Method for producing positive electrode active material, positive electrode active material, and battery

Abstract

Disclosed is a method for producing a positive electrode active material having an O2-type structure and having a low resistance when applied to a solid-state battery.SOLUTION: The production method of the present disclosure is a method for producing a positive electrode active material used in a solid-state battery, the method including obtaining Na-containing oxide particles having a P2-type structure, and ion-exchanging at least a part of Na of the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure, wherein the Na-containing oxide particles are spherical particles having an average particle size of 1.0 μm or more and less than 3.5 μ m, and the Li-containing oxide particles are spherical particles having a hollow single-layer structure.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present application discloses a method for producing a positive electrode active material, a positive electrode active material, and a battery. [Background technology]

[0002] Positive electrode active materials having an O2-type structure are known. As disclosed in Patent Document 1, a positive electrode active material having an O2-type structure is obtained by ion-exchanging at least a portion of Na in a sodium-containing oxide having a P2-type structure with Li. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-170994 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional positive electrode active materials having an O2-type structure have room for improvement in terms of resistance when applied to solid-state batteries, or in terms of rate characteristics when applied to liquid-state batteries. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A method for producing a positive electrode active material used in a solid-state battery, comprising: Obtaining Na-containing oxide particles having a P2 type structure, and and ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. the Na-containing oxide particles are spherical particles having an average particle size of 1.0 μm or more and less than 3.5 μm, The Li-containing oxide particles are spherical particles having a hollow single-layer structure. Manufacturing method. <Aspect 2> The manufacturing method of embodiment 1, The Na-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. Manufacturing method. <Aspect 3> A positive electrode active material for use in a solid-state battery, comprising Li-containing oxide particles, the Li-containing oxide particles have an O2 type structure, the Li-containing oxide particles are spherical particles having a hollow single-layer structure, The Li-containing oxide particles have an average particle size of 1.0 μm or more and less than 3.5 μm. Cathode active material. <Aspect 4> The positive electrode active material of Aspect 3, The Li-containing oxide particles have a diameter of 4.5 m 2 / g or less specific surface area, Cathode active material. <Aspect 5> The positive electrode active material of Aspect 3 or 4, The Li-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. Cathode active material. <Aspect 6> A solid-state battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, the positive electrode active material layer includes the positive electrode active material of any one of Aspects 3 to 5, The positive electrode active material layer contains a solid electrolyte. solid state battery. <Aspect 7> A method for producing a positive electrode active material used in a liquid battery, comprising: Obtaining Na-containing oxide particles having a P2 type structure, and and ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. the Na-containing oxide particles are spherical particles having an average particle diameter of 3.5 μm or more, The Li-containing oxide particles are spherical particles having a hollow multilayer structure. Manufacturing method. <Aspect 8> The manufacturing method of embodiment 7, The Na-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. Manufacturing method. <Aspect 9> A positive electrode active material for use in a liquid battery, comprising Li-containing oxide particles, the Li-containing oxide particles have an O2 type structure, the Li-containing oxide particles are spherical particles having a hollow multilayer structure, The Li-containing oxide particles have an average particle size of 3.5 μm or more. Cathode active material. <Aspect 10> The positive electrode active material of Aspect 9, The Li-containing oxide particles have a diameter of 4.5 m 2 / g or more specific surface area, Cathode active material. <Aspect 11> The positive electrode active material of Aspect 9 or 10, The Li-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. Cathode active material. <Aspect 12> A liquid battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, the positive electrode active material layer includes the positive electrode active material of any one of Aspects 9 to 11, The positive electrode active material layer contains a liquid electrolyte. Liquid battery. [Effects of the Invention]

[0006] The positive electrode active material of the present disclosure has low resistance when applied to a solid-state battery, or has excellent rate characteristics when applied to a liquid-state battery. [Brief explanation of the drawings]

[0007] [Figure 1A] 1 shows an example of a flow of a method for manufacturing a positive electrode active material used in a solid-state battery. [Figure 1B] 1 shows an example of a method for manufacturing a positive electrode active material used in a liquid battery. [Figure 2A] 1 shows a schematic cross-sectional shape of a spherical particle having a hollow single-layer structure. [Figure 2B] 1 shows a schematic cross-sectional shape of a spherical particle having a hollow multilayer structure. [Figure 2C] 1 shows a schematic cross-sectional shape of a spherical particle having a hollow multilayer structure. [Figure 3] 1 shows a schematic diagram of an example of a battery configuration. [Figure 4] The cross-sectional shapes of positive electrode active materials A to D are shown. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1.First form The positive electrode active material according to the first embodiment is used in a solid state battery.

[0009] 1.1 Manufacturing method for cathode active materials used in solid-state batteries As shown in FIG. 1A, a method for producing a positive electrode active material used in a solid-state battery includes the following steps: Obtaining Na-containing oxide particles having an S1:P2 type structure, and S2: Ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. The Na-containing oxide particles are spherical particles having an average particle size of 1.0 μm or more and less than 3.5 μm, and the Li-containing oxide particles are spherical particles having a hollow single-layer structure, as shown in FIG.

[0010] In this application, unless otherwise specified, the term "average particle size" refers to the particle size at 50% cumulative value (D50, median size) in the volume-based particle size distribution determined by a laser diffraction / scattering method.

[0011] In the present application, "spherical particles" refers to particles having a circularity of 0.80 or more. The circularity of spherical particles may be 0.81 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, or 0.90 or more. The circularity of a particle is 4πS / L 2 where S is the orthogonal projected area of ​​the particle, and L is the perimeter of the orthogonal projected image of the particle. The circularity of a particle can be determined by observing the appearance or cross-sectional shape of the particle using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an optical microscope. When a particle is made up of multiple particles, the circularity is measured, for example, as an average value as follows. (1) First, the particle size distribution of the particles is measured. Specifically, the particle diameter at 10% of the cumulative value (D10) and the particle diameter at 90% of the cumulative value (D90) in the volume-based particle size distribution are determined by laser diffraction / scattering. (2) The appearance of the particles whose particle size distribution has been measured is observed by image observation using an SEM, TEM, or optical microscope, and 100 particles having a circle-equivalent diameter (the diameter of a circle having the same area as the orthogonal projection area of ​​the particle) of not less than D10 and not more than D90, as determined in (1), are randomly selected from the particles contained in the image. (3) The circularity of each of the 100 extracted particles is determined by image processing, and the average value is regarded as the "circularity of the particle."

[0012] 1.1.1 S1 In S1, Na-containing oxide particles having a P2 type structure are obtained. Here, the Na-containing oxide particles obtained in S1 are spherical particles having an average particle diameter of 1.0 μm or more and less than 3.5 μm.

[0013] The sodium-containing oxide particles having a P2 type structure, a predetermined average particle size, and a spherical shape can be produced, for example, through the following steps S1-1, S1-2, and S1-3. S1-1: Obtaining precursor particles S1-2: Coating the surface of the precursor particles with a Na source to obtain composite particles. S1-3: Calcining the composite particles

[0014] In S1-1, precursor particles are obtained. The precursor particles contain, for example, at least one element selected from Mn, Ni, and Co. The precursor particles may contain at least Mn and one or both of Ni and Co, or may contain at least Mn, Ni, and Co. The precursor particles may be a salt containing at least one element selected from Mn, Ni, and Co. For example, the precursor particles may be at least one of carbonate, sulfate, nitrate, and acetate. Alternatively, the precursor particles may be a compound other than a salt. For example, the precursor particles may be a hydroxide. The precursor particles may be a hydrate. The precursor particles may be a combination of multiple types of compounds. The precursor particles are spherical particles. The size of the precursor particles is determined according to the average particle diameter of the desired Na-containing oxide particles.

[0015] In S1-1, a precipitate as the precursor particles may be obtained by coprecipitation using an ion source capable of forming a precipitate in an aqueous solution with transition metal ions and a transition metal compound containing at least one element selected from Mn, Ni, and Co. This results in spherical particles as the precursor particles. The "ion source capable of forming a precipitate in an aqueous solution with transition metal ions" may be, for example, at least one selected from sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above salt or hydroxide containing at least one element selected from Mn, Ni, and Co. Specifically, in S1-1, the ion source and the transition metal compound may be prepared as separate solutions, and the respective solutions may be added dropwise and mixed to obtain the precipitate as the precursor particles. In this case, water, for example, is used as the solvent. Various sodium compounds may be used as bases, and aqueous ammonia or the like may be added to adjust the basicity. In the case of the coprecipitation method, for example, an aqueous solution of the transition metal compound and an aqueous solution of sodium carbonate are prepared, and the respective aqueous solutions are added dropwise and mixed to obtain the precipitate as the precursor particles. Alternatively, precursor particles can be obtained by a sol-gel method, and in particular, by a co-precipitation method, spherical particles can be efficiently obtained as precursor particles.

[0016] In S1-1, the precursor particles may contain element M. Element M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. These elements M have the function of stabilizing, for example, the P2-type structure or the O2-type structure. The method for obtaining precursor particles containing element M is not particularly limited. When the precursor particles are obtained by coprecipitation in S1-1, for example, an aqueous solution of a transition metal compound containing at least one of Mn, Ni, and Co, an aqueous solution of sodium carbonate, and an aqueous solution of a compound of element M are prepared, and then the respective aqueous solutions are added dropwise and mixed to obtain a precursor containing element M together with at least one element of Mn, Ni, and Co. Alternatively, element M may not be added in S1-1, and element M may be doped during the Na-doping calcination in S1-2 and S1-3 described below.

[0017] In S1-2, the surfaces of the precursor particles obtained in S1-1 are coated with a Na source to obtain composite particles. The Na source may be a salt containing Na, such as a carbonate or nitrate, or a compound other than a salt, such as sodium oxide or sodium hydroxide. In S1-2, the amount of Na source coated on the surfaces of the precursor particles may be determined taking into account the amount of Na lost during the subsequent calcination.

[0018] In S1-2, the coverage of the Na source on the surface of the precursor particle is not particularly limited. For example, in S1-2, the composite particles may be obtained by coating 40 area% or more, 50 area% or more, 60 area% or more, or 70 area% or more of the surface of the precursor particle with the Na source. Here, when the precursor obtained in S1-1 is a spherical particle and the composite particles obtained in S1-2 are obtained by coating 40 area% or more of the surface of the precursor particle with the Na source, the Na-containing oxide particles having a P2 structure in S1-3 described below tend to be spherical particles. If the coverage of the Na source is low, abnormal growth of P2 crystals tends to occur on the surface of the composite particle when the composite particle is fired, and the Na-containing oxide particles tend to become plate-like particles. If the coverage of the Na source is high, the crystallites of the P2 crystals tend to become small when the composite particle is fired, and the Na-containing oxide particles tend to become spherical particles corresponding to the shape of the precursor particle.

[0019] In S1-2, the method for coating the surface of the precursor particles with the Na source is not particularly limited. As described above, when 40% or more of the surface area of ​​the precursor particles is to be coated with the Na source, various methods can be used. For example, a tumbling fluidized coating method or a spray drying method can be used. That is, a coating solution in which a Na source is dissolved is prepared, and the coating solution is brought into contact with the surface of the precursor particles, and the solution is dried at the same time as or after the contact. By adjusting the coating conditions (temperature, time, number of times, etc.), 40% or more of the surface area of ​​the precursor particles can be coated with the Na source.

[0020] In S1-2, the precursor particles may be coated with an M source together with the Na source. For example, in S1-2, composite particles may be obtained by mixing the precursor particles obtained in S1-1 with a Na source and an M source containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. The M source may be, for example, a salt containing the element M, such as a carbonate or a sulfate, or a compound other than a salt, such as an oxide or a hydroxide. The amount of the M source relative to the precursor particles may be determined depending on the chemical composition of the Na-containing oxide particles after firing.

[0021] In S1-3, the composite particles obtained in S1-2 are fired to obtain a Na-containing oxide having a P2 type structure. S1-3 may include, for example, the following S1-3-1, S1-3-2, and S1-3-3. S1-3-1: Preliminary baking of the composite particles at a temperature of 300°C or higher and lower than 700°C for 2 hours or higher and 10 hours or lower. S1-3-2: Following the preliminary firing, the composite particles are subjected to main firing at a temperature of 700°C or higher and 1100°C or lower for 30 minutes or higher and 48 hours or lower. S1-3-3: Following the main sintering, the composite particles are rapidly cooled from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower.

[0022] In S1-3-1, the composite particles are pre-fired at a temperature of 300°C or higher but lower than 700°C for 2 hours to 10 hours. In S1-3-1, the composite particles may be optionally shaped and then pre-fired. The pre-fired temperature is lower than that of the main firing. By performing the pre-fired temperature sufficiently, the P2 phase can be appropriately generated in the main firing, while suppressing the generation of crystalline phases other than the P2 phase. That is, in S1-3-1, the pre-fired temperature is 300°C or higher but lower than 700°C, and the pre-fired time is 2 hours to 10 hours, so that the composite particles can be sufficiently pre-fired. In the Na-containing oxide particles obtained through S1-3-2 and S1-3-3 described below, the P2 phase can be appropriately generated, while suppressing the generation of phases other than the P2 phase. As a result, the Li-containing oxide particles obtained through S2 have an O2-type structure, a hollow single-layer structure, and a spherical shape. The pre-firing temperature may be 400°C or higher and lower than 700°C, 450°C or higher and lower than 700°C, 500°C or higher and lower than 700°C, 550°C or higher and lower than 700°C, or 550°C or higher and lower than 650°C. The pre-firing time may be 2 hours or higher and lower than 8 hours, 3 hours or higher and lower than 8 hours, 4 hours or higher and lower than 8 hours, 5 hours or higher and lower than 8 hours, or 5 hours or higher and lower than 7 hours. The pre-firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere.

[0023] In S1-3-2, following the pre-calcination, the composite particles are subjected to main calcination at a temperature of 700°C to 1100°C for 30 minutes to 48 hours. In S1-3-2, the main calcination temperature of the composite particles is 700°C to 1100°C, preferably 800°C to 1000°C. If the main calcination temperature is too low, the P2 phase will not be formed, while if the main calcination temperature is too high, an O3 phase or the like will likely form instead of the P2 phase. The temperature rise conditions from the pre-calcination temperature to the main calcination temperature are not particularly limited. As described above, the main calcination time may be 30 minutes to 48 hours. However, the shape of the Na-containing oxide particles can be controlled by the main calcination time. As described above, if the coverage of the Na source on the composite particles is 40 area % or more, small P2-type crystals are likely to form on the surface of the composite particles when the composite particles are calcined. In S1-3-2, the P2 crystals are grown along the surface of the particles so as to connect one P2 crystallite to another, thereby making the shape of the Na-containing oxide particles correspond to that of the precursor particles. For example, if the precursor particles are spherical, the Na-containing oxide particles will also be spherical. If the firing time is too short, the P2 phase will not be generated sufficiently. On the other hand, if the firing time is too long, the P2 phase will grow excessively, and the Na-containing oxide particles will become plate-like particles rather than spherical. As far as the inventors have confirmed, spherical Na-containing oxide particles are more likely to be obtained when the firing time is 30 minutes or more and 3 hours or less. The Na-containing oxide particles obtained after firing may have a structure in which multiple crystallites are present on the surface and the crystallites are connected to each other.

[0024] In step S1-3-3, following the main firing, the composite particles (P2 type particles) after the main firing are rapidly cooled (cooled at a cooling rate of 20°C / min or more) from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower. The preliminary firing and main firing are performed, for example, in a heating furnace. In step S1-3-3, for example, after the main firing of the composite particles in the heating furnace, the interior of the heating furnace is cooled to a temperature T1 of 200°C or higher. After the temperature T1 is reached, the fired product is removed from the heating furnace and rapidly cooled outside the furnace to a temperature T2 of 100°C or lower. The temperature T1 may be any temperature of 200°C or higher or any temperature of 250°C or higher. The temperature T2 may be any temperature of 100°C or lower or any temperature of 50°C or lower, or may be the cooling end temperature. During the period from temperature T1 to temperature T2, moisture is likely to penetrate between the layers of the P2 type structure due to atomic vibration, molecular motion, etc. When cooling the composite particles (P2-type particles) after the main firing, it is believed that the amount of moisture that penetrates between the layers of the P2-type structure can be reduced by shortening the time during which the temperature remains in the moisture-prone temperature range (i.e., by rapid cooling). In this regard, when cooling the composite particles after the main firing in step S1-3-3, by allowing them to cool outside the furnace (e.g., in a dry atmosphere outside the furnace) from a temperature T1 of 200°C or higher to a temperature T2 of 100°C or lower, the cooling rate from temperature T1 to temperature T2 is high (e.g., 20°C / min or higher), making it difficult for moisture to penetrate between the layers of the P2-type structure and suppressing collapse of the P2-type structure. As a result, in step S2 described below, Na can be efficiently ion-exchanged with Li, and the Li-containing oxide particles obtained through step S2 have an O2-type structure, a hollow single-layer structure, and are spherical particles.

[0025] By the above method, spherical Na-containing oxide particles having a P2 type structure can be obtained.

[0026] The Na-containing oxide particles have at least a P2 type structure (belonging to the space group P63 / mmc) as a crystal structure. The Na-containing oxide particles have the P2 type structure, and may also have a crystal structure other than the P2 type structure. Examples of the crystal structure other than the P2 type structure include various crystal structures formed when Na is deintercalated from the P2 type structure. The Na-containing oxide particles may have the P2 type structure as a main phase.

[0027] The Na-containing oxide particles contain, for example, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. In particular, when the constituent elements contain at least Na, Mn, at least one of Ni and Co, and O, and especially when the constituent elements contain at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material obtained via S2 described below is likely to be further improved. The Na-containing oxide particles contain Na c Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2. Here, 0 < c ≤ 1.00, x + y + z = 1, and 0 ≤ p + q + r < 0.17. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the Na-containing oxide particles have such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c may be greater than 0, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. x is 0 or more, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, 0.10 or more, or 0.20 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, 0.10 or more, or 0.20 or more, and may be 1.00 or less, 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M has a small contribution to charge and discharge. In this regard, in the above chemical composition, when p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the P2-type structure and the O2-type structure are likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more. The composition of O is approximately 2, but it is not necessarily exactly 2.0 and is indefinite.

[0028] In the first embodiment, in step S2 described below, spherical particles having an average particle size of 1.0 μm or more and less than 3.5 μm are used as the Na-containing oxide particles. The spherical Na-containing oxide particles can be produced, for example, by preparing composite particles using spherical precursor particles and adjusting the firing conditions of the composite particles, as described above. Here, by using spherical precursor particles having an average particle size of less than 3.5 μm, spherical Na-containing oxide particles having an average particle size of 1.0 μm or more and less than 3.5 μm can be obtained. Alternatively, spherical Na-containing oxide particles having an average particle size of 1.0 μm or more and less than 3.5 μm may be produced using precursor particles having random sizes, and then the spherical Na-containing oxide particles having an average particle size of 1.0 μm or more and less than 3.5 μm may be recovered by air classification, sieving, or the like.

[0029] The average particle size of the Na-containing oxide particles is 1.0 μm or more and less than 3.5 μm, and may be 1.2 μm or more and 3.3 μm or less, or 1.4 μm or more and 3.0 μm or less. When the average particle size of the Na-containing oxide particles is 1.0 μm or more and less than 3.5 μm, the Li-containing oxide particles obtained through step S2 described below have a hollow single-layer structure. If the Na-containing oxide particles are too small, the Li-containing oxide particles will not have a hollow structure.

[0030] 1.1.2 S2 In S2, at least a portion of the Na in the Na-containing oxide particles obtained in S1 is ion-exchanged with Li to obtain Li-containing oxide particles having an O2-type structure. Here, the Li-containing oxide particles obtained in S2 are spherical particles having a hollow single-layer structure.

[0031] In S2, the ion exchange can be performed, for example, by using an aqueous solution containing lithium halide or by using a mixture of lithium halide and other lithium salts (e.g., molten salt). From the viewpoint that the P2 type structure is easily broken by the penetration of water and from the viewpoint of crystallinity, the method using molten salt is preferred among the above two methods. That is, by mixing the Na-containing oxide particles having the above-mentioned P2 type structure with the molten salt and heating the mixture to a temperature equal to or higher than the melting point of the molten salt, at least a portion of the Na in the Na-containing oxide particles can be replaced with Li by ion exchange.

[0032] In S2, the lithium halide constituting the molten salt is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. The other lithium salt constituting the molten salt is preferably lithium nitrate. By using the molten salt, the melting point becomes lower than when lithium halide or other lithium salt is used alone, and ion exchange can be performed at a lower temperature.

[0033] In S2, the temperature for ion exchange may be, for example, equal to or higher than the melting point of the molten salt and equal to or lower than 600°C, 500°C, 400°C, or 300°C. If the temperature for ion exchange is too high, the stable O3 structure is likely to be formed rather than the O2 structure. On the other hand, from the viewpoint of shortening the time required for ion exchange, it is preferable that the temperature for ion exchange is as high as possible.

[0034] In S2, at least a portion of the Na in spherical Na-containing oxide particles is ion-exchanged with Li, replacing Na with a large ionic radius with Li with a small ionic radius, shortening the interlayer distance in the crystal structure and causing shrinkage. This shrinkage during ion exchange creates voids inside the particles. When the size of the Na-containing oxide particles is small, the shrinkage creates voids in the center of the particles, resulting in a hollow single-layer structure. On the other hand, when the size of the Na-containing oxide particles is large, the shrinkage creates circumferential cracks inside the particles, resulting in numerous "shells," resulting in a hollow multilayer structure, as described below. Note that when the Na-containing oxide particles have a shape other than spherical, uniform shrinkage does not occur inside the particles, and an appropriate hollow structure cannot be obtained.

[0035] By the above method, Li-containing oxide particles having an O2-type structure, a hollow single-layer structure, spherical particles, and an average particle size of 1.0 μm or more and less than 3.5 μm can be obtained. The Li-containing oxide particles can be used as a positive electrode active material for solid-state batteries.

[0036] 1.2 Cathode active materials used in solid-state batteries The positive electrode active material used in the solid-state battery according to the first embodiment includes Li-containing oxide particles. Here, the Li-containing oxide particles have an O2-type structure. As shown in FIG. 2A, the Li-containing oxide particles are spherical particles having a hollow single-layer structure. The Li-containing oxide particles have an average particle diameter of 1.0 μm or more and less than 3.5 μm.

[0037] 1.2.1 Crystal structure The Li-containing oxide particle according to the first embodiment has at least an O2-type structure (belonging to the space group P63mc) as a crystal structure. The Li-containing oxide particle according to an embodiment has the O2-type structure and may have a crystal structure other than the O2-type structure. Examples of crystal structures other than the O2-type structure include a T#2-type structure (belonging to the space group Cmca) formed when Li is deintercalated from the O2-type structure and an O6-type structure (belonging to the space group R-3m, with a c-axis length of 2.5 nm to 3.5 nm, typically 2.9 nm to 3.0 nm, and different from the O3-type structure also belonging to the space group R-3m). The Li-containing oxide particle according to an embodiment may have an O2-type structure as a main phase. The Li-containing oxide particle according to an embodiment may have a structure other than the O2-type structure (for example, an O6-type structure) as a main phase. The crystal structure of the Li-containing oxide particle as a main phase may change depending on the charge / discharge state.

[0038] 1.2.2 Crystallites The Li-containing oxide particles according to the first embodiment may be polycrystalline having a plurality of crystallites. For example, the surface of the Li-containing oxide particles according to one embodiment may be composed of a plurality of crystallites. In other words, the Li-containing oxide particles may have a structure in which a plurality of crystallites are connected to each other on the surface. When the surface of the Li-containing oxide particles is composed of a plurality of crystallites, crystal grain boundaries are present on the surface. Here, the crystal grain boundaries may serve as inlets and outlets for intercalation. That is, when the Li-containing oxide particles are polycrystalline having a plurality of crystallites, the effects of increasing the number of inlets and outlets for intercalation, thereby reducing reaction resistance, shortening the migration distance of lithium ions, thereby reducing diffusion resistance, and reducing the absolute amount of expansion and contraction during charge and discharge, thereby making cracking less likely to occur, can be expected. The crystallite size may be large or small, but it is believed that smaller crystallite size increases the number of crystal grain boundaries, making the above-mentioned advantageous effects more likely to be exhibited. For example, when the diameter of the crystallites constituting the Li-containing oxide particles is less than 1 μm, higher performance is likely to be obtained. The "crystallite" and "crystallite diameter" can be determined by observing the surface of the Li-containing oxide particle using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, when a single closed region surrounded by a grain boundary is observed upon observing the surface of the Li-containing oxide particle, the region is considered to be a "crystallite." The maximum Feret diameter of the crystallite is determined and considered to be the "crystallite diameter." Alternatively, the crystallite diameter can be determined by EBSD or XRD. For example, the crystallite diameter can be determined based on the Scherrer equation from the half-width of the diffraction line in the XRD pattern. When the diameter of the crystallite determined by either method is less than 1 μm, the Li-containing oxide particle is likely to exhibit higher performance. The crystallite constituting the Li-containing oxide particle may have a first surface exposed on the surface of the particle, and the first surface may be planar. That is, the surface of the Li-containing oxide particle may have a structure in which multiple planes are connected.As described above, when producing Li-containing oxide particles, crystallites having a planar first surface can be easily obtained by growing the crystallites on the surface of the particles until one crystallite and another crystallite are connected to each other.

[0039] 1.2.3 Chemical composition The Li-containing oxide particles according to the first embodiment contain, for example, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. When the Li-containing oxide particles contain, as constituent elements, at least Li, Mn, one or both of Ni and Co, and O, in particular, when the Li-containing oxide particles contain, as constituent elements, at least Li, Mn, Ni, Co, and O, higher performance is likely to be obtained. a Na b Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). When the Li-containing oxide particles have such a chemical composition, the O2-type structure is likely to be maintained. In the above chemical composition, a is greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b is 0 or more, and may be 0.01 or more, 0.02 or more, or 0.03 or more, and is at most 0.20, and may be 0.15 or less, or 0.10 or less. Also, x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, and may be 0.10 or more, or 0.20 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, or 0.30 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, when p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the O2-type structure is likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more.The composition of O is approximately 2, but is not necessarily exactly 2.0 and is variable.

[0040] 1.2.4 Hollow single-layer structure The Li-containing oxide particles according to the first embodiment have a hollow single-layer structure. As shown in FIG. 2A, the "hollow single-layer structure" refers to a structure in which the cross-sectional shape of the particle has an outer shell 1a and the inside of the outer shell is hollow (void). The surface of the outer shell 1a may be composed of, for example, a plurality of crystallites. In the Li-containing oxide particles, the outer shell 1a may be composed of a plurality of crystallites connected along the outer periphery of the particle. The size of the crystallites constituting the outer shell 1a may be large or small. However, smaller crystallite sizes result in more grain boundaries on the particle surface, making it easier to achieve the above-described advantageous effects. Furthermore, the crystallites constituting the outer shell 1a may have a first surface exposed on the particle surface, and the first surface may be planar. The size of the crystallites is as described above. The outer shape (outer peripheral shape) of the outer shell 1a is spherical as described above. On the other hand, the inner shape (inner peripheral shape) of the outer shell 1a is not particularly limited and may be a shape corresponding to the outer shape. However, the outer and inner shapes of the outer shell 1a do not need to be parallel to each other. Both the outer and inner shapes of the outer shell 1a may have irregularities. Furthermore, the outer shell 1a may have voids or gaps. That is, the crystallites constituting the outer shell 1a may have defects such as voids or gaps. Furthermore, the outer shell 1a may have a thickness. The thickness of the outer shell 1a may be, for example, 5% or more and less than 50%, or 5% or more and 45% or less of the diameter (circle-equivalent diameter in the cross-sectional shape) of the Li-containing oxide particle. The size of the voids present inside the outer shell 1a (porosity) is not particularly limited.

[0041] As shown in Fig. 2A, the Li-containing oxide particle according to the first embodiment can be said to have a core-shell structure. That is, the Li-containing oxide particle according to one embodiment can have a shell and a core (void) disposed inside the shell. The "shell" is as described above. On the other hand, the "core" may be entirely void.

[0042] 1.2.5 Spherical particles As described above, Li-containing oxide particles having an O2-type structure can be obtained by ion-exchanging at least a portion of the Na in Na-containing oxide particles having a P2-type structure with Li. Here, the P2-type structure is a hexagonal crystal system with a large diffusion coefficient of Na ions, which facilitates crystal growth in a specific direction. In particular, when at least one of Mn, Ni, and Co is included as a transition metal element constituting the P2-type structure, plate-like crystal growth in a specific direction is facilitated. Therefore, in the past, only plate-like Na-containing oxide particles having a P2-type structure with a large aspect ratio, in which the crystal growth direction is biased in a specific direction, could be produced. As a result, only plate-like Li-containing oxide particles having an O2-type structure could be produced. Furthermore, plate-like growth of the P2-type structure was considered fundamental and unavoidable. Therefore, the performance of conventional O2-type Li-containing oxide particles as active materials was improved by controlling their chemical composition and crystal structure, assuming that they would be plate-like.

[0043] In contrast, as shown in FIG. 2A , the Li-containing oxide particles according to the first embodiment are spherical particles. Spherical Li-containing oxide particles have the advantage that crystallite growth is more easily suppressed and the crystallites are more easily small than non-spherical Li-containing oxide particles (e.g., the plate-like particles described above). That is, when the Li-containing oxide particles are spherical, the reaction resistance is reduced due to the reduction in crystallite size, and the internal diffusion resistance is likely to be reduced. Furthermore, the degree of curvature is reduced by the spheroidization, and when the particles are applied to a positive electrode active material layer, the lithium ion conduction resistance within the layer is thought to be reduced. As a result, spherical Li-containing oxide particles tend to have lower resistance and excellent rate characteristics than non-spherical Li-containing oxide particles.

[0044] 1.2.6 Average particle size The Li-containing oxide particles according to the first embodiment have an average particle diameter of 1.0 μm or more and less than 3.5 μm. The average particle diameter of the Li-containing oxide particles may be 1.2 μm or more and 3.3 μm or less, or 1.4 μm or more and 3.0 μm or less. As described above, when the average particle diameter of the Li-containing oxide particles is 1.0 μm or more and less than 3.5 μm, the Li-containing oxide particles have a hollow single-layer structure, and when applied to a solid-state battery, the Li-containing oxide particles have low resistance. If the Li-containing oxide particles are too small, aggregation of the particles is likely to occur. When the average particle diameter of the Li-containing oxide particles is 1.0 μm or more, such aggregation problems are unlikely to occur.

[0045] 1.2.7 Specific surface area The specific surface area of ​​the Li-containing oxide particles according to the first embodiment is not particularly limited. However, when it is assumed that the particles are used as a positive electrode active material of a solid-state battery, it is considered that the smaller the specific surface area of ​​the Li-containing oxide particles, the fewer voids there are inside the Li-containing oxide particles, and the easier it is to ensure an ion conduction path. In this regard, when the Li-containing oxide particles have a hollow single-layer structure, are spherical particles, and have an average particle diameter of 1.0 μm or more and less than 3.5 μm, the Li-containing oxide particles may have a specific surface area of ​​4.5 μm or less. 2 When the Li-containing oxide particles have a specific surface area of ​​less than 1.0 m / g, they can be expected to have higher performance as a positive electrode active material for solid-state batteries. 2 / g or more 4.5m 2 / g or less, 2.0m 2 / g or more 4.0m 2 / g or less, or 2.5m 2 / g or more 3.5m 2 / g or less.

[0046] 1.2.8 Supplementary Information The positive electrode active material according to the first embodiment may consist solely of the Li-containing oxide particles, or may contain the Li-containing oxide particles together with other positive electrode active materials (other positive electrode active materials). From the viewpoint of further enhancing the effects of the technology of the present disclosure, the proportion of the other positive electrode active materials in the overall positive electrode active material may be small. For example, the content of the Li-containing oxide particles may be 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 99% by mass to 100% by mass, where the overall positive electrode active material is taken as 100% by mass.

[0047] 1.3 Solid state batteries The cathode active material according to the first embodiment is used as the cathode active material of a solid-state battery. The term "solid-state battery" refers to a battery containing a solid electrolyte. The solid-state battery may contain a liquid component together with the solid electrolyte, or may be an all-solid-state battery that does not contain a liquid component. The electrolyte contained in the solid-state battery may be entirely solid electrolyte, or may be a combination of a solid electrolyte and a liquid electrolyte. As shown in FIG. 3 , a solid-state battery 100 according to one embodiment includes a cathode active material layer 10, an electrolyte layer 20, and an anode active material layer 30. The cathode active material layer 10 contains the cathode active material according to the first embodiment. The cathode active material layer 10 also contains a solid electrolyte.

[0048] 1.3.1 Cathode active material layer The positive electrode active material layer 10 contains at least the positive electrode active material according to the first embodiment and a solid electrolyte, and may further contain other electrolytes, conductive additives, binders, and the like. The positive electrode active material layer 10 may further contain various additives. The contents of the positive electrode active material, electrolyte, conductive additive, binder, and the like in the positive electrode active material layer 10 may be appropriately determined depending on the desired battery performance. For example, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, or 100% by mass or less, or 90% by mass or less, where the total weight of the positive electrode active material layer 10 (total solid content) is 100% by mass. The shape of the positive electrode active material layer 10 is not particularly limited, and may be, for example, a sheet-like positive electrode active material layer 10 having a substantially flat surface. The thickness of the positive electrode active material layer 10 is not particularly limited, and may be, for example, 0.1 μm or more or 1 μm or more, and 2 mm or less or 1 mm or less.

[0049] 1.3.1.1 Cathode active material The positive electrode active material is as described above. That is, the positive electrode active material layer 10 contains at least the Li-containing oxide particles as the positive electrode active material. As described above, the positive electrode active material may consist solely of the Li-containing oxide particles, or may contain the Li-containing oxide particles together with other positive electrode active materials (other positive electrode active materials). From the viewpoint of further enhancing the effects of the technology of the present disclosure, the proportion of the other positive electrode active materials in the overall positive electrode active material may be small. For example, the content of the Li-containing oxide particles may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, or 99% by mass or more and 100% by mass or less, where the overall positive electrode active material is taken as 100% by mass.

[0050] Any other cathode active material can be any of those known as cathode active materials for solid-state batteries. The other cathode active materials may be, for example, at least one selected from various lithium compounds other than the above-mentioned Li-containing oxides, elemental sulfur, sulfur compounds, etc. The lithium compound as the other cathode active material may be a Li-containing oxide containing at least one element M, Li, and O. Element M may be, for example, at least one selected from Mn, Ni, Co, Al, Mg, Ca, Sc, V, Cr, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, Bi, Fe, and Ti, or may be at least one selected from the group consisting of Mn, Ni, Co, Al, Fe, and Ti. More specifically, the Li-containing oxide as the other cathode active material is lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium nickel cobalt oxide, lithium nickel manganate, lithium cobalt manganate, lithium nickel cobalt manganate (Li 1±α Ni x Co y Mn z O 2±δ (for example, 0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1), spinel-type lithium compounds (Li 1+x Mn 2-x-y M y O4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element-substituted Li-Mn spinel of the composition represented thereby), lithium nickel cobalt aluminum oxide (for example, Li 1±α Ni p Co q Al r O 2±δThe other positive electrode active material may be at least one selected from the group consisting of lithium phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni), lithium titanate, and lithium metal phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni). In particular, when the other positive electrode active material contains, as constituent elements, a Li-containing oxide containing at least one of Ni, Co, and Mn, Li, and O, the performance of the battery is likely to be further improved. Alternatively, when the other positive electrode active material contains, as constituent elements, a Li-containing oxide containing at least one of Ni, Co, and Al, Li, and O, the performance of the battery is also likely to be further improved. Only one type of other positive electrode active material may be used alone, or two or more types may be used in combination. The shape of the other positive electrode active material may be any shape commonly used for a battery positive electrode active material. The other positive electrode active material may be, for example, particulate. The other positive electrode active material may be solid or may have voids, for example, porous or hollow. The other positive electrode active material may be primary particles or secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter D50 of the other positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less.

[0051] 1.3.1.2 Protection layer An ion-conductive protective layer may be formed on the surface of the positive electrode active material. That is, the positive electrode active material layer 10 may include a composite of the positive electrode active material and the protective layer, and at least a portion of the surface of the positive electrode active material in the composite may be covered with the protective layer. This, for example, makes it easier to suppress reactions between the positive electrode active material and other battery materials (such as the sulfide solid electrolyte described below). The ion-conductive protective layer may include various ion-conductive compounds. The ion-conductive compound may be, for example, at least one selected from ion-conductive oxides and ion-conductive halides.

[0052] The ion-conductive oxide may contain, for example, at least one element selected from B, C, Al, Si, P, S, Ti, La, Zr, Nb, Mo, Zn, and W, Li, and O. The ion-conductive oxide may also be an oxynitride containing N. More specifically, the ion-conductive oxide may be Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, or Li4Ti5O. 12 , Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4, LiPON, Li2O-LaO2, Li2O-ZnO2, etc. The ion-conductive oxide may be one in which some elements are substituted with various doping elements.

[0053] The ion-conductive halide may be, for example, at least one of the various compounds exemplified as halide solid electrolytes described below. The ion-conductive halide may contain, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm, at least one halogen element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may contain at least one element selected from the group consisting of Ti, Al, Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may also contain at least one element selected from the group consisting of Ti and Al, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ion-conductive halide may also be, for example, a complex halide of Li, Ti, Al, and F.

[0054] The coverage (area ratio) of the protective layer with respect to the surface of the positive electrode active material may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, and may be 100 nm or less or 20 nm or less.

[0055] 1.3.1.2 Electrolytes The positive electrode active material layer 10 includes a solid electrolyte. Any known solid electrolyte may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have excellent ionic conductivity and heat resistance. Examples of inorganic solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and ionically bonded inorganic solid electrolytes. Among inorganic solid electrolytes, sulfide solid electrolytes, especially sulfide solid electrolytes containing at least Li, S, and P as constituent elements, have high performance. Alternatively, among inorganic solid electrolytes, ionically bonded solid electrolytes, especially solid electrolytes containing at least Li, Y, and a halogen (at least one of Cl, Br, I, and F) as constituent elements, have high performance. The solid electrolyte may be amorphous or crystalline. The solid electrolyte may be particulate. The average particle diameter (D50) of the solid electrolyte may be, for example, 10 nm or more and 10 μm or less. The ionic conductivity of the solid electrolyte at 25°C may be, for example, 1×10 -5 S / cm or more, 1×10 -4 S / cm or more, or 1×10 -3 The solid electrolyte may be used singly or in combination of two or more kinds.

[0056] Oxide solid electrolytes include lithium lanthanum zirconate, LiPON, and Li 1+X Al X Ge 2-X It may be one or more selected from (PO4)3, Li-SiO-based glass, Li-Al-SO-based glass, etc. Furthermore, when an oxide solid electrolyte is combined with a liquid electrolyte, ionic conductivity can be improved.

[0057] The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte (sulfide glass), a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. The sulfide glass is amorphous. The sulfide glass may have a glass transition temperature (Tg). When the sulfide solid electrolyte has a crystalline phase, examples of the crystalline phase include a Thio-LISICON-type crystalline phase, an LGPS-type crystalline phase, and an Argyrodite-type crystalline phase. The sulfide solid electrolyte may be in a particulate form. The average particle diameter (D50) of the sulfide solid electrolyte may be, for example, 10 nm or more and 100 μm or less.

[0058] The sulfide solid electrolyte may contain, for example, Li, X (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. The sulfide solid electrolyte may also contain S as a main anion element.

[0059] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, and Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In).

[0060] The composition of the sulfide solid electrolyte is not particularly limited. For example, xLi2S·(100-x)P2S5 (70≦x≦80), yLiI·zLiBr·(100-y-z)(xLi2S·(1-x)P2S5) (0.7≦x≦0.8, 0≦y≦30, 0≦z≦30), etc. can be mentioned. Alternatively, the sulfide solid electrolyte has a composition represented by the general formula: Li 4-x Ge 1-x P x S4 (0<x<1). In the above general formula, at least a part of Ge may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, at least a part of P may be substituted with at least one of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. In the above general formula, a part of Li may be substituted with at least one of Na, K, Mg, Ca, and Zn. In the above general formula, a part of S may be substituted with a halogen (at least one of F, Cl, Br, and I). Alternatively, the sulfide solid electrolyte is Li 7-a PS 6-a X a (X is at least one of Cl, Br, and I, and a is a number of 0 or more and 2 or less). a may be 0, or may be greater than 0. In the latter case, a may be 0.1 or more, may be 0.5 or more, and may be 1 or more. Also, a may be 1.8 or less, may be 1.5 or less.

[0061] The ionically bonded solid electrolyte may contain, for example, at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sn, Al, Sc, Ga, Bi, Sb, Zr, Hf, Ti, Ta, Nb, W, Y, Gd, Tb, and Sm. These elements can generate cations in water. The ionically bonded solid electrolyte material may further contain, for example, at least one halogen element selected from the group consisting of Cl, Br, I, and F. These elements can generate anions in water. The ionically bonded solid electrolyte may contain at least one element selected from the group consisting of Gd, Ca, Zr, and Y, at least one element selected from the group consisting of Cl, Br, I, and F, and Li. The ionically bonded solid electrolyte may also contain Li and Y, and at least one element selected from the group consisting of Cl, Br, I, and F. More specifically, the ionic solid electrolyte may contain Li, Y, Cl, and Br, or may contain Li, Ca, Y, Gd, Cl, and Br, or may contain Li, Zr, Y, and Cl. Even more specifically, the ionic solid electrolyte may be Li3YBr2Cl4, Li 2.8 Ca 0.1 Y 0.5 Gd 0.5 Br2Cl4 and Li 2.5 Y 0.5 Zr 0.5 It may be at least one of Cl6.

[0062] The ionically bonded solid electrolyte may be a halide solid electrolyte. The halide solid electrolyte has excellent ion conductivity. Examples of the halide solid electrolyte include a halide solid electrolyte represented by the formula (A): Li α M β X γ (A) It may have a composition represented by the following. Here, α, β, and γ are each independently a value greater than 0, M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, and X is at least one selected from the group consisting of Cl, Br, and I. Note that the "metalloid element" may be at least one selected from the group consisting of B, Si, Ge, As, Sb, and Te. Also, the "metal element" may include (i) all elements (excluding hydrogen) included in Groups 1 to 12 of the periodic table and (ii) all elements (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se) included in Groups 13 to 16 of the periodic table. The metal element can form an inorganic compound with a halide ion and become a cation.

[0063] In formula (A), M may contain Y (i.e., yttrium). The halide solid electrolyte containing Y is Li a Me b Y c It may have a composition represented by X6 (where a + mb + 3c = 6, c > 0, Me is at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y, and m is the valence of Me). Me may be, for example, at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0064] The halide solid electrolyte may have a composition represented by formula (A1): Li 6-3d Y d It may have a composition represented by X6. In formula (A1), X is one or more elements selected from the group consisting of Cl, Br, and I. d may satisfy 0 < d < 2, or d = 1. The halide solid electrolyte may have a composition represented by formula (A2): Li 3-3δ Y 1+δ [[ID=二十二]]It may have a composition represented by Cl6. In formula (A2), 0 < δ ≦ 0.15 may hold. The halide solid electrolyte may have a composition represented by formula (A3): Li 3-3δ Y 1+δIt may have a composition represented by Br6. In formula (A3), 0 < δ ≦ 0.25 may also be applicable. The halide solid electrolyte has the formula (A4): Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by the formula. In formula (A4), Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In formula (A4), for example, -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 are satisfied. The halide solid electrolyte has the formula (A5): Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by the formula. In formula (A5), Me may be at least one selected from the group consisting of Al, Sc, Ga, and Bi. In formula (A5), -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may also be applicable. The halide solid electrolyte has the formula (A6): Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I y and may have a composition represented by the formula. In formula (A6), Me may be at least one selected from the group consisting of Zr, Hf, and Ti. In formula (A6), -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 0 ≦ y ≦ 6, and (x + y) ≦ 6 may also be applicable. The halide solid electrolyte has the formula (A7): Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I yIn formula (A7), Me may be at least one selected from the group consisting of Ta and Nb. In formula (A7), -1<δ<1, 0 <a<1.2、0<(3-3δ-2a)、0<(1+δ-a)、0≦x≦6、0≦y≦6、かつ、(x+y)≦6であってもよい。

[0065] The ionic solid electrolyte may be a complex hydride solid electrolyte. The complex hydride solid electrolyte may be composed of Li ions and complex ions containing H. The complex ions containing H may have, for example, an element M containing at least one of a nonmetal element, a semimetal element, and a metal element, and H bonded to the element M. In addition, the complex ions containing H may have the element M as a central element and H surrounding the element M bonded to each other via a covalent bond. In addition, the complex ions containing H may be composed of (M m H n ) α- In this case, m is any positive number, and n and α can be any positive number depending on m and the valence of element M. Element M may be any nonmetallic element or metallic element capable of forming a complex ion. For example, element M may contain at least one of B, C, and N as a nonmetallic element, or may contain B. Furthermore, for example, element M may contain at least one of Al, Ni, and Fe as a metallic element. In particular, when the complex ion contains B or when it contains C and B, higher ionic conductivity is likely to be ensured. Specific examples of complex ions containing H include (CBH 10 ) - , (CB 11 H 12 ) - , (B 10 H 10 ) 2- , (B 12 H 12 ) 2- , (BH4) - , (NH2) - , (AlH4) - , and combinations thereof. In particular, (CB9H 10 ) - , (CB 11H 12 ) - In other words, the complex hydride solid electrolyte may contain Li, C, B, and H.

[0066] The positive electrode active material layer 10 may or may not contain a liquid electrolyte (electrolytic solution). The electrolytic solution is a liquid containing lithium ions as carrier ions. The electrolytic solution may be an aqueous electrolytic solution or a non-aqueous electrolytic solution. The composition of the electrolytic solution may be the same as that of a known solution. The electrolytic solution may be one in which a lithium salt is dissolved in water or a non-aqueous solvent. Examples of non-aqueous solvents include various carbonate-based solvents. Examples of lithium salts include lithium amide salts and LiPF6.

[0067] 1.3.1.3 Conductive additives Examples of conductive additives that can be contained in the positive electrode active material layer 10 include carbon materials such as vapor grown carbon fiber (VGCF), acetylene black (AB), ketjen black (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metal materials such as nickel, titanium, aluminum, and stainless steel. The conductive additive may be, for example, in the form of particles or fibers, and its size is not particularly limited. Only one type of conductive additive may be used alone, or two or more types may be used in combination.

[0068] 1.3.1.4 Binder Examples of binders that can be contained in the positive electrode active material layer 10 include butadiene rubber (BR)-based binders, butylene rubber (IIR)-based binders, acrylate butadiene rubber (ABR)-based binders, styrene butadiene rubber (SBR)-based binders, polyvinylidene fluoride (PVdF)-based binders, polytetrafluoroethylene (PTFE)-based binders, polyimide (PI)-based binders, etc. Only one type of binder may be used alone, or two or more types may be used in combination.

[0069] 1.3.1.5 Other The positive electrode active material layer 10 may contain various additives in addition to the above components, such as a dispersant and a lubricant.

[0070] 1.3.2 Electrolyte layer The electrolyte layer 20 is disposed between the positive electrode active material layer 10 and the negative electrode active material layer 30. The electrolyte layer 20 may contain one or both of a solid electrolyte and an electrolytic solution. The electrolyte layer 20 may further contain an optional binder or the like. The contents of the electrolyte and binder or the like in the electrolyte layer 20 are not particularly limited. Alternatively, the electrolyte layer 20 may include a separator or the like that holds the electrolyte and prevents contact between the positive electrode active material layer 10 and the negative electrode active material layer 30. The thickness of the electrolyte layer 20 is not particularly limited and may be, for example, 0.1 μm or more or 1 μm or more, or 2 mm or less or 1 mm or less.

[0071] The electrolyte layer 20 may consist of one layer or multiple layers. For example, the electrolyte layer 20 may include a first layer disposed on the positive electrode active material layer 10 side and a second layer disposed on the negative electrode active material layer 30 side, and the first layer may contain the first electrolyte and the second layer may contain the second electrolyte. The first electrolyte and the second electrolyte may be different from each other. The first electrolyte and the second electrolyte may each be at least one selected from the oxide solid electrolyte, sulfide solid electrolyte, and ionic solid electrolyte described above. For example, the first layer may contain the ionic solid electrolyte, and the second layer may contain at least one of the ionic solid electrolyte and the sulfide solid electrolyte.

[0072] The electrolyte contained in the electrolyte layer 20 may be appropriately selected from the examples (solid electrolytes and / or liquid electrolytes) of the electrolytes that can be contained in the positive electrode active material layer 10 described above. The binder that can be contained in the electrolyte layer 20 may also be appropriately selected from the examples of the binders that can be contained in the positive electrode active material layer 10 described above. Each of the electrolytes and binders may be used alone or in combination of two or more. The separator may be a known separator, such as one made of a resin such as polyethylene (PE), polypropylene (PP), polyester, or polyamide. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a two-layer structure of PE / PP, or a three-layer structure of PP / PE / PP or PE / PP / PE. The separator may be made of a nonwoven fabric such as a cellulose nonwoven fabric, a resin nonwoven fabric, or a glass fiber nonwoven fabric.

[0073] 1.3.3 Negative electrode active material layer The negative electrode active material layer 30 contains at least a negative electrode active material. The negative electrode active material layer 30 may also optionally contain an electrolyte, a conductive additive, a binder, various additives, and the like. The content of each component in the negative electrode active material layer 30 may be appropriately determined depending on the desired battery performance. For example, the total solid content of the negative electrode active material layer 30 is taken as 100% by mass, and the content of the negative electrode active material may be 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, less than 100% by mass, 95% by mass or less, or 90% by mass or less. Alternatively, the total content of the negative electrode active material layer 30 may be 85% by volume or more, 90% by volume or more, or 95% by volume or more, and the remainder may be voids or other components. The shape of the negative electrode active material layer 30 is not particularly limited and may be, for example, a substantially flat sheet. The thickness of the negative electrode active material layer 30 is not particularly limited and may be, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, or 30 μm or more, or 2 mm or less, 1 mm or less, 500 μm or less, or 100 μm or less.

[0074] The negative electrode active material may be any known material for use as a negative electrode active material in batteries. Among known active materials, various materials may be used that have a lithium ion absorption / desorption potential (charge / discharge potential) that is lower than that of the positive electrode active material. For example, silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium and lithium alloys may be used. In particular, when the negative electrode active material layer 30 contains Si as the negative electrode active material, the performance of the solid-state battery 100 is likely to be improved. The negative electrode active material may be used alone or in combination of two or more types. The shape of the negative electrode active material may be any shape commonly used for a negative electrode active material in batteries. For example, the negative electrode active material may be particulate. The negative electrode active material particles may be primary particles or secondary particles formed by agglomeration of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material may be in the form of a sheet (foil or film) such as lithium foil. That is, the negative electrode active material layer 30 may be made of a sheet of negative electrode active material.

[0075] Examples of electrolytes that can be contained in the negative electrode active material layer 30 include the above-mentioned solid electrolytes, electrolytic solutions, and combinations thereof. The conductive additives that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, the conductive additives that can be contained in the above-mentioned positive electrode active material layer. The binders that can be contained in the negative electrode active material layer 30 may be appropriately selected from, for example, the binders that can be contained in the above-mentioned positive electrode active material layer. Each of the electrolytes, conductive additives, and binders may be used alone or in combination of two or more.

[0076] 1.3.4 Positive electrode current collector As shown in FIG. 3 , the solid-state battery 100 may include a positive electrode current collector 40 in contact with the positive electrode active material layer 10. Any common positive electrode current collector for batteries can be used as the positive electrode current collector 40. The positive electrode current collector 40 may have at least one shape selected from foil, plate, mesh, punched metal, and foam. The positive electrode current collector 40 may be made of metal foil or metal mesh. Metal foil is particularly advantageous in terms of ease of handling. The positive electrode current collector 40 may be made of multiple foils. Examples of metals constituting the positive electrode current collector 40 include at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, the positive electrode current collector 40 may contain Al from the viewpoint of ensuring oxidation resistance. The positive electrode current collector 40 may have some kind of coating layer on its surface for the purpose of adjusting the resistance, etc. For example, the positive electrode current collector 40 may have a carbon coating layer. Alternatively, the positive electrode current collector 40 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. Furthermore, when the positive electrode current collector 40 is made of multiple sheets of metal foil, some kind of layer may be present between the multiple sheets of metal foil. The thickness of the positive electrode current collector 40 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or may be 1 mm or less or 100 μm or less.

[0077] 1.3.5 Negative electrode current collector As shown in FIG. 3, the solid-state battery 100 may include a negative electrode current collector 50 in contact with the negative electrode active material layer 30. The negative electrode current collector 50 may be any of those commonly used as negative electrode current collectors for batteries. The negative electrode current collector 50 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The negative electrode current collector 50 may be a metal foil or metal mesh, or a carbon sheet. Metal foils are particularly advantageous in terms of ease of handling. The negative electrode current collector 50 may be composed of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 50 include at least one selected from Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, V, Mg, Pb, Ge, In, Sn, Zr, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and being less likely to alloy with lithium, the negative electrode current collector 50 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 50 may have some kind of coating layer on its surface for the purpose of adjusting resistance, etc. For example, the negative electrode current collector 50 may have a carbon coating layer. The negative electrode current collector 50 may be an aluminum foil having a carbon coating layer. The negative electrode current collector 50 may also be a metal foil or a substrate plated or vapor-deposited with the above metal. Furthermore, when the negative electrode current collector 50 is made of multiple sheets of metal foil, some kind of layer may be present between the multiple sheets of metal foil. The thickness of the negative electrode current collector 50 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0078] 1.3.6 Other Configurations In addition to the above configuration, the solid-state battery 100 may also include general battery configurations. For example, tabs, terminals, etc. The solid-state battery 100 may have the above configurations housed inside an exterior body. Any known exterior body for a battery can be used as the exterior body. Furthermore, a plurality of solid-state batteries 100 may be electrically connected and stacked in any desired manner to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. Examples of the shape of the solid-state battery 100 include a coin type, a laminate type, a cylindrical type, and a prismatic type.

[0079] The solid-state battery 100 can be manufactured by applying a known method, except for using the above-mentioned specific positive electrode active material. For example, it can be manufactured as follows. However, the manufacturing method of the solid-state battery 100 is not limited to the following method, and each layer may be formed by, for example, dry molding or the like. (1) The positive electrode active material and other components that constitute the positive electrode active material layer are dispersed in a solvent to obtain a positive electrode layer slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The positive electrode layer slurry is applied to the surface of a positive electrode current collector using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector, resulting in a positive electrode. (2) The negative electrode active material and other components that constitute the negative electrode active material layer are dispersed in a solvent to obtain a negative electrode layer slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The negative electrode layer slurry is applied to the surface of the negative electrode current collector using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, resulting in a negative electrode. (3) The layers are stacked so that the electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode to obtain a laminate having, in this order, the negative electrode current collector, the negative electrode active material layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector. Other members such as terminals are attached to the laminate as necessary. (4) The laminate is housed in a battery case, and the laminate is sealed in the battery case together with an optional electrolyte to form a solid-state battery.

[0080] 2.Second form The positive electrode active material according to the second embodiment is used in a liquid battery.

[0081] 2.1 Manufacturing method of positive electrode active material used in liquid batteries As shown in FIG. 1B, the method for producing a positive electrode active material used in a liquid battery includes the following steps: Obtaining Na-containing oxide particles having an S1:P2 type structure, and S2: Ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. Here, the Na-containing oxide particles are spherical particles having an average particle diameter of 3.5 μm or more, and as shown in FIG. 2B, the Li-containing oxide particles are spherical particles having a hollow multilayer structure.

[0082] 2.1.1 S1 In S1, Na-containing oxide particles having a P2 structure are obtained. Here, the Na-containing oxide particles obtained by S1 are spherical particles with an average particle diameter of 3.5 μm or more. S1 in the second embodiment is the same as S1 in the first embodiment, except that the average particle diameter of the Na-containing oxide particles is different. That is, S1 in the second embodiment may include S1-1, S1-2, and S1-3 described above. For example, by using spherical precursor particles with an average particle diameter of 3.5 μm or more, spherical Na-containing oxide particles with an average particle diameter of 3.5 μm or more can be obtained. Alternatively, spherical Na-containing oxide particles with an average particle diameter of 3.5 μm or more may be produced using precursor particles with random sizes, and then the spherical Na-containing oxide particles with an average particle diameter of 3.5 μm or more may be recovered by air classification, sieving, or the like.

[0083] As described above, the Na-containing oxide particles obtained by S1 in the second embodiment may be similar to the Na-containing oxide particles obtained by S1 in the first embodiment, except for the difference in average particle size. That is, the Na-containing oxide particles have at least a P2-type structure (belonging to the space group P63 / mmc) as a crystal structure. The Na-containing oxide particles may have a P2-type structure as well as a crystal structure other than the P2-type structure. Examples of crystal structures other than the P2-type structure include various crystal structures formed when Na is deintercalated from a P2-type structure. The Na-containing oxide particles may have a P2-type structure as a main phase. Furthermore, the Na-containing oxide particles may contain, for example, at least one element selected from Mn, Ni, and Co, Na, and O as constituent elements. In particular, when the constituent elements include at least Na, Mn, at least one of Ni and Co, and O, and especially when the constituent elements include at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material obtained through step S2 described below is likely to be further improved. c Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2. Here, 0 < c ≤ 1.00, x + y + z = 1, and 0 ≤ p + q + r < 0.17. Also, M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. When the Na-containing oxide particles have such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c may be greater than 0, 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and may also be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. x is 0 or more, may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is 1.00 or less, may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, may be 0.10 or more or 0.20 or more, and is 1.00 or less, may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, may be 0.10 or more, 0.20 or more, or 0.30 or more, and is 1.00 or less, may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, when p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is included, the P2-type structure and the O2-type structure are likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0084] The average particle diameter of the Na-containing oxide particles is 3.5 μm or more. The average particle diameter may be 3.5 μm or more and 20.0 μm or less, 3.5 μm or more and 10.0 μm or less, or 3.5 μm or more and 5.0 μm or less. When the average particle diameter of the Na-containing oxide particles is 3.5 μm or more, the Li-containing oxide particles obtained via S2 described below have a hollow multilayer structure.

[0085] 2.1.2 S2 In S2, at least a portion of the Na in the Na-containing oxide particles obtained in S1 is ion-exchanged with Li to obtain Li-containing oxide particles having an O2-type structure. Here, the Li-containing oxide particles obtained in S2 are spherical particles having a hollow multilayer structure. S2 in the second embodiment is the same as S2 in the first embodiment, except that the average particle size of the Na-containing oxide particles is different.

[0086] As described above, in S2, by ion-exchanging at least a portion of the Na in the spherical Na-containing oxide particles with Li, voids are generated inside the particles due to shrinkage during the ion exchange. As described above, when the size of the Na-containing oxide particles is large, the shrinkage causes cracks to form inside the particles in the circumferential direction, resulting in the generation of numerous "shells" and a hollow multilayer structure.

[0087] By the above method, it is possible to obtain Li-containing oxide particles having an O2-type structure, a hollow multilayer structure, spherical particles, and an average particle size of 3.5 μm or more. The Li-containing oxide particles are used as a positive electrode active material for liquid batteries.

[0088] 2.2 Positive electrode active materials used in liquid batteries The positive electrode active material used in the liquid battery according to the second embodiment includes Li-containing oxide particles. Here, the Li-containing oxide particles have an O2-type structure. As shown in FIG. 2B, the Li-containing oxide particles are spherical particles having a hollow multilayer structure. The Li-containing oxide particles have an average particle diameter of 3.5 μm or more.

[0089] 2.2.1 Crystal structure, crystallites and chemical composition The crystal structure, crystallites, and chemical composition of the Li-containing oxide particles according to the second embodiment may be the same as those of the first embodiment. That is, the Li-containing oxide particles according to the second embodiment may have an O2-type structure, and may have other crystal structures in addition to the O2-type structure. The Li-containing oxide particles according to the second embodiment may be polycrystalline having a plurality of crystallites. The Li-containing oxide particles according to the second embodiment contain, for example, at least one element selected from Mn, Ni, and Co, Li, and O as constituent elements. The Li-containing oxide particles are particularly likely to achieve higher performance when they contain at least Li, Mn, one or both of Ni and Co, and O as constituent elements, and particularly when they contain at least Li, Mn, Ni, Co, and O as constituent elements. The Li-containing oxide particles contain Li a Na b Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). When the Li-containing oxide particles have such a chemical composition, the O2-type structure is likely to be maintained. In the above chemical composition, a is greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, b is 0 or more, and may be 0.01 or more, 0.02 or more, or 0.03 or more, and is at most 0.20, and may be 0.15 or less, or 0.10 or less. Also, x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, and may be 0.10 or more, or 0.20 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, and may be 0.10 or more, 0.20 or more, or 0.30 or more, and is at most 1.00, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M has a small contribution to charge and discharge. In this regard, in the above chemical composition, when p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when the element M is contained, the O2-type structure is likely to be stabilized. In the above chemical composition, p + q + r is 0 or more, and may be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more.The composition of O is approximately 2, but is not necessarily exactly 2.0 and is variable.

[0090] 2.2.2 Hollow multilayer structure The Li-containing oxide particles according to the second embodiment have a hollow multilayer structure. As shown in FIG. 2B, the "hollow multilayer structure" refers to a structure in which the cross-sectional shape of the particle has an outer shell 1a and at least one inner shell 1b or solid portion 1c. As shown in FIG. 2C, the solid portion 1c may not exist and may be a void. The Li-containing oxide particles according to the second embodiment may have multiple shells 1a and 1b, or may have an outer shell 1a and a solid portion 1c. In this case, a void may exist between at least one shell and another shell or between a shell and a solid portion. When the Li-containing oxide particles have multiple shells 1a and 1b, the outer and inner surfaces of each shell can come into contact with a liquid, which tends to increase the contact area between the Li-containing oxide particles and the liquid. For example, when the electrolyte solution is distributed throughout the interior of the Li-containing oxide particles, the contact area between the particles and the electrolyte solution tends to increase. Note that "having multiple shells" means that another shell exists inside one shell. Here, one shell and another shell may be in partial contact with each other or may be partially bonded together. However, even if there is a circumferential gap between one shell and another shell located further inward, if 50% or more of the inner circumference of one shell is bonded to the outer circumference of the other shell located further inward, the one shell and the other shell are not considered separate shells (multi-layer), but are considered to constitute one shell (single layer).

[0091] In the Li-containing oxide particle according to the second embodiment, the surface of the outer shell 1a may be composed of, for example, a plurality of crystallites. In the Li-containing oxide particle, the outer shell 1a may be composed of a plurality of crystallites connected along the periphery of the particle. The size of the crystallites constituting the outer shell 1a may be large or small. However, smaller crystallites increase the number of grain boundaries on the particle surface, making it easier to achieve advantageous effects. The crystallites constituting the outer shell 1a may have a first surface exposed on the particle surface, and the first surface may be planar. The size of the crystallites is as described above. As described above, the outer shape (outer peripheral shape) of the outer shell 1a is spherical. Meanwhile, the inner shape (inner peripheral shape) of the outer shell 1a is not particularly limited and may be a shape corresponding to the outer shape. However, the outer and inner shapes of the outer shell 1a do not need to be parallel to each other. Both the outer and inner shapes of the outer shell may have irregularities. The outer shell 1a may have voids or gaps. That is, the crystallites constituting the outer shell 1a may have defects such as voids or gaps. Furthermore, the outer shell 1a may have a thickness. The thickness of the outer shell 1a may be, for example, 5% to 40% or 5% to 30% of the diameter (circle-equivalent diameter in the cross-sectional shape) of the Li-containing oxide particle. The size (porosity) of the voids present inside the outer shell 1a is not particularly limited. The outer shape (outer peripheral shape) of the inner shell 1b may correspond to the inner peripheral shape of the outer shell 1a, or may be a shape different from the inner peripheral shape of the outer shell 1a. The inner shape (inner peripheral shape) of the inner shell 1b is not particularly limited and may be a shape corresponding to the outer shape. The outer and inner shapes of the inner shell 1b do not need to be parallel to each other. Both the outer and inner shapes of the inner shell 1b may have irregularities. Furthermore, the inner shell 1b may have voids or gaps. That is, the crystallites constituting the inner shell 1b may have defects such as voids or gaps. Furthermore, the inner shell 1b may have a thickness. The thickness of the inner shell 1b may be, for example, 5% to 40% or 5% to 30% of the diameter (equivalent circle diameter in the cross-sectional shape) of the Li-containing oxide particle. The shape and size of the voids existing between the outer shell 1a and the inner shell 1b, and the shape and size of the solid portion 1c or voids existing inside the inner shell 1b are not particularly limited. Furthermore, the porosity of the particle as a whole is not particularly limited.

[0092] As shown in FIG. 2B , in the Li-containing oxide particle according to the second embodiment, voids exist along the inner wall of the outer shell 1a in the cross-sectional structure. The voids may exist continuously around the entire circumference of the inner wall of the outer shell 1a, or may exist continuously or intermittently along a portion of the inner wall of the outer shell 1a. For example, the voids may exist along 50% or more of the entire inner circumference of the outer shell 1a. The size of the voids is not particularly limited. As described above, the shell may be liquid-permeable, and therefore, a liquid that has permeated from the outside of the particle to the inside of the particle through the shell may fill the voids along the inner wall of the shell and come into contact with the inner wall of the shell. In other words, when voids exist along the inner wall of the shell, the contact area between the particle and the liquid is more likely to be increased than when voids are not present. For example, when an electrolyte solution is distributed throughout the interior of the Li-containing oxide particle, the contact area between the particle and the electrolyte solution is more likely to be increased.

[0093] 2B, the Li-containing oxide particle according to the second embodiment can be said to have a core-shell structure. That is, the Li-containing oxide particle according to one embodiment can have a shell (outer shell) and a core (inner shell or solid portion, and voids) disposed inside the shell.

[0094] 2.2.3 Spherical particles As shown in FIG. 2B , the Li-containing oxide particles according to the second embodiment are spherical particles. As described above, spherical Li-containing oxide particles have the advantage that crystallite growth is more easily suppressed and the crystallites are more easily small than non-spherical Li-containing oxide particles. That is, when the Li-containing oxide particles are spherical, the reaction resistance is reduced due to the reduction in crystallite size, and the internal diffusion resistance is likely to be reduced. Furthermore, the degree of curvature is reduced by the spheroidization, and when applied to a positive electrode active material layer, it is thought that the lithium ion conduction resistance within the layer is reduced. As a result, spherical Li-containing oxide particles tend to have lower resistance and excellent rate characteristics compared to non-spherical Li-containing oxide particles.

[0095] 2.2.4 Average particle size The Li-containing oxide particles according to the second embodiment have an average particle diameter of 3.5 μm or more. The average particle diameter of the Li-containing oxide particles may be 3.5 μm or more and 20.0 μm or less, 3.5 μm or more and 10.0 μm or less, or 3.5 μm or more and 5.0 μm or less. As described above, when the average particle diameter of the Li-containing oxide particles is 3.5 μm or more, the Li-containing oxide particles have a hollow multilayer structure, and when applied to a liquid-phase battery, the Li-containing oxide particles have excellent rate characteristics.

[0096] 2.2.5 Specific surface area The specific surface area of ​​the Li-containing oxide particles according to the second embodiment is not particularly limited. However, when it is assumed that the particles are used as a positive electrode active material of a liquid battery, the larger the specific surface area of ​​the Li-containing oxide particles, the more the number of contact interfaces with the electrolyte increases, and it is thought that the more easily an ion conduction path is secured. In this regard, when the Li-containing oxide particles have a hollow multilayer structure, are spherical particles, and have an average particle diameter of 3.5 μm or more, the Li-containing oxide particles have a specific surface area of ​​4.5 μm or more. 2 The specific surface area of ​​the Li-containing oxide particles may be 4.5 m / g or more. 2 / g or more 10.0m 2 / g or less, 4.5m 2 / g or more 8.0m 2 / g or less, or 4.5m 2 / g or more 6.5m 2 / g or less.

[0097] 2.2.6 Supplementary Information The positive electrode active material according to the second embodiment may be composed solely of the Li-containing oxide particles, as in the first embodiment, or may contain the Li-containing oxide particles together with other positive electrode active materials (other positive electrode active materials). From the viewpoint of further enhancing the effects of the technology of the present disclosure, the proportion of the other positive electrode active materials in the overall positive electrode active material may be small. For example, the content of the Li-containing oxide particles may be 50% by mass to 100% by mass, 60% by mass to 100% by mass, 70% by mass to 100% by mass, 80% by mass to 100% by mass, 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 99% by mass to 100% by mass, where the overall positive electrode active material is taken as 100% by mass.

[0098] 2.3 Liquid batteries The positive electrode active material according to the second embodiment is used as the positive electrode active material for a liquid battery. The term "liquid battery" refers to a battery containing a liquid electrolyte (electrolytic solution). The electrolyte contained in a liquid battery may be entirely liquid electrolyte, or may be a combination of a liquid electrolyte and a solid electrolyte. FIG. 3 shows a schematic configuration of a liquid battery according to one embodiment. As shown in FIG. 3, a liquid battery 100 according to one embodiment has a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30. The positive electrode active material layer 10 contains the positive electrode active material according to the second embodiment. The positive electrode active material layer 10 also contains a liquid electrolyte.

[0099] The positive electrode active material layer 10, electrolyte layer 20, and negative electrode active material layer 30 provided in the liquid battery 100 may be the same as those provided in the solid battery 100, except that they contain the positive electrode active material according to the second embodiment as the positive electrode active material and a liquid electrolyte as the electrolyte. The configuration of the liquid battery 100 is self-evident, so a detailed description will be omitted here.

[0100] 3. Vehicles The solid-state battery or liquid-based battery of the present disclosure can be suitably used in at least one type of vehicle selected from, for example, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and an electric vehicle (BEV). That is, the technology of the present disclosure also has an aspect of a vehicle having one or both of the solid-state battery and the liquid-based battery of the present disclosure.

[0101] 4.Effects As described above, the positive electrode active material according to the first embodiment has low resistance when applied to a solid-state battery, and the positive electrode active material according to the second embodiment has excellent rate characteristics when applied to a liquid-based battery. [Example]

[0102] As described above, one embodiment of the manufacturing method of the positive electrode active material, the positive electrode active material, the battery, etc. has been described, but the technology of the present disclosure can be variously modified other than the above embodiment without departing from the gist thereof. Hereinafter, the technology of the present disclosure will be described in more detail with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0103] 1. Preparation of positive electrode active material 1.1 Cathode active material A 1.1.1 Preparation of precursor particles a1 (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed to achieve the desired composition ratio and dissolved in distilled water to a concentration of 1.2 mol / L to obtain solution 1. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain solution 2. (2) 1000 mL of pure water was placed in a reaction vessel (with a baffle plate), and 500 mL of the first solution and 500 mL of the second solution were added dropwise thereto at a rate of about 4 mL / min. (3) After the dropwise addition was completed, the mixture was stirred at room temperature for 1 hour at a stirring speed of 150 rpm to obtain a product. (4) The product was washed with pure water, and the solid was separated into liquid using a centrifuge to recover the precipitate. (5) The obtained precipitate was dried overnight at 120°C, crushed in a mortar, and then separated into coarse particles a1-1 and fine particles a1-2 by air classification. Both the coarse particles a1-1 and the fine particles a1-2 were composite salts containing Mn, Ni, and Co. The coarse particles a1-1 had an average particle diameter D50 of 4.0 μm and were spherical particles. The fine particles a1-2 had an average particle diameter D50 of 1.8 μm and were spherical particles. (6) Coarse particles a1-1 were used as precursor particles a1.

[0104] 1.1.2 Preparation of composite particle a2 (1) Na2CO3 and distilled water were weighed out so that the concentration was 1150 g / L, and then the mixture was stirred using a stirrer until completely dissolved to prepare an aqueous Na2CO3 solution. (2) The above Na2CO3 aqueous solution and the above precursor particles a1 are mixed together to form a mixture having a composition of Na2CO3 after calcination, which will be described later. 0.7 Mn 0.5 Ni 0.2 Co 0.3 The components were weighed and mixed to obtain a slurry. (3) The above slurry was spray-dried by airflow to obtain composite particles a2. Specifically, a spray dryer DL410 was used, with a slurry flow rate of 30 mL / min, an inlet temperature of 200°C, and a circulating air volume of 0.8 m 3 The slurry was dried by airflow at a flow rate of 1 / min and a spray pressure of 0.3 MPa to coat the surfaces of the precursor particles a1 with Na2CO3, thereby obtaining composite particles a2. In the composite particles a2, 77% by area of ​​the surfaces of the precursor particles a1 were coated with Na2CO3.

[0105] 1.1.3 Sintering of composite particles a2 The composite particles a2 were placed in an alumina crucible and fired in an air atmosphere to obtain Na-containing oxide particles a3 having a P2 type structure under the following firing conditions (1) to (7). (1) The alumina crucible containing the composite particles a2 is placed in a heating furnace in an air atmosphere. (2) The temperature inside the heating furnace is raised from room temperature (25°C) to 600°C in 115 minutes. (3) The temperature in the heating furnace is maintained at 600°C for 360 minutes to perform pre-baking. (4) After the preliminary firing, the temperature inside the heating furnace is increased from 600°C to 900°C in 100 minutes. (5) The temperature in the heating furnace is kept at 900°C for 60 minutes to carry out the main firing. (6) After the main firing, the temperature in the heating furnace is lowered from 900°C to 250°C over 120 minutes. (7) At 250°C, the alumina crucible is removed from the heating furnace and allowed to cool in a dry atmosphere outside the furnace until it reaches 25°C in 10 minutes.

[0106] The fired product was then cooled and pulverized in a mortar under a dry atmosphere to obtain sodium-containing oxide particles a3 having a P2 structure (P2 type particles a3). The P2 type particles a3 had an average particle diameter D50 of 3.2 μm and were spherical particles.

[0107] 1.1.4 Ion exchange (1) LiNO3 and LiCl were weighed out to a molar ratio of 50:50, and mixed with the P2 type particles a3 in a molar ratio that was 10 times the minimum Li amount required for ion exchange to obtain a mixture. (2) Using an alumina crucible, ion exchange was carried out at 280°C for 1 hour in an air atmosphere to obtain a product containing a Li-containing oxide. (3) The salt remaining in the product was washed with pure water, and solid-liquid separation was carried out by vacuum filtration to obtain a precipitate. (4) The obtained precipitate was dried overnight at 120°C to obtain a positive electrode active material A.

[0108] 1.2 Cathode active material B 1.2.1 Preparation of precursor particles b1 The above-mentioned fine particles a1-2 were used as precursor particles b1.

[0109] 1.2.2 Preparation and firing of composite particles b2 Composite particles b2 were prepared in the same manner as above, except that precursor particles b1 were used instead of precursor particles a1, and the composite particles b2 were calcined to obtain Na-containing oxide particles b3 having a P2-type structure (P2-type particles b3). The P2-type particles b3 had an average particle diameter D50 of 1.8 μm and were spherical particles.

[0110] 1.2.3 Ion exchange Positive electrode active material B was obtained by carrying out ion exchange in the same manner as above, except that P2 type particles b3 were used instead of P2 type particles a3.

[0111] 1.3 Cathode active material C 1.3.1 Preparation of precursor particle c1 (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed to achieve the desired composition ratio and dissolved in distilled water to a concentration of 2 mol / L to obtain the first solution. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 2 mol / L to obtain the second solution. (2) 1000 mL of pure water was placed in a reaction vessel (with a baffle plate), and 900 mL of the first solution and 900 mL of the second solution were added dropwise thereto at a rate of about 4 mL / min. (3) After the dropwise addition was completed, the mixture was stirred at room temperature for 1 hour at a stirring speed of 150 rpm to obtain a product. (4) The product was washed with pure water, and the solid was separated into liquid using a centrifuge to recover the precipitate. (5) The obtained precipitate was dried overnight at 120°C, crushed in a mortar, and then separated into coarse particles c1-1 and fine particles c1-2 by air classification. Both the coarse particles c1-1 and the fine particles c1-2 were composite salts containing Mn, Ni, and Co. The coarse particles c1-1 had an average particle diameter D50 of 4.8 μm and were spherical particles. (6) Coarse particles c1-1 were used as precursor particles c1.

[0112] 1.3.2 Preparation and firing of composite particles c2 Composite particles c2 were prepared in the same manner as above, except that precursor particles c1 were used instead of precursor particles a1, and the composite particles c2 were calcined to obtain Na-containing oxide particles c3 having a P2 structure (P2-type particles c3). The P2-type particles c3 had an average particle diameter D50 of 4.3 μm and were spherical particles.

[0113] 1.3.3 Ion exchange A positive electrode active material C was obtained by carrying out ion exchange in the same manner as above, except that P2 type particles c3 were used instead of P2 type particles a3.

[0114] 1.4 Cathode active material D 1.4.1 Preparation of precursor particles d1 The above-mentioned fine particles a1-2 were used as precursor particles d1.

[0115] 1.4.2 Preparation of composite particle d2 The precursor particles d1 and Na2CO3 were mixed with Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 The precursor particles d1 and Na2CO3 were weighed out so as to have a composition of 0. The weighed precursor particles d1 and Na2CO3 were mixed in a mortar to obtain composite particles d2. In the composite particles d2, 22 area % of the surface of the precursor particles d1 was covered with Na2CO3.

[0116] 1.4.3 Calcination of composite particles d2 Composite particles d2 were calcined in the same manner as above, except that composite particles d2 were used instead of composite particles a2, to obtain Na-containing oxide particles d3 (P2-type particles d3) having a P2-type structure. The P2-type particles d3 had an average particle diameter D50 of 1.3 μm and were plate-like particles.

[0117] 1.4.4 Ion exchange Positive electrode active material D was obtained by ion exchange in the same manner as above, except that P2 type particles d3 were used instead of P2 type particles a3.

[0118] 2. Evaluation of positive electrode active material 2.1 Elemental analysis and crystal structure identification Elemental analysis was performed on each of the positive electrode active materials A to D, and it was found that the target composition was obtained. Furthermore, X-ray diffraction measurements were performed, and it was found that each of the positive electrode active materials A to D had an O2 type structure.

[0119] 2.2 Measurement of average particle size and specific surface area The average particle diameter D50 and BET specific surface area were measured for each of the positive electrode active materials A to D. The average particle diameter D50 is the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution measured by the laser diffraction / scattering method. The BET specific surface area was measured using a gas adsorption method. Specifically, a specific surface area / pore distribution measurement device (Micromeritics, Tristar) was used to perform the measurement by the constant volume method using nitrogen as the adsorbed gas. That is, a glass tube containing the sample was immersed in liquid nitrogen, the tube was evacuated, and the relative pressure (= adsorption equilibrium pressure / saturated vapor pressure) was then changed to measure the amount of adsorbed nitrogen. The BET specific surface area was calculated from the measured amount of adsorbed nitrogen and the relative pressure.

[0120] 2.3 Observation of shape The appearance and cross-sectional shape of positive electrode active materials A to D were observed by SEM. Figure 4 shows SEM images of the cross-sectional shapes. Positive electrode active material A was spherical particles with a hollow single-layer structure. Positive electrode active material B was spherical particles with a hollow single-layer structure. Positive electrode active material C was spherical particles with a hollow multi-layer structure. Positive electrode active material D was plate-like particles.

[0121] 3. Preparation of evaluation cells 3.1 Fabrication of solid-state batteries A solid-state battery was fabricated using each positive electrode active material according to the following procedure. (1) A positive electrode active material, a sulfide solid electrolyte A (argyrodite-type sulfide solid electrolyte), PVDF, and VGCF were weighed and mixed in a mass ratio of positive electrode active material:sulfide solid electrolyte A:PVDF:VGCF=82.1:14.9:0.6:2.4 to obtain a positive electrode composite. (2) The negative electrode active material (Li15Si4 and elemental Si), sulfide solid electrolyte B (Li2S-P2S5-LiI-LiBr), PVDF, and VGCF were weighed and mixed in a mass ratio of Li15S4:elemental Si:sulfide solid electrolyte B:PVDF:VGCF=30.5:50.7:15.5:0.9:2.4 to obtain a negative electrode composite. (3) The sulfide solid electrolyte B and acrylate butadiene rubber (ABR) were weighed and mixed in a mass ratio of sulfide solid electrolyte B:ABR=99.4:0.6 to obtain an electrolyte mixture. (4) The above electrolyte mixture was placed in a McCorm cylinder and pressed at 9.8 kN for 1 minute to form an electrolyte layer. The above positive electrode mixture was then placed on one side of the electrolyte layer and pressed at 19.6 kN for 1 minute to form a positive electrode active material layer. The above negative electrode mixture was then placed on the other side of the electrolyte layer and pressed at 58 kN for 3 minutes to form a negative electrode active material layer. Finally, current collectors were placed on both ends of each layer in the stacking direction to obtain a solid-state battery.

[0122] 3.2 Preparation of liquid battery A liquid battery was fabricated using each of the positive electrode active materials. The fabrication procedure for the liquid battery was as follows. (1) The positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were weighed out in a mass ratio of positive electrode active material:AB:PVdF = 85:10:5, and dispersed and mixed in N-methyl-2-pyrrolidone to obtain a positive electrode composite slurry. The positive electrode composite slurry was coated onto aluminum foil and vacuum dried overnight at 120°C to obtain a positive electrode, which is a laminate of a positive electrode active material layer and a positive electrode current collector. (2) An electrolyte solution was obtained by dissolving LiPF6 at a concentration of 1 M in a mixed solvent of trifluoropropylene carbonate (TFPC) and trifluoroethyl methyl carbonate (TFEMC) in a ratio of TFPC:TFEMC = 30 vol%:70 vol%. (3) Metallic lithium foil was prepared as the negative electrode. (4) A coin cell (CR2032) was fabricated as a liquid battery using a positive electrode, an electrolyte, and a negative electrode.

[0123] 4. Cell Evaluation 4.1 Measurement of discharge capacity of solid-state batteries The above solid-state battery was charged and discharged in a thermostatic chamber maintained at 25°C at a voltage range of 1.8-4.6V and a 0.1C rate (1C = 220mA / g), and the discharge capacity was measured.

[0124] 4.2 Measurement of DCIR resistance of solid-state batteries The above solid-state battery was charged and discharged twice in a thermostatic chamber maintained at 25°C at a voltage range of 1.8-4.6V and a 0.1C rate (1C = 220mA / g), and then the DCIR resistance was measured by applying a current equivalent to 3C for 10 seconds at an SOC of 50%.

[0125] 4.3 Liquid batteries Each coin cell was charged and discharged in a thermostatic chamber maintained at 25°C at a voltage range of 2.0-4.8V at a 0.1C rate or a 3C rate (1C=220mA / g), and the capacity at 0.1C and the capacity at 3C were measured.

[0126] 5. Evaluation Results The evaluation results of the positive electrode active material are shown in Tables 1 and 2. The evaluation results of the solid battery are shown in Table 1. The evaluation results of the liquid battery are shown in Table 2.

[0127] [Table 1]

[0128] [Table 2]

[0129] As is clear from the results shown in Table 1, positive electrode active materials A and B have low resistance when applied to solid-state batteries, and as is clear from the results shown in Table 2, positive electrode active material C has excellent rate characteristics when applied to liquid-state batteries.

[0130] 6. Supplementary Information In the above examples, precursor particles were obtained by coprecipitation, but the precursor particles can also be obtained by other methods. In the above examples, composite particles were obtained by coating the surfaces of precursor particles with a Na source by spray drying, but the composite particles can also be obtained by other methods. In the above examples, Na-containing oxides having a P2-type structure and Li-containing oxides having an O2-type structure were exemplified as having specific chemical compositions, but the chemical compositions of the Na-containing oxides and Li-containing oxides are not limited thereto. The Na-containing oxides and Li-containing oxides may be doped with an element M other than Mn, Ni, and Co. The element M is as described in the embodiments.

[0131] 7. Summary As described above, in a positive electrode active material containing a Li-containing oxide, if the Li-containing oxide satisfies the following requirements (1) to (3), the resistance will be low when applied to a solid state battery. (1) The Li-containing oxide particles have an O2 type structure. (2) The Li-containing oxide particles are spherical particles having a hollow single-layer structure. (3) The Li-containing oxide particles have an average particle size of 1.0 μm or more and less than 3.5 μm.

[0132] On the other hand, in a positive electrode active material containing a Li-containing oxide, if the Li-containing oxide satisfies the following requirements (4) to (6), the rate characteristics are excellent when applied to a liquid battery. (4) The Li-containing oxide particles have an O2 type structure. (5) The Li-containing oxide particles are spherical particles having a hollow multilayer structure. (6) The Li-containing oxide particles have an average particle size of 3.5 μm or more.

[0133] Furthermore, the Li-containing oxide particles satisfying the above requirements (1) to (3) and the Li-containing oxide particles satisfying the above requirements (4) to (6) can be prepared, for example, depending on the size of the P2 type particles before ion exchange. [Explanation of symbols]

[0134] 100 Batteries (solid batteries, liquid batteries) 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector

Claims

1. A method for producing a positive electrode active material used in a solid-state battery, comprising: Obtaining Na-containing oxide particles having a P2 type structure, and and ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. the Na-containing oxide particles are spherical particles having an average particle size of 1.0 μm or more and less than 3.5 μm, The Li-containing oxide particles are spherical particles having a hollow single-layer structure. Manufacturing method.

2. The method of claim 1, The Na-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. Manufacturing method.

3. A positive electrode active material for use in a solid-state battery, the positive electrode active material comprising Li-containing oxide particles, The Li-containing oxide particles have an O2 type structure, the Li-containing oxide particles are spherical particles having a hollow single-layer structure, The Li-containing oxide particles have an average particle size of 1.0 μm or more and less than 3.5 μm. Cathode active material.

4. The positive electrode active material according to claim 3, The Li-containing oxide particles are 4.5 m ２ / g or less specific surface area, Cathode active material.

5. The positive electrode active material according to claim 3, The Li-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. Cathode active material.

6. A solid-state battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer contains the positive electrode active material according to any one of claims 3 to 5, The positive electrode active material layer contains a solid electrolyte. solid state battery.

7. A method for producing a positive electrode active material used in a liquid battery, comprising: Obtaining Na-containing oxide particles having a P2 type structure, and and ion-exchanging at least a portion of the Na in the Na-containing oxide particles with Li to obtain Li-containing oxide particles having an O2-type structure. the Na-containing oxide particles are spherical particles having an average particle diameter of 3.5 μm or more, The Li-containing oxide particles are spherical particles having a hollow multilayer structure. Manufacturing method.

8. The manufacturing method according to claim 7, The Na-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. Manufacturing method.

9. A positive electrode active material for use in a liquid battery, the positive electrode active material comprising Li-containing oxide particles, The Li-containing oxide particles have an O2 type structure, the Li-containing oxide particles are spherical particles having a hollow multilayer structure, The Li-containing oxide particles have an average particle diameter of 3.5 μm or more. Cathode active material.

10. The positive electrode active material according to claim 9, The Li-containing oxide particles are 4.5 m ２ / g or more specific surface area, Cathode active material.

11. The positive electrode active material according to claim 9, The Li-containing oxide particles contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Li, and O. Cathode active material.

12. A liquid battery having a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, The positive electrode active material layer comprises the positive electrode active material according to any one of claims 9 to 11, The positive electrode active material layer contains a liquid electrolyte. Liquid battery.

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