METHOD FOR MANUFACTURING TYPE P2 Na-CONTAINING OXIDE

Abstract

To reduce unevenness of crystallinity in a type P2 Na-containing oxide.SOLUTION: A method for manufacturing type P2 Na-containing oxide includes obtaining composite particles (10) containing at least one of Mn, Ni and Co and Na, forming a layer (15) of the composite particles (10) in a container (20), and firing the layer (15) to obtain a type P2 Na-containing oxide (30). Herein, the container (20) has at least a bottom face (21), the layer (15) is formed on the bottom face (21), and has a hole or recess at the center (21a) of the bottom face (21).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This application discloses a method for producing a P2-type Na-containing oxide.

Background Art

[0002] Patent Document 1 discloses a method for producing an O2-type Li-containing oxide by ion-exchanging at least a part of Na in a P2-type Na-containing oxide with Li. Further, the P2-type Na-containing oxide can also be used as a positive electrode active material for a sodium-ion battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, there is room for improvement regarding the uneven crystallinity when producing a P2-type Na-containing oxide.

Means for Solving the Problems

[0005] As means for solving the above problems, this application discloses the following multiple aspects. <Aspect 1> A method for producing a P2-type Na-containing oxide, comprising: obtaining composite particles containing at least one of Mn, Ni, and Co and Na; forming a layer of the composite particles in a container; and obtaining the P2-type Na-containing oxide by firing the layer, wherein the container has at least a bottom surface; the layer is formed on the bottom surface; the layer has a hole or a dent at the center of the bottom surface. Method for producing P2-type sodium-containing oxide. <Aspect 2> The method for producing a P2-type sodium-containing oxide according to Aspect 1, After the layer is formed, the center of the bottom surface is exposed, Method for producing P2-type sodium-containing oxide. <Aspect 3> The method for producing a P2-type sodium-containing oxide according to Aspect 1 or 2, The layer has a through hole at the center of the bottom surface, The ratio D1 / D2 of the equivalent diameter D1 of the circle corresponding to the through hole to the equivalent diameter D2 of the circle of the bottom surface is 0.10 or more and 0.50 or less, Method for producing P2-type sodium-containing oxide. <Aspect 4> The method for producing a P2-type sodium-containing oxide according to any one of Aspects 1 to 3, Obtaining precursor particles containing at least one of Mn, Ni, and Co, and Coating the surface of the precursor particles with a Na source to obtain the composite particles, Method for producing P2-type sodium-containing oxide.

Advantages of the Invention

[0006] According to the production method of the present disclosure, unevenness in the crystallinity of the P2-type sodium-containing oxide can be reduced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0008] Hereinafter, an embodiment of the method for producing a P2-type Na-containing oxide of the present disclosure will be described. However, the method for producing a P2-type Na-containing oxide of the present disclosure is not limited to the following embodiment.

[0009] As shown in FIGS. 1 and 2, the method for producing a P2-type Na-containing oxide according to one embodiment is S1: obtaining composite particles 10 containing at least one of Mn, Ni, and Co and Na, S2: forming a layer 15 of the composite particles 10 in a container 20, and S3: obtaining a P2-type Na-containing oxide 30 by firing the layer 15. Here, as shown in FIG. 2, the container 20 has at least a bottom surface 21, and the layer 15 is formed on the bottom surface 21. In the present embodiment, the layer 15 has a hole or a dent at the center 21a (the centroid of the bottom surface 21) of the bottom surface 21.

[0010] 1. S1 In S1, composite particles 10 containing at least one of Mn, Ni, and Co and Na are obtained. The composition of the composite particles 10 is appropriately determined according to the composition of the P2-type Na-containing oxide after firing. The composite particles 10 may be, for example, composite particles of a transition metal source containing at least one of Mn, Ni, and Co and a Na source. Hereinafter, an example of a method for obtaining the composite particles 10 will be described.

[0011] The method for producing a P2-type Na-containing oxide according to one embodiment is S1-1: obtaining precursor particles containing at least one of Mn, Ni, and Co, and S1-2: coating the surface of the precursor particles with a Na source to obtain the composite particles 10. It may also include.

[0012] 1.1 S1-1 In S1-1, precursor particles containing at least one of Mn, Ni, and Co are obtained. 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 of 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 may have various shapes. For example, the precursor particles may be spherical particles. In the present application, the "spherical particles" means particles having a circularity of 0.80 or more. The circularity of the 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 the particles is 4πS / L 2 which is defined as follows. Here, S is the projected area of the particle, and L is the perimeter of the projected image of the particle. The circularity of the particles can be determined by observing the appearance of the particles using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an optical microscope. The particle diameter of the precursor particles is not particularly limited.

[0013] In S1-1, a transition metal ion, an ion source capable of forming a precipitate in an aqueous solution, and a transition metal compound containing at least one element among Mn, Ni, and Co may be used to obtain a precipitate as the above-mentioned precursor particles by a coprecipitation method. Thereby, spherical precursor particles are easily obtained. The "transition metal ion and an ion source capable of forming a precipitate in an aqueous solution" 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-mentioned salts, hydroxides, etc. containing at least one of Mn, Ni, and Co. Specifically, in S1-1, after preparing the ion source and the transition metal compound as respective solutions, a precipitate as precursor particles may be obtained by dropping and mixing each solution. At this time, for example, water is used as the solvent. At this time, various sodium compounds may be used as the base, and an aqueous ammonia solution etc. may be added for adjusting the basicity. In the case of the coprecipitation method, for example, an aqueous solution of a transition metal compound and an aqueous solution of sodium carbonate are prepared, and a precipitate as precursor particles is obtained by dropping and mixing each aqueous solution. Alternatively, it is also possible to obtain precursor particles by a sol-gel method.

[0014] In S1-1, the precursor particles may contain element M. Element M is at least one 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, for example, a function of stabilizing the P2-type structure. The method for obtaining precursor particles containing element M is not particularly limited. When obtaining precursor particles by the coprecipitation method 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 precursor particles containing element M together with at least one of Mn, Ni, and Co are obtained by dropping and mixing each aqueous solution. Alternatively, in the manufacturing method of the present disclosure, element M may not be added in S1-1, and element M may be doped in S1-2 or S3 described later.

[0015] 1.2 S1-2 In S1-2, the surface of the precursor particles obtained by S1-1 is coated with a Na source to obtain composite particles 10. The Na source may be a salt containing Na such as a carbonate or a nitrate, or a compound other than a salt such as sodium oxide or sodium hydroxide. In S1-2, the amount of the Na source coated on the surface of the precursor particles may be determined in consideration of the amount of Na lost during the subsequent firing.

[0016] In S1-2, the coating rate of the Na source on the surface of the precursor particles is not particularly limited. For example, in S1-2, the above composite particles 10 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 above precursor particles with a Na source. Here, when the precursor particles obtained by S1-1 are spherical particles and the composite particles 10 obtained by S1-2 are obtained by coating 40 area% or more of the surface of the precursor particles with the Na source, in S3 described later, the Na-containing oxide having a P2-type structure is likely to be spherical particles. When the coating rate of the Na source is small, when the composite particles 10 are fired, P2-type crystals tend to grow and the Na-containing oxide tends to be plate-shaped. When the coating rate of the Na source is large, when the composite particles 10 are fired, the crystallites of the P2-type crystals tend to be small, and the Na-containing oxide tends to be spherical particles corresponding to the shape of the precursor particles.

[0017] In S1-2, the method of coating the surface of the above precursor particles with a Na source is not particularly limited. As described above, when coating 40 area% or more of the surface of the precursor particles with a Na source, various methods can be mentioned. For example, a rolling fluid coating method or a spray drying method can be mentioned. 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 at the same time, or after being brought into contact, it is dried. By adjusting the coating conditions (temperature, time, number of times, etc.), 40 area% or more of the surface of the precursor particles can be coated with a Na source.

[0018] In S1-2, the precursor particles may be coated with an M source together with a Na source. For example, in S1-2, the precursor particles obtained by S1-1, 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 may be mixed to obtain composite particles 10. The M source may be, for example, a salt containing 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 with respect to the precursor particles may be determined according to the chemical composition of the Na-containing oxide after firing.

[0019] 2.S2 In S2, using the composite particles 10 obtained by S1, a layer 15 of the composite particles 10 is formed in the container 20. More specifically, as shown in FIG. 2, the composite particles 10 are placed inside the container 20, and a layer 15 composed of the composite particles 10 is formed on the bottom surface 21 of the container 20.

[0020] 2.1 Container The container 20 may be made of a material that can withstand the conditions during firing and that does not substantially react with the composite particles 10 during firing. The container 20 may be, for example, a corundum crucible. As shown in FIG. 2, the container 20 may have a bottom surface 21 and a side wall 22 around the bottom surface 21. The shape of the bottom surface 21 and the shape of the container 20 as a whole are not particularly limited. The bottom surface 21 can take various shapes such as a rectangular shape or a circular shape. The size of the container 20 (the size of the bottom surface 21 and the height of the side wall 22) is also not particularly limited. The effects of the method of the present disclosure are exhibited regardless of the size of the container 20. When the bottom surface 21 of the container 20 is rectangular, the length of one side may be, for example, 50 mm or more and 500 mm or less, 75 mm or more and 300 mm or less, or 100 mm or more and 200 mm or less. Alternatively, the equivalent diameter of the circle (area circle equivalent diameter) D2 of the bottom surface 21 of the container 20 may be 55 mm or more and 600 mm or less, 85 mm or more and 350 mm or less, or 110 mm or more and 230 mm or less.

[0021] 2.2 Layer On the bottom surface 21 of the container 20, a layer 15 composed of composite particles 10 is formed. According to the new findings of the present inventor, when firing is performed after forming the layer 15 of the composite particles 10 on the bottom surface 21 of the container 20, the crystallinity of the Na-containing oxide in the central portion in the plane direction (the portion above the center 21a of the bottom surface 21) is likely to decrease. It is considered that this is because the central portion in the plane direction of the layer 15 is likely to be deficient in heat and oxygen during firing. On the other hand, in the method of the present disclosure, a hole or a recess is provided in the central portion in the plane direction of the layer 15, and the amount of the composite particles 10 present in the central portion in the plane direction is intentionally reduced. That is, in the container 20, since the amount of the composite particles 10 in the portion where heat deficiency and oxygen deficiency are likely to occur is relatively small, and relatively many composite particles 10 are arranged in the portion where heat deficiency and oxygen deficiency are less likely to occur, the P2-type Na-containing oxide 30 obtained after firing is likely to have high crystallinity as a whole and little variation in crystallinity.

[0022] Among the layers 15 formed on the bottom surface 21, the thickness T1 of the layer 15 formed on the side wall 22 side and the thickness T2 of the layer 15 formed on the center 21a side are not particularly limited. In the method of the present disclosure, since a hole or a recess is provided in the layer 15 at the center 21a, the thickness T2 naturally becomes smaller than the thickness T1. Thus, as long as the thickness T2 is smaller than the thickness T1, the effects of the method of the present disclosure are exhibited regardless of the thickness T1 of the layer 15 formed on the side wall 22 side and the thickness T2 of the layer 15 formed in the central portion. In particular, as shown in FIG. 2, when there is no layer 15 at the center 21a of the bottom surface 21 (T2 = 0), that is, when the center 21a of the bottom surface 21 is exposed after the layer 15 is formed, the effects of the method of the present disclosure become particularly remarkable.

[0023] When a hole is formed in the layer 15 at the central portion of the bottom surface 21, the shape and size of the hole are not particularly limited. The smaller the hole, the smaller the effect of the method according to the present disclosure, and the larger the hole, the smaller the amount of composite particles 10 that can be processed at one time. Considering the shape of the container, productivity, etc., the shape and size of the hole may be determined. For example, as shown in FIG. 2, when the layer 15 has a through hole at the center 21a of the bottom surface 21, when the ratio D1 / D2 of the equivalent circular diameter D1 of the through hole to the equivalent circular diameter D2 of the bottom surface 21 is 0.10 or more and 0.50 or less, particularly when it is 0.10 or more and 0.40 or less, and even more particularly when it is 0.10 or more and 0.30 or less, it is easy to increase the effect of reducing the unevenness of the crystallinity of the P2-type Na-containing oxide while maintaining high productivity. Note that the "equivalent circular diameter D1 of the through hole" is determined based on the exposed area of the bottom surface 21 due to the hole.

[0024] 3.S3 In S3, by firing the layer 15 obtained in S2, a P2-type Na-containing oxide 30 is obtained. S3 can be carried out, for example, in a known heating furnace. S3 may include, for example, the following S3-1, S3-2, and S3-3.

[0025] 3.1 S3-1 In S3-1, pre-firing is performed on layer 15 (with respect to the composite particles 10 contained in layer 15). The pre-firing is carried out at a temperature lower than the main firing. If the pre-firing in S3-1 is insufficient, in the finally obtained P2-type Na-containing oxide 30, the formation of the P2 phase may be insufficient. In S3-1, when the pre-firing temperature is 250 °C or higher and lower than 700 °C, and the pre-firing time is 2 hours or longer and 50 hours or shorter, sufficient pre-firing can be performed on the composite particles 10, the heat uniformity is enhanced, and the P2-type Na-containing oxide 30 obtained through S3-2 and S3-3 described later is more likely to be appropriate. The pre-firing temperature may be 280 °C or higher and lower than 700 °C, 350 °C or higher and lower than 700 °C, 450 °C or higher and lower than 700 °C, 550 °C or higher and lower than 700 °C, or 550 °C or higher and 650 °C or lower. Also, the pre-firing time may be 2 hours or longer and 40 hours or shorter, 3 hours or longer and 30 hours or shorter, or 4 hours or longer and 20 hours or shorter. The pre-firing atmosphere is not particularly limited, and for example, an oxygen-containing atmosphere such as an air atmosphere may be used. The pre-firing may be performed in multiple steps, such as performing pre-firing at a relatively low temperature first and then at a relatively high temperature.

[0026] 3.2 S3-2 In S3-2, following the above pre-firing, main firing is performed on layer 15 (on composite particles 10 included in layer 15) at a temperature of 700°C or higher and 1100°C or lower for 30 minutes or longer and 10 hours or shorter. In S3-2, the main firing temperature is preferably 800°C or higher and 1000°C or lower. If the main firing temperature is too low, the P2 phase is not generated. If the main firing temperature is too high, phases other than the P2 phase, such as the O3 phase, are likely to be generated. The temperature rising conditions from the pre-firing temperature to the main firing temperature are not particularly limited. The main firing time is not particularly limited and may be, for example, 30 minutes or longer and 48 hours or shorter. However, the shape of the Na-containing oxide can be controlled by the main firing time. As described above, in the method of the present disclosure, when the coating rate of the Na source in the composite particles 10 is 40 area% or more, when the composite particles 10 are fired, P2-type crystals with small crystallites are likely to be formed on the surface thereof. In the method of the present disclosure, by growing P2-type crystals along the surface of the particles so that one P2-type crystallite is connected to another P2-type crystallite, the shape of the P2-type Na-containing oxide 30 corresponds to the shape of the precursor particles. For example, when the precursor particles are spherical particles, the P2-type Na-containing oxide 30 can also be spherical particles. If the main firing time is too short, the generation of the P2 phase becomes insufficient. On the other hand, if the main firing time is too long, the P2 phase grows excessively and becomes plate-like particles instead of spherical particles. As far as the inventor has confirmed, when the main firing time is 30 minutes or longer and 3 hours or shorter, spherical particles of the P2-type Na-containing oxide 30 are likely to be obtained. The P2-type Na-containing oxide 30 obtained after the main firing may have a structure in which a plurality of crystallites exist on the surface and the crystallites are connected to each other.

[0027] 3.3 S3-3 In S3-3, following the above main firing, rapid cooling (cooling at a temperature drop rate of 20°C / min or higher) is performed from a temperature T of 200°C or higher 1 to a temperature T of 100°C or lower. 2 The above pre-firing and main firing are performed, for example, in a heating furnace as described above. In step S3-3, for example, after performing the above main firing in a heating furnace, the composite particles 10 included in layer 15 are cooled to an arbitrary temperature T of 200°C or higher 1 and at this temperature T1 After that, the container 20 is taken out from the heating furnace, and the temperature T is set to any temperature below 100 °C 2 and rapid cooling is performed outside the furnace until the temperature reaches T. The temperature T 1 is any temperature of 200 °C or higher, and may be any temperature of 250 °C or higher. The temperature T 2 is any temperature of 100 °C or lower, may be any temperature of 50 °C or lower, or may be the cooling end temperature. The temperature T 1 From the temperature T 2 to the temperature T 1 in a predetermined temperature range, moisture is likely to penetrate between the layers of the P2-type structure due to atomic vibrations, molecular motion, etc. When cooling the composite particles (P2-type Na-containing oxide 30) after this firing, by shortening the time in the temperature range where such moisture is likely to penetrate (that is, rapid cooling), it is considered that the amount of moisture penetrating between the layers of the P2-type structure is reduced. In this regard, in step S3-3, when cooling the composite particles after this firing, from any temperature T 2 of 200 °C or higher to any temperature T 1 of 100 °C or lower, for example, by allowing it to cool in a dry atmosphere outside the furnace, the cooling rate from the temperature T 2 to the temperature T becomes high (for example, 20 °C / min or higher), making it difficult for moisture to penetrate between the layers of the P2-type structure and suppressing the collapse of the P2-type structure, etc.

[0028] 4. P2-type Na-containing oxide As described above, the P2-type Na-containing oxide 30 can be produced by S1 to S3. The P2-type Na-containing oxide 30 contains, for example, at least one of Mn, Ni, and Co, Na, and O as constituent elements. In particular, when it contains at least Na, Mn, at least one of Ni and Co, and O as constituent elements, among them, when it contains at least Na, Mn, Ni, Co, and O as constituent elements, it is likely to become a P2-type Na-containing oxide 30 having higher performance. The P2-type Na-containing oxide 30 contains Na c Mn x-p Ni y-q Co z-r M p+q+r O2 It may have the chemical composition shown herein. 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 P2-type Na-containing oxide 30 has such a chemical composition, the P2-type structure is more likely to be maintained. In the above chemical composition, c 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 less than 1.00, and may be 0.90 or less, 0.80 or less, or 0.70 or less. x is 0 or more, and may be 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. Also, y is 0 or more, and may be 0.10 or more or 0.20 or more, and 1.00 or less, 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, 0.30 or more, or 0.40 or more, and 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, or 0.40 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, a high charge and discharge capacity is likely to be ensured. 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, 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 indefinite.

[0029] The P2-type Na-containing oxide 30 produced as described above can be used, for example, as a positive electrode active material of a sodium ion battery. Alternatively, by ion-exchanging at least a part of Na in the P2-type Na-containing oxide 30 with Li, an O2-type Li-containing oxide can be obtained. The O2-type Li-containing oxide can be used, for example, as a positive electrode active material of a lithium ion battery.

Example

[0030] Hereinafter, while showing examples, the technology of the present disclosure will be described in more detail. However, the technology of the present disclosure is not limited to the following examples.

[0031] 1. Preparation of P2-type Na-containing oxide 1.1 Preparation of precursor particles (1) MnSO 4 ·5H 2 O, NiSO 4 ·6H 2 O, CoSO 4 ·7H 2 O were weighed so as to have the target composition ratio and dissolved in distilled water to a concentration of 1.2 mol / L to obtain a first solution. Also, in another container, Na 2 CO 3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain a second solution. (2) 1000 mL of pure water was put into a reaction vessel (with a baffle), and 500 mL of the first solution and 500 mL of the second solution were each dropped therein at a rate of about 4 mL / min. (3) After the dropping was completed, the mixture was stirred at a stirring speed of 150 rpm for 1 hour at room temperature to obtain a product. (4) The product was washed with pure water and solid-liquid separated by a centrifuge to recover the precipitate. (5) The obtained precipitate was dried at 120 °C overnight, pulverized in a mortar, and fine particles were removed by air classification to obtain precursor particles. Here, the precursor particles were spherical particles composed of a composite salt containing Mn, Ni, and Co.

[0032] 1.2 Preparation of composite particles (1) Na 2CO 3 After weighing CO and distilled water, stir using a stirrer until completely dissolved to prepare an aqueous solution of Na 2 CO 3 . (2) Mix the above-mentioned precursor particles into the aqueous solution of Na 2 CO 3 to obtain a slurry. Na 2 CO 3 and the above-mentioned precursor particles are mixed so that the target composition after firing described below is Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 O 2 . (3) By drying the obtained slurry by spray drying, more than 70% of the surface area of the above-mentioned precursor particles is coated with Na 2 CO 3 to obtain composite particles.

[0033] 1.3 Formation of Layers Put 240 g of the above-mentioned composite particles into an alumina crucible having a bottom surface of 150 mm square, and form a layer on the bottom surface. Here, for Examples 1 to 3, as shown in FIG. 2, a layer having a through hole in the central part of the bottom surface was formed, and the center of the bottom surface of the crucible was exposed to the outside through the through hole. For Example 1, the ratio D1 / D2 of the equivalent diameter D1 of the hole to the equivalent diameter D2 of the bottom surface was set to 0.29, and the layer thickness outside the hole was set to about 30 mm. For Example 2, the ratio D1 / D2 was set to 0.18, and the layer thickness outside the hole was set to about 25 mm. For Example 3, the ratio D1 / D2 was set to 0.12, and the layer thickness outside the hole was set to about 23 mm. On the other hand, for the comparative example, a layer with a uniform thickness of about 20 mm was formed without providing holes or recesses. Table 1 below summarizes the layer formation conditions for each of Examples 1 to 3 and the comparative example.

[0034] [Table 1]

[0035] 1.4 Firing The crucible was placed in a heating furnace and fired in an air atmosphere to obtain a Na-containing oxide having a P2-type structure. The firing conditions are as follows (1) to (7). (1) The crucible having the above layer formed thereon was placed in a heating furnace with an air atmosphere. (2) The temperature inside the heating furnace was raised from room temperature (25 °C) to 280 °C over 2 hours and held at 280 °C for 4 hours to perform the first-stage pre-firing. (3) After the first-stage pre-firing, the temperature inside the heating furnace was raised from 280 °C to 600 °C over 6 hours and held at 600 °C for 2 hours to perform the second-stage pre-firing. (4) After the second-stage pre-firing, the temperature inside the heating furnace was raised from 600 °C to 900 °C over 3 hours and held at 900 °C for 2 hours to perform the main firing. (5) After the main firing, the temperature inside the heating furnace was lowered from 900 °C to 250 °C over 2 hours and 20 minutes. (6) The crucible was taken out of the heating furnace at 250 °C and cooled in a dry atmosphere to obtain Na-containing oxide particles for evaluation.

[0036] 2. Evaluation of Na-containing oxide 2.1 Shape When the Na-containing oxide particles obtained as described above were confirmed by SEM, spherical particles were obtained in Examples 1 to 3 and the comparative example.

[0037] 2.2 Crystal phase When the crystal phase of the Na-containing oxide particles was confirmed by XRD, it was substantially a P2 single phase in Examples 1 to 3 and the comparative example.

[0038] 2.3 Crystallinity 2.3.1 Difference in crystallinity depending on sampling position As shown in FIG. 3A, for Example 1, among the layers in the alumina crucible after firing, Sample 1-1 for crystallinity evaluation was collected from the surface of the layer existing at the crucible corner (1). Also, Sample 1-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing at the crucible corner (1). Also, Sample 2-1 for crystallinity evaluation was collected from the surface of the layer existing near the side wall at the center of the crucible (2). Also, Sample 2-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing near the side wall at the center of the crucible (2). Also, Sample 3-1 for crystallinity evaluation was collected from the surface of the layer existing near the hole at the center of the crucible (3). Also, Sample 3-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing near the hole at the center of the crucible (3). For each of Samples 1-1 to 3-2, an X-ray diffraction pattern was obtained. The results are shown in FIG. 4. Incidentally, FIG. 4 also shows, for reference, the X-ray diffraction pattern of the Na-containing oxide particles obtained when 1.3 g of a small amount of composite particles was fired under the same conditions as above.

[0039] Also, as shown in FIG. 3B, for Comparative Example 1, among the layers in the alumina crucible after firing, Sample 4-1 for crystallinity evaluation was collected from the surface of the layer existing at the back of the crucible corner (4). Also, Sample 4-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing at the back of the crucible corner (4). Also, Sample 5-1 for crystallinity evaluation was collected from the surface of the layer existing at the center of the crucible (5). Also, Sample 5-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing at the center of the crucible (5). Also, Sample 6-1 for crystallinity evaluation was collected from the surface of the layer existing in front of the crucible corner (6). Also, Sample 6-2 for crystallinity evaluation was collected from the bottom surface side of the layer existing in front of the crucible corner (6). For each of Samples 4-1 to 6-2, an X-ray diffraction pattern was obtained. The results are shown in FIG. 5. Also in FIG. 5, as in FIG. 4, the X-ray diffraction pattern of the Na-containing oxide particles obtained when 1.3 g of a small amount of composite particles was fired under the same conditions as above is also shown.

[0040] As is clear from FIGS. 4 and 5, for Example 1, regardless of the sampling position in the sagger, there was substantially no difference in the X-ray diffraction peak intensity, and the crystallinity unevenness was suppressed. On the other hand, for Comparative Example 1, there was a difference in the X-ray diffraction peak intensity depending on the sampling position in the sagger. In particular, Sample 5-2 collected from the bottom surface side at the center of the sagger had deteriorated crystallinity compared to other samples. Among the layers present in the central portion of the sagger, particularly the bottom portion not exposed on the layer surface was likely to have insufficient heat and insufficient oxygen during firing, which is considered to have deteriorated the crystallinity after firing.

[0041] When the same evaluation was performed for Examples 2 and 3, it was confirmed that the crystallinity unevenness was suppressed more than that of Comparative Example 1.

[0042] 2.3.2 Peak intensity ratio The entire Na-containing oxide of each of Examples 1 to 3 and Comparative Example 1 was taken out from the sagger, pulverized in a mortar and uniformly mixed, and then an X-ray diffraction pattern was obtained. For the X-ray diffraction pattern, using the average value at 35° ± 0.2° as the background, the peak integrated intensity value between 36.00° and 36.60° was defined as the "(100) plane intensity", and the peak integrated intensity value between 39.00° and 40.50° was defined as the "(102) plane intensity". By dividing the (102) plane intensity by the (100) plane intensity to obtain the "(102) / (100) intensity ratio", the crystal phase of the Na-containing oxide was evaluated. The larger the intensity ratio, the more likely it is to have high crystallinity as a whole P2-type structure. The results are shown in Table 2 below.

[0043]

Table 2

[0044] As shown in Table 2, the Na-containing oxides according to Examples 1 to 3 had higher crystallinity than the Na-containing oxide according to Comparative Example 1.

[0045] 3. Supplementary From the above results, it can be said that according to the following method, it is possible to produce a P2-type Na-containing oxide while suppressing crystallinity unevenness.

[0046] A method for producing a P2-type Na-containing oxide, obtaining composite particles containing at least one of Mn, Ni, and Co and Na, forming a layer of the composite particles in a container, and obtaining the P2-type Na-containing oxide by firing the layer, including the container having at least a bottom surface, the layer being formed on the bottom surface, the layer having a hole or a dent at the center of the bottom surface, A method for producing a P2-type Na-containing oxide.

[0047] In addition, in the examples, the case of producing spherical particles having a specific chemical composition as the P2-type Na-containing oxide was exemplified, but the chemical composition and shape of the P2-type Na-containing oxide are not limited thereto. It can be said that the effects of the above method are achieved regardless of the chemical composition and shape of the P2-type Na-containing oxide.

Explanation of Symbols

[0048] 10 Composite particles 15 Layer 20 Container 21 Bottom surface 21a Center 22 Side wall 30 P2-type Na-containing oxide

Claims

1. A method for producing a P2-type Na-containing oxide, comprising: obtaining composite particles containing at least one of Mn, Ni, and Co and Na; forming a layer of the composite particles in a container; and firing the layer to obtain the P2-type Na-containing oxide, wherein the container has at least a bottom surface, the layer is formed on the bottom surface, the layer has a hole or a dent at the center of the bottom surface, A method for producing a P2-type Na-containing oxide.

2. The method for producing a P2-type Na-containing oxide according to Claim 1, wherein after the layer is formed, the center of the bottom surface is exposed, A method for producing a P2-type Na-containing oxide.

3. The method for producing a P2-type Na-containing oxide according to Claim 1, wherein the layer has a through hole at the center of the bottom surface, and the ratio D1 / D2 of the equivalent circular diameter D1 of the through hole to the equivalent circular diameter D2 of the bottom surface is 0.10 or more and 0.50 or less, A method for producing a P2-type Na-containing oxide.

4. The method for producing a P2-type Na-containing oxide according to any one of Claims 1 to 3, comprising obtaining precursor particles containing at least one of Mn, Ni, and Co, and coating the surface of the precursor particles with a Na source to obtain the composite particles, A method for producing a P2-type Na-containing oxide.

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