Method for producing a positive electrode active material precursor, positive electrode active material precursor, and method for producing a positive electrode active material using the positive electrode active material precursor

Abstract

The present invention relates to a method for producing a cobalt-free permanganate positive electrode active material precursor in which surface impurities are reduced or absent, a positive electrode active material precursor produced from the same and free of impurities such as surface manganese oxides, and a method for producing a positive electrode active material using the positive electrode active material precursor.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0179591, filed December 20, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing a cobalt-free permanganate positive electrode active material precursor in which surface impurities are reduced or absent, a positive electrode active material precursor produced from the same and free of impurities such as manganese oxides on the surface, and a method for producing a positive electrode active material using the positive electrode active material precursor. [Background technology]

[0003] With the technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Lithium-transition metal composite oxides are used as the positive electrode active material for lithium secondary batteries, and the lithium-cobalt composite metal oxide LiCoO2 is the most commonly used, due to its high operating voltage and excellent capacity characteristics. However, LiCoO2 has very poor thermal properties due to the destabilization of its crystal structure caused by lithium removal, and is also expensive, which limits its use in large quantities as a power source in fields such as electric vehicles.

[0005] Materials being developed as alternatives to LiCoO2 include lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), and lithium nickel composite metal oxides (such as LiNiO2). Among these, active research and development has been conducted on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 250 mAh / g and are easy to use in large-capacity batteries. However, LiNiO2 has poorer thermal stability than LiCoO2, and if an internal short circuit occurs due to external pressure while the battery is charged, the positive electrode active material itself decomposes, resulting in the battery exploding and catching fire.

[0006] Therefore, as a way to improve the low thermal stability of LiNiO2 while maintaining the excellent reversible capacity, nickel-cobalt-manganese-based lithium composite metal oxides (hereinafter simply referred to as "NCM-based lithium oxides") were developed, in which part of the Ni was replaced with Mn and Co or Al.

[0007] However, due to the recent rise in the price of cobalt (Co), development is underway for lithium-rich (Li-rich) NCM-based positive electrode active materials that contain relatively low or no cobalt (Co) content but can still provide high capacity.

[0008] On the other hand, cobalt-free, Li- and Mn-rich cathode active materials require more Li than typical NCM-based cathode active materials. Therefore, a cathode active material precursor with a high specific surface area capable of contacting Li is required, which is synthesized by a coprecipitation method without using a complexing agent. However, when a precursor is produced without using a complexing agent, unreacted materials remain in solution even after the desired particle size is reached and the reaction is terminated. These unreacted materials react with oxygen in the air to form oxides that remain on the surface of the precursor. As a result, these impurities remain on the surface of the cathode active material produced using the precursor, causing a problem of reduced capacity.

[0009] Therefore, there is a need to develop a positive electrode active material precursor that has reduced or no surface impurities. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] CN109970106A (2019.07.05.) Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for producing a cobalt-free positive electrode active material precursor that suppresses the formation of manganese oxide impurities by including a step of adding an ammonium cation complex-forming agent in a specific amount after the coprecipitation reaction and then aging the mixture.

[0012] Another object of the present invention is to provide a cobalt-free permanganese positive electrode active material precursor produced by the above-mentioned production method, which has a high specific surface area and contains no or only a small amount of manganese oxide as an impurity.

[0013] It is another object of the present invention to provide a method for producing a positive electrode active material using the positive electrode active material precursor. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a method for producing a positive electrode active material precursor, a method for producing a positive electrode active material precursor, and a method for producing a positive electrode active material.

[0015] (1) The present invention provides a method for producing a positive electrode active material precursor, comprising: a step (S1) of co-precipitating a transition metal solution containing Ni and Mn in a nitrogen atmosphere in the presence of a basic solution and an ammonium cation complex-forming agent; and a step (S2) of, after completion of the co-precipitation reaction, adding an additional ammonium cation complex-forming agent while maintaining the nitrogen atmosphere and aging the mixture, wherein the ammonium cation complex-forming agent in step (S2) is added in a weight ratio of 1:0.5 to 1:3.5 relative to the ammonium cation complex-forming agent in step (S1).

[0016] (2) The present invention provides a method for producing a positive electrode active material precursor according to (1) above, wherein the coprecipitation reaction in step (S1) is carried out by a step (S1-1) of adding a basic solution and an ammonium cation complex-forming agent to a reactor in which a nitrogen atmosphere has been created, and mixing them to create an atmosphere of pH 12.0 or less, and a step (S1-2) of adding a transition metal solution containing Ni and Mn and a basic solution to the reactor, and carrying out a coprecipitation reaction under conditions of pH 11.0 or less.

[0017] (3) The present invention provides the method for producing a positive electrode active material precursor according to (2) above, wherein the pH in step (S1-1) is 11.5 to 12.0, and the pH in step (S1-2) is 10.5 to 11.0.

[0018] (4) The present invention provides a method for producing a positive electrode active material precursor according to any one of (1) to (3), wherein the ammonium cation complex-forming agent in step (S1) is used in an amount of 0.006 mol to 0.012 mol per 1 mol of transition metal in the transition metal solution.

[0019] (5) The present invention provides the method for producing a positive electrode active material precursor according to any one of (1) to (4), wherein the transition metal solution further contains one or more selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt.

[0020] (6) The present invention provides the method for producing a positive electrode active material precursor according to any one of (1) to (5) above, wherein the transition metal solution contains 60 mol % or more of Mn.

[0021] (7) The present invention provides a method for producing a transition metal hydroxide having a specific surface area of ​​30 m2, comprising: 2 / g~45m 2 / g, and when the manganese oxide is contained, the manganese oxide content is 0.3 wt % or less.

[0022] [Chemical formula 1] [Ni a Mn b M c ](OH)2

[0023] In the above Chemical Formula 1, M is one selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt; 0.1≦a≦0.4, 0.5 <b≦0.80、0≦c≦0.1、a+b+c=1である。

[0024] (8) The present invention provides a method for producing a positive electrode active material, comprising the steps of mixing the positive electrode active material precursor according to (7) above with a lithium source material, and firing the mixture.

[0025] (9) The present invention provides the method for producing a positive electrode active material according to (8) above, wherein the positive electrode active material precursor and the lithium source material are mixed so that the molar ratio of lithium elements in the positive electrode active material precursor and the lithium source material is 1:1.2 to 1:1.6. [Effects of the Invention]

[0026] The method for producing a cobalt-free positive electrode active material precursor according to the present invention includes a step of adding an ammonium cation complex-forming agent at a specific ratio after the coprecipitation reaction and then aging the mixture, thereby suppressing the formation of manganese oxide and producing a positive electrode active material precursor free of surface impurities.

[0027] Furthermore, the positive electrode active material precursor according to the present invention has a large specific surface area, contains no manganese oxide or contains only a very small amount of manganese oxide, and has the effect of providing excellent initial capacity and capacity retention rate. [Brief explanation of the drawings]

[0028] The following drawings attached to this specification are intended to illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited only to the matters shown in these drawings. [Figure 1] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Example 1. [Figure 2] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Example 2. [Figure 3] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Example 3. [Figure 4] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Comparative Example 1. [Figure 5] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Comparative Example 2. [Figure 6] 1 is an SEM image (magnification 10K) of the positive electrode active material precursor produced in Comparative Example 3. [Figure 7] 1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Example 1. [Figure 8] 1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Example 2. [Figure 9]1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Example 3. [Figure 10] 1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Comparative Example 1. [Figure 11] 1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Comparative Example 2. [Figure 12] 1 is an SEM image (magnification 10K) of a positive electrode active material produced using the positive electrode active material precursor of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0029] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0030] The present invention provides a method for producing a cobalt-free, surface-impurity-free permanganate positive electrode active material precursor, a positive electrode active material precursor, and a method for producing a positive electrode active material using the positive electrode active material precursor.

[0031] The present invention will be described in more detail below.

[0032] Method for producing a positive electrode active material precursor The present invention provides a method for producing a cobalt-free permanganate positive electrode active material precursor.

[0033] A method for producing the positive electrode active material precursor according to one embodiment of the present invention includes the steps of: (S1) co-precipitation of a transition metal solution containing Ni and Mn in a nitrogen atmosphere in the presence of a basic solution and an ammonium cation complex-forming agent; and (S2) after the co-precipitation is complete, adding an additional ammonium cation complex-forming agent while maintaining the nitrogen atmosphere, and aging the mixture. The ammonium cation complex-forming agent in step (S2) may be added in a weight ratio of 1:0.5 to 1:3.5 relative to the ammonium cation complex-forming agent in step (S1).

[0034] Cobalt-free, Li- and Mn-rich cathode active materials require more Li than typical NCM-based cathode active materials, which requires a cathode active material precursor with a high specific surface area that can contact Li, and are synthesized using a coprecipitation method that does not use a complexing agent. However, in this case, unreacted materials remain in the solution even after the reaction is completed, reacting with oxygen in the air to form oxides that remain on the surface of the precursor. These remain as impurities on the surface of the cathode active material manufactured using this material, causing a problem of reduced capacity.

[0035] However, in the method for producing a cathode active material precursor according to the present invention, after the co-precipitation reaction, an ammonium cation complex-forming agent is additionally added in a weight ratio of 1:0.5 to 3.5 relative to the ammonium cation complex-forming agent used before the co-precipitation reaction while maintaining a nitrogen atmosphere, which is an inert atmosphere, and an aging step is performed to co-precipitate the unreacted material, thereby suppressing the formation of oxide impurities such as manganese oxide and producing a cathode active material precursor without impurities remaining on the surface.

[0036] Specifically, the method for producing the cathode active material precursor according to the present invention will be described step by step.

[0037] (S1) Step Step 1 is a step of co-precipitating transition metals, and may be performed by co-precipitating a transition metal solution containing Ni and Mn in the presence of a basic solution and an ammonium cation complex-forming agent under a nitrogen atmosphere.

[0038] As another example, the coprecipitation reaction may be carried out by a step (S1-1) of adding a basic solution and an ammonium cation complex-forming agent to a reactor in which a nitrogen atmosphere has been created, and mixing them to create an atmosphere of pH 12.0 or less, and a step (S1-2) of adding a transition metal solution containing Ni and Mn and a basic solution to the reactor, and carrying out the coprecipitation reaction under conditions of pH 11.0 or less.

[0039] Specifically, the pH in the step (S1-1) may be 11.5 to 12.0, and the pH in the step (S1-2) may be 10.5 to 11.0.

[0040] The transition metal solution may be prepared by adding a transition metal source material to a solvent, specifically, deionized water or a mixed solvent of deionized water and an organic solvent (e.g., alcohol) that is uniformly miscible with deionized water, and then mixing the two together. Alternatively, the transition metal solution may be prepared by mixing an aqueous solution of the transition metal source material.

[0041] The transition metal source material may be a transition metal sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide.

[0042] Specific examples of the Ni source material include, but are not limited to, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and more specific examples include, but are not limited to, Ni(OH), NiO, NiOOH, NiCO·2Ni(OH)·4H2O, NiCO·2H2O, Ni(NO)·6H2O, NiSO·6H2O, fatty acid nickel salts, nickel halides, and combinations thereof.

[0043] Furthermore, the Mn source material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide. More specific examples include, but are not limited to, manganese oxides such as MnO, MnO, and MnO; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or combinations thereof.

[0044] As yet another example, the transition metal solution may further include one or more selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt. In this case, the transition metal solution may further include a source material containing Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, or Pt, and the source material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or the like containing each of the metals.

[0045] The transition metal solution may contain more than 50 mol %, specifically 60 mol % or more of Mn among the transition metals in the solution.

[0046] As another example, the transition metal solution does not contain Co.

[0047] The basic solution may also be a precipitant, which may be an alkali metal or alkaline earth metal hydroxide, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof.

[0048] Alternatively, the basic solution may be used in the form of an aqueous solution, and the solvent may be deionized water or a mixture of deionized water and an organic solvent (e.g., alcohol) that is uniformly miscible with deionized water.

[0049] The basic solution may also serve to adjust the pH in the reactor during the coprecipitation reaction, and by adjusting the amount of the basic solution added, the pH in the reactor can be controlled to a desired condition.

[0050] The ammonium cation complexing agent may include at least one selected from the group consisting of NHOH, (NH)SO, NHNO, NHCl, CHCOONH, and NHCO. The ammonium cation complexing agent may be used in the form of an aqueous solution, which may be prepared by mixing the ammonium cation complexing agent with deionized water or a mixture of deionized water and an organic solvent (e.g., alcohol) that is uniformly miscible with deionized water.

[0051] In step (S1), the ammonium cation complexing agent may be used in an amount of 0.006 mol to 0.012 mol, specifically 0.007 mol to 0.011 mol, based on 1 mol of the transition metal in the transition metal solution. In this case, the initial particle nuclei can be smoothly formed and grown to satisfy the desired particle size distribution.

[0052] On the other hand, the coprecipitation reaction may be carried out at a temperature of 40°C to 70°C with stirring. The stirring speed is not particularly limited, but stirring at 100 rpm to 2,000 rpm may be used since this facilitates an increase in the reaction rate.

[0053] (S2) Step Step (S2) is a step for producing a cathode active material precursor free of surface impurities by suppressing and removing oxide formation by involving unreacted materials in a coprecipitation reaction. After the coprecipitation reaction is completed, an ammonium cation complex-forming agent is added while maintaining a nitrogen atmosphere, and then aging is performed.

[0054] The aging may be performed in a nitrogen atmosphere. If the precursor is left in an air atmosphere, the unreacted transition metal reacts with oxygen, generating impurities on the surface of the precursor. However, in the present invention, the aging is performed in a nitrogen atmosphere, i.e., an inert atmosphere, where the unreacted transition metal in the reactor easily reacts with OH- due to the additional addition of an ammonium cation complexing agent, thereby preventing impurities from being generated in the final cathode active material precursor.

[0055] The ammonium cation complex-forming agent additionally added in step (S2) may be added in a weight ratio of 1:0.5 to 1:3.5 relative to the ammonium cation complex-forming agent in step (S1), specifically, a weight ratio of 1:0.5 to 1:3. In this case, all unreacted transition metals react in the reactor, and no surface impurities are generated even when the finally produced positive electrode active material precursor is exposed to the air.

[0056] The ammonium cation complex-forming agent in step (S2) may be the same as the ammonium cation complex-forming agent used in step (S1), or may be one or more selected from the above-mentioned ammonium cation complex-forming agents.

[0057] In addition, in the method for preparing a cathode active material precursor according to the embodiment of the present invention, after step (S2), one or more steps selected from washing with water and drying may be further performed. In this case, the washing with water and drying may be performed by a conventional method known in the art.

[0058] For example, the water washing may be carried out by adding the precursor to ultrapure water and stirring it, and the water washing temperature may be 70°C or less, specifically 40°C to 70°C, and the water washing time may be 10 minutes to 1 hour.

[0059] The drying method is not particularly limited as long as it can dry the produced precursor without causing any chemical change. For example, a drying method using a spray dryer or a rotary evaporator, a vacuum drying method, or an air drying method may be used.

[0060] Positive electrode active material precursor The present invention provides a positive electrode active material precursor free from surface impurities, which is produced by the above-described production method.

[0061] The positive electrode active material precursor according to one embodiment of the present invention includes a transition metal hydroxide represented by the following Chemical Formula 1 and, optionally, manganese oxide (Mn3O4), and has a specific surface area of ​​30 m 2 / g~45m 2 / g, and when manganese oxide is contained, the content of manganese oxide is 0.3 wt % or less.

[0062] Here, the manganese oxide content was measured from the peak intensity of the crystalline structure of manganese oxide in an XRD spectrum obtained by XRD measurement using non-monochromated CuKα rays.

[0063] [Chemical formula 1] [Ni a Mn b M c ](OH)2

[0064] In the above Chemical Formula 1, M is one selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt; 0.1≦a≦0.4, 0.5 <b≦0.80、0≦c≦0.1、a+b+c=1である。

[0065] The cathode active material precursor may be composed of polycrystalline particles composed of secondary particles formed by agglomeration of primary particles. Meanwhile, the primary particles of the present invention are formed and grown by the above-described manufacturing method and have a fine flaky structure, and the cathode active material precursor of the present invention composed of polycrystalline particles composed of secondary particles formed by agglomeration of such primary particles may have high specific surface area characteristics.

[0066] Here, the term "polycrystalline grain" refers to a particle in which a crystal lattice structure is assembled in an irregular orientation throughout the particle, and may be composed of secondary particles formed by the aggregation of primary particles. Here, secondary particles are generally contrasted with primary particles in that smaller primary particles are physically and / or chemically aggregated to form relatively larger particles.

[0067] Positive electrode active material and method for producing the same The present invention provides a positive electrode active material produced using the positive electrode active material precursor, and a method for producing the positive electrode active material.

[0068] The positive electrode active material according to one embodiment of the present invention is produced using the positive electrode active material precursor, and thus has the effect of reducing surface impurities and by-products and providing an excellent capacity retention rate.

[0069] The method for producing the positive electrode active material may include mixing the positive electrode active material precursor with a lithium source material, and firing the mixture.

[0070] Specifically, the method for producing a positive electrode active material according to the present invention may be performed by a method for producing a positive electrode active material known in the art, except for using the positive electrode active material precursor according to the present invention, and the method is not particularly limited.

[0071] Examples of the lithium source material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). One of these may be used alone, or two or more may be used in combination.

[0072] The positive electrode active material precursor and the lithium source material may be mixed by solid-phase mixing using a jet mill or the like, and the mixing ratio of the positive electrode active material precursor and the lithium source material may be determined within a range that satisfies the molar fraction of each component in the final positive electrode active material. More specifically, the positive electrode active material precursor and the lithium source material may be mixed so that the molar ratio of the lithium element in the positive electrode active material precursor and the lithium source material is 1:1.2 to 1:1.6.

[0073] Although not essential, during the mixing, in addition to the positive electrode active material precursor and the lithium source material, a source material for doping a portion of the transition metal and / or oxygen of the positive electrode active material may be further included. For example, during the mixing, the above-mentioned M 1 Contains raw materials and / or M 2 The X-containing raw material and the X-containing raw material described below may be further mixed. In this case, examples of the X-containing raw material include, but are not limited to, Na3PO4, K3PO4, Mg3(PO4)2, AlF3, NHF, and LiF. When a portion of oxygen is replaced with an X element as described above, the effect of suppressing oxygen desorption and reaction with the electrolyte during charge and discharge of the secondary battery can be obtained.

[0074] On the other hand, the firing may be carried out at 800°C to 1,000°C, specifically 850°C to 950°C, and the firing time may be 5 hours to 30 hours, specifically 8 hours to 15 hours, but is not limited to these.

[0075] Positive electrodes and secondary batteries The present invention provides a positive electrode including the positive electrode active material, and a lithium secondary battery including the positive electrode.

[0076] The positive electrode according to one embodiment of the present invention includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material.

[0077] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for the use of the positive electrode active material. For example, the positive electrode may be manufactured by dissolving or dispersing the components constituting the positive electrode active material layer, i.e., the positive electrode active material and a conductive material and / or a binder, in a solvent to manufacture a positive electrode mixture, applying the positive electrode mixture to at least one surface of a positive electrode current collector, and then drying and rolling the mixture. Alternatively, the positive electrode may be manufactured by casting the positive electrode mixture on a separate support, peeling it from the support, and laminating the resulting film on the positive electrode current collector.

[0078] 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 whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the adhesion of the positive electrode active material may be enhanced by forming fine irregularities on the surface of the current collector. Various forms are possible, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0079] A positive electrode active material layer containing the positive electrode active material according to the present invention and optionally further containing at least one of a conductive material and a binder is located on at least one surface of the current collector.

[0080] The positive electrode active material may be contained in an amount of 80 to 99 wt %, more specifically 85 to 98 wt %, based on the total weight of the positive electrode active material layer. When contained in this range, excellent capacity characteristics can be exhibited.

[0081] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. One of these may be used alone, or two or more may be used in combination. The conductive material may be contained in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer.

[0082] The binder also serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One of these may be used alone, or two or more may be used in combination. The binder may be contained in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0083] Meanwhile, the solvent used in preparing the cathode composite may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, either alone or in combination. The amount of the solvent used may be adjusted appropriately in consideration of the coating thickness, production yield, viscosity, etc. of the slurry.

[0084] In addition, the lithium secondary battery according to the present invention includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode according to the present invention.

[0085] Meanwhile, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0086] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector.

[0087] The negative electrode may be manufactured by a conventional method for manufacturing a negative electrode generally known in the art. For example, the negative electrode may be manufactured by dissolving or dispersing components constituting the negative electrode active material layer, i.e., the negative electrode active material, and a conductive material and / or a binder, in a solvent to prepare a negative electrode mixture, applying the negative electrode mixture to at least one surface of a negative electrode current collector, drying, and rolling the mixture, or by casting the negative electrode mixture on a separate support, peeling it from the support, and laminating the resulting film on the negative electrode current collector.

[0088] 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 surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys may be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. Various forms are possible, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0089] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. 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, and Al alloys; and SiO. v(0 < v < 2), metal oxides capable of doping and undoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and a carbonaceous material, such as Si-C composites or Sn-C composites, etc. Any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, both low-crystalline carbon and high-crystalline carbon can be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of high-crystalline carbon are amorphous, plate-like, flaky, spherical, or fibrous natural graphite 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.

[0090] Further, the binder and the conductive material are the same as those described above for the positive electrode.

[0091] Meanwhile, in the secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte impregnation ability are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric materials can also be used, and they can be selectively used in single-layer or multi-layer structures.

[0092] On the other hand, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like that can be used in manufacturing a secondary battery, but is not limited thereto.

[0093] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0094] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable electrolytes include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as Ra-CN (where Ra is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred, as they have high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries. In this case, a mixture of the cyclic carbonate and the linear carbonate at a volume ratio of approximately 1:1 to 9 can provide excellent electrolyte performance.

[0095] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0096] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0097] As described above, the secondary battery including the cathode active material according to the present invention has excellent capacity characteristics and high-temperature stability, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0098] The secondary battery according to the present invention may be used as a unit cell of a battery module, and the battery module may be applied to a battery pack. The battery module or the battery pack may be used as a power source for one or more medium- to large-sized devices, including power tools, electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), and power storage systems.

[0099] Example Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0100] Example 1 NiSO4 and MnSO4 were mixed in deionized water in amounts that gave a molar ratio of Ni:Mn of 35:65 to prepare a 2.4 M aqueous transition metal solution.

[0101] A 10-L continuous stirred tank reactor was charged with 2.6 L of deionized water and purged with nitrogen gas at 2 L / min to remove dissolved oxygen and create a non-oxidizing atmosphere. While continuing to flow nitrogen gas at 2 L / min, 3.87 mL of a 25 wt% NaOH aqueous solution and 88.8 mL of a 9 wt% NH4OH aqueous solution were added, and the mixture was stirred at 150 rpm at 50°C until the pH in the reactor reached approximately 12.0.

[0102] Then, while stirring at 1000 rpm, a transition metal aqueous solution and an NaOH aqueous solution were continuously added to the reactor at 0.83 L / hr and 0.29 L / hr, respectively, and a coprecipitation reaction was carried out so that the pH in the reactor reached approximately 11.0 within 2 hours. The coprecipitation reaction was then continued for 48 hours at approximately pH 11.0. After the coprecipitation reaction was completed, 87.8 ml of a 9 wt% NH4OH aqueous solution was added while maintaining an inert nitrogen atmosphere inside the reactor, and the mixture was aged by stirring at 150 rpm for 1 hour.

[0103] Thereafter, the generated precursor particles were separated and washed, and then dried at 120° C. for 12 hours to prepare a positive electrode active material precursor.

[0104] Example 2 A positive electrode active material precursor was prepared in the same manner as in Example 1, except that after the coprecipitation reaction, 44.4 ml of a 9 wt % NH4OH aqueous solution was added for aging.

[0105] Example 3 A positive electrode active material precursor was prepared in the same manner as in Example 1, except that after the coprecipitation reaction, 266.3 ml of a 9 wt % NH4OH aqueous solution was added for aging.

[0106] Comparative Example 1 NiSO4 and MnSO4 were mixed in deionized water in amounts that gave a molar ratio of Ni:Mn of 35:65 to prepare a 2.4 M aqueous transition metal solution.

[0107] A 10-L continuous stirred tank reactor was charged with 2.6 L of deionized water and purged with nitrogen gas at 2 L / min to remove dissolved oxygen and create a non-oxidizing atmosphere. While continuing to flow nitrogen gas at 2 L / min, 3.87 mL of a 25 wt% NaOH aqueous solution and 88.8 mL of a 9 wt% NH4OH aqueous solution were added, and the reactor was stirred at 150 rpm at 50°C until the pH in the reactor reached approximately 12.0.

[0108] Then, while stirring at 1000 rpm, a transition metal aqueous solution and a NaOH aqueous solution were continuously added to the reactor at 0.83 L / hr and 0.29 L / hr, respectively, and a coprecipitation reaction was carried out so that the pH in the reactor reached approximately 11.0 within 2 hours. The coprecipitation reaction was then continued for 48 hours at approximately pH 11.0. After the coprecipitation reaction was completed, the generated precursor particles were separated and washed, and then dried at 120°C for 12 hours to produce a cathode active material precursor.

[0109] Comparative Example 2 A positive electrode active material precursor was prepared in the same manner as in Example 1, except that after the coprecipitation reaction, 22.2 ml of a 9 wt % NH4OH aqueous solution was added for aging.

[0110] Comparative Example 3 A positive electrode active material precursor was prepared in the same manner as in Example 1, except that after the coprecipitation reaction, 355.0 ml of a 9 wt % NH4OH aqueous solution was added for aging.

[0111] Experimental Example 1 The positive electrode active material precursors prepared in the Examples and Comparative Examples were analyzed for the presence or absence of surface impurities (manganese oxide), the manganese oxide content, and the specific surface area. The results are shown in Table 1 below and FIGS. 1 to 6.

[0112] (1) Presence or absence of surface impurities The presence or absence of surface impurities (manganese oxide, Mn3O4) was confirmed by SEM analysis, which was carried out using an SEM (QUANTA FEG 250, Thermo Fisher) at a magnification of 10K.

[0113] (2) Manganese oxide content (wt%) The manganese oxide content in the precursor was confirmed by XRD analysis. Specifically, an XRD spectrum was obtained using a Bruker D8 ADVANCE powder x-ray diffractometer (Bruker) at a current of 40 kV, a voltage of 40 mA, CuKα, 2θ (Bragg angle) = 15° to 95°, and a scan speed of 0.02° / 0.20 sec. The manganese oxide content was calculated by quantitative analysis based on the intensity of the crystalline peak of the manganese oxide.

[0114] (3) Specific surface area (m 2 / g) The specific surface area was measured by the BET method and calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a Tristar II (Micromeritics).

[0115] [Table 1]

[0116] As shown in Table 1, the positive electrode active material precursors of Examples 1 to 3 have a manganese oxide content of 0.3 wt % or less and a specific surface area of ​​30 to 45 m 2 / g was confirmed.

[0117] 1 to 3 and 4, it can be clearly seen that there are no impurities on the surfaces of the positive electrode active material precursors of Examples 1 to 3. Specifically, Fig. 4 shows the SEM analysis results of the positive electrode active material precursor of Comparative Example 1, which was produced under the same conditions as Example 1 except that the aging step was not performed after the coprecipitation reaction was completed, and impurities are present surrounding the entire surface of the precursor. However, Figs. 1 to 3, which show the SEM analysis results of the positive electrode active material precursors of Examples 1 to 3, show that there are no impurities on the surfaces of the precursors.

[0118] In addition, an aging step was performed after the co-precipitation reaction was completed. However, it was confirmed that impurities were present on the surface of the cathode active material precursor of Comparative Example 2, which was prepared by adding NH4OH, an ammonium cation complexing agent, in a weight ratio of 1:0.25 relative to the NH4OH added before the co-precipitation reaction, surrounding the entire surface of the precursor, as in Comparative Example 1 (see FIG. 5).

[0119] On the other hand, the cathode active material precursor of Comparative Example 3, which was prepared by performing an aging step after the coprecipitation reaction and adding the ammonium cation complexing agent NH4OH in a weight ratio of 1:4 relative to the NH4OH added before the coprecipitation reaction, showed no impurities on the precursor surface, but the use of an excessive amount of ammonium cation complexing agent resulted in the formation of irregular, oversized particles due to aggregation of unreacted materials (see Figure 6). Furthermore, the aggregated precursor of Comparative Example 3, when used as a cathode active material, is likely to have poor conductivity, which could lead to poor battery capacity and efficiency. These issues are clearly confirmed by the results in Table 2 below.

[0120] Experimental Example 2 Positive electrode active materials were produced using the positive electrode active material precursors produced in the Examples and Comparative Examples, and batteries were produced using the positive electrode active materials, after which the battery performance was evaluated.

[0121] (1) Manufacturing of positive electrode active material Each positive electrode active material precursor was mixed with LiOH so that the molar ratio of Li in the precursor and LiOH was 1:1.35, and then calcined at 900°C for 15 hours in an air atmosphere to produce each positive electrode active material.

[0122] The prepared positive electrode active material was observed using a SEM (QUANTA FEG 250, Thermo Fisher Scientific) at a magnification of 10K to check for remaining surface impurities, and the results are shown in FIGS. 7 to 12.

[0123] (2) Manufacturing of the positive electrode The prepared positive electrode active materials, carbon black conductive material, and PVdF binder were mixed in a weight ratio of 92.5:3.0:4.5 in N-methylpyrrolidone solvent to prepare a positive electrode mixture (viscosity: 5000 mPa s). The mixture was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode.

[0124] (3) Battery manufacturing Lithium metal was used as the negative electrode.

[0125] An electrode assembly was fabricated by interposing a porous polyethylene separator between the cathode and anode, and the electrode assembly was placed inside a case. An electrolyte solution was then injected into the case to fabricate a lithium secondary battery. The electrolyte solution was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate (EC / EMC volume ratio = 3 / 7).

[0126] Half cells of each lithium secondary battery prepared as described above were charged to 4.4 V at 0.1 C and 0.33 C in CCCV mode at 25°C, and then discharged to 2.5 V at constant currents of 0.1 C and 0.33 C to measure the initial charge / discharge capacity and efficiency. The ratio of the capacity when charged at 0.1 C and discharged at 0.1 C to the capacity when discharged at 0.33 C (0.33 C / 0.1 C, %) was also measured, as well as the capacity retention after 30 cycles of charging at 0.1 C and discharging at 0.1 C. The results are shown in Table 2 below.

[0127] [Table 2]

[0128] 7 to 9 confirm that no impurities are present on the surface of the cathode active materials prepared using the cathode active material precursors of Examples 1 to 3. In contrast, FIGS. 10 to 12 confirm that a considerable amount of impurities are present overall on the surface of the cathode active materials prepared using the cathode active material precursors of Comparative Examples 1 and 2, and that the cathode active material prepared using the cathode active material precursor of Comparative Example 3 has irregular, oversized particles formed due to aggregation. Furthermore, Table 2 confirms that the initial charge capacities of the cathode active materials of Examples 1 to 3 show a significant increase of about 3 to 5% compared to Comparative Examples 1 to 3, indicating an increased capacity retention rate.

Claims

1. A step (S1) of co-precipitating a transition metal solution containing Ni and Mn in the presence of a basic solution and an ammonium cation complexing agent under a nitrogen atmosphere; After the coprecipitation reaction is completed, an ammonium cation complexing agent is added while maintaining a nitrogen atmosphere, and the mixture is aged (S2). The method for producing a positive electrode active material precursor, wherein the ammonium cation complex-forming agent in step (S2) is added in a volume ratio of 1:0.5 to 1:3.5 relative to the ammonium cation complex-forming agent in step (S1).

2. The coprecipitation reaction in the step (S1) is A step (S1-1) of adding and mixing a basic solution and an ammonium cation complexing agent into a reactor in which a nitrogen atmosphere has been created, to create an atmosphere of pH 12.0 or less; and (S1-2) adding a transition metal solution containing Ni and Mn and a basic solution to the reactor and co-precipitation reacting them under conditions of pH 11.0 or less.

3. 3. The method for producing a positive electrode active material precursor according to claim 2, wherein the pH in step (S1-1) is 11.5 to 12.0, and the pH in step (S1-2) is 10.5 to 11.

0.

4. 2. The method for producing a cathode active material precursor according to claim 1, wherein the ammonium cation complex-forming agent in step (S1) is used in an amount of 0.006 mol to 0.012 mol based on 1 mol of the transition metal in the transition metal solution.

5. 2. The method for producing a positive electrode active material precursor according to claim 1, wherein the transition metal solution further contains one or more selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt.

6. The method for producing a positive electrode active material precursor according to claim 1 , wherein the transition metal solution contains more than 50 mol % of Mn.

7. A transition metal hydroxide represented by the following chemical formula 1 and, optionally, manganese oxide (Mn ３ O ４ ) and Specific surface area is 30m ２ / g~45m ２ / g, When the positive electrode active material precursor contains manganese oxide, the manganese oxide content is 0.3 wt % or less. [Chemical formula 1] [Ni ａ Mn ｂ M ｃ ](OH) ２ (In the above Chemical Formula 1, M is one selected from Zr, Al, Cu, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, and Pt; 0.1≦a≦0.4, 0.5<b≦0.80, 0≦c≦0.1, a+b+c=1.)

8. mixing the positive electrode active material precursor of claim 7 with a lithium source material; and firing the mixture.

9. 9. The method for producing a cathode active material according to claim 8, wherein the cathode active material precursor and the lithium source material are mixed so that the molar ratio of lithium elements in the cathode active material precursor and the lithium source material is 1:1.2 to 1:1.6.

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