Positive electrode active material for all-solid-state batteries, positive electrode for all-solid-state batteries containing the same, and all-solid-state battery

Abstract

The present invention relates to a positive electrode active material for an all-solid-state battery, comprising: a core portion containing a lithium metal oxide; and a coating portion containing a dielectric having a cubic crystal structure on the surface of the core portion; and a positive electrode and an all-solid-state battery containing the same.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0090983 dated July 22, 2022, and incorporates all the contents disclosed in the said Korean Patent Application as part of this Specification.

[0002] The present invention relates to a positive electrode active material for all-solid-state batteries, a positive electrode for all-solid-state batteries containing the same, and an all-solid-state battery. [Background technology]

[0003] Lithium-ion batteries are widely used as power sources for portable devices, including IT mobile devices, and the market has recently seen significant growth from small lithium-ion batteries to medium and large-sized batteries. In particular, their use as automotive batteries is rapidly increasing. To use lithium-ion batteries as power sources for electric vehicles, high energy density and high output characteristics are required, and ensuring safety is especially important.

[0004] Conventional lithium-ion batteries use liquid, non-aqueous organic electrolytes, which pose a risk of ignition and explosion. Since explosion accidents involving products using this technology continue to occur, resolving this issue is a matter of urgency.

[0005] All-solid-state batteries replace these organic electrolytes with solid electrolytes, and all battery components, such as electrodes and electrolytes, are made of solid material. Due to the high safety of the solid electrolyte itself, the risk of ignition and explosion can be fundamentally eliminated.

[0006] Candidate solid electrolytes used in all-solid-state lithium-ion secondary batteries include gel-type polymer electrolytes, sulfide-based electrolytes, and oxide-based solid electrolytes, but among these, sulfide-based solid electrolytes are the most popular. -2It shows a high lithium ion conductivity value of S / cm or more and has a wide potential window of 5V or more. Therefore, there is little deterioration of characteristics even in extreme environments, which also has great advantages for the design of high energy density lithium ion secondary batteries.

[0007] In the case of all-solid-state batteries applying such sulfide-based solid electrolytes, there is a problem that the capacity cannot be properly exhibited due to the high interfacial resistance generated at the interface between the positive electrode active material and the sulfide-based solid electrolyte. As the main causes of such interfacial resistance, 1) the phenomenon of the space charge layer where the lithium-deficient layer at the solid electrolyte interface is formed due to the difference in chemical potential between the positive electrode active material and the solid electrolyte, and 2) the formation of an interfacial impurity layer due to the chemical reaction at the interface between the positive electrode active material and the solid electrolyte have been proposed.

[0008] Conventionally, as a solution to these problems, a lithium metal oxide (LiMe x O y ) having lithium ion conductivity was coated as a buffer layer on the positive electrode active material and the solid electrolyte interface to try to suppress the formation of the space charge layer. However, in the method of coating with lithium metal oxide, the formation of the space charge layer was not sufficiently suppressed. Therefore, the development of a new coating material that can suppress the interfacial resistance between the solid electrolyte and the positive electrode active material is required.

Summary of the Invention

Problems to be Solved by the Invention

[0009] In order to solve the above problems, as a result of extensive research by the present inventors, it was found that coating the surface of the lithium metal oxide with a dielectric having a cubic crystal structure can reduce the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte, and the present invention was completed.

[0010] Therefore, an object of the present invention is to provide a positive electrode active material capable of reducing the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte and a positive electrode containing the same.

[0011] Furthermore, the present invention aims to provide an all-solid-state battery including the positive electrode that is excellent in initial efficiency, rate characteristics, and reproducibility, and can reduce overvoltage. [Means for solving the problem]

[0012] In order to achieve the aforementioned objective, The present invention includes a core portion containing a lithium metal oxide; and The present invention provides a positive electrode active material for an all-solid-state battery, which includes a coating portion on the surface of the core portion containing a dielectric with a cubic crystal structure.

[0013] Furthermore, the present invention includes a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material. The positive electrode active material is the positive electrode active material of the present invention, providing a positive electrode for an all-solid-state battery.

[0014] Furthermore, the present invention provides an all-solid-state battery comprising the positive electrode; negative electrode; and a solid electrolyte layer between the positive electrode and the negative electrode. [Effects of the Invention]

[0015] The positive electrode active material of the present invention has a dielectric material with a cubic crystal structure coated on its surface, which can reduce the resistance generated at the interface between the sulfide-based solid electrolyte and the positive electrode active material.

[0016] Furthermore, the all-solid-state battery containing the positive electrode active material of the present invention can improve initial efficiency, rate characteristics, and reproducibility, and reduce overvoltage. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing the direction of dipole formation in a dielectric material due to voltage application. [Figure 2] This is an SEM image of the positive electrode active material of Example 1. [Figure 3] This is an SEM image of the positive electrode active material in Example 2. [Figure 4] This is an SEM image of the positive electrode active material of Comparative Example 1. [Figure 5]This is an SEM image of the positive electrode active material of Comparative Example 2. [Figure 6] These are XRD pattern graphs of the positive electrode active materials for Example 1, Example 2, and Comparative Example 2. [Figure 7] These are graphs of the initial charge and discharge curves of all-solid-state batteries for Example 1, Example 2, Comparative Example 1, and Comparative Example 2. [Figure 8] These are graphs showing the initial irreversible capacity measurements of all-solid-state batteries for Example 1, Example 2, Comparative Example 1, and Comparative Example 2. [Figure 9] This graph shows the measurement of the initial charge-discharge reproducibility of the all-solid-state battery in Example 1. [Figure 10] This graph shows the initial charge-discharge reproducibility of the all-solid-state battery in Comparative Example 2. [Figure 11] These are discharge curve graphs for the all-solid-state batteries of Example 1, Example 2, and Comparative Example 2 at 0.05C and 2C. [Figure 12] This figure schematically shows an exploded perspective view of the all-solid-state battery manufactured in this embodiment. Modes for carrying out the invention

[0018] The present invention will be described in more detail below.

[0019] Solid-state batteries use a solid electrolyte to conduct lithium ions, so the movement of lithium ions during charging and discharging occurs in a solid state. In other words, since lithium ions can only move through the actual contact area between the positive electrode and the solid electrolyte, minimizing the interfacial resistance between the positive electrode and the solid electrolyte can improve the performance of solid-state batteries.

[0020] Therefore, the present invention aims to provide a positive electrode active material that can reduce the interfacial resistance between the positive electrode and the solid electrolyte.

[0021] Cathode active material for all-solid-state batteries The present invention includes a core portion containing a lithium metal oxide; and The present invention relates to a positive electrode active material for an all-solid-state battery, which includes a coating portion containing a dielectric with a cubic crystal structure on the surface of the core portion.

[0022] The positive electrode active material of the present invention has a core-shell structure, and the core part contains a lithium metal oxide, and the coating part corresponding to the shell may contain a dielectric with a cubic structure.

[0023] The lithium metal oxide is a substance capable of inserting and desorbing lithium ions, and is not particularly limited as long as it can be used as a positive electrode active material of a lithium ion secondary battery. Preferably, the lithium metal oxide may be a compound represented by the following Chemical Formula 2.

[0024] [Chemical Formula 2] Li x M y O2

[0025] In Chemical Formula 2, M contains one or more selected from the group consisting of Co, Mn, Ni, Al, Fe, V, Zn, Cr, Ti, Ta, Mg, Mo, Zr, W, Sn, Hf, Nd, and Gd, x is 0 < x ≤ 1.5, y is 0 < y ≤ 1.

[0026] Also, in Chemical Formula 2, M may preferably contain one or more selected from the group consisting of Co, Mn, and Ni.

[0027] Specific examples of Chemical Formula 2 include layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with more transition metals (Li 1+a [Ni x Mn y Co (1-x-y) M z O2 (where 0 ≤ a ≤ 0.2, 0.4 ≤ x ≤ 0.9, 0 < x + y < 1, M is one or more elements selected from the group consisting of Co, Mn, Ni, Al, Fe, V, Cr, Ti, Ta, Mg, Mo, Zr, W, Sn, Hf, Nd, and Gd, and 0 ≤ z ≤ 0.1.) may also be used.

[0028] On the other hand, in one embodiment of the present invention, the lithium metal oxide is, independently of or simultaneously with the lithium metal oxide of chemical formula 2, Li 1+x Mn 2-x O4 (where 0 ≤ x ≤ 0.33), Li 1.1 Mn 1.9 Lithium manganese oxides such as O4 and LiMn2O4; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; LiNi 1-x M x Lithium nickel oxide is O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, Zr, or Ga, and 0 ≤ x ≤ 0.3); LiMn 2-x M x Lithium manganese composite oxide represented as O2 (where M = Co, Ni, Fe, Cr, Zn, Zr, or Ta, and 0.01 ≤ x ≤ 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, Zr, or Zn); LiNi x Mn 2-x It may further contain one or more selected from the group consisting of: a lithium manganese composite oxide with a spinel structure represented by O4; LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0029] The coating applied to the surface of the core portion includes a dielectric with a cubic crystal structure.

[0030] In other words, the positive electrode active material for an all-solid-state battery of the present invention is in a form in which a lithium metal oxide is coated with a dielectric material having a cubic crystal structure. The coating means that the dielectric material having a cubic crystal structure is physically and / or chemically bonded to the surface of the core. More specifically, the dielectric material having a cubic crystal structure may be distributed on the surface of the core in an island-type configuration and may be separated from each other by predetermined intervals.

[0031] Thus, when the dielectric with the cubic crystal structure is coated on the surface of the lithium metal oxide in a sea-island pattern, the concentration of lithium increases around the region coated with the dielectric, securing a pathway for lithium ions to move, and thus reducing the interfacial resistance with the sulfide-based solid electrolyte.

[0032] If the dielectric material with the cubic crystal structure is coated in the form of a layer that covers the entire surface of the core, it may become difficult to secure a path for lithium to move, increasing interfacial resistance and potentially leading to a decrease in output characteristics. The dielectric material having the cubic crystal structure may also be paraelectric.

[0033] Because the dielectric material has paraelectric properties, an all-solid-state battery containing it can suppress irreversible reactions during the initial charging stage, thereby achieving improved initial efficiency.

[0034] Figure 1 is a schematic diagram showing the direction of dielectric dipole formation when a voltage is applied to a positive electrode active material in which the lithium metal oxide surface is coated with a tetragonal dielectric and a positive electrode active material in which the lithium metal oxide surface is coated with a cubic dielectric.

[0035] The aforementioned tetragonal dielectric is ferroelectric, while the cubic dielectric is paraelectric.

[0036] Referring to Figure 1, since the tetragonal dielectric material is ferroelectric, it inherently possesses a dipole direction, and the direction of the dipoles on the surface of the lithium metal oxide is randomly distributed depending on the direction in which the tetragonal dielectric material is coated. Therefore, the direction of the dipoles does not change under the voltage applied during charging and discharging of the all-solid-state battery, but rather depends on the orientation of the materials when the lithium metal oxide surface is coated. Because the direction of the dipoles is randomly distributed, there is a problem in that the reproducibility of charging and discharging the all-solid-state battery is low.

[0037] On the other hand, since the cubic dielectric material is paraelectric, it does not have dipole properties before voltage is applied, and the dipole arrangement becomes vertical under the voltage applied during charging and discharging. Therefore, uniform dielectric properties can be ensured, and high reproducibility can be achieved during charging and discharging of all-solid-state batteries.

[0038] In other words, the present invention can provide an all-solid-state battery with excellent reproducibility by including a dielectric material with a cubic crystal structure having paraelectric properties.

[0039] The dielectric material of the present invention, having a cubic crystal structure and possessing paraelectric properties, preferably has a dielectric constant of 100 to 400 at 25°C.

[0040] The dielectric material having a cubic crystal structure may contain one or more compounds selected from those represented by the following chemical formula 1.

[0041] [Chemical formula 1] ABO3

[0042] In the aforementioned chemical formula 1, A is one or more elements selected from the group consisting of Ba, Pb, K, Na, Bi, Sr, Ca, and La. B is one or more elements selected from the group consisting of Ti, Nb, Ta, Fe, Zr, Bi, Ca, Ru, Pr, and Sn. A and B are different from each other.

[0043] The aforementioned chemical formula 1 preferably contains one or more elements selected from the group consisting of BaTiO3, SrTiO3, PbTiO3, KNbO3, NaTaO3, BiFeO3, and PbZrTiO3, and most preferably contains one or more elements selected from the group consisting of BaTiO3 and SrTiO3.

[0044] Furthermore, the dielectric material with the cubic crystal structure may have an average grain size of 1 to 100 nm, preferably 3 to 80 nm, and most preferably 25 to 60 nm. Having an average grain size of 1 to 100 nm for the dielectric material with the cubic crystal structure allows for uniform coating of the lithium metal oxide surface. If the average grain size is less than 1 nm, the dielectric material becomes excessively small, leading to aggregation and a failure to achieve the desired reduction in interfacial resistance. If the average grain size exceeds 100 nm, uncoated spaces are created on the lithium metal oxide surface, which is undesirable.

[0045] Furthermore, the cubic dielectric material is included in an amount of 0.5 to 5% by weight relative to the total weight of the positive electrode active material, preferably 2 to 3% by weight. Within the range of 0.5 to 5% by weight, the effect of reducing interfacial resistance can be obtained, but beyond this range, the interfacial resistance increases, and it becomes impossible to improve the electrochemical properties of the all-solid-state battery containing it.

[0046] The positive electrode active material for all-solid-state batteries of the present invention can be manufactured by the following method. First, lithium metal oxide and a cubic dielectric are prepared, and then dispersed in a suitable solvent to prepare a dispersion. The solvent is not particularly limited as long as it can rapidly remove the lithium metal oxide without degrading its electrochemical properties.

[0047] In one embodiment of the present invention, the material can preferably be prepared by stirring in a solvent so that the material powder does not aggregate and has a uniform dispersed phase. Then, the dispersion is heated to about 50°C to 100°C, and the solvent is evaporated and removed while the temperature is maintained. In one embodiment of the present invention, it is preferable that the dispersion is stirred so that the material powder does not precipitate while the solvent is being removed from the dispersion. After the solvent is removed, the resulting product is sintered at about 300°C to 500°C. However, the method for producing the positive electrode active material is not limited to the above method, and any method that can produce a positive electrode active material having the structure described above may be used without limitation.

[0048] Positive electrode for all-solid-state batteries Furthermore, the present invention relates to a positive electrode for an all-solid-state battery, wherein the positive electrode may include a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material, and the positive electrode active material is the positive electrode active material of the present invention as described above.

[0049] Furthermore, the positive electrode may contain a binder resin as needed.

[0050] The solid electrolyte may include a polymer-based solid electrolyte and / or an inorganic solid electrolyte, and preferably an inorganic solid electrolyte. The inorganic solid electrolyte may include a sulfide-based solid electrolyte or an oxide-based solid electrolyte, and in the present invention, the solid electrolyte may preferably include a sulfide-based solid electrolyte.

[0051] The polymer-based solid electrolyte may contain a polymer resin and a lithium salt, and may be a solid polymer electrolyte having the form of a mixture of a solvent-treated lithium salt and a polymer resin, or a polymer gel electrolyte in which an organic electrolyte containing an organic solvent and a lithium salt is incorporated into the polymer resin.

[0052] The sulfide-based solid electrolyte contains a sulfur atom among its electrolyte components and is not limited to any particular component. It may contain one or more of the following: crystalline solid electrolytes, amorphous solid electrolytes (vitreous solid electrolytes), and glass-ceramic solid electrolytes. Specific examples of the sulfide-based solid electrolyte include LPS-type sulfides containing sulfur and phosphorus, and Li 4-x Ge-P x S4 (0.1 ≤ x ≤ 2, specifically 2 / 3 ≤ x ≤ 3 / 4), Li 10±1 MP2X 12 (M=Ge,Si,Sn,Al,X=S,Se), Li 3.833 Sn 0.833 As 0.166 S4, Li4SnS4, Li 3.25 Ge 0.25 P 0.75S4, Li2S-P2S5, B2S3-Li2S, xLi2S-(100-x)P2S5(70≦x≦80), Li2SSiS2-Li3N, Li2S-P2S5-LiI, Li2S-SiS2-LiI, Li2S-B2S3-LiI, Li 3.25 Ge 0.25 P 0.75 Examples include S4, but the list is not limited to these.

[0053] The aforementioned oxide-based solid electrolytes are LLTO-based compounds (La,Li)TiO3 and Li6La2CaTa2O 12 Li6La2ANb2O 12 (A=Ca,Sr), Li2Nd3TeSbO 12 Li3BO 2.5 N 0.5 , Li9SiAlO8, LAGP-based compounds (Li 1+x Al x Ge 2-x (PO4)3, where 0≦x≦1, 0≦y≦1), LATP-based compounds such as Li2OAl2O3-TiO2-P2O5 (Li 1+x Al x Ti 2-x (PO4)3, where 0≦x≦1, 0≦y≦1), Li 1+x Ti 2-x Al x Si y (PO4) 3-y (Here, 0≦x≦1, 0≦y≦1), LiAl x Zr 2-x (PO4)3 (where 0≦x≦1, 0≦y≦1), LiTi x Zr 2-x (PO4)3 (where 0≦x≦1, 0≦y≦1), Li3N, LISICON, LIPON-based compounds (Li 3+y PO 4-x N x Here, examples include perovskite compounds ((La,Li)TiO3), nasicone compounds such as LiTi2(PO4)3, and LLZO compounds containing lithium, lanthanum, zirconium, and oxygen as constituent components, and one or more of these may be included.

[0054] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black; carbon fibers such as VGCF (Vapor grown carbon fiber) and conductive fibers such as metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives, and may contain one or more mixtures selected therefrom.

[0055] all solid state battery The present invention also relates to an all-solid-state battery including a positive electrode; a negative electrode; and a solid electrolyte layer between the positive electrode and the negative electrode.

[0056] The negative electrode includes a negative electrode active material, a solid electrolyte, and a conductive material, and any material can be used as the negative electrode active material as long as it can be used as a negative electrode active material of a lithium ion secondary battery. For example, the negative electrode active material is carbon such as non-graphitizable carbon, graphite-based carbon; Li x Fe2O3(where 0≦x≦1), Li x WO2(where 0≦x≦1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; indium-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxides; lithium titanium oxides, etc., and one or more selected therefrom may be used. The solid electrolyte and conductive material included in the negative electrode can be the same as those described for the positive electrode.

[0057] The solid electrolyte layer contains an ion-conducting material, which may include polymer-based solid electrolytes and / or inorganic solid electrolyte components, and may be used without limitation as a solid electrolyte for an all-solid-state battery. In the present invention, the ion-conducting material contained in the solid electrolyte layer can be described by referring to the above-mentioned information regarding polymer-based solid electrolytes and inorganic solid electrolytes.

[0058] Furthermore, the present invention provides a battery module including the secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the aforementioned devices include, but are not limited to, power tools powered by battery-powered motors; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0059] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and the scope of the present invention is not limited to these.

[0060] <Manufacturing of all-solid-state batteries> Example 1. 0.05 g of BaTiO3 (MTI Korea), which has a cubic crystal structure with an average particle size of 50-60 nm, and 5 g of LiCoO2 were added to 60 mL of isopropyl alcohol. The aggregated BaTiO3 particles were dispersed using ultrasound. Then, the isopropyl alcohol was evaporated while stirring the dispersion at 70°C, and the dispersion was heat-treated at 400°C for 4 hours in an air atmosphere to remove the solvent and other impurities, thereby producing a positive electrode active material in which BaTiO3 particles coated the surface of LiCoO2. At this time, BaTiO3 was present at 1% by weight relative to the total weight of the positive electrode active material. When the positive electrode active material was examined using SEM, it was confirmed that BaTiO3 was coated on the surface of LiCoO2 (Figure 2).

[0061] A positive electrode mixture was prepared by mixing a positive electrode active material, a solid electrolyte, and a conductive material in a weight ratio of 60:35:5, and this mixture was coated onto the surface of an aluminum current collector to manufacture the positive electrode.

[0062] In this case, the solid electrolyte was Li6PS5Cl, the conductive material was Super-P, and the current collector was a composite material consisting of a laminated mesh and foil made of aluminum.

[0063] As the relative electrode, a thin film of lithium-indium alloy (100 μm thick) was bonded to the surface of a copper current collector. The current collector itself was a composite material consisting of a copper mesh and a thin film layered together.

[0064] Next, a solid electrolyte layer was prepared. 100 mg of Li6PS5Cl was compressed at a pressure of 250 MPa to form a solid electrolyte layer with a thickness of approximately 500 μm.

[0065] The prepared positive electrode, solid electrolyte layer, and negative electrode were sequentially stacked in a 10 mm mold-type pressure cell, and a solid-state battery was manufactured by pressurizing it at a pressure of 440 MPa. Figure 12 shows a schematic exploded perspective view of the battery manufactured in this embodiment.

[0066] Example 2. An all-solid-state battery was manufactured in the same manner as in Example 1, except that SrTiO3 (Sigma Aldrich), which has a cubic crystal structure with an average grain size of 50-60 nm, was used instead of BaTiO3, which has a cubic crystal structure with an average grain size of 50-60 nm.

[0067] When the positive electrode active material was examined using a scanning electron microscope (SEM), it was confirmed that SrTiO3 was coated on the surface of LiCoO2 (Figure 3).

[0068] Comparative Example 1. An all-solid-state battery was manufactured in the same manner as in Example 1, except that LiCoO2 was used as the positive electrode active material.

[0069] When the positive electrode active material was examined using a scanning electron microscope (SEM), only LiCoO2 particles were observed (Figure 4).

[0070] Comparative Example 2. An all-solid-state battery was manufactured in the same manner as in Example 1, except that BaTiO3 (Sigma Aldrich) having a tetragonal structure with an average grain size of 50-60 nm was used instead of BaTiO3 having a cubic structure with an average grain size of 50-60 nm.

[0071] When the positive electrode active material was examined using a scanning electron microscope (SEM), it was confirmed that BaTiO3 was coated on the surface of LiCoO2 (Figure 5).

[0072] Experimental Example 1. XRD Measurement of Dielectric Coating Material The cubic structure of BaTiO3 and SrTiO3 used as coating materials in Examples 1 and 2, and the tetragonal structure of BaTiO3 used in Comparative Example 2 were measured by XRD to confirm their crystal structures, which are shown in Figure 6.

[0073] The BaTiO3 of Example 1 and the SrTiO3 of Example 2 showed a peak at (002), indicating that they have a cubic crystal structure. The BaTiO3 of Comparative Example 2 showed peaks at (002) and (200), indicating that it has a tetragonal crystal structure.

[0074] Experimental Example 2. Measurement of Initial Charge and Discharge of All-Solid-State Batteries The initial charge-discharge characteristics of the all-solid-state batteries described in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were measured.

[0075] The above measurement was performed at 0.05C in the voltage range of 2.5 - 4.3V (Li / Li + ) was measured.

[0076] Compared to the all-solid-state battery of Comparative Example 1, the all-solid-state batteries of Examples 1, 2, and Comparative Example 2 showed higher discharge capacities. Furthermore, the all-solid-state batteries of Examples 1 and 2 showed higher discharge capacities than the all-solid-state battery of Comparative Example 2, with Example 2 showing the highest discharge capacity (Figure 7).

[0077] The initial efficiency measurement results are shown in Table 1 below, and the capacity results at 3.9V or less during initial charging are shown in Table 1 and Figure 8 below.

[0078] [Table 1]

[0079] The results in Table 1 show that the capacity due to irreversible reactions below 3.9V during initial charging is lower in the all-solid-state battery of Comparative Example 2 compared to the all-solid-state battery of Comparative Example 1, and that this can be improved by Example 1. In particular, the all-solid-state battery of Example 2 had the lowest irreversible capacity. The superior characteristics of Example 2 compared to Example 1 are thought to be due to the fact that the dielectric constant of the cubic crystal structure SrTiO3 in Example 2 is 300 at 25°C, while the dielectric constant of the cubic crystal structure BaTiO3 is 150 at 25°C, indicating that SrTiO3 has a higher dielectric constant than BaTiO3.

[0080] Furthermore, the initial efficiency of the all-solid-state battery in Example 2 was the highest, which is believed to be a result of the suppression of the initial irreversible reaction.

[0081] In other words, it can be seen that a positive electrode active material in which the surface of a lithium metal oxide is coated with a dielectric material with a cubic crystal structure suppresses the development of irreversible capacity during the initial charging process.

[0082] Experimental Example 3. Measurement of the reproducibility of all-solid-state batteries To confirm the reproducibility of the all-solid-state batteries in Example 1 and Comparative Example 2, three all-solid-state batteries manufactured using the method of Example 1 and four all-solid-state batteries manufactured using the method of Comparative Example 2 were prepared, and the initial charge-discharge characteristics of these batteries were measured using the same method as in Experimental Example 2.

[0083] As a result, it was found that the three all-solid-state batteries in Example 1 had the same level of charge / discharge capacity and charge / discharge curve behavior with almost no variation (Figure 9).

[0084] On the other hand, the four all-solid-state batteries in Comparative Example 2 showed variations in charge and discharge capacity (Figure 10).

[0085] The aforementioned differences in reproducibility are due to differences in the crystal structure of the dielectric material used as a coating for the lithium metal oxide.

[0086] Specifically, ferroelectric dielectrics with a tetragonal crystal structure have an irregular distribution of dipole directions and poor reproducibility, whereas paraelectric dielectrics with a cubic crystal structure have a uniform distribution of dipole directions perpendicular to the surface, resulting in high reproducibility.

[0087] Therefore, it can be seen that using a cubic structure dielectric with paraelectric properties ensures reproducibility of dielectric properties at the positive electrode surface, thereby achieving superior characteristics for all-solid-state batteries.

[0088] Experimental Example 4. Evaluation of Rate Characteristics of All-Solid-State Batteries The rate characteristics of the all-solid-state batteries described above in Example 1, Example 2, and Comparative Example 2 were measured.

[0089] The evaluation of rate characteristics was conducted to verify the effect of crystal structure on the dielectric, specifically to confirm that the crystal structure of the dielectric coated on the surface of the lithium metal oxide reduces the interfacial resistance between the positive electrode and the solid electrolyte.

[0090] The above measurement was performed at 0.05C and 2C in the voltage range of 2.5 - 4.3 V (vs Li / Li + I went there.

[0091] The measurement results are shown in Table 2 and Figure 11 below.

[0092] [Table 2]

[0093] The all-solid-state batteries in Example 1 and Comparative Example 2 showed similar results at a low rate of 0.05C, but at a high rate of 2C, the all-solid-state battery in Example 1 showed a higher discharge capacity than the all-solid-state battery in Comparative Example 2, and the overvoltage was significantly improved. Furthermore, Example 2 showed superior characteristics compared to Example 1 at both low and high rate conditions, which is thought to be due to the fact that cubic SrTiO3 has a higher dielectric constant than cubic BaTiO3.

[0094] From this, it can be seen that a dielectric material with a cubic crystal structure possessing paraelectricity can reduce interfacial resistance more effectively than a dielectric material with a tetragonal crystal structure possessing ferroelectricity, thereby improving rate characteristics and enabling the provision of an all-solid-state battery with improved overvoltage. Furthermore, it can be seen that the higher the dielectric constant of the dielectric material with a cubic crystal structure, the greater the aforementioned effect.

Claims

1. Core portion containing lithium metal oxide; and A positive electrode active material comprising a coating portion on the surface of the core portion containing a dielectric with a cubic crystal structure; The dielectric material having a cubic crystal structure comprises one or more compounds selected from those represented by the following chemical formula 1. The positive electrode active material is a positive electrode active material for all solid-state batteries that contains 0.5% to 5% by weight of a dielectric material relative to the total weight of the positive electrode active material: [Chemical formula 1] ABO ３ In the aforementioned chemical formula 1, A is one or more elements selected from the group consisting of Ba, Pb, K, Na, Bi, Sr, Ca, and La. B is one or more elements selected from the group consisting of Ti, Nb, Ta, Fe, Zr, Bi, Ca, Ru, Pr, and Sn. A and B are different from each other.

2. The dielectric material for an all-solid-state battery according to claim 1, wherein the dielectric material having a cubic crystal structure is paraelectric.

3. The dielectric is a cubic BaTiO ３ and SrTiO ３ The positive electrode active material for an all-solid-state battery according to claim 1, comprising one or more selected from the group consisting of the above.

4. The dielectric material for an all-solid-state battery according to claim 2, wherein the dielectric material having a cubic crystal structure and paraelectric properties has a dielectric constant of 100 to 400 F / m at 25°C.

5. The positive electrode active material for an all-solid-state battery according to claim 1, wherein the average particle size of the dielectric is 1 nm to 100 nm.

6. The dielectric material having a cubic crystal structure is distributed in a sea-island configuration on the surface of the core portion, with predetermined intervals between them, in the positive electrode active material for an all-solid-state battery according to claim 1.

7. The lithium metal oxide is represented by the following chemical formula 2, and is the positive electrode active material for an all-solid-state battery according to claim 1: [Chemical formula 2] Li ｘ M ｙ O ２ In the aforementioned chemical formula 2, M includes one or more elements selected from the group consisting of Co, Mn, Ni, Al, Fe, V, Zn, Cr, Ti, Ta, Mg, Mo, Zr, W, Sn, and Hf. The above x is 0 < x ≤ 1.5, The above y is 0 < y ≤ 1.

8. It comprises a positive electrode active material, a sulfide-based solid electrolyte, and a conductive material. The positive electrode for an all-solid-state battery is the positive electrode active material described in any one of claims 1 to 7.

9. A solid-state battery comprising a positive electrode; a negative electrode; and a solid electrolyte layer between the positive electrode and the negative electrode, as described in claim 8.

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