Precursor of positive electrode active material for secondary battery, positive electrode active material, method for producing the same, and lithium secondary battery including the same

Abstract

The present invention provides a method for producing a positive electrode active material precursor for a secondary battery, the method comprising the steps of: continuously feeding a solution containing nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cations, an alkaline solution, and an ammonium ion-containing solution into a reactor; and co-precipitation while continuously feeding an oxygen-containing gas or no gas into the reactor to form a positive electrode active material precursor in which nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form. The present invention also provides a positive electrode active material precursor for a secondary battery, the positive electrode active material precursor comprising nickel (Ni), cobalt (Co), and manganese (Mn), in which the nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0024312, filed February 28, 2019, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material precursor for a secondary battery, a positive electrode active material, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have been attracting attention as a driving power source for portable devices. Therefore, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries have an organic or polymer electrolyte solution filled between a positive electrode and a negative electrode, which are made of active materials that allow for the intercalation and deintercalation of lithium ions. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted and deintercalated at the positive and negative electrodes.

[0005] The positive electrode active materials used in lithium secondary batteries are mainly lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compound (LiFePO4). In addition, as a method to improve the low thermal stability of LiNiO2 while maintaining the excellent reversible capacity, a method of substituting part of the nickel (Ni) with cobalt (Co) or manganese (Mn) has been proposed. However, LiNi 1-α Co αO2 (α = 0.1 to 0.3) exhibits excellent charge / discharge characteristics and life characteristics, but has low thermal stability. On the other hand, nickel-manganese-based lithium composite metal oxides, in which part of the nickel (Ni) is replaced with manganese (Mn), which has excellent thermal stability, and nickel-cobalt-manganese-based lithium composite metal oxides, in which part of the nickel (Ni) is replaced with manganese (Mn) and cobalt (Co) (hereinafter simply referred to as "NCM-based lithium oxides"), have the advantage of being relatively excellent in cycle characteristics and thermal stability.

[0006] 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 can achieve high capacity while containing relatively low Cobalt (Co) content. Lithium-rich (Li-rich) NCM-based positive electrode active materials have advantages in terms of high energy density and price.

[0007] Generally, precursors of NCM-based positive electrode active materials are synthesized by coprecipitation and are mainly in the form of hydroxide or carbonate. 1-α1-β1 Co α1 Mn β1 In the case of (OH)2 (0<α1<1.0, 0<β1<1.0), the primary particles are very large (approximately 1-3 μm) and not dense, resulting in low ionic conductivity and poor electrochemical performance and density. Carbonate precursor Ni 1-α2-β2 Co α2 Mn β2 In the case of CO3 (0<α2<1.0, 0<β2<1.0), the primary particles are very small at about 10~40nm, and the carbon dioxide is released during the firing process, making the pores in the secondary particles very large, resulting in low strength. Also, the particles are crushed during rolling, resulting in a significant drop in density.

[0008] Therefore, there is still a need to develop a cathode active material and its precursor that has high density due to small primary particles and dense secondary particles, prevents particle cracking during rolling due to excellent particle strength, and can exhibit excellent battery performance such as high capacity, efficiency, and rate characteristics when applied to secondary batteries. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides an NCM-based cathode active material precursor that has small primary particles and dense secondary particles, exhibiting high density and excellent particle strength, and a method for manufacturing the same.

[0010] In addition, the present invention provides a lithium-rich (Li-rich) NCM-based cathode active material prepared using the cathode active material precursor, which can exhibit excellent battery performance such as high capacity, efficiency, and rate characteristics when applied to a secondary battery, and a method for preparing the same. [Means for solving the problem]

[0011] The present invention provides a positive electrode active material precursor for a secondary battery, comprising nickel (Ni), cobalt (Co), and manganese (Mn), wherein the nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form, and the manganese (Mn) is in an oxidized form.

[0012] The present invention also provides a method for producing a cathode active material precursor for a secondary battery, the method including the steps of: continuously feeding a solution containing transition metal cations of nickel (Ni), cobalt (Co), and manganese (Mn), an alkaline solution, and an ammonium ion-containing solution into a reactor; and co-precipitation while continuously feeding an oxygen-containing gas or no gas into the reactor, thereby forming a cathode active material precursor in which nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form.

[0013] The present invention also provides a method for producing a positive electrode active material for a secondary battery, the method including the steps of: mixing the positive electrode active material precursor produced as described above with a lithium source material; and, after the mixing, firing the mixture at 750 to 1,000°C to form a lithium composite transition metal oxide.

[0014] The present invention also provides a positive electrode active material produced as described above, a positive electrode containing the same, and a lithium secondary battery. [Effects of the Invention]

[0015] According to the present invention, it is possible to prepare an NCM-based cathode active material precursor that has small primary particles and dense secondary particles, thereby exhibiting high density and excellent particle strength.

[0016] In addition, a lithium-rich (Li-rich) NCM-based cathode active material prepared using the cathode active material precursor can exhibit excellent battery performance such as high capacity, efficiency, and rate characteristics when applied to a secondary battery. [Brief explanation of the drawings]

[0017] [Figure 1] 1 shows XPS data of the positive electrode active material precursor produced in Example 1. [Figure 2] This is a reference for XPS data of manganese oxide. [Figure 3] 1 shows XRD data of the positive electrode active material precursor produced in Comparative Example 1. [Figure 4] 1 shows XRD data of the positive electrode active material precursor produced in Comparative Example 2. [Figure 5] 1 is a scanning electron microscope (SEM) photograph showing an enlarged view of the positive electrode active material precursor prepared in Example 1. [Figure 6] 1 is a scanning electron microscope (SEM) photograph showing an enlarged view of a positive electrode active material precursor prepared in Comparative Example 1. [Figure 7] 1 is a scanning electron microscope (SEM) photograph showing an enlarged view of a positive electrode active material precursor prepared in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in more detail below to facilitate understanding of the present invention. In this regard, the terms and words used in the 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 concept of the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0019] <Positive electrode active material precursor> The cathode active material precursor of the present invention is prepared by the steps of: continuously feeding a solution containing nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cations, an alkaline solution, and an ammonium ion-containing solution into a reactor; and co-precipitation while continuously feeding an oxygen-containing gas or no gas into the reactor to form a cathode active material precursor in which nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form.

[0020] The method for preparing the cathode active material precursor will now be described in detail step by step.

[0021] First, a solution containing nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cations, an alkaline solution, and an ammonium ion-containing solution are continuously charged into a reactor.

[0022] The transition metal cation-containing solution includes a nickel (Ni)-containing source material, a cobalt (Co)-containing source material, and a manganese (Mn)-containing source material.

[0023] The nickel (Ni)-containing raw material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0024] The cobalt (Co)-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or a combination thereof.

[0025] The manganese (Mn)-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically may be, but is not limited to, manganese oxides such as MnO, MnO, MnO, etc.; manganese salts such as MnCO, Mn(NO), MnSO, ​​manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salt; manganese oxyhydroxide, manganese chloride, or a combination thereof.

[0026] The transition metal cation-containing solution may be prepared by adding a nickel (Ni)-containing raw material, a cobalt (Co)-containing raw material, and a manganese (Mn)-containing raw material to a solvent, specifically water or a mixed solvent of an organic solvent (e.g., alcohol) that is uniformly miscible with water, or by mixing an aqueous solution of a nickel (Ni)-containing raw material, an aqueous solution of a cobalt (Co)-containing raw material, and a manganese (Mn)-containing raw material.

[0027] The ammonium ion-containing solution may contain, as a complexing agent, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, ( NH4 ) The ammonium ion-containing solution may include, but is not limited to, ammonium ion, ammonium ion-containing ammonium salt ...

[0028] The alkaline solution may contain, as a precipitant, an alkaline metal or alkaline earth metal hydroxide, a hydrate thereof, or a combination thereof, such as NaOH, KOH, or Ca(OH). The alkaline solution may also be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water. The alkaline solution is added to adjust the pH of the reaction solution and may be added in an amount that adjusts the pH of the metal solution to 11 to 13.

[0029] Next, co-precipitation is carried out while continuously feeding an oxygen-containing gas or without feeding gas into the reactor, to form a cathode active material precursor in which nickel (Ni) and cobalt (Co) are in the non-oxidized hydroxide form and manganese (Mn) is in the oxidized form.

[0030] Conventional co-precipitation reactions of NCM-based cathode active material precursors involve either synthesizing hydroxide-type precursors in an inert atmosphere by introducing nitrogen (N2) or argon (Ar) gas, or synthesizing carbonate-type precursors by introducing nitrogen (N2), argon (Ar), or carbon dioxide (H2CO3) gas. However, conventional hydroxide-type precursors have disadvantages: primary particles are very large (approximately 1-3 μm) and not dense, resulting in low ionic conductivity and reduced electrochemical performance and density. Carbonate-type precursors have disadvantages: primary particles are very small (approximately 10-40 nm), and carbon dioxide desorption during the firing process increases the pore size within the particles, resulting in reduced strength. Furthermore, particles are easily crushed during rolling, resulting in significantly reduced density.

[0031] Therefore, in order to provide an NCM-based cathode active material precursor that has small primary particles and dense secondary particles, resulting in high density and excellent particle strength, the present invention fabricates a cathode active material precursor by co-precipitation of the precursors without gas input or while continuously inputting an oxygen-containing gas, thereby forming a cathode active material precursor in which nickel (Ni) and cobalt (Co) are in the unoxidized hydroxide form and manganese (Mn) is in the oxidized form.

[0032] In the present invention, no gas is fed during the coprecipitation reaction, or an oxygen-containing gas is continuously fed, so that even if manganese (Mn) ions do not react with an alkali compound after forming a coordinate bond with ammonium ions, they can combine with oxygen (O2) gas fed in or from the air and precipitate as an oxide, or even if they react with an alkali compound and precipitate, they can be oxidized in the reactor, which can significantly increase the reaction rate and form small primary particles.

[0033] Unlike conventional methods of introducing nitrogen (N), argon (Ar), and / or carbon dioxide (HCO) gas into the reactor during the coprecipitation reaction, the present invention does not require introducing nitrogen (N), argon (Ar), and carbon dioxide (HCO) gas into the reactor during the coprecipitation reaction. Alternatively, an oxygen-containing gas may be continuously introduced. According to one embodiment of the present invention, the introduction flow rate of oxygen (O) gas specifically satisfies the following formula 1:

[0034] [Formula 1] (Amount of manganese (Mn) fed per hour (mol) × 2) / 0.089 ≦ Oxygen (O2) gas feed rate (L / h) ≦ 1.1 × {(Amount of manganese (Mn) fed per hour (mol) × 2) / 0.089}

[0035] For example, when a 3.2 mol / L transition metal cation-containing solution containing nickel (Ni), cobalt (Co), and manganese (Mn) in a 2:1:7 ratio is continuously fed at 0.3 L per hour, the oxygen (O2) gas feed flow rate may be 15.1 L / h to 16.61 L / h. If the gas contains 20% by volume of oxygen (O2), the total gas feed flow rate may be 75.5 L / h to 83.05 L / h.

[0036] By satisfying the oxygen (O2) gas input flow rate (L / h), a positive electrode active material precursor can be formed in which nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form, thereby resulting in small primary particles and dense secondary particles, which exhibit high density and excellent particle strength.

[0037] The positive electrode active material precursor prepared according to an embodiment of the present invention may be represented by the following Chemical Formula 1: [Chemical formula 1] x(Ni 1-a-b Co a M 1 b (OH)2)·y(MnO2)

[0038] In the above Chemical Formula 1, M 1is at least one selected from the group consisting of Fe, V, Mo, Al, Na, Ti, Cu, Cr, Nb, Zr, Mg, and K, 0.25≦x≦0.5, 0.5≦y≦0.75, x+y=1, and 0 <a≦0.6、0≦b≦0.4である。

[0039] The cathode active material precursor prepared according to the present invention contains nickel (Ni), cobalt (Co), and manganese (Mn), wherein the nickel (Ni) and cobalt (Co) are in the unoxidized hydroxide form, and the manganese (Mn) is in the oxidized form.

[0040] The cathode active material precursor is in the form of secondary particles formed by aggregation of primary particles, and the particle size of the primary particles may be 50 to 500 nm, preferably 80 to 400 nm, and more preferably 100 to 300 nm. In the cathode active material precursor according to one embodiment of the present invention, manganese (Mn) ions can be coordinated with ammonium ions and then precipitate as oxides by combining with oxygen (O2) gas or air introduced, even if they do not react with an alkali compound. Even if they react with an alkali compound and precipitate, they are oxidized in the reactor, resulting in a very fast reaction rate, allowing for the formation of smaller primary particles than conventional hydroxide-form precursors. Because the cathode active material precursor satisfies the above primary particle size range, the primary particles are small and the secondary particles are dense, resulting in high density and excellent particle strength.

[0041] The positive electrode active material precursor may have a high tap density of 1.4 g / cc or more, preferably 1.4 to 2.0 g / cc, and more preferably 1.5 to 1.8 g / cc. The tap density is measured by placing 50 g of the positive electrode active material precursor in a 50 ml mass cylinder and performing 1,250 strokes using a STAV-2 tap density measuring device (J. Engelsmann AG).

[0042] <Cathode active material> The present invention also provides a positive electrode active material produced using the positive electrode active material.

[0043] The cathode active material of the present invention includes the steps of mixing the cathode active material precursor with a lithium raw material, and, after the mixing, firing the mixture at 750 to 1,000° C. to form a lithium composite transition metal oxide.

[0044] First, the positive electrode active material precursor of the present invention and a lithium source material are mixed together. The positive electrode active material precursor includes nickel (Ni), cobalt (Co), and manganese (Mn), wherein the nickel (Ni) and cobalt (Co) are in the unoxidized hydroxide form, and the manganese (Mn) is in the oxidized form.

[0045] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium source may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CHClO1, Li2O, Li2SO4, CHClO1, or Li3C6H5O7, or a mixture of any one or more of these.

[0046] The positive electrode active material precursor and the lithium (Li) of the lithium source material may be mixed so as to have a molar ratio of 1:1.2 to 1:1.6, preferably 1:1.2 to 1:1.55, and more preferably 1:1.25 to 1:1.5. By mixing the positive electrode active material precursor and the lithium source material so as to have the above molar ratio, a lithium-rich (Li-rich) lithium composite transition metal oxide can be formed, thereby achieving a high capacity.

[0047] Next, after the mixing, the mixture is fired at 750 to 1,000° C. to form a lithium composite transition metal oxide. The firing may be performed at preferably 800 to 975° C., more preferably 850 to 950° C., for 5 to 20 hours, preferably 7 to 15 hours.

[0048] The positive electrode active material of the present invention thus produced is a lithium-rich (Li-rich) lithium composite transition metal oxide having a molar ratio (Li / M) of lithium (Li) to all metals (M) excluding lithium of 1.2 to 1.6, and yet has a high pellet density of 2.0 g / cc or more, preferably 2.2 to 3.0 g / cc, and more preferably 2.3 to 2.9 g / cc. The pellet density is measured by placing 5 g of the positive electrode active material in a mold with a diameter of 22 mm and using an HPRM-A2 (manufactured by Hantech) at a pressure of 2 tons.

[0049] <Positive electrodes and lithium secondary batteries> According to another embodiment of the present invention, there is provided a positive electrode for a secondary battery and a lithium secondary battery, each including the positive electrode active material.

[0050] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0051] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0052] The positive electrode active material layer may include a conductive material and a binder in addition to the positive electrode active material.

[0053] The conductive material is used to impart conductivity to the electrode, and any material that does not cause chemical changes and has electronic conductivity in the resulting battery can be used without particular limitations. 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 powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. One of these materials may be used alone, or two or more may be used in combination. The conductive material may typically be contained in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0054] The binder also serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode 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 or more of these may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0055] The positive electrode can be fabricated by a conventional positive electrode fabrication method, except for using the positive electrode active material. Specifically, the positive electrode can be fabricated by coating a composition for forming a positive electrode active material layer, including the positive electrode active material and, optionally, a binder and a conductive material, on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0056] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used is sufficient to dissolve or disperse the cathode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent application to produce a cathode, taking into consideration the coating thickness of the slurry and the production yield.

[0057] Alternatively, the positive electrode can be produced by casting the composition for forming the positive electrode active material layer on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0058] According to another embodiment of the present invention, there is provided an electrochemical device including the positive electrode. The electrochemical device may be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0059] The lithium secondary battery specifically 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, and may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0060] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0061] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 to 500 μm. As with 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. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0062] The negative electrode active material layer includes a negative electrode active material and, optionally, a binder and a conductive material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode-forming composition including the negative electrode active material and, optionally, the binder and the conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode-forming composition onto a separate support, peeling it off from the support, and laminating the resulting film onto the negative electrode current collector.

[0063] 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. βExamples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide (0<β<2); or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0064] The binder and conductive material may be the same as those previously described for the positive electrode.

[0065] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidifying ability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0066] Furthermore, examples of the electrolyte used in the present invention include 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 production of lithium secondary batteries, but are not limited to these.

[0067] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0068] The organic solvent may be any solvent that can act as a medium for transferring 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) and diethylcarbonate (DEC). ,workman Examples of suitable solvents include carbonate-based solvents such as ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based 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 that 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 high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which can provide excellent electrolyte performance.

[0069] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt is preferably used at a concentration in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0070] 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 reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0071] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, 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).

[0072] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0073] The battery module or 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); or power storage systems.

[0074] The present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein, although the present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein.

[0075] Example 1 A coprecipitation reactor (20 L capacity) was charged with 4 L of distilled water and maintained at 50°C. 100 mL of a 28 wt% aqueous ammonia solution was then added. A 3.2 mol / L transition metal cation-containing solution (NiSO4, CoSO4, and MnSO4 mixed in a nickel:cobalt:manganese molar ratio of 2:2:6) was then continuously added at 300 mL / hr, followed by 28 wt% aqueous ammonia at 42 mL / hr. The impeller was stirred at 400 rpm, and a 40 wt% sodium hydroxide solution was added to maintain the pH at 9.5.

[0076] At this time, oxygen (O2) gas was supplied at 13.0 L / hr while the coprecipitation reaction was carried out for 24 hours. 0.5 Co 0.5 Precursor particles of ((OH)2)·0.6(MnO2) were prepared. The precursor particles were separated, washed, and then dried in an oven at 130°C to prepare a cathode active material precursor.

[0077] Comparative Example 1 Four liters of distilled water was placed in a coprecipitation reactor (20 L capacity). The temperature was maintained at 50°C, and nitrogen (N2) gas was purged into the reactor at a rate of 2 L / min for 1 hour to remove oxygen from the reactor and create a non-oxidizing atmosphere. After adding 100 mL of a 28 wt% aqueous ammonia solution, a 3.2 mol / L aqueous metal solution containing NiSO4, CoSO4, and MnSO4 in a molar ratio of nickel:cobalt:manganese of 2:2:6 was added at 300 mL / hr, followed by 28 wt% aqueous ammonia at 42 mL / hr. The impeller was stirred at 400 rpm. A 40 wt% sodium hydroxide solution was added to maintain the pH at 10.0. The coprecipitation reaction was allowed to proceed for 24 hours, and Ni was obtained. 0.2 Co 0.2 Mn 0.6 (OH)2 precursor particles were formed, which were separated, washed, and then dried in an oven at 130°C to prepare a cathode active material precursor.

[0078] Comparative Example 2 Four liters of distilled water was added to a coprecipitation reactor (20 L capacity). The temperature was maintained at 50°C. Nitrogen (N2) gas was purged into the reactor at a rate of 2 L / min for 1 hour to remove oxygen and create a non-oxidizing atmosphere. 100 mL of a 28 wt% aqueous ammonia solution was then added. A 3.2 mol / L aqueous metal solution containing NiSO4, CoSO4, and MnSO4 in a molar ratio of nickel:cobalt:manganese of 2:2:6 was then added at 300 mL / hr, followed by 28 wt% aqueous ammonia at 42 mL / hr. The impeller was stirred at 400 rpm. A 20 wt% sodium carbonate solution was added to maintain the pH at 7.5. The coprecipitation reaction was allowed to proceed for 24 hours, and Ni was obtained. 0.2 Co 0.2 Mn 0.6 CO3 precursor particles were formed, separated and washed, and then dried in an oven at 130°C to prepare a cathode active material precursor.

[0079] [Experimental Example 1: Confirmation of precursor particles] The positive electrode active material precursors prepared in Example 1 and Comparative Examples 1 and 2 were characterized using XPS and XRD. The results are shown in Figures 1 to 4. Specifically, XPS analysis was performed using an ESCALAB 250 (Thermo Fisher Scientific) instrument under the following analytical conditions: an accelerating voltage of 15 kV (power: 150 W), an energy resolution of approximately 1.0 eV, an analysis area diameter of 500 micrometers, and a sputtering rate of 0.1 nm / sec. Survey scan and narrow scan spectra were obtained to obtain XPS spectroscopy. XRD analysis was performed using a D4 ENDEAVOR (Bruker AXS GmbH) instrument using a Cu target. XRD diffraction measurements were performed within the range of 10 to 90° at a rate of 3° per minute, with an accelerating voltage of 40 kV and an accelerating current of 40 mA.

[0080] Referring to Figures 1 and 2 (XPS of Example 1 (Figure 1) and Reference Material (Figure 2)), the oxidation number of Mn can be determined from the energy difference between two peaks separated from the 3s XPS spectrum of Mn. As can be seen from the Reference Material in Figure 2, it can be confirmed that Mn is in the form of tetravalent MnO2.

[0081] 3 and 4 (XRD of Comparative Examples 1 and 2), it was confirmed that Comparative Example 1 was in the form of hydroxides of Ni, Co, and Mn, and Comparative Example 2 was in the form of carbonates of Ni, Co, and Mn.

[0082] Meanwhile, FIGS. 5 to 7 show enlarged photographs of the positive electrode active material precursors produced in Example 1 and Comparative Examples 1 and 2 observed with a scanning electron microscope (SEM). 6 is the hydroxide-type cathode active material precursor of Comparative Example 1, and it can be seen that the primary particles are large and the secondary particles are not dense. 7 1 is the positive electrode active material precursor of Comparative Example 2 in the form of carbonate, and it can be seen that the primary particles are too small and the pores within the particles are large. 5is the positive electrode active material precursor of Example 1, and it can be confirmed that the primary particles are small and have a dense secondary particle shape.

[0083] [Experimental Example 2: Measurement of tap density] 50 g of each of the positive electrode active material precursors prepared in Example 1 and Comparative Examples 1 and 2 was placed in a 50 ml measuring cylinder, and the tap density was measured by performing 1,250 strokes using a STAV-2 tap density measuring instrument (J. Engelsmann AG). The results are shown in Table 1 below.

[0084] [Table 1]

[0085] Referring to Table 1, it can be seen that the positive electrode active material precursor of Example 1 has a significantly higher tap density than the positive electrode active material precursors of Comparative Examples 1 and 2, which are in the hydroxide / carbonate form.

[0086] Example 2 and Comparative Examples 3-4 The positive electrode active material precursors prepared in Example 1 and Comparative Examples 1 and 2 were mixed with the lithium source material LiOH in a molar ratio of 1:1.35 (Li:Li:LiOH), and the powder was placed in an alumina crucible and heated to 550°C in an air atmosphere. After calcining for 5 hours, the mixture was cooled to room temperature. The calcined product was crushed and sieved, and then heated to 900°C and calcined for 10 hours to prepare the positive electrode active materials of Example 2 and Comparative Examples 3 and 4.

[0087] [Experimental Example 3: Measurement of pellet density] 5 g of each of the positive electrode active materials produced in Example 2 and Comparative Examples 3 and 4 was placed in a mold with a diameter of 22 mm, and the pellet density was measured at a pressure of 2 tons using an HPRM-A2 (manufactured by Hantech Co., Ltd.) The results are shown in Table 2 below.

[0088] [Table 2]

[0089] Referring to Table 2, it can be seen that the positive electrode active material of Example 2 has a significantly higher pellet density than the positive electrode active materials of Comparative Examples 3 and 4 prepared using a positive electrode active material precursor in the hydroxide / carbonate form.

[0090] [Experimental Example 4: Performance evaluation of lithium secondary batteries] The positive electrode active materials prepared in Example 2 and Comparative Examples 3 and 4, the carbon black conductive material, and the PVdF binder were mixed in a weight ratio of 96:2:2 in N-methylpyrrolidone solvent to prepare positive electrode composites. The positive electrode composites were then applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare positive electrodes.

[0091] As the negative electrode, lithium metal was used.

[0092] An electrode assembly was fabricated by interposing a porous polyethylene separator between the cathode and anode fabricated as described above, 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 / diethyl carbonate / (EC / EMC / DEC mixed in a volume ratio of 3 / 5 / 2).

[0093] Each lithium secondary battery half cell fabricated as described above was charged at 0.1 C in CCCV mode at 25°C to 4.65 V (termination current 0.05 C), and then discharged at a constant current of 0.1 C to 2.0 V to measure the initial charge / discharge capacity and efficiency. The C-rate was also measured, which is the ratio of the capacity when charged at 0.1 C and discharged at 0.1 C to the capacity when discharged at 0.5 C and 1 C, respectively. The results are shown in Table 3.

[0094] [Table 3]

[0095] Referring to Table 3, when the positive electrode active material of Example 2 was used, superior initial capacity, efficiency, and C-rate were exhibited compared to when the positive electrode active materials of Comparative Examples 3 and 4 were used.

Claims

1. comprising nickel (Ni), cobalt (Co), and manganese (Mn); The nickel (Ni) and cobalt (Co) are in a non-oxidized hydroxide form, and the manganese (Mn) is in an oxidized form. A positive electrode active material precursor for a secondary battery, represented by the following chemical formula 1. [Chemical formula 1] x(Ni １－ａ－ｂ Co ａ M １ ｂ (OH) ２ )・y(MnO ２ ) (In the above chemical formula 1, M １ is at least one selected from the group consisting of Fe, V, Mo, Al, Na, Ti, Cu, Cr, Nb, Zr, Mg, and K, 0.25≦x≦0.5, 0.5≦y≦0.75, x+y=1, 0<a≦0.6, 0≦b≦0.

4.

2. 2. The positive electrode active material precursor for a secondary battery according to claim 1, wherein the positive electrode active material precursor is in the form of secondary particles formed by aggregation of primary particles, and the particle diameter of the primary particles is 50 to 500 nm.

3. 3. The positive electrode active material precursor for a secondary battery according to claim 1, wherein the positive electrode active material precursor has a tap density of 1.4 g / cc or more.

4. Sequentially charging a reactor with a nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cation-containing solution, an alkaline solution, and an ammonium ion-containing solution; co-precipitation while continuously feeding an oxygen-containing gas or no gas into the reactor to form a positive electrode active material precursor in which nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form and manganese (Mn) is in an oxidized form; The present invention relates to a method for producing a positive electrode active material precursor for a secondary battery, comprising the steps of:

5. Nitrogen (N ２ ), argon (Ar), and carbonic acid (H ２ CO ３ 5. The method for producing a positive electrode active material precursor for a secondary battery according to claim 4, wherein no gas is introduced.

6. When the oxygen-containing gas is introduced, oxygen (O ２ 6. The method for producing a positive electrode active material precursor for a secondary battery according to claim 4 or 5, wherein the flow rate of the gas to be introduced satisfies the following formula 1: [Formula 1] (Manganese (Mn) input amount per hour (mol) × 2) / 0.089≦Oxygen (O ２ ) Gas input flow rate (L / h)≦1.1×{(manganese (Mn) input amount per hour (mol)×2) / 0.089}

7. The method for producing a positive electrode active material precursor for a secondary battery according to claim 4 , wherein the positive electrode active material precursor is represented by the following Chemical Formula 1: [Chemical formula 1] x(Ni １－ａ－ｂ Co ａ M １ ｂ (OH) ２ )・y(MnO ２ ) (In the above chemical formula 1, M １ is at least one selected from the group consisting of Fe, V, Mo, Al, Na, Ti, Cu, Cr, Nb, Zr, Mg, and K, 0.25≦x≦0.5, 0.5≦y≦0.75, x+y=1, 0<a≦0.6, 0≦b≦0.

4.

8. mixing the cathode active material precursor produced according to claim 4 with a lithium source material; After the mixing, the mixture is fired at 750 to 1,000°C to form a lithium composite transition metal oxide; The method for producing a positive electrode active material for a secondary battery includes the steps of:

9. 9. The method for producing a positive electrode active material for a secondary battery according to claim 8, wherein the positive electrode active material precursor and lithium (Li) of the lithium raw material are mixed in a molar ratio of 1:1.2 to 1:1.

6.

10. 10. The positive electrode active material for a secondary battery produced according to claim 9, having a pellet density of 2.0 g / cc or more.

11. A positive electrode for a secondary battery, comprising the positive electrode active material according to claim 10.

12. A lithium secondary battery comprising the positive electrode according to claim 11.

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