Method for producing Na-containing oxide, and Na-containing oxide

Abstract

To provide a Na containing oxide having a P2 type structure wherein O3 phase is reduced.SOLUTION: A method for producing a Na containing oxide of the present disclosure comprises obtaining a precursor containing at least one element of Mn, Ni and Co, coating the surface of the precursor with a Na source to obtain a composite, and firing the composite to obtain the Na containing oxide having the P2 type structure, wherein the atmosphere in firing the composite contains 50 vol.% or more of oxygen.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a Na-containing oxide having a P2-type structure and having a chemical composition represented by Na x Fe y Mn 1-y O2 (where x is less than 1 and y is not less than 1 / 3 and less than 2 / 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a Na-containing oxide having a P2-type structure, an O3 phase is likely to be formed together with the P2 phase. In a Na-containing oxide having a P2-type structure, a new technology capable of reducing the O3 phase is required.

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 Na-containing oxide having a P2-type structure, comprising: obtaining a precursor containing at least one element of Mn, Ni, and Co; coating the surface of the precursor with a Na source to obtain a composite; and firing the composite to obtain a Na-containing oxide having a P2-type structure. including The firing atmosphere of the composite contains 50% by volume or more of oxygen. Manufacturing method. <Aspect 2> The manufacturing method of Aspect 1, wherein the precursor is spherical particles, the composite is obtained by coating 40% by area or more of the surface of the precursor with the Na source, and the Na-containing oxide having the P2-type structure is spherical particles. Manufacturing method. <Aspect 3> The manufacturing method of Aspect 1 or 2, wherein a transition metal ion and 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 are used, and a precipitate as the precursor is obtained by a coprecipitation method. Manufacturing method. <Aspect 4> The manufacturing method according to any one of Aspects 1 to 3, wherein the Na-containing oxide having the P2-type structure is Na a Mn x-p Ni y-q Co z-r M p+q+r O2 (where 0 < a ≤ 1.00, 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). Manufacturing method. <Aspect 5> A Na-containing oxide, comprising as constituent elements, at least one element among Mn, Ni, and Co, Na, and O, having a P2-type structure, when an X-ray diffraction pattern using CuKα as a radiation source is obtained for the Na-containing oxide, the ratio I P2 of the diffraction peak intensity I O3 derived from the P2-type structure to the diffraction peak intensity I P2 derived from the O3-type structure in the X-ray diffraction pattern, IO3 is from 1.0 to 20.0, and is spherical particles, a Na-containing oxide.

Advantages of the Invention

[0006] According to the method of the present disclosure, when producing a Na-containing oxide having a P2-type structure, the O3 phase can be reduced.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0008] 1. Method for Producing Na-Containing Oxide Having P2-Type Structure As shown in FIG. 1, a method for producing a Na-containing oxide having a P2-type structure according to one embodiment includes obtaining a precursor containing at least one element of Mn, Ni, and Co (S1), coating the surface of the precursor with a Na source to obtain a composite (S2), and firing the composite to obtain a Na-containing oxide having a P2-type structure (S3). Here, the firing atmosphere of the composite contains 50% by volume or more of oxygen.

[0009] 1.1 S1 In S1, a precursor containing at least one element among Mn, Ni, and Co is obtained. The precursor may contain at least Mn and one or both of Ni and Co, or may contain at least Mn, Ni, and Co. The precursor may be a salt containing at least one element among Mn, Ni, and Co. For example, the precursor may be at least one of carbonate, sulfate, nitrate, and acetate. Alternatively, the precursor may be a compound other than a salt. For example, the precursor may be a hydroxide. The precursor may be a hydrate. The precursor may be a combination of multiple types of compounds. The precursor may have various shapes. For example, the precursor may be particulate, and may be spherical particles as described later. The particle diameter of the particles composed of the precursor is not particularly limited.

[0010] In S1, 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 by a coprecipitation method. Thereby, spherical particles as the precursor 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 salt or hydroxide containing at least one element among Mn, Ni, and Co. Specifically, in S1, after preparing the ion source and the transition metal compound as respective solutions, a precipitate as the precursor 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 or the like 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 the precursor is obtained by dropping and mixing each aqueous solution. Alternatively, it is also possible to obtain a precursor by a sol-gel method. In particular, according to the coprecipitation method, spherical particles as the precursor are easily obtained.

[0011] As described above, the precursor 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 with a scanning electron microscope (SEM), a transmission electron microscope (TEM), or an optical microscope. When it is composed of a plurality of particles, its circularity is measured as an average value, for example, as follows.

[0012] (1) First, measure the particle size distribution of the particles. Specifically, determine the particle diameter (D10) at the integrated value of 10% and the particle diameter (D90) at the integrated value of 90% in the volume-based particle size distribution by the laser diffraction / scattering method. (2) Regarding the appearance of the particles whose particle size distribution has been measured, perform image observation with an SEM, a TEM, or an optical microscope, and arbitrarily extract 100 particles having a circular equivalent diameter (the diameter of a circle having the same area as the projected area of the particle) of D10 or more and D90 or less among the particles included in the image. (3) For each of the 100 extracted particles, determine the circularity by image processing, and regard the average value as the "circularity of the particles".

[0013] In S1, the precursor 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, the function of stabilizing the P2-type structure. The method for obtaining the precursor containing element M is not particularly limited. When obtaining the precursor by coprecipitation in S1, 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 each aqueous solution is dropped and mixed to obtain a precursor containing element M together with at least one element of Mn, Ni, and Co. Alternatively, in the production method of the present disclosure, element M may not be added in S1, and element M may be doped when Na-doped firing is performed in S2 and S3 described below.

[0014] 1.2 S2 In S2, the surface of the precursor obtained in S1 is coated with a Na source to obtain a composite. 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 S2, the amount of the Na source coated on the surface of the precursor may be determined in consideration of the amount of Na disappearance during the subsequent firing.

[0015] In S2, the coverage rate of the Na source on the surface of the precursor is not particularly limited. For example, in S2, the above complex may be obtained by coating 40% or more, 50% or more, 60% or more, or 70% or more of the surface area of the above precursor with the Na source. Here, when the precursor obtained by S1 is spherical particles and the complex obtained by S2 is obtained by coating 40% or more of the surface area of the precursor 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 coverage rate of the Na source is small, when the complex is fired, P2-type crystals tend to grow abnormally on the surface of the complex, and the Na-containing oxide tends to be plate-shaped. When the coverage rate of the Na source is large, when the complex is fired, the crystallites of the P2-type crystal tend to become small, and the Na-containing oxide tends to be spherical particles corresponding to the shape of the precursor.

[0016] In S2, the method of coating the surface of the above precursor with the Na source is not particularly limited. As described above, when coating 40% or more of the surface area of the precursor with the 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 the Na source is dissolved is prepared, and the coating solution is brought into contact with the surface of the precursor, and at the same time or after contact, it is dried. By adjusting the coating conditions (temperature, time, number of times, etc.), 40% or more of the surface area of the precursor can be coated with the Na source.

[0017] In S2, the precursor may be coated with an M source together with the Na source. For example, in S2, the precursor obtained by S1, the 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 a complex. 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 with respect to the precursor may be determined according to the chemical composition of the Na-containing oxide after firing.

[0018] 1.3 S3 In S3, by firing the complex obtained by S2, a Na-containing oxide having a P2-type structure is obtained. Here, the firing atmosphere of the complex contains 50% by volume or more of oxygen. Note that the "firing atmosphere" refers to the atmosphere in the "main firing" for generating the P2 phase. When pre-firing is performed before the main firing, the atmosphere in the pre-firing may or may not contain 50% by volume or more of oxygen. When the atmospheres in both the pre-firing and the main firing contain 50% by volume or more of oxygen, a higher effect is more easily obtained.

[0019] In S3, the above complex may be arbitrarily shaped, arbitrarily pre-fired, and then main-fired. The pre-firing of the complex may be performed at a temperature lower than the main firing. For example, the pre-firing can be performed at a temperature of less than 700°C. The pre-firing time is not particularly limited. Also, the pre-firing atmosphere is not particularly limited. The pre-firing atmosphere may be the same as or different from the main firing atmosphere. The pre-firing atmosphere may contain 50% by volume or more of oxygen.

[0020] In S3, the main firing of the complex may be performed, for example, at a temperature of 700°C or higher and 1100°C or lower. Preferably, it is 800°C or higher and 1000°C or lower. If the main firing temperature is too low, Na doping is not performed, and 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.

[0021] The firing time is not particularly limited and may be, for example, 30 minutes or more and 48 hours or less. However, the shape of the Na-containing oxide can be controlled by the firing time. As described above, in the method of the present disclosure, when the coverage rate of the Na source in the composite is 40% by area or more, when the composite is fired, P2-type crystals with small crystallites are likely to be formed on its surface. 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 Na-containing oxide becomes corresponding to the shape of the precursor. For example, when the precursor is spherical particles, the Na-containing oxide can also be spherical particles. If the firing time is too short, Na doping will not occur and the target P2-type structure cannot be obtained. On the other hand, if the firing time is too long, the P2-type structure grows excessively and becomes plate-like particles instead of spherical ones. As far as the present inventors have confirmed, when the firing time is 30 minutes or more and 3 hours or less, spherical particles of the Na-containing oxide are likely to be obtained. The Na-containing oxide obtained after the firing may have a structure in which a plurality of crystallites are present on the surface and the crystallites are connected to each other.

[0022] As described above, in S3, at least the firing atmosphere in the firing contains 50% by volume or more of oxygen. According to the new findings of the present inventors, when the firing is performed in an atmosphere with an oxygen concentration lower than 50% by volume such as the air atmosphere, the O3 phase is likely to occur. In contrast, by increasing the oxygen concentration during firing to 50% by volume or more, the P2 phase can be appropriately generated while reducing the O3 phase. The detailed mechanism is unclear, but it is considered that when the oxygen concentration during firing is low, some third phase is generated and this third phase becomes the O3 phase. In S3, when the oxygen concentration during firing is 50% by volume or more, the generation of this third phase is suppressed, and as a result, it is considered that the O3 phase is less likely to occur.

[0023] 2. Na-containing oxide having a P2-type structure By the above method, a Na-containing oxide having a P2-type structure and with the O3 phase reduced can be produced. Hereinafter, the Na-containing oxide according to one embodiment will be described.

[0024] 2.1 Chemical composition The Na-containing oxide according to one embodiment contains, as constituent elements, at least one element among at least Mn, Ni, and Co, Na, and O. In particular, when the constituent elements include at least Na, Mn, and one or both of Ni and Co, and O, among others, higher performance is more likely to be obtained when the constituent elements include at least Na, Mn, Ni, Co, and O. In one embodiment, the Na-containing oxide having a P2-type structure is Na a 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, 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 Na-containing oxide has such a chemical composition, the P2-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 1.00 or less, and may be 0.90 or less, 0.80 or less, or 0.70 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 1.00 or less, 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 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, or 0.30 or more, and is 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, 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, 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 contained, the P2-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 indefinite.

[0025] 2.2 Crystal Structure The Na-containing oxide according to one embodiment has at least a P2-type structure (belonging to the space group P63mc) as a crystal structure. The Na-containing oxide has a 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 / inserted from the P2-type structure. Here, the Na-containing oxide according to the present embodiment has a P2-type structure while having a small amount of O3-type structure. The Na-containing oxide according to the present embodiment may have a P2-type structure as a main phase. For example, when an X-ray diffraction pattern using CuKα as a radiation source is obtained for the Na-containing oxide according to the present embodiment, the diffraction peak intensity I P2 derived from the P2-type structure and the diffraction peak intensity I O3 derived from the O3-type structure in the X-ray diffraction pattern, the ratio I P2 / I O3 can be 1.0 or more, 2.0 or more, 3.0 or more, or 4.0 or more. The upper limit of I P2 / I O3 is not particularly limited and may be, for example, 20.0 or less, 18.0 or less, 16.0 or less, 14.0 or less, or 12.0 or less.

[0026] In addition, the diffraction peak intensity I P2 derived from the P2-type structure is specified as follows. (1) In the X-ray diffraction pattern using CuKα as a radiation source, as the background, the average value I 35.0 of the diffraction peak intensities at 35.0° ± 0.2° is obtained. (2) In the X-ray diffraction pattern, the maximum value I 39.85 of the diffraction peak intensity at 39.85° ± 0.1° is obtained. The diffraction peak at 39.85° ± 0.1° corresponds to the (102) plane of the P2-type structure. (3) The value obtained by subtracting I 39.85 from I 35.0 is defined as the above I P2 (I P2 = I 39.85 - I 35.0 ).

[0027] The diffraction peak intensity IO3 is specified as follows. (1) In the X-ray diffraction pattern using CuKα as the radiation source, as the background, the average value I of the diffraction peak intensity at 35.0° ± 0.2° 35.0 is obtained. (2) In the X-ray diffraction pattern, the maximum value I of the diffraction peak intensity at 38.0° ± 0.2° 38.0 is obtained. The diffraction peak at 38.0° ± 0.1° corresponds to the (012) plane of the O3-type structure. (3) The value obtained by subtracting I 38.0 from I 35.0 is defined as the above I O3 (I O3 = I 38.0 - I 35.0 ).

[0028] The Na-containing oxide according to one embodiment may be a single crystal composed of one crystallite, or may be a polycrystal having a plurality of crystallites. For example, the surface of the Na-containing oxide according to one embodiment may be composed of a plurality of crystallites. In other words, the Na-containing oxide may have a structure in which a plurality of crystallites are connected to each other on its surface. When the surface of the Na-containing oxide is composed of a plurality of crystallites, grain boundaries will exist on the surface. Here, the grain boundaries may serve as the inlets and outlets of intercalation. That is, when the Na-containing oxide is a polycrystal having a plurality of crystallites, effects such as an increase in the number of inlets and outlets of intercalation resulting in a decrease in reaction resistance, a shortening of the migration distance of sodium ions leading to a reduction in diffusion resistance, a decrease in the absolute amount of expansion and contraction during charge and discharge, and a reduced likelihood of cracking can be expected. The size of the crystallites may be large or small, but it is considered that the smaller the size of the crystallites, the more grain boundaries there will be, and the more easily the above-mentioned advantageous effects will be exerted. For example, when the diameter of the crystallites constituting the Na-containing oxide is less than 1 μm, higher performance is more likely to be obtained. Incidentally, the "crystallite" and the "diameter of the crystallite" can be determined by observing the surface of the Na-containing oxide with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, when observing the surface of the Na-containing oxide and a single closed region surrounded by grain boundaries is observed, the region is regarded as a "crystallite". The maximum Feret diameter of the crystallite is determined, and this is regarded as the "diameter of the crystallite". Incidentally, if the Na-containing oxide is composed of a single crystal, the particle itself can be said to be one crystallite, and the maximum Feret diameter of the particle is the "diameter of the crystallite". Alternatively, the diameter of the crystallite can also be determined by EBSD or XRD. For example, the diameter of the crystallite can be determined based on Scherrer's formula from the half-width of the diffraction line of the XRD pattern. When the diameter of the crystallite specified by any method for the Na-containing oxide is less than 1 μm, higher performance is more likely to be exhibited.

[0029] 2.3 Shape The P2-type structure is hexagonal, has a large diffusion coefficient of Na ions, and is prone to crystal growth in a specific direction. In particular, when at least one of Mn, Ni, and Co is included as the transition metal element constituting the P2-type structure, it is prone to crystal growth in a plate shape in a specific direction. Therefore, the Na-containing transition metal oxide having the P2-type structure usually becomes plate-like particles with a large aspect ratio in which the crystal growth direction is biased in a specific direction. On the other hand, the Na-containing oxide according to one embodiment may be spherical particles as described above. When the Na-containing oxide is spherical particles, as described above, the reaction resistance is reduced by reducing the crystallite size, and the diffusion resistance inside the particles is likely to be reduced. Furthermore, when applied to a secondary battery or the like, it is considered that the degree of bending is reduced by spheroidization, and the sodium ion conduction resistance is reduced. Thereby, for example, the rate characteristics are improved and the reversible capacity is likely to increase.

[0030] The Na-containing oxide according to one embodiment may be solid particles, hollow particles, or particles having voids. The size of the Na-containing oxide particles is not particularly limited, but it is considered that a smaller size is advantageous. For example, the average particle diameter (D50) of the Na-containing oxide particles may be 0.1 μm or more and 10 μm or less, 1.0 μm or more and 8.0 μm or less, or 2.0 μm or more and 6.0 μm or less. Note that the average particle diameter (D50) is the particle diameter (D50, median diameter) at 50% of the integrated value in the volume-based particle size distribution by the laser diffraction / scattering method.

[0031] 2.4 Supplementary Summarizing the above, the Na-containing oxide according to one embodiment may have, for example, the following configurations (1) to (4). (1) The Na-containing oxide contains, as constituent elements, at least one element of at least one of Mn, Ni, and Co, Na, and O. (2) The Na-containing oxide has a P2-type structure. (3) When an X-ray diffraction pattern using CuKα as a radiation source is obtained for the Na-containing oxide, the diffraction peak intensity I P2and the diffraction peak intensity I derived from the O3-type structure O3 and the ratio I P2 / I O3 is 1.0 or more and 20.0 or less. (4) The Na-containing oxide is spherical particles.

[0032] 3. Use The Na-containing oxide having a P2-type structure produced by the above method can be used, for example, as a positive electrode active material of a sodium ion battery. A sodium ion battery according to an embodiment includes a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and is characterized in that the positive electrode active material layer contains, as a positive electrode active material, the Na-containing oxide having the P2-type structure of the present disclosure. The sodium ion battery may have the same configuration as the conventional one except for including the above specific positive electrode active material.

Example

[0033] As described above, an embodiment of a method for producing a Na-containing oxide having a P2-type structure has been described. However, the production method and the like 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 while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0034] 1. Preparation of Na-containing oxide having a P2-type structure 1.1 Preparation of precursor (1) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed so as to have a target composition ratio and dissolved in distilled water to a concentration of 1.4 mol / L to obtain a first solution. Further, Na2CO3 was dissolved in distilled water to a concentration of 1.4 mol / L in another container to obtain a second solution. (2) 800 mL of pure water was put into a reaction vessel (with a baffle plate), 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 at room temperature for 1 hour to obtain a product. (4) The product was washed with pure water and solid-liquid separation was carried out using 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. The precursor particles were composite salts containing Mn, Ni, and Co, and were spherical particles having a roundness of 0.80 or more.

[0035] 1.2 Preparation of composite (1) Na2CO3 as the Na source and the above-mentioned precursor particles were weighed so that the composition after firing described below would be Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 O2. (2) The weighed Na source and precursor particles were mixed by spray drying. Specifically, the weighed Na source and precursor particles were added to a solvent, and spray drying was performed on the dispersion solution in which the Na source was dissolved and the precursor particles were dispersed. The temperature of spray drying was 200 °C and the spray pressure was 0.3 MPa. By spray drying, a composite in which 75 area% of the surface of the precursor particles was covered with the Na source was obtained.

[0036] 1.3 Firing of composite 6 g of the composite was placed in an alumina crucible and fired. The firing atmosphere was an air atmosphere for the comparative example, an oxygen 92% atmosphere for Example 1, an oxygen 75% atmosphere for Example 2, and an oxygen 50% atmosphere for Example 3. In Examples 1 to 3, gas substitution in the system was performed at the start of firing, and the oxygen concentration was changed by changing the mixing ratio of pure oxygen and air. Also, oxygen gas was flowed at 0.05 L / min during firing. The conditions in the firing process were as follows (1) to (7). (1) Place an alumina crucible containing the above composite in a heating furnace. (2) Heat the inside of the heating furnace from room temperature to 600 °C over 2 hours. (3) Hold the inside of the heating furnace at 600 °C for 2 hours for pre-firing. (4) After pre-firing, heat the inside of the heating furnace from 600 °C to 900 °C over 2 hours. (5) Hold the inside of the heating furnace at 900 °C for 1 hour to perform the main firing. (6) After the main firing, cool down the inside of the heating furnace from 900 °C to 250 °C over 4 hours. (7) Take out the alumina crucible from the heating furnace at 250 °C and air-cool it.

[0037] By pulverizing the fired product after air-cooling using a mortar in a dry atmosphere, Na-containing oxide particles having a P2-type structure were obtained. The Na-containing oxide particles are Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 and have a chemical composition represented by O2.

[0038] 2. Evaluation of Na-containing oxide particles 2.1 Appearance observation by SEM Fig. 2 shows the SEM photograph of the appearance of the Na-containing oxide according to Example 1. Also, Fig. 3 shows the SEM photograph of the appearance of the Na-containing oxide according to the comparative example. As is clear from Figs. 2 and 3, the Na-containing oxides according to Example 1 and the comparative example are spherical particles having a circularity of 0.80 or more. Also, it can be seen that the surface of the spherical particles is composed of a plurality of crystallites, and the crystallite diameter is less than 1 μm. The Na-containing oxides according to Examples 2 and 3 had the same form as Example 1.

[0039] 2.2 Identification of crystal structure by X-ray diffraction measurement For each of the Na-containing oxides of Examples 1 to 3 and the comparative example, X-ray diffraction measurement using CuKα as the radiation source was performed to obtain an X-ray diffraction pattern. From the X-ray diffraction pattern, the diffraction peak intensity I P2 derived from the P2-type structure and the diffraction peak intensity I O3 derived from the O3-type structure, and the ratio I P2 / I O3 were determined. Fig. 4 shows the X-ray diffraction patterns of the Na-containing oxides of Examples 1 to 3 and the comparative example. Also, Fig. 5 shows the oxygen concentration during firing and the peak intensity ratio I P2 / I O3The relationship with is shown. As shown in FIGS. 4 and 5, the Na-containing oxide according to the comparative example has a diffraction peak intensity I P2 derived from the P2-type structure and a diffraction peak intensity I O3 derived from the O3-type structure. The ratio I P2 / I O3 was less than 1.0, that is, it contained a large amount of the O3 phase. On the other hand, the Na-containing oxides according to Examples 1 to 3 had a ratio I P2 / I O3 of 1.0 or more, and the amount of the O3 phase was significantly reduced compared to the comparative example. In Examples 1 to 3, it is considered that the generation of the O3 phase was suppressed because the oxygen concentration during the main firing was 50% by volume or more.

[0040] 3. Supplementary In addition, in the above examples, the case of obtaining the precursor by the coprecipitation method was exemplified, but the precursor can also be obtained by other methods. Also, in the above examples, the case of obtaining the composite by coating the surface of the precursor with the Na source by spray drying was exemplified, but the composite can also be obtained by other methods. Further, in the above examples, as the Na-containing oxide having the P2-type structure, one having a predetermined chemical composition was exemplified, but the chemical composition of the Na-containing oxide is not limited thereto. Various chemical compositions adopting the P2-type structure can be employed. Also, the Na-containing oxide may be doped with an element M other than Mn, Ni, and Co. The element M is as described in the embodiment. Further, in the above examples, the case of finally obtaining spherical Na-containing oxide particles by using spherical precursors was exemplified, but the precursors and Na-containing oxides are not limited to spherical particles. However, in the case of spherical particles, for example, high effects can be expected as a positive electrode active material for a battery.

[0041] 4. Summary As described above, according to the method for producing a Na-containing oxide having a P2-type structure, which has the following steps S1 to S3, the generation of the O3 phase in the Na-containing oxide can be suppressed. That is, a Na-containing oxide having a P2-type structure and a reduced O3 phase can be produced. S1: Obtain a precursor containing at least one element among Mn, Ni, and Co. S2: Coat the surface of the precursor with a Na source to obtain a composite. S3: Bake the composite to obtain a Na-containing oxide having a P2-type structure. Here, the baking atmosphere of the composite contains 50% by volume or more of oxygen.

[0042] Also, according to the above manufacturing method, for example, a Na-containing oxide satisfying the following configurations (1) to (4) can be obtained. That is, the Na-containing oxide (1) contains at least one element among Mn, Ni, and Co, Na, and O as constituent elements. (2) has a P2-type structure. (3) When an X-ray diffraction pattern using CuKα as a radiation source is obtained, the diffraction peak intensity I P2 derived from the P2-type structure in the X-ray diffraction pattern, and the diffraction peak intensity I O3 derived from the O3-type structure, and the ratio I P2 / I O3 is 1.0 or more and 20.0 or less. (4) is spherical particles.

Claims

1. A method for producing a Na-containing oxide having a P2-type structure, comprising: obtaining a precursor containing at least one element among Mn, Ni, and Co; coating the surface of the precursor with a Na source to obtain a composite; and firing the composite to obtain a Na-containing oxide having a P2-type structure, wherein the firing atmosphere of the composite contains 50% by volume or more of oxygen. The manufacturing method.

2. The manufacturing method according to Claim 1, wherein the precursor is spherical particles, the composite is obtained by coating 40% by area or more of the surface of the precursor with the Na source, and the Na-containing oxide having the P2-type structure is spherical particles. The manufacturing method.

3. The manufacturing method according to Claim 2, comprising: using a transition metal ion and 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, and obtaining a precipitate as the precursor by a coprecipitation method. The manufacturing method.

4. The manufacturing method according to any one of Claims 1 to 3, The Na-containing oxide having the P2-type structure is Na ａ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (where 0 < a ≤ 1.00, 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). having a chemical composition represented by The manufacturing method.

Images