Positive electrode active material for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a positive electrode active material for lithium secondary batteries in which a content of impurities is low, and provide a lithium secondary battery improved in charge / discharge capacity and efficiency characteristics.SOLUTION: Positive electrode active materials, methods of fabricating the positive electrode active materials, positive electrodes including the positive electrode active materials, and lithium secondary batteries including the positive electrodes are disclosed. More specifically, the positive electrode active material includes a positive electrode active material including particles containing lithium composite oxide represented by Chemical Formula 1: LiaNixM1-xOb. In the chemical formula 1, a is 0.5 to 1.5. x is 0.6 to 0.99. b is 1.8 to 2.2. 1-x may be 0.01 to 0.4. M includes at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The particle contains sodium (Na) and sulfur (S). A mass fraction (Na / S) of the Na to the S is 0.03 to 0.2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery including the positive electrode.

Background Art

[0002] A battery that generates electrical energy through physical or chemical reactions of substances and supplies power externally is used when it is not possible to obtain an AC power supply supplied to a building or when a DC power supply is required due to the living environment surrounded by various electrical and electronic devices.

[0003] Among such secondary batteries, primary batteries and secondary batteries, which are chemical batteries using chemical reactions, are generally used. A primary battery is commonly referred to as a dry battery and is a consumable battery. On the other hand, a secondary battery is a rechargeable battery that can repeat an oxidation / reduction reaction between a positive electrode and a negative electrode. When a reduction reaction occurs at the positive electrode by an electric current, the battery is charged, and when an oxidation reaction occurs at the positive electrode, the battery is discharged. Such charging and discharging of the secondary battery are repeated.

[0004] In a lithium secondary battery, a positive electrode active material made of a lithium composite oxide containing a high content of nickel has attracted attention. Although the positive electrode active material has a high energy density, there is a problem that the battery life and stability rapidly decrease as the nickel content increases.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the present invention is to provide a positive electrode active material for a lithium secondary battery with a low content of impurities.

[0006] Another problem to be solved by the present invention is to provide a lithium secondary battery with improved charge / discharge capacity and efficiency characteristics.

Means for Solving the Problems

[0007] The positive electrode active material according to the concept of the present invention includes particles containing a lithium composite oxide of the following Chemical Formula 1: [Chemical Formula 1] Li a Ni x M 1-x O b In Chemical Formula 1, a is from 0.5 to 1.5, x is from 0.6 to 0.99, b is from 1.8 to 2.2, 1 - x is from 0.01 to 0.4, and M may include at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The particles contain sodium (Na) and sulfur (S), and the mass fraction of Na with respect to S (Na / S) may be from 0.03 to 0.2.

[0008] A method for manufacturing a positive electrode active material according to another concept of the present invention may include a step of forming a nickel-based hydroxide precursor, a step of mixing the nickel-based hydroxide precursor and a lithium raw material to form a mixture, a step of firing the mixture to form particles containing a lithium composite oxide, and a step of performing a wet coating process on the particles. The particles on which the wet coating process has been performed contain sodium (Na) and sulfur (S), and the mass fraction of Na with respect to S (Na / S) may be from 0.03 to 0.2.

[0009] A positive electrode for a lithium secondary battery according to still another concept of the present invention may include the above-described positive electrode active material.

[0010] A lithium secondary battery according to still another concept of the present invention may include the above-described positive electrode.

Advantages of the Invention

[0011] The positive electrode active material for a lithium secondary battery according to the present invention may contain sodium (Na) and sulfur (S), and the mass fraction of Na with respect to S (Na / S) may be from 0.03 to 0.2.

[0012] Accordingly, the lithium secondary battery using the positive electrode active material of the present invention can have improved capacity and efficiency characteristics.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0014] To fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be realized in various forms and can be subjected to various modifications, not limited to the embodiments disclosed below. However, it is provided to make the disclosure of the present invention complete by the description of the present embodiment and to fully inform those having ordinary knowledge in the technical field to which the present invention pertains of the scope of the invention.

[0015] In this specification, when a certain component is referred to as being on another component, it means that it can be directly formed on the other component or a third component can be interposed therebetween. Also, in the drawings, the thickness of the components is exaggerated for an effective explanation of the technical content. Throughout the specification, parts denoted by the same reference numerals indicate the same components.

[0016] The embodiments described herein are described with reference to cross-sectional and / or plan views that are ideal exemplary diagrams of the present invention. In the drawings, the thicknesses of films and regions are exaggerated for an effective explanation of the technical content. Thus, the regions illustrated in the drawings have schematic attributes, and the patterns of the regions illustrated in the drawings are for exemplifying specific forms of the regions of the elements and not for limiting the scope of the invention. In various embodiments of the present specification, terms such as first, second, third, etc. are used to describe various components, but these components should not be limited to such terms. These terms are merely used to distinguish one component from another. The examples described and illustrated herein include their complementary embodiments as well.

[0017] The terms used herein are for explaining the embodiments and are not for limiting the present invention. In this specification, the singular form also includes the plural form unless specifically stated otherwise in the sentence. The "comprises" and / or "comprising" used in the specification do not exclude the presence or addition of one or more other components of the recited component.

[0018] FIG. 1 is a conceptual diagram schematically showing a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 1, the lithium secondary battery may include a positive electrode 100, a negative electrode 200, an electrolyte 300, and a separator 400.

[0019] The positive electrode 100 and the negative electrode 200 may be separated from each other with the separator 400 interposed therebetween. The separator 400 may be disposed between the positive electrode 100 and the negative electrode 200. The positive electrode 100, the negative electrode 200, and the separator 400 may be in contact with the electrolyte 300. The positive electrode 100, the negative electrode 200, and the separator 400 may be impregnated in the electrolyte 300.

[0020] The electrolyte 300 may be a medium for transferring ions between the positive electrode 100 and the negative electrode 200. In the electrolyte 300, the lithium ions may move through the separator 400 toward the positive electrode 100 or the negative electrode 200.

[0021] The positive electrode 100 may include a first current collector COL1 and a positive electrode active material layer AML1 on the first current collector COL1. The first current collector COL1 may include a metal selected from the group consisting of aluminum, copper, copper plated with nickel, stainless steel, nickel, titanium, palladium, and an aluminum-cadmium alloy. The first current collector COL1 may have a form such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, or a non-woven fabric body.

[0022] The positive electrode active material layer AML1 may include a binder, a conductive material, and a positive electrode active material. The positive electrode active material may be contained in a content of 80 wt% to 99 wt%, more specifically 85 wt% to 98 wt% based on the total weight of the positive electrode active material layer AML1. The positive electrode active material may be a source of lithium ions. The positive electrode active material is a lithium transition metal oxide and may further contain at least one transition metal in addition to lithium. Specific descriptions of the positive electrode active material according to embodiments of the present invention will be described later.

[0023] The conductive material may impart conductivity to the positive electrode active material layer AML1. The conductive material may include at least one of a carbon-based material (e.g., graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, or carbon fiber), a metal powder, a metal fiber, a conductive whisker, a conductive metal oxide, a conductive polymer, and combinations thereof. The conductive material may be contained in a content of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer AML1.

[0024] The binder can improve the adhesion between the positive electrode active material and the first current collector COL1. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, and combinations thereof. The binder may be included in a content of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer AML1.

[0025] The negative electrode 200 may include a second current collector COL2 and a negative electrode active material layer AML2 on the second current collector COL2. The description of the second current collector COL2 may be the same as or similar to that of the first current collector COL1 described above. The second current collector COL2 may include the same or different metals as the first current collector COL1. The second current collector COL2 may have the same or different forms as the first current collector COL1.

[0026] The negative electrode active material layer AML2 may include a binder, a conductive material, and a negative electrode active material. The binder and the conductive material may be the same as those described for the positive electrode active material layer AM1 above. The negative electrode active material may be included in a content of 80 wt% to 99 wt%, more specifically 85 wt% to 98 wt% based on the total weight of the negative electrode active material layer AML2. The negative electrode active material may include at least one selected from the group consisting of carbon materials, lithium metal or lithium metal oxides, silicon or silicon compounds, and tin or tin compounds. Metal oxides such as TiO2 and SnO2 with a potential of less than 2V can also be used as the negative electrode active material. The carbon material may include low - crystalline carbon and / or highly crystalline carbon.

[0027] The separator 400 may include a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. The separator 400 may include a single porous polymer film or a laminate of a plurality of porous polymer films. As another embodiment of the present invention, the separator 400 may include a normal porous nonwoven fabric, for example, a high melting point glass fiber or a polyethylene terephthalate fiber.

[0028] The electrolyte 300 may contain a salt having a structure such as A + B - . A + may include at least one or more alkali metal cations selected from the group consisting of Li + , Na + , and K + . B - may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , AlO4 - , AlCl4 - , PF6 - , SbF6 - , AsF6 - , BF2C2O4 - , BC4O8 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -- , C4F9SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C -, (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - may contain at least one negative ion selected from the group consisting of

[0029] As one embodiment of the present invention, the electrolyte 300 can be used by dissolving it in an organic solvent. The organic solvent may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl methyl carbonate (EMC), γ-butyrolactone, or a mixture thereof.

[0030] The casing of the secondary battery according to the embodiment of the present invention can adopt those commonly used in the relevant technical field, and there is no limitation on the outer shape according to the use of the battery. For example, the casing of the secondary battery may include a cylindrical shape, a rectangular shape, a pouch shape, or a coin shape.

[0031] The positive electrode active material according to the embodiment of the present invention may include particles containing a lithium composite oxide represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Ni x M 1-x O b

[0032] In the chemical formula 1, a is from 0.5 to 1.5, x is from 0.6 to 0.99, b is from 1.8 to 2.2, 1 - x is from 0.01 to 0.4, and M may contain at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. As one embodiment, M may contain Co, Al, and Mn. The lithium composite oxide represented by the chemical formula 1 may have a layered crystal structure.

[0033] The lithium composite oxide may contain Na and S. Na and S may be derived from a wet coating process, and in particular, S may be derived from a metal sulfate. The weight ratio of Na to the total weight of the lithium composite oxide particles may be from 0.001 to 0.002, and the weight ratio of S to the total weight of the lithium composite oxide particles may be from 0.02 to 0.04. The mass fraction (Na / S) of Na with respect to S may be from 0.03 to 0.2, and may be, for example, from 0.03 to 0.1, from 0.03 to 0.07, or from 0.035 to 0.07.

[0034] When Na / S has the above - mentioned mass fraction, the capacity and efficiency characteristics of a lithium secondary battery containing the positive electrode active material can be improved. If Na / S is less than 0.03, the content of Na is low, and it may be difficult to maintain the pH required for wet coating. If Na / S exceeds 0.2, Na acts as an impurity, and the capacity and efficiency may decrease.

[0035] The "mass fraction" used in the present invention is obtained as a result of analyzing the content of impurities in the positive electrode active material using an inductively coupled plasma optical emission spectrometer (ICP), that is, ICP - MS.

[0036] As one embodiment of the present invention, x, which is the molar ratio of Ni in Chemical Formula 1, may be greater than 0.8. If the lithium composite oxide has a high nickel content composition (x > 0.8), the firing of the lithium composite oxide can be carried out at a relatively low temperature. Thereby, in the manufacturing process of the positive electrode active material for a lithium secondary battery described later, lithium composite oxide particles can be formed at a relatively low temperature. Ni in the lithium composite oxide can affect the output and capacity characteristics of the lithium secondary battery. The present invention can provide a high-output lithium secondary battery by utilizing a lithium composite oxide having a high nickel content composition.

[0037] As the content of Ni in the lithium composite oxide increases, the stability of the positive electrode or the secondary battery may decrease. As one embodiment of the present invention, the lithium composite oxide may further contain Co, thereby improving the stability and capacity retention characteristics of the secondary battery.

[0038] The lithium composite oxide particles according to the embodiment of the present invention may have a granular or spherical shape. As one embodiment of the present invention, the lithium composite oxide particles may have a form of secondary particles in which primary particles are aggregated. As another example of the present invention, the lithium composite oxide may have a form of single particles. The form of the single particles may include the form of primary particles or the form of secondary particles formed by aggregating several primary particles. The form of the single particles may include one crystal grain or several crystal grains. The crystal grain may be the smallest unit in which the lithium composite oxide particles have one crystal direction. For example, the lithium composite oxide particles according to the present invention may include one primary particle and / or one single particle in which a plurality of particles are integrally merged.

[0039] The lithium composite oxide particles according to the embodiment of the present invention may have an average particle size of 10.0 μm to 20.0 μm. The "average particle size" used in the present invention, that is, D50, is the particle size when the volume cumulative percentage corresponds to 50% in the particle size distribution obtained from the volume of the particles. For example, the average particle size can be measured by a particle size analyzer (PSA).

[0040] Hereinafter, a method for manufacturing a positive electrode active material according to one aspect will be described in detail.

[0041] First, a precursor can be prepared. The precursor can contain Ni and M of Chemical Formula 1 described above. M can be at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. For example, M can contain Co and Al.

[0042] As one embodiment, the precursor can be prepared by a coprecipitation method. For example, the coprecipitation method can include dissolving a raw material substance of a transition metal in a solvent such as distilled water, and continuously introducing the transition metal salt solution into a reactor together with a chelating agent and a basic aqueous solution to cause precipitation. After collecting the precipitate in a slurry state, the slurry solution can be filtered and dried to obtain a precursor that is a metal composite oxide.

[0043] In the present invention, the raw material substance of the transition metal can contain a metal salt of at least one element selected from the group consisting of Ni, Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn. The metal salt can be a sulfate, nitrate, acetate, halide, hydroxide, etc., and is not particularly limited as long as it can be dissolved in a solvent. The raw material substance of the transition metal according to this example can contain a nickel salt, a cobalt salt, and an aluminum salt. The raw material substance of the transition metal can be mixed by adjusting the molar ratio so that the positive electrode active material has high-capacity characteristics. For example, x in Chemical Formula 1 can be determined by the molar ratio.

[0044] The precursor can be mixed with a lithium raw material in a certain ratio to form a mixture. For example, the precursor and the lithium raw material can be mixed at a molar ratio of about 1:1. The lithium raw material is not particularly limited as long as it is a substance commonly used in manufacturing the positive electrode active material. For example, the lithium raw material can include a lithium salt such as lithium carbonate, lithium nitrate, lithium hydroxide, or lithium sulfate.

[0045] The mixture can be charged into a furnace (Furnace, FRC) and fired at a first temperature. The first temperature can be from 700°C to 1,000°C. More specifically, the first temperature can be from 700°C to 800°C. The firing process can be carried out in an oxidizing atmosphere such as air or oxygen. The heat treatment time of the firing process can be from 10 hours to 30 hours. In another embodiment of the present invention, a pre-firing may be additionally performed at 150°C to 800°C before the firing process.

[0046] Lithium composite oxide particles can be formed from a mixture containing a precursor and a lithium raw material by the firing process. A grinding process can be performed on the formed particles. The ground particles can have an average particle size of 10.0 μm to 20.0 μm.

[0047] A coating process can be performed on the lithium composite oxide. The coating process can be performed wet. Specifically, the lithium composite oxide particles and the coating raw material can be mixed. The lithium composite oxide particles and the coating raw material can be charged into a solvent (for example, distilled water) and mixed. The coating raw material can contain a metal sulfate.

[0048] The metal sulfate can contain a compound represented by M1SO4. M1 can be at least one selected from the group consisting of Zr, Al, Na, K, Mg, Ca, S, Ni, Co, Ti, B, Sn, Mn, Cr, Fe, and V. For example, the metal sulfate can be CoSO4 or Al2(SO4)3. The lithium composite oxide particles and the coating raw material can be uniformly mixed by a stirrer. After filtering and drying the lithium composite oxide particles, a surface treatment can be performed on the lithium composite oxide particles. The surface treatment can include performing a heat treatment process in an oxidizing atmosphere such as air or oxygen. The surface treatment can be performed at a temperature of 300°C to 800°C.

[0049] According to an embodiment of the present invention, the coating process can be performed as a wet process. For example, after dissolving metal sulfate powder in distilled water to form a solution, a lithium composite oxide is added to the solution and stirred for a certain period of time, whereby surface coating can be performed. The content of the metal sulfate in the metal sulfate solution can be 0.5 to 3 mol%. In the wet process, an aqueous NaOH solution is generally added to adjust the pH, but in the present invention, NaOH can be omitted to reduce the content of impurities in the positive electrode active material.

[0050] The present invention can use a lithium composite oxide having a high-content nickel composition as the positive electrode active material. In this case, the residual lithium value of the primary product active material can increase. Even if the residual lithium dissolves in the solvent during washing to increase the pH and NaOH is omitted, a metal coating can be smoothly performed on the surface of the active material particles.

[0051] If NaOH is excluded in the wet coating process, the content of impurities, particularly the contents of Na and S, can be reduced. If the content of impurities is reduced, the charge-discharge capacity characteristics and efficiency characteristics of the lithium secondary battery can be improved.

[0052] The positive electrode 100 of FIG. 1 can be manufactured by a normal method for manufacturing a positive electrode except that the positive electrode active material according to the embodiment of the present invention is used. Specifically, the positive electrode active material, binder, and conductive material of the present invention can be dissolved or dispersed in a solvent to produce a mixture. The binder and the conductive material can be the same as those described above for the positive electrode active material layer AM1 of FIG. 1. After applying the mixture onto the first current collector COL1, the positive electrode 100 can be manufactured by drying and rolling.

[0053] The solvent can be a solvent generally used in the relevant technical field. For example, it can include at least one of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, and combinations thereof.

[0054] As another embodiment, the mixture may be cast onto a separate support to produce a film, i.e., the positive electrode active material layer AML1. The positive electrode 100 may be manufactured by laminating the positive electrode active material layer AML1 onto the first current collector COL1.

[0055] FIG. 2 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment of the present invention. Referring to FIG. 2, the lithium secondary battery may include a positive electrode 100, a negative electrode 200, and a separator 400. The descriptions of the positive electrode 100, the negative electrode 200, and the separator 400 in FIG. 8 may be substantially the same as those described above for the lithium secondary battery of FIG. 1.

[0056] The positive electrode 100, the negative electrode 200, and the separator 400 in FIG. 2 may be wound or folded to form an electrode assembly. The electrode assembly may be housed in a battery case 500. The electrode assembly may include a plurality of electrode assemblies. A separator 400 may be provided between the electrode assemblies. The electrode assemblies stacked sequentially may be provided in the battery case 500. The inside of the battery case 500 may be filled with an electrolytic solution (see 300 in FIG. 1). The battery case 500 may be sealed by a cap assembly 600. The battery case 500 according to an embodiment of the present invention may be cylindrical, rectangular, or pouch-shaped. The lithium secondary battery according to an embodiment of the present invention may be used in devices such as a notebook computer, a smartphone, or an electric vehicle.

[0057] Hereinafter, the present invention will be described in more detail with reference to examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

[0058] (Manufacture of Positive Electrode Active Material) Using the coprecipitation method, nickel-based metal hydroxide (Ni 0.98 Co 0.02(OH)2) precursors were manufactured. As raw material substances for nickel-based metal hydroxides, nickel sulfate (NiSO4·6H2O) and cobalt sulfate (CoSO4·7H2O) were dissolved in distilled water as a solvent to prepare a metal raw material mixture in a molar ratio of 98:2. To form a complex compound, a diluted solution of aqueous ammonia (NH4OH) and lithium hydroxide (NaOH) as a precipitate were prepared. Next, the mixture of metal raw materials, aqueous ammonia, and sodium hydroxide were introduced into a reactor. Lithium hydroxide was introduced to maintain the pH of the mixture in the reactor. The reaction was carried out for about 20 hours while stirring the mixture in the reactor.

[0059] The slurry solution in the reactor was filtered and washed with high-purity distilled water. The washed substance was dried in a hot air oven at 190 °C for 24 hours, and a precursor (Ni 0.98 Co 0.02 (OH)2) powder was obtained. After that, the obtained powder was oxidized between 300 °C and 500 °C to obtain a final oxide precursor (Ni 0.98 Co 0.02 O2) powder.

[0060] The precursor and anhydrous lithium hydroxide (LiOH) were mixed dry using a Henschel mixer. Lithium and transition metals were mixed in a molar ratio of about 1:1. The transition metal is the total (Ni + Co) of the transition metals contained in the large-particle precursor. The mixture was heat-treated at about 900 °C for 10 hours in an oxygen atmosphere to synthesize lithium composite oxide particles. The particles were pulverized with a jet mill at a pressure of 3 bar to obtain first particles.

[0061] Example 1 The first particles were introduced into distilled water together with a coating raw material substance to coat the surface of the particles.

[0062] Specifically, after dissolving CoSO4·6H2O as a coating raw material substance at 0.5 mol% to 3 mol% in distilled water, a total of 224 L was poured into a tank, and additionally distilled water (about 625 L, 9 °C) was poured into the tank and mixed with the cobalt sulfate solution. After adding about 1100 kg of the first particles to the metal sulfate solution, it was stirred for a certain period of time to coat the surface of the particles.

[0063] At this time, the addition of caustic soda (that is, NaOH) was omitted. The solution was filtered and dried to obtain the first particles. The first particles were heat-treated at about 700 °C for 15 hours in an oxygen atmosphere to complete the cobalt (Co) coating process. After the coating process, the impurity content and specific surface area of the lithium composite oxide particles were measured and shown in the following table. The impurity content was measured by performing ICP (Inductively Coupled Plasma) emission spectroscopic analysis. The specific surface area was measured by the BET flow method using a dynamic flow method with a gas of 30% N2 and 70% He (using Macsorb, HM Model-1208).

[0064] Example 2 The coating process was carried out in the same manner as in Example 1, except that the temperature of the additionally added distilled water was 20 °C. After the coating process, the impurity content and specific surface area of the lithium composite oxide particles were measured and shown in the following table.

[0065] Example 3 The coating process was carried out in the same manner as in Example 1, except that the additionally added distilled water was about 600 L and 20 °C. After the coating process, the impurity content and specific surface area of the lithium composite oxide particles were measured and shown in the following table.

[0066] Production Example 1 In the coating process of Example 1, the first particles were coated in the same manner as in Example 1, except that after the first particles were introduced into the metal sulfate solution, approximately 73 L of a 20% NaOH aqueous solution was gradually added. The impurity content and specific surface area of the coated first particles were measured and shown in the following table.

[0067] Production Example 2 In the coating process of Example 2, the first particles were coated in the same manner as in Example 2, except that after the first particles were introduced into the metal sulfate solution, approximately 73 L of a 20% NaOH aqueous solution was gradually added. The impurity content and specific surface area of the coated first particles were measured and shown in the following table.

[0068] Production Example 3 In the coating process of Example 3, the first particles were coated in the same manner as in Example 3, except that after the first particles were introduced into the metal sulfate solution, approximately 73 L of a 20% NaOH aqueous solution was gradually added. The impurity content and specific surface area of the coated first particles were measured and shown in the following table.

[0069] Production Example 4 The coating process was carried out in the same manner as in Example 1, except that the additional distilled water added was approximately 700 L and at 20 °C. After the coating process, the impurity content and specific surface area of the lithium composite oxide particles were measured and shown in the following table.

[0070] Production Example 5 In the coating process of Production Example 4, the first particles were coated in the same manner as in Production Example 4, except that the first particles were heat-treated at approximately 650 °C for 15 hours in an oxygen atmosphere. The impurity content and specific surface area of the coated first particles were measured and shown in the following table.

[0071] Production Example 6 In the coating process of Production Example 4, the first particles were coated in the same manner as in Production Example 4, except that the first particles were heat-treated at about 750°C for 15 hours in an oxygen atmosphere. The impurity content and specific surface area of the coated first particles were measured and shown in the following table.

[0072]

Table 1

[0073] Referring to Table 1, as shown in Examples 1 to 3, it can be confirmed that if NaOH is omitted in the wet coating process, the contents of Na and S among the impurities are significantly reduced. In addition, it can be confirmed that the mass fraction of Na to S (Na / S) is significantly reduced and the specific surface area of the active material particles is increased. If the specific surface area is excessively small, the reactivity of the active material particles will decrease, and the capacity and efficiency characteristics may be reduced.

[0074] (Manufacture of secondary battery) Experimental Example 1 96 g of the positive electrode active material of Example 1, 2 g of polyvinylidene fluoride, 47 g of the solvent N-methylpyrrolidone, and 2 g of the conductive agent carbon black were mixed to produce an active material slurry.

[0075] The active material slurry was coated on an aluminum foil using a doctor blade to produce a thin plate-like electrode plate. After drying the electrode plate at 135°C for 3 hours or more, a positive electrode was produced through a rolling and vacuum drying process.

[0076] As a counter electrode to the positive electrode, a 2032-type coin cell was manufactured using a lithium metal counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode. An electrolyte was injected to fabricate a 2032-type coin cell. As the electrolyte, a solution in which 1.1 M of LiPF6 was dissolved in a solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:5 was used.

[0077] For each sample, three coin cells were manufactured using the Toyo system equipment, and the charge-discharge capacity and efficiency of the manufactured secondary battery were evaluated as follows under the conditions of 0.2C / 0.2C (3~4.3V).

[0078] The measured capacity characteristics are shown in Table 2 below.

[0079] Experimental Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Example 2 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0080] Experimental Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Example 3 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0081] Comparative Experimental Example 1 A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Comparative Example 1 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0082] Comparative Experimental Example 2 A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Comparative Example 2 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0083] Comparative Experimental Example 3 A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material of Comparative Example 3 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0084] Comparative Experimental Example 4 A secondary battery was manufactured in the same manner as in Example 1 except that the positive electrode active material of Comparative Example 4 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0085] Comparative Experimental Example 5 A secondary battery was manufactured in the same manner as in Example 1 except that the positive electrode active material of Comparative Example 5 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0086] Comparative Experimental Example 6 A secondary battery was manufactured in the same manner as in Example 1 except that the positive electrode active material of Comparative Example 6 was used. The charge-discharge capacity and efficiency characteristics of the secondary battery were measured in the same manner as in Experimental Example 1 and are shown in Table 2 below.

[0087]

Table 2

[0088] Referring to Table 2 above, it can be confirmed that if the mass fraction of Na to S (Na / S) in the positive electrode active material is 0.03 or more and 0.2 or less, the secondary battery has a larger charge-discharge capacity and exhibits high efficiency characteristics.

Claims

1. A positive electrode active material, The lithium composite oxide particles include a lithium composite oxide represented by the following formula 1: [Chemical formula 1] Li a Ni x M 1-x O b In Formula 1, a is 0.5 to 1.5, x is 0.6 to 0.99, b is 1.8 to 2.2, 1-x is 0.01 to 0.4, and M is at least one element selected from the group consisting of Co, Al, Mn, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Ga, C, Si, and Sn; The particles include sodium (Na) and sulfur (S), A positive electrode active material in which a mass fraction of the Na to the S (Na / S) is 0.03 to 0.

2.

2. The positive electrode active material of claim 1 , wherein x is 0.8 to 0.

99.

3. The positive electrode active material according to claim 1 , wherein the lithium composite oxide has a layered crystal structure.

4. The positive electrode active material of claim 1 , wherein the particles are secondary particles including a plurality of primary particles.

5. The positive electrode active material according to claim 1 , wherein the particles have an average particle size of 10.0 μm to 20.0 μm.

6. The Na and the S are derived from a wet coating process; The cathode active material of claim 1 , wherein NaOH is excluded from the wet coating process.

7. forming a nickel-based hydroxide precursor; mixing the nickel-based hydroxide precursor with a lithium source to form a mixture; calcining the mixture to form particles containing a lithium composite oxide; and subjecting the particles to a wet coating process, The particles subjected to the wet coating process contain sodium (Na) and sulfur (S), A method for producing a positive electrode active material, wherein a mass fraction of the Na to the S (Na / S) is 0.03 to 0.

2.

8. The wet coating process uses metal sulfate. The method of claim 7 , wherein the wet coating process does not use NaOH.

9. The method for producing a positive electrode active material according to claim 8 , wherein the metal sulfate comprises cobalt sulfate.

10. The method for producing a positive electrode active material according to claim 8 , wherein the S is derived from the metal sulfate.

11. The method for producing a positive electrode active material according to claim 7 , further comprising the step of milling the particles before the wet-coating step.

12. The method for producing a positive electrode active material according to claim 7, wherein the particles have an average particle size of 10.0 μm to 20.0 μm.

13. The wet coating process comprises: mixing the metal sulfate solution with the particles; performing a heat treatment process on the particles; The method for producing a positive electrode active material according to claim 7 , comprising:

14. A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1 .

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

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