Positive electrode active material for lithium secondary battery, and method for manufacturing same

Abstract

The present invention relates to a positive electrode active material having high energy density and excellent thermal stability, a method for manufacturing same, and a secondary battery including same and having excellent discharge capacity and retention rate thereof. Specifically, the present invention relates to: a positive electrode active material having excellent energy density, wherein the occurrence of cracks in particles during charge-discharge cycles is suppressed such that the capacity retention rate of the secondary battery is excellent and the thermal stability of the positive electrode active material is excellent, thereby enabling manufacture at high temperature; and a method for manufacturing the positive electrode active material having the above effects.

Description

Cathode active material for lithium secondary batteries and method for producing the same

[0001] The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery using an ion exchange method and a positive electrode active material for a lithium secondary battery produced by the method.

[0002] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0003] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high price of cobalt, which is the raw material, and its supply are unstable, making it difficult to commercially apply it to large-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient cycle life characteristics. On the other hand, lithium manganese oxide has excellent stability but has the problem of poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to complement the problems of lithium transition metal oxides containing only Ni, Co, or Mn. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0004] Conventional lithium nickel cobalt manganese oxides were generally in the form of spherical secondary particles in which hundreds of primary particles were aggregated. However, in the case of lithium nickel cobalt manganese oxides in the form of secondary particles in which many primary particles were aggregated, there is a problem that the primary particles are easily broken during the rolling process during the manufacture of the positive electrode, and cracks occur inside the particles during the charge and discharge process. When the particles of the positive electrode active material are broken or cracked, the contact area with the electrolyte increases, which increases gas generation and active material degradation due to side reactions with the electrolyte, and this causes a problem that the life characteristics are reduced. In particular, in the case of positive electrode active materials with a high nickel content, when the battery is repeatedly charged and discharged, the highly reactive Ni 4+ There is a problem that a large amount of ions are generated, causing the structure of the positive electrode active material to collapse, which causes the deterioration of the positive electrode active material to occur more quickly and further deteriorates the life characteristics and safety of the battery.

[0005] Accordingly, there have been attempts to use the above-mentioned positive electrode active material in a single crystal form with excellent particle strength. However, since the surface area of ​​the positive electrode active material in the single crystal form is relatively large, the specific surface area of ​​the positive electrode active material as a whole may be small, and the low specific surface area may reduce the expressed capacity (see Fig. 1).

[0006] Therefore, it is necessary to develop a technology that can secure a positive electrode active material with low resistance and high developed capacity while using the positive electrode active material in the form of a single crystal.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] (Patent Document 0001) Korean Patent Publication No. 10-2010-0062744 (June 10, 2010)

[0010] The present invention has been devised to solve the above-described technical problem, and the problem to be solved by the present invention is to provide a positive electrode active material and a method for manufacturing the same, which can maintain the developed capacity at a high level when using a lithium composite transition metal oxide in a single crystal form as a positive electrode active material.

[0011] The purposes of the invention are not limited to those mentioned above, and other unmentioned purposes and advantages of the invention can be understood through the following description and will be more clearly understood through the embodiments of the invention. Furthermore, it will be readily apparent that the purposes and advantages of the invention can be realized by the means and combinations thereof set forth in the claims.

[0012] In order to solve the above-described technical problem, the present invention provides a method for manufacturing a cathode active material, comprising the steps of (S1) mixing nickel raw material powder and sodium raw material powder and firing them to manufacture a sodium composite metal oxide; (S2) mixing the sodium composite metal oxide with lithium raw material powder containing lithium (Li) in a molar ratio of 8 to 15 times that of sodium in the sodium composite metal oxide in an oxygen atmosphere and heating the mixture to perform ion exchange to exchange sodium ions with lithium ions; and (S3) annealing.

[0013] [Chemical Formula 1]

[0014] Li[Ni x M1 1-x ]O2

[0015] In the above chemical formula 1, M1 is one or more metals selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), iron (Fe), magnesium (Mg), chromium (Cr), titanium (Ti), copper (Cu), calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), tungsten (W), and bismuth (Bi), and x is 0.3 <x≤1이다.

[0016] In one embodiment of the present invention, the firing in step (S1) may be performed at 600°C to 800°C for 12 to 36 hours.

[0017] In one embodiment of the present invention, the step (S1) may further include a step of adding an M1-containing raw material.

[0018] In one embodiment of the present invention, the nickel (Ni) ions and sodium (Na) ions of the positive electrode active material can satisfy the following relationship.

[0019] [Relationship 1]

[0020] 0.001 ≤ N Na / N Ni ≤ 0.01

[0021] In the above relational expression 1, N Na is the number of moles of sodium ions contained in the positive electrode active material, N Ni Each represents the number of moles of nickel ions contained in the positive electrode active material.

[0022] In one embodiment of the present invention, in the step (S2), the lithium raw material powder includes a lithium salt compound represented by the following chemical formula 2, and the step (S2) may be performed at a temperature of 250°C to 400°C for 3 to 10 hours.

[0023] [Chemical Formula 2]

[0024] LiaX

[0025] In the above chemical formula 2, X is F - , Cl - , Br - , I - , NO3 - , SO4 2- and PO4 3- One selected from among, and if X is an anion n, a represents n.

[0026] The present invention provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material manufactured by the manufacturing method of the present invention; a negative electrode; an electrolyte interposed between the positive electrode and the negative electrode; and a separator.

[0027] The solutions to the above problems do not enumerate all features of the present invention. The various features of the present invention, along with their corresponding advantages and effects, can be understood in more detail by referring to the specific examples below.

[0028] Since the lithium secondary battery includes a lithium composite transition metal oxide in the form of a single crystal including a cathode active material according to the present invention, the capacity and life performance of the battery can be improved.

[0029] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0030] Figure 1 is a schematic diagram showing the single crystal form and polycrystalline form of the positive electrode active material.

[0031] Figure 2 is a schematic diagram showing the single crystal form and polycrystal form of a conventional positive electrode active material.

[0032] Figure 3 is a schematic diagram showing the single crystal form of the positive electrode active material according to the present invention.

[0033] Figure 4 is a schematic diagram schematically showing a method for manufacturing a positive electrode active material according to a preferred embodiment of the present invention.

[0034] Figure 5 shows the XRD measurement results of LiNiO2 manufactured according to Examples 1 to 3.

[0035] Figure 6 shows the average particle diameter (D50) of LiNiO2 manufactured according to Examples 1 to 3.

[0036] Figure 7 shows an FE-SEM image of LiNiO2 manufactured according to Example 1.

[0037] Figure 8 shows an FE-SEM image of LiNiO2 manufactured according to Comparative Example 1.

[0038] Figure 9 shows voltage-capacity curves of lithium secondary batteries including the positive electrode active materials of Example 1 (LS-LNO), Comparative Example 1 (P-LNO), and Comparative Example 5 (SS-LNO).

[0039] Figure 10 shows the life performance of lithium secondary batteries including the positive electrode active materials of Example 1 (LS-LNO), Comparative Example 1 (P-LNO), and Comparative Example 5 (SS-LNO).

[0040] Figure 11 shows the coulombic efficiency of a lithium secondary battery including the positive electrode active material of Example 1 (LS-LNO) and Comparative Example 1 (P-LNO).

[0041] Figure 12 shows the results of a DEMS (Differential Electrochemical Mass Spectrometer) cell experiment of a lithium secondary battery including the positive electrode active materials of Example 1 (LS-LNO), Comparative Example 1 (P-LNO), and Comparative Example 5 (SS-LNO).

[0042] The principles of preferred embodiments of the present invention will be described in detail with reference to the attached drawings and descriptions below. However, the drawings and descriptions below are intended to illustrate preferred implementation methods among various methods for effectively explaining the features of the present invention, and the present invention is not limited to the drawings and descriptions below.

[0043] While terms such as "first" or "second" may be used to describe various components, these terms should be interpreted solely to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

[0044] Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "has" should be understood to indicate the presence of a described feature, number, step, operation, component, part, or combination thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0045] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0046] In explaining the present invention, "average particle diameter D 50 " means the particle size based on 50% of the volume cumulative particle size distribution of the lithium composite transition metal oxide powder or positive electrode active material powder. The average particle diameter D 50 can be measured using a laser diffraction method. For example, after dispersing lithium composite transition metal oxide powder or positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz with an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0047] Hereinafter, the present invention will be described in more detail.

[0048] As described above, lithium nickel cobalt manganese oxide (NCM-based cathode active material), which has been conventionally used to improve energy density, generally has a polycrystalline structure. However, lithium nickel cobalt manganese oxide with a polycrystalline structure has problems in that particle breakage easily occurs during the rolling process during the manufacture of the cathode, and cracks occur inside the particles during the charge and discharge process. When particle breakage or cracks occur in the cathode active material, the contact area with the electrolyte increases, which increases gas generation and active material degradation due to side reactions with the electrolyte, and this causes problems in that the life characteristics are reduced.

[0049] The single crystal cathode active material manufactured according to the manufacturing method of the present invention can manufacture a single crystal of large particles without particle breakage during electrode rolling for manufacturing a high-density electrode while increasing the Ni content.

[0050] In particular, in the past, small single crystalline was used to solve the disadvantages of large polycrystalline, but according to the manufacturing method of the present invention, large single crystalline can be manufactured, and thus, when manufacturing an ultra-high-density electrode, it can exhibit superior performance compared to the conventional polycrystalline positive electrode active material (see FIGS. 2 and 3).

[0051] <Cathode active material and method for manufacturing the cathode active material>

[0052] In order to solve these problems, the present invention provides an embodiment of a lithium composite metal oxide in a single crystal form using an ion exchange method.

[0053] Specifically, the present invention

[0054] (S1) A step of mixing nickel raw material powder and sodium raw material powder and calcining them to produce a sodium composite metal oxide;

[0055] (S2) A step of mixing and heating a lithium raw material powder containing lithium (Li) in a molar ratio of 8 to 15 times that of sodium in the sodium composite metal oxide to perform ion exchange to exchange sodium ions with lithium ions; and

[0056] (S3) A method for manufacturing a positive electrode active material of the following chemical formula 1, including an annealing step, is provided.

[0057] [Chemical Formula 1]

[0058] Li[Ni x M1 1-x ]O2

[0059] In the above chemical formula 1, M1 is at least one metal selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), iron (Fe), magnesium (Mg), chromium (Cr), titanium (Ti), copper (Cu), calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), tungsten (W), and bismuth (Bi), and preferably may be at least one metal selected from the group consisting of cobalt (Co), manganese (Mn), and aluminum (Al).

[0060] In the above chemical formula 1, x is 0.3 <x≤1이며, 바람직하게는 0.5<x≤1, 더 바람직하게는 0.6<x≤1일 수 있다.

[0061] A method for manufacturing a positive electrode active material according to a preferred embodiment of the present invention is schematically illustrated in FIG. 4.

[0062] In one embodiment of the present invention, the step (S1) may be performed by mixing nickel raw material powder and sodium raw material powder and calcining to produce a sodium composite metal oxide. Here, the calcination may be performed at 600 to 800°C for 12 to 36 hours, and if the calcination time is less than 12 hours, the crystal grains forming the single crystal may not grow sufficiently.

[0063] In a preferred embodiment of the present invention, in the step (S1), a sodium composite metal oxide powder having an average particle diameter (D50) of 5 μm to 30 μm can be manufactured. In the subsequent step (S2), in which a lithium composite metal oxide powder is obtained from the sodium composite metal oxide powder by an ion exchange reaction, the grain size does not change, so the calcination temperature and time are controlled in the step (S1) to grow the grain size.

[0064] Meanwhile, the nickel raw material is a precursor containing nickel, and may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, fatty acid nickel salt, nickel halide, or a combination thereof.

[0065] Meanwhile, in the step (S1), an M1-containing raw material may be further added, and the M1-containing raw material may be an M1-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, specifically, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide and / or an aluminum-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide. For example, the M1-containing raw material may be a manganese oxide such as Mn2O3, MnO2, Mn3O4, etc.; a manganese salt such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylic acid salt, manganese citrate, and manganese fatty acid salt; It may be, but is not limited to, manganese oxyhydroxide, manganese chloride, Al2O3, Al(OH)3, AlSO4, AlCl3, Al-isopropoxide, AlNO3, AlF or a combination thereof.

[0066] In a preferred embodiment of the present invention, in the step (S2), lithium raw material powder containing lithium (Li) in a molar ratio of 8 to 15 times that of sodium of the sodium composite metal oxide is mixed and heated to perform ion exchange to replace Na ions of the sodium composite metal oxide with Li ions.

[0067] In this step, only the Na ions of the sodium composite metal oxide are replaced by Li ions, and the monoclinic crystal structure changes into a hexagonal crystal structure, thereby obtaining a lithium composite metal oxide.

[0068] When the manufacturing method of the present invention, which obtains a lithium composite metal oxide by performing ion exchange, is followed, crystal growth at high temperatures is possible. Conventional NCM cathode active materials, when grown at high temperatures, can undergo phase transitions due to thermal instability, making it difficult to form crystal grains of the desired size. However, the method for manufacturing a cathode active material according to a preferred embodiment of the present invention enables sufficient growth of crystal grains as single crystals even when calcined at high temperatures.

[0069] In the above step (S3), the obtained lithium composite metal oxide powder may be washed and then annealed. Through the annealing step, the deterioration of the surface of the positive electrode active material particles can be improved, and the stoichiometry of Li-Ni can be adjusted to 1:1, and the crystal grain size can be further increased. However, since lithium composite metal oxides, unlike sodium composite metal oxides, can undergo phase transition at high temperatures, the annealing temperature is preferably performed in the range of 500°C to 800°C.

[0070] Additionally, preferably, the above step (S3) can be performed by mixing with LiOH·H2O.

[0071] Meanwhile, the cathode active material according to the present invention has the following chemical formula 1, includes particles made of single-crystal grains, and provides a cathode active material for a lithium secondary battery, characterized in that the average particle diameter (D50) of the particles made of the single-crystal grains is 10 ㎛ to 30 ㎛.

[0072] [Chemical Formula 1]

[0073] Li[Ni x M1 1-x ]O2

[0074] In the above chemical formula 1, M1 is at least one metal selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), iron (Fe), magnesium (Mg), chromium (Cr), titanium (Ti), copper (Cu), calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), tungsten (W), and bismuth (Bi), and preferably may be at least one metal selected from the group consisting of cobalt (Co), manganese (Mn), and aluminum (Al).

[0075] In the above chemical formula 1, x is 0.3 <x≤1이며, 바람직하게는 0.5<x≤1, 더 바람직하게는 0.6<x≤1일 수 있다.

[0076] In a preferred embodiment of the present invention, the lithium transition metal oxide of the chemical formula 1 may be LiNiO2.

[0077] The cathode active material for a lithium secondary battery of the present invention is composed of single crystal grains, and includes particles having the composition and average particle diameter as described above, thereby providing a cathode active material for a lithium secondary battery having excellent thermal stability and high energy density and excellent lifespan characteristics.

[0078] In addition, the above-mentioned positive electrode active material has excellent thermal stability, so it can be manufactured at high temperatures during the manufacturing process, and thus it is easy to manufacture a single-crystal positive electrode active material having a high nickel composition by sufficiently growing crystal grains.

[0079] In one embodiment of the present invention, the average particle diameter of the positive electrode active material may be 10 ㎛ to 30 ㎛, preferably 15 ㎛ to 25 ㎛, and more preferably 18 ㎛ to 22 ㎛. When the average particle diameter of the positive electrode active material satisfies the above range, the occurrence of breakage of the positive electrode active material can be suppressed even during rolling, and a lithium diffusion path can be secured, thereby improving the output characteristics.

[0080] Meanwhile, the positive electrode active material for a lithium secondary battery manufactured according to the present invention may include nickel (Ni) ions and sodium (Na) ion impurities in a molar ratio satisfying the following relationship 1.

[0081] [Relationship 1]

[0082] 0.001 ≤ N Na / N Ni ≤ 0.01

[0083] In the above relational expression 1, N Na is the number of moles of Na ions included in the positive electrode active material of the present invention, N Ni Each represents the molar number of Ni ions included in the positive electrode active material of the present invention. Since the positive electrode active material according to the present invention is obtained by ion-exchanging a lithium composite metal from a sodium composite metal oxide, it is important to sufficiently remove Na ions. If the molar number of Na ions exceeds 0.01 (1%) relative to the molar number of Ni ions, improved performance may not be achieved compared to the case of using a conventional polycrystalline NCM positive electrode active material. However, if the molar number of Na ions is reduced to 0.001 (0.1%) or less relative to the molar number of Ni ions, the manufacturing cost may significantly increase.

[0084] In a preferred embodiment of the present invention, the positive electrode active material has a BET specific surface area of ​​0.2 m 2 / g to 1.5 m 2 / g may be. The positive electrode active material according to a preferred embodiment of the present invention has a smaller surface area than conventional polycrystalline positive electrode active materials, and thus can significantly reduce the occurrence of cracks and side reactions.

[0085] Bipolar

[0086] The positive electrode active material according to the invention can be used in the manufacture of a positive electrode of a lithium secondary battery. Specifically, the positive electrode according to the invention comprises the positive electrode active material according to the invention. More specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may comprise the positive electrode active material according to the invention.

[0087] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material according to the present invention is used. For example, the positive electrode can be manufactured by dissolving or dispersing components constituting the positive electrode active material layer, i.e., the positive electrode active material, a conductive agent, and / or a binder, etc., in a solvent to manufacture a positive electrode composite, applying the positive electrode composite to at least one surface of a positive electrode current collector, and then drying and rolling the positive electrode composite, or by casting the positive electrode composite onto a separate support, and then laminating the film obtained by peeling it from the support onto a positive electrode current collector.

[0088] At this time, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0089] A positive electrode active material layer comprising a positive electrode active material according to the present invention is positioned on at least one surface of the above-described collector, and optionally further comprising at least one of a conductive material and a binder, if necessary.

[0090] The above positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above-mentioned amount range, excellent capacity characteristics may be exhibited.

[0091] The conductive material is used to provide conductivity to the electrode, and can be used without any special restrictions as long as it does not cause a chemical change 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, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0092] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0093] Meanwhile, the solvent used in the manufacture of the positive electrode composite may be a solvent commonly used in the relevant technical field, and for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water may be used alone or in a mixture thereof. The amount of the solvent used may be appropriately adjusted in consideration of the coating thickness of the slurry, manufacturing yield, viscosity, etc.

[0094] <Cathode and secondary battery>

[0095] A lithium secondary battery according to another embodiment of the present invention may include the positive electrode of the above-described embodiment. Specifically, the lithium secondary battery includes a positive electrode, an anode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0096] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0097] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0098] The above negative electrode active material layer optionally includes a negative electrode binder and a negative electrode conductive material together with the negative electrode active material.

[0099] 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 alloy, Sn alloy, or Al alloy; SiOβ (0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0100] In addition, a metallic lithium thin film may be used as the negative active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative 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, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0101] The above-described negative electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and has electronic conductivity can be used without special restrictions. 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, carbon fiber, and carbon nanotube; 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, and the like. One type alone or a mixture of two or more types of these may be used. The negative electrode conductive material may typically be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0102] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above negative electrode binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode active material layer.

[0103] The above-described negative electrode active material layer may be manufactured by, for example, applying and drying a negative electrode slurry containing a negative electrode active material, and optionally a negative electrode binder and a negative electrode conductive material, onto a negative electrode current collector, or by casting the negative electrode slurry onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling it off from the support.

[0104] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0105] In addition, examples of the electrolyte 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.

[0106] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0107] As the organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol, isopropyl alcohol, etc.; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferable, 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 / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.

[0108] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, 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 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0109] In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either singly or in mixtures, but are not limited thereto. The additives may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0110] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0111] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0112] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0113] Hereinafter, the effects of the present invention will be described in detail with specific examples and experimental results. The following examples are merely examples to specifically understand the embodiments of the present invention and do not limit the scope of the present invention. A person reading this specification should understand that a person skilled in the art can implement the present invention by adding other components except for the essential components of the present invention or deleting or replacing non-essential components, and this can be easily done from the description of this specification, and such embodiments are also within the scope of the present invention.

[0114] <Example>

[0115] Example 1: Preparation of single-crystal nickel-based cathode active material (LS-LNO)

[0116] 5 g of nickel oxide (NiO) powder and 5.25 g of anhydrous sodium hydroxide (NaOH) powder were each placed in a reactor and ball milled at 3,000 rpm for 15 minutes to ensure uniform mixing. The mixture was calcined at a temperature of approximately 650°C for approximately 18 hours in an oxygen atmosphere. After the calcination process, NaNiO2 powder was obtained.

[0117] The above NaNiO2 powder was mixed with 55 g of lithium raw material powder containing LiNO3 and LiCl in a weight ratio of 2:1, and mixed in an oxygen atmosphere at about 300°C for about 5 hours to perform a Li-Na ion exchange reaction. As a result of the reaction, LiNiO2 powder was obtained.

[0118] The obtained LiNiO2 powder was washed with deionized water for approximately 5 minutes and dried overnight in an oven at 70°C. Afterwards, a small amount of LiOH·H2O was added to improve surface damage during washing, and then calcined at approximately 600°C for 10 hours to produce a large-particle single-crystal nickel-based cathode active material (LS-LNO).

[0119] Example 2

[0120] A nickel-based positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering temperature was changed to 500°C.

[0121] Example 3

[0122] A nickel-based positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering temperature was changed to 900°C.

[0123] Comparative Example 1: Preparation of polycrystalline nickel-based cathode active material (P-LNO)

[0124] A lithium precursor (LiOH·H2O) and a nickel precursor (NiO) were mixed so that the molar ratio of lithium to nickel was 1:1, and calcined at approximately 650°C in an oxygen atmosphere. The obtained nickel-based cathode active material powder was cooled and washed to prepare a polycrystalline nickel-based cathode active material powder (P-LNO).

[0125] Comparative Example 2: Polycrystalline NCM cathode active material

[0126] Polycrystalline NCM523 (LiNi) commercially available 0.5 Co 0.2 Mn 0.3 O2 (Sigma Aldrich) was prepared as a cathode active material.

[0127] Comparative Example 3: Polycrystalline NCM cathode active material

[0128] Polycrystalline NCM622 (LiNi) commercially available 0.6 Co 0.2 Mn 0.2 O2 (Sigma Aldrich) was prepared as a cathode active material.

[0129] Comparative Example 4: Polycrystalline NCM cathode active material

[0130] Polycrystalline NCM (LiNi) on the market 0.7 Co 0.15 Mn 0.15 O2 (Sigma Aldrich) was prepared as a cathode active material.

[0131] Comparative Example 5: Single-crystal NCM cathode active material (SS-LNO)

[0132] Small-particle single-crystal LNO (SS-LNO) was prepared via the molten method. NaCl and KCl fluxes were mixed in an appropriate ratio to reach the eutectic point. NiO (99.99%, Sigma-Aldrich):LiOH·H2O:flux = 1.0:1.5:2.5 was ground, transferred to an alumina crucible, and calcined at approximately 850°C for 10 h in an oxygen atmosphere. The product was then washed with distilled water and dried overnight in an oven at 70°C. Subsequently, a small amount of LiOH·H2O was mixed to improve surface damage during washing, and the sample was calcined again at 600°C for 10 h in an oxygen atmosphere and then naturally cooled to obtain a small-sized single-crystal nickel-based cathode active material (SS-LNO).

[0133] <Experimental Example>

[0134] Experimental Example 1: XRD Measurement

[0135] The XRD of the positive electrode active material manufactured in the example was measured, and the results are shown in Fig. 5.

[0136] Referring to Figure 5, when an ion exchange reaction is performed according to the present invention, it can be confirmed that the peak corresponding to LiNiO2 is well developed, and it can be confirmed that almost no impurity peaks exist.

[0137] Experimental Example 2: Comparison of particle sizes

[0138] The average particle diameter (D50) of the positive electrode active material powder manufactured in the example was measured and shown in Table 1 and Figure 6 below.

[0139] Average particle size D50 (㎛) Example 1 (firing temperature 850℃) 21.9 Example 2 (firing temperature 750℃) 11.5 Example 3 (firing temperature 650℃) 6.49

[0140] By combining Table 1 and Fig. 6 with the XRD results of Fig. 5, it was confirmed that the average particle size increased as the sintering temperature increased, and it was confirmed that when a positive electrode active material was manufactured according to the manufacturing method of the present invention, even when sintered at a high temperature of 850°C, phase transition did not occur and crystal growth was possible.

[0141] Experimental Example 3: Comparison of particle sizes

[0142] FE-SEM images of the nickel-based positive electrode active material powder manufactured in Example 1 and Comparative Example 1 are shown in FIGS. 7 and 8.

[0143] Unlike the cathode active material of Comparative Example 1, in which secondary particles are aggregated to form a single cathode active material, it can be confirmed that the cathode active material of Example 1 is a cathode active material in the form of a single crystal.

[0144] Experimental Example 4: Measurement of the composition of Li, Na, and Ni

[0145] The nickel-based positive electrode active material powders manufactured in Example 1 and Comparative Example 1 were analyzed for the molar ratios of Li, Na, and Ni ions using ICP-AES, and the results are shown in Table 2 below. Through the results below, it can be confirmed that when the positive electrode active material was manufactured according to the manufacturing method of the present invention, the positive electrode active material was manufactured with a molar ratio of Li and Ni of 1:1, and the content of Na was negligible.

[0146] Distinction number of moles Ni (standard) LiNa Example 111.008510.00586 Comparative example 110.899080.00101

[0147] Experimental Example 5: Electrochemical Performance Evaluation

[0148] The positive electrode active material powders manufactured in Example 1 and Comparative Examples 1 and 5, PVDF binder, and carbon black conductive agent were mixed at a mass ratio of 94:3:3, and NMP (N-Methyl-2-Pyrrolidone) was added to manufacture a positive electrode slurry. The positive electrode slurry was applied onto aluminum foil and then dried to manufacture a final positive electrode.

[0149] After laminating the final positive electrode, lithium metal, and separator, a lithium secondary battery was manufactured by injecting an electrolyte in which 1.2 M of 2 mass% vinylene carbonate LiPF6 was dissolved in a solvent containing 1:1 volume ratio of ethylene carbonate and ethyl methyl carbonate. The voltage-capacity curve when charging and discharging at 0.1 C rate is shown in Fig. 9, the life characteristics measured while charging and discharging at 0.5 C rate are shown in Fig. 10, and the coulombic efficiency according to charging and discharging is shown in Fig. 11.

[0150] Referring to FIG. 9, it can be confirmed that a lithium secondary battery manufactured using the large particle single crystal positive electrode active material (LS-LNO) of the present invention exhibits a greater capacity than a lithium secondary battery manufactured using the small particle single crystal positive electrode active material (SS-LNO). The polycrystalline positive electrode active material (P-LNO) exhibits a greater initial capacity than the large particle single crystal positive electrode active material (LS-LNO) due to its large surface area, but the life performance and coulombic efficiency are significantly lower than those of the large particle single crystal positive electrode active material (LS-LNO), as can be confirmed through FIGS. 10 and 11.

[0151] Referring to FIGS. 10 and 11, it can be confirmed that a lithium secondary battery manufactured using the large particle single crystal positive electrode active material of the present invention exhibits superior electrochemical performance than a comparative example using a polycrystalline positive electrode active material or a small particle single crystal positive electrode active material.

[0152] Experimental Example 6: Safety Evaluation

[0153] A Differential Electrochemical Mass Spectrometer (DEMS) cell was assembled using the final positive electrode manufactured in Experimental Example 5 and the electrolyte used in Experimental Example 5. The CO2 content generated during charge / discharge cycles at 0.1 C rate at 60°C was measured, and the results are shown in Fig. 12. It can be seen that a significantly smaller amount of CO2 gas was generated in the DEMS cell using the positive electrode active material manufactured in Example 1. This is believed to be because cracks in the active material rarely occurred during the electrode manufacturing stage.

Claims

1. In the method for manufacturing a positive electrode active material of the following chemical formula 1, (S1) A step of mixing nickel (Ni) raw material powder and sodium (Na) raw material powder and calcining them to produce a sodium composite metal oxide; (S2) A step of mixing and heating a lithium raw material powder containing lithium (Li) in a molar ratio of 8 to 15 times that of sodium in the sodium composite metal oxide to perform ion exchange to exchange sodium ions with lithium ions; and (S3) A method for manufacturing a positive electrode active material, comprising an annealing step. [Chemical Formula 1] [Ni x M1 1-x ]O2 In the above chemical formula 1, M1 is one or more metals selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), iron (Fe), magnesium (Mg), chromium (Cr), titanium (Ti), copper (Cu), calcium (Ca), zinc (Zn), zirconium (Zr), niobium (Nb), molybdenum (Mo), strontium (Sr), tungsten (W), and bismuth (Bi), and x is 0.3 <x≤1이다.

2. In paragraph 1, The plasticity of the above (S1) step A method for producing a positive electrode active material, which is performed at 600 to 800°C for 12 to 36 hours.

3. In paragraph 1, A method for manufacturing a positive electrode active material, wherein, in the above step (S1), an M1-containing raw material is further added.

4. In paragraph 1, A method for manufacturing a positive electrode active material, wherein the nickel (Ni) ions and sodium (Na) ions of the positive electrode active material satisfy the following relationship. [Relationship 1] 0.001 ≤ N Na / N Ni ≤ 0.01 In the above relational expression 1, N Na is the number of moles of sodium ions contained in the positive electrode active material, N Ni Each represents the number of moles of nickel ions contained in the positive electrode active material.

5. In paragraph 1, In the above step (S2), the lithium raw material powder may be a lithium acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, and specifically, it includes at least one selected from manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide and / or aluminum-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide. Method for manufacturing positive electrode active material.

6. In paragraph 1, A method for manufacturing a positive electrode active material, wherein the above step (S2) is performed at a temperature of 250°C to 400°C for 3 to 10 hours.

7. A positive electrode comprising a positive electrode active material manufactured by the manufacturing method of any one of claims 1 to 5; a negative electrode; an electrolyte interposed between the positive electrode and the negative electrode; and a separator; comprising* Lithium secondary battery.

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