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 priority under Korean Patent Application No. 10-2019-0024312 dated February 28, 2019, and all content disclosed in the documents of the said Korean Patent Application is incorporated herein by reference.

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

[0003] Recently, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, yet relatively high-capacity rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. As a result, research and development efforts to improve the performance of lithium-ion batteries are being actively pursued.

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

[0005] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) are mainly used as positive electrode active materials for lithium secondary batteries. Furthermore, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, a method has been proposed in which some of the nickel (Ni) is replaced with cobalt (Co) or manganese (Mn). However, LiNiO2 in which some of the nickel is replaced with cobalt... 1-α Co αIn the case of O2 (α=0.1~0.3), while it exhibits excellent charge / discharge characteristics and life characteristics, it has low thermal stability. On the other hand, nickel-manganese lithium composite metal oxides, in which some of the nickel (Ni) is replaced with manganese (Mn), which has excellent thermal stability, and nickel-cobalt-manganese lithium composite metal oxides, in which manganese (Mn) and cobalt (Co) are replaced (hereinafter simply referred to as "NCM lithium oxides"), have the advantage of relatively superior cycle characteristics and thermal stability.

[0006] However, due to the recent rise in cobalt (Co) prices, development is underway on lithium-rich NCM-based cathode active materials that can achieve high capacity while containing relatively low cobalt (Co) content. Lithium-rich NCM-based cathode active materials offer advantages in terms of high energy density and price.

[0007] Generally, precursors of NCM-based cathode active materials are synthesized by coprecipitation, and mainly exist in the form of hydroxides or carbonates. Hydroxide precursor Ni 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, about 1-3 μm, and not dense, resulting in low ionic conductivity and a disadvantage of reduced 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, about 10-40 nm in size. During the firing process, carbon dioxide is removed, causing the pores within the secondary particles to become very large. This results in low strength, and the particles are crushed during rolling, leading to a significant drop in density.

[0008] Therefore, there is still a need to develop positive electrode active materials and their precursors that have small primary particles, dense secondary particles that exhibit high density, excellent particle strength that prevents particle cracking during rolling, and can exhibit excellent battery performance such as high capacity, efficiency, and rate characteristics when applied to secondary batteries. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide an NCM-based cathode active material precursor and a method for producing the same, which exhibits excellent particle strength due to its small primary particles, dense secondary particles, and high density.

[0010] Furthermore, we aim to provide a lithium-rich (Li-rich) NCM-based positive electrode active material produced using the positive electrode active material precursor, which can exhibit excellent battery performance such as high capacity, efficiency, and rate characteristics when applied to secondary batteries, as well as a method for producing the same. [Means for solving the problem]

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

[0012] Furthermore, the present invention provides a method for producing a positive electrode active material precursor for a secondary battery, comprising the steps of: continuously feeding a nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cation-containing solution, an alkaline solution, and an ammonium ion-containing solution into a reactor; and coprecipitation either without feeding gas into the reactor or while continuously feeding oxygen-containing gas into the reactor, thereby forming a positive electrode active material precursor in which nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms and manganese (Mn) is in an oxidized form.

[0013] Furthermore, the present invention provides a method for producing a positive electrode active material for a secondary battery, comprising the steps of mixing a positive electrode active material precursor manufactured as described above with a lithium raw material, and after mixing, firing at 750 to 1,000°C to form a lithium composite transition metal oxide.

[0014] Further, the present invention provides a positive electrode active material manufactured as described above, a positive electrode containing the same, and a lithium secondary battery.

Advantages of the Invention

[0015] According to the present invention, it is possible to manufacture an NCM-based positive electrode active material precursor in which primary particles are small, secondary particles are dense, exhibit a high density, and can exhibit excellent particle strength.

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

Brief Description of the Drawings

[0017] [Figure 1] XPS data of the positive electrode active material precursor manufactured in Example 1. [Figure 2] Reference materials for XPS data of manganese oxide. [Figure 3] XRD data of the positive electrode active material precursor manufactured in Comparative Example 1. [Figure 4] XRD data of the positive electrode active material precursor manufactured in Comparative Example 2. [Figure 5] Scanning electron microscope (SEM) photograph of the positive electrode active material precursor manufactured in Comparative Example 1 observed at an enlarged scale. [Figure 6] Scanning electron microscope (SEM) photograph of the positive electrode active material precursor manufactured in Comparative Example 2 observed at an enlarged scale. [Figure 7] Scanning electron microscope (SEM) photograph of the positive electrode active material precursor manufactured in Example 1 observed at an enlarged scale.

Modes for Carrying Out the Invention

[0018] The present invention will now be described in more detail to aid in understanding it. In this regard, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0019] <Positive electrode active material precursor> The positive electrode active material precursor of the present invention is manufactured by the steps of: continuously feeding a nickel (Ni), cobalt (Co), and manganese (Mn) transition metal cation-containing solution, an alkaline solution, and an ammonium ion-containing solution into a reactor; and coprecipitation either without feeding gas into the reactor or while continuously feeding oxygen-containing gas into the reactor, thereby forming a positive electrode active material precursor in which nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms and manganese (Mn) is in an oxidized form.

[0020] The method for producing the positive electrode active material precursor will be described in detail step by step.

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

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

[0023] The nickel (Ni)-containing raw material may be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and may specifically be, but 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 aforementioned 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, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof. Specifically, it may be, but is not limited to, manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate salts, manganese citrate, manganese fatty acid salts; manganese oxyhydroxide, manganese chloride, or combinations thereof.

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

[0027] The ammonium ion-containing solution may contain, but is not limited to, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof as a complex-forming agent. On the other hand, the ammonium ion-containing solution may be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (specifically, alcohol, etc.) may be used as the solvent.

[0028] The alkaline solution may contain, as a precipitating agent, alkali metal or alkaline earth metal hydroxides such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof, or alkali compounds. The alkaline solution may also be used in aqueous solution form, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (specifically, alcohol, etc.) may be used as the solvent. The alkaline solution is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution becomes 11 to 13.

[0029] Next, the reactor is either left empty or continuously supplied with an oxygen-containing gas while coprecipitation is performed to form a positive electrode active material precursor in which nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms, and manganese (Mn) is in an oxidized form.

[0030] Conventionally, in the coprecipitation reaction of precursors of general NCM-based cathode active materials, a hydroxide-form precursor was synthesized under an inert atmosphere by introducing nitrogen (N2) or argon (Ar) gas, or a carbonate-form precursor was synthesized by introducing nitrogen (N2), argon (Ar), or carbonic acid (H2CO3) gas. However, conventional hydroxide-form precursors have disadvantages: the primary particles are very large, about 1-3 μm, are not dense, have low ionic conductivity, and suffer from reduced electrochemical performance and density. Carbonate-form precursors have disadvantages: the primary particles are very small, about 10-40 nm, and carbon dioxide is removed during the calcination process, resulting in very large pores within the particles, leading to low strength, particle pulverization during rolling, and a very low density.

[0031] Therefore, in this invention, in order to provide an NCM-based cathode active material precursor that exhibits excellent particle strength due to its small primary particles, dense secondary particles, and high density, the cathode active material precursor was produced by either not introducing gas during the coprecipitation reaction of the precursor or by coprecipitation while continuously introducing an oxygen-containing gas. As a result, a cathode active material precursor is formed in which nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms, and manganese (Mn) is in an oxidized form.

[0032] In this invention, during the coprecipitation reaction, either no gas is introduced or an oxygen-containing gas is continuously introduced. As a result, even if manganese (Mn) ions do not react with the alkali compound after coordinating with ammonium ions, they can combine with the introduced oxygen (O2) gas or oxygen (O2) gas in the air to precipitate as an oxide, or even if they precipitate by reacting with the alkali compound, they can be oxidized in the reactor, resulting in a very fast reaction rate and the formation of small primary particles.

[0033] Conventionally, during the coprecipitation reaction, nitrogen (N2), argon (Ar), and / or carbonic acid (H2CO3) gas were introduced. However, in the present invention, during the coprecipitation reaction, nitrogen (N2), argon (Ar), and carbonic acid (H2CO3) gas may not be introduced into the reactor. Alternatively, an oxygen-containing gas may be continuously introduced. According to one embodiment of the present invention, the input flow rate of oxygen (O2) gas can specifically satisfy the following formula 1.

[0034] [Formula 1] ((Manganese (Mn) input amount per hour (mol) × 2) / 0.089) ≤ Input flow rate of oxygen (O2) gas (L / h) ≤ 1.1 × {((Manganese (Mn) input amount per hour (mol) × 2) / 0.089)}

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

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

[0037] The cathode active material precursor produced according to one embodiment of the present invention can 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 chemical formula 1, M 1x is at least one selected from the group consisting of Fe, V, Mo, Al, Na, Ti, Cu, Cr, Nb, Zr, Mg, and K, and 0.25≦x≦0.5, 0.5≦y≦0.75, x+y=1, 0 <a≦0.6、0≦b≦0.4である。

[0039] The positive electrode active material precursor produced by the present invention comprises nickel (Ni), cobalt (Co), and manganese (Mn), wherein the nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms, and the manganese (Mn) is in an oxidized form.

[0040] Furthermore, the positive electrode active material precursor is in the form of secondary particles formed by the 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 positive electrode active material precursor according to one embodiment of the present invention, even if the manganese (Mn) ions do not react with the alkali compound after coordinating with the ammonium ions, they can combine with the introduced oxygen (O2) gas or air and precipitate as an oxide, or even if they react with the alkali compound and precipitate, they are oxidized in the reactor and the reaction rate is very fast, so that primary particles smaller than those of conventional hydroxide-form precursors can be formed. By the positive electrode active material precursor satisfying the particle size range of the primary particles, the primary particles are small and the secondary particles are dense and show high density, resulting in excellent particle strength.

[0041] Furthermore, the positive electrode active material precursor has 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 the tap density measured when 50 g of the positive electrode active material precursor is placed in a 50 ml mass cylinder and the tap density is measured using a STAV-2 tap density meter (J. Engelsmann AG) after 1250 strokes.

[0042] <Cathode active material> Furthermore, the present invention provides a positive electrode active material manufactured using the positive electrode active material.

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

[0044] First, the cathode active material precursor of the present invention and the lithium raw material are mixed. The positive electrode active material precursor comprises nickel (Ni), cobalt (Co), and manganese (Mn), wherein the nickel (Ni) and cobalt (Co) are in unoxidized hydroxide forms, and the manganese (Mn) is in an oxidized form.

[0045] The lithium raw material may be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, 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, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and one or more of these may be used as a mixture.

[0046] The positive electrode active material precursor and the lithium (Li) of the lithium raw material may be mixed in 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 raw material in the aforementioned molar ratio, a lithium-rich lithium composite transition metal oxide can be formed, thereby achieving high capacity.

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

[0048] The positive electrode active material of the present invention manufactured in this manner is a lithium-rich lithium composite transition metal oxide with a molar ratio of lithium (Li) to total metal (M) excluding lithium (Li / M) of 1.2 to 1.6, while having 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 aforementioned pellet density is the pellet density measured when 5 g of the positive electrode active material is placed in a mold with a diameter of 22 mm and measured at a pressure of 2 tons using an HPRM-A2 (manufactured by Hantech).

[0049] <Positive electrode and lithium secondary battery> Another embodiment of the present invention provides a positive electrode for a secondary battery and a lithium secondary battery, both containing 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 containing the positive electrode active material.

[0051] In the positive electrode, the positive electrode current collector 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 with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0052] Furthermore, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material described above.

[0053] In this case, the conductive material is used to impart conductivity to the electrodes and can be used in the constructed battery without particular limitations, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used. The conductive material is usually included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0054] Furthermore, the binder plays a role in improving adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used. The binder may be present in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0055] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, it can be manufactured by coating a composition for forming a positive electrode active material layer, which selectively includes the positive electrode active material and a binder and conductive material, onto 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 any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for cathode manufacturing, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0057] Alternatively, the positive electrode can also be manufactured by casting the composition for forming the positive electrode active material layer onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0058] Another embodiment of the present invention provides an electrochemical element including the positive electrode. The electrochemical element may be specifically 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 positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is as described above. The lithium secondary battery may also selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing 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, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0062] The negative electrode active material layer selectively includes a binder and a conductive material along with the negative electrode active material. The negative electrode active material layer can also be manufactured, for example, by coating a negative electrode forming composition containing the negative electrode active material and selectively a binder and a conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0063] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. The carbon material may be low-crystallinity carbon or high-crystallinity carbon. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0064] Furthermore, the binder and conductive material may be the same as those described earlier for the positive electrode.

[0065] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in secondary batteries can be used without particular limitations, and it is especially preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as a single-layer or multi-layer structure.

[0066] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[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 through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, which may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of about 1:1 to about 1:9 can produce an electrolyte with excellent performance.

[0069] The lithium salt may be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0070] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0071] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0072] Accordingly, according to another embodiment of the present invention, a battery module and a battery pack containing the lithium secondary battery as a unit cell are provided.

[0073] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0074] The embodiments of the present invention will be described in detail below so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention may be realized in various different forms and is not limited to the embodiments described herein.

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

[0076] During this process, oxygen (O2) gas is supplied at a rate of 13.0 L / hr while the coprecipitation reaction is carried out for 24 hours, resulting in 0.4 (Ni 0.5 Co 0.5 Precursor particles of (OH)2)·0.6(MnO2) were formed. After separating and washing the precursor particles, they were dried in an oven at 130°C to produce a cathode active material precursor.

[0077] Comparative Example 1 After adding 4 liters of distilled water to 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 and create a non-oxidizing atmosphere. After adding 100 ml of 28 wt% aqueous ammonia solution, a 3.2 mol / L metal aqueous solution, prepared by mixing NiSO4, CoSO4, and MnSO4 in a nickel:cobalt:manganese molar ratio of 2:2:6, was continuously added to the reactor at a rate of 300 ml / hr, followed by 42 ml / hr of 28 wt% aqueous ammonia solution. The impeller was stirred at a speed of 400 rpm. A 40 wt% sodium hydroxide solution was added to maintain the pH at 10.0. The coprecipitation reaction was carried out for 24 hours, and Ni 0.2 Co 0.2 Mn 0.6 (OH)2 precursor particles were formed. After separating and washing the precursor particles, they were dried in an oven at 130°C to produce a cathode active material precursor.

[0078] Comparative Example 2 After adding 4 liters of distilled water to 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 and create a non-oxidizing atmosphere. After adding 100 ml of 28 wt% aqueous ammonia solution, a 3.2 mol / L metal aqueous solution, prepared by mixing NiSO4, CoSO4, and MnSO4 in a nickel:cobalt:manganese molar ratio of 2:2:6, was continuously added to the reactor at a rate of 300 ml / hr, followed by 42 ml / hr of 28 wt% aqueous ammonia solution. The impeller was stirred at a speed of 400 rpm. To maintain the pH, a 20 wt% sodium carbonate solution was added to maintain the pH at 7.5. The coprecipitation reaction was carried out for 24 hours, and Ni 0.2 Co 0.2 Mn 0.6 CO3 precursor particles were formed. After separating and washing the precursor particles, they were dried in an oven at 130°C to produce a cathode active material precursor.

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

[0080] Referring to Figures 1-2 (XPS of Example 1 (Figure 1) and reference material (Figure 2)), the oxidation state of Mn can be determined from the energy difference between the two peaks separated from the 3s XPS spectrum of Mn, and as can be seen from the reference material in Figure 2, it can be confirmed that Mn exists in the form of tetravalent MnO2.

[0081] Referring to Figures 3-4 (XRD of Comparative Examples 1-2), it was confirmed that Comparative Example 1 is in the hydrogenated form of Ni, Co, and Mn, and Comparative Example 2 is in the carbonate form of Ni, Co, and Mn.

[0082] On the other hand, Figures 5 to 7 show magnified images of the positive electrode active material precursors produced in Example 1 and Comparative Examples 1 and 2, taken with a scanning electron microscope (SEM). Figure 5 shows the positive electrode active material precursor of Comparative Example 1, which is in the form of a hydroxide, and it can be seen that the primary particles are large and the secondary particles are not dense. Figure 6 shows the positive electrode active material precursor of Comparative Example 2, which is in the form of a carbonate, and it can be seen that the primary particles are excessively small and the pores within the particles are large. Conversely, Figure 7 shows the positive electrode active material precursor of Example 1, and it can be seen that the primary particles are small and the secondary particle shape is dense.

[0083] [Experimental Example 2: Measurement of Tap Density] 50 g each of the positive electrode active material precursors produced in Example 1 and Comparative Examples 1-2 were placed in a 50 ml mass cylinder, and the tap density was measured by performing 1250 strokes using a STAV-2 tap density meter (J.Engelsmann AG). The results are shown in Table 1 below.

[0084] [Table 1]

[0085] Referring to Table 1, it can be confirmed 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 form of hydroxide / carbonate.

[0086] Examples 2 and Comparative Examples 3-4 The cathode active material precursors and lithium raw material LiOH produced in Example 1 and Comparative Examples 1-2 were mixed in a molar ratio of 1:1.35. The resulting powder was placed in an alumina vessel, heated to 550°C under an air atmosphere, calcined for 5 hours, then cooled to room temperature. The calcined product was then crushed and sieved, and the temperature was raised to 900°C for 10 hours to produce the cathode active materials of Example 2 and Comparative Examples 3-4.

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

[0088] [Table 2]

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

[0090] [Experimental Example 4: Performance Evaluation of Lithium-ion Rechargeable Batteries] The positive electrode active materials, carbon black conductive material, and PVdF binder produced in Example 2 and Comparative Examples 3-4 were mixed in N-methylpyrrolidone solvent in a weight ratio of 96:2:2 to produce a positive electrode composite material. This composite material was then applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0091] Lithium metal was used as the negative electrode.

[0092] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and negative electrode manufactured as described above. After positioning the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte 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 volume ratio = 3 / 5 / 2).

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

[0094] [Table 3]

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

Claims

1. comprising nickel (Ni), cobalt (Co), and manganese (Mn); The nickel (Ni) and cobalt (Co) are in an unoxidized hydroxide form, and the manganese (Mn) is in an oxidized form.

2. The positive electrode active material precursor for a secondary battery according to claim 1 , 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.

3. 3. 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.

4. 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.

5. 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:

6. Nitrogen (N ２ ), argon (Ar), and carbonic acid (H ２ CO ３ 6. The method for producing a positive electrode active material precursor for a secondary battery according to claim 5, wherein no gas is introduced.

7. When the oxygen-containing gas is introduced, oxygen (O ２ 7. The method for producing a positive electrode active material precursor for a secondary battery according to claim 5 or 6, 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}

8. The reactor ａ The method for producing a positive electrode active material precursor for a secondary battery according to claim 5 , further comprising the step of adding a cation-containing solution to cause coprecipitation.

9. The method for producing a positive electrode active material precursor for a secondary battery according to claim 5 , 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.

10. mixing the cathode active material precursor produced according to claim 5 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:

11. The method for producing a positive electrode active material for a secondary battery according to claim 10, 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.

12. A positive electrode active material for a secondary battery produced according to claim 10.

13. The positive electrode active material for a secondary battery according to claim 12 , wherein the positive electrode active material has a pellet density of 2.0 g / cc or more.

14. A positive electrode for a secondary battery, comprising the positive electrode active material according to claim 12.

15. A lithium secondary battery comprising the positive electrode according to claim 14.

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