Bimodal cathode active material, method of making the same, and all-solid-state battery comprising the same

Abstract

An embodiment of the present invention provides a bimodal cathode active material comprising a first lithium metal oxide and a second lithium metal oxide, wherein the average particle size (D) of the first lithium metal oxide is... 50 The average particle size (D) of the second lithium metal oxide is greater than that of the second lithium metal oxide. 50 The first lithium metal oxide comprises a first coating applied to all or part of its surface, and the second lithium metal oxide comprises a second coating applied to all or part of its surface. The first and second coatings contain a Zr-containing compound, an Nb-containing compound, or a combination thereof, wherein the Zr-containing compound is of chemical formula 1, and the Nb-containing compound is of chemical formula 2. [Chemical Formula 1] Li x Zr y O z [Chemical Formula 2] Li a Nb b O c In the chemical formula 1, 0

Description

Technical Field

[0001] This invention relates to a bimodal cathode active material, its preparation method, and an all-solid-state battery containing it, specifically to a bimodal cathode active material comprising medium and small particle sizes, its preparation method, and an all-solid-state battery containing it. Background Technology

[0002] Today, rechargeable batteries are widely used in everything from large equipment such as automobiles and energy storage systems to small devices like mobile phones and laptops. As the application areas of rechargeable batteries expand, the demand for improved battery safety and high performance is growing.

[0003] Among secondary batteries, lithium-ion batteries have advantages over nickel-manganese or nickel-cadmium batteries, including higher energy density and larger capacity per unit area. However, because the electrolytes used in lithium-ion batteries are mostly liquid electrolytes such as organic solvents, safety issues arise, such as electrolyte leakage and the resulting fire risk.

[0004] Therefore, research on all-solid-state batteries is actively underway as a material to improve the safety and energy density of conventional secondary batteries. All-solid-state batteries replace the liquid electrolyte used in conventional lithium-ion secondary batteries with a solid electrolyte. Because flammable solvents are not used in the battery, fires or explosions caused by the decomposition reactions of conventional electrolytes are avoided, thus improving battery safety.

[0005] For this reason, LiCoO2 cathode active material was widely used in the past, but recently, research and development has been carried out on high-nickel-based lithium nickel cobalt manganese oxide as a material, which can achieve high capacity and has excellent price competitiveness.

[0006] In addition, in order to achieve high energy density, research and development is underway on so-called bimodal cathode active materials, which can improve compaction density by mixing small- and large-particle-size cathode active materials.

[0007] However, high-nickel-based lithium metal oxides are inherently weak in particle strength and have low structural stability. Therefore, when the electrode is subjected to strong compaction in order to further improve the compaction density of the bimodal cathode active material, there is a problem of capacity characteristics decreasing due to the collapse of the surface structure of the cathode active material.

[0008] Therefore, in order to improve the energy density of bimodal cathode active materials, efforts are needed to address the problem of decreased capacity characteristics caused by increasing volumetric energy density. Summary of the Invention

[0009] (a) Technical problems to be solved An object of the present invention is to provide a all-solid-state battery that uses a bimodal lithium metal oxide containing a high content of nickel, that is, a bimodal positive electrode active material coated with zirconium or niobium on its surface, so as to improve the volumetric energy density while maintaining the capacity.

[0010] (II) Technical solution An embodiment of the present invention provides a bimodal positive electrode active material, which includes a first lithium metal oxide and a second lithium metal oxide. The average particle size (D 50 ) of the first lithium metal oxide is greater than the average particle size (D 50 ) of the second lithium metal oxide. The first lithium metal oxide includes a first coating coated on all or part of its surface, and the second lithium metal oxide includes a second coating coated on all or part of its surface. The first coating and the second coating contain a Zr-containing compound, a Nb-containing compound or a combination thereof. The Zr-containing compound is represented by the following Chemical Formula 1, and the Nb-containing compound is represented by the following Chemical Formula 2.

[0011] [Chemical Formula 1] Li x Zr y O z [Chemical Formula ²] Li a Nb b O [[ID= 28]] c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4.

[0012] The electronic conductivity of the bimodal positive electrode active material can be 10~50 mS / cm.

[0013] The average particle size (D 50 ) of the first lithium metal oxide can be 7.0~8.0 µm, and the average particle size (D 50 ) of the second lithium metal oxide can be 4.0~5.0 µm.

[0014] The weight ratio of the first lithium metal oxide to the second lithium metal oxide can be 90:10~60:40.

[0015] Based on the total weight of the first lithium metal oxide, the content of the coating element of the first coating can be 0.1~3.0 wt%.

[0016] Based on the total weight of the second lithium metal oxide, the content of the coating element of the second coating can be 0.1~3.0 wt%.

[0017] The thickness of the first coating may be 5 to 50 nm.

[0018] The thickness of the second coating may be 5 to 50 nm.

[0019] Based on the total molar number of metals other than lithium, the nickel content in the first lithium metal oxide and the second lithium metal oxide may be 80 to 90 mol%.

[0020] The particle density of the bimodal positive electrode active material may be 3.0 to 3.7 g / cm 3 .

[0021] Another embodiment of the present invention provides a method for preparing a bimodal positive electrode active material, which includes the following steps: preparing a first metal hydroxide and a second metal hydroxide; forming a mixture containing the first metal hydroxide or the second metal hydroxide and a lithium raw material; firing the mixture to form a first lithium metal oxide or the second lithium metal oxide; forming a first coating containing a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the first lithium metal oxide; and forming a second coating containing a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the second lithium metal oxide, wherein the Zr-containing compound contains the following Chemical Formula 1, the Nb-containing compound contains the following Chemical Formula 2, and the average particle size (D 50 ) of the first lithium metal oxide is greater than the average particle size (D 50 ) of the second lithium metal oxide.

[0022] [Chemical Formula 1] Li x Zr y O z [Chemical Formula 2] Li a Nb b O c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4.

[0023] Another embodiment of the present invention provides a positive electrode including a bimodal positive electrode active material for an all-solid-state battery. <00​​​​​One embodiment of the present invention provides a bimodal cathode active material comprising medium- and small-particle-size lithium metal oxides containing a high nickel content, and improving stability by coating the surface of the cathode active material with Zr or Nb, thereby increasing the volumetric energy density while maintaining the capacity of an all-solid-state battery. Best practice

[0026] The terms "first," "second," and "third," etc., are used to describe various parts, components, regions, layers, and / or segments, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or segment from another. Therefore, the first part, component, region, layer, or segment described below may be referred to as the second part, component, region, layer, or segment without departing from the scope of the invention.

[0027] The technical terms used herein are for reference only to specific embodiments and are not intended to limit the invention. The singular forms used herein include the plural forms unless the context clearly indicates otherwise. As used in this specification, "comprising" means to embody a particular feature, region, integer, step, action, element, and / or component, and does not exclude the presence or addition of other features, regions, integers, steps, actions, elements, and / or components.

[0028] When one part is mentioned as being "above" or "on top of" another part, it can be directly above or on top of the other part, or it may be accompanied by other parts in between. Conversely, when one part is mentioned as being "directly above" another part, there are no other parts in between.

[0029] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries are further interpreted as having meanings consistent with relevant technical literature and current disclosure, and are not to be construed as having ideal or overly formal meanings unless otherwise defined.

[0030] In addition, unless otherwise stated, “%” means weight %, 1 ppm is 0.0001 weight.

[0031] In this specification, the term "combination of them" as described in the Markush form means a mixture or combination of one or more of the constituent elements described in the Markush form, indicating that it includes one or more of the constituent elements.

[0032] Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0033] 1. Bimodal cathode active material The bimodal cathode active material according to an embodiment of the present invention includes a first lithium metal oxide and a second lithium metal oxide. The average particle size (D 50 ) of the first lithium metal oxide is greater than the average particle size (D 50 ) of the second lithium metal oxide. The first lithium metal oxide includes a first coating coated on all or part of its surface. The second lithium metal oxide includes a second coating coated on all or part of its surface. The first coating and the second coating include a Zr-containing compound, a Nb-containing compound, or a combination thereof. The Zr-containing compound is represented by the following Chemical Formula 1, and the Nb-containing compound is represented by the following Chemical Formula 2.

[0034] [Chemical Formula 1] Li x Zr y O z [Chemical Formula 2] Li a Nb b O c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4. <0000 186>The Zr-containing compound may be Chemical Formula 1 above, and the Nb-containing compound may be Chemical Formula 2 above, but is not limited thereto. As long as it is an element that can coat all or part of the surface of the first lithium metal oxide or the second metal oxide, it is acceptable.

[0036] In a bimodal cathode active material according to an embodiment of the present invention, the electronic conductivity of the bimodal cathode active material can be 10~50 mS / cm, specifically 20~40 mS / cm. When the electronic conductivity of the bimodal cathode active material meets the specified range, the first lithium metal oxide and the second lithium metal oxide can be uniformly mixed, resulting in increased conductivity compared to using lithium metal oxide alone, thereby improving the electrochemical characteristics of the lithium secondary battery. Conversely, when the electronic conductivity of the bimodal cathode active material is below 10 mS / cm, the two cathode active materials, the first lithium metal oxide and the second lithium metal oxide, may exhibit non-uniform contact, potentially leading to a decrease in the discharge capacity of the cathode active material in the electrode. This phenomenon is particularly pronounced under conditions of high current density, i.e., a large C-rate. Furthermore, when the electronic conductivity of the bimodal cathode active material exceeds 50 mS / cm, although the electronic conductivity increases, the insufficient contact interface between the first and second lithium metal oxides and the solid electrolyte leads to uneven ion transport between the cathode active material and the solid electrolyte. This may result in a decrease in the discharge capacity of the cathode active material and a potential decline in thermal stability. This phenomenon is particularly pronounced under conditions of high current density, i.e., a large C-rate.

[0037] In a bimodal cathode active material according to an embodiment of the present invention, the average particle size (D) of the first lithium metal oxide is... 50 The average particle size (D) of the second lithium metal oxide can be 7.0~8.0µm, specifically 7.3~8.0µm; 50 The average particle size (D) of the first lithium metal oxide can be 4.0~5.0µm, specifically 4.3~5.0µm. 50 When the specified range is met, the compound exhibits excellent density and surface stability, thereby improving volumetric energy density while maintaining the capacity of the all-solid-state battery. Conversely, when the average particle size (D) of the first lithium metal oxide is within the specified range... 50 When the average particle size (D) of the first lithium metal oxide is less than 7.0 µm, the density of the compound decreases, the specific surface area increases, leading to increased surface reactivity and decreased high-voltage stability, which may shorten battery life. Furthermore, when the average particle size (D) of the first lithium metal oxide is less than 7.0 µm, the density of the compound decreases, the specific surface area increases, leading to increased surface reactivity and decreased high-voltage stability, which may shorten battery life. 50 When the particle size exceeds 8.0 µm, the time required for Li ion diffusion becomes longer, which may lead to a decrease in high capacity and high output characteristics, and the characteristic degradation caused by particle size may become significant.

[0038] When the average particle size of the second lithium metal oxide meets the aforementioned range, the volumetric energy density can be increased while maintaining the all-solid-state battery capacity. Conversely, when the average particle size of the second lithium metal oxide is less than 4.0 µm, the particles are too small, making processing difficult and leading to decreased process efficiency. Furthermore, it may be necessary to increase the content of conductive carbon when constructing the electrode. In this case, carbon particles may hinder the contact between the solid electrolyte and the positive electrode active material, and the carbon may undergo side reactions with the solid electrolyte material, potentially reducing the electrode energy density. Additionally, when the average particle size of the second lithium metal oxide exceeds 5.0 µm, the particles are too large, making it difficult for small particles to be effectively positioned within the space between medium particles. This may lead to a decrease in the electrolyte density, and the larger the secondary particle size of the small particles, the more likely it is to hinder high output characteristics.

[0039] The weight ratio of the first lithium metal oxide to the second lithium metal oxide can be from 90:10 to 60:40, specifically within the range of 80:20 to 70:30. When the weight ratio of the first lithium metal oxide to the second lithium metal oxide meets this range, the final filling density of the cathode active material can be increased, thereby increasing the volumetric capacity. Conversely, when the weight of the small-diameter particles of the second lithium metal oxide exceeds approximately 30% of the total weight of the medium-diameter particles of the first lithium metal oxide and the small-diameter particles of the second lithium metal oxide, the volume of the small-diameter particles becomes larger than the space between the medium-diameter particles, thus reducing the relative filling density of the electrode and potentially leading to a decrease in volumetric energy density. Furthermore, when the weight of the small-diameter particles of the second lithium metal oxide is less than approximately 10% of the total weight of the medium-diameter particles of the first lithium metal oxide and the small-diameter particles of the second lithium metal oxide, the deviation between the occupancy rates of the medium-diameter particles of the first lithium metal oxide and the small-diameter particles of the second lithium metal oxide becomes significant, thus potentially limiting the improvement in the electrochemical characteristics and stability of the bimodal cathode active material.

[0040] In a bimodal positive electrode active material according to an embodiment of the present invention, the content of coating elements in the first coating can be 0.1~3.0 wt%, specifically 0.3~2.0 wt%, based on the total weight of the first lithium metal oxide. When the content of coating elements in the first coating meets the range specified in the description, the structural stability of the first lithium metal oxide can be improved. Furthermore, when the positive electrode active material is used in a lithium secondary battery, its high-temperature storage stability and lifespan characteristics can be improved. In addition, while reducing residual lithium on the surface of the first lithium metal oxide, it also acts as a pathway for lithium ions, thereby affecting the improvement of the efficiency characteristics of the lithium secondary battery. Conversely, when the content of coating elements in the first coating is less than 0.1 wt%, it is impossible to coat all or part of the surface of the first lithium metal oxide, which may lead to a decrease in the stability and lifespan characteristics of the positive electrode active material. Furthermore, when the coating element content of the first coating exceeds 3.0 wt% based on the total weight of the first lithium metal oxide, the coating on all or part of the surface of the first lithium metal oxide becomes thicker, resulting in an increase in the resistance of the positive electrode active material, which may make it difficult to achieve the charge and discharge capacity of the positive electrode active material.

[0041] In a bimodal positive electrode active material according to an embodiment of the present invention, the content of coating elements in the second coating can be 0.2~3.0 wt%, specifically 0.3~2.0 wt%, based on the total weight of the second lithium metal oxide. When the content of coating elements in the second coating meets the range based on the total weight of the second lithium metal oxide, the structural stability of the second lithium metal oxide can be improved, and when the positive electrode active material is used in a lithium secondary battery, the high-temperature storage stability and lifespan characteristics of the positive electrode active material can be improved. Conversely, when the content of coating elements in the second coating is less than 0.2 wt%, based on the total weight of the second lithium metal oxide, it is impossible to coat all or part of the surface of the second lithium metal oxide, which may lead to a decrease in the stability and lifespan characteristics of the positive electrode active material. Furthermore, when the content of coating elements in the second coating exceeds 3.0 wt%, based on the total weight of the second lithium metal oxide, the coating element substances remaining after coating all or part of the surface of the second lithium metal oxide act as impurities, which may lead to a decrease in the efficiency characteristics of the lithium secondary battery.

[0042] In a bimodal cathode active material according to an embodiment of the present invention, the thickness of the first coating can be 5-50 nm, specifically 5-20 nm. When the thickness of the first coating meets the specified range, the structural stability of the first lithium metal oxide is improved, thereby resulting in excellent electrochemical properties. Conversely, when the thickness of the first coating is less than 5 nm, the electrochemical properties and stability of the first lithium metal oxide may decrease. Furthermore, when the thickness of the first coating exceeds 50 nm, the occupancy of the first coating on the surface of the first lithium metal oxide becomes excessive, leading to a difference between the resistance of the cathode active material and the surface properties of the first lithium metal oxide, which may reduce the electrochemical properties and stability of the cathode active material.

[0043] In a bimodal cathode active material according to an embodiment of the present invention, the thickness of the second coating can be 5-50 nm, specifically 10-20 nm. When the thickness of the second coating meets the specified range, the structural stability of the second lithium metal oxide is improved, thereby resulting in excellent electrochemical properties. Conversely, when the thickness of the second coating is less than 5 nm, the electrochemical properties and stability of the first lithium metal oxide may decrease. Furthermore, when the thickness of the second coating exceeds 50 nm, the occupancy of the second coating on the surface of the second lithium metal oxide becomes excessive, leading to differences in the surface properties of the second lithium metal oxide, which may reduce the electrochemical properties and stability of the cathode active material.

[0044] In a bimodal cathode active material according to an embodiment of the present invention, the nickel content in the first lithium metal oxide and the second lithium metal oxide can be 80-90 mol%, based on the total molar number of metals other than lithium. When the nickel content meets the specified range, the energy density of the battery is increased, thereby enabling the manufacture of electric vehicles with increased driving range and higher power on a single charge. Furthermore, nickel has high energy density, the advantage of instantaneous release of strong energy, and is price-competitive with other metals.

[0045] In one embodiment of the bimodal cathode active material of the present invention, the particle density of the bimodal cathode active material can be 3.0~3.7 g / cm³. 3 Specifically, it can be 3.5~3.6 g / cm³. 3 When the particle density of the bimodal cathode active material meets the specified range, it has the advantage of increased energy density per unit volume. Conversely, when the particle density of the bimodal cathode active material is less than 3.0 g / cm³, it exhibits the advantage of increased energy density per unit volume. 3 At this point, the energy density per unit volume may be low. Furthermore, when the particle density exceeds 3.7 g / cm³... 3 When the absolute amount of the contact interface between the positive electrode active material and the solid electrolyte decreases, it may lead to an increase in resistance and a decrease in discharge capacity.

[0046] 2. Preparation Method of Bimodal Cathode Active Material The preparation method of the bimodal cathode active material according to another embodiment of the present invention includes: the step of preparing a first metal hydroxide and a second metal hydroxide; the step of forming a mixture containing the first metal hydroxide or the second metal hydroxide and a lithium raw material; the step of firing the mixture to form a first lithium metal oxide or the second lithium metal oxide; the step of forming a first coating including a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the first lithium metal oxide; and the step of forming a second coating including a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the second lithium metal oxide, wherein the Zr-containing compound contains the following Chemical Formula 1, the Nb-containing compound contains the following Chemical Formula 2, and the average particle size (D 50 ) of the first lithium metal oxide is greater than the average particle size (D 50 ) of the second lithium metal oxide.

[0047] [Chemical Formula 1] Li x Zr y O z [Chemical Formula 2] Li a Nb b O c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4.

[0048] Next, the preparation method of the bimodal cathode active material according to another embodiment of the present invention will be described in detail step by step.

[0049] First, in the step of preparing a first metal hydroxide and a second metal hydroxide, the first metal hydroxide and the second metal hydroxide are precursors of the cathode active material. The precursor of the cathode active material may be secondary particles formed by the aggregation of primary particles.

[0050] The transition metal hydroxide can be prepared, for example, by adding an ammonia solution and a caustic soda solution to a transition metal-containing solution and performing a coprecipitation reaction. Among them, the transition metal-containing solution contains: a nickel raw material substance, a cobalt raw material substance, a manganese raw material substance, and a doping raw material substance including Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo or a combination thereof.

[0051] The nickel raw material is not particularly limited as long as it is a substance used in the preparation of precursors for positive electrode active materials in this field. For example, the nickel raw material can be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or hydroxyoxide, etc. Specifically, it can be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel salts of fatty acids, nickel halides, or combinations thereof, but is not limited to these.

[0052] There are no particular limitations on the cobalt raw material as long as it is used in the art to prepare a precursor for positive electrode active materials. For example, the cobalt raw material can be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or hydroxyoxide, etc. Specifically, it can be CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof, but is not limited thereto.

[0053] There are no particular limitations on the manganese raw material as long as it is used in the art to prepare a precursor for positive electrode active materials. For example, the manganese raw material can be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, hydroxy oxide, or a combination thereof. Specifically, it can be a manganese salt (such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese salts of fatty acids), manganese oxide (such as Mn2O3, MnO2, and Mn3O4), hydroxy oxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0054] The transition metal-containing solution can be prepared by adding the raw material to a solvent (specifically, water or a mixture of organic solvents (e.g., alcohols) that are homogeneous with water), or by mixing an aqueous solution containing the raw material.

[0055] The ammonia solution is a complex forming agent, and may contain, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof, but is not limited thereto. Alternatively, the ammonia solution may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent (specifically an alcohol, etc.) that is homogeneous with water can be used as the solvent.

[0056] The caustic soda solution is a precipitant or pH adjuster and may contain alkali metal or alkaline earth metal hydroxides (such as NaOH, KOH, or Ca(OH)2), their hydrates, or combinations thereof as basic compounds. The caustic soda solution can also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent (specifically alcohols, etc.) that is homogeneous with water can be used as the solvent.

[0057] The coprecipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon.

[0058] Next, a mixture comprising the first metal hydroxide or the second metal hydroxide and a lithium feedstock can be formed.

[0059] The lithium raw material can be any lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or hydroxyoxide, as long as it is soluble in water, there are no particular restrictions. Specifically, the lithium raw material can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, Li₃C₆H₅O₇ or a combination thereof, but is not limited to these.

[0060] The mixture may further include doped material containing Al, Mg, Ti, Nb, W, Sc, Zr, Si, V, Fe, Y, Mo or a combination thereof.

[0061] Next, the mixture can be calcined to form a first lithium metal oxide or a second lithium metal oxide.

[0062] The average particle size (D) of the first lithium metal oxide 50 The average particle size (D) of the second lithium metal oxide can be 7.0~8.0µm, specifically 7.3~8.0µm; 50 The average particle size (D) of the positive electrode active material within the target range can be 4.0~5.0µm, specifically 4.3~5.0µm. Therefore, the average particle size (D) of the positive electrode active material within the target range can be easily obtained. 50 ).

[0063] At this point, the firing can be carried out at a maximum temperature of 700~800°C. When the firing temperature meets this range, it has the advantage of ensuring optimal grain size.

[0064] The firing can be carried out in an oxygen atmosphere.

[0065] The maximum temperature holding time for the firing process can be 3 to 24 hours, more specifically, 5 to 15 hours.

[0066] Next, the process may include forming a first coating containing a Zr-containing compound, an Nb-containing compound, or a combination thereof on all or part of the surface of the first lithium metal oxide; and forming a second coating containing a Zr-containing compound, an Nb-containing compound, or a combination thereof on all or part of the surface of the second lithium metal oxide. The Zr and Nb compounds are described above, and therefore detailed descriptions are omitted.

[0067] On the other hand, there are no particular limitations on the coating formation method. For example, it can be formed by spraying a coating solution containing coating raw materials onto the surface of a first lithium metal oxide or a second lithium metal oxide, followed by heat treatment and drying, but it is not limited thereto, and any methods available in the art can be used without limitation.

[0068] 3. All-solid-state battery Another embodiment of the present invention provides a cathode comprising the above-described bimodal cathode active material for all-solid-state batteries.

[0069] 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. The positive electrode active material layer may include the aforementioned positive electrode active material for all-solid-state batteries, a sulfide-based solid electrolyte, and a conductive material. Furthermore, the positive electrode active material layer may further include a binder.

[0070] At this time, the sulfide-based solid electrolyte may be, for example, a sulfide-based solid electrolyte with a sulfide-germanium ore-type crystal structure.

[0071] The sulfide-based solid electrolyte with a sulfide-germanium sulfide crystal structure can be, for example, Li6PS5Cl, Li6PS5Br, Li6PS5I or a combination thereof, but is not limited thereto.

[0072] At least a portion of the crystal structure of the sulfide-based solid electrolyte having a sulfide-germanium ore-type crystal structure can be doped with doping elements.

[0073] The conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon nanofibers, carbon nanotubes, or combinations thereof.

[0074] The adhesive may be, for example, polyvinylidene fluoride, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, or a combination thereof.

[0075] In addition to the aforementioned positive electrode active material, solid electrolyte, binder, and conductive material, the positive electrode active material layer may further include additives such as filler, coating agent, dispersant, and ion conduction aid.

[0076] 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 between the positive electrode and the negative electrode, wherein the positive electrode comprises the above-described positive electrode active material for an all-solid-state battery.

[0077] The description of the positive electrode is as previously stated, and therefore omitted.

[0078] The solid electrolyte layer may contain a sulfide-based solid electrolyte.

[0079] The sulfide-based solid electrolyte may, for example, contain components selected from Li. 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6- x Br x (0≤x≤2) and Li 7-x PS 6-x I x The electrolyte may contain one or more Argyrodite-type compounds selected from (0 ≤ x ≤ 2). Specifically, the sulfide-based solid electrolyte may contain one or more Argyrodite-type compounds selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I. However, it is not limited to these compounds.

[0080] At least a portion of the crystal structure of the sulfide-based solid electrolyte of the above-mentioned silver-germanium ore type compound can be doped with doping elements.

[0081] The solid electrolyte layer may further include an adhesive. The adhesive included in the solid electrolyte layer may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these; any adhesive used in this technical field is acceptable. The adhesive of the solid electrolyte layer may be the same as or different from the adhesives included in the positive electrode active material layer and the negative electrode active material layer.

[0082] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer may contain a negative electrode active material.

[0083] The negative electrode active material includes materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping and dedoping lithium, or transition metal oxides.

[0084] As a material capable of reversibly embedding / desorbing lithium ions, carbon materials can be used, and any carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used. As representative examples, crystalline carbon, amorphous carbon, or they can be used simultaneously can be used. Examples of the crystalline carbon can include graphite (such as natural graphite or artificial graphite in amorphous, flaky, scaly (flake), spherical or fibrous form), and examples of the amorphous carbon can include soft carbon (soft carbon: low-temperature fired carbon), hard carbon, mesophase pitch carbide, fired coke, etc.

[0085] As an 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.

[0086] As a material capable of doping and undoping lithium, Si, SiO x (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 listed, and 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 combinations thereof.

[0087] Examples of the transition metal oxide can include vanadium oxide, lithium vanadium oxide, etc.

[0088] [[ID=1,4]]The negative electrode active material layer may further contain a binder and may selectively further contain a conductive material.

[0089] The binder serves to adhere the negative electrode active material particles to each other well and to adhere the negative electrode active material well to the current collector. As representative examples, 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. can be used, but are not limited thereto.

[0090] The conductive material is used to impart conductivity to the electrodes. In the constructed battery, any electronically conductive material that does not cause chemical changes can be used. Examples of such materials include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.); metallic materials (such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.); conductive polymer materials (such as polyphenylene derivatives, etc.); or conductive materials containing mixtures thereof.

[0091] As the current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof can be used. Detailed Implementation

[0092] The following embodiments describe implementation examples of the present invention in more detail. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0093] Example 1: Preparation method of bimodal positive electrode active material (1) Preparation method of medium particle size Average particle size (D) 50 Ni with a thickness of 6~7µm 0.83 Co 0.12 Mn 0.05 (OH)₂ metal hydroxide precursor and LiOH∙H₂O, a lithium feedstock, are mixed at a molar ratio of 1:1.05 to form a mixture. 1 kg of the mixture is charged into a tube furnace and heated at a rate of 2.5 °C / min. The calcination temperature is 750 °C, held for 10 hours, and then cooled at a rate of 2.5 °C / min. During calcination, pure O₂ is supplied to maintain the O₂ concentration above 99%, thereby forming an average particle size (D). 50 The first lithium metal oxide, LiNi, has a thickness of 7~8µm. 0.83 Co 0.12 Mn 0.05 O2.

[0094] For the first coating applied to all or part of the surface of the first lithium metal oxide, the first lithium metal oxide is dissolved in dehydrated ethanol, and then zirconium(IV) tetrapropoxide (dissolved in 1-propanol at a concentration of 70 wt%) is added in a molar ratio of first lithium metal oxide to zirconium ions = 2:1. The mixture is stirred to prepare a coating solution containing lithium ions and zirconium ions. At this point, the concentration of zirconium ions in the coating solution is 0.1 mol / L.

[0095] The coating process was performed using a flow coating apparatus (MP-01, POWREX) to spray 400 mL of the first coating solution onto 1 kg of the formed first lithium metal oxide. The operating conditions of the flow coating apparatus were: inlet gas (nitrogen), inlet gas temperature (80°C), and inlet air volume (0.3 m³ / s). 3 The spraying time was 40 minutes, with a rotation speed of 400 rpm and a coating solution spraying rate of 10 mL / min. The lithium transition metal oxide coated with the first coating solution was then placed in a saggar and heat-treated at 300°C in a box furnace while oxygen was supplied, thereby preparing a positive electrode active material with an amorphous Li2ZrO3 coating on the surface of the lithium transition metal oxide.

[0096] (2) Preparation method of small particle size Ni with an average particle size of 4µm 0.83 Co 0.12 Mn 0.05 (OH)₂ transition metal hydroxide precursor and LiOH∙H₂O, a lithium feedstock, are mixed at a molar ratio of 1:1.05 to form a mixture. 1 kg of the mixture is charged into a tube furnace and heated at a rate of 2.5 °C / min. The calcination temperature is 750 °C, held for 10 hours, and then cooled at a rate of 2.5 °C / min. During calcination, pure O₂ is supplied to maintain an O₂ concentration above 99%, thereby forming an average particle size (D). 50 The second lithium transition metal oxide, LiNi, has a thickness of 5 µm. 0.83 Co 0.12 Mn 0.05 O2.

[0097] For the first coating applied to all or part of the surface of the second lithium metal oxide, the second lithium metal oxide is dissolved in dehydrated ethanol, and then an amount of zirconium(IV) tetrapropoxide (dissolved in 1-propanol at a concentration of 70 wt%) is added at a molar ratio of second lithium metal oxide to zirconium ions = 2:1. The mixture is stirred to prepare a coating solution containing lithium ions and zirconium ions. At this point, the concentration of zirconium ions in the coating solution is 0.1 mol / L.

[0098] The coating process was performed using a flow coating apparatus (MP-01, POWREX) to spray 400 mL of the second coating solution onto 1 kg of the formed second lithium metal oxide. The operating conditions of the flow coating apparatus were: inlet gas (nitrogen), inlet gas temperature (80°C), and inlet air volume (0.3 m³ / s). 3The spraying time was 40 minutes, with a rotation speed of 400 rpm and a coating solution spraying rate of 10 mL / min. The lithium transition metal oxide coated with the second coating solution was then placed in a saggar and heat-treated at 300°C in a box furnace while oxygen was supplied, thereby preparing a positive electrode active material with an amorphous Li2ZrO3 coating on the surface of the lithium transition metal oxide.

[0099] (3) Preparation method of bimodal positive electrode active material Using a mixer, 70% by weight (wt%) of the first lithium transition metal oxide LiNi, which has a first coating layer, is applied to all or part of the surface. 0.83 Co 0.12 Mn 0.05 O2 and 30 wt% of the second lithium transition metal oxide LiNi, the surface of which is wholly or partially coated with a second coating. 0.83 Co 0.12 Mn 0.05 O2 was mixed for 30 minutes to prepare a bimodal cathode material.

[0100] (4) Preparation method of all-solid-state battery The prepared bimodal positive electrode active material (75 wt%), the silver-germanium sulfide solid electrolyte (Li6PS5Cl) (22 wt%), and Super C as a conductive material (3 wt%) were used. 65 A slurry was prepared by thoroughly mixing the slurry with a solvent containing a small amount of binder. Electrode plates were then prepared using the slurry and dried to create a composite electrode plate for the positive electrode. In a fixture used for all-solid-state battery evaluation, 100 mg of a silver-germanium sulfide solid electrolyte (Li6PS5Cl) acting as a separator was first loaded and pressurized to over 300 MPa to achieve a thickness of approximately 800 µm. A positive electrode plate was then placed on one side surface, and secondary pressurization was applied to create the positive electrode portion. Subsequently, a Li-In alloy was placed on the other side surface, and appropriate pressure was applied to create a battery for all-solid-state battery evaluation.

[0101] Comparative Example 1: Preparation Method of Positive Electrode Active Material (1) Preparation method of medium particle size Ni with an average particle size of 6~7µm 0.83 Co 0.12 Mn 0.05(OH)₂ metal hydroxide precursor and LiOH∙H₂O, a lithium feedstock, are mixed at a molar ratio of 1:1.05 to form a mixture. 1 kg of the mixture is charged into a tube furnace and heated at a rate of 2.5 °C / min. The calcination temperature is 750 °C, held for 10 hours, and then cooled at a rate of 2.5 °C / min. During calcination, pure O₂ is supplied to maintain the O₂ concentration above 99%, thereby forming an average particle size (D). 50 The first lithium metal oxide, LiNi, has a thickness of 7~8µm. 0.83 Co 0.12 Mn 0.05 The coating of the first lithium metal oxide with O2 was carried out in the same manner as in Example 1.

[0102] (2) Preparation method of small particle size Ni with an average particle size of 4µm 0.83 Co 0.12 Mn 0.05 The (OH)2 metal hydroxide precursor is mixed with LiOH∙H2O, which is used as a lithium raw material, at a molar ratio of 1:1.05 to form a mixture.

[0103] 1 kg of the mixture was charged into a tube furnace and heated at a rate of 2.5 °C / min. The firing temperature was 750 °C, held for 10 hours, and then cooled at a rate of 2.5 °C / min. During firing, pure O2 was supplied to maintain the O2 concentration above 99%, thereby forming an average particle size (D... 50 The second lithium metal oxide, LiNi, has a thickness of 5µm. 0.83 Co 0.12 Mn 0.05 The coating of O2 and the second lithium metal oxide was carried out in the same manner as in Example 1.

[0104] Experimental Example 1: Particle Size Evaluation of Bimodal Cathode Active Materials The average particle size (D) of the positive electrode active material used in the examples and comparative examples 50 After dispersing the positive electrode active material powder in distilled water, the dispersion state was maintained well by using an ultrasonic vibrator built into the particle size analyzer. Under this state, the particle size was analyzed using a Horiba LA-960V2 particle size analyzer.

[0105] Experimental Example 2: Evaluation of the Electrochemical Characteristics of All-Solid-State Batteries (1) Evaluation of initial capacity and initial efficiency After fabricating the lithium-ion rechargeable battery half-cells, they were aged at 30°C for 4 hours, followed by charge-discharge tests at 30°C. For initial capacity evaluation, a standard capacity of 200 mAh / g was used, and the cells were charged at a constant current of 0.1C to 3.63V. Then, the voltage was switched to a constant voltage, and charging continued until the termination current reached 0.05C. After charging, a 10-minute resting period was allowed, followed by discharge at a constant current of 0.1C to 1.9V, again using a standard capacity of 200 mAh / g.

[0106] (2) Lifetime characteristics evaluation (30℃, 60 cycles) After fabricating the lithium-ion rechargeable battery half-cell, it was charged at 30°C with a constant current of 0.5C to 3.63V, then switched to a constant voltage and continued charging until the termination current reached 0.1C. After charging, it was allowed to rest for 10 minutes, and then discharged at a constant current of 0.5C to 1.9V. Thirty charge-discharge cycles were performed under these conditions, and the capacity retention rate of the 30th cycle relative to the first cycle was calculated.

[0107] [Table 1] As shown in Table 1, the initial capacity of the bimodal cathode active material of Example 1 is better than that of the medium-sized initial capacity of Comparative Example 1, but there is no significant difference between it and the small-sized initial capacity of Comparative Example 2. However, the cycling performance (0.5C / 0.1C) results of Example 1, Comparative Example 1, and Comparative Example 2 show that the cycling performance of the bimodal cathode active material of Example 1 is better than that of Comparative Example 1 and Comparative Example 2.

[0108] The preferred embodiments of the present invention have been described above, but the present invention is not limited thereto. Various modifications can be made within the scope of the claims, specification and drawings, which undoubtedly also fall within the scope of the present invention.

[0109] Therefore, the substantive scope of the present invention will be defined by the claims and their equivalents.

Claims

1. A bimodal cathode active material comprising a first lithium metal oxide and a second lithium metal oxide, The average particle size D of the first lithium metal oxide 50 The average particle size D of the second lithium metal oxide is greater than that of the second lithium metal oxide. 50 , wherein the first lithium metal oxide comprises a first coating coated on all or part of its surface, the second lithium metal oxide comprises a second coating coated on all or part of its surface, the first coating and the second coating comprise a Zr-containing compound, a Nb-containing compound or a combination thereof, the Zr-containing compound is represented by Chemical Formula 1 below, and the Nb-containing compound is represented by Chemical Formula 2 below, [Chemical Formula 1] Li x Zr y About z [Chemical Formula 2] Li a No b O c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4.

2. The bimodal positive electrode active material according to claim 1, wherein, The electronic conductivity of the bimodal cathode active material is 10~50 mS / cm.

3. The bimodal positive electrode active material according to claim 1, wherein, The average particle size D of the first lithium metal oxide 50 The average particle size D of the second lithium metal oxide is 7.0~8.0µm. 50 The value is 4.0~5.0µm.

4. The bimodal positive electrode active material according to claim 1, wherein, The weight ratio of the first lithium metal oxide to the second lithium metal oxide is 90:10~60:

40.

5. The bimodal positive electrode active material according to claim 1, wherein, Based on the total weight of the first lithium metal oxide, the content of the coating elements of the first coating is 0.1~3.0 wt%.

6. The bimodal positive electrode active material according to claim 1, wherein, Based on the total weight of the second lithium metal oxide, the content of the coating elements of the second coating is 0.1~3.0 wt%.

7. The bimodal positive electrode active material according to claim 1, wherein, The thickness of the first coating is 5~50 nm.

8. The bimodal positive electrode active material according to claim 1, wherein, The thickness of the second coating is 5~50 nm.

9. The bimodal positive electrode active material according to claim 1, wherein, Based on the total molar number of metals other than lithium, the nickel content in the first lithium metal oxide and the second lithium metal oxide is 80~90 mol%.

10. The bimodal positive electrode active material according to claim 1, wherein, The particle density of the bimodal positive electrode active material is 3.0~3.7 g / cm³. 3 .

11. A method for preparing a bimodal cathode active material, comprising the following steps: Preparing a first metal hydroxide and a second metal hydroxide; Forming a mixture comprising the first metal hydroxide or the second metal hydroxide and a lithium raw material; Calcining the mixture to form the first lithium metal oxide or the second lithium metal oxide; Forming a first coating containing a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the first lithium metal oxide; And Forming a second coating containing a Zr-containing compound, a Nb-containing compound or a combination thereof on all or part of the surface of the second lithium metal oxide, wherein the Zr-containing compound comprises Chemical Formula 1 below, and the Nb-containing compound comprises Chemical Formula 2 below, The average particle size D of the first lithium metal oxide 50 The average particle size D of the second lithium metal oxide is greater than that of the second lithium metal oxide. 50 , [Chemical Formula 1] Li x Zr y About z [Chemical Formula 2] Li a No b O c In Chemical Formula 1, 0 < x ≤ 3, 0 < y ≤ 2, 0 < z ≤ 4; in Chemical Formula 2, 0 < a ≤ 3, 0 < b ≤ 2, 0 < c ≤ 4.

12. A cathode comprising the bimodal cathode active material according to any one of claims 1~10.

13. An all-solid-state battery, comprising: A cathode; an anode; and a solid electrolyte layer disposed between the cathode and the anode, wherein the cathode comprises the bimodal cathode active material according to any one of claims 1~10.

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