Positive active material for all-solid-state battery, method for preparing same, and all-solid-state battery comprising same

Abstract

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

Description

Technical Field

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

[0002] Recently, in the lithium secondary battery market, the requirements for increasing the driving distance and improving the safety of electric vehicles have been increasing. Therefore, it has become very important to develop a lithium secondary battery that has both excellent safety and high weight and volume energy densities. In particular, the energy capacity applied to electric vehicles reaches the level of dozens of kilowatt-hours, and there is a possibility of large-scale fires and explosions when the battery is damaged. Therefore, researchers are actively conducting research on replacing the liquid electrolyte with a solid electrolyte.

[0003] In particular, for the convenience of manufacturing, all-solid-state batteries mainly adopt a structure in which a solid electrolyte is applied inside the positive electrode as a secondary electrolyte for forming a lithium ion conduction path. For sulfide-based solid electrolytes, since they have high ionic conductivity and are easily deformed under pressure, high density can be achieved, and thus a large amount of research has been conducted.

[0004] For the positive electrode active material mixed with the sulfide-based solid electrolyte in the positive electrode, similar to lithium ion batteries, recently, oxide-based positive electrode active materials having a layered structure of the NCM type or the NCA type have been mainly adopted. However, these positive electrode active materials react at the interface with the sulfide-based solid electrolyte to form a high-resistance layer. Therefore, in order to prevent such reactions on the surface of the active material, research on coating a lithium ion conductive oxide to improve the performance has been continuously carried out.

[0005] However, compared with the uncoated case, the conventional active materials coated with a lithium ion conductive oxide have been considerably improved in terms of the initial capacity and efficiency of the battery and the charge-discharge life characteristics. However, when the loading amount of the electrode active material is increased or at a high c-rate, there is a problem of a significant decrease in the discharge capacity. Summary of the Invention

[0006] Technical Problem to be Solved

[0007] Therefore, an aspect of the present invention aims to provide a positive electrode active material for an all-solid-state battery, a method for preparing the same, and an all-solid-state battery including the same, which can improve the discharge capacity of the battery at a high c-rate.

[0008] Technical Solution

[0009] One embodiment of the present invention provides a positive electrode active material for an all-solid-state battery, which comprises: a core of a layered lithium transition metal oxide; and a coating disposed on the core and containing a lithium ion conductive oxide; secondary particles formed by aggregation of a plurality of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less; when analyzed by X-ray diffraction spectroscopy, the full width at half maximum FWHM(110) of the diffraction peak of the (110) plane is 0.2 or less.

[0010] The positive electrode active material for the all-solid-state battery comprises primary particles located on the surface of the secondary particles and having a major axis oriented in the horizontal direction of the surface of the secondary particles.

[0011] At least a part of the secondary particles comprises a structure in which the major axes of the primary particles are radially arranged.

[0012] The average grain size of the positive electrode active material for the all-solid-state battery is 104 nm or more.

[0013] The a-axis length of the positive electrode active material for the all-solid-state battery is to The c-axis length is to

[0014] The molar ratio of lithium / transition metal (Li / Me) in the lithium transition metal oxide is 1.01 to 1.05.

[0015] In X-ray diffraction spectrum analysis, the ratio I(003) / I(104) of the diffraction peak intensity of the (003) plane to the diffraction peak intensity of the (104) plane of the positive electrode active material for the all-solid-state battery is 1.19 to 1.25.

[0016] The positive electrode active material for the all-solid-state battery satisfies the following formula 1:

[0017] <Formula 1>

[0018] 0.37 ≤ [I(006) + I(102)] / I(101) ≤ 0.42

[0019] In the formula 1, I(006), I(102) and I(101) respectively represent the diffraction peak intensities of the (006) plane, (102) plane and (101) plane in X-ray diffraction spectrum analysis.

[0020] The lithium transition metal oxide is represented by the following chemical formula 1:

[0021] [Chemical formula 1]

[0022] Li a [Ni x1 Coy1 M z1 O2

[0023] In the formula 1, 1.01 ≤ a ≤ 1.05, 0.60 ≤ x1 < 1, 0 ≤ y1 ≤ 0.2, 0 < z1 ≤ 0.2, and x1 + y1 + z1 = 1, where M is Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof.

[0024] The lithium ion conductive oxide is represented by the following formula 2:

[0025] [Formula 2]

[0026] Lix2Ay2Oz2

[0027] In the formula 2, 0 ≤ x2 ≤ 3, 0 < y2 ≤ 2, 0 < z2 ≤ 4, and A is Zr, Nb, Ti, or a combination thereof.

[0028] The lithium ion conductive oxide is Li2ZrO3, ZrO2, LiNbO3, Nb2O3, Li2TiO3, TiO2, or a combination thereof.

[0029] Based on the total weight of the positive electrode active material, the content of the coating is 0.5 wt% to 1.5 wt%.

[0030] The average particle size (D50) of the secondary particles is 3 μm to 6 μm.

[0031] The specific surface area of the positive electrode active material of the all-solid-state battery is 0.4 m 2 / g to 0.7 m 2 / g.

[0032] Another embodiment of the present invention provides a method for preparing a positive electrode active material of an all-solid-state battery, which includes: a step of preparing a transition metal hydroxide containing nickel, which is a secondary particle formed by aggregation of primary particles, wherein the primary particles have a flake or needle shape and an average thickness of less than 50 nanometers; a step of forming a mixture containing the transition metal hydroxide and a lithium raw material substance; a step of firing the mixture to form a lithium transition metal oxide; and a step of forming a coating containing a lithium ion conductive oxide on the surface of the lithium transition metal oxide.

[0033] In the step of forming the mixture, the molar ratio (Li / Me) of lithium (Li) in the lithium raw material substance to the transition metal (Me) in the transition metal hydroxide is mixed in the range of 1.01 to 1.05.

[0034] In the step of preparing the transition metal hydroxide, at least a part of the secondary particles includes a structure in which the long axes of the primary particles are radially arranged.

[0035] In the step of forming the lithium transition metal oxide, the firing is carried out at a temperature of 720 °C to 770 °C.

[0036] Another embodiment of the present invention provides a positive electrode including the positive electrode active material of the all-solid-state battery described above.

[0037] Another embodiment of the present invention provides an all-solid-state battery including a positive electrode; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the positive electrode includes the positive electrode active material of the all-solid-state battery described above.

[0038] Advantageous Effects

[0039] The positive electrode active material of the all-solid-state battery according to an embodiment of the present invention, the positive electrode active material for the all-solid-state battery has a plate-like or needle-like morphology and has a structure of secondary particles formed by aggregation of primary particles with a thin thickness. When performing X-ray diffraction spectroscopy analysis, the full width at half maximum FWHM(110) of the diffraction peak of the (110) plane is small, and the discharge capacity of the battery can be improved at a high c-rate. Brief Description of the Drawings

[0040] Figure 1 are SEM images of the precursors and positive electrode active materials used in Example 1 and Comparative Example 1. Detailed Description

[0041] The terms first, second, third, etc. are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, and / or segment described below can also be described as the second part, component, region, layer, and / or segment.

[0042] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless the context clearly gives the opposite meaning, the singular forms used are also intended to include the plural forms. It should also be understood that the term "including" used in the specification can specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, fields, integers, steps, actions, elements, and / or components.

[0043] If a part is described as being above another part, there may be other parts directly above or between the other parts. When a part is described as being directly above another part, there are no other parts therebetween.

[0044] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0045] In addition, unless otherwise specified, % represents weight %, and 1 ppm represents 0.0001 weight %.

[0046] In this specification, "combinations thereof" described in a Markush-type expression refers to a mixture or combination of one or more selected from the group consisting of the components recited in the Markush-type expression, meaning including one or more selected from the group consisting of the above components.

[0047] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention belongs can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0048] 1. Cathode active material for all-solid-state battery

[0049] One embodiment of the present invention provides a cathode active material for an all-solid-state battery, which includes: a core of layered lithium transition metal oxide; and a coating disposed on the core and containing a lithium ion conductive oxide; secondary particles formed by aggregation of a plurality of primary particles, the primary particles having a flake or needle shape and an average thickness of 50 nm or less; when analyzed by X-ray diffraction spectroscopy, the full width at half maximum FWHM(110) of the (110) plane diffraction peak is 0.2 or less.

[0050] The cathode active material according to one embodiment of the present invention can be used for an all-solid-state battery. More specifically, it can be a cathode active material of a composite cathode material for use with a sulfide-based solid electrolyte.

[0051] The cathode active material for an all-solid-state battery according to one embodiment of the present invention may include a core and a coating disposed on the core.

[0052] At this time, the cathode active material for an all-solid-state battery according to one embodiment of the present invention may be secondary particles formed by aggregation of a plurality of primary particles.

[0053] In this specification, a "primary particle" refers to the smallest particle unit that is distinguishable as a single piece when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and can be composed of a single crystal grain or multiple crystal grains.

[0054] The primary particles are in the form of flakes or needles, with an average thickness of 50 nm or less. Due to the extremely thin shape of the primary particles being in the form of flakes or needles, the mobility of lithium ions can be promoted, thereby significantly enhancing the high-output characteristics of the battery. More specifically, the average thickness of the primary particles can be 50 nm or 40 nm or less.

[0055] The positive electrode active material of the all-solid-state battery may include primary particles located on the surface of the secondary particles and having a major axis oriented in the horizontal direction of the secondary particle surface.

[0056] By having the above structure, the mobility of lithium ions is improved, and the high-output characteristics of the battery can be further enhanced.

[0057] At least a part of the secondary particles includes a structure in which the major axes of the primary particles are radially arranged. Primary particles having such an orientation are particularly likely to be present in large quantities inside the secondary particles.

[0058] In this way, radially oriented primary particles with the major axis pointing towards the center direction mainly exist inside the active material secondary particles, and on the surface of the secondary particles, due to the presence of primary particles with the major axis aligned with the horizontal direction of the surface, the high-power characteristics of the battery can be maximized.

[0059] According to an embodiment of the present invention, when the all-solid-state positive electrode active material is analyzed by X-ray diffraction spectroscopy, the full width at half maximum FWHM(110) of the diffraction peak of its (110) plane is 0.2 or less, and more specifically, it can be 0.19 or less. When the full width at half maximum FWHM(110) of the diffraction peak of the (110) plane satisfies the above range, since the proportion of the plane where lithium ions are easily mobile at the contact interface between the positive electrode material and the solid electrolyte particles is maximized, the high-output characteristics of the battery can be improved.

[0060] The average crystallite size of the positive electrode active material of the all-solid-state battery can be 104 nm or more, and specifically can be 106 nm or 108 nm or more.

[0061] In this specification, "crystal grain" refers to a single-crystalline grain unit with a regular atomic arrangement. For the size of the crystal grain, for example, a high-resolution transmission electron microscope (HR-TEM) TITAN G2 can be used to measure it by magnifying the sample surface 800,000 to 2,000,000 times, and the average crystal grain size can be obtained by calculating the arithmetic mean of the measured crystal grain sizes of each one.

[0062] When the average crystal grain size of the positive electrode active material satisfies the above range, the entry and exit of lithium ions inside the positive electrode material particles will proceed smoothly, thereby more ideally achieving the effect of improving the battery performance.

[0063] The a-axis length of the positive electrode active material of the all-solid-state battery is to The c-axis length is to

[0064] When the a-axis length and c-axis length of the positive electrode active material satisfy the above range, the improvement effect of the battery performance can be more ideally achieved, and it is also more advantageous in terms of discharge capacity and life characteristics. The a-axis length and c-axis length can be measured by X-ray diffraction spectroscopy analysis.

[0065] The lithium / transition metal (Li / Me) molar ratio in the lithium transition metal oxide can be 1.01 to 1.05. When the lithium / transition metal (Li / Me) molar ratio satisfies the above range, the maximum contact interface between the positive electrode material and the solid electrolyte that is beneficial for the entry and exit of lithium ions can be achieved.

[0066] In the X-ray diffraction spectrum analysis, the ratio I(003) / I(104) of the diffraction peak intensity of the (003) plane to the diffraction peak intensity of the (104) plane of the positive electrode active material of the all-solid-state battery is 1.19 to 1.25.

[0067] When the peak intensity ratio I(003) / I(104) satisfies the above range, the aforementioned battery performance improvement effect can be more ideally achieved.

[0068] The positive electrode active material of the all-solid-state battery can satisfy the following formula 1:

[0069] <Formula 1>

[0070] 0.37 ≤ [I(006) + I(102)] / I(101) ≤ 0.42

[0071] 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 spectral analysis. When the cathode active material for the all-solid-state battery satisfies Formula 1, the battery performance improvement effect can be more ideally achieved.

[0072] Generally, the peak intensity value refers to the height value of the peak or the integrated area value obtained by integrating the area of the peak. In this embodiment, the peak intensity value refers to the area value of the peak.

[0073] The average particle size (D50) of the secondary particles can be 3 μm to 6 μm. When the average particle size of the secondary particles satisfies the above range, the contact interface between the cathode material and the solid electrolyte is maximized, and due to the increased contact between the cathodes, there is an advantage that the resistance of the cathode is also easily reduced.

[0074] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume cumulative amount on the particle size distribution curve of the particles. For the average particle size (D50), for example, the laser diffraction method can be used for measurement.

[0075] The specific surface area of the all-solid-state battery cathode active material can be 0.4 m 2 / g to 0.7 m 2 / g. When the specific surface area of the cathode active material satisfies the above range, it is not only beneficial to maximize the contact interface between the cathode / solid electrolyte, but also reduces the resistance of the electrode due to the increased contact interface between the cathode materials.

[0076] In this specification, the specific surface area of the active material can be measured for the active material particles by the BET method (surface area and pore analyzer) (Micromeritics, ASAP2020).

[0077] The lithium transition metal oxide can be more specifically represented by Chemical Formula 1:

[0078] [Chemical Formula 1]

[0079] Li a [Ni x1 Co y1 M z1 O2

[0080] 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.

[0081] In the lithium transition metal oxide of Chemical Formula 1, lithium may be present in an amount corresponding to a, i.e., 1.01 ≤ a ≤ 1.05. When a satisfies the above range, it is beneficial to achieve primary particles with the above orientation.

[0082] In the lithium transition metal oxide of Chemical Formula 1, nickel may be present in an amount corresponding to x1, i.e., 0.60 ≤ x < 1 may be included. When x is not less than 0.60 and large enough, a sufficient amount of nickel can be ensured during charge and discharge processes, thereby achieving a high capacity of the battery. More specifically, 0.80 ≤ x < 1 may be adopted.

[0083] In the lithium transition metal oxide of Chemical Formula 1, cobalt may be present in an amount corresponding to y1, i.e., 0 ≤ y1 ≤ 0.2 may be included. When the content of cobalt is too low, it is difficult to achieve sufficient rate performance and a high powder density of the active material simultaneously. When the content of cobalt is too high, the overall raw material cost increases, and the reversible capacity decreases.

[0084] In the lithium transition metal oxide of Chemical Formula 1, M is an element other than lithium, nickel, and cobalt, and M may be Mn, Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof. These Ms may be present in an amount corresponding to z1, i.e., 0 < z1 ≤ 0.2 may be included.

[0085] The positive electrode active material of the all-solid-state battery according to an embodiment of the present invention includes a coating containing a lithium ion conductive oxide disposed on the inner core. By including such a coating, a high-resistance layer generated by a side reaction between the layered lithium transition metal oxide and the sulfide-based solid electrolyte can be prevented, thereby improving the capacity and life characteristics of the battery.

[0086] More specifically, the lithium ion conductive oxide may be represented by the following Chemical Formula 2:

[0087] [Chemical Formula 2]

[0088] Li x2 A y2 O z2

[0089] In Chemical Formula 2, 0 ≤ x2 ≤ 3, 0 < y2 ≤ 2, 0 < z2 ≤ 4, and A is Zr, Nb, Ti, or a combination thereof. For example, the lithium ion conductive oxide may be Li2ZrO3, ZrO2, LiNbO3, Nb2O3, Li2TiO3, TiO2, or a combination thereof, but not limited thereto.

[0090] The content of the coating may be 0.5 wt% to 1.5 wt% of the total weight of the positive electrode active material. If the content of the coating is too small, the above-described battery performance improvement effect may not be obvious; if the content of the coating is too large, the content of the lithium transition metal oxide will be reduced, resulting in a decrease in battery capacity.

[0091] 2. Preparation method of positive electrode active material for all-solid-state battery

[0092] Another embodiment of the present invention provides a method for preparing a positive electrode active material for an all-solid-state battery, which includes: a step of preparing a transition metal hydroxide, the transition metal hydroxide containing nickel, being secondary particles formed by aggregation of primary particles, wherein the primary particles have a flake or needle shape and an average thickness of 50 nm or less; a step of forming a mixture containing the transition metal hydroxide and a lithium raw material substance; a step of firing the mixture to form a lithium transition metal oxide; and a step of forming a coating containing a lithium ion conductive oxide on the surface of the lithium transition metal oxide.

[0093] Hereinafter, the method for preparing a positive electrode active material for an all-solid-state battery according to another embodiment of the present invention will be described according to each step.

[0094] First, a transition metal hydroxide is prepared, which contains nickel, is secondary particles formed by aggregation of primary particles, wherein the primary particles have a flake or needle shape and an average thickness of 50 nm or less.

[0095] The transition metal hydroxide is a precursor of the positive electrode active material.

[0096] At this time, at least a part of the secondary particles contains a structure in which the major axes of the primary particles are radially arranged.

[0097] Since the transition metal hydroxide is secondary particles formed by aggregation of primary particles having the above shape and thickness and having the above orientation, the structure of the positive electrode active material manufactured using the transition metal hydroxide and the shape of the primary particles can be as described in the positive electrode active material part.

[0098] For the transition metal hydroxide, for example, an ammonia solution and a caustic soda solution may be added to a transition metal-containing solution containing a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and a doping raw material substance containing Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo, or a combination thereof to perform a coprecipitation reaction, thereby preparing the transition metal hydroxide.

[0099] For the nickel raw material substance, if it is a substance used in the relevant industry for preparing the precursor of the positive electrode active material, there is no special limitation. For example, the nickel raw material substance may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide, etc. Specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide or a combination thereof, but not limited thereto.

[0100] For the cobalt raw material substance, if it is a substance used in the relevant industry for preparing the precursor of the positive electrode active material, there is no special limitation. For example, the cobalt raw material substance may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide, etc. Specifically, it may be CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O or a combination thereof, but not limited thereto.

[0101] For the manganese raw material substance, if it is a substance used in the relevant industry for preparing the precursor of the positive electrode active material, there is no special limitation. For example, the manganese raw material substance may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof. Specifically, it may be manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salt, manganese citrate and manganese fatty acid salt, manganese oxides such as Mn2O3, MnO2 and Mn3O4, manganese oxyhydroxide, manganese chloride or a combination thereof, but not limited thereto.

[0102] For the transition metal-containing solution, the transition metal-containing solution can be prepared by adding the raw material substance to a solvent. The solvent may specifically be a mixed solvent of water or an organic solvent that can be uniformly mixed with water (for example, alcohol, etc.), or the transition metal-containing solution can be prepared by mixing aqueous solutions containing each raw material substance.

[0103] The ammonia solution as a complexing agent may, for example, contain NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof, but not limited thereto. On the other hand, the ammonia solution may also be in the form of an aqueous solution. In this case, the solvent may be water or a mixture of water and an organic solvent that can be uniformly mixed with water (specifically, alcohol, etc.).

[0104] The caustic soda solution, as a precipitating agent or pH regulator, may contain basic compounds such as hydroxides of alkali metals or alkaline earth metals, their hydrates or combinations thereof, such as NaOH, KOH or Ca(OH)2. The caustic soda solution may also be in the form of an aqueous solution, in which case the solvent may be water or a mixture of water and an organic solvent (specifically, alcohols, etc.) that can be uniformly mixed with water.

[0105] The coprecipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0106] Next, a mixture containing a transition metal hydroxide and a lithium raw material substance is formed.

[0107] In particular, the molar ratio (Li / Me) of lithium (Li) in the lithium raw material substance to the transition metal (Me) in the transition metal hydroxide is mixed in the range of 1.01 to 1.05. More specifically, the molar ratio can be 1.02 to 1.04.

[0108] When the Li / Me molar ratio satisfies the above range, a positive electrode material with a large number of exposed edge surfaces of plate-like particles can be achieved, which is beneficial for the entry and exit of lithium ions, as described in the positive electrode active material description, thereby making the movement of lithium ions smoother and improving the capacity and output characteristics of the battery.

[0109] The lithium raw material substance can use lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides or hydroxyoxides, etc., as long as they are soluble in water, there is no special limitation. Specifically, the lithium raw material substance can be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a combination thereof, but not limited thereto.

[0110] The mixture may further contain a doping raw material substance containing Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo or a combination thereof.

[0111] Next, the mixture is fired to form a lithium transition metal oxide.

[0112] At this time, the firing can be carried out at a temperature of 720 °C to 770 °C, more specifically, it can be carried out at a temperature of 730 °C to 760 °C. When the firing temperature satisfies the above range, it has the advantage of being able to achieve a positive electrode material with a crystal structure that facilitates the entry and exit of lithium ions.

[0113] The firing can be carried out for 5 hours to 20 hours, more specifically, it can be carried out for 5 hours to 15 hours or 8 hours to 12 hours.

[0114] The firing can be carried out in an oxygen atmosphere.

[0115] Next, a coating containing a lithium ion conductive oxide is formed on the surface of the lithium transition metal oxide.

[0116] The lithium ion conductive oxide is as described above, so detailed description is omitted.

[0117] On the other hand, the coating formation method is not particularly limited. For example, a coating solution containing coating raw material substances can be sprayed on the surface of the lithium transition metal oxide and then formed by heat treatment and drying, but it is not limited thereto, and any method used in the relevant industry can be adopted without limitation.

[0118] 3. All-solid-state battery

[0119] Another embodiment of the present invention provides a positive electrode comprising the aforementioned all-solid-state battery positive electrode active material.

[0120] More specifically, the positive electrode may comprise a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer may comprise the aforementioned all-solid-state battery positive electrode active material, a sulfide-based solid electrolyte, and a conductive material. In addition, the positive electrode active material layer may further comprise a binder.

[0121] For the sulfide-based solid electrolyte, for example, it may be a sulfide-based solid electrolyte having a thiogermanate crystal structure.

[0122] For the sulfide-based solid electrolyte having a thiogermanate crystal structure, specifically, it may be a compound represented by Li 7- x PS 6-x D x (0≤x≤2, D is F, Cl, Br, I or a combination thereof).

[0123] For example, the sulfide-based solid electrolyte having a thiogermanate crystal structure may be Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof, but it is not limited thereto.

[0124] For the sulfide-based solid electrolyte having a thiogermanate crystal structure, at least a part of its crystal structure may be doped with a doping element. Thereby, the air stability can be improved.

[0125] For the conductive material, it can be, for example, graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, Tokai black, Denka black, Super P, carbon nanotubes, carbon nanofibers, graphene, fullerenes, or a combination thereof, but not limited thereto.

[0126] For the binder, it can be, for example, polyvinylidene fluoride (PVDF), polyvinylidene 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 not limited thereto.

[0127] For the positive electrode active material layer, in addition to the aforementioned positive electrode active material, solid - state electrolyte, binder, and conductive material, it can also contain additives such as fillers, coating agents, dispersants, and ion - conduction aids, for example.

[0128] Another embodiment of the present invention provides a all - solid - state battery, which includes a positive electrode; a negative electrode; and a solid - state electrolyte layer disposed between the positive electrode and the negative electrode, and the positive electrode contains the aforementioned all - solid - state battery positive electrode active material.

[0129] The description of the positive electrode is as above, so the repeated description is omitted.

[0130] The solid - state electrolyte layer can contain sulfide - based solid - state electrolytes.

[0131] For the sulfide - based solid - state electrolyte, for example, it can be a sulfide - based solid - state electrolyte with a thiargite - type crystal structure.

[0132] For the sulfide - based solid - state electrolyte with a thiargite - type crystal structure, specifically, it can be a compound represented by Li 7-x PS 6- x D x (0 ≤ x ≤ 2, D is F, Cl, Br, I, or a combination thereof).

[0133] For example, the sulfide-based solid electrolyte with a thiargyrite crystal structure can be Li6PS5Cl, Li6PS5Br, Li6PS5I, or a combination thereof, but is not limited thereto.

[0134] For the sulfide-based solid electrolyte with a thiargyrite crystal structure, at least a part of its crystal structure can be doped with a doping element. Thereby, the air stability can be improved.

[0135] The solid electrolyte contained in the positive electrode active material layer and the solid electrolyte contained in the solid electrolyte layer can be the same or different.

[0136] The solid electrolyte layer may further contain a binder. For the binder contained in the solid electrolyte layer, for example, it can be polyvinylidene fluoride (PVDF), polyvinylidene 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 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.

[0137] At this time, 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 can be the same or different.

[0138] 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 contain a negative electrode active material.

[0139] The negative electrode active material includes a substance capable of reversibly inserting and extracting lithium ions, lithium metal, an alloy of lithium metal, a substance capable of doping and dedoping lithium, or a transition metal oxide.

[0140] As the substance that enables reversible insertion / extraction of lithium ions, any carbonaceous negative electrode active material generally used in lithium ion secondary batteries as a carbon material can be used. As typical examples thereof, crystalline carbon, amorphous carbon, or a combination thereof can be used. As an example of the crystalline carbon, natural graphite or artificial graphite such as amorphous, plate-like, flaky, spherical, or fibrous graphite can be cited. As an example of the amorphous carbon, soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, etc. can be cited.

[0141] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0142] As the substance that enables lithium doping and dedoping, Si, SiOx (0 < x < 2), Si-Y alloy (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Sn, SnO2, Sn-Y (where Y is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), etc. can be cited. At least one of them can also be used in combination with SiO2. The element Y can be selected from 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 their combinations.

[0143] As the transition metal oxide, vanadium oxide, lithium vanadium oxide, etc. can be cited.

[0144] The negative electrode active material layer also contains a binder, and may also selectively further contain a conductive material.

[0145] The binder serves to bond the negative electrode active material particles to each other well and to bond the negative electrode active material well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0146] The conductive material is used to impart conductivity to the electrode, and any conductive material can be used as long as it does not cause chemical changes in the formed battery. Examples thereof may include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal materials such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymer materials such as polyphenylene derivatives; or mixtures thereof.

[0147] As the current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer material coated with a conductive metal, and combinations thereof can be used.

[0148] Hereinafter, embodiments of the present invention will be described in further detail through examples. However, the following examples are a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

[0149] Example 1

[0150] (1) Preparation of the positive electrode active material

[0151] (Preparation of the transition metal hydroxide) It is a secondary particle formed by aggregation of primary particles, and the primary particles have a plate-like morphology, a relatively thin average thickness, and a structure in which the long axes of the primary particles inside the secondary particles are radially arranged.

[0152] (Formation of the lithium transition metal oxide) The molar ratio (Li / Me) of lithium (Li) in LiOH to the transition metal (Me) in the transition metal hydroxide is mixed to be 1.03, and it is fired in an oxygen atmosphere at a temperature of 740 °C to form a lithium transition metal oxide.

[0153] (Formation of the coating) Next, lithium metal is dissolved in absolute ethanol to prepare a lithium ethoxide solution. A propanol solution of 70 wt% zirconium(IV) tetrapropanolate is mixed into the prepared solution, and then stirred for more than 10 minutes to prepare a coating solution. The prepared coating solution is placed in a fluidized bed coating device, and after loading the prepared lithium transition metal oxide, wet coating is performed. The solution concentration is 0.03 mol, the solution supply rate is 6 cc / minute, and the spraying time of the coating solution is 60 minutes. Then, heat treatment is performed at 300 °C in an oxygen atmosphere for 2 hours, thereby preparing a positive electrode active material having a Li2ZrO3 coating formed on the surface of the lithium transition metal oxide.

[0154] (2) Preparation of the all-solid-state battery

[0155] 72 wt% of the prepared cathode active material was mixed with 25 wt% of argyrodite solid electrolyte (Li6PS5Cl) and 3 wt% of Super C65 as a conductive material to prepare a mixed powder.

[0156] First, 100 mg of argyrodite solid electrolyte (Li6PS5Cl) with a diaphragm function was loaded into a jig for all-solid-state battery evaluation, pressed at a pressure of 300 Mpa or more to a thickness of about 100 μm, and then the mixed powder was loaded on one side so that the amount of the cathode active material reached 14.4 mg, followed by secondary pressing to fabricate the cathode part.

[0157] Then, the Li-In alloy was loaded on the other side and an appropriate pressure was applied to fabricate a battery for all-solid-state battery evaluation.

[0158] Comparative Example 1

[0159] Except that when preparing the transition metal hydroxide, by changing the conditions of the coprecipitation reaction, a transition metal hydroxide with a relatively thick average thickness was prepared, and when forming the lithium transition metal oxide, it was fired at a temperature of 730 °C, the cathode active material and the all-solid-state battery were prepared in the same manner as in Example 1.

[0160] Experimental Example 1: SEM Image Analysis of Precursors and Active Materials

[0161] The SEM (scanning electron microscope) images of the transition metal hydroxides (precursors) used in Example 1 and Comparative Example 1 and the cathode active materials prepared therefrom are shown in Figure 1 in.

[0162] Referring to Figure 1 , it can be confirmed that the transition metal hydroxide of Example 1 is a secondary particle aggregated by primary particles in the form of very thin plates or needles. In addition, the cathode active material prepared therefrom is also a secondary particle aggregated by primary particles in the form of very thin plates or needles, and it can be confirmed that there are some primary particles on the surface of the secondary particle whose long axes are aligned with the horizontal direction of the surface of the secondary particle.

[0163] On the other hand, it can be confirmed that the transition metal hydroxide of Comparative Example 1 is a secondary particle aggregated by primary particles in the form of relatively thick plates or needles. In addition, the cathode active material prepared therefrom is also a secondary particle aggregated by primary particles in the form of relatively thick plates or needles.

[0164] Experimental Example 2: Physical Property Evaluation of Cathode Active Materials

[0165] The physical properties of the cathode active materials prepared according to the examples and comparative examples were evaluated and shown in Table 2 below.

[0166] (1) Evaluation of c-axis, a-axis length, I(003) / I(104), [I(006)+I(102)] / I(101), FWHM(110)

[0167] The physical properties were measured by X-ray diffraction spectroscopy (XRD).

[0168] (2) Evaluation of average grain size

[0169] The surface of the sample was magnified 800,000 to 2,000,000 times using a high-resolution transmission electron microscope (HR-TEM) TITAN G2, and the average grain size was obtained by calculating the arithmetic mean of the measured grain sizes.

[0170] (3) Volume evaluation

[0171] The volume of the active material was evaluated.

[0172] (4) Evaluation of average primary particle thickness

[0173] The SEM (or TEM) images of the positive electrode active material were analyzed, and the arithmetic mean was calculated.

[0174]

Table 2

[0175]

[0176] Experimental Example 4: Evaluation of the electrochemical characteristics of a lithium secondary battery

[0177] The electrochemical characteristics of the lithium secondary batteries prepared according to the examples and comparative examples were evaluated and shown in Table 3 below. The specific experimental method is as follows.

[0178] (1) Evaluation of 0.1C initial charge and discharge capacity, initial efficiency

[0179] The fabricated all-solid-state battery cell for evaluation was installed on a charger / discharger, and the charge and discharge characteristics were evaluated at 30 degrees. For the charge and discharge method, the first charge was performed by the constant current-voltage method at a current density of 0.1C. The charge termination voltage was set to 3.7V, and the charge termination current was set to a current of 0.02C. During discharge, a constant current method of 0.1C was used for discharge, and the charge termination voltage was set to 1.9V. The charge capacity, discharge capacity, and initial efficiency were measured at this time.

[0180] (2) Evaluation of 2.0C high-rate discharge capacity

[0181] The high-rate discharge capacity was evaluated at 2C, which is 20 times higher than 0.1C.

[0182] (3) Evaluation of life characteristics (30 cycles, 0.5C)

[0183] After performing 2C high-rate discharge, in the same battery as in Example 1, the current density was increased by 5 times from 0.1C, that is, charged and discharged at 0.5C to evaluate the life characteristics.

[0184]

Table 3

[0185]

[0186] Referring to Table 2, it can be confirmed that in Example 1, the thickness of the primary particles, FWHM(110), grain size and other physical properties were appropriately adjusted, and its capacity, output and life characteristics were all very excellent. On the contrary, in Comparative Examples 1 and 2, the thickness of the primary particles was too thick, FWHM(110) was too large, and the grain size was too small, resulting in a decrease in capacity, output and life characteristics.

[0187] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the specification and the drawings, and these modifications also fall within the scope of the present invention.

[0188] Therefore, the scope of the substantial rights of the present invention is defined by the claims and their equivalents.

Claims

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

2. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the positive electrode active material for an all-solid-state battery contains primary particles located on the surface of the secondary particles and having a major axis oriented in the horizontal direction of the secondary particle surface.

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

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

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

05.

7. 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 (003) plane to the diffraction peak intensity of the (104) plane is 1.19 to 1.

25.

8. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the following formula 1 is satisfied: <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) plane, (102) plane, and (101) plane 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 O2 In the 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, where 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] Lix2Ay2Oz2 In the chemical formula 2, 0 ≤ x2 ≤ 3, 0 < y2 ≤ 2, 0 < z2 ≤ 4, and A is Zr, Nb, Ti, or a combination thereof.

11. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the lithium ion conductive oxide is Li2ZrO3, ZrO2, LiNbO3, Nb2O3, Li2TiO3, TiO2, or a combination thereof.

12. The positive electrode active material of the all-solid-state battery according to claim 1, wherein, Based on the total weight of the positive electrode active material, the content of the coating is 0.5% by weight to 1.5% by weight.

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

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

15. A method for preparing a positive electrode active material of an all-solid-state battery, comprising: A step of preparing a transition metal hydroxide, the transition metal hydroxide containing nickel, being secondary particles formed by aggregation of primary particles, wherein the primary particles have a plate-like or needle-like morphology and an average thickness of 50 nm or less; A step of forming a mixture containing the transition metal hydroxide and a lithium raw material substance; A step of firing the mixture to form a lithium transition metal oxide; and A step of forming a coating containing a lithium ion conductive oxide on the surface of the lithium transition metal oxide.

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

05.

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

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

19. A positive electrode comprising the positive electrode active material of the 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 between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode active material of the all-solid-state battery according to any one of claims 1 to 14.

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