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

Abstract

The invention relates to an oxide solid electrolyte, a coated active material, a battery, and a method for producing the coated active material. The present disclosure provides an oxide solid electrolyte including Li element, B element, P element, and O element, and including a tricoordinated boron having a coordination number of 3.

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 Art

[0002] In recent years, battery development has been actively progressing. For example, in the automotive industry, the development of batteries for battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs) is advancing. Furthermore, it is known to coat the surface of electrode active materials used in batteries with a coating.

[0003] For example, Japanese Patent Application Laid-Open No. 2023-136753 discloses composite particles comprising positive electrode active material particles and a coating film comprising a phosphorus compound that covers at least a portion of the surface of the positive electrode active material particles. Japanese Patent Application Laid-Open No. 2023-136753 further discloses producing composite particles by mixing positive electrode active material particles with an aqueous coating liquid (aqueous coating liquid) containing phosphorus and drying the mixture. Summary of the Invention

[0004] Research has been conducted on coated active materials with a coating layer provided on the surface of the electrode active material. Furthermore, research has been conducted on using solid electrolytes as the material for the coating layer. The coating layer is expected to function as a protective layer that exhibits good ion conductivity and inhibits degradation of the electrode active material. Therefore, the solid electrolyte used in the coating layer is expected to exhibit good chemical stability and ionic conductivity.

[0005] The present disclosure has been made in view of the above-mentioned practical situation, and provides an oxide solid electrolyte that exhibits good chemical stability and has good ion conductivity.

[0006] A first embodiment of the present disclosure is an oxide solid electrolyte comprising Li, B, P, and O, and comprising tri-coordinate boron with a coordination number of 3.

[0007] In the oxide solid electrolyte involved in the first embodiment of the present disclosure, the oxide solid electrolyte may contain tetracoordinate boron with a coordination number of 4. When the peak area of the above-mentioned tricoordinate boron obtained by NMR measurement of the above-mentioned oxide solid electrolyte is set as Sa and the peak area of the above-mentioned tetracoordinate boron is set as Sb, the ratio of the above-mentioned peak area Sa to the sum of the above-mentioned peak area Sa and the above-mentioned peak area Sb, Sa / (Sa+Sb), may be greater than 1%.

[0008] In the oxide solid electrolyte according to the first aspect of the present disclosure, the ratio Sa / (Sa+Sb) may be 45% or less.

[0009] In the oxide solid electrolyte according to the first aspect of the present disclosure, the ratio Sa / (Sa+Sb) may be 3% or more and 37% or less.

[0010] In the oxide solid electrolyte according to the first aspect of the present disclosure, the ratio of the Li element to the total of the B element and the P element (Li / (B+P)) can be 0.10 or more and 1.20 or less.

[0011] In the oxide solid electrolyte according to the first embodiment of the present disclosure, the ion conductivity at 25°C can be 1.50×10 -9 S / cm or more.

[0012] In the oxide solid electrolyte according to the first embodiment of the present disclosure, the average particle size D of the oxide solid electrolyte is 50 The thickness may be 3.0 μm or more and 8.0 μm or less.

[0013] A second aspect of the present disclosure is a coated active material comprising: an electrode active material; and a coating layer coating the electrode active material, wherein the coating layer contains the oxide solid electrolyte.

[0014] In the coated active material according to the second aspect of the present disclosure, the electrode active material may be an oxide active material.

[0015] In the coated active material according to the second aspect of the present disclosure, the oxide active material may be at least one of lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt manganese aluminum oxide.

[0016] In the coated active material according to the second embodiment of the present disclosure, the electrode active material may include a negative electrode active material, the negative electrode active material may be a Si-based active material, and the Si-based active material may have a clathrate I-type crystal phase or a clathrate II-type crystal phase.

[0017] The third embodiment of the present disclosure is a battery, comprising: a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer arranged between the above-mentioned positive electrode active material layer and the above-mentioned negative electrode active material layer, wherein at least one of the above-mentioned positive electrode active material layer and the above-mentioned negative electrode active material layer contains a coated active material, the above-mentioned coated active material has an electrode active material, and a coating layer coating the above-mentioned electrode active material, and the above-mentioned coating layer contains the above-mentioned oxide solid electrolyte.

[0018] In the battery according to the third aspect of the present disclosure, the positive electrode active material layer may contain the coating active material.

[0019] In the battery according to the third aspect of the present disclosure, the battery may be a solid-state battery.

[0020] The fourth scheme disclosed in the present invention is a method for manufacturing a coated active material, which is a method for manufacturing a coated active material having an electrode active material and a coating layer coating the above-mentioned electrode active material, comprising: preparing the above-mentioned oxide solid electrolyte; and using a dry method to coat the above-mentioned electrode active material with the above-mentioned oxide solid electrolyte to form the above-mentioned coating layer, wherein the above-mentioned preparation comprises: a precursor preparation process of preparing a precursor of the above-mentioned oxide solid electrolyte in powder form containing Li element, B element, P element and O element; and a sintering process of sintering the above-mentioned precursor at a temperature below 450°C.

[0021] In the method for producing a coated active material according to the fourth aspect of the present disclosure, the precursor is fired at a temperature of 120° C. or higher in the firing treatment.

[0022] The present disclosure achieves the effect of being able to provide an oxide solid electrolyte that exhibits good chemical stability and has good ion conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements, and wherein:

[0024] Figure 1 This is a schematic cross-sectional view illustrating the coated active material of the present disclosure.

[0025] Figure 2 This is a schematic cross-sectional view illustrating a battery according to the present disclosure.

[0026] Figure 3 This is a flow chart illustrating the method for producing the coated active material disclosed herein.

[0027] Figure 4 NMR (solid 11 B-MNR) results.

[0028] Figure 5 NMR (solid 31 P-MNR) results.

[0029] Figure 6 For Example 4 NMR (solid 11 B-MNR) results. DETAILED DESCRIPTION

[0030] The oxide solid electrolyte, coated active material, battery, and method for producing the coated active material disclosed herein are described in detail below. The following figures are schematic, and the size and shape of each part are exaggerated as appropriate for easier understanding.

[0031] A. Oxide Solid Electrolyte

[0032] The oxide solid electrolyte disclosed herein is an oxide solid electrolyte containing Li, B, P, and O, and contains boron with a coordination number of 3 (tricoordinated B).

[0033] The oxide solid electrolyte disclosed herein contains Li, B, P, and O, and includes tricoordinate B. Therefore, it exhibits excellent chemical stability and ionic conductivity. In this disclosure, chemical stability refers to oxidation resistance.

[0034] It is known that an oxide solid electrolyte (LBPO) comprising a Li element, a B element, a P element and an O element is a chemically stable solid electrolyte. On the other hand, there is still room for further improvement in ionic conductivity. In this regard, the oxide solid electrolyte disclosed herein has good ionic conductivity because it comprises tricoordinate B. The oxide solid electrolyte generally comprises boron with a coordination number of 4 (tetracoordinate B). Tetracoordinate B is chemically more stable than tricoordinate B. In this regard, the inventors unexpectedly discovered that when the oxide solid electrolyte comprises tricoordinate B, the ionic conductivity becomes even better. Although tricoordinate B is not chemically as stable as tetracoordinate B, it can exist as a quasi-stable state. In addition, although the reason why the ionic conductivity becomes even better is still uncertain, it is speculated that the reason is that a slight strain is generated in the crystal structure of the oxide solid electrolyte, and the space (room) in which carrier ions such as Li ions can move is increased. It should be noted that academic papers have disclosed oxide solid electrolytes containing Li, B, P and O (Li-doped BPO4), but as described in the examples described later, such oxide solid electrolytes generally do not contain tricoordinate B.

[0035] The oxide solid electrolyte disclosed herein contains Li element, B element, P element, and O element. Furthermore, the oxide solid electrolyte contains boron having a coordination number of 3 (tricoordinated B).

[0036] For example, NMR (solid 11 B-NMR) was used to confirm the presence of tricoordinate B. Tricoordinate B has a peak top in the range of 15 ppm±3 ppm, for example.

[0037] In addition, the oxide solid electrolyte of the present disclosure may contain boron having a coordination number of 4 (tetracoordinated B).

[0038] For example, NMR (solid 11 B-NMR) to confirm the presence of tetracoordinate B. The tetracoordinate B element has a peak top in the range of, for example, -3 ppm ± 5 ppm.

[0039] In the case where the oxide solid electrolyte contains the above-mentioned tricoordinate B and tetracoordinate B, when the peak area of the tricoordinate B determined by NMR measurement of the oxide solid electrolyte is denoted as Sa and the peak area of the tetracoordinate B is denoted as Sb, the ratio of the above-mentioned Sa to the total of the above-mentioned Sa and Sb (Sa / (Sa+Sb)) is, 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) is, for example, 45% or less, 40% or less, 37% or less, 30% or less, or 20% or less.

[0040] The proportion of the Li element in the oxide solid electrolyte is not particularly limited, and for example, it is 20 mol% or more and 50 mol% or less. The proportion of the B element in the oxide solid electrolyte is not particularly limited, and for example, it is 5 mol% or more and 15 mol% or less. The proportion of the P element in the oxide solid electrolyte is not particularly limited, and for example, it is 5 mol% or more and 15 mol% or less. The proportion of each element can be calculated, for example, by ICP (high-frequency inductively coupled plasma) analysis.

[0041] 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, 0.30 or more, or 0.50 or more. On the other hand, Li / (B+P) is, for example, 1.20 or less, 1.00 or less, or 0.80 or less.

[0042] The ratio of the O element can be determined as the oxygen concentration, for example, by a thermal melting method. The oxygen concentration of the oxide solid electrolyte disclosed herein, as determined by the thermal melting method, is, for example, 45% by weight or more and 60% by weight or less. The molar ratio of the O element in the oxide solid electrolyte is not particularly limited, but is, for example, 30% by mole or more and 60% by mole or less.

[0043] The oxide solid electrolyte may contain elements other than the aforementioned 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 disclosed herein.

[0044] The oxide solid electrolyte is typically in the form of particles. The average particle size (D 50 ) is, for example, 0.1 μm or more, 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 50For example, it can be 10.0 μm or less, 8.0 μm or less, 6.0 μm or less, or 5.0 μm or less. 90 ) is not particularly limited, and is, for example, 2.0 μm or more. 50 It refers to the cumulative 50% particle size in the volume-based particle size distribution using a laser diffraction particle size distribution analyzer. 90 This is a particle size corresponding to 90% by volume of the cumulative distribution from the small particle side as measured by a laser diffraction particle size distribution analyzer.

[0045] The ionic conductivity of the oxide solid electrolyte at 25°C is, for example, 1.5×10 -9 S / cm or above, can be 2.0×10 -9 S / cm or above, can be 5.0×10 -9 S / cm or above, can be 1.0×10 -8 S / cm or above, can be 1.0×10 -7 S / cm or more. On the other hand, the ion conductivity is, for example, 1.0×10 -6 S / cm or less.

[0046] The oxide solid electrolyte may be crystalline or amorphous. Amorphous refers to a halo peak (a broad peak in a halo pattern) observed in XRD measurements using CuKα radiation. When the oxide solid electrolyte is crystalline, examples of the observed crystal phase include Li3PO4.

[0047] The density (specific gravity) of the oxide solid electrolyte is not particularly limited, but is, for example, 1.50 g / cm 3 Above and 3.00g / cm 3 The specific gravity can be determined by, for example, a gas replacement method using He gas.

[0048] B. Coating active material

[0049] Figure 1 This is a schematic cross-sectional view illustrating the coated active material in the present disclosure. Figure 1 The coated active material 10 shown 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 above-mentioned oxide solid electrolyte.

[0050] The coated active material in the present disclosure has a coating layer containing the above-mentioned oxide solid electrolyte, and therefore is chemically stable and has excellent ion conductivity.

[0051] 1. Electrode active material

[0052] The electrode active material is not particularly limited as long as it is an active material generally used in batteries. Examples of the electrode active material include oxide active materials. Examples of the oxide active material include lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt manganese aluminum oxide (NCMA).

[0053] An example of the composition of lithium nickel cobalt aluminum oxide (NCA) is LiNi. x Co y Al z O2 (0.80≤x, 0<y, 0<z, x+y+z=1). x can be 0.85 or more, or 0.90 or more. y is, for example, 0.19 or less. z is, for example, 0.10 or less.

[0054] An example of the composition of lithium nickel cobalt manganese oxide (NCM) is LiNi. a Co b Mn c O2 (0.80≤a, 0<b, 0<c, a+b+c=1). a can be 0.85 or more, or 0.90 or more. b is, for example, 0.19 or less. c is, for example, 0.10 or less.

[0055] An example of the composition of lithium nickel cobalt manganese aluminum oxide (NCMA) is LiNi. α Co β Mn γ Al δ O2 (0.80≤α, 0<β, 0<γ, 0<δ, α+β+γ+δ=1). α can be 0.85 or greater, or 0.90 or greater. β is, for example, 0.19 or less. γ is, for example, 0.08 or less. σ is, for example, 0.08 or less.

[0056] In addition, as the oxide active material, for example, Li4Ti5O 12 Lithium titanate and SiO 2 , etc. In addition, as the electrode active material, simple substances and alloys of metals such as Si can also be listed.

[0057] The electrode active material may have a predetermined crystal structure. The crystal structure is not particularly limited, and examples thereof include a rock salt layer structure, a spinel structure, and an olivine structure.

[0058] The coating active material may contain one type of electrode active material or two or more types of electrode active materials.

[0059] The electrode active material is usually in the form of particles. 50 For example, it may be 100 nm or more, 1 μm or more, or 5 μm or more. 50For example, it is 50 μm or less, and can be 20 μm or less. 50 As mentioned above.

[0060] 2. Coating layer

[0061] The coating layer covers the electrode active material and contains the oxide solid electrolyte. The oxide solid electrolyte is the same as described in "A. Oxide Solid Electrolyte".

[0062] There is no particular limitation on the coverage, but a higher coverage is preferred. The coverage is, for example, 50% or more, 60% or more, or 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). In addition, the coverage can be determined based on X-ray photoelectron spectroscopy (XPS) measurements. It should be noted that in XPS measurements, the element ratio can be calculated from the intensity ratio of each main element, and the coverage can be determined as the ratio of the elements contained in the coating layer relative to the total of the elements contained in the electrode active material and the elements contained in the coating layer.

[0063] The thickness of the coating layer is not particularly limited, and may be, for example, 1 nm to 100 nm, 5 nm to 50 nm, or 10 nm to 30 nm. The thickness of the coating layer can be determined, for example, as the average value of the thicknesses of a plurality of samples (e.g., 100 or more samples) observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0064] The coating layer may directly coat the electrode active material. On the other hand, the coating layer may indirectly coat the electrode active material. The so-called indirect coating means that a layer that does not contain the oxide solid electrolyte of the present disclosure is disposed between the electrode active material and the coating layer. Furthermore, even if a layer that does not contain the oxide solid electrolyte is disposed between the electrode active material and the coating layer in a portion of the coated active material, if there is a portion where the electrode active material is directly in contact with the coating layer, it can be considered that the coating layer directly coats the electrode active material.

[0065] 3. Coating active material

[0066] The coated active material disclosed herein is typically used in batteries. The electrode active material in the coated active material can be either 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.

[0067] The coated active material is usually in the form of particles. The average particle size D of the coated active material is 50 For example, it can be 101 nm or more, 1 μm or more, or 5 μm or more. 50 For example, it is 50 μm or less. 50 As mentioned above.

[0068] C.Battery

[0069] Figure 2 This is a schematic cross-sectional view illustrating a battery in the present disclosure. Figure 2 The illustrated battery 20 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 the coating active material described in "B. Coating Active Material."

[0070] The above-mentioned coated active material exhibits good ion conductivity and is inhibited from deteriorating, so batteries using such coated active materials have excellent cycle characteristics. As mentioned above, the coated active material can be either a positive electrode active material or a negative electrode active material, with the former being preferred. Therefore, details are provided for batteries in which the coated active material is a positive electrode active material, that is, a positive electrode active material layer containing the coated active material.

[0071] 1. Positive electrode active material layer

[0072] The positive electrode active material layer in the present disclosure contains the above-mentioned coating active material (positive electrode active material). The coating active material is the same as that described in "B. Coating active material", so the description here is omitted.

[0073] In addition, the positive electrode active material layer may contain a conductive material, a binder, and an electrolyte as needed. Examples of the conductive material include carbon materials, metal particles, and conductive polymers. Examples of the carbon material include acetylene black (AB), Ketjen black (KB), and other particulate carbon materials; and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs). In addition, examples of the binder include rubber-based binders and fluoride-based binders. The electrolyte is the same as described in "3. Electrolyte Layer".

[0074] The thickness of the positive electrode active material layer is, for example, 0.1 μm to 1000 μm, 0.1 μm to 500 μm, or 0.1 μm to 100 μm. In addition, as a method for forming the positive electrode active material layer, for example, a method of coating a positive electrode composite material containing a coated active material on a positive electrode current collector can be cited.

[0075] 2. Negative electrode active material layer

[0076] The negative electrode active material layer is a layer containing at least a negative electrode active material. In addition, the negative electrode active material layer may contain at least one of an electrolyte, a conductive material, and a binder as needed.

[0077] 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, Li4Ti5O 12 Oxide active substances.

[0078] The negative electrode active material is preferably a Si-based active material. This is because it can achieve high capacity of the battery. The Si-based active material is an active material with Si as the main component. The Si-based active material can be Si simple substance, Si alloy, or Si oxide. In addition, the Si-based active material can have a diamond-type crystal phase, an inclusion compound type I crystal phase, or an inclusion compound type II crystal phase. In the inclusion compound type I or type II crystal phase, a plurality of Si elements are used to form a polyhedron (cage) containing pentagons or hexagons. The polyhedron has a space inside that can accommodate Li ions, so that the volume change caused by charging and discharging can be suppressed.

[0079] The shape of the negative electrode active material can be, for example, a particle shape. 50 There is no particular limitation, and for example, it is 10 nm or more, and can be 100 nm or more. On the other hand, the particle size D of the negative electrode active material 50 For example, it is 50 μm or less, and may be 20 μm or less.

[0080] The electrolyte used in the negative electrode active material layer is the same as described in "3. Electrolyte Layer." Furthermore, 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 to 1000 μm, but may be 0.1 μm to 500 μm, or 0.1 μm to 100 μm.

[0081] 3. Electrolyte layer

[0082] 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 can be a solid electrolyte or a liquid electrolyte (electrolyte), with the former being preferred. Furthermore, the electrolyte layer may contain a binder as needed. Regarding the binder, the contents are the same as those described in "1. Positive Electrode Active Material Layer."

[0083] The solid electrolyte may be an inorganic solid electrolyte such as a sulfide solid electrolyte or an oxide solid electrolyte. Of these, a sulfide solid electrolyte is preferred because it has high ion conductivity.

[0084] Sulfide solid electrolytes generally contain at least Li and S. Sulfide solid electrolytes preferably further contain Me (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). Sulfide solid electrolytes may also contain halogen elements such as F, Cl, Br, and I.

[0085] The sulfide solid electrolyte may be a glassy (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 such crystalline phases include the Thio-Lisicon phase, the Argentite phase, and the LGPS phase.

[0086] The composition of the sulfide solid electrolyte is not particularly limited. 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. In addition, as another example of the composition of the sulfide solid electrolyte, Li 7-x-2y PS 6-x-y X y X is at least one of F, Cl, Br, and I, and x and y satisfy 0≤x, 0≤y. In addition, as another example of the composition of the sulfide solid electrolyte, Li 4-x Me 1-x P x S4 (0<x<1). Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi.

[0087] The thickness of the electrolyte layer is, for example, 0.1 μm to 1000 μm, may be 0.1 μm to 500 μm, or may be 0.1 μm to 100 μm.

[0088] Generally, an electrolyte layer containing the above-mentioned 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. Furthermore, a solid battery may be a semi-solid battery or a fully solid battery. When the solid electrolyte layer in a solid battery contains only the above-mentioned inorganic solid electrolyte as an electrolyte, the solid battery is referred to as a fully solid battery.

[0089] 4. Other components

[0090] The battery disclosed herein preferably includes a positive electrode current collector for collecting current from the positive electrode active material layer, and a negative electrode current collector for collecting current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon.

[0091] The battery of the present disclosure may further include a constraining fixture for applying a constraining pressure to the positive electrode active material layer, the electrolyte layer, and the negative electrode active material layer along the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, in order to form a good ion conduction path and an electron conduction path, it is preferred to apply a constraining pressure. The constraining pressure is, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the constraining pressure is, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0092] 5.Battery

[0093] 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 an 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 a primary battery or a secondary battery, with a secondary battery being preferred. This is because they can be repeatedly charged and discharged, and can be used, for example, as a vehicle battery.

[0094] Examples of battery applications include power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, the battery is preferably used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). Furthermore, the battery can be used as a power source for mobile objects other than vehicles (e.g., railways, ships, and aircraft), and can also be used as a power source for electrical products such as information processing devices.

[0095] D. Method for producing coated active material

[0096] Figure 3 This is a flow chart illustrating a method for producing a coated active material in the present disclosure. Figure 3 In the manufacturing method shown, first, the above-mentioned oxide solid electrolyte is prepared (preparation step). Next, the electrode active material is coated with the oxide solid electrolyte using a dry method to form a coating layer (coating layer formation step). In this way, a coated active material having an electrode active material and a coating layer coating the electrode active material can be manufactured.

[0097] In the present disclosure, the oxide solid electrolyte can be prepared by calcining a predetermined precursor of the oxide solid electrolyte at a temperature of 450° C. or lower. Furthermore, in the present disclosure, since the coating layer is formed by a dry process, the coated active material can be produced while suppressing the effects of moisture, such as degradation of the electrode active material.

[0098] 1. Preparation process

[0099] The preparation step is the process of preparing the aforementioned solid electrolyte. This step includes a precursor preparation process, in which a powdered precursor containing Li, B, P, and O is prepared; and a calcination process, in which the precursor is calcined at a temperature of 450°C or below. Furthermore, the preparation step may include the preparation of an electrode active material. The electrode active material is the same as described in "B. Coating Active Material."

[0100] (1) Precursor preparation and processing

[0101] In the precursor preparation process, a powdery precursor containing Li element, B element, P element, and O element is prepared.

[0102] 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 liquid, and then the coating liquid is dried to prepare a powdered precursor.

[0103] As a Li source, there is no particular limitation as long as it is a simple substance or compound containing the Li element, and for example, lithium hydroxide monohydrate (LiOH·H2O) can be listed. As a B source, there is no particular limitation as long as it is a simple substance or compound containing the B element, and for example, boric acid (H3BO3) can be listed. As a P source, there is no particular limitation as long as it is a simple substance or compound containing the P element, and for example, orthophosphoric acid (H3PO4) and metaphosphoric acid (HPO3) can be listed. As an O source, for example, the O element contained in the above-mentioned B source or P source can be listed. In addition, as a solvent, for example, water can be listed. The amount of the Li source, etc. is appropriately adjusted to obtain the above-mentioned oxide solid electrolyte of the present disclosure.

[0104] A specific example of a method for preparing a coating solution includes the following: First, a first aqueous solution is prepared by dissolving orthophosphoric acid (H3PO4) or metaphosphoric acid (HPO3) in water. Next, a second aqueous solution is prepared by dissolving boric acid (H3BO3) in the first aqueous solution. Finally, lithium hydroxide (LiOH) is dissolved in the second aqueous solution to prepare the coating solution. The pH of the coating solution is not particularly limited, but is, for example, between 6.0 and 9.0. For example, if the amount of lithium hydroxide is excessive, the coating solution becomes strongly alkaline, potentially forming precipitates or causing compositional deviations.

[0105] The coating liquid can be dried to produce a powdered precursor as coarse particles. The drying method is not particularly limited, and examples thereof include a spray dryer, an electric furnace, and a vacuum drying furnace.

[0106] In addition, during the precursor preparation process, the coarse particles obtained by drying the coating liquid can be micronized. By micronizing the coarse particles, an oxide solid electrolyte having a desired particle size can be produced. As a micronization method, for example, mechanical grinding such as bead milling and ball milling can be listed. Mechanical grinding can be carried out in a dry manner or in a wet manner. When wet grinding is carried out, it is preferred to use a solvent other than water.

[0107] (2) Firing treatment

[0108] In the calcination process, the precursor is calcined at a temperature of 450° C. or lower.

[0109] In the production of oxide solid electrolytes, calcination at high temperatures, such as 500°C or higher, is typically performed to improve crystallinity. However, in the method disclosed herein, the precursor is calcined at a relatively low temperature of 450°C or lower. The specific reason for this is unclear, but it is speculated that calcination in the presence of Li at low temperatures produces a metastable phase of tricoordinate B.

[0110] The firing temperature may be 400°C or lower, or 300°C or lower. Alternatively, 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 may be, for example, 30 minutes or longer and 20 hours or shorter. The firing atmosphere is not particularly limited, but may be, for example, air. Furthermore, the firing atmosphere may be one with a controlled dew point. The dew point is not particularly limited, but may be, for example, -20°C or lower.

[0111] 2. Coating layer formation process

[0112] The covering layer forming step is a step of covering the electrode active material with the oxide solid electrolyte by a dry method to form the covering layer.

[0113] As a dry method, for example, a method of applying shear treatment to a mixture containing an electrode active material and an oxide solid electrolyte can be cited. The above-mentioned mixture is basically free of water and may contain a small amount of water to the extent that its influence can be ignored. The shear treatment is, for example, a process of rotating a shredder arranged in a container. As another example of a shear treatment, a method of applying compressive shear energy to the mixture between the scraper and the wall of the container by rotating a scraper arranged in the container can be cited. In addition, there is no particular limitation on the conditions for the shear treatment, and it is preferably appropriately adjusted in such a manner as to obtain the coated active material described in "B. Coated active material".

[0114] 3. Coating active material

[0115] 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".

[0116] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any technical solution having substantially the same structure and achieving the same effects as the technical concept described in the patent claims of the present disclosure is included in the technical scope of the present disclosure.

[0117] [Example 1]

[0118] Metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and ion-exchanged water were mixed at a weight ratio of 4.52:191.8 to prepare an aqueous solution. Boric acid (manufactured by Nacalai Tesque Co., Ltd.) was added as a B source and dissolved in the aqueous solution. Furthermore, the boric acid was added in an amount such that the ratio (molar ratio) of the B element relative to the P element was 1.0. Furthermore, lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as a Li source and dissolved in the solution. Furthermore, the lithium hydroxide monohydrate was added in an amount such that the ratio (molar ratio) of the Li element relative to the total of the B element and the P element was 0.1. Thus, a precursor solution was prepared.

[0119] The precursor solution was dried using a spray dryer to obtain a white powder as a precursor. The obtained precursor was heat-treated at 230°C for 5 hours in air with a dew point controlled to less than -30°C. This yielded an oxide solid electrolyte (LBPO).

[0120] [Examples 2-3]

[0121] 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 the Li element to the total of the B element and the P element was 0.5 or 0.9.

[0122] [Comparative Example 1]

[0123] As the oxide solid electrolyte, an electrolyte not containing the Li element (BPO 4 : manufactured by Yoneyama Chemical Industry Co., Ltd.) was prepared.

[0124] [Comparative Example 2]

[0125] 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), an oxide solid electrolyte (Li-doped BPO4:LBPO) was prepared in which the ratio (molar ratio) of the Li element relative to the total of the B element and the P element was 0.5. Boric acid (manufactured by Aldrich) was used as the B source, orthophosphoric acid (manufactured by Kishida Chemical Co., Ltd.) was used as the P source, and lithium hydroxide monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the Li source. Calcination conditions were 500°C for 6 hours in air with a dew point controlled below -30°C. Note that, although the above-mentioned academic paper describes the use of phosphorus pentoxide (P2O5) as the P element source, phosphorus pentoxide becomes orthophosphoric acid by mixing with water, and therefore the same conditions apply to the starting materials.

[0126] [Comparative Example 3]

[0127] Hydrogen peroxide water (mass concentration 30%), ion exchange water and niobic acid (Nb2O5·3H2O) were added to the container. Furthermore, ammonia water (mass concentration 28%) was added to the above container. In addition, lithium hydroxide monohydrate was added. The container was stirred to obtain a solution containing Li element, Nb element and O element. Furthermore, in the above solution, it is speculated that the Nb element exists as a peroxide complex. The above solution was dried using a spray drying device to obtain a white powder. The obtained powder was heat-treated under atmospheric atmosphere at 200°C for 5 hours. Thus, an oxide solid electrolyte (LiNbO3) was obtained.

[0128] [Evaluation 1]

[0129] (ICP Analysis)

[0130] For the solid electrolytes of Examples 1 to 3 and Comparative Examples 1 and 3, elemental analysis was carried out using ICP emission spectrometry. First, concentrated hydrochloric acid was added to 0.01 g of the solid electrolyte and boiled to dissolve the solid electrolyte to prepare an evaluation sample. In addition, 0.01 g of the standard solution of Li, B, and P (1000 ppm, 10000 ppm) was diluted with pure water to prepare a standard sample. By measuring the standard sample, a calibration curve was prepared, and based on the calibration curve, the evaluation sample was measured to calculate the mass concentration of each element. Then, the element ratio (molar ratio) of Li, P and B was calculated from the mass concentration. In addition, as a measuring device, ICPR-9800 manufactured by Shimadzu Corporation was used. The results are shown in Table 1.

[0131] As shown in Table 1, it was confirmed that oxide solid electrolytes could be synthesized without compositional deviation in Examples 1 to 3. Furthermore, as shown in Table 1, Na was detected in the ICP analysis. This is believed to be derived from additives contained in commercially available metaphosphoric acid.

[0132]

Table 1

[0133]

[0134] (Particle size distribution measurement)

[0135] The average particle size (D 50 ). The results are shown in Table 2.

[0136] As shown in Table 2, the synthesized oxide solid electrolyte has a smaller average particle size than commercially available products.

[0137] (XRD measurement)

[0138] XRD measurements were performed on the oxide solid electrolytes of Comparative Examples 1 and 3 and Examples 1 to 3 using a device (Smartlab) manufactured by RIGAKU CORPORATION. The X-ray source was Cu, and the scanning range was 10° to 90°. The resulting diffraction patterns confirmed the presence of crystalline phases and identified the crystalline phases. The results are shown in Table 2.

[0139] As shown in Tables 1 and 2, no crystalline phase was observed in Comparative Example 3 and Examples 1 and 2, which were fired at relatively low temperatures. On the other hand, as shown in Example 3, even at relatively low firing temperatures, crystallinity was improved by increasing the Li ratio sufficiently.

[0140] (NMR measurement)

[0141] for 11The B nucleus was determined by NMR (solid 11 B-NMR). As a measuring device, a Fourier transform nuclear magnetic resonance device (FT-NMR device) ECA-500 manufactured by JEOL was used. The measuring conditions were set to single pulse mode, repetition time 60 seconds, cumulative number of times 8 times, and rotation speed 18 kHz. From the obtained graph, the presence or absence of tricoordinate B and tetracoordinate B was confirmed. Then, Sa / (Sa+Sb) was calculated from the peak area (Sa) of tricoordinate B and the peak area (Sb) of tetracoordinate B. The results are shown in Table 2.

[0142] As shown in Table 2, tricoordinate B was not confirmed in Comparative Examples 1 and 2. Furthermore, Academic Papers 1 and 2 concerning Comparative Example 2 also state that tricoordinate B was not confirmed (page 77 of Academic Paper 1 and page 316 of Academic Paper 2).

[0143] (Measurement of ionic conductivity and evaluation of chemical stability)

[0144] The solid electrolytes in the examples and comparative examples were each sandwiched between carbon-coated aluminum foils and uniaxially pressed for 120 seconds using a pressure of 2 tons. Evaluation samples were thus prepared. Each evaluation sample was placed in a thermostat at 25°C and AC impedance measurements were performed. The ion conductivity (lithium ion conductivity at 25°C) was calculated from the size of the resulting arc. The results are shown in Table 2.

[0145] Chemical stability was evaluated by performing CV measurement (oxidation current measurement). Specifically, the solid electrolytes in the examples and comparative examples were mixed with acetylene black in a volume ratio of 1:1 to produce a powder compact (green compact). The powder compact was used as the working electrode, the layer of sulfide solid electrolyte (10LiI-15LiBr-75Li3PS4) was used as the separator layer, and the Li-In alloy was used as the counter electrode to produce an evaluation battery cell. The evaluation battery cell was placed in a thermostatic bath at 25°C, and the potential was scanned at 0.1 mV / second in the voltage range of 1.9V to 4.4V to measure the oxidation current. The oxidation current of the second cycle was integrated (accumulated) and the area was calculated. Based on the size of the above area, the chemical stability was evaluated. It should be noted that the lower the chemical stability, the larger the integrated area. The results are shown in Table 2.

[0146] As shown in Table 2, while Comparative Example 1 exhibited good chemical stability, its ionic conductivity was low. Furthermore, Comparative Example 3 exhibited good ionic conductivity but low chemical stability. In contrast, Examples 1 to 3 exhibited both good ionic conductivity and chemical stability. This confirms that the oxide solid electrolytes disclosed herein exhibit both good chemical stability and good ionic conductivity.

[0147]

Table 2

[0148]

[0149] [Comparative Example 4]

[0150] Metaphosphoric acid and boric acid were mixed and fired at 230° C. for 5 hours in air with a dew point controlled to less than −30° C. Thus, an electrolyte (BPO 4 ) not containing the lithium element was synthesized as an oxide solid electrolyte.

[0151] [Comparative Example 5]

[0152] BPO4 was synthesized in the same manner as in Comparative Example 4 except that the calcination temperature was changed to 120°C.

[0153] [Evaluation 2]

[0154] (NMR measurement)

[0155] For the BPO4 of Comparative Examples 4 and 5, solid 11 B-NMR measurement. The results of Examples 2, 3 and Comparative Example 1 are shown together. Figure 4 .

[0156] like Figure 4 As shown, it was confirmed that even if sintering was performed at a low temperature, tricoordinate B could not be obtained in the absence of the Li element.

[0157] [Example 4]

[0158] An oxide solid electrolyte was synthesized in the same manner as in Example 3 except that the calcination temperature was changed to 450°C.

[0159] [Evaluation 3]

[0160] (NMR measurement)

[0161] For Examples 2 to 4 and Comparative Example 4, solid 31 The P element in the oxide solid electrolyte was analyzed by P-NMR. The results are shown in Figure 5 .

[0162] like Figure 5 As shown in Table 2, the higher the calcination temperature, the more peaks of P element derived from Li3PO4 are confirmed. Combined with the results of XRD measurement shown in Table 2, it is confirmed that the crystallinity is improved by increasing the calcination temperature.

[0163] In addition, if Figure 6 As shown, the oxide solid electrolyte of Example 4 was also solidified. 11 The results of B-NMR measurement were the same as those in Example 3, and a peak of tricoordinate B and a peak of tetracoordinate B were confirmed.

Claims

1. An oxide solid electrolyte comprising Li, B, P and O, characterized in that: Contains tricoordinate boron with a coordination number of 3.

2. The oxide solid electrolyte according to claim 1, characterized in that The oxide solid electrolyte contains tetracoordinate boron with a coordination number of 4, When the peak area of the tricoordinate boron obtained by NMR measurement of the oxide solid electrolyte is set as Sa and the peak area of the tetracoordinate boron is set as Sb, the ratio of the peak area Sa to the total of the peak area Sa and the peak area Sb, Sa / (Sa+Sb), is greater than 1%.

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

4. The oxide solid electrolyte according to claim 3, characterized in that The ratio Sa / (Sa+Sb) is 3% or more and 37% or less.

5. The oxide solid electrolyte according to claim 1, characterized in that The 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.

6. The oxide solid electrolyte according to claim 1, characterized in that The ionic conductivity at 25°C is 1.50×10 -9 S / cm or more.

7. The oxide solid electrolyte according to claim 1, characterized in that The average particle size D of the oxide solid electrolyte 50 It is 3.0 μm or more and 8.0 μm or less.

8. A coated active material, characterized in that include: An electrode active material and a coating layer covering the electrode active material, wherein the coating layer contains the oxide solid electrolyte according to any one of claims 1 to 7.

9. The coated active material according to claim 8, characterized in that The electrode active material is an oxide active material.

10. The coated active material according to claim 9, characterized in that The oxide active material is at least one of lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt manganese aluminum oxide.

11. The coated active material according to claim 8, characterized in that The electrode active material includes a negative electrode active material, the negative electrode active material is a Si-based active material, and the Si-based active material has an inclusion compound type I crystal phase or an inclusion compound type II crystal phase.

12. A battery, characterized in that include: 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, wherein: 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 coating the electrode active material, wherein the coating layer contains the oxide solid electrolyte according to any one of claims 1 to 7.

13. The battery according to claim 12, characterized in that The positive electrode active material layer contains the coating active material.

14. The battery according to claim 12, characterized in that The battery is a solid-state battery.

15. A method for producing a coated active material comprising an electrode active material and a coating layer coating the electrode active material, wherein: include: preparing an oxide solid electrolyte according to any one of claims 1 to 7; and The electrode active material is coated with the oxide solid electrolyte by a dry method to form the coating layer, Wherein, the preparation comprises: a precursor preparation process for preparing a precursor of the oxide solid electrolyte in a powdery form containing Li element, B element, P element, and O element; and The precursor is subjected to a calcination treatment in which the precursor is calcined at a temperature of 450° C. or lower.

16. The method according to claim 15, characterized in that In the calcination process, the precursor is calcined at a temperature of 120° C. or higher.

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