Positive electrode active material, method for preparing same, positive electrode including same, and all-solid-state battery

Abstract

A positive electrode active material according to one embodiment includes: a core including a lithium-transition metal composite oxide; a first coating layer formed on a surface of the core; and a second coating layer formed on a surface of the first coating layer, in which the first coating layer includes a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide included in the core, and the second coating layer includes a sulfur compound.

Description

Technical Field

[0001] This invention relates to a positive electrode active material, its preparation method, a positive electrode containing the material, and an all-solid-state battery. Background Technology

[0002] In recent years, due to environmental issues such as global warming, there has been increasing attention on environmentally friendly electric vehicles that can replace fossil fuel-based vehicles. Lithium-ion batteries, with their high energy density and advanced industrial technology, have become one of the leading energy sources in the current electric vehicle market. However, existing lithium-ion batteries using liquid electrolytes such as organic solvents have problems such as the risk of electrolyte leakage and fire upon impact, and the risk of battery expansion and explosion due to electrolyte chemical decomposition and gas generation. Therefore, to solve these technical problems, all-solid-state batteries using solid-state electrolytes have attracted much attention as a next-generation energy source, and active research and development are underway. Summary of the Invention

[0003] (a) Technical problems to be solved One aspect of the present invention is to provide a positive electrode active material that can improve the lifespan characteristics of a battery.

[0004] Another aspect of the present invention is to provide a high-capacity positive electrode active material.

[0005] Another aspect of the present invention is to provide a positive electrode active material with excellent resistivity.

[0006] Another aspect of the present invention is to provide an all-solid-state battery with excellent electrochemical performance.

[0007] Another aspect of the present invention is to provide an all-solid-state battery with excellent safety.

[0008] (II) Technical Solution According to one embodiment, the positive electrode active material comprises: a core comprising a lithium-transition metal complex oxide; a first coating formed on the surface of the core; and a second coating formed on the surface of the first coating, wherein the first coating comprises a lithium-transition metal complex oxide having a different structure from the lithium-transition metal complex oxide contained in the core, and the second coating comprises a sulfur compound.

[0009] The core may comprise a layered lithium-transition metal composite oxide.

[0010] The core may comprise a lithium-transition metal complex oxide according to the following chemical formula 1.

[0011] [Chemical Formula 1] Li a Ni b M c O2 In the aforementioned chemical formula 1, M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, 0.90 <a<1.5,0.33≤b≤1,0≤c≤0.7。

[0012] The first coating may comprise a spinel-structured lithium-transition metal composite oxide.

[0013] The first coating may further comprise at least one of a rock-salt structured lithium-transition metal composite oxide and a layered structured lithium-transition metal composite oxide.

[0014] The first coating may comprise a lithium-transition metal composite oxide according to the following chemical formula 2.

[0015] [Chemical Formula 2] Li x M y O z In the chemical formula 2, M is one or more elements selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, where 0 ≤ x ≤ 4, 0 ≤ y ≤ 4, and 0 ≤ z ≤ 8.

[0016] The thickness of the first coating can be from 0.1 nm to 500 nm.

[0017] The cation mixing ratio of the positive electrode active material can be below 7%.

[0018] The sulfur compound may contain one or more compounds according to the following chemical formula 3.

[0019] [Chemical Formula 3] Li x M y S z O f In the aforementioned chemical formula 3, M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 0≤x≤10, 0≤y≤10, 0 <z≤10,0≤f≤24。

[0020] The sulfur compound may include sulfur oxides.

[0021] Based on the total weight of the second coating, the content of sulfur oxides can be from 200 ppm to 8000 ppm.

[0022] The second coating may further contain one or more elements selected from P, B, Si, Al and W.

[0023] A method for preparing a positive electrode active material according to a specific embodiment is used to prepare the positive electrode active material described in any of the above specific embodiments.

[0024] The method for preparing the positive electrode active material may include: a base material preparation step, which involves performing a dry heat treatment process on a mixture containing a precursor of transition metal raw material and a lithium raw material to form a core; and a base material pretreatment step, which involves forming a precursor coating on the surface of the core.

[0025] The method for preparing the positive electrode active material may further include: a coating formation step, forming a first coating and a second coating.

[0026] In the coating formation step, the first coating can be formed by heat treatment of the core.

[0027] In the coating forming step, the second coating may be formed from a complex sulfate compound according to the following chemical formula 4.

[0028] [Chemical Formula 4] In the chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 1≤a≤5, 1≤b≤5.

[0029] In the coating formation step, the heat treatment process can be carried out in air at a temperature below 300°C and for a time of less than 20 hours.

[0030] The positive electrode according to one specific embodiment comprises the positive electrode active material described in any of the above specific embodiments.

[0031] An all-solid-state battery according to one specific embodiment includes a positive electrode as described in any of the above specific embodiments.

[0032] The all-solid-state battery may further include a sulfide-based solid electrolyte.

[0033] The sulfide-based solid electrolyte can be an Argyrodite-based solid electrolyte.

[0034] (III) Beneficial Effects According to one specific embodiment of the present invention, direct contact between the solid electrolyte and the positive electrode active material can be suppressed.

[0035] According to another specific embodiment of the present invention, the battery life performance can be improved.

[0036] According to another specific embodiment of the present invention, the smooth migration of lithium ions inside the battery can be induced.

[0037] According to another specific embodiment of the present invention, leakage current generated inside the battery can be reduced.

[0038] According to another specific embodiment of the present invention, a high-capacity positive electrode active material with excellent resistivity can be provided.

[0039] According to another specific embodiment of the present invention, an all-solid-state battery with excellent electrochemical performance can be provided.

[0040] According to another specific embodiment of the present invention, an all-solid-state battery with excellent safety can be provided. Attached Figure Description

[0041] Figure 1 It is a diagram that conceptually illustrates the morphology of a positive electrode active material according to a specific implementation.

[0042] Figure 2a and Figure 2b These are diagrams that conceptually illustrate, in turn, the preparation methods of the positive electrode active material according to a specific implementation scheme.

[0043] Figure 3a This is a graph showing the evaluation results of the formation charge-discharge capacity of batteries containing positive electrode active materials according to the embodiments and comparative examples.

[0044] Figure 3b This is a graph showing the evaluation results of the discharge capacity values ​​of batteries containing positive electrode active materials according to the embodiments and comparative examples, based on the number of cycles.

[0045] Figure 3c This is a graph showing the evaluation results of the discharge capacity retention rate of batteries containing positive electrode active materials according to the embodiments and comparative examples, based on the number of cycles.

[0046] Figure 4 This is a graph showing the evaluation results of the resistance characteristics of batteries containing positive electrode active materials according to the embodiments and comparative examples. Best practice

[0047] The preferred implementation form is described below with reference to various implementation schemes. However, the implementation form is not limited to the specific implementation scheme described below, but can be modified into various other forms.

[0048] In this specification, "base material" refers to the lithium-transition metal composite oxide corresponding to core 100, and is a substance obtained by mixing a precursor containing transition metal raw material and lithium raw material and calcining it, which may have substantially the same composition as core 100.

[0049] For the commercialization of all-solid-state batteries as a next-generation energy source, interfacial stability between the active material and the solid electrolyte is likely required. When the positive electrode active material is in direct contact with the solid electrolyte, a resistive layer may form due to interfacial diffusion of the constituent elements. Furthermore, as the battery cycles, the positive electrode active material repeatedly contracts and expands; cracks resulting from these volume changes may induce contact failure with the electrolyte, partial deactivation of the positive electrode active material, and other issues, potentially restricting lithium-ion migration pathways. This can induce performance degradation due to overvoltage. Therefore, to substantially overcome these problems, a suitable surface film for the positive electrode active material may be necessary to ensure interfacial stability.

[0050] According to one specific implementation, to address the aforementioned issues, a single coating of active material containing a spinel structure can be formed on the surface of the positive electrode active material. However, such a single coating may have limitations in controlling interfacial diffusion between the positive electrode active material and the solid electrolyte.

[0051] According to a specific embodiment, a high-capacity positive electrode active material can be provided. This positive electrode active material, through a multi-layer coating structure, suppresses direct contact between the solid electrolyte and the active material, interfacial diffusion of constituent elements, and side reactions, thereby improving battery life performance. Furthermore, by facilitating the smooth migration of lithium ions and reducing leakage current, the positive electrode active material exhibits excellent resistive properties. The following refers to… Figures 1 to 4 The specific details will be made public.

[0052] Figure 1 It is a diagram that conceptually illustrates the morphology of a positive electrode active material according to a specific implementation.

[0053] Figure 2a and Figure 2b These are diagrams that conceptually illustrate, in turn, the preparation methods of the positive electrode active material according to a specific implementation scheme.

[0054] Figure 3a This is a graph showing the evaluation results of the formation charge-discharge capacity of batteries containing positive electrode active materials according to the embodiments and comparative examples.

[0055] Figure 3b This is a graph showing the evaluation results of the discharge capacity values ​​of batteries containing positive electrode active materials according to the embodiments and comparative examples, based on the number of cycles.

[0056] Figure 3c This is a graph showing the evaluation results of the discharge capacity retention rate of batteries containing positive electrode active materials according to the embodiments and comparative examples, based on the number of cycles.

[0057] Figure 4 This is a graph showing the evaluation results of the resistance characteristics of batteries containing positive electrode active materials according to the embodiments and comparative examples.

[0058] Positive electrode active material According to one embodiment, the positive electrode active material 1000 comprises: a core 100 comprising a lithium-transition metal complex oxide; a first coating 110 formed on the surface of the core; and a second coating 120 formed on the surface of the first coating, wherein the first coating comprises a lithium-transition metal complex oxide having a different structure from the lithium-transition metal complex oxide contained in the core, and the second coating comprises a sulfur compound.

[0059] The surface of the positive electrode active material 1000 has a multi-layer structure, specifically a bi-layer coating, which provides excellent structural stability and thus improves electrochemical performance such as lifetime characteristics. The core 100, the first coating 110, and the second coating 120 of the positive electrode active material will be described in more detail below.

[0060] <Nuclear> The core 100 refers to the composition corresponding to the base material of the positive electrode active material containing lithium-transition metal composite oxide, and specifically refers to the portion on its surface where a coating is formed (described in detail below). Specifically, the core 100 can be substantially formed from lithium-transition metal composite oxide in particulate form. That is, the core itself can be lithium-transition metal composite oxide particles.

[0061] The lithium-transition metal composite oxide contained in the core 100 can have a layered structure. That is, the core can contain a layered lithium-transition metal composite oxide. The layered structure of the lithium-transition metal composite oxide is a structure in which lithium and transition metal are arranged in different layers. Compared with lithium iron phosphate (LFP) with an olivine structure, the layered lithium-transition metal composite oxide has a lithium diffusion coefficient that is more than 10,000 times higher and an electrical conductivity that is more than 1,000 times higher, thus having the advantage of high energy density.

[0062] The lithium-transition metal composite oxide contained in the core 100 can be represented by the following Chemical Formula 1. That is, the core 100 can contain a lithium-transition metal composite oxide according to the following Chemical Formula 1.

[0063] [Chemical Formula 1] Li a Ni b M c O2 In Chemical Formula 1, M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, 0.90 < a < 1.5, 0.33 ≤ b ≤ 1, and 0 ≤ c ≤ 0.7. When the core 100 contains a lithium-transition metal composite oxide according to Chemical Formula 1, the capacity of the positive electrode active material can be improved, and the first coating 110 (described below) can be more easily formed through the core.

[0064] The lithium-transition metal composite oxide can be secondary particles formed by aggregation of multiple primary particles and substantially formed into one particle, or can be in the form of single particles. The single particle form can mean that the primary particles exist in a single or partially aggregated form, or can mean that they exist in the form of a single crystal (SC). In a specific embodiment, the positive electrode active material can include all single particles, secondary particles, or a mixed form thereof.

[0065] <First Coating> The first coating 110 is a coating formed on the surface of the core 100, and the first coating 110 contains a lithium-transition metal composite oxide having a structure different from that of the lithium-transition metal composite oxide contained in the core. The migration of lithium ions in the first coating 110 is relatively smooth, so that the ion conduction characteristics and capacity of the positive electrode active material can be improved, and even if the battery undergoes multiple charge and discharge cycles, it can contribute to maintaining a high capacity retention rate.

[0066] The lithium-transition metal composite oxide contained in the first coating 110 can have a spinel structure. That is, the first coating 110 can contain a lithium-transition metal composite oxide having a spinel structure. At this time, the lithium-transition metal composite oxide contained in the core can have a layered structure. When the lithium-transition metal composite oxide has a stable three-dimensional channel structure, that is, a spinel structure, the lithium diffusion barrier is relatively low compared with the layered structure, so that it can have excellent lithium ion conductivity and can further improve the capacity of the positive electrode active material.

[0067] The first coating 110 may further comprise at least one of a rock salt structure lithium-transition metal composite oxide and a layered structure lithium-transition metal composite oxide. Specifically, in addition to comprising a spinel structure lithium-transition metal composite oxide, the first coating 110 may further comprise at least one of a rock salt structure lithium-transition metal composite oxide and a layered structure lithium-transition metal composite oxide.

[0068] The first coating 110 can be formed on the surface of the core 100 by heat treatment, and the structure of the lithium-transition metal composite oxide contained in the first coating 110 can vary depending on the heat treatment temperature. Therefore, during the formation of the first coating 110, lithium-transition metal composite oxides with structures other than spinel structures can be formed in the first coating, and such lithium-transition metal composite oxides can remain in the first coating of the finally prepared positive electrode active material. The process for forming the first coating will be described in more detail below.

[0069] The lithium-transition metal composite oxide contained in the first coating 110 can be represented by the following chemical formula 2. That is, the first coating 110 can contain a lithium-transition metal composite oxide according to the following chemical formula 2.

[0070] [Chemical Formula 2] Li x M y O z In the aforementioned chemical formula 2, M is one or more elements selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, where 0 ≤ x ≤ 4, 0 ≤ y ≤ 4, and 0 ≤ z ≤ 8. When the first coating 110 contains a lithium-transition metal composite oxide according to chemical formula 2, lithium ions readily migrate through the first coating, thereby improving the electrochemical performance of the positive electrode active material to an excellent level and ensuring the structural stability of the first coating.

[0071] The thickness of the first coating 110 can be from 0.1 nm to 500 nm. Specifically, the thickness of the first coating can be greater than 5 nm and less than 100 nm. There is no particular limitation on the method for measuring the thickness of the first coating 110. For example, the thickness can be calculated by using transmission electron microscopy (TEM) measurement and fast Fourier transform (FFT) analysis.

[0072] The cation mixing ratio of the positive electrode active material 1000 can be below 7%. Specifically, the cation mixing ratio of the positive electrode active material 1000 can be below 5%, and can be above 2.2%.

[0073] The cation mixing ratio is an indicator used in X-ray diffraction (XRD) analysis of cathode active materials to confirm the degree of mixing and rearrangement of cations such as lithium and transition metals. The cation mixing ratio can vary depending on the structure and composition of the cathode active material.

[0074] For example, in a layered cathode active material containing lithium (Li) and nickel (Ni), Li and Ni are arranged in different layers, but their positions may interchange as the Ni content increases or the number of charge-discharge cycles increases. When the cations contained in the layered cathode active material undergo such a mixed rearrangement, the layered structure may transform into a spinel structure or a rock salt structure.

[0075] Therefore, since the first coating comprises a lithium-transition metal composite oxide having a structure different from that of the core, the degree of formation of the first coating in the positive electrode active material can be confirmed by measuring the cation mixing ratio of the positive electrode active material containing the core 100 and the first coating 110. For example, as the measured cation mixing ratio of the positive electrode active material increases, it can be determined that the first coating 110 is formed thicker.

[0076] When the cation mixing ratio of the positive electrode active material 1000 is within the above range, a first coating of appropriate degree can be formed without hindering the effect brought about by the nucleus, thereby preparing a positive electrode active material with excellent performance.

[0077] <Second Coating> The second coating 120 is a coating containing a sulfur compound. The second coating 120 can be formed on the surface of the first coating 110, thereby helping to further improve the interfacial stability and electrochemical performance of the positive electrode active material. Specifically, the sulfur compound can combine with lithium residues on the surface of the positive electrode active material, thereby helping to reduce leakage current and improve resistance characteristics.

[0078] The sulfur compound may contain one or more compounds according to the following chemical formula 3.

[0079] [Chemical Formula 3] Li x M y S z O f In Chemical Formula 3, M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, where 0 ≤ x ≤ 10, 0 ≤ y ≤ 10, 0 < z ≤ 10, and 0 ≤ f ≤ 24. When the sulfur compound contained in the second coating 120 includes a compound of the above type, diffusion of constituent elements between the solid electrolyte and the positive electrode active material and side reactions can be effectively suppressed, formation of an interfacial resistance layer and degradation of the cycle performance of the battery can be prevented, and electrochemical performance can be improved.

[0080] The sulfur compound may include sulfur oxides. Based on the total weight of the second coating 120, the content of the sulfur oxides may be 200 ppm to 8000 ppm. The sulfur oxides may be included in the second coating 120 in the form of sulfur monoxide (SO), sulfur dioxide (SO2), sulfur trioxide (SO3), etc. The content of the sulfur oxides contained in the second coating 120 may be measured by mass analysis according to inductively coupled plasma (ICP), etc. When the second coating 120 contains sulfur oxides within the above range, the capacity retention rate, etc. can be further improved.

[0081] The second coating 120 may further include one or more elements selected from P, B, Si, Al, and W.

[0082] The positive electrode active material 1000 may be prepared by a preparation method described in any one of the specific embodiments described below.

[0083] [[ID=!12]]Preparation method of positive electrode active material The preparation method of the positive electrode active material according to a specific embodiment is used to prepare the positive electrode active material 1000 described in any one of the above specific embodiments. Hereinafter, referring to Figure 2a and Figure 2b , the preparation method of the positive electrode active material will be specifically described.

[0084] <Base material preparation step (S0) and base material pretreatment step (S1)> The preparation method of the positive electrode active material may include a base material preparation step (S0) as a process for synthesizing a base material. Specifically, the base material preparation step (S0) may form a core by subjecting a mixture of a precursor containing a transition metal raw material and a lithium raw material to a dry heat treatment process. Exemplarily, the lithium raw material may be lithium hydroxide (LiOH), lithium carbonate (Li2CO3), or a combination thereof. The base material prepared through the base material preparation step (S0) may have substantially the same composition as the core 100.

[0085] The dry heat treatment process can be carried out by heat treatment at 700°C or above for more than 6 hours.

[0086] The method for preparing the positive electrode active material may further include a pretreatment step (S1) of the parent material, i.e., the core 100, prepared as described above. Specifically, the parent material pretreatment step (S1) is the step of forming a precursor coating 105 on the surface of the core, which may include a process of water washing followed by drying and heat treatment. More specifically, the parent material pretreatment step (S1) may include a water washing process (S1-1) and a drying and heat treatment process (S1-2) of the core 100 (see reference). Figure 2a ).

[0087] The water washing process (S1-1) can be carried out as follows: an aqueous solution containing a coating precursor substance is prepared, wherein the content of the coating precursor substance corresponds to an appropriate stoichiometric ratio of the substance to be coated on the positive electrode active material, the positive electrode active material is added to the aqueous solution, and then the positive electrode active material is dried to remove moisture.

[0088] The aqueous solution may contain a complex sulfate compound according to the following chemical formula 4.

[0089] [Chemical Formula 4] In the chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 1≤a≤5, 1≤b≤5.

[0090] The drying heat treatment process (S1-2) can be carried out by heat treatment at 80°C or above for more than 6 hours.

[0091] The coating of the precursor coating 105 formed in the drying process after washing not only means adhesion in the form of a complete film, but may also include the case where the components of the precursor coating are partially adhered to the surface of the core 100.

[0092] <Coating Formation Step (S2)> The method for preparing the positive electrode active material may include a coating formation step (S2) for forming a first coating 110 and a second coating 120. In the coating formation step (S2), the first coating 110 may be formed by heat treatment of the core 100. According to a specific embodiment, the coating formation step (S2) may be performed by heat treatment of the core 100, and the first coating 110 may be a coating including a spinel structure formed by a phase transition on the outer surface of the core 100 through heat treatment in the coating formation step (S2).

[0093] According to another specific embodiment, the coating formation step (S2) can be performed by a heat treatment process on the core 100 on which the precursor coating 105 is formed. The precursor coating 105 can be a multilayer structure comprising a first precursor coating and a second precursor coating, wherein the first precursor coating has a layered structure that undergoes a partial phase transition on the outer surface of the core 100, and the second precursor coating is formed on the surface of the first precursor coating. In this case, the first coating 110 can be a coating comprising a spinel structure formed by deforming the first precursor coating through a heat treatment process in the coating formation step (S2).

[0094] The heat treatment process can be carried out at a temperature below 300°C. Specifically, the temperature of the heat treatment process can be below 280°C or below 200°C, and can be above 80°C, above 100°C, or above 150°C. Furthermore, the heat treatment process can last for less than 20 hours. Specifically, the heat treatment time can be less than 15 hours or less than 10 hours, and can be more than 1 hour or more than 3 hours.

[0095] As described above, the structure of the lithium-transition metal composite oxide can change depending on the conditions of the heat treatment process for the nucleus 100. Specifically, as the heat treatment temperature increases, the structure of the lithium-transition metal composite oxide can change in the order of layered structure, spinel structure, and rock salt structure. For example, the lithium-transition metal composite oxide can have a layered structure below 80°C, can transform from a layered structure to a spinel structure between 80°C and 280°C, can transform from a spinel structure to a rock salt structure at temperatures exceeding 280°C, and can have a complete rock salt structure at 600°C.

[0096] Therefore, when the temperature, time, and other conditions of the heat treatment process of the core 100 are adjusted to the above range, a first coating 110 can be effectively formed. The first coating 110 contains a lithium-transition metal composite oxide with a structure different from that of the lithium-transition metal composite oxide contained in the core 100.

[0097] In the coating forming step (S2), the second coating 120 may be formed from a complex sulfate compound according to the following chemical formula 4.

[0098] [Chemical Formula 4] In the aforementioned chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, ammonium ions, substituted or unsubstituted aliphatic hydrocarbon groups, and combinations thereof, where 1 ≤ a ≤ 5 and 1 ≤ b ≤ 5. When compounds of the above types are used as the aforementioned complex sulfate compounds, improved capacity and relatively excellent capacity retention can be expected.

[0099] According to one specific embodiment, the second coating 120 can be formed by heat treatment of a mixture of the core 100 on which the first coating 110 is formed and the composite sulfate compound.

[0100] There are no particular limitations on the preparation method of the mixture of the core 100 and the composite sulfate compound for the first coating 11 and the second coating 120; dry mixing or wet mixing can be used.

[0101] The dry mixing method can be used alone or in combination with dry mixers such as mortars and pestles, and vortex mixers. Alternatively, the wet mixing method can use solvents such as water or ethanol to dissolve the components.

[0102] According to another specific embodiment, the second coating 120 can be formed by heat treatment of the core 100 on which the precursor coating 105 is formed. In this case, the precursor coating 105 can be a multilayer structure including a first precursor coating and a second precursor coating, wherein the first precursor coating has a layered structure that undergoes a partial phase transition on the outer surface of the core 100, the second precursor coating is formed on the surface of the first precursor coating, and the second coating 120 can be a coating formed by deforming the second precursor coating through a heat treatment process in the coating formation step (S2).

[0103] Furthermore, the second precursor coating may be a coating formed on the surface of the core 100 by a drying heat treatment process after the core 100 is washed with water in the above-mentioned pretreatment step (S1) of the parent material. In this case, the water washing treatment may be carried out using an aqueous solution in which the complex sulfate compound according to the chemical formula 4 is dissolved together in water.

[0104] In the coating formation step (S2), the heat treatment process of the mixture of the core 100 with the first coating 110 formed on its surface and the composite sulfate compound, or the core 100 with the precursor coating 105 formed on its surface, can be performed at a temperature below 300°C. Specifically, the temperature of the heat treatment process can be below 280°C or below 200°C, and can be above 80°C, above 100°C, or above 150°C. Furthermore, the heat treatment process can be performed for 20 hours or less. Specifically, the time of the heat treatment process can be below 15 hours or below 10 hours, and can be above 1 hour or above 3 hours.

[0105] Based on the weight of the positive electrode active material on the surface of the core 100 where the first coating 110 is formed, the content of the added composite sulfate compound can be from 200 ppm to 5000 ppm.

[0106] The mixture or aqueous solution may further contain an additional compound containing one or more elements selected from P, B, Si, Al, and W. When the mixture or aqueous solution further contains such an additional compound, the second coating 120 may further contain one or more elements selected from P, B, Si, Al, and W.

[0107] Positive electrode and all-solid-state battery The positive electrode according to one embodiment comprises the positive electrode active material described in any of the above embodiments. Exemplarily, the positive electrode may include a positive electrode current collector and a positive electrode mixture layer formed on at least one side of the positive electrode current collector, the positive electrode mixture layer comprising the positive electrode active material described in any of the above embodiments.

[0108] The composition of the positive electrode current collector is not particularly limited. The positive electrode current collector can be a plate or foil formed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or alloys thereof.

[0109] The positive electrode mixture layer may further include an adhesive. Exemplarily, the adhesive may include one or more of the following: polyvinylidene fluoride, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, and polymethyl methacrylate.

[0110] The positive electrode mixture layer may further include a conductive material. Exemplarily, the conductive material may include one or more of the following substances: graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube (CNT); metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0111] A all-solid-state battery according to a specific embodiment includes the positive electrode described in any one of the above specific embodiments. Exemplarily, the all-solid-state battery may include: the positive electrode described in any one of the above specific embodiments; and a negative electrode.

[0112] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer formed on at least one surface of the negative electrode current collector.

[0113] The composition of the negative electrode current collector is not particularly limited, and the negative electrode current collector may be a sheet or foil formed of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0114] The negative electrode mixture layer may include carbon-based active materials such as artificial graphite and natural graphite, silicon-based active materials such as silicon oxide (SiOx; 0 < x < 2), Si-C composites, and metals such as lithium metal as negative electrode active materials.

[0115] The negative electrode mixture layer may further include an adhesive. Exemplarily, the adhesive may include one or more of styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc.

[0116] The negative electrode mixture layer may further include a conductive material. Exemplarily, the conductive material may include one or more of the following substances: graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube (CNT); metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives.

[0117] The all-solid-state battery may further include a solid electrolyte. The solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte, specifically a sulfide-based solid electrolyte. That is, an all-solid-state battery according to a specific embodiment may further include a sulfide-based solid electrolyte. Exemplarily, the all-solid-state battery may include: a positive electrode as described in any of the above specific embodiments; a negative electrode; and a sulfide-based solid electrolyte disposed between the positive and negative electrodes.

[0118] The sulfide-based solid electrolyte can be selected from Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (m and n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, and In), 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 One or more of (0≤x≤2).

[0119] The sulfide-based solid electrolyte may be a sulfosilver-germanium ore-based solid electrolyte. The sulfosilver-germanium ore-based solid electrolyte may be a compound represented by the following chemical formula 5.

[0120] [Chemical Formula 5] Li a + A + b Q c X -d In the chemical formula 5, 1≤a≤12, 0≤b≤5, 0≤c≤10, 0≤d≤2, A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, Q is at least one of S, Se or Te, and X is at least one of Cl, Br, I, F, CN, OCN, SCN or N3.

[0121] Specifically, the sulfur-silver-germanium ore-based solid electrolyte can be made of chemical formula Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2), Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 6.5 Sb 0.5 Ge 0.5 S5I, Li 5.7 PS 4.7 Cl 1.3 Li 6.6 Sb 0.5 Si 0.6 Compounds represented by S5I, etc. Detailed Implementation

[0122] Example 1. Manufacturing of positive electrode active materials and composite positive electrodes 1) Example (1) Preparation of the parent material A cathode active material precursor is prepared by calcining a metal hydroxide and a lithium salt. Specifically, an aqueous solution containing a metal salt is continuously added in a co-precipitation environment to obtain a mixture. The mixture is then washed with water, filtered, and dried, and subsequently subjected to dry heat treatment in an oven at or above 700°C for at least 6 hours to obtain a core as an NCM-based cathode active material with a layered structure, wherein the core comprises a lithium-transition metal composite oxide according to the following chemical formula 1.

[0123] [Chemical Formula 1] Li a Ni b M c O2 In the aforementioned chemical formula 1, M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, 0.90 <a<1.5,0.33≤b≤1,0≤c≤0.7。

[0124] (2) Pretreatment of the base material and formation of the coating The NCM-based positive electrode active material core with a layered structure prepared as described above was washed with deionized water (DW) (see reference). Figure 2a Specifically, when washing the base material with water, an aqueous solution containing a complex sulfate compound represented by the following chemical formula 4 dissolved in deionized water (DW) is used to form a precursor coating for forming a wet coating on the surface of the positive electrode active material core.

[0125] [Chemical Formula 4] In the chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 1≤a≤5, 1≤b≤5.

[0126] At this point, the content of the added complex sulfate compound is adjusted to 200 ppm to 5000 ppm based on the weight of the positive electrode active material on which the first coating is formed on the core surface. Then, the water-washed positive electrode active material is dried by heat treatment at above 80°C for at least 6 hours, calcined in a calcining furnace, and dry heat-treated in air at 180°C for at least 3 hours to form the first coating through a phase transition of the core surface layer. The precursor coating is then heat-treated and calcined to form the second coating. The precursor coating is a coating precursor material (refer to...) that is adhered to the surface of the existing positive electrode substrate using a wet coating process. Figure 2b ).

[0127] 2) Comparative Example 1 and Comparative Example 2 The following active material was used as the positive electrode active material in Comparative Example 1: the active material is a lithium-transition metal composite oxide with a layered structure, and it was not subjected to the first coating formation process and the second coating formation process, so that no first coating and second coating were formed. Furthermore, the following active material was used as the positive electrode active material in Comparative Example 2: the active material was prepared by the same method as in the examples, but it was not subjected to the second coating formation process, so that no second coating was formed.

[0128] 2. Manufacturing of composite cathodes A composite positive electrode is prepared by mixing the positive electrode active material, the sulfide-based solid electrolyte, and the conductive material (including substances such as carbon black) according to the examples and comparative examples. In this case, based on the total weight of the composite positive electrode, the content of the positive electrode active material is 60% by weight or more, the content of the conductive material is 6% by weight or less, and the remaining proportion consists of the content of the sulfide-based solid electrolyte.

[0129] 3. Manufacturing of pressurized battery cells Following the sequence of sulfide-based solid electrolyte, prepared positive electrode, and Li-In negative electrode, the powder was added to a 1 cm diameter pressurized cell mold, and then pressurized to produce a dry-type pressurized cell. The pressurized cell mold was then placed on the lower body, and the upper body was closed. A wing screw was used for compression, and the mold was tightened with a torque wrench. Furthermore, to prevent the sulfide-based solid electrolyte from contacting moisture in the air, which could lead to hydrogen sulfide generation and reduced conductivity, O-rings were used to seal the space between the pressurized cells, and parafilm was used to seal the cap and body.

[0130] 4. Performance Evaluation 1) Formation charge / discharge capacity For the pressurized battery cell prepared as described above, constant current charging was performed at 30°C with a rate of 0.1C until the voltage reached 3.65V. After switching to a constant voltage state of 3.65V, the remaining range was charged, and the charging capacity was measured. Next, constant current charging was performed at a rate of 0.1C until the voltage reached 1.88V, and the discharge capacity was measured. The measured charging and discharging capacity values ​​for each embodiment and comparative example are shown below. Figure 3a And in Table 1.

[0131] 2) Lifetime performance (capacity retention) For the pressurized battery cell at 30°C, the process is the same as described above: constant current charging at a rate of 0.1C is performed until the voltage reaches 3.65V. The mode is then changed to a constant voltage state of 3.65V, and the remaining range is charged, measuring the charging capacity. Next, constant current discharging is performed at a rate of 0.1C until the voltage reaches 1.88V, and the discharging capacity is measured. This cycle is repeated at least 30 times under the following conditions, and the partial discharge capacity values ​​measured based on the number of cycles are then presented. Figure 3b In addition, the discharge capacity retention rate (expressed as a percentage (%)) relative to the initial cycle discharge capacity was measured, and the results are shown in [the table / document / etc.]. Figure 3c And in Table 1.

[0132] At this point, Comparative Example 1, Comparative Example 2, and Example 3 refer to three positive electrode active materials that have undergone different treatments. More specifically, Comparative Example 1 refers to a positive electrode active material in its uncoated substrate state, Comparative Example 2 refers to a positive electrode active material containing a first coating with spinel structure components, and Example 4 refers to a final positive electrode active material with a double-layer coating.

[0133] 3) The resistive characteristics of the battery cell After recharging the battery cells that had undergone more than 30 cycles at 30°C to the SOC 100% range, the following steps were performed on the battery cells of Comparative Example 1 and Example 1 at 25°C: the impedance change within the impregnated battery cells was measured using a potentiostat and electrochemical impedance spectroscopy (EIS). The results, represented by a Nyquist plot, are shown below. Figure 4 In this case, the measurement scan range is set to 7MHz to 100mHz, the resistance is measured at 10 point intervals, and the sinus amplitude is set to 50mV.

[0134] [Table 1] See Table 1 and Figures 3a to 4 In the case of using the active material of Example 1, which has both a first coating and a second coating, the capacity value and capacity retention of the voltage-charged cell are relatively superior compared to the cases of using the active material of Comparative Example 1, which does not have a separate coating, and the active material of Comparative Example 2, which only has a first coating. It is determined that this is because the lithium-ion conductivity is improved due to the second coating containing sulfur compounds, thereby increasing the capacity of the active material. Furthermore, with the second coating containing sulfur compounds, the intermediate layer between these substrates and the solid electrolyte can remain more stable during cycling, thus improving the lifetime characteristics.

[0135] Furthermore, when using the coating of Example 1, the cell resistance value is relatively low compared to Comparative Example 1. Specifically, refer to... Figure 4 In the Nyquist plot, the resistance of the embodiment is approximately 950 ohms lower than that of Comparative Example 1, indicating an improvement in resistance performance of approximately 23.1%. Considering that the difference between Comparative Example 1 and the embodiment is based solely on the positive electrode active material, it can be predicted that... Figure 4The semi-circle in the EIS data shown is related to the resistance of the positive electrode active material. Specifically, the resistance of the positive electrode active material can be divided into the interfacial resistance between the positive electrode active material and the solid electrolyte, and the resistance generated by Li ion diffusion within the positive electrode active material. Considering the frequency range, it is possible to predict the resistance based on... Figure 4 The resistivity measured by the EIS data shown is the interfacial resistance between the positive electrode active material and the solid electrolyte.

[0136] Therefore, based on the judgment, if a second coating containing a sulfur compound according to the following chemical formula 3 is formed on the first coating, the resistance reduction effect brought about by the high Li ion conductivity of the second coating can be expected.

[0137] [Chemical Formula 3] Li x M y S z O f In the aforementioned chemical formula 3, M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 0≤x≤10, 0≤y≤10, 0 <z≤10,0≤f≤24。

[0138] Furthermore, it was determined that, in the case of the active material of Example 1 with a robust double-layer coating, the inter-diffusion phenomenon between elements is suppressed during charge / discharge cycles, and the formation of a resistive layer is reduced. Therefore, as shown in Example 1, when optimal double-layer coatings are formed on the positive electrode active material containing lithium-transition metal composite oxides, electrochemical performance, including capacity characteristics, lifetime characteristics, and resistive characteristics, becomes excellent, and an advanced positive electrode active material suitable for all-solid-state batteries can be provided.

[0139] The embodiments of the present invention have been described in detail above, but the scope of the present invention is not limited thereto. Various modifications and variations can be made without departing from the technical concept of the present invention as described in the claims, which will be obvious to those skilled in the art.

[0140] Explanation of reference numerals in the attached figures: 100: Positive electrode active material core 105: Precursor Coating 110: First coating 120: Second coating 1000: Positive electrode active material Industrial applicability As described above, the features of the present invention can be applied in whole or in part to positive electrode active materials, their preparation methods, positive electrodes containing them, and all-solid-state batteries.

Claims

1. A positive electrode active material, comprising: The core comprises a lithium-transition metal composite oxide; A first coating is formed on the surface of the core; as well as A second coating is formed on the surface of the first coating. The first coating comprises a lithium-transition metal composite oxide having a different structure from the lithium-transition metal composite oxide contained in the core. The second coating contains sulfur compounds.

2. The positive electrode active material according to claim 1, wherein, The core comprises a layered lithium-transition metal composite oxide.

3. The positive electrode active material according to claim 1, wherein, The core comprises a lithium-transition metal complex oxide according to the following chemical formula 1. [Chemical Formula 1] Li a Ni b M c O2 In the aforementioned chemical formula 1, M is one or more elements selected from Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, 0.90 <a<1.5,0.33≤b≤1,0≤c≤0.7。 4. The positive electrode active material according to claim 1, wherein, The first coating comprises a spinel-structured lithium-transition metal composite oxide.

5. The positive electrode active material according to claim 4, wherein, The first coating further comprises at least one of a rock-salt structured lithium-transition metal composite oxide and a layered structured lithium-transition metal composite oxide.

6. The positive electrode active material according to claim 1, wherein, The first coating comprises a lithium-transition metal composite oxide according to the following chemical formula 2. [Chemical Formula 2] Li x M y O z In the chemical formula 2, M is one or more elements selected from Ni, Co, Mn, Na, Mg, Ca, Ti, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Ba, where 0 ≤ x ≤ 4, 0 ≤ y ≤ 4, and 0 ≤ z ≤ 8.

7. The positive electrode active material according to claim 1, wherein, The thickness of the first coating is from 0.1 nm to 500 nm.

8. The positive electrode active material according to claim 1, wherein, The cationic mixing ratio of the positive electrode active material is less than 7%.

9. The positive electrode active material according to claim 1, wherein, The sulfur compound comprises one or more compounds according to the following chemical formula 3. [Chemical Formula 3] Li x M y S z O f In the aforementioned chemical formula 3, M is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 0≤x≤10, 0≤y≤10, 0 <z≤10,0≤f≤24。 10. The positive electrode active material according to claim 1, wherein, The sulfur compound comprises sulfur oxides, and the content of the sulfur oxides is between 200 ppm and 8000 ppm based on the total weight of the second coating.

11. The positive electrode active material according to claim 1, wherein, The second coating further comprises one or more elements selected from P, B, Si, Al and W.

12. A method for preparing a positive electrode active material, used to prepare the positive electrode active material according to any one of claims 1 to 11.

13. The method for preparing the positive electrode active material according to claim 12, wherein, The preparation method includes: The base material preparation step involves a dry heat treatment process on a mixture containing a transition metal raw material and a lithium raw material to form a nucleus; and The pretreatment step involves forming a precursor coating on the surface of the core.

14. The method for preparing the positive electrode active material according to claim 13, wherein, The preparation method further includes: a coating formation step, forming a first coating and a second coating. In the coating formation step, the first coating is formed by heat treatment of the core.

15. The method for preparing the positive electrode active material according to claim 14, wherein, In the coating forming step, the second coating is formed from a complex sulfate compound according to the following chemical formula 4. [Chemical Formula 4] In the chemical formula 4, X is selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, Group 16 elements, rare earth elements, substituted or unsubstituted aliphatic hydrocarbon groups and combinations thereof, 1≤a≤5, 1≤b≤5.

16. The method for preparing the positive electrode active material according to claim 14, wherein, In the coating formation step, the heat treatment process is carried out in air at a temperature below 300°C and for a time of less than 20 hours.

17. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 11.

18. An all-solid-state battery comprising the positive electrode as described in claim 17.

19. The all-solid-state battery according to claim 18, wherein, The all-solid-state battery further includes a sulfide-based solid electrolyte.

20. The all-solid-state battery according to claim 19, wherein, The sulfide-based solid electrolyte is a sulfosilver germanium ore-based solid electrolyte.

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