Positive electrode active material particles, sodium ion secondary battery, and method for manufacturing positive electrode active material particles

Abstract

To increase the reversible capacitance of a P2-type positive electrode active material particle.SOLUTION: A positive electrode active material particle of the present disclosure is spherical, has a P2-type structure and contains at least as configuration elements at least one transition metal element of Mn, Ni, and Co, Na, and O.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

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

[0002] Positive electrode active materials having a P2 type structure are known. For example, Patent Document 1 discloses Na as a positive electrode active material having a P2 type structure. x Fe y Mn 1-y Patent Document 2 discloses a composite metal oxide represented by the formula: O2 (x is less than 1, and y is 1 / 3 or more and less than 2 / 3). 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O2 is disclosed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-201588 [Patent Document 2] JP 2017-045600 A Summary of the Invention [Problem to be solved by the invention]

[0004] Positive electrode active materials with a P2 structure have the problem of low reversible capacity. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. (Aspect 1) Positive electrode active material particles, It has a P2 structure, As constituent elements, it contains at least one transition metal element of at least Mn, Ni, and Co, Na, and O. Spherical Positive electrode active material particles. (Aspect 2) The positive electrode active material particles of Aspect 1, in which the particle surface is composed of a plurality of crystallites. (Aspect 3) The positive electrode active material particles of Aspect 2, in which the diameter of the crystallite is less than 1 μm. (Aspect 4) The positive electrode active material particles of any one of Aspects 1 to 3, containing Na, Mn, Ni, Co, and O as constituent elements. (Aspect 5) The positive electrode active material particles of any one of Aspects 1 to 3, containing Na, Mn, Fe, and O as constituent elements. (Aspect 6) Na a Mn x-p Ni y-q Co z-r M p+q+r Having a chemical composition represented by O2 (where 0 < a ≤ 1.00, x + y + z = 1, and 0 ≤ p + q + r ≤ 0.15, and 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), the positive electrode active material particles of any one of Aspects 1 to 5. (Aspect 7) A sodium-ion secondary battery having a positive electrode, an electrolyte layer, and a negative electrode. The positive electrode contains the positive electrode active material particles of any one of Aspects 1 to 6. Sodium-ion secondary battery. (Aspect 8) A method for manufacturing positive electrode active material particles, including: Obtaining precursor particles; Coating the surface of the precursor particles with a Na salt to obtain coated particles; and Firing the coated particles to obtain Na-containing transition metal oxide particles having a P2-type structure. The precursor particles are a salt containing at least one transition metal of Mn, Ni, and Co. the precursor particles are spherical; The coated particles are obtained by coating 40% by area or more of the surface of the precursor particles with the Na salt, The Na-containing transition metal oxide particles are spherical. Manufacturing method. [Effects of the Invention]

[0006] The positive electrode active material particles having a P2 type structure according to the present disclosure have a large reversible capacity. [Brief explanation of the drawings]

[0007] [Figure 1A] FIG. 2 is a SEM photograph showing an example of the external shape of positive electrode active material particles according to the present disclosure. [Figure 1B] FIG. 2 is a SEM photograph showing an example of the external shape of positive electrode active material particles according to the present disclosure. [Figure 2] FIG. 1 is a SEM photograph showing the external shape of conventional P2-type positive electrode active material particles. [Figure 3] 1 shows a schematic configuration of a sodium ion secondary battery. [Figure 4] 1 shows an example of the flow of a method for producing positive electrode active material particles according to the present disclosure. [Figure 5A] 1 is an X-ray diffraction pattern of P2 type positive electrode active material particles according to Example 1. [Figure 5B] 1 shows an X-ray diffraction pattern of P2 type positive electrode active material particles according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1.Cathode active material particles 1A and 1B show positive electrode active material particles according to one embodiment. The positive electrode active material particles according to one embodiment include: It has a P2 structure, As constituent elements, the alloy contains at least one transition metal element selected from Mn, Ni, and Co, Na, and O, and It is spherical.

[0009] 1.1 Crystal structure The positive electrode active material particles of the present disclosure have at least a P2 type structure (belonging to the space group P63mc) as a crystal structure. The positive electrode active material particles have the P2 type structure, and may also have a crystal structure other than the P2 type structure. Examples of crystal structures other than the P2 type structure include various crystal structures (P3 type structure, etc.) formed upon desorption / insertion of Na from the P2 type structure. The positive electrode active material particles may have the P2 type structure as a main phase, or may have a crystal structure other than the P2 type structure as a main phase. The crystal structure of the positive electrode active material particles, which is the main phase, may change depending on the charge / discharge state.

[0010] The positive electrode active material particles of the present disclosure may be single crystals consisting of one crystallite, or may be polycrystalline having multiple crystallites. For example, as shown in Figures 1A and 1B, the positive electrode active material particles may have a surface composed of multiple crystallites. In other words, the particle surface may have a structure in which multiple crystallites are connected to each other.

[0011] When the surface of the positive electrode active material particle of the present disclosure is constituted by a plurality of crystallites, a crystal grain boundary is present on the surface of the particle. Here, the crystal grain boundary may become an inlet and an outlet for intercalation. That is, when the positive electrode active material particle has a plurality of crystallites, the effect of increasing the number of inlets and outlets for intercalation and thereby reducing the reaction resistance, the effect of shortening the migration distance of sodium ions and thereby reducing the diffusion resistance, the effect of reducing the absolute amount of expansion and contraction during charge and discharge and thereby making cracks less likely to occur, and the like can be expected.

[0012] The size of the crystallites constituting the positive electrode active material particles of the present disclosure may be large or small. However, smaller crystallite sizes result in more grain boundaries, making it easier to achieve the above-mentioned advantageous effects. For example, when the diameter of the crystallites constituting the positive electrode active material 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 positive electrode active material particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). That is, when observing the surface of a positive electrode active material particle, if a single closed region surrounded by grain boundaries is observed, that region is considered to be a "crystallite." The maximum Feret diameter of the crystallite is determined and considered to be the "crystallite diameter." If a particle is composed of a single crystal, the particle itself can be considered a single crystallite, and the maximum Feret diameter of the particle is the "crystallite diameter." Alternatively, the crystallite diameter can be determined using EBSD or XRD. For example, the crystallite diameter can be determined from the half-width of the diffraction line in the XRD pattern based on the Scherrer equation. When the crystallite diameter determined by any of these methods is less than 1 μm, the positive electrode active material particles of the present disclosure tend to exhibit higher performance.

[0013] The crystallites constituting the positive electrode active material particles of the present disclosure may have a first surface exposed on the particle surface, and the first surface may be planar. The surface of the positive electrode active material particle may have a structure in which a plurality of planes are connected. As will be described later, when producing the positive electrode active material particles, crystallites having planar first surfaces can be easily obtained by growing the crystallites on the particle surface until one crystallite and another crystallite are connected to each other.

[0014] 1.2 Chemical composition The positive electrode active material particles of the present disclosure contain, as constituent elements, at least one transition metal 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, However, when the constituent elements include at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material particles is more likely to be enhanced. Alternatively, when the constituent elements include at least Na, Mn, Fe, and O, the performance of the positive electrode active material particles is also more likely to be enhanced. However, during charging, for example, Na may be released from the positive electrode active material particles, and the abundance of Na may approach zero.

[0015] The positive electrode active material particles of the present disclosure contain Na a Mn x-p Ni y-q Co z-r M p+q+r may have a chemical composition represented by NaaMnxNiyCoz(PO4)1−p−q−r(MpOq)rO2. Here, 0 < a ≤ 1.00, x + y + z = 1, and 0 ≤ p + q + r ≤ 0.15. Further, 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 positive electrode active material particles have such a chemical composition, the P2-type structure is more likely to be maintained.

[0016] In the above chemical composition, a may be greater than 0, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, 0.50 or greater, or 0.60 or greater, and may be 1.00 or less, 0.90 or less, 0.80 or less, or 0.70 or less. In the above chemical composition, x may be 0 or greater, 0.10 or greater, 0.20 or greater, 0.30 or greater, 0.40 or greater, or 0.50 or greater, 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. In the above chemical composition, y may be 0 or greater, 0.10 or greater, or 0.20 or greater, 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. In the above chemical composition, z may be 0 or more, 0.10 or more, 0.20 or more, or 0.30 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. Many Ms do not contribute to charge and discharge. In this regard, a high charge and discharge capacity is easily ensured by having p+q+r be 0.15 or less. p+q+r may be 0.10 or less, or even 0. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0017] 1.3 Particle shape 1A and 1B, the positive electrode active material particles of the present disclosure are spherical. In the present application, "spherical particles" means that the circularity of the particles is 0.80 or more. The circularity of the positive electrode active material 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 where S is the orthogonal projection area of ​​the particle, and L is the perimeter of the orthogonal projection image of the particle. The circularity of the positive electrode active material 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. When the positive electrode active material particles are composed of multiple particles, the circularity is measured as an average value as follows.

[0018] (1) First, the particle size distribution of the positive electrode active material 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 a laser diffraction / scattering method. (2) The appearance of the positive electrode active material 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 positive electrode active material particles."

[0019] The positive electrode active material particles of the present disclosure may be solid particles, hollow particles, or particles having voids.

[0020] 1.4 Particle size The size of the positive electrode active material particles of the present disclosure is not particularly limited, but a smaller size is advantageous. For example, the average particle diameter (D50) of the positive electrode active material particles of the present disclosure 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. The average particle diameter (D50) of the positive electrode active material particles is the particle diameter (D50, median diameter) at 50% cumulative value in the volume-based particle size distribution determined by a laser diffraction / scattering method.

[0021] 1.5 Effects (compared to conventional P2-type positive electrode active material particles) Figure 2 shows the external shape of conventional P2-type positive electrode active material particles. The P2-type structure is a hexagonal crystal system with a large diffusion coefficient for 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, conventionally, only plate-like particles with a large aspect ratio, as shown in Figure 2, in which the crystal growth direction is biased in a specific direction, could be produced as Na-containing transition metal oxide particles with a P2-type structure. Furthermore, plate-like growth of the P2-type structure was considered fundamental and unavoidable. Therefore, for conventional P2-type positive electrode active material particles, the performance as an active material was improved by controlling their chemical composition and crystal structure, assuming that they would be plate-shaped.

[0022] In contrast, the positive electrode active material particles of the present disclosure have a P2 structure, contain at least one transition metal element selected from Mn, Ni, and Co, and are spherical. When spherical positive electrode active material particles are included in the positive electrode of a sodium-ion secondary battery, crystallite growth is more easily suppressed, resulting in smaller crystallites, compared with when non-spherical positive electrode active material particles (e.g., the plate-like particles described above) are included. That is, when the positive electrode active material particles are spherical, the reduction in crystallite size reduces reaction resistance and the diffusion resistance within the active material. Furthermore, it is believed that the degree of tortuosity is reduced by the spheroidization, thereby reducing the sodium ion conduction resistance within the layers constituting the positive electrode. As a result, rate characteristics are improved and reversible capacity is likely to increase. Such spherical positive electrode active material particles can be produced by a new method developed by the present inventors. A method for producing positive electrode active material particles will be described later.

[0023] 2. Positive electrode The technology of the present disclosure also has an aspect of a positive electrode including the above-described positive electrode active material. That is, the positive electrode of the present disclosure has the above-described positive electrode active material particles of the present disclosure as positive electrode active material particles. As shown in FIG. 3, a positive electrode 10 according to one embodiment may include a positive electrode active material layer 11 and a positive electrode current collector 12. In this case, the positive electrode active material layer 11 may include the above-described positive electrode active material particles.

[0024] 2.1 Cathode active material layer The positive electrode active material layer 11 contains at least the above-described positive electrode active material particles as the positive electrode active material, and may further contain, optionally, an electrolyte, a conductive additive, a binder, and the like. Furthermore, the positive electrode active material layer 11 may also contain various other additives. The respective contents of the positive electrode active material particles, electrolyte, conductive additive, binder, and the like in the positive electrode active material layer 11 may be appropriately determined depending on the desired battery performance. For example, the content of the positive electrode active material particles may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 100% by mass or less, or 90% by mass or less, where the entire positive electrode active material layer 11 (total solid content) is taken as 100% by mass. The shape of the positive electrode active material layer 11 is not particularly limited, and may be, for example, a sheet-like positive electrode active material layer 11 having a substantially flat surface. The thickness of the positive electrode active material layer 11 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.

[0025] 2.1.1 Cathode active material The positive electrode active material layer 11 may contain only the positive electrode active material particles of the present disclosure as the positive electrode active material particles. Alternatively, the positive electrode active material layer 11 may contain, in addition to the positive electrode active material particles of the present disclosure, a different type of positive electrode active material (another positive electrode active material). From the viewpoint of further enhancing the effects of the technology of the present disclosure, the content of the other positive electrode active material in the positive electrode active material layer 11 may be small. For example, the content of the positive electrode active material particles of the present disclosure may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more, where the total positive electrode active material contained in the positive electrode active material layer 11 is taken as 100% by mass.

[0026] 2.1.2 Electrolytes The electrolyte that can be contained in the positive electrode active material layer 11 may be a solid electrolyte, a liquid electrolyte (electrolytic solution), or a combination thereof.

[0027] The solid electrolyte may be any known solid electrolyte for sodium ion secondary batteries. 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 Na3Zr2PSi2O 12 and oxides such as Na2O-11Al2O3; NaBH4, NaB 10 H 10 , NaCB9H 10 , NaCB 11 H 12 , NaB 12 Cl 12 Hydrides and borides such as Na3PS4, Na3SbS4, Na 2.88 Sb 0.88 W 0.12 The solid electrolyte may be at least one selected from sulfides such as NaPF6 and NaBF4; and fluorides such as NaPF6 and NaBF4. The solid electrolyte may be, for example, in the form of particles. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0028] The electrolyte may contain, for example, sodium ions as carrier ions. The electrolyte may be an aqueous electrolyte or a non-aqueous electrolyte. The composition of the electrolyte may be the same as that of known electrolytes for sodium ion secondary batteries. For example, the electrolyte may be a carbonate-based solvent in which a sodium salt is dissolved at a predetermined concentration. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). Examples of sodium salts include NaPF6.

[0029] 2.1.3 Conductive additives Examples of conductive additives that can be contained in the positive electrode active material layer 11 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, 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.

[0030] 2.1.4 Binder Examples of binders that can be contained in the positive electrode active material layer 11 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.

[0031] 2.2 Positive electrode current collector As shown in FIG. 3 , the positive electrode 10 may include a positive electrode current collector 12 in contact with the positive electrode active material layer 11. Any common positive electrode current collector for batteries can be used as the positive electrode current collector 12. The positive electrode current collector 12 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The positive electrode current collector 12 may be made of a metal foil or metal mesh. Metal foils are particularly easy to handle. The positive electrode current collector 12 may be made of multiple foils. Metals constituting the positive electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, and the like. In particular, the positive electrode current collector 12 may contain Al to ensure oxidation resistance. The positive electrode current collector 12 may have a coating layer on its surface for purposes such as adjusting resistance. The positive electrode current collector 12 may be a metal foil or a substrate plated or vapor-deposited with the above metal. When the positive electrode current collector 12 is made of multiple metal foils, some layer may be present between the multiple metal foils. The thickness of the positive electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more, 1 μm or more, or 1 mm or less, or 100 μm or less.

[0032] 2.3 Other In addition to the above configuration, the positive electrode 10 may also have a configuration generally used for a positive electrode of a secondary battery. For example, a tab, a terminal, etc. The positive electrode 10 can be manufactured by a known method, except that the positive electrode active material particles have the above-mentioned P2 type structure. For example, the positive electrode active material layer 11 can be easily formed by dry or wet molding a positive electrode mixture containing the above-mentioned various components. The positive electrode active material layer 11 may be molded together with the positive electrode current collector 12, or may be molded separately from the positive electrode current collector 12.

[0033] 3. Sodium-ion secondary battery As shown in FIG. 3 , a sodium ion secondary battery 100 according to one embodiment has a positive electrode 10, an electrolyte layer 20, and a negative electrode 30. Here, the positive electrode 10 contains the above-described positive electrode active material particles of the present disclosure. As described above, the positive electrode active material particles of the present disclosure have a large reversible capacity. In this regard, when the positive electrode of the sodium ion secondary battery 100 contains the positive electrode active material particles of the present disclosure, the performance of the secondary battery 100 is likely to be improved. The configuration of the positive electrode 10 of the sodium ion secondary battery 100 is as described above.

[0034] 3.1 Electrolyte layer The electrolyte layer 20 contains at least an electrolyte. When the sodium ion secondary battery 100 is a solid-state battery (a battery containing a solid electrolyte in which a liquid electrolyte is used in part, or an all-solid-state battery containing no liquid electrolyte), the electrolyte layer 20 contains a solid electrolyte and may further contain a binder or the like. In this case, the contents of the solid electrolyte and binder or the like in the electrolyte layer 20 are not particularly limited. On the other hand, when the sodium ion secondary battery 100 is an electrolyte battery, the electrolyte layer 20 contains an electrolyte solution and may further have a separator or the like for retaining the electrolyte solution and preventing contact between the positive electrode active material layer 11 and the negative electrode active material layer 31. 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.

[0035] The electrolyte contained in the electrolyte layer 20 may be appropriately selected from the electrolytes exemplified above as those that can be contained in the positive electrode active material layer. Similarly, the binder contained in the electrolyte layer 20 may be appropriately selected from the binders exemplified above as those that can be contained in the positive electrode active material layer. Each of the electrolytes and binders may be used alone or in combination of two or more. The separator may be any separator commonly used in sodium ion secondary batteries, such as those made of resins such as polyethylene (PE), polypropylene (PP), polyester, and 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.

[0036] 3.2 Negative electrode As shown in FIG. 3, the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode current collector 32.

[0037] 3.2.1 Negative electrode active material layer The negative electrode active material layer 31 contains at least a negative electrode active material and may further contain, optionally, an electrolyte, a conductive additive, a binder, and the like. Furthermore, the negative electrode active material layer 31 may also contain various other additives. The contents of the negative electrode active material, electrolyte, conductive additive, binder, and the like in the negative electrode active material layer 31 may be appropriately determined depending on the desired battery performance. For example, the content of the negative 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 negative electrode active material layer 31 (total solid content) is taken as 100% by mass. The shape of the negative electrode active material layer 31 is not particularly limited, and may be, for example, a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 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.

[0038] As the negative electrode active material, various substances can be used that have a potential (charge / discharge potential) at which sodium ions are absorbed and released that is lower than that of the positive electrode active material of the present disclosure. For example, an inorganic negative electrode active material such as metallic sodium may be used, or a negative electrode active material made of an organic compound may be used. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination.

[0039] The shape of the negative electrode active material may be any shape commonly used for negative electrode active materials in batteries. For example, the negative electrode active material may be in a particulate form. The negative electrode active material particles may be primary particles or secondary particles formed by aggregation 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 a sheet form (foil or film form) such as sodium foil. That is, the negative electrode active material layer 31 may be made of a sheet of negative electrode active material.

[0040] Examples of electrolytes that can be contained in the negative electrode active material layer 31 include the above-mentioned solid electrolytes, electrolytic solutions, and combinations thereof. Examples of conductive additives that can be contained in the negative electrode active material layer 31 include the above-mentioned carbon materials and metal materials. The binder that can be contained in the negative electrode active material layer 31 may be appropriately selected from, for example, the binders that can be contained in the above-mentioned positive electrode active material layer 11. Only one type of electrolyte or binder may be used alone, or two or more types may be used in combination.

[0041] 3.2.2 Negative electrode current collector As shown in FIG. 3 , the negative electrode 30 may include a negative electrode current collector 32 in contact with the negative electrode active material layer 31. The negative electrode current collector 32 may be any of those commonly used as negative electrode current collectors for batteries. The negative electrode current collector 32 may be in the form of a foil, plate, mesh, punched metal, foam, or the like. The negative electrode current collector 32 may be a metal foil or metal mesh, or a carbon sheet. Metal foil is particularly advantageous in terms of ease of handling. The negative electrode current collector 32 may be composed of multiple foils or sheets. Examples of metals constituting the negative electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance, the negative electrode current collector 32 may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 32 may have some kind of coating layer on its surface for the purpose of adjusting the resistance, etc. Alternatively, the negative electrode current collector 32 may be a metal foil or a substrate on which the above metal is plated or vapor-deposited. Alternatively, when the negative electrode current collector 32 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 32 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.

[0042] 3.3 Other matters The sodium ion secondary battery 100 may have the above components housed inside an exterior body. Any known exterior body for a battery can be used as the exterior body. Furthermore, a plurality of batteries 100 may be electrically connected and stacked in any manner to form an assembled battery. In this case, the assembled battery may be housed inside a known battery case. The sodium ion secondary battery 100 may also include other obvious components such as necessary terminals. The sodium ion secondary battery 100 may have, for example, a coin type, a laminate type, a cylindrical type, a prismatic type, or the like.

[0043] The sodium ion secondary battery 100 can be manufactured by applying a known method. For example, it can be manufactured as follows. However, the manufacturing method of the sodium ion secondary 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 in the case of an electrolyte battery, the battery case is filled with an electrolyte, and the laminate is immersed in the electrolyte and sealed in the battery case to form a secondary battery. In the case of an electrolyte battery, the electrolyte may be impregnated into the negative electrode active material layer, the separator, and the positive electrode active material layer at the step (3) above.

[0044] 4. Method for producing positive electrode active material particles The technology of the present disclosure also has an aspect of a method for producing positive electrode active material particles. As shown in FIG. 4, the method for producing positive electrode active material particles according to one embodiment includes the steps of: Obtaining precursor particles (step S1), Coating the surface of the precursor particles with a Na salt to obtain coated particles (step S2); and and calcining the coated particles to obtain Na-containing transition metal oxide particles having a P2 type structure (step S3). where: the precursor particles are salts containing at least one transition metal element selected from Mn, Ni, and Co; the precursor particles are spherical; The coated particles are obtained by coating 70% or more by area of ​​the surface of the precursor particles with the Na salt, The Na-containing transition metal oxide particles are spherical.

[0045] 4.1 Process S1 In step S1, precursor particles are obtained. The precursor particles are salts containing at least one transition metal element selected from Mn, Ni, and Co. The precursor particles may be, for example, at least one of carbonate, sulfate, nitrate, acetate, and hydroxide. Specifically, the precursor particles may be a salt represented by MeCO3 (where Me is at least one transition metal element selected from Mn, Ni, and Co), a salt represented by MeSO4, a salt represented by Me(NO3)2, a salt represented by Me(CH3COO)2, or a compound represented by Me(OH)2. In addition to the transition metal element Me, the precursor particles may also contain at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W.

[0046] The precursor particles are spherical. The definition of "spherical" is as described above. When the precursor particles are spherical, the shape of the finally obtained positive electrode active material particles is also likely to be spherical. The size of the spherical precursor particles is not particularly limited. The spherical precursor particles can be obtained by, for example, a solution method such as a coprecipitation method or a sol-gel method. Specifically, in the case of the coprecipitation method, an aqueous solution of MeSO4 and an aqueous solution of Na2CO3 are prepared, and each aqueous solution is dropped and mixed to obtain a precipitate. The precipitate is a spherical precursor particle represented by MeCO3. A carbonate containing Me and M may be obtained as the precursor particle by dissolving a sulfate of M or the like in the aqueous solution of MeSO4.

[0047] 4.2 Process S2 In step S2, the surfaces of the precursor particles are coated with a sodium salt to obtain coated particles. The coated particles are obtained by coating 40% or more of the surface area of ​​the precursor particles with a sodium salt. The coated particles may be obtained by coating 50% or more, 60% or more, or 70% or more of the surface area of ​​the precursor particles with a sodium salt. Examples of sodium salts include carbonates and nitrates.

[0048] Various methods can be used to coat 40% or more of the surface area of ​​precursor particles with Na salt. Examples include tumbling fluidized coating and spray drying. Specifically, a coating solution containing dissolved Na salt is prepared, and the entire surface of the precursor particles is brought into contact with the coating solution, followed by drying. 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 Na salt. According to the inventor's findings, if the coverage rate of Na salt is low, abnormal growth of P2-type crystals is likely to occur on the surface of the coated particles when the coated particles are calcined, preventing the production of spherical Na-containing transition metal oxide particles. If the coverage rate of Na salt is high, the crystallites of the P2-type crystals can be reduced when the coated particles are calcined, and the shape of the coated particles is likely to become "spherical" corresponding to the shape of the precursor particles. The amount of Na salt coated on the coated particles should be sufficient to obtain a P2-type structure (so that a sufficient amount of Na is doped).

[0049] 4.3 Process S3 In step S3, the coated particles are calcined to obtain sodium-containing transition metal oxide particles having a P2 structure, where the sodium-containing transition metal oxide particles are spherical.

[0050] The firing temperature may be any temperature at which a P2 type structure is formed and the Na-containing transition metal oxide particles become spherical. If the firing temperature is too low, Na doping is not performed and it is difficult to obtain a P2 type structure. On the other hand, if the firing temperature is too high, an O3 type structure is likely to be formed instead of a P2 type structure. The firing temperature may be, for example, 700°C or higher and 1100°C or lower, or 800°C or higher and 1000°C or lower.

[0051] The calcination time may be any time long enough to make the Na-containing transition metal oxide particles spherical. As described above, in the method of the present disclosure, the coverage of the coated particles with Na salt is high, so when the coated particles are calcined, small P2-type crystals are easily formed on the particle surface. In the method of the present disclosure, spherical Na-containing transition metal oxide particles can be obtained by growing P2-type crystals along the particle surface so that one P2-type crystallite is connected to another P2-type crystallite. If the calcination time is too short, Na doping is not performed, and the desired P2-type structure is not obtained. On the other hand, if the calcination time is too long, the P2-type structure grows excessively, resulting in plate-like particles rather than spherical ones. As far as the inventors have confirmed, spherical Na-containing transition metal oxide particles are easily obtained when the calcination time is 30 minutes or more and 3 hours or less. In general, when synthesizing a positive electrode active material by calcination, the calcination time is often long (e.g., 5 hours or more) to obtain the desired crystal phase. In contrast, in the method of the present disclosure, the calcination time is set to 3 hours or less, thereby suppressing excessive growth of P2 type crystals and obtaining spherical Na-containing transition metal oxide particles. The Na-containing transition metal oxide particles obtained after calcination may have a structure in which multiple crystallites are present on the surface and the crystallites are connected to each other.

[0052] The firing atmosphere is not particularly limited, and may be, for example, an oxygen-containing atmosphere such as air atmosphere or an inert gas atmosphere.

[0053] 5. Method for increasing the reversible capacity of sodium-ion secondary batteries The technology of the present disclosure also has an aspect as a method for increasing the reversible capacity of a sodium ion secondary battery. That is, the method for increasing the reversible capacity of a sodium ion secondary battery of the present disclosure is characterized by using the above-described positive electrode active material particles of the present disclosure in the positive electrode of the sodium ion secondary battery.

[0054] 6. Vehicles equipped with sodium-ion secondary batteries As described above, when the positive electrode active material particles of the present disclosure are contained in the positive electrode of a sodium ion secondary battery, an increase in the reversible capacity of the sodium ion secondary battery can be expected. A sodium ion secondary battery with such a large reversible capacity can be suitably used in, for example, at least one type of vehicle selected from 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 a sodium ion secondary battery, the sodium ion secondary battery having a positive electrode, an electrolyte layer, and a negative electrode, and the positive electrode containing the positive electrode active material particles of the present disclosure. [Example]

[0055] As described above, one embodiment of the cathode active material particles, sodium ion secondary battery, and method for manufacturing cathode active material particles according to the present disclosure has been described, but the cathode active material particles, sodium ion secondary battery, and method for manufacturing cathode active material particles according to the present disclosure can be modified in various ways other than the above embodiment without departing from the gist thereof. Below, 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.

[0056] 1. Example 1 1.1 Preparation of precursor particles (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) 500 mL of the first solution and 500 mL of the second solution were each added dropwise at a rate of about 4 mL / min to a reaction vessel (with a baffle) containing 1000 mL of pure water. (3) After the dropwise addition was completed, the mixture was stirred at room temperature at a stirring speed of 150 rpm for 1 hour to obtain a product. (4) The product was washed with pure water and subjected to solid-liquid separation using a centrifuge to obtain a precipitate. (5) The precipitate was dried overnight at 120°C, crushed in a mortar, and then fine particles were removed by air classification to obtain precursor particles. The precursor particles were carbonates of transition metals (Mn, Ni, and Co), and were spherical particles with a circularity of 0.98.

[0057] 1.2 Preparation of coated particles (1) Na2CO3, which is a sodium salt, and the above precursor particles are mixed together to form a Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 It was weighed to have a composition of O2. (2) The weighed Na salt and precursor were mixed by spray drying. Specifically, the weighed Na salt and precursor were added to a solvent (water), and the dispersion solution in which the Na salt was dissolved and the precursor was dispersed was spray dried. The spray drying temperature was 200°C, and the spray pressure was 0.3 MPa. By spray drying, coated particles in which 77 area% of the surface of the precursor particles was coated with Na salt were obtained.

[0058] 1.3 Preparation of Na-containing transition metal oxide particles with P2-type structure (1) The coated particles were fired in an alumina crucible under air atmosphere at a firing temperature of 900°C for 1 hour to obtain a fired product. (2) The fired product was crushed in a mortar in a dry atmosphere to obtain Na-containing transition metal oxide particles having a P2 type structure (P2 type particles) as positive electrode active material particles.

[0059] 1.4 Evaluation and observation of the physical properties of positive electrode active material particles Fig. 5A shows the X-ray diffraction pattern of the positive electrode active material particles according to Example 1. As shown in Fig. 5A, the positive electrode active material particles according to Example 1 had a P2 type structure belonging to the space group P63mc. Furthermore, elemental analysis revealed that the positive electrode active material particles according to Example 1 contained Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 It was confirmed to have a chemical composition indicated by O2.

[0060] FIG. 1A shows an SEM photograph of the appearance of the positive electrode active material particles according to Example 1. Image analysis revealed that the positive electrode active material particles according to Example 1 were spherical particles with a circularity of 0.86. As shown in FIG. 1A, the surface of the positive electrode active material particles according to Example 1 was composed of a plurality of crystallites, and the diameter of the crystallites was less than 1 μm. As shown in FIG. 1A, the crystallites had a first surface exposed on the particle surface, and the first surface was planar. Furthermore, the average particle diameter (D50) of the positive electrode active material particles according to Example 1 was 3.6 μm.

[0061] 2. Example 2 2.1 Preparation of precursor particles (1) MnSO4·5H2O and FeSO4·7H2O were weighed to achieve the desired composition ratio and dissolved in distilled water to a concentration of 1.2 mol / L to obtain a first solution. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain a second solution. (2) 500 mL of the first solution and 500 mL of the second solution were each added dropwise at a rate of about 4 mL / min to a reaction vessel (with a baffle) containing 1000 mL of pure water. (3) After the dropwise addition was completed, the mixture was stirred at room temperature at a stirring speed of 150 rpm for 1 hour to obtain a product. (4) The product was washed with pure water and subjected to solid-liquid separation using a centrifuge to obtain a precipitate. (5) The precipitate was dried overnight at 120°C, crushed in a mortar, and then fine particles were removed by air classification to obtain precursor particles. The precursor particles were carbonates of transition metals (Mn and Fe) and were spherical particles with a circularity of 0.87.

[0062] 2.2 Preparation of coated particles (1) Na2CO3, which is a sodium salt, and the above precursor particles are mixed together to form a Na 0.7 Mn 0.5 Fe 0.5 It was weighed to have a composition of O2. (2) The weighed Na salt and precursor were mixed by spray drying. Specifically, the weighed Na salt and precursor were added to a solvent (water), and the dispersion solution in which the Na salt was dissolved and the precursor was dispersed was spray dried. The spray drying temperature was 200°C, and the spray pressure was 0.3 MPa. By spray drying, coated particles in which 75 area% of the surface of the precursor particles was coated with Na salt were obtained.

[0063] 2.3 Preparation of Na-containing transition metal oxide particles with P2-type structure (1) The coated particles were fired in an alumina crucible under air atmosphere at a firing temperature of 900°C for 1 hour to obtain a fired product. (2) The fired product was crushed in a mortar in a dry atmosphere to obtain Na-containing transition metal oxide particles having a P2 type structure (P2 type particles) as positive electrode active material particles.

[0064] 2.4 Evaluation and observation of the physical properties of positive electrode active material particles Fig. 5B shows the X-ray diffraction pattern of the positive electrode active material particles according to Example 2. As shown in Fig. 5B, the positive electrode active material particles according to Example 2 have a P2 type structure belonging to the space group P63mc. Furthermore, elemental analysis revealed that the positive electrode active material particles according to Example 2 contain Na 0.7 Mn 0.5 Fe 0.5 It was confirmed to have a chemical composition indicated by O2.

[0065] FIG. 1B shows an SEM photograph of the appearance of the positive electrode active material particles according to Example 2. Image analysis revealed that the positive electrode active material particles according to Example 2 were spherical particles with a circularity of 0.90. As shown in FIG. 1B, the surface of the positive electrode active material particles according to Example 2 was composed of a plurality of crystallites, and the diameter of the crystallites was less than 1 μm. As shown in FIG. 1B, the crystallites had a first surface exposed on the particle surface, and the first surface was planar. Furthermore, the average particle diameter (D50) of the positive electrode active material particles according to Example 2 was 4.8 μm.

[0066] 3. Comparative Example 1 3.1 Preparation of precursor particles In the same manner as in Example 1, spherical precursor particles were prepared.

[0067] 3.2 Preparation of coated particles (1) Na2CO3 as a sodium salt and the above precursor particles are mixed together to form a Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 It was weighed to have a composition of O2. (2) The weighed Na salt and precursor were mixed in a mortar to obtain coated particles in which 28% by area of ​​the surface of the precursor particles was coated with Na salt.

[0068] 3.3 Preparation of Na-containing transition metal oxide particles with P2-type structure Na-containing transition metal oxide particles having a P2 type structure (P2 type particles) were obtained as positive electrode active material particles in the same manner as in Example 1, except that the coated particles with the above coverage of 28 area % were used.

[0069] 3.4 Evaluation and observation of the physical properties of positive electrode active material particles When the X-ray diffraction pattern of the positive electrode active material particles according to Comparative Example 1 was confirmed, it was found that they had a P2 type structure belonging to the space group P63mc, similar to the positive electrode active material particles according to Example 1. Furthermore, when elemental analysis was carried out, it was found that the positive electrode active material particles according to Comparative Example 1 contained Na, similar to the positive electrode active material particles according to Example 1. 0.7 Mn 0.5 Ni 0.2 Co 0.3 It was confirmed to have a chemical composition indicated by O2.

[0070] Fig. 2 shows an SEM photograph of the appearance of the positive electrode active material particles according to Comparative Example 1. The positive electrode active material particles according to Comparative Example 1 were plate-like particles having an aspect ratio of 2 or more, and their circularity was 0.63. As shown in Fig. 2, the positive electrode active material particles according to Comparative Example 1 were composed of single crystallites that had grown coarsely into a plate shape, and the diameter of each crystallite was several µm (more than 1 µm).

[0071] 4. Comparative Example 2 4.1 Preparation of precursor particles In the same manner as in Example 2, spherical precursor particles were prepared.

[0072] 4.2 Preparation of coated particles (1) Na2CO3 as a sodium salt and the above precursor particles are mixed together to form a Na 0.7 Mn 0.5 Fe 0.5 It was weighed in a dry atmosphere to give a composition of O2. (2) The weighed Na salt and precursor were mixed in a mortar to obtain coated particles in which 22% by area of ​​the surface of the precursor particles was coated with Na salt.

[0073] 4.3 Preparation of Na-containing transition metal oxide particles with P2-type structure Na-containing transition metal oxide particles having a P2 type structure (P2 type particles) were obtained as positive electrode active material particles in the same manner as in Example 2, except that the coated particles with the above coverage of 22 area % were used.

[0074] 4.4 Evaluation and observation of the physical properties of positive electrode active material particles When the X-ray diffraction pattern of the positive electrode active material particles according to Comparative Example 2 was confirmed, it was found that they had a P2 type structure belonging to the space group P63mc, similar to the positive electrode active material particles according to Example 2. Furthermore, when elemental analysis was carried out, it was found that the positive electrode active material particles according to Comparative Example 2 contained Na, similar to the positive electrode active material particles according to Example 2. 0.7 Mn 0.5 Fe 0.5 It was confirmed to have a chemical composition indicated by O2.

[0075] Furthermore, when the appearance of the positive electrode active material particles according to Comparative Example 2 was observed with an SEM, the positive electrode active material particles according to Comparative Example 2 were plate-like particles having an aspect ratio of 2 or more and a circularity of 0.68. Similarly to the positive electrode active material according to Comparative Example 1, the positive electrode active material particles according to Comparative Example 2 were formed by the growth of a single crystallite into a coarse, plate-like shape, with the diameter of each crystallite being several μm (more than 1 μm).

[0076] 5. Preparation of Cell for Evaluation Coin cells were fabricated using the positive electrode active material particles of each of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. The coin cell fabrication procedure was as follows. (1) Positive electrode active material particles, 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 particles: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) The electrolyte used was a solvent in which EC and DEC were mixed in a volume ratio of 1:1, and NaPF6 was dissolved to a concentration of 1M. (3) Metallic sodium foil was prepared as the negative electrode. (4) A coin cell (CR2032) was fabricated using the positive electrode, electrolyte, and negative electrode.

[0077] 6.Charge / Discharge Characteristics Evaluation (1) The reversible capacity of each of the coin cells of Example 1 and Comparative Example 1 was measured by charging and discharging at 0.1 C in a voltage range of 1.0 to 4.5 V in a thermostatic chamber maintained at 25° C. The results are shown in Table 1 below. (2) The reversible capacity of each of the coin cells of Example 2 and Comparative Example 2 was measured by charging and discharging at 0.1 C in a voltage range of 1.0 to 4.3 V in a thermostatic chamber maintained at 25° C. The results are shown in Table 1 below.

[0078] [Table 1]

[0079] As shown in Table 1, the coin cells of Examples 1 and 2 had a larger reversible capacity than the coin cells of Comparative Examples 1 and 2. As described above, the positive electrode active material particles of Examples 1 and 2 were spherical. Therefore, it is believed that crystallite growth was suppressed and the crystallites were smaller than in the plate-shaped positive electrode active material particles of Comparative Examples 1 and 2, resulting in lower reaction resistance and lower diffusion resistance within the active material. Furthermore, it is believed that the spheroidization reduced the degree of curvature, thereby lowering the ionic conduction resistance within the layers that make up the positive electrode. As a result, it is believed that the rate characteristics were improved and the reversible capacity was increased. In this regard, the effect of spheroidizing the P2-type positive electrode active material particles was confirmed.

[0080] 7. Supplementary Information In the above examples, positive electrode active material particles having a specific chemical composition are exemplified, but the chemical composition of the positive electrode active material particles of the present disclosure is not limited thereto. However, according to the findings of the present inventors, when at least one of Mn, Ni, and Co is contained as a transition metal, the P2 type structure is likely to undergo crystal growth in a specific direction and become plate-like. The problem solved by the technology of the present disclosure is particularly pronounced when at least one of Mn, Ni, and Co is contained as a transition metal.

[0081] 8. Summary From the above examples, it can be said that positive electrode active material particles that (1) have a P2 type structure, (2) contain at least one transition metal element selected from Mn, Ni, and Co, Na, and O as constituent elements, and (3) are spherical have a large reversible capacity. [Explanation of symbols]

[0082] 10 positive electrode 11 Cathode active material layer 12 Positive electrode current collector 20 Electrolyte layer 30 negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Sodium-ion secondary battery

Claims

[Claim 1] A method for producing positive electrode active material particles, comprising: Obtaining precursor particles; Coating the surface of the precursor particles with a Na salt to obtain coated particles; and calcining the coated particles to obtain Na-containing transition metal oxide particles having a P2 type structure; Including, the precursor particles are salts containing at least one transition metal selected from Mn, Ni, and Co; the precursor particles are particles obtained by a coprecipitation method and have a circularity of 0.80 or more; the coated particles are obtained by coating 70% by area or more of the surface of the precursor particles with the Na salt by a tumbling fluidized coating method or a spray drying method, The firing temperature is 700°C or higher and 1100°C or lower, The baking time is 30 minutes or more and 3 hours or less, The Na-containing transition metal oxide particles are Constituent elements include Na, Mn, Ni, Co and O, containing Na, Mn, Fe and O as constituent elements, or Na ａ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (wherein 0<a≦1.00, x+y+z=1, and 0≦p+q+r≦0.15, and 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), the surface of the Na-containing transition metal oxide particle is composed of a plurality of crystallites, The circularity of the Na-containing transition metal oxide particles is 0.80 or more. Manufacturing method.

Images