Positive electrode active material for all-solid-state battery, method for producing the same, and all-solid-state battery including the same

Abstract

The present invention relates to a positive electrode active material for an all-solid-state battery, comprising: a core containing a layered lithium transition metal oxide; and a coating layer disposed on the core and containing a lithium ion conductive oxide, wherein the secondary particles are formed by agglomeration of a plurality of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less, and exhibiting a full width at half maximum (FWHM(110)) of a (110) plane diffraction peak of 0.2 or less in X-ray diffraction spectrum analysis.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for an all-solid-state battery, a method for producing the same, and an all-solid-state battery including the same, and more specifically to a layered positive electrode active material for an all-solid-state battery, a method for producing the same, and an all-solid-state battery including the same. [Background technology]

[0002] In recent years, the lithium secondary battery market has seen increasing demand for longer driving ranges and improved safety for electric vehicles, making it extremely important to develop lithium secondary batteries that are safe and have high weight and volume energy density.In particular, the energy capacity used in electric vehicles is in the tens of kWh range, and there is a high risk of large-scale fires and explosions if the battery is damaged, so research is being actively conducted to replace liquid electrolytes with solid electrolytes.

[0003] In particular, for ease of manufacturing, all-solid-state batteries mainly adopt a structure in which a solid electrolyte is used as a secondary electrolyte that forms a lithium ion conduction path inside the positive electrode. In the case of sulfide-based solid electrolytes, they have high ionic conductivity, are easily deformed by pressure, and can be made denser, so much research is being conducted on them.

[0004] As with lithium-ion batteries, oxide-based cathode active materials with layered structures such as NCM or NCA have been mainly used in recent years as cathode active materials mixed with sulfide-based solid electrolytes in cathodes. However, these cathode active materials react at the interface with sulfide-based solid electrolytes to form a high-resistance layer, and research is ongoing to improve performance by coating the surface of the active material with a lithium-ion conductive oxide to prevent this reaction.

[0005] However, while conventional lithium ion conductive oxide coated active materials significantly improve the initial capacity, efficiency, and charge / discharge life characteristics of batteries compared to those without a coating, they have problems such as increasing the active material loading on the electrode and significantly reducing discharge capacity at high output (high c-rate). Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a positive electrode active material for an all-solid-state battery that can improve the discharge capacity of the battery at high output (high c-rate), a method for producing the same, and an all-solid-state battery including the same. [Means for solving the problem]

[0007] One embodiment of the present invention provides a cathode active material for an all-solid-state battery, comprising: a core containing a layered lithium transition metal oxide; and a coating layer containing a lithium ion conductive oxide disposed on the core, wherein the secondary particles are formed by agglomeration of a plurality of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less, and an X-ray diffraction spectrum analysis of which shows a full width at half maximum (FWHM(110)) of a (110) plane diffraction peak of 0.2 or less.

[0008] The positive electrode active material for an all-solid-state battery may include primary particles located on the surfaces of the secondary particles and having their major axes oriented parallel to the surfaces of the secondary particles.

[0009] At least some of the secondary particles may have a structure in which the major axes of the primary particles are arranged radially.

[0010] The positive electrode active material for an all-solid-state battery may have an average crystallite size of 104 nm or more.

[0011] The positive electrode active material for an all-solid-state battery may have an a-axis length of 2.871 to 2.872 Å and a c-axis length of 14.227 to 14.229 Å.

[0012] The lithium transition metal oxide may have a lithium / transition metal (Li / Me) molar ratio of 1.01 to 1.05.

[0013] When analyzing the X-ray diffraction spectrum of the positive electrode active material for the all-solid-state battery, the ratio I(003) / I(104) of the diffraction peak intensity of the (104) plane to the diffraction peak intensity of the (003) plane may be 1.19 to 1.25.

[0014] The positive electrode active material for the all-solid-state battery can satisfy the following formula 1.

[0015] <Formula 1>

[0016] 0.37 ≦ [I(006) + I(102)] / I(101) ≦ 0.42

[0017] In Formula 1, I(006), I(102), and I(101) respectively represent the diffraction peak intensities of the (006) plane, (102) plane, and (101) plane during X-ray diffraction spectrum analysis.

[0018] The lithium transition metal oxide can be represented by the following Chemical Formula 1. [Chemical Formula 1] [[ID=2,5]]Li a [Ni x1 Co y1 M z1 O2 In Chemical Formula 1, 1.01 ≦ a ≦ 1.05, 0.60 ≦ x1 < 1, 0 ≦ y1 ≦ 0.2, 0 < z1 ≦ 0.2, x1 + y1 + z1 = 1, and M is Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

[0019] The lithium ion conductive oxide can be represented by the following Chemical Formula 2. ][Chemical Formula 2] [[ID=,43]]Li x2 A y2 O[[ID=4,8]] z2 In Chemical Formula 2, 0 ≦ x2 ≦ 3, 0 < y2 ≦ 2, 0 < z2 ≦ 4, and A is Zr, Nb, Ti, or a combination thereof.

[0020] The lithium ion conducting oxide may be Li2ZrO3, ZrO2, LiNbO3, Nb2O3, Li2TiO3, TiO2, or a combination thereof.

[0021] The content of the coating layer may be 0.5 to 1.5 wt % based on the total weight of the positive electrode active material.

[0022] The secondary particles may have an average particle size (D50) of 3 to 6 μm.

[0023] The positive electrode active material for the all-solid-state battery has a specific surface area of ​​0.4 to 0.7 m 2 / g.

[0024] Another embodiment of the present invention provides a method for manufacturing a cathode active material for an all-solid-state battery, the method comprising the steps of: preparing a transition metal hydroxide containing nickel, the transition metal hydroxide being secondary particles formed by aggregation of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less; forming a mixture containing the transition metal hydroxide and a lithium source material; firing the mixture to form a lithium transition metal oxide; and forming a coating layer containing a lithium ion conductive oxide on a surface of the lithium transition metal oxide, wherein in the step of forming the mixture, the transition metal (Me) of the transition metal hydroxide and the lithium (Li) of the lithium source material are mixed at a molar ratio (Li / Me) of 1.01 to 1.05.

[0025] In the step of forming the mixture, the transition metal (Me) of the transition metal hydroxide and the lithium (Li) of the lithium source material may be mixed at a molar ratio (Li / Me) of 1.01 to 1.05.

[0026] In the step of preparing the transition metal hydroxide, at least some of the secondary particles may include a structure in which primary particles are radially arranged.

[0027] In the step of forming the lithium transition metal oxide, the firing can be carried out at a temperature of 720 to 770°C.

[0028] Another embodiment of the present invention provides a cathode including the above-described cathode active material for an all-solid-state battery.

[0029] Another embodiment of the present invention provides an all-solid-state battery comprising: a positive electrode; a negative electrode; and a solid electrolyte layer disposed therebetween, wherein the positive electrode comprises the above-described positive electrode active material for an all-solid-state battery. [Effects of the Invention]

[0030] The cathode active material for an all-solid-state battery according to one embodiment of the present invention has a secondary particle structure formed by aggregation of thin primary particles having a flake or needle shape, and has a small full width at half maximum (FWHM(110)) of the (110) plane diffraction peak in an X-ray diffraction spectrum analysis, thereby improving the discharge capacity of the battery at high output (high-rate). [Brief explanation of the drawings]

[0031] [Figure 1] 1 shows SEM images of precursors and positive electrode active materials used in Example 1 and Comparative Example 1.

[0032] Shapes for carrying out the invention

[0033] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0034] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form "a," "an," or "an" includes the plural form unless the context clearly dictates otherwise. As used herein, the term "comprising" refers to the inclusion of particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0035] When a part is referred to as being "on" or "above" another part, it means that it is exactly on or above the other part, and there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0036] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0037] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0038] In this specification, the term "combination(s) thereof" used in a maxi-format expression means a mixture or combination of one or more elements selected from the group of elements described in the maxi-format expression, and means including any one or more elements selected from the group of elements. [Example]

[0039] While the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0040] 1.Cathode active material for all-solid-state batteries

[0041] One embodiment of the present invention provides a cathode active material for an all-solid-state battery, comprising: a core containing a layered lithium transition metal oxide; and a coating layer containing a lithium ion conductive oxide disposed on the core, wherein the secondary particles are formed by agglomeration of a plurality of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less, and an X-ray diffraction spectrum analysis of which shows a full width at half maximum (FWHM(110)) of a (110) plane diffraction peak of 0.2 or less.

[0042] The positive electrode active material according to one embodiment of the present invention may be used for an all-solid-state battery, and more specifically, may be used as a positive electrode active material for a composite positive electrode material used together with a sulfide-based solid electrolyte.

[0043] A positive electrode active material for an all-solid-state battery according to one embodiment of the present invention includes a core and a coating layer disposed on the core.

[0044] In this case, the positive electrode active material for an all-solid-state battery according to one embodiment of the present invention is a secondary particle formed by agglomeration of a plurality of primary particles.

[0045] In this specification, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross section of a positive electrode active material is observed through a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains.

[0046] In particular, the primary particles have a flake or needle shape and an average thickness of 50 nm or less. The extremely thin, plate-like or needle-like shape of the primary particles can facilitate lithium ion mobility and significantly improve the high-power characteristics of the battery. More specifically, the average thickness of the primary particles may be 50 or 40 nm or less.

[0047] The cathode active material for an all-solid-state battery may include at least one primary particle located on the surface of the secondary particle, the primary particle having a major axis oriented parallel to the surface of the secondary particle. This structure improves lithium ion mobility, thereby further enhancing the high-power characteristics of the battery.

[0048] In addition, at least some of the secondary particles may have a structure in which primary particles are radially arranged, and primary particles having such an orientation may be present in particularly large amounts inside the secondary particles.

[0049] In this way, the interior of the active material secondary particles mainly contains a large number of radially oriented primary particles whose major axes point toward the center, and the surfaces of the secondary particles contain primary particles whose major axes are oriented horizontally to the surface, thereby maximizing the high-power characteristics of the battery.

[0050] In an X-ray diffraction spectrum analysis of a positive electrode active material for an all-solid-state battery according to one embodiment of the present invention, the full width at half maximum (FWHM(110)) of the (110) diffraction peak may be 0.2 or less, more specifically, 0.19 or less. When the full width at half maximum (FWHM(110)) of the (110) diffraction peak satisfies this range, the fraction of the plane through which lithium ions can easily move is maximized at the contact interface between the positive electrode material and the solid electrolyte particles, thereby improving the high-power characteristics of the battery.

[0051] The positive electrode active material for an all-solid-state battery may have an average crystallite size of 104 nm or more, more specifically, 106 or 108 nm or more.

[0052] As used herein, the term "crystal grain" refers to a single-crystal particle unit having a regular atomic arrangement. The size of the crystal grains can be measured by, for example, using a high-resolution transmission electron microscope (HR-TEM) TITAN G2, magnifying the surface of a sample by 800,000 to 2,000,000 times, and the average crystal grain size can be measured by calculating the arithmetic mean value of the sizes of the individual crystal grains measured.

[0053] When the average crystal grain size of the positive electrode active material satisfies the above range, lithium ions can move smoothly inside the positive electrode material particles, and the above-mentioned improvement in battery performance can be more effectively achieved.

[0054] The cathode active material for an all-solid-state battery may have an a-axis length of 2.871 to 2.872 Å and a c-axis length of 14.227 to 14.229 Å. When the a-axis length and c-axis length of the cathode active material satisfy the above ranges, the aforementioned improvement in battery performance is more effectively realized, and is preferable in terms of discharge capacity and life characteristics. The a-axis length and c-axis length can be measured by X-ray diffraction spectroscopy.

[0055] The lithium / transition metal (Li / Me) molar ratio of the lithium transition metal oxide may be 1.01 to 1.05. When the lithium / transition metal (Li / Me) molar ratio satisfies this range, the contact interface between the cathode material and the solid electrolyte, which allows easy ingress and egress of lithium ions, can be maximized.

[0056] The positive electrode active material for an all-solid-state battery may have a ratio of the diffraction peak intensity of the (104) plane to the diffraction peak intensity of the (003) plane, I(003) / I(104), of 1.19 to 1.25, in an X-ray diffraction spectrum analysis. When the peak intensity ratio I(003) / I(104) satisfies this range, the aforementioned improvement in battery performance can be more preferably realized.

[0057] The positive electrode active material for an all-solid-state battery can satisfy the following formula 1. <Expression 1> 0.37≦[I(006)+I(102)] / I(101)≦0.42 In the formula 1, I(006), I(102) and I(101) respectively represent the diffraction peak intensities of the (006), (102) and (101) planes in X-ray diffraction spectrum analysis.

[0058] When the positive electrode active material for an all-solid-state battery satisfies Formula 1, the above-described battery performance improvement effect can be more favorably realized.

[0059] Generally, the peak intensity value means a peak height value or an integrated area value obtained by integrating the area of ​​the peak, and in this embodiment, the peak intensity value means a peak area value.

[0060] The average particle size (D50) of the secondary particles may be 3 to 6 μm. When the average particle size of the secondary particles satisfies this range, the contact interface between the cathode material and the solid electrolyte is maximized, and the increased contact between the cathodes results in a simple reduction in the resistance of the cathode.

[0061] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle size (D50) can be measured, for example, by using a laser diffraction method.

[0062] The specific surface area of ​​the positive electrode active material for the all-solid-state battery is 0.4 to 0.7 m 2 When the specific surface area of ​​the positive electrode active material satisfies this range, the positive electrode / solid electrolyte contact interface can be easily maximized, and the increased contact interface between the positive electrode materials can advantageously reduce the resistance of the electrode.

[0063] In this specification, the specific surface area of ​​the active material can be measured by applying a BET (Surface Area and Porosity Analyzer) method (Micromeritics, ASAP2020) to the active material powder.

[0064] More specifically, the lithium transition metal oxide may be represented by the following Chemical Formula 1: [Chemical formula 1] Li a [Ni x1 Co y1 M z1 ]O2 In Chemical Formula 1, 1.01 ≦ a ≦ 1.05, 0.60 ≦ x1 < 1, 0 ≦ y1 ≦ 0.2, 0 < z1 ≦ 0.2, and x1 + y1 + z1 = 1, and M is Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

[0065] In the lithium transition metal oxide of Chemical Formula 1, lithium may be contained in a content corresponding to a, that is, 1.01 ≦ a ≦ 1.05. When a satisfies the above range, primary particles having the above-described orientation can be easily realized.

[0066] In the lithium transition metal oxide of Chemical Formula 1, nickel may be contained in a content corresponding to x1, that is, 0.60 ≦ x < 1. When x is sufficiently large at 0.60 or more, a sufficient amount of nickel contributing to charge and discharge is ensured, and the high capacity of the battery can be achieved. More specifically, 0.80 ≦ x < 1 may be satisfied.

[0067] In the lithium transition metal oxide of Chemical Formula 1, cobalt may be contained in a content corresponding to y1, that is, 0 ≦ y1 ≦ 0.2. When the content of cobalt is too small, there is a problem that it is difficult to simultaneously achieve sufficient rate characteristics and a high powder density of the active material. When the content of cobalt is too large, there is a problem that the cost of the raw material increases as a whole and the reversible capacity decreases.

[0068] In the lithium transition metal oxide of Chemical Formula 1, M is an element other than lithium, nickel, and cobalt, and M is Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof. Such M can be contained in a content corresponding to z1, that is, 0 < z1 ≦ 0.2.

[0069] The positive electrode active material for an all-solid-state battery according to an embodiment of the present invention includes a coating layer containing a lithium ion conductive oxide and disposed on a core. By including such a coating layer, it is possible to prevent the formation of a high-resistance layer due to a side reaction between the layered lithium transition metal oxide and the sulfide-based solid electrolyte, and improve the battery capacity and life characteristics.

[0070] More specifically, the lithium ion conductive oxide can be represented by the following Chemical Formula 2. [Chemical Formula 2] Li x2 A y2 O z2 In Chemical Formula 2, 0 ≦ x2 ≦ 3, 0 < y2 ≦ 2, 0 < z2 ≦ 4, and A is Zr, Nb, Ti, or a combination thereof.

[0071] For example, the lithium ion conductive oxide may be Li2ZrO3, ZrO2, LiNbO3, Nb2O3, Li2TiO3, TiO2, or a combination thereof, but is not limited thereto.

[0072] The content of the coating layer may be 0.5 to 1.5% by weight based on the total weight of the positive electrode active material. If the content of the coating layer is too small, the improvement effect of the battery performance described above is negligible. If the content of the coating layer is too large, the content of the lithium transition metal oxide decreases, and the capacity of the battery may decrease.

[0073] 2. Method for manufacturing a positive electrode active material for an all-solid-state battery

[0074] Another embodiment of the present invention provides a method for manufacturing a cathode active material for an all-solid-state battery, comprising the steps of: preparing a transition metal hydroxide containing nickel, the transition metal hydroxide being secondary particles formed by aggregation of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less; forming a mixture containing the transition metal hydroxide and a lithium source material; calcining the mixture to form a lithium transition metal oxide; and forming a coating layer containing a lithium ion conductive oxide on a surface of the lithium transition metal oxide.

[0075] Hereinafter, each step of a method for producing a positive electrode active material for an all-solid-state battery according to another embodiment of the present invention will be described in detail.

[0076] First, a transition metal hydroxide containing nickel is prepared, which is a secondary particle formed by agglomeration of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less.

[0077] The transition metal hydroxide is a precursor of the positive electrode active material.

[0078] At this time, at least some of the secondary particles may have a structure in which the major axes of the primary particles are arranged radially.

[0079] The transition metal hydroxide is a secondary particle formed by agglomeration of primary particles having the above shape and thickness, and has the above orientation, so that the structure of the positive electrode active material and the shape of the primary particles manufactured using the transition metal hydroxide can be obtained as described in the positive electrode active material section.

[0080] The transition metal hydroxide may be prepared by, for example, adding an ammonia solution and a caustic soda solution to a transition metal-containing solution containing a nickel source material, a cobalt source material, a manganese source material, and a doping source material containing Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof, and co-precipitation reaction.

[0081] The nickel source material is not particularly limited as long as it is one commonly used in the art for preparing a positive electrode active material precursor. For example, the nickel source material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, such as, but not limited to, NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiCO2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide, or a combination thereof.

[0082] The cobalt source material is not particularly limited as long as it is one commonly used in the art for preparing a cathode active material precursor, and may be, for example, a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, such as, but not limited to, CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof.

[0083] The manganese source material is not particularly limited as long as it is one commonly used in the art for preparing a cathode active material precursor. For example, the manganese source material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically, but not limited to, MnSO4, MnCO3, Mn(NO3)2, manganese salts such as manganese acetate, manganese dicarboxylate, manganese citrate, and fatty acid manganese salt, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof.

[0084] The transition metal-containing solution may be prepared by adding the raw materials to a solvent, specifically, a mixed solvent of water or an organic solvent (e.g., alcohol) that is uniformly miscible with water, or by mixing aqueous solutions containing the respective raw materials.

[0085] The ammonia solution may include, but is not limited to, a complexing agent such as NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. Meanwhile, the ammonia solution may be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0086] The caustic soda solution is a precipitant or pH adjuster and may contain alkali compounds such as hydroxides of alkali metals or alkaline earth metals, hydrates thereof, or combinations thereof, such as NaOH, KOH, or Ca(OH)2. The caustic soda solution may also be used in the form of an aqueous solution, and the solvent may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0087] The co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0088] Subsequently, a mixture containing the transition metal hydroxide and a lithium source material is formed.

[0089] In particular, the molar ratio (Li / Me) of the transition metal (Me) of the transition metal hydroxide to the lithium (Li) of the lithium source material may be 1.01 to 1.05, more specifically, 1.02 to 1.04. When the Li / Me molar ratio satisfies this range, a cathode material having a structure with many exposed corners of the plate-like particles, which facilitates the ingress and egress of lithium ions as described in the cathode active material description, can be realized, facilitating the movement of lithium ions and improving the capacity and output characteristics of the battery.

[0090] The lithium source material may be, but is not limited to, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, as long as it is soluble in water. Specifically, the lithium source material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0091] The mixture may further include a doping source material including Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

[0092] The mixture is then calcined to form the lithium transition metal oxide.

[0093] In particular, the sintering may be performed at a temperature of 720 to 770° C., more specifically, at a temperature of 730 to 760° C. When the sintering temperature is within this range, it is advantageous to realize a cathode material having a crystalline structure that allows easy ingress and egress of lithium ions.

[0094] The calcination can be carried out for 5 to 20 hours, more specifically, for 5 to 15 hours or 8 to 12 hours.

[0095] The firing can be carried out in an oxygen atmosphere.

[0096] Then, a coating layer containing a lithium ion conductive oxide is formed on the surface of the lithium transition metal oxide.

[0097] The lithium ion conductive oxide is the same as that described above, and therefore a detailed description thereof will be omitted.

[0098] Meanwhile, the method for forming the coating layer is not particularly limited, and for example, the coating layer may be formed by spraying a coating solution containing a coating raw material onto the surface of a lithium transition metal oxide, followed by heat treatment and drying, but the method is not limited thereto and may be any method available in the art.

[0099] 3.All-solid-state battery

[0100] Another embodiment of the present invention provides a cathode including the above-described cathode active material for an all-solid-state battery.

[0101] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include the above-described positive electrode active material for an all-solid-state battery, a sulfide-based solid electrolyte, and a conductive material. The positive electrode active material layer may further include a binder.

[0102] The sulfide-based solid electrolyte may be, for example, a sulfide-based solid electrolyte having an argyrodite-based crystal structure.

[0103] The sulfide-based solid electrolyte having an argyrodite-based crystal structure is specifically Li 7-x PS 6-x D x (0≦x≦2, D is F, Cl, Br, I or a combination thereof).

[0104] For example, the sulfide-based solid electrolyte having an argyrodite-based crystal structure may be, but is not limited to, Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof.

[0105] The sulfide-based solid electrolyte having an argyrodite-based crystal structure may have at least a portion of its crystal structure doped with a doping element, thereby improving its atmospheric stability.

[0106] The conductive material may be, for example, graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, toka black, denka black, super P, carbon nanotubes, carbon nanofibers, graphene, fullerene, or a combination thereof, but is not limited thereto.

[0107] The binder may be, for example, 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, polymethacrylate, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile-butadiene rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-ethylene-butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), fluororubber, or a combination thereof, but is not limited thereto.

[0108] The positive electrode active material layer may further include additives such as a filler, a coating agent, a dispersant, and an ion-conductive additive in addition to the positive electrode active material, solid electrolyte, binder, and conductive material.

[0109] Yet another embodiment of the present invention provides an all-solid-state battery comprising: a positive electrode; a negative electrode; and a solid electrolyte layer disposed therebetween, wherein the positive electrode comprises the above-described positive electrode active material for an all-solid-state battery.

[0110] The description of the positive electrode is omitted since it is the same as that described above.

[0111] The solid electrolyte layer may include a sulfide-based solid electrolyte.

[0112] The sulfide-based solid electrolyte may be, for example, a sulfide-based solid electrolyte having an argyrodite-based crystal structure.

[0113] The sulfide-based solid electrolyte having an argyrodite-based crystal structure is specifically Li 7-x PS 6-x D x (0≦x≦2, D is F, Cl, Br, I or a combination thereof).

[0114] For example, the sulfide-based solid electrolyte having an argyrodite-based crystal structure may be, but is not limited to, Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof.

[0115] The sulfide-based solid electrolyte having an argyrodite-based crystal structure may have at least a portion of its crystal structure doped with a doping element, thereby improving its atmospheric stability.

[0116] The solid electrolyte contained in the positive electrode active material layer and the solid electrolyte contained in the solid electrolyte layer may be the same or different.

[0117] The solid electrolyte layer may further include a binder, such as, but not limited to, 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, polymethacrylate, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile-butadiene rubber (NBR), styrene-butadiene-styrene block polymer (SBS), styrene-ethylene-butadiene block polymer (SEB), styrene-(styrene-butadiene)-styrene block polymer, natural rubber (NR), isoprene rubber (IR), fluororubber, or a combination thereof.

[0118] In this case, the binder contained in the solid electrolyte layer and the binder contained in the positive electrode active material layer or the negative electrode active material layer may be the same or different.

[0119] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material.

[0120] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0121] It is a substance capable of reversibly intercalating / deintercalating lithium ions, a carbonaceous substance, and any of the carbonaceous negative electrode active materials generally used in lithium ion secondary batteries can be used. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0122] As the alloy of the lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn can be used.

[0123] Examples of the substance capable of doping and undoping lithium include Si, SiOx (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements and combinations thereof, and is not Sn), and the like. Also, at least one of these can be mixed with SiO2 and used. The element Y can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof.

[0124] Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

[0125] The negative electrode active material layer may also include a binder and, optionally, may further include a conductive material.

[0126] The binder serves to firmly adhere negative electrode active material particles to each other and to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0127] The conductive material is used to impart conductivity to the electrodes, and any material can be used as long as it does not undergo chemical change in the constructed battery and is electronically conductive. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, silver, and the like; conductive polymer materials such as polyphenylene derivatives; and conductive materials containing mixtures of these.

[0128] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0129] Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are merely preferred examples of the present invention and are not intended to limit the scope of the present invention.

[0130] Example 1

[0131] (1) Manufacture of positive electrode active material

[0132] (Preparation of transition metal hydroxide) A transition metal hydroxide was prepared, which is a secondary particle formed by aggregation of primary particles, the primary particles having a plate-like shape and a thin average thickness, and having a structure in which the major axes of the primary particles located inside the secondary particles are radially arranged.

[0133] (Formation of lithium transition metal oxide) The transition metal hydroxides were mixed so that the molar ratio (Li / Me) of lithium (Li) in LiOH to the transition metal (Me) in the transition metal hydroxide was 1.03, and the mixture was fired at 740°C in an oxygen atmosphere to form a lithium transition metal oxide.

[0134] (Coating Layer Formation) Next, lithium metal was dissolved in anhydrous ethanol to prepare a lithium ethoxide solution. A 70 wt% propanol solution of zirconium(IV) tetrapropoxide was mixed with the prepared solution and stirred for 10 minutes or more to prepare a coating solution. The prepared coating solution was placed in a fluidized bed coating device, and a lithium transition metal oxide of the prepared composition was added. Wet coating was performed with a solution concentration of 0.03 mol, a solution supply rate of 6 cc / min, and a coating solution spray time of 60 minutes. This was followed by heat treatment at 300°C for 2 hours in an oxygen atmosphere to produce a cathode active material with a Li2ZrO3 coating layer formed on the surface of the lithium transition metal oxide.

[0135] (2) All-solid-state battery manufacturing

[0136] 72 wt% of the prepared positive electrode active material, 25 wt% of Argyrodite solid electrolyte (Li6PS5Cl), and 3 wt% of Super C65 as a conductive material were mixed to prepare a mixed powder.

[0137] First, 100 mg of Argyrodite solid electrolyte (Li6PS5Cl) which acts as a separator was placed in the jig for evaluating solid-state batteries, and pressure was applied to over 300 MPa to make the thickness about 100 μm. Then, mixed powder was placed on one side so that the amount of positive electrode active material was 14.4 mg, and a second pressure was applied to make the positive electrode part.

[0138] Then, a Li-In alloy was placed on the other side and an appropriate pressure was applied to produce a battery for all-solid-state battery evaluation.

[0139] Comparative Example 1

[0140] A positive electrode active material and an all-solid-state battery were manufactured in the same manner as in Example 1, except that the conditions for the coprecipitation reaction during preparation of the transition metal hydroxide were changed to prepare a transition metal hydroxide with a thick average thickness, and the lithium transition metal oxide was formed by firing at a temperature of 730°C.

[0141] Experimental Example 1: SEM image analysis of positive electrode active material

[0142] SEM (Scanning Electron Microscope) images of the transition metal hydroxides (positive electrode active material precursors) used in Example 1 and Comparative Example 1 and the positive electrode active materials produced therefrom were taken and are shown in FIG.

[0143] 1, it was confirmed that the transition metal hydroxide of Example 1 was a secondary particle formed by agglomeration of very thin plate-like or needle-like primary particles. In addition, it was confirmed that the cathode active material prepared therefrom was also a secondary particle formed by agglomeration of very thin plate-like or needle-like primary particles, and that some primary particles on the surface of the secondary particles had their major axes oriented parallel to the surface of the secondary particles.

[0144] On the other hand, it was confirmed that the transition metal hydroxide of Comparative Example 1 was a secondary particle formed by agglomeration of relatively thick plate-like or needle-like primary particles, and that the cathode active material produced therefrom was also a secondary particle formed by agglomeration of relatively thick plate-like or needle-like primary particles.

[0145] Experimental Example 2: Evaluation of the properties of positive electrode active material

[0146] The properties of the positive electrode active materials prepared in the examples and comparative examples were evaluated and are shown in Table 2 below.

[0147] (1) c-axis, a-axis length, I(003) / I(104), [I(006)+I(102)] / I(101), FWHM(110) evaluation

[0148] The physical properties were measured by X-ray diffraction spectroscopy (XRD).

[0149] (2) Average grain size evaluation

[0150] The sample surface was measured using a high-resolution transmission electron microscope (HR-TEM) TITAN G2 at 800,000 to 2,000,000 times magnification, and the average grain size was calculated by calculating the arithmetic mean value of each measured grain size.

[0151] (3) Volume evaluation

[0152] The volume of the active material was evaluated.

[0153] (4) Evaluation of the average thickness of primary particles

[0154] The SEM (or TEM) images of the positive electrode active material were analyzed and the arithmetic mean was calculated.

[0155] [Table 2]

[0156] Experimental Example 4: Evaluation of electrochemical characteristics of all-solid-state batteries

[0157] The electrochemical properties of the lithium secondary batteries manufactured in the Examples and Comparative Examples were evaluated and are shown in Table 3. The specific experimental method is as follows.

[0158] (1) 0.1C initial charge and discharge capacity, initial efficiency evaluation

[0159] The fabricated all-solid-state battery cell for evaluation was installed in the charge / discharge cycle and its charge / discharge characteristics were evaluated at 30°C. The charge / discharge method was a constant current-voltage method at a current density of 0.1C. The charge end voltage was set to 3.7V, and the charge cut-off current was set to 0.02C. During discharge, the cell was discharged at a constant current of 0.1C, and the discharge cut-off voltage was set to 1.9V. The charge capacity, discharge capacity, and initial efficiency were measured.

[0160] (2) 2.0C high-rate discharge capacity evaluation

[0161] The high rate discharge capacity was evaluated at 2C, which is 20 times higher than 0.1C.

[0162] (3) Lifetime characteristic evaluation (30 cycles, 0.5C)

[0163] After performing a 2C high-rate discharge, the same cell as in Example 1 was continuously charged and discharged at 0.5C, which was five times the current density of 0.1C, to evaluate the life characteristics.

[0164] [Table 3]

[0165] Referring to Table 2, it was confirmed that Example 1, in which the primary particle thickness, FWHM(110), crystal grain size, and other physical properties were all appropriately controlled, had excellent capacity, output, and lifespan characteristics. On the other hand, it was confirmed that Comparative Examples 1 and 2, in which the primary particle thickness was very thick, the FWHM(110) was very large, and the crystal grain size was very small, had poor capacity, output, and lifespan characteristics.

[0166] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these also fall within the scope of the present invention.

[0167] Therefore, the true scope of the invention is defined by the appended claims and their equivalents.

Claims

1. a core comprising a layered lithium transition metal oxide; and a coating layer disposed on the core and containing a lithium ion conductive oxide; The secondary particles are formed by agglomeration of a plurality of primary particles, and the primary particles have a flake or needle shape and an average thickness of 50 nm or less; A positive electrode active material for an all-solid-state battery, wherein the full width at half maximum (FWHM(110)) of a (110) plane diffraction peak is 0.2 or less when analyzed by X-ray diffraction spectroscopy.

2. 2 . The positive electrode active material for an all-solid-state battery according to claim 1 , comprising primary particles located on surfaces of the secondary particles, the major axes of which are oriented horizontally to the surfaces of the secondary particles.

3. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein at least a portion of the secondary particles have a structure in which the major axes of the primary particles are arranged radially.

4. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the average crystallite size is 104 nm or more.

5. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the length of the a-axis is 2.871 to 2.872 Å and the length of the c-axis is 14.227 to 14.229 Å.

6. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the lithium transition metal oxide has a lithium / transition metal (Li / Me) molar ratio of 1.01 to 1.

05.

7. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein, in X-ray diffraction spectrum analysis, the ratio I(003) / I(104) of the diffraction peak intensity of the (104) plane to the diffraction peak intensity of the (003) plane is 1.19 to 1.

25.

8. The positive electrode active material for an all-solid-state battery according to claim 1, which satisfies the following formula 1: <Formula 1> 0.37≦[I(006)+I(102)] / I(101)≦0.42 In the formula 1, I(006), I(102), and I(101) respectively represent the diffraction peak intensities of the (006), (102), and (101) planes in X-ray diffraction spectrum analysis.

9. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the lithium transition metal oxide is represented by the following chemical formula 1: [Chemical formula 1] Li ａ [Ni ｘ１ Co ｙ１ M ｚ１ ]O ２ In Chemical Formula 1, 1.01≦a≦1.05, 0.60≦x1<1, 0≦y1≦0.2, 0<z1≦0.2, x1+y1+z1=1, and M is Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

10. The positive electrode active material for an all-solid-state battery according to claim 1 , wherein the lithium ion conductive oxide is represented by the following chemical formula 2: [Chemical formula 2] Li ｘ２ A ｙ２ O ｚ２ In the above Chemical Formula 2, 0≦x2≦3, 0<y2≦2, 0<z2≦4, and A is Zr, Nb, Ti, or a combination thereof.

11. The lithium ion conductive oxide is Li ２ ZrO ３ , ZrO ２ , LiNbO ３ , Nb ２ O ３ , Li ２ TiO ３ , TiO ２ 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the positive electrode active material is a hydroxyapatite or a combination thereof.

12. 2. The cathode active material for an all-solid-state battery according to claim 1, wherein the content of the coating layer is 0.5 to 1.5 wt % based on the total weight of the cathode active material.

13. 2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the average particle size (D50) of the secondary particles is 3 to 6 μm.

14. Specific surface area is 0.4 to 0.7 m ２ The positive electrode active material for an all-solid-state battery according to claim 1, wherein the SiO2 content is 1 / g.

15. preparing a transition metal hydroxide containing nickel, the secondary particles being formed by agglomeration of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less; forming a mixture comprising the transition metal hydroxide and a lithium source material; calcining the mixture to form a lithium transition metal oxide; and forming a coating layer containing a lithium ion conductive oxide on a surface of the lithium transition metal oxide; A method for producing a positive electrode active material for an all-solid-state battery.

16. In the step of forming the mixture, 16. The method for producing a positive electrode active material for an all-solid-state battery according to claim 15, wherein the lithium source material is mixed with the transition metal (Me) of the transition metal hydroxide in a molar ratio (Li / Me) of 1.01 to 1.

05.

17. In the step of preparing the transition metal hydroxide, The method for producing a positive electrode active material for an all-solid-state battery according to claim 15 , wherein at least some of the secondary particles have a structure in which the major axes of primary particles are arranged radially.

18. In the step of forming the lithium transition metal oxide, The method for producing a positive electrode active material for an all-solid-state battery according to claim 15, wherein the firing is carried out at a temperature of 720 to 770°C.

19. A positive electrode comprising the positive electrode active material for an all-solid-state battery according to any one of claims 1 to 14.

20. An all-solid-state battery comprising: a positive electrode; a negative electrode; and a solid electrolyte layer disposed therebetween, wherein the positive electrode comprises the positive electrode active material for an all-solid-state battery according to any one of claims 1 to 14.

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