Aqueous liquid, powder, solid electrolyte, positive electrode active material for coated lithium secondary batteries, all-solid-state battery, and method for producing these

Abstract

The purpose of the present invention is to provide an aqueous liquid for coating a positive electrode active material having a composition in which the values of the molar ratios Li / (Li+M+P+Na), M / (Li+M+P+Na), and Na / (Li+M+P+Na) are within a predetermined range, where M indicates one or more elements selected from Al, Zn, and Sn, and "molar ratio X / (Li+M+P+Na)" represents the ratio of the amount element X (in moles) to the total amount of Li, M, P, and Na (in moles).

Description

Aqueous liquids, powders, solid electrolytes, positive electrode active materials for coated lithium secondary batteries, all-solid-state batteries, and methods for manufacturing the same.

[0001] The present invention relates to aqueous liquids, powders, solid electrolytes, positive electrode active materials for coated lithium secondary batteries, all-solid-state batteries, and methods for manufacturing the same.

[0002] In an all-solid-state lithium-ion secondary battery (sometimes referred to as "all-solid-state battery" in this invention), a solid electrolyte that functions as a separator is placed between the positive electrode active material and the negative electrode active material, and lithium ions are conducted between the two active materials via the solid electrolyte. Various types of solid electrolytes, such as sulfide-based, oxide-based, and polymer-based electrolytes, have been developed, but from the viewpoint of ionic conductivity and manufacturing cost, sulfide-based electrolytes are currently considered advantageous.

[0003] In all-solid-state batteries, there is a problem in that the interfacial resistance between the positive electrode active material and the sulfide-based solid electrolyte separator increases, which tends to degrade performance such as battery capacity. This increase in interfacial resistance is mainly due to the reaction between the positive electrode active material and the sulfide-based solid electrolyte, which forms high-resistance regions on the surface of the positive electrode active material.

[0004] Therefore, the provision of a protective material to separate the positive electrode active material from the sulfide-based solid electrolyte has been considered. For example, attempts have been made to avoid the reaction between the positive electrode active material and the sulfide-based solid electrolyte by coating the surface of the positive electrode active material with a solid electrolyte made of a lithium-ion conductive oxide or the like that functions as a protective material. For example, Patent Documents 1 and 2 describe coating the surface of the positive electrode active material with lithium niobate (LiNbO2). ３ It has been proposed to cover it with ).

[0005] Japanese Patent Publication No. WO2007 / 004590, Japanese Patent Publication No. 2020-066570

[0006] From the standpoint of energy density, a higher charging voltage for a battery is preferable. However, if the charging voltage is increased excessively, a problem arises in which the solid electrolyte, which is a protective material for the positive electrode active material, reacts with the sulfide-based solid electrolyte, which is a separator, and decomposes. When the protective material decomposes, the positive electrode active material and the sulfide-based solid electrolyte come into contact, forming high-resistance regions.

[0007] For example, lithium niobate (LiNbO) as shown in Patent Documents 1 and 2 ３ If ) is used as a protective material, the charging voltage is at a potential (V) relative to Li. ｖｓ It is known that when the voltage exceeds 4.45V (Li), it reacts with the sulfide-based solid electrolyte. Therefore, conventionally, it has been difficult to increase the charging voltage above 4.45V. In this invention, unless otherwise specified, the potential value (V) is the potential (V) relative to Li. ｖｓ Represents Li. Li-referenced potential (V ｖｓ Li) is the potential (V) relative to In-Li. ｖｓ This is the value obtained by adding 0.6V to (In-Li).

[0008] The present invention aims to provide a solid electrolyte suitable as a protective material for a positive electrode active material, which exhibits excellent properties (sometimes referred to as "decomposition resistance" in this invention) that prevent the decomposition of the protective material due to reaction with the sulfide-based solid electrolyte separator, even when a charging voltage higher than 4.45V is applied to an all-solid-state battery; an aqueous liquid and powder suitable for forming the solid electrolyte; a coated lithium secondary battery positive electrode active material protected by the solid electrolyte; an all-solid-state battery using the coated lithium secondary battery positive electrode active material; and methods for manufacturing the same.

[0009] The inventors of this invention have conducted diligent research to solve the above-mentioned problems and have arrived at the following invention. That is, the first invention for solving the above-mentioned problems is an aqueous liquid having the following composition. When one or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount of element X (moles) to the total amount (moles) of Li, M, P, and Na is expressed as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less. The second invention is an aqueous liquid according to the first invention, wherein the content of Li, M, P, and Na in the aqueous liquid is as follows: Li: 0.05% by mass or more and 3.5% by mass or less, M: 0.04% by mass or more and 2% by mass or less, P: 0.15% by mass or more and 3.0% by mass or less, Na: 0% by mass or more and 2% by mass or less. The third invention is an aqueous liquid according to the first or second invention, wherein the total content of Li, M, P, and Na in the aqueous liquid is 0.50% by mass or more and 10.0% by mass or less. The fourth invention is a powder having the following composition. When one or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na is expressed as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less. The fifth invention is a solid electrolyte having the following composition.When one or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na is expressed as the X / (Li+M+P+Na) molar ratio, the following conditions apply: Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less. The sixth invention is an aqueous liquid for coating a positive electrode active material having the composition described in any of the first to third inventions. The seventh invention is a powder for coating a positive electrode active material having the composition described in the fourth invention. The eighth invention is a method for producing a coated lithium secondary battery positive electrode active material, comprising the step of coating the surface of the positive electrode active material for a lithium secondary battery with an aqueous liquid described in any of the first to third or sixth inventions. The ninth invention is a method for producing a coated lithium secondary battery positive electrode active material, comprising the step of coating the surface of the positive electrode active material for a lithium secondary battery with a powder described in the fourth invention. The tenth invention is an all-solid-state battery in which a solid electrolyte described in the fifth invention exists between the conductive material on the positive electrode side and the conductive material on the negative electrode side. The eleventh invention is a method for producing an aqueous liquid, comprising the step of obtaining an aqueous liquid having the following composition, where M is denoted as one or more elements selected from Al, Zn, and Sn, and the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na is denoted as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less. The twelfth invention is a method for producing a powder, comprising the step of drying the aqueous liquid obtained in the eleventh invention to obtain a powder. The thirteenth invention is a method for producing the powder described in the twelfth invention, comprising the step of crushing the powder.The fourteenth invention is a method for producing a powder, comprising a drying step of maintaining an aqueous liquid obtained by the manufacturing method described in the eleventh invention at a temperature of 120°C to 220°C. The fifteenth invention is a method for producing a solid electrolyte, comprising a heat treatment step of maintaining a powder obtained by the manufacturing method described in the twelfth or thirteenth invention at a temperature of over 110°C and 500°C. The 16th invention is a coated lithium secondary battery positive electrode active material in which one or more elements selected from Al, Zn, and Sn are denoted as M, and the content of Li, M, P, Na, and O when the surface of the powder particles of the coated lithium secondary battery positive electrode active material is measured by XPS is as follows: Li: 2.58 at% or more and 44.38 at% or less, M: 0.94 at% or more and 14.99 at% or less, P: 4.78 at% or more and 25.50 at% or less, Na: 0 at% or more and 12.52 at% or less, O: 43.98 at% or more and 68.89 at% or less.

[0010] According to the present invention, a new solid electrolyte with excellent decomposition resistance has been realized. By using this solid electrolyte as a protective material for the positive electrode active material in an all-solid-state battery, it is possible to improve the charging voltage of the all-solid-state battery.

[0011] Figure 4 shows a schematic cross-sectional view of an all-solid-state battery. Figure 5 shows a schematic cross-sectional view of an all-solid-state battery using positive electrode active material particles coated with Li-M-P solid electrolyte and a sulfide-based solid electrolyte. Figure 6 shows a schematic cross-sectional view of an all-solid-state battery using Li-M-P solid electrolyte and a sulfide-based solid electrolyte mainly composed of sulfides. Figure 7 shows a schematic cross-sectional view of the current collector (positive electrode side), the conductive material on the positive electrode side, and the sulfide-based solid electrolyte in an all-solid-state battery. Figure 8 shows a schematic cross-sectional view of the current collector (positive electrode side), the conductive material on the positive electrode side, and the sulfide-based solid electrolyte in an all-solid-state battery in a different embodiment from Figure 4. Figure 9 shows a schematic cross-sectional view of the current collector (positive electrode side), the conductive material on the positive electrode side, and the sulfide-based solid electrolyte in an all-solid-state battery. Figure 1 shows a schematic cross-sectional view of the powders according to Examples 1, 5, 9, 11, and 13. Figure 1 shows a schematic cross-sectional view of the stacked structure of electrochemical cell A. Figure 1 shows a schematic cross-sectional view of the powder according to Example 5. Figure 2 shows a schematic cross-sectional view of the powder according to Example 6.

[0012] Referring to FIGS. 1 to 5, the following describes an all-solid-state battery using the positive electrode active material for coated lithium secondary batteries protected by the solid electrolyte according to the present invention (positive electrode active material), the positive electrode active material for lithium secondary batteries protected by the solid electrolyte according to the present invention (positive electrode active material), the solid electrolyte according to the present invention suitable as a protective material for the positive electrode active material for lithium secondary batteries (positive electrode active material), and an aqueous liquid and powder suitable for producing the positive electrode active material for lithium secondary batteries protected by the solid electrolyte according to the present invention. In FIGS. 1 to 5 and 7 of the present invention, members denoted by the same reference numerals are the same members.

[0013] [Configuration of Each Material in All-Solid-State Battery] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery 11 using the positive electrode active material for coated lithium secondary batteries protected by the solid electrolyte according to the present invention (may be referred to as "all-solid-state battery 11" in the present invention). Although details will be described later, the solid electrolyte according to the present invention has a composition containing Li, a specific metal M, P (phosphorus), and optionally Na, and is also referred to as a Li-M-P solid electrolyte. The all-solid-state battery 11 has a structure in which a positive electrode-side conductive material 3, a sulfide-based solid electrolyte 2 serving as a separator, and a negative electrode-side conductive material 4 are laminated between a current collector 55 (positive electrode side) and a current collector 56 (negative electrode side).

[0014] (Positive Electrode-Side Conductive Material) The positive electrode-side conductive material 3 has two types of embodiments: an embodiment consisting of the Li-M-P solid electrolyte according to the present invention, a positive electrode active material, a conductive aid, and a sulfide-based solid electrolyte; and an embodiment consisting of the Li-M-P solid electrolyte, a positive electrode active material, and a conductive aid. Note that the positive electrode active material is both an ion conductive substance and a conductive substance. Further, the Li-M-P solid electrolyte according to the present invention can be formed from the aqueous liquid according to the present invention or the powder according to the present invention described later.

[0015] As the positive electrode active material, known substances can be applied, and if a new positive electrode active material is developed, it can also be applied. As typical known positive electrode active materials, 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 Examples include (silicate type).

[0016] (Sulfide-based solid electrolyte) As the sulfide-based solid electrolyte 2, which is the separator, known substances with ionic conductivity can be used, and if new ionic conductive materials are developed, they may also be applicable. Typical known ionic conductive materials include Li ６ PS 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 PO 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 Examples include (glass ceramics).

[0017] (Conductive material on the negative electrode side) The conductive material 4 on the negative electrode side is usually composed of a negative electrode active material and conductive material other than the negative electrode active material. In actual all-solid-state batteries, the negative electrode material is generally composed of conductive members such as a current collector and numerous particles of the negative electrode active material, as well as particles of an ion-conducting material (solid electrolyte) that are mixed to fill the spaces between the particles of the negative electrode active material.

[0018] (Modes of conductive materials on the positive and negative electrodes) Figures 2 and 3 are schematic cross-sectional views that are extremely simplified to illustrate in more detail two types of modes relating to the structure and positional relationship of each component, in order to explain in more detail the conductive material 3 on the positive electrode side, the sulfide-based solid electrolyte 2, and the conductive material 4 on the negative electrode side, as described in Figure 1. In Figures 2 and 3, the positive electrode active material 31 is schematically shown as a single positive electrode active material particle.

[0019] First, in the embodiment shown in Figure 2, the positive electrode active material 31 is in contact with the sulfide-based solid electrolyte 2 and the conductive additive 32 while being coated with the Li-M-P solid electrolyte 1 according to the present invention. That is, in the embodiment shown in Figure 2, the coating layer containing the Li-M-P solid electrolyte 1 coated on the surface of the positive electrode active material 31 functions as a protective material separating the positive electrode active material 31 from the sulfide-based solid electrolyte 2.

[0020] Furthermore, in the embodiment shown in Figure 2, the negative electrode active material 41, together with the conductive material 42 other than the negative electrode active material, constitutes the conductive material 4 on the negative electrode side, and both the negative electrode active material 41 and the conductive material 42 other than the negative electrode active material are in contact with the sulfide-based solid electrolyte 2, which is a separator.

[0021] In the embodiment shown in Figure 2, the tunnel effect is achieved by making the thickness of the coating layer containing the Li-M-P solid electrolyte 1 according to the present invention sufficiently thin, ensuring electrical conductivity between the positive electrode active material 31 and the conductive additive 32 even if they are not in direct contact. A sulfide-based solid electrolyte 2, which acts as a separator, is laminated on top of the conductive material 3 on the positive electrode side.

[0022] Next, in the embodiment shown in Figure 3, the positive electrode active material 31 is in contact with the Li-M-P solid electrolyte 1 and conductive additive 32 according to the present invention, and is in contact with the sulfide-based solid electrolyte 2 via the Li-M-P solid electrolyte 1. That is, in the embodiment shown in Figure 3 as well, the Li-M-P solid electrolyte 1 functions as a protective material (intervening layer) separating the positive electrode active material 31 from the sulfide-based solid electrolyte 2, which is a separator.

[0023] Furthermore, in the embodiment shown in Figure 3, the negative electrode active material 41, together with the conductive material 42 other than the negative electrode active material, constitutes the conductive material 4 on the negative electrode side, and both the negative electrode active material 41 and the conductive material 42 other than the negative electrode active material are in contact with the sulfide-based solid electrolyte 2, which is a separator.

[0024] In other words, in the present invention, the "protective material" is a Li-M-P solid electrolyte. The Li-M-P solid electrolyte separates the positive electrode active material from the sulfide-based solid electrolyte in two ways: the Li-M-P solid electrolyte is a "coating layer" that covers the surface of the positive electrode active material, or the Li-M-P solid electrolyte is present as an "intervening layer" between the area where the positive electrode active material is located and the sulfide-based solid electrolyte.

[0025] On the other hand, Figures 2 and 3 schematically illustrate the arrangement relationship between the conductive material 4 on the negative electrode side and the sulfide-based solid electrolyte 2, specifically the portion of the negative electrode material composed of conductive members. The configuration of the conductive material 4 on the negative electrode side, and the arrangement relationship between the conductive material 4 on the negative electrode side and the sulfide-based solid electrolyte 2, can be the same as that of known all-solid-state batteries. A negative electrode coating layer may be placed between the sulfide-based solid electrolyte 2 and the conductive material 4 on the negative electrode side, if necessary.

[0026] Next, the configuration of the conductive material 3 on the positive electrode side according to the embodiments shown in Figures 2 and 3 above will be explained using Figures 4 and 5. Figures 4 and 5 are schematic cross-sectional views that illustrate the conductive material 3 on the positive electrode side in a manner closer to reality than Figures 2 and 3. Figure 4 corresponds to Figure 2, and Figure 5 corresponds to Figure 3.

[0027] In the positive electrode conductive material 3 shown in Figure 4, a positive electrode active material 31 coated with the Li-M-P solid electrolyte 1 according to the present invention and a conductive additive 32 are dispersed in a sulfide-based solid electrolyte 2. One side of the positive electrode conductive material 3 is joined to the sulfide-based solid electrolyte 2, which functions as a separator, located above in Figure 4, and the other side is joined to the current collector 55. As a result, the positive electrode conductive material 3 realizes the configuration of each component described in Figure 2, and each component constituting the positive electrode conductive material 3 exhibits its effect. The positive electrode active material 31 is in direct electrical contact with each other, or in electrical contact via the conductive additive 32, to constitute the positive electrode conductive material 3.

[0028] On the other hand, in the positive electrode conductive material 3 shown in Figure 5, the positive electrode active material 31 and the conductive additive 32 are dispersed in the Li-M-P solid electrolyte 1 according to the present invention. One end of the positive electrode conductive material 3 is bonded to the sulfide-based solid electrolyte 2, which is a separator, and the other end is bonded to the current collector 55. As a result, the positive electrode conductive material 3 realizes the configuration of each component described in Figure 3, and each component constituting the positive electrode conductive material 3 exhibits its effect. Note that the positive electrode active material 31 is not present at the location where the Li-M-P solid electrolyte 1 is in contact with the sulfide-based solid electrolyte 2, thereby separating the positive electrode active material 31 from the sulfide-based solid electrolyte 2.

[0029] Furthermore, the positive electrode active materials 31 are in direct electrical contact with each other, or in electrical contact via the conductive additive 32, thereby constituting the conductive material 3 on the positive electrode side.

[0030] A common feature of the two different embodiments of the positive electrode conductive material shown in Figures 4 and 5 is that the Li-M-P solid electrolyte 1 and the sulfide-based solid electrolyte 2 are in contact, and the Li-M-P solid electrolyte 1 and the positive electrode active material 31 are in contact. That is, in the embodiment shown in Figure 4, the coating layer of Li-M-P solid electrolyte 1 covering the surface of the positive electrode active material 31 functions as a protective material separating the positive electrode active material 31 from the sulfide-based solid electrolyte 2. In the embodiment shown in Figure 5, the Li-M-P solid electrolyte 1 present at the boundary between the sulfide-based solid electrolyte 2, which acts as a separator, and the positive electrode conductive material 3 functions as a protective material separating the positive electrode active material 31 from the sulfide-based solid electrolyte 2.

[0031] In this invention, by using a Li-M-P solid electrolyte with excellent degradation resistance as a protective material, the decomposition of the protective material due to reaction with sulfide-based solid electrolytes is suppressed even when a high charging voltage is applied to the all-solid-state battery, thus contributing to the realization of an all-solid-state battery that can be charged at high voltage.

[0032] [Li-M-P Solid Electrolyte] The Li-M-P solid electrolyte according to the present invention, as described above and discovered through the inventors' research, is a Li-M-P solid electrolyte having a composition range in which the Li / (Li+M+P+Na) molar ratio is 0.069 to 0.800, the M / (Li+M+P+Na) molar ratio is 0.024 to 0.300, the P / (Li+M+P+Na) molar ratio is 0.095 to 0.800, and the Na / (Li+M+P+Na) molar ratio is 0.000 to 0.326. Furthermore, it exhibits significantly superior degradation resistance compared to lithium niobate, which has been widely used as a protective material for positive electrode active materials.

[0033] In this invention, one or more elements selected from Al (aluminum), Zn (zinc), and Sn (tin) may be denoted as M. Also, any element selected from Li (lithium), M, P (phosphorus), and Na (sodium) may be denoted as "X". Furthermore, the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na may be expressed as "X / (Li+M+P+Na) molar ratio".

[0034] Furthermore, if element M contains two or more elements, i.e., Al + Zn, Al + Sn, Zn + Sn, or Al + Zn + Sn, the number of moles of element M is the sum of the number of moles of Al, Zn, and Sn.

[0035] As a more preferred composition range for the Li-M-P solid electrolyte according to the present invention described above, from the viewpoint of degradation resistance, a range of Li / (Li+M+P+Na) molar ratio of 0.140 or more and 0.617 or less, M / (Li+M+P+Na) molar ratio of 0.051 or more and 0.147 or less, P / (Li+M+P+Na) molar ratio of 0.178 or more and 0.520 or less, and Na / (Li+M+P+Na) molar ratio of 0.000 or more and 0.295 or less can be mentioned. Furthermore, a more preferred composition range includes a Li / (Li+M+P+Na) molar ratio of 0.162 to 0.435, an M / (Li+M+P+Na) molar ratio of 0.054 to 0.123, a P / (Li+M+P+Na) molar ratio of 0.334 to 0.520, and a Na / (Li+M+P+Na) molar ratio of 0.000 to 0.283.

[0036] From the viewpoint of degradation resistance, the Li content (mass%) in the Li-M-P solid electrolyte according to the present invention is preferably 0.5% to 25% by mass, more preferably 1.5% to 17% by mass, and even more preferably 1.9% to 8% by mass. From the viewpoint of degradation resistance, the M content (mass%) in the Li-M-P solid electrolyte is preferably 1% to 65% by mass, more preferably 2% to 40% by mass, and even more preferably 3% to 33% by mass. From the viewpoint of degradation resistance, the P content (mass%) in the Li-M-P solid electrolyte is preferably 5% to 45% by mass, more preferably 15% to 40% by mass, and even more preferably 20% to 38% by mass. From the viewpoint of degradation resistance, the Na content (mass%) in the Li-M-P solid electrolyte is preferably 0% to 20% by mass. Furthermore, the Na content (mass%) in the Li-M-P solid electrolyte may be, for example, 15% by mass or less, 13% by mass or less, or 5% by mass or less.

[0037] Furthermore, according to EDX (energy-dispersive X-ray fluorescence analysis) spectroscopy, the Li-M-P solid electrolyte according to the present invention contains O (oxygen) as a constituent element. That is, the Li-M-P solid electrolyte according to the present invention is considered to be an oxide.

[0038] In other words, the Li-M-P solid electrolyte according to the present invention contains O (oxygen) in the form of the remainder of Li, M, P, Na, and other elements. The content (mass%) of each of Li, M, P, and Na is measured, for example, by ICP (inductively coupled plasma) emission spectroscopy. The O content is obtained by subtracting the total content of each of the above-mentioned constituent elements from the Li-M-P solid electrolyte according to the present invention (100 mass% - total mass% of each constituent element), and from the viewpoint of decomposition resistance, it is preferably 30 mass% to 60 mass%.

[0039] Furthermore, the Li-M-P solid electrolyte according to the present invention may contain elements other than Li, M, P, Na, and O, to the extent that it does not impair the effects of the invention. For example, N (nitrogen) and C (carbon). The content of elements other than Li, M, P, Na, and O is 3% by mass or less, preferably 2% by mass or less.

[0040] The Li-M-P solid electrolyte according to the present invention is 1.0 × 10 －１１ It is preferable that the lithium ion conductivity be S / cm or higher.

[0041] It is presumed that the Li-M-P solid electrolyte according to the present invention exhibits excellent degradation resistance under voltage application higher than 4.45 V because the presence of covalent P-O and M-O bonds in its structure makes it difficult for oxygen to be released under high potential.

[0042] The Li-M-P solid electrolyte according to the present invention may be an amorphous solid. In the present invention, "amorphous solid" refers to a solid material in which the crystallite size calculated from the maximum diffraction peak (the diffraction peak with the highest peak height) in the region of 2θ to 60° in an X-ray diffraction pattern using CuKα rays is 50 nm or less, or a solid material in which no clear diffraction peak is observed in the region of 2θ to 60°, and a so-called halo pattern appears. A "halo" is a gentle undulation of X-ray intensity, which is observed as a broad rise in the XRD spectrum. The full width at half maximum of the halo is 2° or more at 2θ.

[0043] [Aqueous liquid and powder for forming Li-M-P solid electrolyte] When protecting the positive electrode active material 31 by providing a coating layer containing the Li-M-P solid electrolyte 1 according to the present invention as described above on the positive electrode active material 31 (as shown in Figure 4), or by dispersing the positive electrode active material 31 in the Li-M-P solid electrolyte 1 (as shown in Figure 5), it is preferable to use the aqueous liquid and powder according to the present invention.

[0044] (Composition range of aqueous liquid and powder) From the viewpoint of resistance to decomposition, the composition range of the aqueous liquid and powder according to the present invention is as follows: Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less. A more preferred composition range is one in which the Li / (Li+M+P+Na) molar ratio is 0.140 or more and 0.617 or less, the M / (Li+M+P+Na) molar ratio is 0.051 or more and 0.147 or less, the P / (Li+M+P+Na) molar ratio is 0.178 or more and 0.520 or less, and the Na / (Li+M+P+Na) molar ratio is 0 or more and 0.295 or less. An even more preferred composition range is one in which the Li / (Li+M+P+Na) molar ratio is 0.162 or more and 0.435 or less, the M / (Li+M+P+Na) molar ratio is 0.054 or more and 0.123 or less, the P / (Li+M+P+Na) molar ratio is 0.334 or more and 0.520 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.283 or less.

[0045] (Properties of aqueous liquids and powders) <Aqueous liquids> The aqueous liquids according to the present invention are a general term for liquids in which all of Li, M, P, and Na are dissolved in an aqueous liquid medium (aqueous solutions), liquids in which some of Li, M, P, and Na are dissolved in an aqueous liquid medium and the remainder is dispersed as solid particles, and liquids in which all of Li, M, P, and Na are dispersed as solid particles in an aqueous liquid medium.

[0046] Among aqueous solutions containing Li, M, P, and Na, any solution other than an aqueous solution is called a "dispersion." In dispersions, turbidity is usually observed due to solid particles dispersed in the liquid.

[0047] A water-based liquid medium refers to a liquid medium consisting of water, or a mixture of water and other solvent components in which water accounts for 50% by mass or more. Preferably, the liquid medium contains 80% by mass or more water, and may contain 90% by mass or more, 95% by mass or more, or 100% by mass.

[0048] The aqueous solution according to the present invention can be used as a coating solution to form a protective coating layer (for example, "Li-M-P solid electrolyte 1" in Figure 2, described later) on the surface of positive electrode active material particles. From the viewpoint of forming a highly uniform coating layer, it is more effective if the aqueous solution is an aqueous solution. Coating methods include the spray dryer method, the rolling flow method, and the immersion method, but the spray dryer method is superior in terms of productivity.

[0049] The total content of Li, M, P, and Na in the aqueous solution according to the present invention is preferably 0.50% by mass or more and 10.0% by mass or less, and more preferably 0.80% by mass or more and 5.00% by mass or less, from the viewpoint of decomposition resistance. If the total content of Li, M, P, and Na is too low, it is necessary to increase the amount of aqueous solution to obtain the required thickness of the coating layer, which increases the amount of liquid medium in the aqueous solution and is therefore disadvantageous in terms of cost. If the total content of Li, M, and P in the aqueous solution is too high, the viscosity of the aqueous solution increases, which increases the risk of clogging the narrow piping of the equipment used for the coating process.

[0050] From the viewpoints described above and from the viewpoint of decomposition resistance, the Li content (mass%) in the aqueous liquid according to the present invention is preferably 0.05% to 3.5% by mass, more preferably 0.20% to 2.50% by mass, and even more preferably 0.25% to 1.2% by mass. From the viewpoints described above and from the viewpoint of decomposition resistance, the M content (mass%) in the aqueous liquid according to the present invention is preferably 0.04% to 2% by mass, more preferably 0.08% to 1.5% by mass, and even more preferably 0.10% to 1.0% by mass. From the viewpoints described above, the P content (mass%) in the aqueous liquid according to the present invention is preferably 0.15% to 3.0% by mass, more preferably 0.3% to 2.5% by mass, and even more preferably 0.5% to 2.0% by mass. From the viewpoints described above, the Na content (mass%) in the aqueous liquid according to the present invention is preferably 0% to 2% by mass. Furthermore, the Na content (mass%) in the aqueous solution according to the present invention may be, for example, 1.5% by mass or less, or 1.0% by mass or less.

[0051] The absorbance of the aqueous solution according to the present invention at a wavelength of 660 nm is an indicator of the intensity of scattered light due to fine particles present in the aqueous solution. A high absorbance at that wavelength means that there is a large amount of fine particles present in the aqueous solution. When the aqueous solution is used as a coating liquid for wet forming a coating layer (for example, "Li-M-P solid electrolyte 1" in Figure 2) on the surface of positive electrode active material particles, if the absorbance value of the aqueous solution at a wavelength of 660 nm is 0.20 or less, the amount of fine particles in the aqueous solution is sufficiently small, and adverse effects on the uniformity of the coating layer thickness and coverage rate are suppressed. The absorbance value is preferably 0.10 or less. The absorbance value was measured using a UV-Vis spectrophotometer with the aqueous solution temperature at 25°C and the absorbance at a wavelength of 660 nm. In this case, the lower limit of the absorbance is 0.000. However, the detection limit on the UV-Vis spectrophotometer used for absorbance measurement is 0.001.

[0052] <Powder> The powder according to the present invention can be obtained by removing (drying) the liquid medium component from the aqueous solution according to the present invention. Details of the drying method will be described later. As a result of drying, the composition ratio of Li, M, P, and Na in the powder becomes the same as that of the aqueous solution before the removal of the liquid medium component.

[0053] When considering the use of the powder according to the present invention as a solid electrolyte, from the viewpoint of obtaining a solid electrolyte with high uniformity and a dense structure, the particle size should be such that the cumulative 50% particle size (D50) in the volume-based particle size distribution measured by laser diffraction and scattering is, for example, 1.5 μm or more and 4.0 μm or less.

[0054] (Method of using aqueous liquid and powder (Method of forming Li-M-P solid electrolyte)) The application of the aqueous liquid and powder according to the present invention to positive electrode active material particles will be described below with reference to Figures 3 and 2.

[0055] The aqueous solution according to the present invention can be used as a coating solution when wet-forming a protective coating layer (for example, Li-M-P solid electrolyte 1 in Figure 2) on the surface of positive electrode active material particles. In this case, it is preferable to coat the positive electrode active material with an aqueous solution with a low concentration of fine particles. By coating with an aqueous solution with a low concentration of fine particles, it is possible to avoid fine particles adhering to the surface of the positive electrode active material and causing the coating layer to become uneven, and to make the thickness of the coating layer uniform. If the thickness of the coating layer is uniform, it is possible to avoid the occurrence of thin film areas with insufficient coating thickness, or even areas that are not coated at all, and to ensure a high coverage rate.

[0056] The powder according to the present invention is useful in the production of a Li-M-P solid electrolyte used as a protective material for isolating the positive electrode active material and the sulfide-based solid electrolyte (for example, "Li-M-P solid electrolyte 1" in Figure 3). It can also be used as a protective material when forming a protective coating layer (for example, "Li-M-P solid electrolyte 1" in Figure 2) on the surface of positive electrode active material particles using a dry process.

[0057] One dry coating method for forming a coating layer on the surface of positive electrode active material particles from the powder according to the present invention is to mix the positive electrode active material particles and the powder according to the present invention using a powder processing device such as Novilta® (manufactured by Hosokawa Micron) or a ball mill grinder to form the coating layer.

[0058] The coating layer produced by drying an aqueous solution coated on the surface of the positive electrode active material, the powder obtained by removing the liquid medium component from the aqueous solution, and the powder coating layer coated on the surface of the positive electrode active material all exhibit lithium ion conductivity, and therefore can already be said to be solid electrolytes.

[0059] However, the coating layer formed by simply drying the aqueous liquid (applied to the surface of the positive electrode active material) and the powder according to the present invention may contain impurities originating from the raw materials (for example, nitrogen compounds derived from ammonium dihydrogen phosphate). Therefore, it is effective to remove impurities from these coating layers and powders by subjecting them to a heat treatment held at a temperature between 110°C and 500°C to enhance lithium ion conductivity and obtain the Li-M-P solid electrolyte according to the present invention. In this invention, this heat treatment may be referred to as "calcination".

[0060] The firing atmosphere can be open air. The firing time can be set, for example, within a range of 1 to 15 hours. Furthermore, to suppress coagulation and cracking during firing, it is preferable to set the firing temperature to 400°C or lower.

[0061] The thickness of the coating layer provided on the surface of the positive electrode active material particles can be 5 nm or more and 40 nm or less, preferably 8 nm or more and 30 nm or less, and more preferably 20 nm or less.

[0062] Furthermore, the coverage rate of the coating layer provided on the surface of the positive electrode active material particles can be 70% or more, preferably 75% or more, and more preferably 80% or more. The coverage rate is usually 99% or less.

[0063] [Method for manufacturing aqueous liquids and powders] The aqueous liquids and powders according to the present invention described above can be manufactured, for example, by the following process.

[0064] (Li, M, P, (Na)-containing liquid formation process) An aqueous liquid is produced in which a Li-containing substance, an M-containing substance, and a P-containing substance are dissolved or dispersed in an aqueous liquid medium so that the total amount of each element Li, M, P, and Na falls within the composition range described in "(Composition range of aqueous liquids and powders)" (for example, by mixing the Li-containing substance, M-containing substance, P-containing substance, and aqueous liquid medium). One or more of Al-containing substances, Zn-containing substances, and Sn-containing substances are used as the M-containing substance.

[0065] Li-containing substances include lithium hydroxide, lithium oxide, lithium chloride, lithium citrate, lithium acetate, lithium sulfate, lithium phosphate, lithium borate, and lithium carbonate. From the viewpoint of solubility in water, the more preferred raw materials are lithium hydroxide, lithium oxide, lithium phosphate, and lithium carbonate.

[0066] Examples of aluminum-containing substances include aluminum oxide, aluminum hydroxide, aluminum sulfate, potassium aluminum sulfate, aluminum chloride, aluminum fluoride, aluminum nitrate notahydrate, aluminum cobalt oxide, lithium aluminum oxide, and sodium aluminate. From the viewpoint of solubility in water, more preferred raw materials include aluminum oxide, aluminum hydroxide, aluminum chloride, and aluminum nitrate notahydrate.

[0067] Examples of Zn-containing substances include zinc oxide, zinc hydroxide, zinc nitrate hexahydrate, zinc chloride, zinc sulfide, zinc sulfate, zinc chromate, zinc stearate, zinc stannate, zinc gluconate, and zinc phosphide. From the viewpoint of solubility in water, more preferred raw materials include zinc oxide, zinc hydroxide, zinc nitrate hexahydrate, and zinc chloride.

[0068] Examples of Sn-containing substances include tin oxide, dibutyltin oxide, tin hydroxide, tin chloride dihydrate, sodium stannate trihydrate, and potassium stannate trihydrate. From the viewpoint of solubility in water, more preferred raw materials include tin oxide, tin hydroxide, and tin chloride dihydrate.

[0069] Examples of phosphorus-containing substances include phosphoric acid, metaphosphoric acid, polyphosphoric acid, pyrophosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphonate, calcium phosphate, calcium phosphonate, lithium phosphate, lithium phosphonate, magnesium phosphate, magnesium phosphinate, sodium phosphate, sodium phosphinate, sodium phosphonate, and sodium metaphosphate. From the viewpoint of solubility in water, more preferred raw materials include phosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, metaphosphoric acid, and lithium phosphate.

[0070] Na is present as an accompanying substance to the P-containing substance when sodium salt of P, such as sodium metaphosphate, is used.

[0071] This Li, M, P, (Na)-containing liquid formation process yields the aqueous liquid according to the present invention. The aqueous liquid according to the present invention can be used as a coating liquid for coating the surface of positive electrode active material particles.

[0072] (Drying process) The powder according to the present invention can be obtained by removing the liquid medium component from the aqueous liquid obtained in the "(Li, M, P, (Na)-containing liquid formation process)" (i.e., drying it). There are no particular restrictions on the method of removing the liquid medium component, but for example, the evaporation to dryness method can be applied. When the evaporation to dryness method is applied, it is preferable to set the temperature in the range of 120°C to 220°C, and the atmosphere can be air. By providing a drying process, the removal of impurities originating from the raw material substances mixed in the powder according to the present invention (for example, nitrogen compounds derived from ammonium dihydrogen phosphate) can be further promoted in the calcination process described later.

[0073] (Grinding Process) When obtaining the Li-M-P solid electrolyte according to the present invention using the powder obtained in the (drying process), it is preferable to perform grinding from the viewpoint of obtaining a calcined body with high uniformity and a dense structure. The particle size after grinding is preferably adjusted so that the cumulative 50% particle size (D50) in the volume-based particle size distribution measured by laser diffraction and scattering is, for example, 1.5 μm or more and 4.0 μm or less. Ball mill grinding, bead mill grinding, etc. can be used as grinding methods.

[0074] (Firing Process) The powder after the "(Drying Process)" or the further "(Grinding Process)" exhibits lithium ion conductivity and can therefore be said to be a solid electrolyte. However, the powder according to the present invention may contain impurities (for example, nitrogen compounds derived from ammonium dihydrogen phosphate) originating from the raw materials. To remove these and improve lithium ion conductivity, it is effective to perform a heat treatment held at a temperature between 110°C and 500°C. The firing atmosphere can be air. The firing time can be set in the range of, for example, 1 hour to 15 hours. The firing time may also be set in the range of 3 hours or more, or 7 hours or more.

[0075] The present invention will be described below with reference to the examples. However, the present invention is not limited to these examples. [Example 1] (1) Li, M, P-containing liquid manufacturing process Lithium hydroxide monohydrate (LiOH・H ２ O) Dissolve 12.6 g (Wako Special Grade) in 236 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 7.65 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0076] Ammonium dihydrogen phosphate (NH ４ H ２ PO ４ ) 17.25 g (Wako Special Grade) was dissolved in 105 g of pure water to obtain an aqueous phosphoric acid solution. This solution was then added in its entirety to the aqueous solution containing the above-mentioned dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and the mixture was stirred for 15 minutes to obtain a cloudy aqueous solution according to Example 1 containing Li, Al, and P.

[0077] In Example 1, element M is Al, and Na is not present. 0.1 g of the sample taken from the aqueous solution of Example 1 was weighed, and 15 mL of pure water and 5 mL of 36% by mass hydrochloric acid were added to it. After heating and cooling, 2 mL of 35% by mass hydrogen peroxide solution was added. The volume of the cooled solution was diluted with pure water to 100 mL, and the concentrations of Li, M, P, and Na in the diluted solution were measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES, Agilent Technologies, CP-720). Based on the analysis results, the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na in the aqueous solution is expressed as "X / (Li+M+P+Na) molar ratio". The values ​​of the Li / (Li+M+P+Na) molar ratio, M / (Li+M+P+Na) molar ratio, P / (Li+M+P+Na) molar ratio, and Na / (Li+M+P+Na) molar ratio are listed in Table 1 (the same values ​​are listed in Table 1 for Examples 2-13 and Comparative Example 2 below, except for Comparative Example 1).

[0078] (2) Absorbance Measurement 3.5 mL of the aqueous solution from Example 1 was taken into a quartz cell (10 mm × 10 mm × 45 mm), and the absorbance at wavelengths of 400 to 700 nm was measured using a Hitachi High-Technologies U-2800 spectrophotometer. The temperature of the aqueous solution during measurement was 25°C. The results are shown in Table 1 (the same results are shown in Table 1 for Examples 2-13 and Comparative Examples 1 and 2 below). The zero point of the absorbance was determined by using the absorbance measured when ultrapure water with an electrical conductivity of 17 MΩ·cm or higher and at 25°C was placed in the measurement cell.

[0079] (3) Drying process The entire amount of the aqueous liquid obtained in Example 1 was evaporated to dryness in an air atmosphere at 110°C using a dryer to obtain a powder which is a dried solid product.

[0080] (4) Grinding process 1 g of the obtained powder and 17 zirconia beads with a diameter of 10 mm were placed in a 45 ml zirconia pot and ground for 5 hours using a planetary ball mill. After grinding, the zirconia beads were separated from the contents of the pot to obtain the ground powder.

[0081] (5) Calcination process The obtained pulverized powder was calcined by holding it at 120°C in an air atmosphere for 12 hours to obtain the Li-M-P solid electrolyte according to Example 1, which is a Li-Al-P system composition. This powder according to Example 1 was used as a test material for the following tests.

[0082] (6) X-ray diffraction measurement The X-ray diffraction pattern of the powder was measured using an X-ray diffractometer (Shimadzu Corporation, XRD-6100) with CuKα rays under the following conditions: tube voltage 40kV, tube current 30mA, divergence slit 1.0°, scattering slit 1.0°, receiving slit 0.3mm, scan speed 2.0° / min, step width 0.02° / step, measurement time 0.25s, and measurement 2θ range 10-60°. Peak search was performed using the analysis software attached to the X-ray diffractometer (XRD-6100) under the following conditions: smoothing: automatic, background processing: 100, Kα1-α2 ratio: 50, peak search: automatic.

[0083] If a clear diffraction peak was observed in the region where 2θ is 10° to 60° in the above-mentioned X-ray diffraction measurement, the crystallite size was calculated. The crystallite size was calculated from the maximum diffraction peak (the diffraction peak with the highest peak height) in the region where 2θ is 10° to 60° using the powder X-ray analysis software PDXL2 (manufactured by Rigaku Co., Ltd.) with a σ cut-off value of 3.00 and refinement ON. As a result, the powder obtained in Example 1 was Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 48 nm, indicating an amorphous solid. This result is shown in Table 2 (similarly, it is shown in Table 2 for Examples 2-13 and Comparative Examples 1 and 2 below). The XRD spectrum of the powder according to Example 1 is shown in Figure 6.

[0084] (7) Composition analysis (ICP emission spectrometry) 0.1 g of powder sample separated from the powder of Example 1 was weighed, and 15 mL of pure water and 5 mL of 36% by mass hydrochloric acid were added to it. After heating, it was allowed to cool, and then 2 mL of 35% by mass hydrogen peroxide solution was added. The volume of the liquid after cooling was diluted to 100 mL, and the concentrations of Li, M, P, and Na in the diluted solution were measured using an inductively coupled plasma emission spectrometer (ICP-AES, Agilent Technologies, CP-720).

[0085] Based on the analysis results, the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na in the powder sample is expressed as "X / (Li+M+P+Na) molar ratio". The values ​​of the Li / (Li+M+P+Na) molar ratio, M / (Li+M+P+Na) molar ratio, P / (Li+M+P+Na) molar ratio, and Na / (Li+M+P+Na) molar ratio are listed in Table 2 (the same values ​​are listed in Table 2 for Examples 2-13 and Comparative Example 2 below, except for Comparative Example 1).

[0086] (8) SEM-EDX Analysis The powder sample separated from the powder according to Example 1 was observed using a scanning electron microscope (SEM-EDX, JEOL JSM-7800F), and energy-dispersive X-ray spectroscopy (EDX) analysis was performed on the powder sample using the EDX device attached to the SEM described above. Elemental mapping and measurement results confirmed that the powder sample contained O (oxygen) as a constituent element, and it was considered that this powder sample was an oxide (the same was true in Examples 2-13 and Comparative Example 2 below).

[0087] (9) Particle size distribution measurement (laser diffraction scattering method) The cumulative 50% particle size (D50) based on volume of the powder sample was measured using a laser diffraction scattering particle size distribution analyzer (HELOS & RODOS (airflow type dispersion module) manufactured by SYMPATEC) at a dispersion pressure of 5 bar. As a result, the particle size of the powder in Example 1 was 2.7 μm. This result is shown in Table 2 (similarly, it is shown in Table 2 for Examples 2-13 and Comparative Examples 1 and 2 below).

[0088] (10) 0.15 g of the powder sample of the test material for ionic conductivity measurement was placed in a cylindrical container with a diameter of 10 mm and pressed with a press machine at 300 MPa to obtain a compacted powder. The ionic conductivity of the obtained compacted powder was measured under a nitrogen atmosphere at 25°C using a potentiometer / galvanostat (Prinston, VersaSTAT 4) by the AC impedance method in the range of 0.1 Hz to 1 MHz and with an amplitude voltage of 100 mV. The resistance value of the powder sample was determined from the Cole-Cole plot (complex impedance plane plot) of the measured values, and the ionic conductivity of the test material was calculated from the obtained resistance value. As a result, the powder according to Example 1 was 1.0 × 10⁻⁶ －１１ It was confirmed that the solid electrolyte exhibits a lithium ion conductivity of S / cm or higher. Furthermore, the ionic conductivity of the powders related to Examples 2-13 and Comparative Examples 1 and 2, described later, was measured and found to be 1.0 × 10⁻⁶. －１１ It was a solid electrolyte exhibiting a lithium ion conductivity of S / cm or higher.

[0089] (11) Evaluation of Degradation Resistance A schematic cross-sectional diagram showing the layered structure of the electrochemical cell An all-solid-state electrochemical cell was prepared in which a solid electrolyte made of powder (Li-M-P solid electrolyte) and a sulfide-based solid electrolyte were adjacent to each other, and the current generated due to the oxidation reaction of the test material was investigated. Specifically, the experiment was carried out as follows.

[0090] The electrochemical cell 15, shown in Figure 7, a schematic cross-sectional view illustrating the layered structure of the electrochemical cell, was fabricated as follows: Algyrodite-type sulfide (Li) was used as the sulfide-based solid electrolyte. ６ PS ５ A solution of chlorine (Cl) was prepared. 57 mg of this sulfide was placed into an insulating outer cylinder 59 (inner diameter 9.5 mm) made of alumina tubing, and a layer of sulfide-based solid electrolyte 2 was formed by pressurizing and molding at a pressure of 80 MPa.

[0091] Next, 20 mg of the test material powder was placed on top of the sulfide-based solid electrolyte 2 layer, and a layer of Li-M-P solid electrolyte 1 was formed by pressurizing and molding at a pressure of 80 MPa.

[0092] Next, 20 mg of the mixture obtained by mixing the powder of the test material and the powder of stainless steel (SUS316) in a mortar in a volume ratio of 50:50 was placed on top of the Li-M-P solid electrolyte 1 layer, and a layer 52 of the mixture was formed by pressurizing at a pressure of 360 MPa.

[0093] Next, a 200 μm thick sheet of metallic indium (In), a 300 μm thick sheet of metallic Li, and a 200 μm thick sheet of metallic In were laminated in the order described above beneath the sulfide-based solid electrolyte 2 layer (on the opposite side of the Li-M-P solid electrolyte), and then pressurized at a pressure of 80 MPa to form a counter electrode layer 54 consisting of an In / Li / In three-phase structure.

[0094] Next, a current collector 57 (working electrode side) made of stainless steel (SUS316) sheet material was placed on top of the composite material layer, and a current collector 58 (counter electrode side) was placed below the counter electrode member layer 54, and a current collector lead was provided for each current collector.

[0095] In this manner, an electrochemical cell 15 was fabricated having a working electrode consisting of a layer of Li-M-P solid electrolyte 1, a composite material layer 52, and a current collector 57 (working electrode side) placed on the composite material layer, a counter electrode consisting of a counter electrode member layer 54, and a current collector 58 (counter electrode side) placed below the counter electrode member layer, and a layer of sulfide-based solid electrolyte 2 formed between the working electrode and the counter electrode. The electrochemical cell 15 was placed in a constant temperature bath at 25°C, with the composite material layer 52 side as the working electrode (high potential electrode) and the counter electrode member layer 54 side as the counter electrode (low potential electrode). The voltage was swept from the open-circuit voltage of the electrochemical cell 15 to 5.0V vs Li (equivalent to 4.4V vs In-Li) at a sweep speed of 1mV / s, and the current fluctuation was measured.

[0096] Solid electrolytes are inherently insulating materials in terms of electrical conduction based on electron transfer. However, when the voltage applied to the working electrode in the electrochemical cell described above is swept towards higher potentials, initially, a small current flows, which is thought to originate from non-Faraday reactions that do not involve the transfer of electrons, or from side reactions of adsorbed water and impurities. Then, as the Li-M-P solid electrolyte undergoes decomposition through oxidation and changes in its state, a current associated with this decomposition reaction becomes observable.

[0097] In this test, the decomposition resistance of the test material was evaluated by the current value when the applied voltage was increased to 5.0V. The current value of the powder in Example 1 when 5.0V was applied was 4.01 μA. On the other hand, as Comparative Example 1, lithium niobate (LiNbO), a common protective material that has been widely used in the past, was evaluated. ３ In the evaluation of decomposition resistance using the test material, the current value when 5.0V was applied was 35.0μA. As a result, it was found that the present invention significantly improves decomposition resistance compared to lithium niobate according to Comparative Example 1.

[0098] Therefore, by applying the powder according to Example 1 to, for example, the Li-M-P solid electrolyte 1 in an all-solid-state battery with the arrangement structure shown in Figures 2 and 3, excellent decomposition resistance is exhibited, and the reliability of the all-solid-state battery is improved when the charging voltage is increased (the same applies to the powders in Examples 2-13 below).

[0099] [Example 2] In Example 2, the pulverized material was calcined at 300°C in an air atmosphere for 5 hours in the "(5) calcination process" of Example 1. Except for this, the turbid aqueous liquid and the Li-Al-P composition powder (Li-M-P solid electrolyte) according to Example 2 were obtained in the same manner as in Example 1. X-ray diffraction measurements were performed on the obtained powder according to Example 2, and the result showed that Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 46 nm, indicating an amorphous solid. The particle size (D50) of the powder in Example 2 was 2.8 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder in Example 2, the current value at an applied 5.0 V was 4.32 μA.

[0100] [Example 3] Lithium hydroxide monohydrate (LiOH·H ２ O) Dissolve 16.3 g (Wako Special Grade) in 342 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 9.902 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0101] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass３ ) ｎ An aqueous phosphoric acid solution prepared by dissolving 20.00 g (Wako Special Grade) in 110 g of pure water was added in its entirety to the aforementioned aqueous solution containing dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and stirred for 15 minutes to obtain a clear aqueous solution containing Li, Al, and P.

[0102] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎ It contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0103] The aqueous solution obtained in Example 3 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain a powder of the Li-Al-P system composition (Li-M-P solid electrolyte) according to Example 3.

[0104] X-ray diffraction measurements were performed on the powder obtained in Example 3, and the result was that Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 46 nm, indicating an amorphous solid. Furthermore, the particle size (D50) of the powder in Example 3 was 2.7 μm.

[0105] When the powder obtained in Example 3 was subjected to the degradation resistance evaluation described in Example 1, the current value when 5.0V was applied was 4.11μA.

[0106] [Example 4] The procedure was carried out in the same manner as in Example 3, except that the pulverized powder according to Example 3 was calcined at 300°C in an air atmosphere, to obtain a transparent aqueous liquid according to Example 4 and a Li-M-P solid electrolyte according to the powder of Example 4. X-ray diffraction measurement of the obtained powder according to Example 4 was performed, and the result showed that Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 47 nm, indicating an amorphous solid. The particle size (D50) of the powder in Example 4 was 2.8 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder in Example 4, the current value at an applied voltage of 5.0 V was 4.17 μA.

[0107] [Example 5] Lithium hydroxide monohydrate (LiOH·H ２ O) Dissolve 6.52 g (Wako Special Grade) in 224 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 43.960 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0108] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ A phosphoric acid aqueous solution prepared by dissolving 20.00 g (Wako Special Grade) in 110 g of pure water was added in its entirety to the above-mentioned aqueous solution containing dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and stirred for 15 minutes to obtain the clear aqueous solution according to Example 5.

[0109] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎ It contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0110] The aqueous solution obtained in Example 5 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain the powder (Li-M-P solid electrolyte) of Example 5. X-ray diffraction measurement of the powder of Example 5 revealed that no clear diffraction peaks were observed, indicating that it was an amorphous solid. The particle size (D50) of the powder of Example 5 was 3.0 μm. The XRD spectrum of the powder of Example 5 is shown in Figure 6, and the SEM-EDX spectrum is shown in Figure 8. When the decomposition resistance evaluation described in Example 1 was performed on the powder of Example 5, the current value at an applied voltage of 5.0 V was 3.22 μA.

[0111] (Wet coating test) 20 g of the aqueous solution according to Example 5 described above, and positive electrode active material (LiNi １／３ Mn １／３ Co １／３ O ２ , specific surface area 0.538m ２40 g of ( / g) was mixed to obtain a slurry. The obtained mixed slurry was put into a coating apparatus (JD-1 Kawata), and the aqueous solution according to Example 5 was coated onto the positive electrode active material and dried to obtain a positive electrode active material coated by wet coating. The coating conditions were: slurry supply rate: 3 mL / min, dispersion air pressure 500 kPa, dispersion air temperature 200 °C, drying air temperature 135 °C, drying blower airflow rate 900 L / min, and classification blower airflow rate 890 L / min.

[0112] (Semi-quantitative analysis of Li, Al, P, Na, and O in the coating layer by XPS) Semi-quantitative analysis was performed on a positive electrode active material powder coated by wet coating using the aqueous liquid composition according to Example 5 by irradiating the surface of the powder particles with X-rays using an X-ray photoelectron spectroscopy (XPS) apparatus (JEOL, JPS-9200S). The analysis conditions were: X-ray source: Al tube, output: 200W, analysis angle: 45°, background treatment: Shirley method. The elements measured were Li, Al, P, Na, O, and Nb contained in the coating layer, and Ni, Co, and Mn contained in the positive electrode active material (Nb was included in Comparative Example 1).

[0113] In the semi-quantitative analysis of the coated positive electrode active material by XPS, it is preferable that the following values ​​are obtained: Li 2.58 at% to 44.38 at%, M(Al) 0.94 at% to 14.99 at%, P 4.78 at% to 25.50 at%, Na 0 at% to 12.52 at%, and O 43.98 at% to 68.89 at%. Furthermore, it is preferable that Li 6.44 at% to 18.82 at%, M(Al) 2.16 at% to 6.20 at%, P 14.57 at% to 22.78 at%, Na 0 at% to 11.41 at%, and O 56.01 at% to 65.61 at%. The total content of Li, M(Al), P, Na, and O is preferably 95 at% or more, and may be 100 at%.

[0114] (Method for calculating coverage by coating layer using semi-quantitative analysis by XPS) Calculation was performed using the following formula 1 from the content (at%) of each measured element obtained in the aforementioned XPS measurement. Coverage (%) = (Nb + Al + P + Na) / (Ni + Co + Mn + Al + P + Na + Nb) × 100 (Formula 1)

[0115] Table 3 shows the content values (at%) of each measured element in the positive electrode active material powder coated by wet coating using the aqueous liquid-based composition according to Example 5. Table 5 shows the calculated coverage.

[0116] (Method for calculating thickness of coating layer) The coated positive electrode active material powder does not contain Nb, Al, P or Na. Therefore, it can be assumed that Nb, Al, P and Na exist only in the coating layer. Further, the coating layer thickness of the positive electrode active material is obtained on the assumption that Nb, Al, P and Na in the coating liquid are respectively Nb ２ O ５ , Al ２ O ３ , P ２ O ５ , and Na ２ O, and is represented by the following formulas 2 and 3 (the same applies to each example below).

[0117] When the Nb content in the coated positive electrode active material obtained by measuring the coated positive electrode active material powder in the same manner as the aforementioned ICP-AES analysis is a (mass%), the Al content is b (mass%), the P content is c (mass%), and the Na content is d (mass%), the mass ratio C (mass%) of the coating layer relative to the entire coated positive electrode active material powder is determined based on the atomic weights of Nb, Al, P and Na and the Nb ２ O ５ , Al ２ O ３ , P ２ O ５ , Na ２ O molecular weights, and is calculated by the following formula 2. C = a × Nb ２ O ５ molecular weight / (atomic weight of Nb × 2) + b × Al ２ O ３ molecular weight / (atomic weight of Al × 2) + c × P ２ O ５ molecular weight / (atomic weight of P × 2) + d × Na２ Molecular weight of O / (atomic weight of Na × 2) ... (Equation 2)

[0118] Furthermore, the specific surface area S (m²) of the positive electrode active material powder before coating as described above. ２ The density D (g / cm³) of the powder (solid electrolyte) ３ Using ), the average film thickness t (nm) of the coating layer is expressed by the following equation 3. Note that 10 on the right-hand side of equation 3 is the conversion factor. t (nm) = 10 × C / (D × S) ... (Equation 3)

[0119] The density D of the powder (solid electrolyte) (measured using an Anton Paar MICRO-ULTRAPY C1200e pycnometer) was 2.477 g / cm³ in the case of the powder according to Example 5. ３ Therefore, the value calculated using that value was used as the film thickness. The film thickness can be, for example, 1 to 30 nm, and preferably 20 nm or less.

[0120] Table 4 shows the ICP measurement results for each element in a positive electrode active material powder coated with a wet coating using the aqueous liquid composition according to Example 5, and the C value calculated using Equation 2. The calculated film thickness is shown in Table 5.

[0121] (Dry coating test) 2.3 g of the powder (Li-Al-P-Na composition) according to Example 5 described above, and positive electrode active material (LiNi １／３ Mn １／３ Co １／３ O ２ , specific surface area 0.538m ２ 40 g of the powder ( / g) was mixed in a mortar to obtain a mixture. The obtained mixture was placed in a coating apparatus (NHS-0, manufactured by Nara Machine Works Co., Ltd.) and the powder according to Example 5 was used to coat the positive electrode active material to obtain a positive electrode active material coated by dry coating. The coating conditions were a rotation speed of 60 m / s and a processing time of 60 sec.

[0122] Using a positive electrode active material powder coated with a dry coating using the powder composition according to Example 5, the same procedure as in the case of a positive electrode active material powder coated with a wet coating using the aqueous liquid composition described above was performed to measure the coverage rate and film thickness of the coating layer. These values ​​are shown in Table 5.

[0123] [Example 6] The procedure was the same as in Example 5, except that the pulverized powder according to Example 5 was calcined at 300°C in an air atmosphere for 5 hours to obtain a transparent aqueous liquid and a powder (Li-M-P solid electrolyte) according to Example 6. X-ray diffraction measurement of the powder according to Example 6 revealed that it was an amorphous solid with no clear diffraction peaks. The particle size (D50) of the powder according to Example 6 was 3.0 μm. The SEM-EDX spectrum of the powder according to Example 6 is shown in Figure 9. When the decomposition resistance evaluation described in Example 1 was performed on the powder according to Example 6, the current value when 5.0 V was applied was 3.76 μA.

[0124] [Example 7] Lithium hydroxide monohydrate (LiOH·H ２ O) Dissolve 2.62 g (Wako Special Grade) in 95 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 1.59 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0125] (H) with a P concentration of 34.5% by mass ｎ＋２ P ｎ O ３ｎ＋１ A phosphoric acid aqueous solution prepared by dissolving 7 g (Wako Special Grade) in 40 g of pure water was added in its entirety to the above-mentioned aqueous solution containing dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and stirred for 15 minutes to obtain the clear aqueous solution according to Example 7. The aqueous solution according to Example 7 does not contain Na.

[0126] The aqueous solution obtained in Example 7 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain the powder (Li-M-P solid electrolyte) of Example 7. X-ray diffraction measurement of the powder of Example 7 revealed that no clear diffraction peaks were observed, indicating that it was an amorphous solid. The particle size (D50) of the powder of Example 7 was 3.0 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder of Example 7, the current value at an applied voltage of 5.0 V was 3.29 μA.

[0127] [Example 8] The procedure was carried out in the same manner as in Example 7, except that the pulverized powder according to Example 7 was calcined at 300°C in an air atmosphere for 5 hours to obtain a transparent aqueous liquid and a powder (Li-M-P solid electrolyte) according to Example 8. X-ray diffraction measurement of the powder according to Example 8 revealed that it was an amorphous solid with no clear diffraction peaks. The particle size (D50) of the powder according to Example 8 was 3.0 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder according to Example 8, the current value when 5.0 V was applied was 3.21 μA.

[0128] [Example 9] Lithium hydroxide monohydrate (LiOH·H ２ O) Dissolve 4.62 g (Wako Special Grade) in 206 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 2.806 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0129] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ A phosphoric acid aqueous solution prepared by dissolving 20.00 g (Wako Special Grade) in 105 g of pure water was added in its entirety to the above-mentioned aqueous solution containing dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and stirred for 15 minutes to obtain the clear aqueous solution according to Example 9.

[0130] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎ It contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0131] The clear aqueous liquid obtained in Example 9 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain the powder (Li-M-P solid electrolyte) of Example 9. X-ray diffraction measurement of the powder of Example 9 revealed that no clear diffraction peaks were observed, indicating that it was an amorphous solid. The particle size (D50) of the powder of Example 9 was 3.3 μm. The XRD spectrum of the powder of Example 9 is shown in Figure 6. When the decomposition resistance evaluation described in Example 1 was performed on the powder of Example 9, the current value at an applied voltage of 5.0 V was 3.36 μA.

[0132] [Example 10] The same procedure as in Example 9 was followed to obtain the aqueous liquid and powder (Li-M-P solid electrolyte) according to Example 10, except that the pulverized powder according to Example 9 was calcined at 300°C in an air atmosphere for 5 hours. X-ray diffraction measurement of the powder according to Example 10 revealed that it was an amorphous solid with no clear diffraction peaks. The particle size (D50) of the powder according to Example 10 was 3.2 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder according to Example 10, the current value when 5.0 V was applied was 3.27 μA.

[0133] [Example 11] Zinc hydroxide (Zn(OH)) was added to a mixed solvent of 50 mL of pure water and 60.71 g of 28% by mass aqueous ammonia (Nacalai Tesque special grade). ２ 0.993 g (Wako Special Grade) of lithium hydroxide (LiOH·H) was dissolved in a zinc aqueous solution at room temperature (25°C), and lithium hydroxide monohydrate (LiOH·H) was added to it. ２ O) 1.667 g (Wako Special Grade) was added, and this solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Zn were dissolved.

[0134] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ An aqueous phosphoric acid solution, prepared by dissolving 2.058 g (Wako Special Grade) in 26 g of pure water, was added in its entirety to the aforementioned aqueous solution containing dissolved Li and Zn using a tube pump at an addition rate of 5 mL / min, and stirred for 15 minutes to obtain the clear aqueous solution according to Example 11.

[0135] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎ It contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0136] The aqueous solution obtained in Example 11 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain the powder (Li-M-P solid electrolyte) of Example 11. X-ray diffraction measurements of the powder of Example 11 were performed, and the results showed that Li ３ PO ４ Peaks attributed to ZnO were observed, and the maximum diffraction peak was attributed to ZnO, indicating a solid with a crystallite size of 60 nm. The particle size (D50) of the powder in Example 11 was 2.2 μm. The XRD spectrum of the powder in Example 11 is shown in Figure 6. When the decomposition resistance evaluation described in Example 1 was performed on the powder in Example 11, the current value at an applied voltage of 5.0 V was 5.35 μA.

[0137] [Example 12] A mixed solvent of 50 mL of pure water and 60.71 g of 28% by mass aqueous ammonia (Nacalai Tesque special grade) was prepared, and zinc hydroxide (Zn(OH) ２ ) 0.993 g (Wako Special Grade) dissolved in a zinc aqueous solution at room temperature (25°C), lithium hydroxide monohydrate (LiOH·H) ２ O) 1.667 g (Wako Special Grade) was added, and this solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Zn were dissolved.

[0138] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ 5.145 g (Wako Special Grade) was dissolved in 129 g of pure water to obtain an aqueous phosphoric acid solution. This solution was then added in its entirety to the aqueous solution containing the above-mentioned dissolved Li and Zn using a tube pump at an addition rate of 5 mL / min, and the mixture was stirred for 15 minutes to obtain the clear aqueous solution according to Example 12.

[0139] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎIt contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0140] The aqueous solution obtained in Example 12 was processed in the same manner as in Example 1 to obtain a pulverized powder, which was then calcined in the same manner as in Example 1 to obtain the powder (Li-M-P solid electrolyte) of Example 12. X-ray diffraction measurement of the powder of Example 12 revealed a peak attributed to lithium pyrophosphate (including monohydrate), and the crystallite size was 60 nm, indicating it was a solid. The particle size (D50) of the powder of Example 12 was 2.1 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder of Example 12, the current value at an applied voltage of 5.0 V was 4.49 μA.

[0141] [Example 13] Tin chloride monohydrate (SnCl ２ ・H ２ O) (Wako Special Grade) was added to a mixed solvent of 299 g of pure water and 3.02 g of 28% by mass aqueous ammonia (Nacalai Tesque Special Grade), and the white precipitate of tin hydroxide (Sn(OH)) was obtained. ２ A solution containing tin hydroxide was obtained. The resulting tin hydroxide-containing solvent was filtered by suction to obtain a cake on the filter (a diffraction pattern of tin hydroxide was observed from the cake by XRD measurement). The entire amount of the obtained cake was converted into lithium hydroxide monohydrate (LiOH·H). ２ O) 4.175 g (Wako Special Grade) was dissolved in 225.2 ml of pure water and added all at once to a lithium aqueous solution at room temperature (25°C). This solution was then stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Sn were dissolved.

[0142] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ A phosphoric acid aqueous solution prepared by dissolving 5.120 g (Wako Special Grade) in 35 ml of pure water was added to the above-mentioned aqueous solution containing dissolved Li and Sn using a tube pump at an addition rate of 5 mL / min, and the mixture was stirred for 15 minutes to obtain the clear aqueous solution according to Example 13.

[0143] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎIt contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0144] The entire volume of the aqueous system containing Li, Sn, and P obtained in Example 13 was evaporated to dryness in an air atmosphere at 110°C using a dryer to obtain a powder. 1 g of the obtained powder and 17 φ10 mm zirconia beads were placed in a 45 ml zirconia pot and ground for 5 hours using a planetary ball mill. After grinding, the zirconia beads were separated from the contents of the pot to obtain the ground powder.

[0145] The obtained pulverized powder was calcined in an air atmosphere at 120°C for 12 hours to obtain the Li-Sn-P-Na-based composition powder according to Example 13. X-ray diffraction measurements of the powder according to Example 13 were performed, and the results showed that Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 65 nm, indicating a solid. The particle size (D50) of the powder in Example 13 was 2.3 μm. The XRD spectrum of the powder in Example 13 is shown in Figure 6. When the decomposition resistance evaluation described in Example 1 was performed on the powder in Example 13, the current value at an applied voltage of 5.0 V was 5.78 μA.

[0146] [Comparative Example 1] A hydrogen peroxide aqueous solution was prepared by adding 7.7 g of 35% by mass hydrogen peroxide solution (Wako Grade 1) to 19.6 g of pure water. Nb ２ O ５ Niobium (Nb) has a content of 58.0% by mass. ２ O ５ nH ２ O) After adding 4.4 g (manufactured by HC Starck), the liquid temperature was maintained at 20-30°C, and 3.5 g of 28% by mass aqueous ammonia (Nacalai Tesque special grade) was added. The mixture was then thoroughly stirred under an atmospheric environment to obtain a clear solution.

[0147] Next, in a nitrogen atmosphere, lithium hydroxide monohydrate (LiOH·H) is added to this transparent solution. ２ O) 0.9 g (Wako Special Grade) was added to obtain a clear aqueous solution according to Comparative Example 1, which is a clear aqueous solution containing lithium and a niobium peroxo complex.

[0148] The resulting aqueous solution was heated in a nitrogen atmosphere on a hot plate at 100°C and evaporated to dryness to obtain a powder. 1 g of the obtained powder and 17 zirconia beads with a diameter of 10 mm were placed in a 45 mL zirconia pot and ground for 5 hours using a planetary ball mill. After grinding, the zirconia beads were separated from the contents of the pot to obtain the ground powder.

[0149] The obtained pulverized powder was calcined at 120°C in an air atmosphere for 12 hours to obtain a composition consisting of the powder according to Comparative Example 1. X-ray diffraction measurements of the powder according to Comparative Example 1 showed that no clear diffraction peaks were observed, indicating that it was an amorphous solid. The particle size (D50) of the powder according to Comparative Example 1 was 3.8 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder according to Comparative Example 1, the current value when 5.0 V was applied was 35.0 μA.

[0150] (Wet coating test) 20 g of the aqueous solution according to Comparative Example 1 described above, and positive electrode active material (LiNi １／３ Mn １／３ Co １／３ O ２ , specific surface area 0.538m ２ Using 40 g of ( / g), the same procedure as in Example 5 was performed, and a wet coating test was conducted to obtain a coating according to Comparative Example 1. The same procedure as in Example 5 was performed on the obtained coating according to Comparative Example 1, and the coverage rate and film thickness of the coating layer were measured. The results are shown in Table 5. However, the measured value of the density D of the solid electrolyte was 3.305 g / cm³. ３ That was the case.

[0151] (Dry coating test) 1.5 g of the composition consisting of the powder according to Comparative Example 1 described above, and positive electrode active material (LiNi １／３ Mn １／３ Co １／３ O ２ , specific surface area 0.538m ２ Using 40 g of ( / g), the same procedure as in Example 5 was performed, and a dry coating test was conducted to obtain a coating according to Comparative Example 1. The same procedure as in Example 5 was performed on the obtained coating according to Comparative Example 1, and the coverage rate and film thickness of the coating layer were measured. The results are shown in Table 5.

[0152] [Comparative Example 2] Lithium hydroxide monohydrate (LiOH·H ２ O) Dissolve 9.29 g (Wako Special Grade) in 85 ml of pure water to make a lithium aqueous solution at room temperature (25°C), then add aluminum oxide (Al ２ O ３ 2.55 g (Wako Special Grade) was added all at once, and the solution was stirred at room temperature (25°C) for 60 minutes to obtain an aqueous solution in which Li and Al were dissolved.

[0153] Metaphosphoric acid (HPO) with a P concentration of 30.1% by mass ３ ) ｎ A phosphoric acid aqueous solution prepared by dissolving 1.00 g (Wako Special Grade) in 10 g of pure water was added to the above-mentioned aqueous solution containing dissolved Li and Al using a tube pump at an addition rate of 5 mL / min, and the mixture was stirred for 15 minutes to obtain the turbid aqueous solution according to Comparative Example 2.

[0154] Furthermore, the metaphosphate reagent used as the P source contained sodium metaphosphate (NaPO) as a molding agent. ３ ) ｎ It contains (based on the ICP measurement results of the reagent), and its Na / P molar ratio is 0.6045 / 1.

[0155] The entire volume of the aqueous system containing Li, Al, and P obtained in Comparative Example 2 was evaporated to dryness at 110°C in an air atmosphere using a dryer to obtain a powder. 1 g of the obtained powder and 17 10 mm diameter zirconia beads were placed in a 45 ml zirconia pot and ground for 5 hours using a planetary ball mill. After grinding, the zirconia beads were separated from the contents of the pot to obtain the ground powder.

[0156] The obtained pulverized powder was calcined in an air atmosphere at 120°C for 12 hours to obtain the powder according to Comparative Example 2. X-ray diffraction measurements were performed on the powder according to Comparative Example 2, and the results showed that Li ３ PO ４ A peak attributable to was observed, and the crystallite size was 59 nm, indicating a solid. The particle size (D50) of the powder in Comparative Example 2 was 3.2 μm. When the decomposition resistance evaluation described in Example 1 was performed on the powder in Comparative Example 2, the current value when 5.0 V was applied was 12.6 μA.

[0157]

[0158]

[0159]

[0160]

[0161]

[0162] 1 Li-M-P solid electrolyte 2 Sulfide-based solid electrolyte 3 Conductive material on the positive electrode side 4 Conductive material on the negative electrode side 11 All-solid-state battery 15 Electrochemical cell 31 Positive electrode active material 32 Conductive material other than the positive electrode active material 41 Negative electrode active material 42 Conductive material other than the negative electrode active material 52 Layer of composite material 54 Layer of counter electrode material 55 Current collector (positive electrode side) 56 Current collector (negative electrode side) 57 Current collector (working electrode side) 58 Current collector (counter electrode side) 59 Insulating outer cylinder

Claims

1. An aqueous solution having the following composition: When one or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount of element X (moles) to the total amount (moles) of Li, M, P, and Na is expressed as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less.

2. The aqueous liquid according to claim 1, wherein the content of Li, M, P, and Na in the aqueous liquid is as follows: Li is 0.05% by mass or more and 3.5% by mass or less, M is 0.04% by mass or more and 2% by mass or less, P is 0.15% by mass or more and 3.0% by mass or less, and Na is 0% by mass or more and 2% by mass or less.

3. The aqueous liquid according to claim 1, wherein the total content of Li, M, P, and Na in the aqueous liquid is 0.50% by mass or more and 10.0% by mass or less.

4. A powder having the following composition: When one or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount of element X (moles) to the total amount (moles) of Li, M, P, and Na is expressed as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less.

5. A solid electrolyte having the following composition. One or more elements selected from Al, Zn, and Sn are denoted as M, and the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na is denoted as the X / (Li+M+P+Na) molar ratio, where the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less.

6. An aqueous solution for coating a positive electrode active material, having the composition described in claim 1.

7. A powder for coating a positive electrode active material, having the composition described in claim 4.

8. A method for producing a coated lithium secondary battery positive electrode active material, comprising the step of performing a coating treatment on the surface of the positive electrode active material for a lithium secondary battery using the aqueous solution described in claim 1.

9. A method for producing a coated lithium secondary battery positive electrode active material, comprising the step of performing a coating treatment on the surface of the positive electrode active material for a lithium secondary battery using the powder described in claim 4.

10. An all-solid-state battery in which the solid electrolyte described in claim 5 is present between the conductive material on the positive electrode side and the conductive material on the negative electrode side.

11. A method for producing an aqueous liquid, comprising the step of obtaining an aqueous liquid having the following composition, where M is denoted as one or more elements selected from Al, Zn, and Sn, and the ratio of the amount (moles) of element X to the total amount (moles) of Li, M, P, and Na is denoted as the X / (Li+M+P+Na) molar ratio, the Li / (Li+M+P+Na) molar ratio is 0.069 or more and 0.800 or less, the M / (Li+M+P+Na) molar ratio is 0.024 or more and 0.300 or less, the P / (Li+M+P+Na) molar ratio is 0.095 or more and 0.800 or less, and the Na / (Li+M+P+Na) molar ratio is 0.000 or more and 0.326 or less.

12. A method for producing powder, comprising the step of drying the aqueous liquid obtained in claim 11 to obtain a powder.

13. A method for producing powder according to claim 12, comprising the step of grinding the powder.

14. A method for producing powder, comprising a drying step of maintaining the aqueous liquid obtained by the production method described in claim 11 at a temperature of 120°C or higher and 220°C or lower.

15. A method for producing a solid electrolyte, comprising a heat treatment step of maintaining the powder obtained by the manufacturing method described in claim 12 or 13 at a temperature greater than 110°C and less than or equal to 500°C.

16. A coated lithium secondary battery positive electrode active material in which one or more elements selected from Al, Zn, and Sn are denoted as M, and the content of Li, M, P, Na, and O when the surface of the coated lithium secondary battery positive electrode active material powder particles is measured by XPS is as follows: Li: 2.58 at% or more and 44.38 at% or less, M: 0.94 at% or more and 14.99 at% or less, P: 4.78 at% or more and 25.50 at% or less, Na: 0 at% or more and 12.52 at% or less, O: 43.98 at% or more and 68.89 at% or less.

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