Oxide solid electrolyte, coating active material, battery, and method for producing coating 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] This disclosure relates to an oxide solid electrolyte, a coated active material, a battery, and a method for producing a coated active material. [Background technology]

[0002] In recent years, battery development has been booming. For example, in the automotive industry, development is progressing on batteries used in electric vehicles (BEVs), plug-in hybrid vehicles (PHEVs), and hybrid electric vehicles (HEVs). It is also known that the surface of the electrode active material used in batteries is coated with a coating layer.

[0003] For example, Patent Document 1 discloses composite particles comprising positive electrode active material particles and a coating film containing a phosphorus compound that covers at least a portion of the surface of the positive electrode active material particles. Furthermore, Patent Document 1 discloses the production of composite particles by mixing positive electrode active material particles with an aqueous coating liquid (aqueous coating solution) containing phosphorus and drying the mixture. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-136763 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] A coated active material, in which a coating layer is provided on the surface of the electrode active material, is being investigated. Furthermore, the use of a solid electrolyte as the material for the coating layer is being considered. The coating layer is expected to have good ionic conductivity and function as a protective layer that suppresses the degradation of the electrode active material. Therefore, it is desirable that the solid electrolyte used in the coating layer exhibits good chemical stability and good ionic conductivity.

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

Means for Solving the Problems

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

[0008] [2] Containing boron with a coordination number of 4 (4 - coordinated B), When the peak area of the above 3 - coordinated B is denoted as Sa and the peak area of the above 4 - coordinated B is denoted as Sb, which are obtained by NMR measurement of the above oxide solid electrolyte, the ratio of Sa to the sum of Sa and Sb (Sa / (Sa + Sb)) is 1% or more, the oxide solid electrolyte according to [1].

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

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

[0011] [5] The ionic conductivity at 25 °C is 1.50×10 , , , , , , 50 , ,

[0012] , ,

[0011] , , -9 , ,

[0013] S / cm or more, the oxide solid electrolyte according to any one of [1] to [4].

[0012] [6] The average particle diameter (D 50 ) is 3.0 μm or more and 8.0 μm or less, the oxide solid electrolyte according to any one of [1] to [5].

[0013] [7] A coated active material comprising an electrode active material and a coating layer covering the electrode active material, A coating active material wherein the coating layer contains an oxide solid electrolyte as described in any of [1] to [6].

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

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

[0016]

[10] A battery comprising 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 covering the electrode active material. A battery wherein the coating layer contains an oxide solid electrolyte as described in any of [1] to [6].

[0017]

[11] The battery according to

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

[0018]

[12] The battery described above is a solid-state battery, as described in

[10] or

[11] .

[0019]

[13] A method for producing a coated active material, comprising an electrode active material and a coating layer covering the electrode active material, A preparation step is to prepare an oxide solid electrolyte as described in any of [1] to [6], The process includes a coating layer formation step in which the electrode active material is coated with the oxide solid electrolyte by a dry method to form the coating layer, The above preparation process includes a precursor preparation process to produce a powdered precursor containing Li, B, P, and O elements, A method for producing a coated active material, comprising a calcination treatment in which the above precursor is calcined at a temperature of 450°C or lower. [Effects of the Invention]

[0020] This disclosure offers the advantage of providing an oxide solid electrolyte that exhibits good chemical stability and good ionic conductivity. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic cross-sectional view illustrating an example of a coated active material in this disclosure. [Figure 2] This is a schematic cross-sectional view illustrating a battery in this disclosure. [Figure 3] This is a flowchart illustrating the method for producing the coated active material in this disclosure. [Figure 4] These are the NMR (solid-state 11B-MNR) results for the examples and comparative examples. [Figure 5] These are the NMR (solid-state 31P-MNR) results for the examples and comparative examples. [Figure 6] This shows the NMR (solid-state 11B-MNR) results in Example 4. [Modes for carrying out the invention]

[0022] The oxide solid electrolyte, coating active material, battery, and method for producing the coating active material described herein will be explained in detail below. Note that the following figures are schematic representations, and the size and shape of each part have been exaggerated as appropriate for ease of understanding.

[0023] A. Oxide solid electrolyte The oxide solid electrolyte in this disclosure is an oxide solid electrolyte comprising elements Li, B, P, and O, and includes boron (3-coordinate B) with a coordination number of 3.

[0024] The oxide solid electrolyte in this disclosure contains elements Li, B, P, and O, and also contains 3-coordinate B, thus exhibiting good chemical stability and good ionic conductivity. In this disclosure, chemical stability refers to oxidation resistance.

[0025] Oxide solid electrolytes (LBPO) containing Li, B, P, and O elements are known to be chemically stable solid electrolytes. However, there is room for further improvement in their ionic conductivity. In contrast, the oxide solid electrolyte of this disclosure has good ionic conductivity because it contains 3-coordinate B. Oxide solid electrolytes usually contain boron with a coordination number of 4 (4-coordinate B). 4-coordinate B is chemically more stable than 3-coordinate B. Surprisingly, the inventors have found that when oxide solid electrolytes contain 3-coordinate B, the ionic conductivity is better. Although 3-coordinate B is chemically less stable than 4-coordinate B, it can exist in a metastable state. Furthermore, although the reason for the better ionic conductivity is not clear, it is presumed that a slight strain occurs in the crystal structure of the oxide solid electrolyte, increasing the room for carrier ions such as Li ions to move. While academic papers have disclosed oxide solid electrolytes (Li-doped BPO4) containing elements Li, B, P, and O, such oxide solid electrolytes typically do not contain 3-coordinate B, as described in the examples below.

[0026] The oxide solid electrolyte in this disclosure comprises elements Li, B, P, and O. Furthermore, the oxide solid electrolyte comprises boron (3-coordinate B) with a coordination number of 3.

[0027] Having 3-coordinate B means, for example, NMR (solid) 11 This can be confirmed by 1B-NMR. 3-coordinate 1B has a peak top in the range of, for example, 15 ppm ± 3 ppm.

[0028] Furthermore, the oxide solid electrolyte in this disclosure may also contain boron with a coordination number of 4 (4-coordinate B).

[0029] Having 4-coordinate B means, for example, NMR (solid state) 11 This can be confirmed by 1B-NMR. Element B in 4-coordinate state has a peak top in the range of, for example, -3 ppm ± 5 ppm.

[0030] Furthermore, if the oxide solid electrolyte contains the three-coordinate B and four-coordinate B described above, the peak area of ​​the three-coordinate B determined by NMR measurement of the oxide solid electrolyte is denoted as Sa, and the peak area of ​​the four-coordinate B is denoted as Sb. In this case, the ratio of Sa to the sum of Sa and Sb (Sa / (Sa+Sb)) may be, for example, 1% or more, 3% or more, 5% or more, 10% or more, or 15% or more. On the other hand, Sa / (Sa+Sb) may be, for example, 45% or less, 40% or less, 37% or less, 30% or less, or 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 (molar ratio; Li / (B+P)) of the Li element to the sum of the B and P elements is, for example, 0.10 or more, may be 0.30 or more, or 0.50 or more. On the other hand, Li / (B+P) is, for example, 1.20 or less, may be 1.00 or less, or 0.80 or less.

[0033] In addition, the proportion of the O element can be determined as the oxygen concentration by, for example, a heating fusion method. The oxygen concentration determined by the heating fusion method for the oxide solid electrolyte in the present disclosure is, for example, 45% by weight or more and 60% by weight or less. Note that the molar ratio of the 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] In addition, the oxide solid electrolyte may contain elements other than the above-described Li element, B element, P element, and O element as impurity elements. Examples of the impurity element include Na. The proportion (mol%) of the impurity element is preferably small enough not to impair the function of the oxide solid electrolyte in the present disclosure.

[0035] The oxide solid electrolyte is typically in a particulate form. The average particle diameter (D 50 ) is, for example, 0.1 μm or more, and may be 0.5 μm or more, 1.0 μm or more, 3.0 μm or more, or 4.0 μm or more. On the other hand, D 50 is, for example, 10.0 μm or less, and may be 8.0 μm or less, 6.0 μm or less, or 5.0 μm or less. In addition, the average particle diameter (D 90 ) of the oxide solid electrolyte is not particularly limited, but is, for example, 2.0 μm or more. D 50 refers to the cumulative 50% particle diameter in the volume-based particle diameter distribution measured by a laser diffraction particle size distribution measuring device. Also, D 90 corresponds to the particle diameter corresponding to 90 volume% cumulative from the small particle side measured by a laser diffraction particle size distribution measuring device.

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

[0037] Oxide solid electrolytes may be crystalline or amorphous. Amorphous refers to the presence of a halo peak (a broad peak in the halo pattern) in XRD measurements using CuKα radiation. When the oxide solid electrolyte is crystalline, an example of the observed crystalline phase is Li3PO4.

[0038] The density (specific gravity) of the oxide solid electrolyte is not particularly limited, but for example, 1.50 g / cm³ 3 More than 3.00g / cm 3 The specific gravity can be determined, for example, by the gas displacement method using He gas.

[0039] B. Coated active material Figure 1 is a schematic cross-sectional view illustrating a coated active material in this disclosure. The coated active material 10 shown in Figure 1 comprises an electrode active material 1 and a coating layer 2 that covers the electrode active material 1. Furthermore, in the coated active material 10, the coating layer 2 contains the oxide solid electrolyte described above.

[0040] The coating active material in this disclosure has a coating layer containing the oxide solid electrolyte described above, and is therefore a coating 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 electrode active materials include oxide active materials. Examples of oxide active materials include lithium nickel-cobalt aluminate (NCA), lithium nickel-cobalt manganeseate (NCM), and lithium nickel-cobalt manganese aluminate (NCMA).

[0042] An example of the composition of lithium nickel-cobalt aluminate (NCA) is LiNi x Coy Al z Examples of the composition of LiNiCoMnO₂ (NCM) include LiNiₓCoᵧMnᶻO₂ (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 of the composition of LiNiCoMnAlO₂ (NCMA) include LiNiₐCoᵦMnᶜAlᵟO₂ (0.80 ≤ a, 0 < b, 0 < c, 0 < d, a + b + c + d = 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 of the composition of LiNiCoMnAlO₂ (NCMA) include LiNiₐCoᵦMnᶜAlᵟO₂ (0.80 ≤ α, 0 < β, 0 < γ, 0 < δ, α + β + γ + δ = 1). α may be 0.85 or more, or may be 0.90 or more. β is, for example, 0.19 or less. γ is, for example, 0.08 or less. δ is, for example, 0.08 or less.

[0045] Examples of the oxide active material include lithium titanate such as Li₄Ti₅O₁₂ and SiO₂. Examples of the electrode active material include simple metals such as Si and alloys. 12 Examples of the oxide active material include lithium titanate such as Li₄Ti₅O₁₂ and SiO₂. Examples of the electrode active material include simple 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 shape of the electrode active material is usually particulate. The average particle size D of the electrode active material. 50 For example, it may be 100 nm or larger, and may also be 1 μm or larger, or 5 μm or larger. On the other hand, the average particle diameter D of the electrode active material 50 For example, it may be 50 μm or less, or 20 μm or less. Average particle size D 50 This is as stated above.

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

[0050] The coverage rate is not particularly limited, but a higher rate is preferable. The coverage rate may be, for example, 50% or more, 60% or more, or 75% or more. On the other hand, the coverage rate may be 100%, or less than 100%. The coverage rate may be 95% or less, 90% or less, or 80% or less. The coverage rate can be determined, for example, by observation using a scanning electron microscope (SEM). Alternatively, the coverage rate can be calculated based on X-ray photoelectron spectroscopy (XPS) measurements. In XPS measurements, the elemental ratio can be calculated from the intensity ratio of each major element, and the coverage rate 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 for example, it may be between 1 nm and 100 nm, between 5 nm and 50 nm, or between 10 nm and 30 nm. The thickness of the coating layer can be determined, for example, as the average thickness of multiple samples (e.g., 100 or more samples) observed by 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. Indirect coating means that a layer not containing the oxide solid electrolyte as defined in this disclosure is placed between the electrode active material and the coating layer. Even if a layer not containing the oxide solid electrolyte is placed between the electrode active material and the coating layer in a portion of the coating active material, if there is a portion where the electrode active material and the coating layer are in direct contact, the coating layer can be considered to directly coat the electrode active material.

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

[0054] The shape of the coated active material is usually particulate. Average particle size D of the coated active material. 50 For example, it is 101 nm or larger, may be 1 μm or larger, or 5 μm or larger. On the other hand, the particle size D of the electrode active material 50 For example, particle size D is 50 μm or less. 50 This is as stated above.

[0055] C.Battery Figure 2 is a schematic cross-sectional view illustrating a battery in this disclosure. The battery 20 shown in Figure 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 for collecting current from the positive electrode active material layer 11, and a negative electrode current collector 15 for collecting current from the negative electrode active material layer 12. In this disclosure, the positive electrode active material layer 11 or the negative electrode active material layer 12 contains a coating active material as described in "B. Coating Active Material".

[0056] The coating active material described above exhibits suppressed degradation and good ionic conductivity, resulting in batteries using this coating active material with good cycle characteristics. As mentioned above, the coating active material may be either a positive electrode active material or a negative electrode active material, but the former is preferred. Therefore, we will describe in detail the case where the coating active material is a positive electrode active material, that is, a battery in which the positive electrode active material layer contains the coating active material.

[0057] 1.Cathode active material layer The positive electrode active material layer in this disclosure contains the coated active material (positive electrode active material) described above. The coated active material is the same as described in "B. Coated Active Material," so its description is omitted here.

[0058] Furthermore, 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 Ketjenblack (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). Examples of binders include rubber-based binders and fluoride-based binders. The electrolyte is the same as described in "3. Electrolyte Layer".

[0059] The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less. Furthermore, a method for forming the positive electrode active material layer is, for example, a method of coating a positive electrode composite material containing a coating active material onto 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. The negative electrode active material layer may also optionally contain at least one of an electrolyte, a conductive material, and a binder.

[0061] Examples of negative electrode active materials include metallic active materials such as Li and Sn, Si-based active materials, carbon active materials such as laphite, and Li4Ti5O 12 Examples of oxide-active materials include the following.

[0062] The negative electrode active material is preferably a Si-based active material because it allows for higher battery capacity. A Si-based active material is an active material whose main component is Si. The Si-based active material may be pure Si, a Si alloy, or a Si oxide. Furthermore, the Si-based active material may have a diamond-type crystalline phase, a clathrate I-type crystalline phase, or a clathrate II-type crystalline phase. In the clathrate I-type or II-type crystalline phase, multiple Si elements form polyhedra (cages) containing pentagons or hexagons. Since these polyhedra have spaces inside that can encapsulate Li ions, volume changes due to charging and discharging can be suppressed.

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

[0064] The electrolyte used in the negative electrode active material layer is the same as described in "3. Electrolyte Layer". The conductive material and binder used in the negative electrode active material layer are the same as 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, and may be 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0065] 3. Electrolyte layer The electrolyte layer is a layer positioned 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 (electrolyte solution), but the former is preferred. The electrolyte layer may also contain a binder as needed. The binder is the same as described in "1. Positive Electrode Active Material Layer".

[0066] The solid electrolyte may be an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Among these, a sulfide solid electrolyte is preferred because it has high ionic conductivity.

[0067] Sulfide solid electrolytes typically contain at least Li and S elements. Preferably, sulfide solid electrolytes also contain Me (where Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, or In). Sulfide solid electrolytes may also contain halogen elements such as F, Cl, Br, and 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 include xLi2S·(1-x)P2S5 (0.5≦x<1) and yLiI·zLiBr·(100-yz)(xLi2S·(1-x)P2S5) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In these compositions, it is preferable that x 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 described herein is not particularly limited, but is typically a lithium-ion battery. Furthermore, the battery described herein is typically a solid-state battery having a solid electrolyte layer as the electrolyte layer. In particular, an all-solid-state battery is preferred. The battery described herein may be a primary battery or a secondary battery, but is preferably a secondary battery because it can be repeatedly charged and discharged, making it useful, for example, as an in-vehicle battery.

[0075] Applications of batteries include, for example, powering vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, they are preferred for use as a power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Batteries may also be used as a power source for other mobile devices (e.g., trains, ships, aircraft), or as a power source for electrical products such as information processing devices.

[0076] D. Method for producing coated active material Figure 3 is a flowchart illustrating a method for producing a coated active material in this disclosure. In the production method shown in Figure 3, first, the oxide solid electrolyte described above is prepared (preparation step). Next, the electrode active material is coated with the oxide solid electrolyte by a dry method to form a coating layer (coating layer formation step). This makes it possible to produce a coated active material having an electrode active material and a coating layer that covers the electrode active material.

[0077] In this disclosure, the above-mentioned oxide solid electrolyte can be prepared by calcining a predetermined precursor at a temperature of 450°C or lower. Furthermore, in this disclosure, since the coating layer is formed by a dry method, the coating active material can be manufactured while suppressing the effects of moisture, such as the degradation of the electrode active material.

[0078] 1. Preparation process The preparation step is the step of preparing the solid electrolyte described above. The preparation step includes a precursor preparation process to produce a powdered precursor containing Li, B, P, and O elements, and a calcination process to calcine the precursor at a temperature of 450°C or lower. In addition, an electrode active material may be prepared in the preparation step. The electrode active material is the same as described in "B. Coating Active Material".

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

[0080] In the precursor preparation process, for example, a solute containing a Li source, a B source, a P source, and an O source is dissolved in a solvent to prepare a coating solution. Then, by drying the coating solution, a powdered precursor can be produced.

[0081] The Li source is not particularly limited as long as it is an element or compound containing the element Li, but an example is lithium hydroxide monohydrate (LiOH·H2O). The B source is not particularly limited as long as it is an element or compound containing the element B, but an example is boric acid (H3BO3). The P source is not particularly limited as long as it is an element or compound containing the element P, but an example is orthophosphoric acid (H3PO4) and metaphosphoric acid (HPO3). The O source is, for example, the element O contained in the B source or P source mentioned above. The solvent is, for example, water. The amounts of the Li source and other components are adjusted as appropriate to obtain the oxide solid electrolyte described in this disclosure.

[0082] A specific example of a method for preparing the 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 finally prepare the coating solution by dissolving lithium hydroxide (LiOH) in the second aqueous solution. The pH of the coating solution is not particularly limited, but for example, it is between 6.0 and 9.0. For example, if the amount of lithium hydroxide is too high and the coating solution becomes strongly alkaline, there is a risk of precipitate formation or compositional deviations.

[0083] By drying the above coating liquid, a powdery precursor can be produced as a coarse granule. The drying method is not particularly limited, but examples include spray drying, electric furnace, and vacuum drying oven.

[0084] Furthermore, in the precursor preparation process, the coarse particles obtained by drying the coating solution may be micronized. By micronizing the coarse particles, an oxide solid electrolyte having a desired particle size can be produced. Examples of micronization methods include mechanical milling such as bead mills and ball mills. Mechanical milling may be performed dry or wet. When performed wet, it is preferable to use a solvent other than water.

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

[0086] In the production of oxide solid electrolytes, it is assumed that calcination at high temperatures, such as 500°C or higher, is performed to increase crystallinity. In contrast, the method of this disclosure calcines the precursor at a relatively low temperature of 450°C or lower. Although the detailed reason is unclear, it is presumed that the metastable 3-coordinate B phase is obtained by calcining at a low temperature in the presence of Li element.

[0087] The firing temperature may be 400°C or lower, or 300°C or lower, while the firing temperature may be, for example, 120°C or higher, 150°C or higher, or 200°C or higher. The firing time is not particularly limited, but for example, it may be 30 minutes or more and 20 hours or less. The firing atmosphere is not particularly limited, but for example, it may be an atmospheric atmosphere. The firing atmosphere may also be an atmosphere with a controlled dew point. The dew point is not particularly limited, but for example, it may be -20°C or lower.

[0088] 2.Coating layer formation process The coating layer formation process involves coating the electrode active material with the oxide solid electrolyte using a dry method to form the coating layer.

[0089] As a dry method, for example, a method is to apply a shearing treatment to a mixture containing an electrode active material and an oxide solid electrolyte. The above mixture basically does not contain water, but may contain a small amount of water whose effect can be ignored. The shearing treatment is, for example, a process of rotating a chopper placed in a container. Another example of shearing treatment is a method of applying compressive shear energy to the mixture present between the blade and the wall of the container by rotating a blade placed in the container. Furthermore, the conditions for the shearing treatment are not particularly limited and are preferably adjusted as appropriate so that the coated active material described in "B. Coated Active Material" is obtained.

[0090] 3.Coated active material The coating active material obtained in each of the above steps is not particularly limited, but it is preferably one of the coating active materials described in "B. Coating Active Material".

[0091] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

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

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

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

[0095] [Comparative Example 1] As an oxide solid electrolyte, we prepared an electrolyte that does not contain the element Li (BPO4: manufactured by Yoneyama Chemical Industries, Ltd.).

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

[0097] [Comparative Example 3] Hydrogen peroxide solution (30% by mass), deionized water, and niobium acid (Nb2O5·3H2O) were added to a container. Ammonia solution (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 presumed that the Nb element exists as a peroxo complex in this solution. The solution was dried using a spray-drying apparatus to obtain a white powder. The obtained powder was heat-treated at 200°C for 5 hours under atmospheric conditions. This yielded an oxide solid electrolyte (LiNbO3).

[0098] [Rating 1] (ICP analysis) Elemental analysis of the solid electrolytes of Examples 1-3 and Comparative Examples 1 and 3 was performed by ICP emission spectrometry. First, concentrated hydrochloric acid was added to 0.01 g of the solid electrolyte and boiled to dissolve the electrolyte and prepare the evaluation sample. In addition, standard samples were prepared by diluting 0.01 g of standard solutions (1000 ppm and 10000 ppm) for Li, B, and P with pure water. A calibration curve was created by measuring the standard samples, and the mass concentration of each element was calculated by measuring the evaluation samples based on this calibration curve. Then, the elemental ratios (molar ratios) of Li, P, and B were calculated from the mass concentrations. The measuring instrument used was the 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 could be synthesized in Examples 1-3 without any deviation in composition. Furthermore, as shown in Table 1, the element Na was detected in the ICP analysis. This is thought to be due to additives contained in commercially available metaphosphoric acid.

[0100] [Table 1]

[0101] (Particle size distribution measurement) Using a Microtrac-Bell device (Aerotrac II), the average particle size (D) of the oxide solid electrolytes of Comparative Examples 1 and 3 and Examples 1-3 was determined. 50 The following was measured. The results are shown in Table 2.

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

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

[0104] As shown in Tables 1 and 2, the crystalline phase could not be observed in Comparative Example 3 and Examples 1-2, where the firing temperature was low. On the other hand, as shown in Example 3, it was confirmed that even at low firing temperatures, crystallinity could be increased by sufficiently increasing the proportion of Li.

[0105] (NMR measurement) 11 NMR measurement of B nuclei (solid) 11 A 1B-NMR spectrum (FT-NMR) was performed. The measurement device used was a JEOL ECA-500 Fourier transform nuclear magnetic resonance spectrometer (FT-NMR spectrometer). The measurement conditions were single-pulse mode, repetition time 60 seconds, 8 integration cycles, and rotation speed 18 kHz. The presence or absence of 3-coordinate B and 4-coordinate B was confirmed from the obtained chart. Then, Sa / (Sa+Sb) was calculated from the peak areas of 3-coordinate B (Sa) and 4-coordinate B (Sb). The results are shown in Table 2.

[0106] As shown in Table 2, three-coordinate B was not detected in Comparative Examples 1 and 2. Furthermore, the academic papers 1 and 2 concerning Comparative Example 2 also state that three-coordinate B was not detected (page 77 of academic paper 1, page 316 of academic paper 2).

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

[0108] Chemical stability was evaluated by CV measurement (oxidation current measurement). Specifically, the solid electrolytes from the examples and comparative examples were mixed with acetylene black in a 1:1 volume ratio to prepare compacted powders. An evaluation cell was prepared using this compacted powder 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 constant temperature bath at 25°C, and the oxidation current was measured by scanning the potential at 0.1mV / sec in the voltage range of 1.9V to 4.4V. The oxidation current from the second cycle was integrated, and the area was calculated. Chemical stability was evaluated based on the size of the 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 exhibited good chemical stability but low ionic conductivity. Similarly, Comparative Example 3 exhibited good ionic conductivity but low chemical stability. In contrast, Examples 1 to 3 showed good ionic conductivity and chemical stability. From this, it was confirmed that the oxide solid electrolytes in this disclosure exhibit good chemical stability and good ionic conductivity.

[0110] [Table 2]

[0111] [Comparative Example 4] Metaphosphoric acid and boric acid were mixed and calcined at 230°C in air with a controlled dew point below -30°C for 5 hours. This synthesized a lithium-free electrolyte (BPO4) as an oxide solid electrolyte.

[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) For BPO4 in Comparative Examples 4 and 5, the same evaluation method as in Evaluation 1 was used to determine the solid 11 1B-NMR measurements were performed. The results for Examples 2 and 3 and Comparative Example 1 are shown in Figure 4.

[0114] As shown in Figure 4, it was confirmed that even when fired at low temperatures, 3-coordinate B cannot be obtained in the absence of Li.

[0115] [Example 4] The 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) Examples 2-4 and Comparative Example 4 are solid 31 P-NMR was performed to analyze the P element in oxide solid electrolytes. The results are shown in Figure 5.

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

[0118] Furthermore, as shown in Figure 6, the oxide solid electrolyte of Example 4 is also solid. 11 When B-NMR measurements were performed, peaks for 3-coordinate B and 4-coordinate B were confirmed, similar to 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 elements Li, B, P and O, It includes boron with a coordination number of 3 (3-coordinate B) and boron with a coordination number of 4 (4-coordinate B), An oxide solid electrolyte in which, when the peak area of ​​the 3-coordinate B is determined by NMR measurement of the oxide solid electrolyte and the peak area of ​​the 4-coordinate B is determined to be Sa, the ratio of Sa to the sum of Sa and Sb (Sa / (Sa+Sb)) is 3% or more.

2. The oxide solid electrolyte according to claim 1, wherein the Sa / (Sa+Sb) ratio is 45% or less.

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

4. The ionic conductivity at 25°C is 1.50 × 10⁻⁶. －９ The oxide solid electrolyte according to claim 1, wherein the S / cm is 1 or higher.

5. An oxide solid electrolyte comprising Li, B, P and O, It contains boron with a coordination number of 3 (3-coordinate B), Average particle diameter (D ５０ An oxide solid electrolyte having a particle size of 3.0 μm or more and 8.0 μm or less.

6. A coated active material comprising an electrode active material and a coating layer covering the electrode active material, The coating layer contains an oxide solid electrolyte according to any one of claims 1 to 5, wherein the coating is a coating active material.

7. The coating active material according to claim 6, wherein the electrode active material is an oxide active material.

8. The coating active material according to claim 7, wherein the oxide active material is at least one of nickel cobalt aluminate lithium (NCA), nickel cobalt manganese oxide lithium (NCM), and nickel cobalt manganese aluminate lithium (NCMA).

9. A battery comprising 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 covers the electrode active material. A battery wherein the coating layer contains the oxide solid electrolyte described in any one of claims 1 to 5.

10. The battery according to claim 9, wherein the positive electrode active material layer contains the coating active material.

11. The battery according to claim 9, wherein the battery is a solid-state battery.

12. A method for producing a coated active material, comprising an electrode active material and a coating layer covering the electrode active material, A preparation step involves preparing an oxide solid electrolyte containing elements Li, B, P, and O, and boron (3-coordinate B) having a coordination number of 3. The process includes a coating layer formation step in which the electrode active material is coated with the oxide solid electrolyte by a dry method to form the coating layer, The aforementioned preparation step includes a precursor preparation process for producing a powdered precursor containing Li, B, P, and O elements, A method for producing a coated active material, comprising a calcination treatment in which the precursor is calcined at a temperature of 450°C or lower.

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