Oxide solid electrolyte, coated active material, battery, and method for producing coated active material

Abstract

To provide an oxide solid electrolyte which exhibits good chemical stability and has good ionic conductivity.SOLUTION: In the present disclosure, the problem is solved by providing an oxide solid electrolyte comprising an Li element, a B element, a P element, and an O element, and containing boron having a coordination number of 3 (three-coordinated B).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an oxide solid electrolyte, a coated active material, a battery, and a method for producing the coated active material. [Background technology]

[0002] In recent years, the development of batteries has been actively pursued. For example, in the automotive industry, development of batteries for use in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs) is underway. It is also known to coat the surface of the electrode active material used in batteries with a coating layer.

[0003] For example, Patent Document 1 discloses composite particles including positive electrode active material particles and a coating film containing a phosphorus compound, which coats at least a portion of the surface of the positive electrode active material particles. Patent Document 1 also discloses a method for producing composite particles by mixing positive electrode active material particles with an aqueous coating liquid containing phosphorus (aqueous coating liquid) and drying the mixture. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-136763 Summary of the Invention [Problem to be solved by the invention]

[0005] Coated active materials in which a coating layer is provided on the surface of an electrode active material have been studied. The use of solid electrolytes as the material for the coating layer has also been studied. The coating layer is expected to have good ionic conductivity and function as a protective layer that suppresses deterioration of the electrode active material. Therefore, it is desirable for the solid electrolyte used in the coating layer to exhibit good chemical stability and good ionic conductivity.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide an oxide solid electrolyte that exhibits good chemical stability and good ionic conductivity. [Means for solving the problem]

[0007] [1] An oxide solid electrolyte containing Li, B, P and O elements, An oxide solid electrolyte containing boron with a coordination number of 3 (tricoordinated B).

[0008] [2] containing boron with a coordination number of 4 (tetracoordinate B), [1] The oxide solid electrolyte according to [1], wherein, when the peak area of ​​the three-coordinate B is Sa and the peak area of ​​the four-coordinate B is Sb, the ratio of Sa to the total of Sa and Sb (Sa / (Sa+Sb)) is 1% or more, as determined by NMR measurement of the oxide solid electrolyte.

[0009] [3] The oxide solid electrolyte according to [2], wherein the Sa / (Sa+Sb) is 45% or less.

[0010] [4] The oxide solid electrolyte according to any one of [1] to [3], wherein a ratio of the Li element to the total of the B element and the P element (Li / (B+P)) is 0.10 or more and 1.20 or less.

[0011] [5] The ionic conductivity at 25°C is 1.50 x 10 -9 [4] The oxide solid electrolyte according to any one of [1] to [4], wherein the oxide solid electrolyte has a viscosity of 1000 S / cm or more.

[0012] [6] Average particle diameter (D 50 ) is 3.0 μm or more and 8.0 μm or less.

[0013] [7] A coated active material having an electrode active material and a coating layer that coats the electrode active material, The coated active material, wherein the coating layer contains the oxide solid electrolyte according to any one of [1] to [6].

[0014] [8] The coated active material according to [7], wherein the electrode active material is an oxide active material.

[0015] [9] The coated active material according to [8], wherein the oxide active material is at least one of nickel cobalt lithium aluminum oxide (NCA), nickel cobalt lithium manganese oxide (NCM), and nickel cobalt manganese lithium aluminum oxide (NCMA).

[0016]

[10] A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, at least one of the positive electrode active material layer and the negative electrode active material layer contains a coated active material having an electrode active material and a coating layer that coats the electrode active material; A battery in which the coating layer contains the oxide solid electrolyte according to any one of [1] to [6].

[0017]

[11] The battery according to

[10] , wherein the positive electrode active material layer contains the coated active material.

[0018]

[12] The battery according to

[10] or

[11] , wherein the battery is a solid-state battery.

[0019]

[13] A method for producing a coated active material, comprising producing a coated active material having an electrode active material and a coating layer that coats the electrode active material, A preparation step of preparing the oxide solid electrolyte according to any one of [1] to [6]; a coating layer forming step of coating the electrode active material with the oxide solid electrolyte by a dry method to form the coating layer, The preparation step includes a precursor preparation process for preparing a powder precursor containing Li, B, P, and O elements; and calcining the precursor at a temperature of 450°C or less. [Effects of the Invention]

[0020] The present disclosure has the effect of providing an oxide solid electrolyte that exhibits good chemical stability and good ionic conductivity. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic cross-sectional view illustrating a coated active material according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a battery according to the present disclosure. [Figure 3] 1 is a flowchart illustrating a method for producing a coated active material according to the present disclosure. [Figure 4] 1 shows the results of NMR (solid-state 11B-NMR) in Examples and Comparative Examples. [Figure 5] 1 shows the results of NMR (solid-state 31P-NMR) in Examples and Comparative Examples. [Figure 6] 1 shows the results of NMR (solid-state 11B-NMR) in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0022] The oxide solid electrolyte, coated active material, battery, and method for manufacturing the coated active material according to the present disclosure will be described in detail below. Note that the drawings shown below are schematic illustrations, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0023] A. Oxide solid electrolyte The oxide solid electrolyte in the present disclosure is an oxide solid electrolyte containing the elements Li, B, P, and O, and contains boron with a coordination number of 3 (three-coordinated B).

[0024] The oxide solid electrolyte of the present disclosure contains Li, B, P, and O elements, and also contains three-coordinated B, and therefore exhibits good chemical stability and has good ionic conductivity. Note that in the present disclosure, chemical stability means oxidation resistance.

[0025] Oxide solid electrolytes (LBPO) containing elements Li, B, P, and O are known to be chemically stable solid electrolytes. However, there is room for further improvement in ionic conductivity. In contrast, the oxide solid electrolyte of the present disclosure has good ionic conductivity due to the inclusion of tricoordinated B. Oxide solid electrolytes typically contain boron (tetracoordinated B), which has a coordination number of four. Tetracoordinated B is chemically more stable than tricoordinated B. In this regard, the inventors surprisingly found that when an oxide solid electrolyte contains tricoordinated B, the ionic conductivity is improved. Although tricoordinated B is chemically less stable than tetracoordinated B, it can exist in a metastable state. Furthermore, the reason for the improved ionic conductivity is unclear, but it is presumed to be due to slight distortion in the crystal structure of the oxide solid electrolyte, which increases the space for carrier ions such as Li ions to move. In addition, an oxide solid electrolyte containing elements Li, B, P, and O (Li-doped BPO4) has been disclosed in an academic paper. However, as will be described in the Examples below, such an oxide solid electrolyte does not usually contain three-coordinated B.

[0026] The oxide solid electrolyte in the present disclosure contains the elements Li, B, P, and O. Furthermore, the oxide solid electrolyte contains boron, which has a coordination number of 3 (three-coordinated B).

[0027] The presence of three-coordinate B can be confirmed by, for example, NMR (solid state 11 This can be confirmed by B-NMR. Three-coordinate B has a peak top in the range of 15 ppm ± 3 ppm, for example.

[0028] The oxide solid electrolyte of the present disclosure may also contain boron having a coordination number of four (tetracoordinate B).

[0029] The presence of tetracoordinate B can be confirmed by, for example, NMR (solid state 11 This can be confirmed by B-NMR. The tetracoordinated B element has a peak top in the range of, for example, -3 ppm ± 5 ppm.

[0030] Furthermore, when the oxide solid electrolyte contains the above-mentioned tricoordinate B and tetracoordinate B, the peak area of ​​the tricoordinate B determined by NMR measurement of the oxide solid electrolyte is defined as Sa, and the peak area of ​​the tetracoordinate B is defined as Sb. In this case, the ratio of Sa to the total of Sa and Sb (Sa / (Sa+Sb)) is, for example, 1% or more, or may be 3% or more, 5% or more, 10% or more, or 15% or more. On the other hand, Sa / (Sa+Sb) is, for example, 45% or less, or may be 40% or less, or may be 37% or less, or may be 30% or less, or may be 20% or less.

[0031] The proportion of Li element in the oxide solid electrolyte is not particularly limited, but is, for example, 20 mol% or more and 50 mol% or less. The proportion of B element in the oxide solid electrolyte is not particularly limited, but is, for example, 5 mol% or more and 15 mol% or less. The proportion of P element in the oxide solid electrolyte is not particularly limited, but is, for example, 5 mol% or more and 15 mol% or less. The proportion of each element can be calculated, for example, by ICP (inductively coupled plasma) analysis.

[0032] The ratio of the Li element to the total of the B element and the P element (molar ratio; Li / (B+P)) is, for example, 0.10 or more, or may be 0.30 or more, or may be 0.50 or more, while Li / (B+P) is, for example, 1.20 or less, or may be 1.00 or less, or may be 0.80 or less.

[0033] The proportion of O element can be determined as oxygen concentration by, for example, a thermal fusion method. The oxygen concentration of the oxide solid electrolyte according to the present disclosure determined by the thermal fusion method is, for example, 45% by weight or more and 60% by weight or less. The molar ratio of O element in the oxide solid electrolyte is not particularly limited, but is, for example, 30 mol% or more and 60 mol% or less.

[0034] The oxide solid electrolyte may contain elements other than the above-mentioned Li, B, P, and O as impurity elements. Examples of impurity elements include Na. The proportion (mol %) of the impurity elements is preferably small enough not to impair the function of the oxide solid electrolyte of the present disclosure.

[0035] The oxide solid electrolyte is typically in the form of particles. The average particle diameter (D 50 ) is, for example, 0.1 μm or more, may be 0.5 μm or more, may be 1.0 μm or more, may be 3.0 μm or more, or may be 4.0 μm or more. 50 is, for example, 10.0 μm or less, may be 8.0 μm or less, may be 6.0 μm or less, or may be 5.0 μm or less. 90 ) is not particularly limited, but is, for example, 2.0 μm or more. 50 refers to the cumulative 50% particle size in the volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer. 90 corresponds to the particle size equivalent to 90% cumulative volume from the small particle side, as measured using a laser diffraction particle size distribution analyzer.

[0036] The ionic conductivity of the oxide solid electrolyte at 25°C is, for example, 1.5 × 10 -9 S / cm or more, 2.0 × 10 -9 S / cm or more, and 5.0 × 10 -9 S / cm or more, and 1.0 × 10 -8 S / cm or more, and 1.0 × 10 -7On the other hand, the ionic conductivity may be, for example, 1.0×10 -6 S / cm or less.

[0037] The oxide solid electrolyte may be crystalline or amorphous. Amorphous refers to a state in which a halo peak (a broad peak in a halo pattern) is observed in XRD measurement using CuKα radiation. When the oxide solid electrolyte is crystalline, Li3PO4, for example, can be observed as a crystalline phase.

[0038] The density (specific gravity) of the oxide solid electrolyte is not particularly limited, but is, for example, 1.50 g / cm 3 More than 3.00g / cm 3 The specific gravity can be determined by, for example, a gas substitution method using He gas.

[0039] B. Coated active material Fig. 1 is a schematic cross-sectional view illustrating a coated active material according to the present disclosure. The coated active material 10 shown in Fig. 1 includes an electrode active material 1 and a coating layer 2 that coats the electrode active material 1. In the coated active material 10, the coating layer 2 contains the oxide solid electrolyte described above.

[0040] The coated active material according to the present disclosure has a coating layer containing the above-described oxide solid electrolyte, and therefore is a coated active material that is chemically stable and has good ionic conductivity.

[0041] 1. Electrode active material The electrode active material is not particularly limited as long as it is an active material commonly used in batteries. Examples of the electrode active material include oxide active materials. Examples of the oxide active material include nickel-cobalt-lithium aluminum oxide (NCA), nickel-cobalt-lithium manganese oxide (NCM), and nickel-cobalt-lithium manganese aluminum oxide (NCMA).

[0042] An example of the composition of nickel cobalt lithium aluminum oxide (NCA) is LiNi x Coy Al z Examples include AlO₂ (0.80 ≤ x, 0 < y, 0 < z, x + y + z = 1). x may be 0.85 or more, or may be 0.90 or more. y is, for example, 0.19 or less. z is, for example, 0.10 or less.

[0043] As an example of the composition of lithium nickel cobalt manganese oxide (NCM), LiNi a Co b Mn c Examples include O₂ (0.80 ≤ a, 0 < b, 0 < c, a + b + c = 1). a may be 0.85 or more, or may be 0.90 or more. b is, for example, 0.19 or less. c is, for example, 0.10 or less.

[0044] As an example of the composition of lithium nickel cobalt manganese aluminum oxide (NCMA), LiNi α Co β Mn γ Al δ Examples include O₂ (0.80 ≤ α, 0 < β, 0 < γ, 0 < δ, α + β + γ + δ = 1). a may be 0.85 or more, or may be 0.90 or more. b is, for example, 0.19 or less. γ is, for example, 0.08 or less. σ is, for example, 0.08 or less.

[0045] In addition, examples of the oxide active material include lithium titanate such as Li₄Ti₅O 12 and SiO₂. Examples of the electrode active material also include simple substances of metals such as Si and alloys.

[0046] The electrode active material may have a predetermined crystal structure. The crystal structure is not particularly limited, and examples include a rock salt layered structure, a spinel structure, and an olivine structure.

[0047] The coating active material may contain one type of electrode active material or may contain two or more types of electrode active materials.

[0048] The electrode active material is usually in the form of particles. The average particle diameter D of the electrode active material 50 is, for example, 100 nm or more, may be 1 μm or more, or may be 5 μm or more. 50 The average particle diameter D is, for example, 50 μm or less, and may be 20 μm or less. 50 is as described above.

[0049] 2.Coating layer The coating layer coats the electrode active material and contains the above-mentioned oxide solid electrolyte, which is the same as that described in "A. Oxide Solid Electrolyte."

[0050] The coverage is not particularly limited, but a higher coverage is preferable. The coverage is, for example, 50% or more, may be 60% or more, or may be 75% or more. On the other hand, the coverage may be 100% or less. The coverage may be 95% or less, 90% or less, or 80% or less. The coverage can be determined, for example, by observation using a scanning electron microscope (SEM). The coverage can also be calculated based on X-ray photoelectron spectroscopy (XPS) measurement. In XPS measurement, the element ratio is calculated from the intensity ratio of each major element, and the coverage can be determined as the ratio of the elements contained in the coating layer to the total of the elements contained in the electrode active material and the elements contained in the coating layer.

[0051] The thickness of the coating layer is not particularly limited, but may be, for example, 1 nm to 100 nm, or may be 5 nm to 50 nm, or may be 10 nm to 30 nm. The thickness of the coating layer is determined as the average thickness of multiple samples (e.g., 100 or more samples) observed by, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0052] The coating layer may directly coat the electrode active material. Alternatively, the coating layer may indirectly coat the electrode active material. "Indirectly coating" refers to a case where a layer not containing the oxide solid electrolyte of the present disclosure is disposed between the electrode active material and the coating layer. Even if a layer not containing the oxide solid electrolyte is disposed between a part of the coated active material and the electrode active material and the coating layer, the coating layer can be considered to directly coat the electrode active material if there is a portion where the electrode active material and the coating layer are in direct contact with each other.

[0053] 3.Coated active material The coated active material of the present disclosure is typically used in batteries. The electrode active material in the coated active material may be a positive electrode active material or a negative electrode active material, with the former being preferred. The method for producing the coated active material is not particularly limited, but the method described in "D. Method for producing coated active material" is preferred.

[0054] The coated active material is usually in the form of particles. The average particle diameter D of the coated active material 50 is, for example, 101 nm or more, may be 1 μm or more, or may be 5 μm or more. 50 is, for example, 50 μm or less. 50 is as described above.

[0055] C.Battery Fig. 2 is a schematic cross-sectional view illustrating a battery according to the present disclosure. The battery 20 shown in Fig. 2 includes a positive electrode active material layer 11, a negative electrode active material layer 12, an electrolyte layer 13 disposed between the positive electrode active material layer 11 and the negative electrode active material layer 12, a positive electrode current collector 14 that collects current from the positive electrode active material layer 11, and a negative electrode current collector 15 that collects current from the negative electrode active material layer 12. In the present disclosure, the positive electrode active material layer 11 or the negative electrode active material layer 12 contains the coated active material described in "B. Coated active material."

[0056] The coated active material described above exhibits suppressed deterioration and good ionic conductivity, and therefore a battery using the coated active material described above exhibits good cycle characteristics. As described above, the coated active material may be a positive electrode active material or a negative electrode active material, but the former is preferred. Therefore, the details of a battery in which the coated active material is a positive electrode active material, i.e., a positive electrode active material layer contains the coated active material, will be described below.

[0057] 1.Cathode active material layer The positive electrode active material layer in the present disclosure contains the above-described coated active material (positive electrode active material). The coated active material is the same as that described in "B. Coated active material," and therefore will not be described here.

[0058] The positive electrode active material layer may contain a conductive material, a binder, and an electrolyte, as needed. Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include rubber-based binders and fluoride-based binders. The electrolyte is the same as that described in "3. Electrolyte Layer."

[0059] The thickness of the positive electrode active material layer is, for example, 0.1 μm to 1000 μm, or may be 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm. In addition, examples of a method for forming the positive electrode active material layer include a method in which a positive electrode mixture containing a coated active material is applied to a positive electrode current collector.

[0060] 2.Negative electrode active material layer The negative electrode active material layer is a layer containing at least a negative electrode active material, and may also contain at least one of an electrolyte, a conductive material, and a binder, as necessary.

[0061] Examples of the negative electrode active material include metal active materials such as Li and Sn, Si-based active materials, carbon active materials such as graphite, and Li4Ti5O 12 Examples of oxide active materials include:

[0062] The negative electrode active material is preferably a Si-based active material, as this allows for a higher battery capacity. The Si-based active material is an active material whose main component is Si. The Si-based active material may be simple Si, a Si alloy, or a Si oxide. The Si-based active material may have a diamond-type crystalline phase, a clathrate I crystalline phase, or a clathrate II crystalline phase. In the clathrate I or II crystalline phase, multiple Si elements form a polyhedron (cage) containing pentagons or hexagons. This polyhedron has a space inside that can encapsulate Li ions, thereby suppressing volumetric changes during charging and discharging.

[0063] The shape of the negative electrode active material may be, for example, particulate. 50 is not particularly limited, but may be, for example, 10 nm or more, or may be 100 nm or more. 50 is, for example, 50 μm or less, and may be 20 μm or less.

[0064] The electrolyte used in the negative electrode active material layer is the same as that described in "3. Electrolyte Layer." The conductive material and binder used in the negative electrode active material layer are the same as those described in "1. Positive Electrode Active Material Layer." The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, or may be 0.1 μm or more and 500 μm or less, or may be 0.1 μm or more and 100 μm or less.

[0065] 3. Electrolyte layer The electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer, and contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution), with the former being preferred. The electrolyte layer may also contain a binder, if necessary. The binder is the same as that described in "1. Positive electrode active material layer."

[0066] The solid electrolyte may be, for example, an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Among these, the solid electrolyte is preferably a sulfide solid electrolyte because of its high ionic conductivity.

[0067] The sulfide solid electrolyte typically contains at least Li and S. Preferably, the sulfide solid electrolyte further contains Me (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). The sulfide solid electrolyte may also contain a halogen element such as F, Cl, Br, or I.

[0068] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide solid electrolyte may have a crystalline phase. Examples of the crystalline phase include a Thio-LISICON-type crystalline phase, an Argyrodite-type crystalline phase, and an LGPS-type crystalline phase.

[0069] The composition of the sulfide solid electrolyte is not particularly limited, but examples thereof include xLi2S·(1-x)P2S5 (0.5≦x<1), yLiI·zLiBr·(100-yz)(xLi2S·(1-x)P2S5) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In these compositions, x preferably satisfies 0.7≦x≦0.8. Another example of the composition of the sulfide solid electrolyte is Li 7-x-2y PS 6-x-y X yinclude. X is at least one of F, Cl, Br, and I, and x and y satisfy 0 ≦ x and 0 ≦ y. Further, as another example of the composition of the sulfide solid electrolyte, Li 4-x Me 1-x P x S4(0 < x < 1) can be mentioned. Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0070] The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less, may be 0.1 μm or more and 500 μm or less, and may be 0.1 μm or more and 100 μm or less.

[0071] Here, generally, the electrolyte layer containing the above inorganic solid electrolyte is referred to as a solid electrolyte layer, and a battery having a solid electrolyte layer is referred to as a solid battery. Note that the solid battery may be a semi-solid battery or a all-solid battery. When the solid electrolyte layer in the solid battery contains only the above inorganic solid electrolyte as the electrolyte, the above solid battery is referred to as an all-solid battery.

[0072] 4. Other configurations The battery in the present disclosure preferably has a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon.

[0073] The battery in the present disclosure may further have a restraining jig that applies a restraining pressure along the thickness direction to the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer. In particular, when the electrolyte layer is a solid electrolyte layer, it is preferable to apply a restraining pressure in order to form a good ion conduction path and electron conduction path. The restraining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, and may be 5 MPa or more. On the other hand, the restraining pressure is, for example, 100 MPa or less, may be 50 MPa or less, and may be 20 MPa or less.

[0074] 5.Battery The type of battery in the present disclosure is not particularly limited, but is typically a lithium-ion battery. Furthermore, the battery in the present disclosure is typically a solid-state battery having a solid electrolyte layer as the electrolyte layer. In particular, the battery in the present disclosure is preferably an all-solid-state battery. Furthermore, the battery in the present disclosure may be either a primary battery or a secondary battery, but a secondary battery is preferred. This is because it can be repeatedly charged and discharged, and is useful, for example, as an in-vehicle battery.

[0075] Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, it is preferable to use the battery as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0076] D. Method for manufacturing coated active material Fig. 3 is a flowchart illustrating a method for producing a coated active material according to the present disclosure. In the production method shown in Fig. 3, first, the above-described oxide solid electrolyte is prepared (preparation step). Next, an electrode active material is coated with the oxide solid electrolyte by a dry method to form a coating layer (coating layer formation step). This allows the production of a coated active material having an electrode active material and a coating layer that coats the electrode active material.

[0077] In the present disclosure, the above-described oxide solid electrolyte can be prepared by firing a predetermined precursor at a temperature of 450° C. or less. Furthermore, in the present disclosure, the coating layer is formed by a dry method, so that the coated active material can be produced while suppressing the influence of moisture, such as deterioration of the electrode active material.

[0078] 1. Preparation process The preparation step is a step of preparing the above-mentioned solid electrolyte. The preparation step includes a precursor preparation process for preparing a powdery precursor containing elements Li, B, P, and O, and a firing process for firing the precursor at a temperature of 450°C or less. The preparation step may also include preparing an electrode active material. The electrode active material is the same as that described in "B. Coated Active Material."

[0079] (1) Precursor preparation process In the precursor preparation process, a powdery precursor containing Li, B, P, and O elements is prepared.

[0080] In the precursor preparation process, for example, a coating liquid is prepared by dissolving a solute containing a Li source, a B source, a P source, and an O source in a solvent, and then drying the coating liquid to prepare a powdery precursor.

[0081] The Li source is not particularly limited as long as it is an element or compound containing Li, and examples thereof include lithium hydroxide monohydrate (LiOH·H2O). The B source is not particularly limited as long as it is an element or compound containing B, and examples thereof include boric acid (H3BO3). The P source is not particularly limited as long as it is an element or compound containing P, and examples thereof include orthophosphoric acid (H3PO4) and metaphosphoric acid (HPO3). The O source is, for example, the O element contained in the above-mentioned B source or P source. Furthermore, examples of the solvent include water. The amount of the Li source, etc. is appropriately adjusted so as to obtain the oxide solid electrolyte of the present disclosure described above.

[0082] A specific example of a method for preparing a coating solution is to first prepare a first aqueous solution by dissolving orthophosphoric acid (H3PO4) or metaphosphoric acid (HPO3) in water, then prepare a second aqueous solution by dissolving boric acid (H3BO3) in the first aqueous solution, and then dissolve lithium hydroxide (LiOH) in the second aqueous solution to prepare the coating solution. The pH of the coating solution is not particularly limited, but is, for example, 6.0 or more and 9.0 or less. For example, if the amount of lithium hydroxide is too large and the coating solution becomes strongly alkaline, there is a risk of precipitation or composition deviation.

[0083] The coating liquid can be dried to produce a powdery precursor as coarse particles. The drying method is not particularly limited, but examples thereof include spray drying, an electric furnace, and a vacuum drying furnace.

[0084] In the precursor preparation process, the coarse particles obtained by drying the coating liquid may be atomized. By atomizing the coarse particles, an oxide solid electrolyte having a desired particle size can be produced. Examples of atomization methods include mechanical milling using a bead mill, a ball mill, or the like. Mechanical milling may be performed in a dry system or a wet system. When performing the wet system, it is preferable to use a solvent other than water.

[0085] (2) Firing treatment In the calcination treatment, the precursor is calcined at a temperature of 450° C. or less.

[0086] In the production of oxide solid electrolytes, firing at high temperatures, such as 500°C or higher, is expected to enhance crystallinity. In contrast, in the method of the present disclosure, the precursor is fired at a relatively low temperature of 450°C or lower. Although the detailed reason is unclear, it is presumed that firing in the presence of Li element at a low temperature results in a metastable three-coordinate B phase.

[0087] The firing temperature may be 400°C or lower, or 300°C or lower, or, for example, 120°C or higher, 150°C or higher, or 200°C or higher. The firing time is not particularly limited, but is, for example, 30 minutes or longer and 20 hours or shorter. The firing atmosphere is not particularly limited, and examples thereof include air atmosphere. The firing atmosphere may also be an atmosphere with a controlled dew point. The dew point is not particularly limited, and is, for example, -20°C or lower.

[0088] 2.Coating layer formation process The coating layer forming step is a step of coating the electrode active material with the oxide solid electrolyte by a dry method to form the coating layer.

[0089] An example of a dry method is a method in which a mixture containing an electrode active material and an oxide solid electrolyte is subjected to shearing. The mixture is essentially water-free, but may contain a small amount of water whose effect is negligible. The shearing treatment is, for example, a treatment in which a chopper placed in a container is rotated. Another example of shearing treatment is a method in which a blade placed in the container is rotated to apply compressive shear energy to the mixture present between the blade and the wall of the container. The conditions for the shearing treatment are not particularly limited, and are preferably adjusted appropriately so as to obtain the coated active material described in "B. Coated Active Material."

[0090] 3.Coated active material The coated active material obtained in each of the above steps is not particularly limited, but is preferably the coated active material described in "B. Coated active material."

[0091] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0092] [Example 1] An aqueous solution was prepared by mixing metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries) and ion-exchanged water in a weight ratio of 4.52:191.8. Boric acid (manufactured by Nacalai Tesque) was added and dissolved in the aqueous solution as a B source. The amount of boric acid added was such that the molar ratio of B to P was 1.0. Lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries) was then added and dissolved as a Li source. The amount of lithium hydroxide monohydrate added was such that the molar ratio of Li to the sum of B and P was 0.1. This produced a precursor solution.

[0093] The precursor solution was dried using a spray dryer to obtain a white powder precursor. The obtained precursor was heat-treated at 230°C for 5 hours in air with a dew point controlled below -30°C. This resulted in the production of a solid oxide electrolyte (LBPO).

[0094] [Examples 2 to 3] An oxide solid electrolyte was prepared in the same manner as in Example 1, except that lithium hydroxide monohydrate was added in an amount such that the ratio (molar ratio) of Li element to the total of B element and P element was 0.5 or 0.9.

[0095] [Comparative Example 1] As the oxide solid electrolyte, an electrolyte not containing Li element (BPO4: manufactured by Yoneyama Chemical Industry Co., Ltd.) was prepared.

[0096] Comparative Example 2 Based on the descriptions in academic paper 1 (Journal of Solid State Chemistry 142, 74-79 (1999)) and academic paper 2 (AJ Dodd, ERH van Eck / Chemical Physics Letters 365 (2002) 313-319), we prepared an oxide solid electrolyte (Li-doped BPO4:LBPO) in which the molar ratio of Li to the sum of B and P was 0.5. Boric acid (Aldrich) was used as the B source, orthophosphoric acid (Kishida Chemical) was used as the P source, and lithium hydroxide monohydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the Li source. The calcination conditions were 500°C for 6 hours in air with a dew point controlled below -30°C. It should be noted that the above academic paper states that diphosphorus pentoxide (P2O5) was used as the P element source, but diphosphorus pentoxide changes to orthophosphoric acid when mixed with water, so the same conditions apply to the starting material.

[0097] Comparative Example 3 A container was charged with hydrogen peroxide (30% by mass), ion-exchanged water, and niobic acid (Nb2O5·3H2O). Ammonia water (28% by mass) was then added to the container. Lithium hydroxide monohydrate was also added. The container was stirred to obtain a solution containing Li, Nb, and O elements. It is believed that Nb exists as a peroxo complex in the solution. The solution was dried using a spray dryer to obtain a white powder. The powder was then heat-treated in air at 200°C for 5 hours. This resulted in the production of an oxide solid electrolyte (LiNbO3).

[0098] [Rating 1] (ICP analysis) The solid electrolytes of Examples 1 to 3 and Comparative Examples 1 and 3 were subjected to elemental analysis by ICP atomic emission spectrometry. First, concentrated hydrochloric acid was added to 0.01 g of the solid electrolyte, and the mixture was boiled to dissolve the solid electrolyte, thereby preparing an evaluation sample. Furthermore, 0.01 g of standard solutions (1000 ppm, 10000 ppm) for Li, B, and P were diluted with pure water to prepare a standard sample. A calibration curve was created by measuring the standard sample, and the evaluation sample was measured based on this calibration curve to calculate the mass concentration of each element. The element ratios (molar ratios) of Li, P, and B were then calculated from the mass concentrations. The measurement device used was an ICPR-9800 manufactured by Shimadzu Corporation. The results are shown in Table 1.

[0099] As shown in Table 1, it was confirmed that oxide solid electrolytes were synthesized without any deviation in composition in Examples 1 to 3. As shown in Table 1, Na element was detected in the ICP analysis. This is thought to be due to an additive contained in commercially available metaphosphoric acid.

[0100] [Table 1]

[0101] (Particle size distribution measurement) The average particle diameter (D 50 The results are shown in Table 2.

[0102] As shown in Table 2, the synthesized oxide solid electrolyte had a smaller average particle size than commercially available products.

[0103] (XRD measurement) XRD measurements were carried out on the oxide solid electrolytes of Comparative Examples 1 and 3 and Examples 1 to 3 using a Rigaku Corporation device (Smartlab). The radiation source was Cu, and the scan range was 10° to 90°. The presence or absence of a crystalline phase was confirmed from the obtained diffraction chart, and the crystalline phase was identified. The results are shown in Table 2.

[0104] As shown in Tables 1 and 2, no crystalline phase was observed in Comparative Example 3 and Examples 1 and 2, which had low firing temperatures. On the other hand, as shown in Example 3, it was confirmed that even when the firing temperature was low, the crystallinity was increased by increasing the proportion of Li sufficiently.

[0105] (NMR measurement) 11 NMR measurement of B nucleus (solid 11 B-NMR was performed. The measurement device used was a JEOL ECA-500 Fourier transform nuclear magnetic resonance (FT-NMR) device. The measurement conditions were single pulse mode, repetition time 60 seconds, number of integrations 8, and rotation speed 18 kHz. The presence or absence of tricoordinate B and tetracoordinate B was confirmed from the obtained chart. Then, Sa / (Sa+Sb) was calculated from the peak area of ​​tricoordinate B (Sa) and the peak area of ​​tetracoordinate B (Sb). The results are shown in Table 2.

[0106] As shown in Table 2, no tricoordinate B was observed in Comparative Examples 1 and 2. It is also stated in Academic Papers 1 and 2 regarding Comparative Example 2 that no tricoordinate B was observed (Academic Paper 1, page 77; Academic Paper 2, page 316).

[0107] (Measurement of ionic conductivity and evaluation of chemical stability) The solid electrolytes of the examples and comparative examples were sandwiched between carbon-coated aluminum foils and uniaxially pressed at a pressure of 2 tons for 120 seconds. This prepared evaluation samples. Each evaluation sample was placed in a thermostatic chamber at 25°C, and AC impedance measurements were performed. Ion conductivity (lithium ion conductivity at 25°C) was calculated from the size of the resulting arc. The results are shown in Table 2.

[0108] Chemical stability was evaluated by CV measurement (oxidation current measurement). Specifically, the solid electrolytes of the examples and comparative examples were mixed with acetylene black in a 1:1 volume ratio to prepare a compact. An evaluation cell was prepared using this compact as the working electrode, a layer of sulfide solid electrolyte (10LiI-15LiBr-75Li3PS4) as the separator layer, and a Li-In alloy as the counter electrode. The evaluation cell was placed in a thermostatic chamber at 25°C, and potential scanning was performed at 0.1 mV / sec over a voltage range of 1.9 V to 4.4 V to measure the amount of oxidation current. The amount of oxidation current in the second cycle was integrated, and the area was calculated. Chemical stability was evaluated based on the size of this area. Note that the lower the chemical stability, the larger the integrated area. The results are shown in Table 2.

[0109] As shown in Table 2, Comparative Example 1 had good chemical stability but low ionic conductivity. Furthermore, Comparative Example 3 had good ionic conductivity but low chemical stability. In contrast, Examples 1 to 3 had good ionic conductivity and chemical stability. This confirmed that the oxide solid electrolyte of the present disclosure exhibits good chemical stability and has good ionic conductivity.

[0110] [Table 2]

[0111] Comparative Example 4 Metaphosphoric acid and boric acid were mixed and baked at 230°C for 5 hours in air with the dew point controlled to less than -30°C. This resulted in the synthesis of an oxide solid electrolyte (BPO4) that did not contain Li element.

[0112] Comparative Example 5 BPO4 was synthesized in the same manner as in Comparative Example 4, except that the firing temperature was changed to 120°C.

[0113] [Rating 2] (NMR measurement) The BPO4 of Comparative Example 4 and Comparative Example 5 were subjected to the same solid 11 B-NMR measurement was carried out, and the results are shown in FIG.

[0114] As shown in FIG. 4, it was confirmed that tricoordinated B could not be obtained in the absence of Li element even when calcined at a low temperature.

[0115] [Example 4] An oxide solid electrolyte was synthesized in the same manner as in Example 3, except that the firing temperature was changed to 450°C.

[0116] [Rating 3] (NMR measurement) In Examples 2 to 4 and Comparative Example 4, solid 31 P-NMR was performed to analyze the P element in the oxide solid electrolyte, and the results are shown in Figure 5.

[0117] As shown in Figure 5, the higher the firing temperature, the more peaks of the P element derived from Li3PO4 were confirmed. Combined with the results of XRD measurements shown in Table 2, it was confirmed that increasing the firing temperature increases the crystallinity.

[0118] As shown in FIG. 6, the oxide solid electrolyte of Example 4 also exhibited a solid 11 When B-NMR measurement was carried out, a peak due to tricoordinate B and a peak due to tetracoordinate B were confirmed, as in Example 3. [Explanation of symbols]

[0119] 1...electrode active material 2...Covering layer 10...Coated active material 11...Cathode active material layer 12...Negative electrode active material layer 13...electrolyte layer 14...Positive electrode current collector 15...Negative electrode current collector 20...battery

Claims

1. An oxide solid electrolyte containing Li, B, P, and O elements, An oxide solid electrolyte containing boron having a coordination number of three (three-coordinated B).

2. containing boron with a coordination number of 4 (tetracoordinate B), 2. The oxide solid electrolyte according to claim 1, wherein, when a peak area of ​​the three-coordinate B is defined as Sa and a peak area of ​​the four-coordinate B is defined as Sb, a ratio of the Sa to a total of the Sa and the Sb (Sa / (Sa+Sb)) is 1% or more, as determined by NMR measurement of the oxide solid electrolyte.

3. 3. The oxide solid electrolyte according to claim 2, wherein the Sa / (Sa+Sb) ratio is 45% or less.

4. 2. The oxide solid electrolyte according to claim 1, wherein a ratio of the Li element to the total of the B element and the P element (Li / (B+P)) is 0.10 or more and 1.20 or less.

5. The ionic conductivity at 25°C is 1.50 x 10 －９ 2. The oxide solid electrolyte according to claim 1, wherein the conductivity is 0.5 S / cm or more.

6. Average particle diameter (D ５０ 2. The oxide solid electrolyte according to claim 1, wherein the average particle size of the oxide solid electrolyte is 3.0 μm or more and 8.0 μm or less.

7. A coated active material having an electrode active material and a coating layer that coats the electrode active material, A coated active material, wherein the coating layer contains the oxide solid electrolyte according to any one of claims 1 to 6.

8. The coated active material according to claim 7 , wherein the electrode active material is an oxide active material.

9. 9. The coated active material of claim 8, wherein the oxide active material is at least one of nickel cobalt lithium aluminum oxide (NCA), nickel cobalt lithium manganese oxide (NCM), and nickel cobalt manganese lithium aluminum oxide (NCMA).

10. A battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer, At least one of the positive electrode active material layer and the negative electrode active material layer contains a coated active material having an electrode active material and a coating layer that coats the electrode active material, A battery, wherein the coating layer contains the oxide solid electrolyte according to any one of claims 1 to 6.

11. The battery according to claim 10 , wherein the positive electrode active material layer contains the coated active material.

12. The battery of claim 10 , wherein the battery is a solid-state battery.

13. A method for producing a coated active material, comprising producing a coated active material having an electrode active material and a coating layer that coats the electrode active material, a preparation step of preparing the oxide solid electrolyte according to any one of claims 1 to 6; a coating layer forming step of coating the electrode active material with the oxide solid electrolyte by a dry method to form the coating layer, The preparation step includes a precursor preparation process for preparing a powder precursor containing Li, B, P, and O elements; a calcination treatment of calcining the precursor at a temperature of 450°C or less.

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