All-solid-state battery cell, solid electrolyte powder, method for producing solid electrolyte powder, and method for producing covered body

Abstract

Provided are: a solid electrolyte powder which contains 0.7% by mass to 5% by mass of Li, 8% by mass to 60% by mass of Nb, and 1.0% by mass to 30% by mass of P with respect to the solid electrolyte powder, with the content of the non-oxygen remainder, which is the remainder excluding oxygen (O), being 10% by mass or less with respect to the solid electrolyte powder, and which has a crystallite diameter of 100 nm or less; and related art thereof.

Description

All-solid-state battery cell, solid electrolyte powder, method for manufacturing solid electrolyte powder, and method for manufacturing coated body

[0001] The present invention relates to an all-solid-state battery cell, a solid electrolyte powder, a method for manufacturing a solid electrolyte powder, and a method for manufacturing a coated body.

[0002] In all-solid-state lithium-ion secondary batteries (hereinafter sometimes referred to as "all-solid-state batteries"), a solid electrolyte is placed between a positive electrode active material and a negative electrode active material as a separator, and lithium ions are conducted between the two active materials via the solid electrolyte. Various solid electrolytes have been developed, including sulfide-based, oxide-based, and polymer-based solid electrolytes, but sulfide-based solid electrolytes are currently considered to be advantageous in terms of ionic conductivity and manufacturing costs.

[0003] All-solid-state batteries have a problem in that the interfacial resistance between the positive electrode active material and the solid electrolyte separator increases, which tends to reduce battery performance such as capacity. This increase in interfacial resistance is thought to be mainly caused by the reaction between the positive electrode active material and the solid electrolyte, which forms high-resistance areas on the surface of the positive electrode active material, and this problem is likely to occur when a sulfide-based solid electrolyte is used as the separator.

[0004] Therefore, the surface of the positive electrode active material is covered with a lithium ion conductive oxide (typically LiNbO ３ Attempts have been made to prevent the positive electrode active material from reacting with the solid electrolyte, which is the separator, by covering it with a protective solid electrolyte made of a halide or a compound such as methyl methacrylate (well-known examples are listed below).

[0005] Claim 1 of Patent Document 1 discloses an all-solid-state lithium battery using a lithium ion conductive solid electrolyte as an electrolyte, characterized in that the lithium ion conductive solid electrolyte is mainly composed of a sulfide, and the surface of the positive electrode active material is coated with a lithium ion conductive oxide.

[0006] Patent Document 2 describes the following: When the voltage of the working electrode of an electrochemical cell is swept toward the oxidation side, a current resulting from a non-Faradaic reaction that does not involve the exchange of electrons, and a minute current resulting from a side reaction of water adsorbed on the surface of the conductive additive or impurities, flows. Subsequently, an excessive current begins to flow due to oxidative decomposition of the solid electrolyte. In the test example described in Patent Document 2, the voltage at which a current value of 3 μA or more begins to flow is defined as the oxidative decomposition voltage.

[0007] WO2007 / 004590 Pamphlet WO2020 / 174868 Pamphlet

[0008] In recent years, there has been an increasing demand for improved output characteristics and energy density of all-solid-state batteries. Therefore, there is a demand for solid electrolytes that have high lithium ion conductivity and a high decomposition voltage. This decomposition voltage refers to the oxidative decomposition voltage as defined in Patent Document 2.

[0009] The solid electrolyte used as the protective material deteriorates when a high charging voltage is applied. ３ In this case, deterioration accelerates when the charging voltage exceeds 4.45 V. In other words, the LiNbO ３ In this case, the degradation accelerates when the decomposition voltage exceeds about 4.45V.

[0010] An object of the present invention is to provide a solid electrolyte powder that can achieve both high lithium ion conductivity and high decomposition voltage, a method for producing the same, and a method for producing a coating thereof, and to provide an all-solid-state battery cell that achieves both high lithium ion conductivity and high decomposition voltage by using the solid electrolyte powder or the coating thereof.

[0011] A first invention is an all-solid-state battery cell comprising: a high-potential-side conductive material; a first solid electrolyte in contact with the high-potential-side conductive material; a second solid electrolyte in contact with the first solid electrolyte; and a low-potential-side conductive material in contact with the second solid electrolyte, wherein the first solid electrolyte contains at least one of the following solid electrolytes (1) and (2) as a main component, and the second solid electrolyte contains a sulfide as a main component: (1) A solid electrolyte containing 0.7 to 5 mass% of Li, 8 to 60 mass% of Nb, and 1.0 to 30 mass% of P relative to the solid electrolyte, with the content of non-oxygen remainders other than oxygen (O) being 10 mass% or less relative to the solid electrolyte, and having a crystallite diameter of 100 nm or less. (2) A solid electrolyte containing Li, Nb, and P in a molar ratio of Li:Nb:P=x:y:z (x+y+z=100), where x is 15 to 50, y is 5 to 65, and z is 5 to 65, and the crystallite diameter is 100 nm or less.

[0012] A second invention is the all-solid-state battery cell according to the first invention, wherein the first solid electrolyte is the following (3) and (4): (3) A solid electrolyte containing 0.7 to 2.6 mass % of Li, 8 to 60 mass % of Nb, and 2.0 to 30 mass % of P relative to the solid electrolyte, and wherein, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 30 or less, the content of non-oxygen remainders other than oxygen (O) among the remainders is 10 mass % or less relative to the solid electrolyte, and the crystallite size is 100 nm or less; (4) A solid electrolyte containing 15 to 30, y is 5 to 65, and z is 5 to 65 relative to the molar ratio of Li, Nb, and P contained in the solid electrolyte is Li:Nb:P=x:y:z (x+y+z=100), and the crystallite size is 100 nm or less.

[0013] A third invention is the all-solid-state battery cell according to the first or second invention, wherein the high-potential-side conductive material includes a positive electrode active material and other conductive members, and the positive electrode active material and the first solid electrolyte are in contact with each other, but the positive electrode active material and the second solid electrolyte are not in contact with each other.

[0014] A fourth invention is the all-solid-state battery cell according to any one of the first to third inventions, wherein the high-potential-side conductive material includes a positive electrode active material and other conductive members, and the first solid electrolyte coats surfaces of particles of the positive electrode active material.

[0015] A fifth invention is a solid electrolyte powder containing 0.7 to 5 mass % of Li, 8 to 60 mass % of Nb, and 1.0 to 30 mass % of P relative to the solid electrolyte powder, wherein the content of a non-oxygen remainder other than oxygen (O) among the remainders is 10 mass % or less relative to the solid electrolyte powder, and the crystallite size is 100 nm or less.

[0016] A sixth invention is the solid electrolyte powder according to the fifth invention, wherein the solid electrolyte powder contains 0.7 to 2.6 mass% of Li, 8 to 60 mass% of Nb, and 2.0 to 30 mass% of P, and when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 30 or less.

[0017] A seventh invention is the solid electrolyte powder according to the fifth or sixth invention, wherein the content of the transition metal element in the non-oxygen remainder is 3 mass % or less based on the solid electrolyte powder.

[0018] An eighth invention is a solid electrolyte powder, wherein, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65, and the crystallite size is 100 nm or less.

[0019] A ninth invention is the solid electrolyte powder according to the eighth invention, wherein the content of the non-oxygen remainder other than oxygen (O) in the remainder is 10 mass % or less based on the solid electrolyte powder.

[0020] A tenth aspect of the present invention is the solid electrolyte powder according to the eighth or ninth aspect of the present invention, wherein x is 15 to 30, y is 5 to 65, and z is 5 to 65.

[0021] An eleventh invention is the solid electrolyte powder according to any one of the fifth to tenth inventions, wherein the total mass percent of Li, Nb, and P in the solid electrolyte powder according to this embodiment is in the range of 25 to 65 mass percent.

[0022] A twelfth invention is the solid electrolyte powder according to any one of the fifth to eleventh inventions, wherein the particle size of the solid electrolyte powder is a volume-based cumulative 50% particle size (D50) obtained by a laser diffraction / scattering particle size distribution analyzer of 5 to 50 μm.

[0023] A thirteenth invention is the solid electrolyte powder according to any one of the fifth to twelfth inventions, which is for use in an all-solid-state battery cell.

[0024] A fourteenth invention is an all-solid-state battery cell comprising: a high-potential side conductive material; a first solid electrolyte in contact with the high-potential side conductive material; a second solid electrolyte in contact with the first solid electrolyte; and a low-potential side conductive material in contact with the second solid electrolyte, wherein the first solid electrolyte contains the solid electrolyte powder according to any one of the fifth to thirteenth inventions as a main component, and the second solid electrolyte contains a sulfide as a main component.

[0025] A fifteenth invention is a method for producing a solid electrolyte powder according to the fifth or eighth invention, comprising: a step of dry-mixing a Li raw material, a Nb raw material, and a P raw material in an inert atmosphere having a dew point of −20° C. or less to obtain a mixed powder; and a firing step of firing the mixed powder at 350° C. or less in an air atmosphere.

[0026] A sixteenth invention is the method for producing a solid electrolyte powder according to the fifteenth invention, wherein the Li raw material is lithium oxide, the Nb raw material is hydrous niobium oxide, and the P raw material is diphosphorus pentoxide.

[0027] A seventeenth invention is a method for producing a solid electrolyte powder, comprising: a phosphate ion adding step of adding phosphate ions to an aqueous solution containing niobium polyoxide ions and lithium; and a drying step of drying the aqueous solution obtained by the adding step to obtain a solid electrolyte powder, wherein when the molar ratio of Li, Nb, and P in the aqueous solution obtained by the adding step is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65.

[0028] An eighteenth invention is a method for producing a coated body, comprising: a step of adding phosphate ions to an aqueous solution containing niobium polyoxide ions and lithium to obtain an aqueous solution in which x is 15 to 50, y is 5 to 65, and z is 5 to 65 when the molar ratio of Li, Nb, and P in the aqueous solution is Li:Nb:P=x:y:z (x+y+z=100); and a coating step of bringing the aqueous solution obtained by the step into contact with a positive electrode active material to coat the surface of the positive electrode active material with a solid electrolyte, wherein the solid electrolyte satisfies at least one of the following conditions: i) A solid electrolyte containing 0.7 to 5 mass% of Li, 8 to 60 mass% of Nb, and 1.0 to 30 mass% of P relative to the solid electrolyte, wherein the content of non-oxygen remainders other than oxygen (O) is 10 mass% or less relative to the solid electrolyte, and wherein the crystallite size is 100 nm or less. ii) A solid electrolyte wherein, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65, and wherein the crystallite size is 100 nm or less.

[0029] The present invention provides a solid electrolyte powder that can achieve both high lithium ion conductivity and high decomposition voltage, a method for producing the same, and a method for producing a coating body thereof. Furthermore, the present invention also provides an all-solid-state battery cell that achieves both high lithium ion conductivity and high decomposition voltage by using the solid electrolyte powder or the coating body thereof.

[0030] FIG. 1 is a schematic diagram of the cross-sectional structure of one aspect of an all-solid-state battery cell according to the present embodiment. FIG. 2 is a schematic diagram of the cross-sectional structure of another aspect of an all-solid-state battery cell according to the present embodiment. FIG. 3 is a schematic diagram of the cross-sectional structure of a lithium-ion secondary battery utilizing an all-solid-state battery cell according to the present embodiment. FIG. 4 is a flow diagram of a method for producing a solid electrolyte powder according to the present invention. FIG. 5 is a diagram showing the composition ratios of Li, Nb, and P in the molar ratio representation of the solid electrolyte powder obtained in each example. FIG. 6 is a diagram showing the composition ratios of Li, Nb, and P in the molar ratio representation of the solid electrolyte powder obtained in each example, together with the decomposition voltage as a numerical value. FIG. 7 is a diagram showing the potential (unit: V(vs Li / Li)) in the electrochemical evaluation of each example. ＋) on the horizontal axis and current value (unit: μA) on the vertical axis. FIG. 8 is a plot of the evaluation of the crystallinity in each example, with 2θ (unit: °) on the horizontal axis and intensity (cps) on the vertical axis. FIG. 9 is a flow diagram for coating a first solid electrolyte on a positive electrode active material using the coating solution according to the present invention. FIG. 10 is a diagram showing FT-IR spectra of aqueous solutions obtained in Comparative Example 2 and Example 10. FIG. 11 is a schematic diagram of the cross-sectional structure of an electrochemical cell constructed to examine the discharge DCR increase rate in Comparative Example 2 and Example 10.

[0031] Hereinafter, embodiments of the present invention will be described. The symbol "to" indicates a value greater than or equal to a predetermined value and less than or equal to a predetermined value.

[0032] In this specification, the term "high potential side" means that the solid electrolyte is located on the high potential electrode (positive electrode in a battery) side in the charge path relative to the solid electrolyte as a separator disposed between the electrodes. The term "low potential side" means that the solid electrolyte is located on the low potential electrode (negative electrode in a battery) side in the charge path relative to the solid electrolyte as a separator disposed between the electrodes.

[0033] This embodiment will be described in the following order: 1. Solid electrolyte powder 2. All-solid-state battery cell 3. Lithium-ion secondary battery 4. Manufacturing method of solid electrolyte powder

[0034] [1. Solid Electrolyte Powder] The solid electrolyte powder according to this embodiment mainly comprises the following components. <Component 1> The solid electrolyte powder contains 0.7 to 5 mass % of Li, 8 to 60 mass % of Nb, and 1.0 to 30 mass % of P. This component is also referred to as a "mass % component." <Component 2> The content of the non-oxygen remainder other than O, which is oxygen, among the remainder is 10 mass % or less relative to the solid electrolyte powder. <Component 3> The crystallite diameter is 100 nm or less.

[0035] Regarding the above-mentioned configuration 1, when the amount of Li (lithium) contained in the solid electrolyte powder is 0.7 mass % or more and 5.0 mass % or less, this is a sufficient amount as a carrier, and high lithium ion conductivity (hereinafter also referred to as ion conductivity) can be ensured. －１１ S / cm or more, preferably 5.0×10 －１０The lower limit of the amount of Li contained in the solid electrolyte powder may be 1.0 mass%, 1.1 mass%, 1.2 mass%, 1.3 mass%, or 1.4 mass%, and the upper limit of the amount of Li contained in the solid electrolyte powder may be 4.0 mass%, 3.5 mass%, or 2.6 mass%.

[0036] When the amount of Nb (niobium) contained in the solid electrolyte powder is 8% by mass or more and 60% by mass or less, the solid electrolyte can sufficiently function in a battery. The upper limit of the amount of Nb contained in the solid electrolyte powder may be 55% by mass.

[0037] When the amount of P (phosphorus) contained in the solid electrolyte powder is 1.0 mass% or more and 30 mass% or less, sufficient improvement in voltage resistance can be achieved. The lower limit of the amount of P contained in the solid electrolyte powder may be 2.0 mass%. The upper limit of the amount of P contained in the solid electrolyte powder may be 25 mass% or 20 mass%.

[0038] The decomposition voltage obtained by measuring an electrochemical cell prepared using the solid electrolyte powder having the following composition is 5.0 V or more, and the ionic conductivity is 5×10 －１０ S / cm or more, which is preferable. "The solid electrolyte powder contains 0.7 to 2.6 mass% Li, 8 to 60 mass% Nb, and 2.0 to 30 mass% P, and when the molar ratio of Li, Nb, and P is Li:Nb:P = x:y:z (x + y + z = 100), x is 30 or less." Details of how to obtain decomposition voltage and ionic conductivity from the solid electrolyte powder are described in the Examples section. The expression described in the "Means for Solving the Problems" section generalizes these details as much as possible.

[0039] Regarding the above-mentioned configuration 2, the content of elements other than O (i.e., non-oxygen remainder) among the remainders other than Li, Nb, and P in the solid electrolyte powder is specified to be 10 mass % or less with respect to the solid electrolyte powder.

[0040] The abundance ratio (molar ratio) of oxygen is mainly determined by the valences of Li, Nb, and P. That is, Li is +1, Nb is +5, P is +5, and oxygen is -2, and the amount of oxygen is determined so as to compensate for the charge (this is the main amount of oxygen). The general formula is xLi２ O-yNb ２ O ５ -zP ２ O ５ is.

[0041] When the non-oxygen remainder contains elements other than Li, Nb, and P, the amount of oxygen can be calculated in the same way from the valence of the element (referred to as the secondary oxygen amount). The non-oxygen remainder can contain H, C, N, other metal elements, metalloid elements, and non-metal elements. For example, H can be H ２ O is derived from CO ２ N comes from N ２ O ５ It comes from.

[0042] The amount of oxygen (molar ratio) can be calculated from the sum of the amount of main oxygen and the amount of secondary oxygen, and the mass ratio of oxygen can be calculated by further mass conversion. The mass ratio of oxygen can also be measured by a known method such as an oxygen analyzer. This is particularly effective when the valence of the non-oxygen remaining element is unknown.

[0043] The above definition makes it clear that the majority (i.e., 90 mass % or more) of the solid electrolyte powder according to this embodiment is composed of Li, Nb, P, and O. The content of the non-oxygen remainder is preferably 5 mass % or less, and more preferably 1 mass % or less.

[0044] The content of transition metal elements (preferably all metal elements) in the non-oxygen remainder is preferably 3 mass % or less relative to the solid electrolyte powder.

[0045] The content of non-oxygen components can be measured using a nitrogen analyzer for N (nitrogen) and a carbon / sulfur analyzer for C (carbon), and other elements can be measured using an inductively coupled plasma atomic emission spectrometry (ICP-AES). The total content (mass%) of elements other than Li, Nb, P, and O determined by these measurements is defined as the content of the non-oxygen remainder.

[0046] A solid electrolyte powder containing Li, Nb, and P in amounts that satisfy the above-mentioned configuration 1 and having a crystallite size of 100 nm or less (i.e., satisfying the above-mentioned configuration 3) achieves both high lithium ion conductivity and high decomposition voltage when processed into an all-solid-state battery cell, as will be shown in the Examples section below.

[0047] The configuration of the solid electrolyte powder according to this embodiment can also be expressed as follows. That is, in the solid electrolyte powder according to this embodiment, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65, and the crystallite diameter is 100 nm or less. This configuration relating to x, y, and z is also referred to as a "molar ratio expressed configuration."

[0048] When x is 15 or more and 50 or less, the amount is sufficient as a carrier, and high lithium ion conductivity (hereinafter also referred to as ionic conductivity) can be ensured. －１１ S / cm or more of ionic conductivity can be ensured.

[0049] Preferably, x is 30 or less.

[0050] When y is 5 or more and 65 or less, the function as a solid electrolyte in a battery can be sufficiently exhibited.

[0051] If z is 5 or more and 65 or less, the voltage resistance can be sufficiently improved.

[0052] An electrochemical cell prepared using a solid electrolyte powder in which x is 15 to 30, y is 5 to 65, and z is 5 to 65 has a decomposition voltage of 5.0 V or more and an ionic conductivity of 5×10 －１０ This is preferable because it is S / cm or more.

[0053] Regarding the above-mentioned configuration 3, the crystallite diameter of the solid electrolyte powder is specified to be 100 nm or less.

[0054] The crystallite diameter of the solid electrolyte powder is determined by powder X-ray diffraction (XRD) measurement using the Scherrer formula (Dhkl = Kλ / βcosθ) from diffraction peak data observed in the 2θ: 15° to 40° region. The crystallite diameter is preferably 50 nm or less. More preferably, it is 30 nm or less. Even more preferably, the solid electrolyte powder is an amorphous substance in which a halo X-ray chart is observed in the 2θ: 15° to 40° region. Note that a "halo" is observed as a broad rise of gentle undulations in X-ray intensity that does not show a clear peak in the 2θ: 15° to 40° region in the X-ray chart obtained by XRD measurement. The half-width of the halo is 2θ: 2° or more. When the crystallite diameter exceeds 100 nm and the solid electrolyte powder is no longer amorphous, the ionic conductivity decreases to 5×10 －１０ The viscosity drops to less than 1000 kJ / cm.

[0055] It is also preferable to combine the above molar ratio expression with the content of the above structure 1 (i.e., expression in mass %).It is also preferable to combine the above molar ratio expression with the content of the above structure 3.

[0056] The above expressions in mass % or molar ratios may be combined with the following structures.

[0057] The molar ratio of P to Li (P / Li) in the solid electrolyte powder according to this embodiment is preferably 0.2 or more and 3.5 or less. From the viewpoint of voltage resistance, it is more preferably 1.4 or more and 3.5 or less. The molar ratio of P to Nb (P / Nb) in the solid electrolyte powder according to this embodiment is preferably 0.1 or more and 6.5 or less. From the viewpoint of voltage resistance, it is preferably 1.4 or more and 6.5 or less, more preferably 3.0 or more and 6.5 or less, and even more preferably 4.0 or more and 6.5 or less.

[0058] In the solid electrolyte powder according to this embodiment, the total mass % of Li, Nb, and P is preferably in the range of 25 to 65 mass %.

[0059] The particle size of the solid electrolyte powder according to this embodiment is not particularly limited, but the volume-based cumulative 50% particle size (D50) obtained by measuring the volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer is preferably 5 to 50 μm. From the viewpoint of ionic conductivity, the volume-based cumulative 50% particle size (D50) is preferably 5 to 15 μm.

[0060] [2. All-Solid-State Battery Cell] The all-solid-state battery cell according to this embodiment (in other words, the arrangement structure of the solid electrolyte) mainly comprises the following components: A conductive material on a high potential side A first solid electrolyte in contact with the conductive material on the high potential side A second solid electrolyte in contact with the first solid electrolyte A conductive material on a low potential side in contact with the second solid electrolyte Contents that overlap with those explained in [1. Solid Electrolyte Powder] above will not be described below.

[0061] FIG. 1 shows a schematic cross-sectional structure of one embodiment of an all-solid-state battery having an all-solid-state battery cell of the present invention. This diagram shows a simplified cell structure to explain the positional relationship of each component. A high-potential-side conductive material 3 and a low-potential-side conductive material 4 face each other, sandwiching a first solid electrolyte 1 and a second solid electrolyte 2, which serves as a separator. The first solid electrolyte 1 is interposed between the high-potential-side conductive material 3 and the second solid electrolyte 2. There is a contact area between the high-potential-side conductive material 3 and the first solid electrolyte 1, and there is also a contact area between the first solid electrolyte 1 and the second solid electrolyte 2.

[0062] In an all-solid-state battery, the high-potential-side conductive material 3 is typically composed of a cathode active material 31 and a conductive material 32 other than the cathode active material. The cathode active material 31 is both an ion-conductive material and a conductive material. Its form is not limited, and it may be particulate or powder. The conductive material 32 other than the cathode active material may be a current collector, a conductive additive, or the like. In actual all-solid-state batteries, the cathode material is generally composed of conductive materials such as a current collector, a cathode active material, and a conductive additive, as well as particles of an ion-conductive material (solid electrolyte) mixed to fill the spaces between the particles of the cathode active material. The high-potential-side conductive material 3 in FIG. 1 is a schematic diagram illustrating the positional relationship of the conductive material portion of such a cathode material relative to the first solid electrolyte 1. In the illustrated embodiment, the cathode active material 31 and the first solid electrolyte 1 are in contact with each other, and ionic conduction between the second solid electrolyte 2 (a separator) and the cathode active material 31 occurs via the first solid electrolyte 1. Furthermore, since the positive electrode active material 31 is in contact with the conductive material 32 other than the positive electrode active material, electrical conduction is ensured between the positive electrode active material 31 and an external wiring member (not shown) connected to the conductive material 32 other than the positive electrode active material.

[0063] As the positive electrode active material 31, known materials can be used, and if a new positive electrode active material is developed, it can also be used. A representative known positive electrode active material is LiCoO ２ (LCO type), LiNiO ２ (LNO type), LiMn ２ O ４ (LMO type), LiNiCoAlO ２ (NCA type), LiNiCoMnO ２ (NCM type), Li ２ MnO ３ -LiNiCoMnO ２ (solid solution type), LiNiMnO ４ (spinel type), LiMnFePO ４ (phosphate type), Li ２ FeSiO ４ (silicate type), etc.

[0064] The first solid electrolyte 1 comprises at least one of the following solid electrolytes (1) and (2) as a main component: (1) a solid electrolyte containing 0.7 to 5 mass% of Li, 8 to 60 mass% of Nb, and 1.0 to 30 mass% of P relative to the solid electrolyte, with the content of non-oxygen remainders other than oxygen (O) being 10 mass% or less relative to the solid electrolyte, and having a crystallite diameter of 100 nm or less; (2) a solid electrolyte containing Li, Nb, and P in a molar ratio of Li:Nb:P=x:y:z (x+y+z=100), where x is 15 to 50, y is 5 to 65, and z is 5 to 65, and having a crystallite diameter of 100 nm or less.

[0065] The term "main component" as used herein means that the total content of the constituent materials of the first solid electrolyte 1 is 50% by mass or more, which is a solid electrolyte that satisfies at least one of the conditions (1) and (2). The total content of the constituent materials of the first solid electrolyte 1 that satisfy at least one of the conditions (1) and (2) is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0066] The solid electrolyte may be a powder as described above in [1. Solid Electrolyte Powder], but the solid electrolyte may also be provided on the positive electrode in other forms (e.g., layered or film-like). Therefore, the term "solid electrolyte" will be used in this section. However, for simplicity of explanation, hereinafter, solid electrolyte powder will be exemplified.

[0067] The first solid electrolyte 1 preferably further satisfies the following conditions (3) and (4): (3) A solid electrolyte containing 0.7 to 2.6 mass% of Li, 8 to 60 mass% of Nb, and 2.0 to 30 mass% of P relative to the solid electrolyte, and, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 30 or less, the content of non-oxygen residues other than oxygen (O) among the remainders is 10 mass% or less relative to the solid electrolyte, and the crystallite diameter is 100 nm or less; (4) A solid electrolyte containing 0.7 to 2.6 mass% of Li, Nb, and P relative to the solid electrolyte, x is 15 to 30, y is 5 to 65, and z is 5 to 65, when the molar ratio of Li, Nb, and P contained in the solid electrolyte is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 30, y is 5 to 65, and z is 5 to 65, and the crystallite diameter is 100 nm or less.

[0068] In the embodiment shown in Fig. 1 , the conductive material 3 on the high potential side is completely blocked from contact with the second solid electrolyte 2, which is the separator, by the first solid electrolyte 1. Therefore, the components constituting the conductive material 3 on the high potential side are protected from reactions resulting from contact with the second solid electrolyte 2, which mainly contains sulfides or the like. In other words, the first solid electrolyte 1 functions as a protective material. Furthermore, as will be described later, the first solid electrolyte 1 used in the present invention has excellent resistance to deterioration when a high voltage is applied when placed in contact with the second solid electrolyte 2, which mainly contains sulfides or the like. Therefore, the all-solid-state battery cell of the embodiment shown in Fig. 1 is effective in improving the decomposition voltage.

[0069] The second solid electrolyte 2 is composed mainly of sulfide from the viewpoints of ion conductivity and production costs, and functions as a separator. "Composed mainly of sulfide" means that the total sulfide content of the constituent materials of the second solid electrolyte 2 is 50 mass% or more. The total sulfide content of the constituent materials of the second solid electrolyte 2 is preferably 80 mass% or more, and more preferably 90 mass% or more.

[0070] The sulfides may be any known substance having ionic conductivity, and if a new ionic conductive substance is developed, it may also be applicable. ６ P.S. ５ Cl (crystal (argyrodite)), Li ９．５４ Si １．７４ P １．４４ S １１．７ Cl ０．３ (crystal), Li １０ GeP ２ S １２ (crystal), 30Li ２ S・26B ２ S ３ ・44LiI (glass), 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ (glass), 57Li ２ S・38SiS ２ ・5Li ４ SiO ４(glass), 70Li ２ S・30P ２ S ５ (glass), Li ７ P ３ S １１ (glass ceramic), Li ３．２５ P ０．９５ S ４ (glass ceramic), etc.

[0071] In an all-solid-state battery, the low-potential-side conductive material 4 is typically composed of a negative electrode active material 41 and a conductive material 42 other than the negative electrode active material. In actual all-solid-state batteries, the negative electrode material is generally composed of conductive materials such as a current collector and a negative electrode active material, as well as particles of an ion-conductive material (solid electrolyte) mixed to fill the spaces between the particles of the negative electrode active material. The low-potential-side conductive material 4 in FIG. 1 is a schematic illustration of the positional relationship of the conductive material portion of such a negative electrode material relative to the second solid electrolyte 2. The configuration of the low-potential-side conductive material 4 and the positional relationship between the conductive material 4 and the second solid electrolyte 2 can be similar to those of known all-solid-state batteries. If necessary, a third solid electrolyte may be disposed between the second solid electrolyte 2 and the low-potential-side conductive material 4.

[0072] In the embodiment of the all-solid-state battery shown in FIG. 1 , the entire conductive material 3 on the high potential side is separated from the second solid electrolyte (sulfide or the like) serving as a separator by the presence of the first solid electrolyte 1, and therefore the decomposition voltage can be improved without covering the surfaces of the particles of the positive electrode active material 31 with a solid electrolyte serving as a protective material.

[0073] FIG. 2 shows a schematic cross-sectional structure of another embodiment of the all-solid-state battery cell of the present invention. As with FIG. 1, the cell structure is simplified to illustrate the positional relationship of each component. A high-potential-side conductive material 3 and a low-potential-side conductive material 4 face each other across a second solid electrolyte 2, which serves as a separator. A first solid electrolyte 1 is adjacent to the second solid electrolyte 2 and the high-potential-side conductive material 3. In the embodiment of FIG. 2, among the components constituting the high-potential-side conductive material 3, the positive electrode active material 31 contacts the first solid electrolyte 1, thereby avoiding direct contact with the second solid electrolyte, and a conductive material 32 other than the positive electrode active material has a portion that directly contacts the second solid electrolyte 2 without passing through the first solid electrolyte 1. In addition, the first solid electrolyte 1 may completely cover the positive electrode active material 31 and not be in direct contact with the conductive material 32, but if the first solid electrolyte 1 is sufficiently thin, the positive electrode active material 31 and the conductive material 32 are in electrical contact due to the tunnel effect, and the positive electrode active material 31 and the conductive material 32 are at the same potential. The rest of the structure is the same as that of the embodiment shown in FIG. 1 above.

[0074] 2 , ionic conduction between the second solid electrolyte 2, which serves as a separator, and the positive electrode active material 31 occurs via the first solid electrolyte 1. Therefore, in this embodiment, the first solid electrolyte 1 also functions as a protective material. Furthermore, the surface portion of the positive electrode active material 31 that is not in contact with the first solid electrolyte 1 is adjacent to a conductive material 32 other than the positive electrode active material, thereby ensuring electrical conduction between the positive electrode active material 31 and an external wiring member (not shown) connected to the conductive material 32 other than the positive electrode active material.

[0075] Furthermore, when the first solid electrolyte is as thin as several tens of nanometers or less, electrons can overcome the potential barrier of the first solid electrolyte, ensuring electrical conduction between the positive electrode active material 31 and the conductive material 32. Therefore, there is no problem in terms of the battery structure even if the positive electrode active material 31 is completely covered with the first solid electrolyte 1.

[0076] 2 , a case where a positive electrode active material powder is used in which the particle surfaces of the positive electrode active material 31 are coated with a protective material, the first solid electrolyte 1, can be cited. In this case, in an actual all-solid-state battery, the contact portion between the positive electrode active material 31 and the conductive material 32 other than the positive electrode active material corresponds to the portion where particles of a conductive additive (e.g., stainless steel or carbon) penetrate the protective coating layer and are electrically connected to the positive electrode active material 31.

[0077] As a special case, when the positive electrode active material powder is completely covered with the first solid electrolyte 1, if the thickness of the first solid electrolyte (layer) is as thin as several tens of nanometers or less, electrical conduction between the conductive additive and the positive electrode active material is ensured by the tunnel effect, even without providing a contact portion as described above.

[0078] The ion-conductive material (solid electrolyte) filling the gaps between particles of the positive electrode active material 31 conducts ions through a coating layer made of the first solid electrolyte 1, which functions as a protective material. Therefore, a second solid electrolyte 2 (e.g., a sulfide) of the same type as the separator can be used as the ion-conductive material. In FIG. 2 , the portion of the second solid electrolyte 2 in contact with the first solid electrolyte 1 can be considered to correspond to particles of the second solid electrolyte 2 serving as the positive electrode material filling the gaps between particles of the positive electrode active material 31. The particles of the second solid electrolyte 2 are in contact with particles of the second solid electrolyte 2 constituting the separator layer and are responsible for ion conduction. That is, the portion indicated by the reference numeral 2 in FIG. 2 corresponds to a collective description of the particles of the second solid electrolyte 2 serving as the separator and the particles of the second solid electrolyte 2 serving as the positive electrode material filling the gaps between particles of the positive electrode active material 31.

[0079] In any case, it is preferable that the conductive material on the high potential side includes a positive electrode active material and other conductive members, and that the positive electrode active material and the first solid electrolyte are in contact with each other, but the positive electrode active material and the second solid electrolyte are not in contact with each other.

[0080] The all-solid-state battery cell according to this embodiment has a decomposition voltage of 4.5 V or more and an ionic conductivity of 5×10 －１1 Preferably, the decomposition voltage is 5.0 V or more and / or the ionic conductivity is 5×10 －１０ S / cm or more.

[0081] [3. Lithium-ion secondary battery] The technical concept of the present invention is also reflected in a lithium-ion secondary battery that utilizes the all-solid-state battery cell according to this embodiment. A known configuration may be adopted as a specific configuration of the lithium-ion secondary battery other than the all-solid-state battery cell (e.g., FIG. 3).

[0082] [4. Manufacturing Method of Solid Electrolyte Powder] Dry Manufacturing Method of Solid Electrolyte Powder Figure 4 is a flow diagram of the manufacturing method of solid electrolyte powder according to the present invention. The manufacturing method (dry method) of solid electrolyte powder according to this embodiment mainly comprises the following steps: a mixed powder obtaining step in which a Li source material, a Nb source material, and a P source material are dry-mixed in an inert atmosphere with a dew point of -20°C or less to obtain a mixed powder; and a firing step in which the mixed powder is fired at 350°C or less in an air atmosphere. The amounts of raw materials are 0.7 to 5 mass% of the Li source material, 8 to 60 mass% of the Nb source material, and 1.0 to 30 mass% of the P source material, based on the obtained mixed powder, mixed in a dry manner. Then, a solid electrolyte powder having a crystallite diameter of 100 nm or less (preferably amorphous, hereinafter referred to as "amorphous") is manufactured. Details overlapping with those described in [1. Solid Electrolyte Powder] above will be omitted below. [1. The mass % and molar ratio expressions described in [1. Solid electrolyte powder] can also be applied to the amounts of Li raw material, Nb raw material, and P raw material charged in the method for producing a solid electrolyte powder. Also, the amount of the non-oxygen remainder (10 mass % or less) described in [1. Solid electrolyte powder] can be applied to the method for producing a solid electrolyte powder.

[0083] As the Li raw material, it is preferable to prepare a lithium compound such as lithium hydroxide, lithium oxide, or lithium nitrate. The Li raw material is preferably lithium oxide. The reason is that lithium oxide is classified as a network modifier oxide of glass-forming oxides, and is also a suitable intermediate oxide for Nb ２ O ５ This is because when coexisting with lithium oxide, it easily becomes amorphous and it is easy to obtain a solid electrolyte powder with a crystallite size of 100 nm or less.

[0084] As Nb raw materials, NbO, NbO ２ , Nb ２ O ５ ・nH２ It is preferable to prepare niobium oxide such as NbO, which is an intermediate oxide of glass-forming oxides. ２ O ５ ・nH ２ The use of O is preferred because the solid electrolyte powder obtained tends to be amorphous and the crystallite size is likely to be 100 nm or less.

[0085] As the P raw material, it is preferable to prepare phosphorus compounds such as diphosphorus pentoxide, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. ２ O ５ Diphosphorus pentoxide is a network-forming oxide of glass-forming oxides, and the mixed powder tends to become amorphous, making it easy to obtain a solid electrolyte powder with a crystallite size of 100 nm or less.

[0086] A preferred example of a combination of the respective raw materials is when the Li raw material is lithium oxide, the Nb raw material is niobium oxide hydroxide, and the P raw material is diphosphorus pentoxide.

[0087] (Weighing Step) The Li raw material, the Nb raw material, and the P raw material are weighed so that the obtained solid electrolyte powder satisfies the above-mentioned composition expressed in mass % and / or composition expressed in molar ratio.

[0088] (Mixed Powder Obtaining Step) In the method for producing a solid electrolyte powder according to this embodiment, raw materials containing solid substances Li, Nb, and P are mechanically mixed. The mechanical mixing can be performed by a method of pulverizing and mixing using a pulverizer such as a dry ball mill.

[0089] The time for pulverization and mixing is preferably set in the range of 1 to 50 hours so that both substances are mixed thoroughly. The particle size of the mixed powder is preferably set to 5 to 50 μm as described above.

[0090] The atmosphere in the mixing vessel preferably has a dew point of -20°C or lower (preferably -40°C or lower) and is an inert gas atmosphere such as argon or nitrogen. If the dew point of the atmosphere is -20°C or lower, the reaction between the moisture in the atmosphere and the P raw material can be suppressed. As a result, the generation of phosphoric acid, which can be an obstacle when obtaining an amorphous material, can be suppressed, and a solid electrolyte powder with a crystallite size of 100 nm or less can be obtained. The dew point of the atmosphere in the mixing vessel may be set to, for example, -100°C or higher, -90°C or higher, or -80°C or higher.

[0091] (Firing step) The mixed powder obtained by the mechanical mixing is fired to synthesize an amorphous powder containing Li, Nb, and P. The firing atmosphere is preferably air. The firing temperature is preferably in the range of 150 to 350°C. The lower limit of the firing temperature is preferably 200°C. The firing time may be set, for example, in the range of 0.5 to 10 hours. The rate of temperature rise from room temperature to the firing temperature can be 5 to 15°C / min.

[0092] (Pulverization step) The fired powder obtained in the firing step may be further pulverized. In this case, the particle size of the pulverized powder is preferably 5 to 50 μm as described above.

[0093] <<Method for Producing Coating Liquid for Coating Positive Electrolyte with First Solid Electrolyte (Wet Method)>> FIG. 9 is a flow diagram for coating a positive electrode active material with a first solid electrolyte using the coating liquid according to the present invention.

[0094] The coating liquid may be produced as follows. That is, in the method of the present invention for producing an aqueous solution (coating liquid) containing niobium polyacid ions, lithium ions, and phosphate ions, hydrous niobium oxide is used as the niobium starting material. Hydrous niobium oxide and LiOH are dissolved in water to obtain an aqueous solution containing niobium polyacid ions and lithium, and then phosphate ions are added to the aqueous solution to obtain an aqueous solution containing niobium polyacid ions, lithium ions, and phosphate ions. This process is also referred to as the coating liquid production process. Hereinafter, wet processes will be referred to by element names or compound names rather than element symbols.

[0095] In the present invention, an aqueous coating liquid may be used to coat the positive electrode active material powder with the first solid electrolyte 1. As the aqueous lithium niobate coating liquid, an aqueous lithium niobate precursor solution using polyacid ions, which has excellent chemical stability, is used.

[0096] Furthermore, once solubilized in an alkaline solution, niobium polyacid ions maintain the form of polyacid even when phosphoric acid is added and the pH of the system is lowered to about 4. The aqueous solution of the present invention containing niobium polyacid ions, lithium ions, and phosphate ions contains niobium in the form of a polyacid, and therefore has excellent storage stability.

[0097] The reason why the coexistence of niobium polyoxide ions and phosphate ions in an aqueous lithium ion solution suppresses the increase in the specific surface area of ​​the coated positive electrode active material is unclear at present, but the present inventors speculate as follows.

[0098] Specifically, the presence of phosphate ions in an aqueous solution containing niobium polyphosphate ions, lithium ions, and phosphate ions improves the wettability of the aqueous solution to the surface of the positive electrode active material. The phosphate ions in the aqueous solution, which has excellent storage stability, alter the double-layer structure at the interface, resulting in a change in the structure of the coating layer. Alternatively, the use of stable polyphosphate ions can suppress gas generation, which is a cause of pore formation, and the trace amounts of phosphate ions in the coating layer may also suppress the generation of pores during drying.

[0099] Therefore, by using the coating liquid of the present invention, a high coverage rate and uniform coating can be achieved.

[0100] [Nb source] Anhydrous niobium oxide (Nb ２ O ５ Since niobium oxide is poorly soluble in water, the production method of the present invention uses amorphous, water-soluble niobium oxide as the Nb source. ２ O ５ ・nH ２ O (n is not 0, for example, 3≦n≦16).

[0101] [Polyacid ions] Polyacids are anionic species formed by the condensation of oxoacids, and polyacids of transition metal elements can be considered to be molecular ionic species of metal oxides. When there is one type of metal element, they are called isopolyacids, and when there are multiple metal elements, they are called heteropolyacids.

[0102] Although the potential-pH diagram for niobium has not yet been established, niobium hydroxide precipitates in the neutral region, and therefore Nb(OH) ５ or HNbO ３ Solid phases such as these are considered to be stable chemical species.

[0103] When an alkali is added to an aqueous solution containing these solid phases to raise the pH of the system, excess OH － The presence of ions causes niobium to react with, for example, Nb(OH) ６ － and NbO ３ － etc. As the pH of the system is further increased, the soluble niobium oxide is thought to take on various condensation states depending on the pH of the system, but in this specification, the niobium oxide solubilized on the alkaline side is considered to become niobium polyacid ions collectively. Note that niobium polyacid ions once solubilized on the alkaline side maintain the form of a polyacid even when the pH of the system is lowered to about 4 by adding phosphoric acid.

[0104] The aqueous solution of the present invention containing niobium polyacid ions, lithium ions, and phosphate ions has excellent storage stability because it contains niobium in the form of a polyacid. The form of niobium may be a soluble polyacid ion, and its structure is not particularly limited.

[0105] The fact that niobium in an aqueous solution is in the form of a polyacid ion can be confirmed by FT-IR measurement. When niobium in an aqueous solution is in the form of a polyacid ion, the FT-IR spectrum is obtained at a wave number of 850 cm. －１ ±20cm －１ An absorption peak due to Nb—O bonds is observed around this point.

[0106] [Lithium hydroxide] In the production method of the present invention, lithium hydroxide (LiOH) is used as the Li source. LiOH may be either anhydrous or hydrated. The method of the present invention for producing an aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions is characterized in that LiOH is first added to an aqueous solution containing niobic acid to dissolve the niobic acid.

[0107] Since LiOH itself is a strong alkali, when LiOH is added to an aqueous solution containing niobic acid, the pH of the system rises, dissolving the niobium oxide and forming stable niobium polyoxide ions. Hydrogen peroxide is then added to the alkaline aqueous solution containing the niobium polyoxide ions and lithium ions; the effect of hydrogen peroxide will be described later.

[0108] When the molar ratio of Li, Nb, and P in the aqueous solution of the present invention containing niobium polyacid ions, lithium ions, and phosphate ions is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65.

[0109] In the aqueous solution of the present invention containing niobium polyacid ions, lithium ions, and phosphate ions, the niobium is believed to be primarily in the form of a relatively stable polyacid. Adding hydrogen peroxide to the aqueous solution further improves storage stability. Because the aqueous solution of the present invention does not contain organic substances, a coating layer with low volume resistivity can ultimately be obtained.

[0110] [Phosphate ion] A major technical feature of the present invention is that phosphate ions are present in an aqueous solution containing niobium polyphosphate ions and lithium ions. The source of phosphate ions can be water-soluble phosphoric acid (PO ) such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, or their sodium salts or ammonium salts. ４ ３－Phosphoric acid is a tribasic acid that dissociates in three stages in an aqueous solution, and therefore can exist in various forms in the aqueous solution, such as phosphate ion, monohydrogen phosphate ion, dihydrogen phosphate ion, and pyrophosphate ion. However, the form of existence is determined by the pH of the aqueous solution, not by the type of chemical used as a phosphate ion source, and therefore the above ions containing a phosphate group are collectively referred to as phosphate ions.

[0111] In terms of the content of phosphate ions in an aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions, in accordance with the molar ratio expression, z is 5 to 65, preferably 10 to 45, as described above. When z is 5 or more, the effect of adding phosphate ions is sufficient. When z is 65 or less, the effect of adding phosphate ions does not reach saturation.

[0112] The sum of the lithium, niobium, and phosphorus contents in the aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 10% by mass or less. If the sum of the lithium, niobium, and phosphorus contents is 1% by mass or more, it is not necessary to increase the amount of the aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions to obtain the required coating layer thickness, and there is no need to increase the water content, which is cost-effective. If the sum of the lithium, niobium, and phosphorus contents is 20% by mass or less, the viscosity of the aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions is appropriate, and clogging of the narrow piping of the coating treatment equipment can be suppressed.

[0113] The amount of impurity elements other than lithium, niobium, phosphorus, oxygen, and hydrogen in the aqueous solution containing niobium polyoxide ions, lithium ions, and phosphate ions is preferably 10% by mass or less, more preferably 1% by mass or less. A specific example of an impurity element is nitrogen, and the amount of nitrogen is preferably 0.1% by mass or less, 0.01% by mass or less, 0.001% by mass or less, 0.0001% by mass or less (1 ppm) or less, and 0.1 ppm or less, in that order. In addition, carbonate ions and the like are considered as unavoidable impurities. Here, the term "impurities" refers to impurities contained in the evaporation residue when the precursor aqueous solution is evaporated to dryness at 200°C.

[0114] [Hydrogen Peroxide] Hydrogen peroxide can be further added to the aqueous solution of the present invention to improve storage stability. In this case, it is preferable to add hydrogen peroxide so that the concentration of hydrogen peroxide in the aqueous solution is 0.01% by mass or more and 10% by mass or less. If the concentration of hydrogen peroxide is 0.01% by mass or more, the generated niobium polyacid can be prevented from reacting with hydroxide ions and decomposing. Furthermore, if the concentration is 10% by mass or less, the generated niobium polyacid can be prevented from reacting with hydrogen peroxide and decomposing.

[0115] The molar ratio (POA / Nb) of the amount of hydrogen peroxide to niobium added is preferably in the range of 0.1 to 1. A ratio of 0.1 or more is advantageous in avoiding decomposition of the niobium polyacid due to reaction with hydroxide ions. Furthermore, a ratio of 1 or less facilitates decomposition due to reaction of the generated niobium polyacid with hydrogen peroxide.

[0116] From the viewpoint of reactivity, the addition of hydrogen peroxide is preferably carried out after dissolving hydrous niobium oxide with LiOH to form stable niobium polyphosphate ions. Note that the addition of the phosphate ions and the addition of hydrogen peroxide in this section may be carried out in either order.

[0117] Although the added hydrogen peroxide decomposes over time, it is preferable that the aqueous solution contain 0.01% by mass or more and 6.7% by mass or less of hydrogen peroxide. If the hydrogen peroxide content is 0.01% by mass or more, the effect of maintaining the stability of the precursor aqueous solution can be adequately exhibited. Furthermore, if the hydrogen peroxide content is 6.7% by mass or less, the effect of adding hydrogen peroxide does not become saturated.

[0118] Furthermore, the ratio of the number of moles of hydrogen peroxide to 1 mole of niobium (POC / Nb), calculated from the concentration of hydrogen peroxide and the concentration of niobium present in the aqueous solution, is preferably in the range of 0.01 to 1. Within the above range, not only does the effect of adding hydrogen peroxide not become saturated, but also, when used as a coating solution, it does not dissolve the positive electrode active material. If hydrogen peroxide is present in an appropriate amount, not too little, it is possible to suppress the decomposition of niobium polyacid due to reaction with hydroxide ions. A more preferable range of POC / Nb is 0.05 to 0.5.

[0119] [pH] In the production method of the present invention, the pH of the aqueous solution used to form niobium polyacid ions is determined almost automatically by the amounts of LiOH (a strong alkali), phosphoric acid, and hydrogen peroxide added, and therefore no special pH adjustment is required. However, the pH is preferably 7.5 to 12.5, which is on the alkaline side. To ensure stable formation of niobium polyacid ions, a pH of 9.0 to 12.0 is more preferred. Adding phosphoric acid to a solution containing this niobium polyacid and lithium lowers the pH of the system, but it has been confirmed that niobium polyacid exists stably at a pH of 3 or higher. The pH of the solution to which phosphoric acid has been added is preferably 12.5 or less, more preferably 12 or less. The pH value herein is measured using a glass electrode with a pH meter equipped with a temperature-compensated electrode, calibrated according to JIS Z8802 using an appropriate buffer solution appropriate for the pH range to be measured.

[0120] The method for coating a cathode active material with a solid electrolyte using a coating liquid according to this embodiment mainly comprises the following steps. The following steps also have technical significance as a method for producing a coated body in which a cathode active material is coated with a solid electrolyte. Each example described in this specification is applicable to the content described in this paragraph. A phosphate ion addition step of adding phosphate ions to an aqueous solution containing niobium polyacid ions and lithium. A coating step of contacting the aqueous solution obtained by the addition step with the cathode active material to coat the surface of the cathode active material with a solid electrolyte. When the molar ratio of Li, Nb, and P in the aqueous solution obtained by the addition step is Li:Nb:P = x:y:z (x + y + z = 100), x is 15 to 50, y is 5 to 65, and z is 5 to 65. Through each of the above steps, at least one of the following solid electrolytes is coated on the surface of the cathode active material. As a result, a coated body is obtained. i) A solid electrolyte containing 0.7 to 5 mass% of Li, 8 to 60 mass% of Nb, and 1.0 to 30 mass% of P relative to the solid electrolyte, wherein the content of non-oxygen remainder other than oxygen (O) among the remainders is 10 mass% or less relative to the solid electrolyte, and wherein the crystallite size is 100 nm or less. ii) A solid electrolyte containing 0.7 to 5 mass% of Li, 8 to 60 mass% of Nb, and 1.0 to 30 mass% of P relative to the solid electrolyte, wherein the content of non-oxygen remainder other than oxygen (O) is 10 mass% or less relative to the solid electrolyte, and wherein the crystallite size is 100 nm or less.

[0121] A specific embodiment of the coating step will be described later in Example 10. The cathode active material mixing step in Fig. 9 is not limited to a specific method as long as the coating liquid and the cathode active material are mixed. The same applies to the drying step, and the specific method is not limited.

[0122] This section describes the case where a positive electrode active material powder is coated with a first solid electrolyte 1 using an aqueous coating liquid. Alternatively, a solid electrolyte powder may be obtained from this coating liquid. This method mainly comprises the following steps. Each example described herein is applicable to the contents described in this paragraph. A phosphate ion addition step involves adding phosphate ions to an aqueous solution containing niobium polyoxide ions and lithium. A drying step involves drying the aqueous solution obtained by the addition step to obtain a solid electrolyte powder. When the molar ratio of Li, Nb, and P in the aqueous solution obtained by the addition step is Li:Nb:P = x:y:z (x + y + z = 100), x is 15 to 50, y is 5 to 65, and z is 5 to 65. Furthermore, like solid electrolyte powder obtained by a dry process, this solid electrolyte powder may be used to fabricate an all-solid-state battery cell.

[0123] <Modifications, etc.> One aspect of the present invention has been described above, but the above disclosure shows one exemplary aspect of the present invention. In other words, the technical scope of the present invention is not limited to the above exemplary aspect, and various modifications are possible without departing from the gist of the present invention. In addition, the above disclosure can be arbitrarily selected and combined with the following modifications.

[0124] The present invention will be specifically explained below using examples, but the present invention is not limited to the following examples.

[0125] Dry Method Examples: Comparative Example 1, Examples 1 to 9 In each example, lithium oxide (Li, manufactured by Wako Pure Chemical Industries, Ltd.) was used. ２ O), hydrous niobium oxide (manufactured by HC Starck, Nb ２ O ５ ・nH ２ O, Nb ２ O ５ content 56.4%), diphosphorus pentoxide (Wako Pure Chemical Industries, Ltd., P ２ O ５ ) were weighed as the Li raw material, Nb raw material, and P raw material in the amounts shown in Table 1 below. The weighed Li raw material, Nb raw material, and P raw material were mixed and stirred at 380 rpm for 24 hours together with zirconia balls Φ10 mm using a planetary ball mill (manufactured by Fritsch GmbH, P-7) in an argon atmosphere with a dew point temperature of −60° C. to obtain a mixed powder.

[0126] The mixed powder was placed in a hot air drying furnace and heat-treated at a firing temperature of 200°C for 5 hours to obtain a fired powder. The fired powder was then pulverized with zirconia balls (Φ10 mm) in a planetary ball mill (Fritsch, P-7) while stirring at 380 rpm in air for 5 hours to obtain a solid electrolyte powder for each example.

[0127] In Comparative Example 1, a solid electrolyte powder was obtained in the same manner as in each Example, except that the P raw material was not used and the Li raw material and Nb raw material were weighed in the amounts shown in Table 1.

[0128] The solid electrolyte powder obtained in each example was subjected to ICP measurement, and the constituent elements of the solid electrolyte powder were quantitatively analyzed. The contents of niobium, lithium, and phosphorus obtained by the measurement are shown in Table 2. The ICP measurement method is as follows.

[0129] In each example, 0.1 g of the calcined powder (solid electrolyte powder) obtained after the pulverization process was weighed. 1 mL of 46% by mass hydrofluoric acid was added to the powder sample to decompose the sample. The decomposition solution was adjusted to a constant volume using a 100 mL measuring flask and diluted 100 times with 5% by mass hydrochloric acid. The concentrations of the constituent elements of the solid electrolyte powder, including niobium, lithium, and phosphorus, in the diluted solution were measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES, CP-720 manufactured by Agilent Technologies, Inc.).

[0130] The nitrogen content in the solid electrolyte powder obtained in each example was analyzed using a nitrogen analyzer (EMGA-920, manufactured by Horiba, Ltd.). The carbon content in the solid electrolyte powder obtained in each example was analyzed using a trace carbon / sulfur analyzer (ETMA-U510, manufactured by Horiba, Ltd.). The content of the remainder other than lithium, niobium, and phosphorus obtained from the ICP measurement, nitrogen content, and carbon content measurements other than O (i.e., non-oxygen remainder) was 1% by mass or less in all examples.

[0131] FIG. 5 is a diagram showing the composition ratios of Li, Nb, and P in the solid electrolyte powder obtained in each example, expressed as a molar ratio.

[0132] The volume-based cumulative 50% particle size (D50) of the solid electrolyte powder obtained in each example was measured, and the measurement results are shown in Table 2. The volume-based cumulative 50% particle size (D50) was measured in this specification as follows. The particle size distribution of the obtained solid electrolyte powder was measured using a laser diffraction particle size distribution analyzer (HELOS H3758 & RODOS, manufactured by Nippon Laser). The dispersion method was airflow dispersion (nitrogen), the dispersion pressure was 5 bar, and the focal length was 200 mm.

[0133] Here, in accordance with the evaluation method disclosed in Patent Document 2, an all-solid-state electrochemical cell was fabricated in which the solid electrolyte of the test material (first solid electrolyte) and a sulfide-based solid electrolyte (second solid electrolyte) were adjacent to each other, and the decomposition voltage resulting from the oxidation reaction of the test material was determined. Specifically, the experiment was carried out as follows. <1. Preparation of composite mixture> The solid electrolyte powders of the comparative example and example and stainless steel (SUS316) powder were weighed out to a volume ratio of 50:50. Then, they were mixed in a mortar to prepare a composite mixture. <2. Fabrication of electrochemical cell> An argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ 57 mg of HCl was added. This was press-molded at a pressure of 80 MPa to obtain a second solid electrolyte. Next, 20 mg of the solid electrolytes of the Examples and Comparative Examples were added on top of the second solid electrolyte and press-molded at a pressure of 80 MPa to form a first solid electrolyte. Next, 20 mg of the composite mixtures of the Examples and Comparative Examples were added on top of the first solid electrolyte and press-molded at a pressure of 360 MPa to form a composite. Next, metal In (200 μm thick), metal Li (300 μm thick), and metal In (200 μm thick) were stacked in this order below the second solid electrolyte (opposite the first solid electrolyte). This was press-molded at a pressure of 80 MPa to form a counter electrode member with a three-layer structure of In / Li / In. Next, stainless steel plate current collectors were placed on the top and bottom of the laminate, and current collecting leads were attached. An electrochemical cell was fabricated using the above process.

[0134] FIG. 6 is a diagram showing the composition ratios of Li, Nb, and P in the molar ratio representation of the solid electrolyte powder obtained in each example, as well as the decomposition voltage as numerical values.

[0135] The electrochemical evaluation method is as follows. The electrochemical cell was placed in a thermostatic chamber at 25°C. Using a potentio / galvanostat (Prinston VersaSTAT4), an electrochemical measurement device, the voltage was swept from the open circuit voltage of the electrochemical cell to 6.0 V (vs. In-Li) (synonymous with 6.6 V (vs. Li)), and the reaction current was measured to evaluate voltage stability. When the voltage on the working electrode side of the electrochemical cell was swept toward the oxidation side, a current derived from a non-Faradic reaction not involving the transfer of electrons and a minute current derived from a side reaction of adsorbed water and impurities flowed. The current up to 4.0 V (vs. Li) was relatively small, less than 10 μA, and the increase was less than 10 μA / V, so it was determined to be a current derived from a side reaction. When a voltage exceeding 4.0 V was applied, a point where the current value increased appeared, indicating that this reaction was the current associated with the decomposition reaction. In this test, the decomposition voltage was defined as the voltage at which a current of 15 μA flowed.

[0136] FIG. 7 shows the potential (unit: V vs Li / Li) in the electrochemical evaluation of each example. ＋ ) on the horizontal axis and the current value (unit: μA) on the vertical axis.

[0137] The ionic conductivity was measured as follows. 0.2 g of the powder sample according to each example was placed in a cylindrical container with a diameter of 10 mm and pressed at 180 MPa using a press to obtain a green compact. The obtained green compact was again pressed at 300 MPa using a CIP molding machine (CPP-PS200A, CPP28-300B, manufactured by NBA Systems Corporation), and silver paste was applied to both sides to prepare a sample for ionic conductivity measurement. The ionic conductivity of the obtained sample was measured by the AC impedance method using an impedance analyzer (ZENNIUM, manufactured by ZAHNER) at a temperature of 30°C under a nitrogen atmosphere, in a range of 0.1 Hz to 4 MHz, with an amplitude voltage of 500 mV. The resistance of the sample according to the example was then determined from a Cole-Cole plot (complex impedance plane plot) of the measured values, and the ionic conductivity was calculated from the obtained resistance value. The calculated ionic conductivity values ​​are listed in Table 2 above. When the ionic conductivity was 5.0 × 10 －１０ (S / cm) or more is very good, and the ionic conductivity is 5.0 × 10 －１０ (S / cm) Less than 5.0 x 10 －１１ (S / cm) or more was recorded as "good."

[0138] XRD measurement was carried out on the solid electrolyte powder according to each example under the following measurement conditions. FIG. 8 is a plot of the evaluation of the crystallinity in each example, with 2θ (unit: °) on the horizontal axis and intensity (cps) on the vertical axis. <XRD measurement conditions> Measurement device: XRD-6100 (manufactured by Shimadzu Corporation) Tube: Cu (measured at a wavelength of Kα1) Tube voltage: 40 kV Tube current: 30 mA Divergence slit: 1.0° Scattering slit: 1.0° Receiving slit: 0.3 mm Step width: 0.02° / step Measurement time: 0.60 sec

[0139] 8, in the XRD spectrum of the solid electrolyte powder according to each example, a halo with a half-width of 2θ:2° or more was observed in the region of 2θ:15° to 40°, confirming that the solid electrolyte powder according to each example was amorphous.

[0140] As shown in Table 2, the decomposition voltage of each Example was higher than that of Comparative Example 1. As a result, each Example provided an all-solid-state battery cell and a lithium-ion secondary battery that achieved both high lithium-ion conductivity and high decomposition voltage. In other words, it was found that the solid electrolyte powder and the method for producing the same according to each Example can achieve both high lithium-ion conductivity and high decomposition voltage.

[0141] <<Wet Method Examples: Comparative Example 2 and Example 10>> In order to coat the positive electrode active material with the first solid electrolyte, the following first solid electrolyte coating solution was prepared and used to coat the positive electrode active material. The first solid electrolyte coating solution for Comparative Example 2 and Example 10 was prepared as follows. 41 g of lithium hydroxide (LiOH, manufactured by Wako Pure Chemical Industries, Ltd.) and niobium oxide hydroxide (Nb ２ O ５ ・nH ２ O, manufactured by HC Starck, Nb ２ O ５125 g of lithium niobate (content: 56.4%) was mixed with 734 g of water and stirred at 200 rpm. The mixture was then heated to 70°C at a temperature increase rate of 0.75°C / min and maintained at 70°C for 7 hours. After the temperature increase, 29 g of hydrogen peroxide was added and the mixture was filtered to obtain a lithium niobate solution of Comparative Example 2. 49 g of water was added to 35 g of the obtained lithium niobate solution to obtain a coating solution of Comparative Example 2. Furthermore, 48 g of water and 1.1 g of phosphoric acid (Wako Pure Chemical Industries, Ltd., 85% phosphoric acid solution) were added to 35 g of the lithium niobate solution to obtain a coating solution of Example 10. The pH and ICP measurements of the coating solutions obtained in each example were performed. The values ​​obtained by the measurements are listed in Table 3. The components of the coating solution were analyzed using an inductively coupled plasma atomic emission spectroscopy (ICP-AES, Agilent Technology 700 Series). A 0.1 g sample was taken from the precursor solution and weighed. 15 mL of pure water and 5 mL of hydrochloric acid were added, heated, and allowed to cool. 2 mL of hydrogen peroxide solution was then added, allowed to cool, and the solution volume was adjusted to 100 mL. ICP-AES analysis was performed. The mole numbers of the niobium, lithium, and phosphorus contents obtained by this ICP quantitative analysis were used to calculate the molar ratios of the present invention. Furthermore, to confirm whether the niobium in the aqueous solutions of Comparative Example 2 and Example 10 was a polyanion, Fourier transform infrared spectroscopy (FT-IR) was performed using a Thermo Fisher Scientific NICOLET 7600. To eliminate the low-wavenumber peaks of the water solvent, background measurements were performed using water and attenuated total reflection (ATR) spectroscopy. A germanium prism was used for the measurement, and the incident angle was 45°. FT-IR measurements were performed on the aqueous solutions of Comparative Example 2 and Example 10, and the wave number was 850 cm －１ ±20cm －１ An absorption peak due to Nb—O bonds was observed near ≈ ...

[0142] The coating liquids of Comparative Example 2 and Example 10 were dried in the air at 200°C to obtain solid electrolyte powders. The powders (solid electrolyte powders) of Comparative Example 2 and Example 10 obtained after air drying were subjected to quantitative analysis of the constituent elements of the solid electrolyte powder, measurement of the nitrogen content, and measurement of the volume-based cumulative 50% particle size (D50) of the solid electrolyte powder in the same manner as in Example 1. The results are shown in Table 3. Measurements of decomposition voltage and ionic conductivity were also performed. The values ​​obtained by the measurements are shown in Table 4.

[0143] XRD measurements were performed on the powders of Comparative Example 2 and Example 10 obtained after air drying in the same manner as in Example 1. As a result, a halo with a half-width of 2θ:2° or more was observed in the XRD spectrum of the solid electrolyte powder of each example in the region of 2θ:15° to 40°, confirming that the solid electrolyte powder of each example was amorphous.

[0144] Next, as the positive electrode active material powder, LiNi １／３ Mn １／３ Co １／３ O ２ A 4Sorb US cathode active material powder manufactured by Yuasa Ionics Co., Ltd. was used, and the BET specific surface area measured by the single-point BET method was 0.538 m ２ / g. The coating solutions of Comparative Example 2 and Example 10 were used to coat the first solid electrolyte onto the positive electrode active material powder. The coating method was as follows. 40 g of the positive electrode active material powder was mixed with 20 g of the solution of Comparative Example 2 and Example 10 obtained above, and the mixture was coated using a coating device (JD-1 manufactured by Kawata) (positive electrode active material mixing step, drying step). The coating conditions were as follows: Slurry supply rate: 3 mL / min. Dispersion air pressure: 500 kPa Dispersion air temperature: 200°C Drying air temperature: 135°C Drying blower air flow rate: 900 L / min. Classification blower air flow rate: 890 L / min.

[0145] The coverage rate when the first solid electrolyte was coated on the positive electrode active material powder was calculated based on the element amounts measured using an XPS (JPS-9200 manufactured by JEOL Ltd.). The calculation formula is as follows: Equation 1. The calculated coverage rates are shown in Table 5. Coverage rate (%) = (Nb + P) / (Ni + Co + Mn + Nb + P) × 100 (Equation 1)

[0146] In the positive electrode active material powder coated with the first solid electrolyte of this example, it can be assumed that Nb and P, which are not contained in the positive electrode active material powder, exist only in the coating layer. In addition, the thickness of the coating layer of the positive electrode active material coated with the first solid electrolyte is determined by the amount of Nb and P in the coating solution. ２ O ５ and P ２ O ５ This is expressed by the following formula 2 (the same applies to each of the following examples): If the Nb content in the coated positive electrode active material powder is a (mass %) and the P content is b (mass %), the mass ratio of Nb and P in the coating layer, c (mass %), is the ratio of the atomic weight of Nb and P to the atomic weight of Nb. ２ O ５ and P ２ O ５ The Nb content and P content are measured by the method described below. c = a × Nb ２ O ５ Molecular weight of Nb / (atomic weight of Nb×2)+b×P ２ O ５ Molecular weight of P / (atomic weight of P×2) (Equation 2) Furthermore, the specific surface area S (m ２ / g) and the density of the first solid electrolyte (g / cm 3 ), the average film thickness t (nm) of the coating layer is expressed by the following formula: Note that 10 on the right side of the following formula 3 is a conversion coefficient: t (nm) = 10 × C / (d × S) (Formula 3) Note that the density of the first solid electrolyte is 4.13 g / cm 3The calculation was performed using the actual measured values ​​(measured using a MICRO-ULTRAPY C1200e pycnometer manufactured by Anton Paar Corporation for the first solid electrolyte powder in Example 10). The contents (mass%) of Nb and P in the positive electrode active material powder coated with the first solid electrolyte were measured as follows. 0.1 g of the positive electrode active material powder coated with the first solid electrolyte was weighed out. 1 mL of hydrofluoric acid with a concentration of 46 mass% was added to the powder sample to decompose the sample. The decomposition solution was adjusted to a constant volume using a 100 mL measuring flask and diluted 100 times with 5 mass% hydrochloric acid. The concentrations of the constituent elements of the positive electrode active material powder, including niobium and phosphorus, in the diluted solution were measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES, CP-720 manufactured by Agilent Technologies, Inc.).

[0147] FIG. 11 is a schematic diagram of the cross-sectional structure of an electrochemical cell constructed to examine the discharge DCR increase rate in Comparative Example 2 and Example 10. The following electrochemical cells were fabricated using cathode active material powder coated with a first solid electrolyte using the coating liquids of Comparative Example 2 and Example 10. The fabricated electrochemical cells were subjected to float charging at a constant voltage, and the direct current internal resistance (DCR) of the electrochemical cells was measured to determine the discharge DCR increase rate for evaluating the degree of degradation of the electrochemical cells. Specifically, the experiment was carried out as follows. 70 mg of cathode active material coated with the first solid electrolyte, an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ A composite material mixture was prepared by mixing 30 mg of an argyrodite-type sulfide solid electrolyte (LiCl) and 3.1 mg of carbon as a conductive material in a mortar. ６ P.S. ５100 mg of Cr(Cl) was added. This was press-molded at a pressure of 185 MPa to obtain a second solid electrolyte. Next, 10 mg of the composite mixture of the example and comparative example was added on top of the second solid electrolyte and press-molded at a pressure of 370 MPa to form a composite. Next, metal In (thickness 200 μm), metal Li (thickness 300 μm), and metal In (thickness 200 μm) were stacked in this order below the second solid electrolyte (opposite the first solid electrolyte). This was press-molded at a pressure of 185 MPa to form a counter electrode member consisting of a three-layer structure of In / Li / In. Next, stainless steel plate current collectors were placed above and below the laminate, and current collecting leads were attached. An electrochemical cell was fabricated using the above process.

[0148] The battery evaluation method is as follows. The electrochemical cell was placed in a thermostatic chamber at 55°C. Using a charge / discharge measuring device (HJ1001SD8 manufactured by Hokuto Denko Corporation), the voltage was swept from the open circuit voltage of the electrochemical cell to 3.83 V (vs. In-Li) (synonymous with 4.45 V (vs. Li)), and float charging was performed for 30 days. The DCR increase rate was calculated using the following method. After float charging for 30 days, the voltage of the electrochemical cell was adjusted to 3.9 V (vs. Li), and then the cell was discharged for 10 seconds at 1 C (C: current value capable of charging / discharging the cell capacity in 1 hour). The discharge DCR increase rate was calculated by subtracting the voltage at the start of the test (0 seconds) from the voltage at the end of the test (10 seconds) and dividing the value by the current value. The calculated discharge DCR increase rates are shown in Table 6.

[0149] REFERENCE SIGNS LIST 1 First solid electrolyte 2 Second solid electrolyte 3 High potential side conductive material 4 Low potential side conductive material 31 Positive electrode active material 32 Conductive material other than positive electrode active material 41 Negative electrode active material 42 Conductive material other than negative electrode active material

Claims

1. An all-solid-state battery cell comprising: a high-potential side conductive material; a first solid electrolyte in contact with the high-potential side conductive material; a second solid electrolyte in contact with the first solid electrolyte; and a low-potential side conductive material in contact with the second solid electrolyte, wherein the first solid electrolyte contains at least one of the following solid electrolytes (1) and (2) as a main component, and the second solid electrolyte contains a sulfide as a main component: (1) A solid electrolyte containing 0.7 to 5 mass% Li, 8 to 60 mass% Nb, and 1.0 to 30 mass% P relative to the solid electrolyte, with the content of non-oxygen remainders other than oxygen (O) being 10 mass% or less relative to the solid electrolyte, and having a crystallite diameter of 100 nm or less. (2) A solid electrolyte containing Li, Nb, and P in a molar ratio of Li:Nb:P=x:y:z (x+y+z=100), where x is 15 to 50, y is 5 to 65, and z is 5 to 65, and the crystallite diameter is 100 nm or less.

2. The all-solid-state battery cell according to claim 1, wherein the first solid electrolyte is one of the following (3) and (4): (3) A solid electrolyte containing 0.7 to 2.6 mass% Li, 8 to 60 mass% Nb, and 2.0 to 30 mass% P relative to the solid electrolyte, and when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 30 or less, the content of non-oxygen remainder other than oxygen (O) is 10 mass% or less relative to the solid electrolyte, and the crystallite size is 100 nm or less; (4) A solid electrolyte containing 15 to 30, y is 5 to 65, and z is 5 to 65 relative to the solid electrolyte, when the molar ratio of Li, Nb, and P contained in the solid electrolyte is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 30, y is 5 to 65, and z is 5 to 65, and the crystallite size is 100 nm or less.

3. The all-solid-state battery cell according to claim 1, wherein the high potential side conductive material includes a positive electrode active material and another conductive member, the positive electrode active material and the first solid electrolyte are in contact with each other, and the positive electrode active material and the second solid electrolyte are not in contact with each other.

4. The all-solid-state battery cell according to claim 1, wherein the high potential side conductive material includes a positive electrode active material and other conductive members, and the positive electrode active material has a coating formed on the surface of a particle of the positive electrode active material with the first solid electrolyte.

5. A solid electrolyte powder comprising 0.7-5 mass% Li, 8-60 mass% Nb, and 1.0-30 mass% P relative to the mass of the solid electrolyte powder, the content of non-oxygen remainder other than oxygen (O) being 10 mass% or less relative to the mass of the solid electrolyte powder, and a crystallite size of 100 nm or less.

6. The solid electrolyte powder according to claim 5, wherein the solid electrolyte powder contains 0.7 to 2.6 mass% Li, 8 to 60 mass% Nb, and 2.0 to 30 mass% P, and when the molar ratio of Li, Nb, and P is Li:Nb:P = x:y:z (x + y + z = 100), x is 30 or less.

7. The solid electrolyte powder according to claim 5, wherein the content of the transition metal element in the non-oxygen remainder is 3 mass % or less based on the solid electrolyte powder.

8. A solid electrolyte powder in which, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65, and the crystallite size is 100 nm or less.

9. The solid electrolyte powder according to claim 8, wherein the content of non-oxygen remainder other than oxygen (O) in the remainder is 10 mass % or less based on the solid electrolyte powder.

10. The solid electrolyte powder according to claim 8, wherein x is 15 to 30, y is 5 to 65, and z is 5 to 65.

11. The solid electrolyte powder according to any one of claims 5 to 10, wherein the total mass percentage of Li, Nb, and P in the solid electrolyte powder is in the range of 25 to 65 mass percent.

12. The solid electrolyte powder according to any one of claims 5 to 10, wherein the particle size of the solid electrolyte powder is a volume-based cumulative 50% particle size (D50) obtained by a laser diffraction / scattering particle size distribution measurement device, and is 5 to 50 μm.

13. The solid electrolyte powder according to any one of claims 5 to 10, which is for use in an all-solid-state battery cell.

14. An all-solid-state battery cell comprising: a high-potential side conductive material; a first solid electrolyte in contact with the high-potential side conductive material; a second solid electrolyte in contact with the first solid electrolyte; and a low-potential side conductive material in contact with the second solid electrolyte, wherein the first solid electrolyte contains as a main component the solid electrolyte powder according to any one of claims 5 to 10, and the second solid electrolyte contains as a main component a sulfide.

15. A method for producing a solid electrolyte powder according to claim 5 or 8, comprising the steps of: dry-mixing a Li raw material, a Nb raw material, and a P raw material in an inert atmosphere having a dew point of -20°C or less to obtain a mixed powder; and sintering the mixed powder at 350°C or less in an air atmosphere.

16. The method for producing a solid electrolyte powder according to claim 15, wherein the Li raw material is lithium oxide, the Nb raw material is hydrous niobium oxide, and the P raw material is diphosphorus pentoxide.

17. A method for producing a solid electrolyte powder as set forth in claim 5 or 8, comprising: a phosphate ion adding step of adding phosphate ions to an aqueous solution containing niobium polyacid ions and lithium; and a drying step of drying the aqueous solution obtained in the adding step to obtain a solid electrolyte powder, wherein, when the molar ratio of Li, Nb, and P in the aqueous solution obtained in the adding step is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65.

18. A method for producing a coated body, comprising: a step of adding phosphate ions to an aqueous solution containing niobium polyacid ions and lithium to obtain an aqueous solution in which x is 15 to 50, y is 5 to 65, and z is 5 to 65 when the molar ratio of Li, Nb, and P in the aqueous solution is Li:Nb:P = x:y:z (x + y + z = 100); and a coating step of contacting the aqueous solution obtained by the above step with a positive electrode active material to coat the surface of the positive electrode active material with a solid electrolyte, wherein the solid electrolyte satisfies at least any of the following: i) A solid electrolyte comprising 0.7 to 5 mass% Li, 8 to 60 mass% Nb, and 1.0 to 30 mass% P relative to the solid electrolyte, with the content of non-oxygen remainders other than oxygen (O) being 10 mass% or less relative to the solid electrolyte, and with a crystallite diameter of 100 nm or less; ii) A solid electrolyte comprising, when the molar ratio of Li, Nb, and P is Li:Nb:P=x:y:z (x+y+z=100), x is 15 to 50, y is 5 to 65, and z is 5 to 65, and with a crystallite diameter of 100 nm or less.

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