducing surface damage caused by water washing, thus reducing the occurrence of degradation and satisfying formula 1.

[0099] Specifically, the value of I(854eV) / I(855.5eV) may be 0.85 or greater, more specifically 0.90 or greater, 0.99 or less, or 0.95 or less. When the value of I(854eV) / I(855.5eV) is 0.85 or greater, less lithium compound remains on the surface of the particles, and more favorable performance in terms of resistance and lifespan can be achieved.

[0100] In one embodiment of the present invention, the molar ratio of lithium to the total metal elements other than lithium in the first lithium transition metal oxide may be 1.03 to 1.09, preferably 1.03 to 1.06, and more preferably 1.04 to 1.05.

[0101] In one embodiment of the present invention, the first lithium transition metal oxide may be a lithium transition metal oxide containing nickel, cobalt, and manganese, and containing 70 mol% or more of 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.

[0102] Specifically, the first lithium transition metal oxide can be represented by the following chemical formula 1.

[0103] [Chemical formula 1] Li a Ni b Co c Mn d Q e O 2+f

[0104] In the aforementioned chemical formula 1, a, b, c, d, e, and f are such that 1.01 ≤ a ≤ 1.09, 0.7 ≤ b < 1.0, and 0 respectively. <c<0.3、0<d<0.3、0≦e≦0.1、b+c+d+e=1、-0.1≦f≦1.0であり、 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.

[0105] Preferably, a in chemical formula 1 may be 1.02 to 1.06, more preferably 1.03 to 1.05.

[0106] In one embodiment of the present invention, b, c, d and e in Chemical Formula 1 may each satisfy 0.7≦b<1.0, 0<c≦0.15, 0<d≦0.25 and 0≦e≦0.05, and more preferably may satisfy 0.7≦b<1.0, 0<c≦0.1, 0<d≦0.2 and 0≦e≦0.03.

[0107] In one embodiment of the present invention, the first positive electrode active material is in the form of secondary particles formed by aggregation 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 being 8 μm or more is preferable in terms of increasing rolling density; however, if the particle diameter is excessively large, it may penetrate the current collector foil during rolling and lead to electrode breakage, so it is preferable that the diameter does not exceed 15 μm.

[0108] In one embodiment of the present invention, the molar ratio of lithium to the total metal elements other than lithium in the second lithium transition metal oxide may be 1.01 to 1.04, preferably 1.02 to 1.04, more preferably 1.02 to 1.03.

[0109] In one embodiment of the present invention, the first lithium transition metal oxide may be a lithium transition metal oxide containing nickel, cobalt and manganese, and containing nickel in an amount of 70 mol% or more based on the total number of moles of all transition metals. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0110] Specifically, the second lithium transition metal oxide may be represented by Chemical Formula 2 below.

[0111] [Chemical Formula 2] Li g Ni h Co i Mn j Q’ k O 2+q

[0112] In Chemical Formula 2, g, h, i, j, k and q respectively satisfy 1.01 ≤ g ≤ 1.04, 0.7 ≤ h < 1.0, 0 < i < 0.3, 0 < j < 0.3, 0 ≤ k ≤ 0.1, h+i+j+k=1, and -0.1 ≤ q ≤ 1.0, 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.

[0113] Preferably, g in the above Chemical Formula 2 may be 1.02 to 1.04, more preferably 1.02 to 1.03.

[0114] In one embodiment of the present invention, h, i, j and k in the above Chemical Formula 1 may respectively satisfy 0.7 ≤ b < 1.0, 0 < c ≤ 0.15, 0 < d ≤ 0.25 and 0 ≤ e ≤ 0.05, and more preferably may satisfy 0.7 ≤ b < 1.0, 0 < c ≤ 0.1, 0 < d ≤ 0.2 and 0 ≤ e ≤ 0.03.

[0115] In one embodiment of the present invention, the second cathode active material is in the form of secondary particles formed by aggregation of a plurality of primary particles, and D 50 may be 2 μm to 5 μm, preferably 3 μm to 5 μm, more preferably 3 μm to 4 μm. If the size of small particles in a bimodal cathode material is too small, the rolling density will instead decrease, and the amount of gas generated by fine powder may increase. Therefore, D 50 is preferably 3 μm or more, but it is preferable that the size does not exceed 5 μm in consideration of the bimodal effect with large particles and the object of achieving an optimal rolling density.

[0116] positive electrode Next, the cathode according to the present invention will be described.

[0117] The cathode according to the present invention includes the mixed cathode material. Specifically, the cathode includes a cathode current collector and a cathode active material layer that is provided on the cathode current collector and contains the mixed cathode material.

[0118] 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.

[0119] Furthermore, the positive electrode active material layer may include a conductive material and a binder along with the positive electrode active material described above.

[0120] 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 contained 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.

[0121] The binder plays a role in improving adhesion between positive electrode active material particles and 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described.

[0126] 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.

[0127] The negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, which contains a negative electrode active material.

[0128] 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 negative electrode 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.

[0129] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0138] 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.

[0139] 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. The lithium salt is preferably used within 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, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0140] 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.

[0141] As described above, lithium secondary batteries containing the positive electrode material according to the present invention exhibit excellent discharge capacity, output characteristics, and capacity retention rate stably, making them useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0142] 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.

[0143] 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.

[0144] 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.

[0145] [Examples and Comparative Examples: Manufacturing of Cathode Materials] Example 1. Ni 0.7 Co 0.1 Mn 0.2 The (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 the first calcined body. Next, 60g of the first calcined body was placed in a beaker filled with 40g 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 first lithium transition metal oxide having the composition of ]O2 was produced. The produced first lithium transition metal oxide was used as the first positive electrode active material, and its D 50 It was 10 μm.

[0146] Ni 0.7 Co 0.1 Mn 0.2The (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 860°C for 10 hours under an oxygen atmosphere to produce a second calcined body. Next, 60g of the produced second calcined body was placed in a beaker filled with 40g 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 second lithium transition metal oxide having the composition of ]O2 was produced. The produced second lithium transition metal oxide was used as the second positive electrode active material, and its D 50 It was 4 μm.

[0147] Next, the first positive electrode active material and the second positive electrode active material were mixed in a weight ratio of 70:30 to produce a mixed positive electrode material.

[0148] Example 2. Ni 0.7 Co 0.1 Mn 0.2 The (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.05, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce the first calcined body. Next, 60g of the first calcined body was placed in a beaker filled with 40g of water and placed on a stirrer, and washed with water by stirring at 1,500 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 1.05 [Ni 0.7 Co 0.1 Mn 0.2 A first lithium transition metal oxide having the composition of ]O2 was produced. The produced first lithium transition metal oxide was used as the first positive electrode active material, and its D 50 It was 10 μm.

[0149] The second positive electrode active material was manufactured using the same process as in Example 1.

[0150] Next, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to produce a mixed positive electrode material.

[0151] Comparative Example 1. Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH such that the molar ratio of Li / M(Ni+Co+Mn) was 1.00, and heat-treated at 870°C for 10 hours in an oxygen atmosphere to produce a first fired body. Next, 40 g of the produced first fired body was placed in a beaker filled with 60 g of water, placed on a stirrer, and washed with water by stirring at 1,500 rpm for 10 minutes at 15°C. After washing with water, drying was performed by vacuum drying at 130°C for 24 hours to obtain Li 1.00 [Ni 0.7 Co 0.1 Mn 0.2 A first lithium transition metal oxide having a composition of O2 was produced. The produced first lithium transition metal oxide was used as the first positive electrode active material, and its D 50 was 10 µm.

[0152] Ni 0.7 Co 0.1 Mn 0.2 (OH)2 precursor was mixed with LiOH such that the molar ratio of Li / M(Ni+Co+Mn) was 1.00, and heat-treated at 860°C for 10 hours in an oxygen atmosphere to produce a second fired body. Next, 40 g of the produced first fired body was placed in a beaker filled with 60 g of water, placed on a stirrer, and washed with water by stirring at 1,500 rpm for 10 minutes at 15°C. After washing with water, drying was performed by vacuum drying at 130°C for 24 hours to obtain Li 1.00 [Ni 0.7 Co 0.1 Mn 0.2 A second lithium transition metal oxide having a composition of O2 was produced. The produced second lithium transition metal oxide was used as the second positive electrode active material, and its D 50 was 4 µm.

[0153] Next, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to produce a mixed positive electrode material.

[0154] Comparative Example 2. Ni 0.7 Co 0.1 Mn 0.2 (OH)₂ precursor was mixed with LiOH such that the molar ratio of Li / M (Ni+Co+Mn) was 1.12, and heat-treated at 870°C for 10 hours in an oxygen atmosphere to produce a first fired body. Next, 60 g of the produced first fired body was placed in a beaker filled with 40 g of water, placed on a stirrer, and washed with water by stirring at 1,500 rpm for 10 minutes at 15°C. After washing with water, drying was performed by vacuum drying at 130°C for 24 hours to obtain Li 1.12 [Ni 0.7 Co 0.1 Mn 0.2 O₂ to produce a first lithium transition metal oxide having the composition. The produced first lithium transition metal oxide was used as a first positive electrode active material, and its D 50 was 10 μm.

[0155] Ni 0.7 Co 0.1 Mn 0.2 (OH)₂ precursor was mixed with LiOH such that the molar ratio of Li / M (Ni+Co+Mn) was 1.10, and heat-treated at 860°C for 10 hours in an oxygen atmosphere to produce a second fired body. Next, 60 g of the produced first fired body was placed in a beaker filled with 40 g of water, placed on a stirrer, and washed with water by stirring at 1,500 rpm for 10 minutes at 15°C. After washing with water, drying was performed by vacuum drying at 130°C for 24 hours to obtain Li 1.10 [Ni 0.7 Co 0.1 Mn 0.2 O₂ to produce a second lithium transition metal oxide having the composition. The produced second lithium transition metal oxide was used as a second positive electrode active material, and its D 50 was 4 μm.

[0156] Next, the first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 70:30 to produce a mixed positive electrode material.

[0157] Comparative Example 3. Ni 0.7 Co 0.1 Mn 0.2 The (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 the first calcined body. Next, 50 g of the first calcined body was placed in a beaker filled with 50 g 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 first lithium transition metal oxide having the composition of ]O2 was produced. The produced first lithium transition metal oxide was used as the first positive electrode active material, and its D 50 It was 10 μm.

[0158] Ni 0.7 Co 0.1 Mn 0.2 The (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 second calcined body. Next, 50g of the produced second 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 second lithium transition metal oxide having the composition of ]O2 was produced. The produced second lithium transition metal oxide was used as the second positive electrode active material, and its D 50 It was 4 μm.

[0159] Next, the first positive electrode active material and the second positive electrode active material were mixed in a weight ratio of 70:30 to produce a mixed positive electrode material.

[0160] Comparative Example 4. Ni 0.7 Co 0.1 Mn0.2 The (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.00, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce the first calcined body. Next, 40g of the first calcined body was placed in a beaker filled with 60g 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 1.00 [Ni 0.7 Co 0.1 Mn 0.2 A first lithium transition metal oxide having the composition of ]O2 was produced. The produced first lithium transition metal oxide was used as the first positive electrode active material, and its D 50 It was 10 μm.

[0161] Ni 0.7 Co 0.1 Mn 0.2 The (OH)2 precursor was mixed with LiOH and Li / M(Ni+Co+Mn) in a molar ratio of 1.07, and the mixture was heat-treated at 870°C for 10 hours under an oxygen atmosphere to produce a second calcined body. Next, 70g of the produced second 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 1.07 [Ni 0.7 Co 0.1 Mn 0.2 A second lithium transition metal oxide having the composition of ]O2 was produced. The produced second lithium transition metal oxide was used as the second positive electrode active material, and its D 50 It was 4 μm.

[0162] Next, the first positive electrode active material and the second positive electrode active material were mixed in a weight ratio of 70:30 to produce a mixed positive electrode material.

[0163] [Experimental Example: EELS Analysis and Performance Evaluation] Experimental Example 1. EELS Analysis For each of the mixed cathode materials produced in the above examples and comparative examples, a TEM (FEI Ttitan G2 80-200 ChemiSTEM) was used to analyze the particles from the surface down to 100 nm in EELS mode, and spectra were obtained. The results are shown in Figures 1 to 4. Figures 1 and 3 show the results of the analysis of the first cathode active material particles for each mixed cathode material, and Figures 2 and 4 show the results of the analysis of the second cathode active material particles. 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.

[0164] Experimental Example 2. Resistance and Lifetime Evaluation (1) Manufacturing of half cells The mixed cathode material, conductive material (carbon black), and binder (PVDF) prepared in the above examples and comparative examples were mixed in N-methylpyrrolidone in a weight ratio of 96:2:2 to produce a cathode slurry. The cathode slurry was applied to one surface of an aluminum current collector, dried at 100°C, and then rolled to produce a cathode.

[0165] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the lithium metal negative electrode. After this assembly was placed inside a battery case, 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.

[0166] (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.

[0167] (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.

[0168] -Capacity retention rate (%) = (Discharge capacity after 100 cycles / Discharge capacity after 1 cycle) × 100

[0169] (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).

[0170] [Table 1]

[0171] Referring to the results in Table 1, it can be confirmed that using a mixed cathode material in which both the first and second cathode active materials satisfy Formula 1 is effective in lowering the initial resistance, improving the lifespan, and reducing gas generation. On the other hand, in the manufacturing process of the cathode material, in Comparative Example 1, in which the first and second calcined bodies were washed with 150 parts by weight of washing solution per 100 parts by weight of calcined bodies, and in Comparative Example 3, in which the first and second calcined bodies were washed with 100 parts by weight of washing solution per 100 parts by weight of calcined bodies, excessive washing caused severe surface damage, resulting in a lower Ni oxidation state, making it impossible to satisfy Formula 1, and thus worsening the initial resistance and lifespan characteristics.

[0172] On the other hand, in Comparative Example 2, the excess lithium was not properly calcined, and the surface formed a rock salt structure instead of a layered structure, with NiO phase forming Ni 2+ Because of the large amount of lithium by-products present, Equation 1 cannot be satisfied, and as a result, it can be confirmed that the initial resistance and lifetime characteristics have deteriorated. In particular, it can be confirmed that the amount of gas generated has also increased significantly due to the excess lithium by-products remaining on the surface.

[0173] Furthermore, in the case of Comparative Example 4, the second positive electrode active material satisfies Equation 1, but in the case of the first positive electrode active material, the Ni oxidation number is low due to peroxide washing during the manufacturing process, and therefore it cannot satisfy Equation 1, thus confirming that the initial resistance and lifetime characteristics are not good.

Claims

1. The present invention comprises a first positive electrode active material containing a first lithium transition metal oxide and a second positive electrode active material containing a second lithium transition metal oxide, The first lithium transition metal oxide and the second lithium transition metal oxide each have a nickel content of 70 mol% or more of the total metals other than lithium. D of the first positive electrode active material ５０ D of the second positive electrode active material ５０ Larger, The EELS analysis results for the particle surfaces of the first positive electrode active material and the second positive electrode active material satisfy the following formula 1, [Formula 1] 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 shown around 855.5 eV for the mixed cathode material.

2. The mixed cathode material according to claim 1, wherein the value of I(854eV) / I(855.5eV) in formula 1 is 0.85 or greater.

3. The mixed cathode material according to claim 1, wherein the molar ratio of lithium to the total metal elements other than lithium in the first lithium transition metal oxide is 1.01 to 1.

09.

4. The mixed cathode material according to claim 1, wherein the molar ratio of lithium to the total metal elements other than lithium in the second lithium transition metal oxide is 1.01 to 1.

04.

5. The mixed cathode material according to claim 1, wherein the weight ratio of the first cathode active material to the second cathode active material is 6:4 to 8:

2.

6. The first 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 1.01 ≤ 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, respectively. The mixed cathode 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.

7. The second lithium transition metal oxide is represented by the following chemical formula 2, [Chemical formula 2] Li ｇ Ni ｈ Co ｉ Mn ｊ Q' ｋ O ２＋ｑ In the aforementioned chemical formula 2, g, h, i, j, k, and q are such that 1.01 ≤ g ≤ 1.04, 0.7 ≤ h < 1.0, 0 < i < 0.3, 0 < j < 0.3, 0 ≤ k ≤ 0.1, h + i + j + k = 1, and -0.1 ≤ q ≤ 1.0, respectively. The mixed cathode 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.

8. D of the first positive electrode active material ５０ The mixed cathode material according to claim 1, wherein the particle size is 8 μm to 15 μm.

9. D of the second positive electrode active material ５０ The mixed cathode material according to claim 1, wherein the particle size is 2 μm to 5 μm.

10. A first precursor containing 70 mol% or more nickel relative to the total number of moles of transition metals and a first lithium source are mixed and calcined to produce a first calcined body; The first calcined body is washed with water in an amount of 50 to 70 parts by weight of a washing solution per 100 parts by weight of the first calcined body to produce a first lithium transition metal oxide, A second precursor containing 70 mol% or more nickel relative to the total number of moles of transition metals and a second lithium source are mixed and calcined to produce a second calcined body; The process includes the step of washing the second calcined body with 60 to 80 parts by weight of a washing solution per 100 parts by weight of the second calcined body to produce a second lithium transition metal oxide, The first lithium transition metal oxide D ５０ is the D of the second lithium transition metal oxide. ５０ A method for manufacturing a mixed cathode material according to claim 1, which is larger than the method described in claim 1.

11. The step of producing the first calcined body is to provide the first precursor and the first lithium source, where the molar ratio of lithium in the first lithium source to the total metal elements in the first precursor is (Li / M). １ A method for producing a mixed cathode material according to claim 10, wherein the mixture is mixed so that the ratio is 1.03 to 1.

09.

12. The step of producing the second calcined body is to provide the second precursor and the second lithium source, where the molar ratio of lithium in the second lithium source to the total metal elements in the second precursor is (Li / M). ２ A method for producing a mixed cathode material according to claim 10, wherein the mixture is mixed so that the ratio is 1.01 to 1.

04.

13. A method for producing a mixed cathode material according to claim 10, further comprising the step of mixing the first lithium transition metal oxide and the second lithium transition metal oxide in a weight ratio of 6:4 to 8:

2.

14. The method for producing a mixed cathode material according to claim 10, wherein the water washing step for producing the first lithium transition metal oxide is carried out by placing the first 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.

15. The method for producing a mixed cathode material according to claim 10, wherein the water washing step for producing the second lithium transition metal oxide is carried out by placing the second 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.

16. The method for producing a mixed cathode material according to claim 10, wherein the firing in the step of producing the first fired body is carried out at 700°C to 900°C.

17. The method for producing a mixed cathode material according to claim 10, wherein the firing in the step of producing the second fired body is carried out at 700°C to 900°C.

18. A positive electrode comprising the mixed positive electrode material described in claim 1.

19. A lithium secondary battery comprising a positive electrode according to claim 18, 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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